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Sucking in the newborn during a feed
JOURNAL
OF EXPERIMXCNTAL
Sucking JUDITH
CHILD
7, 282-298 (1969)
PSYCHOLOGY
in the
Newborn
DUBIGNON
DUGAL
AND
Queen’s University,
during
Kingston,
a Feed
CAMPBELLI
Ontario
Two components of sucking (suction and expression) were measured under three conditions: when no fluid waz available, when small amounts of dextrose were delivered, and throughout a milk feed. Significant differences in sucking rate, time spent sucking, and pressure were found between the nonnutritive and dextrose conditions; these differences were more marked during the feed. Sucking throughout the feed remained uniform until the end of the last
quarter when a reduction in frequency of sucking, time spent sucking, and sucking pressure took place. There were no changes in sucking rate. Heart rate rose during nutritive sucking and moment-to-moment variation in heart rate was reduced.
Experiments intended to identify the stimuli that control sucking have shown that intraoral stimuli are significant determinants of sucking in the newborn. For example, characteristics of the nipple, such as.& siae, shape, and compressibility, have been found to control the frequency of nonnutritive sucking (Lipsitt and Kaye, 1965; Dubignon and CamIj’bell, 1968a). These results resemble those found in ethological studies. that have shown that feeding behavior in the young of certain species is controlled by relatively specific sign-stimuli (Tinbergen, 1951). Little is known about stimulus control of sucking during feeding; however, among the stimuli that control sucking in a functional context, it is likely that those provided by nutritive fluids are relatively important, as well as other factors, such as satiation and fatigue. Until recently “there have been no reports comparing sucking for liquids and nonnutritive sucking within the same recording system” (Kaye, 1967). In one such study the data suggested that nutritive sucking during a feed is different from nonnutritive sucking. It was found that the delivery of small amounts of dextrose brought about immediate changes in pattern ‘The work reported in this paper Foundation (Grant No. 16) and the We wish to record our thanks to the and to our research assistants, Miss Elizabeth Wood.
was supported by the Ontario Mental Health Association for the Aid of Crippled Children. nursery stat7 of the Kingston General Hospital M. Henderson, Mrs. E. Stephenz, and Miss
282
SUCKING
IN
THE
NEWBORX
283
of sucking: the infants sucked more slowly and gave longer bursts of sucking. Naturalistic observations of breast and bottle feeding suggested that these changes in pattern of sucking became even more marked during feeding. In the same study significant changes in heart rate were found to accompany sucking (Dubignon and Campbell, 1968b). The present experiment was designed to examine further the hypothesis that the stimuli provided by nutritive fluids are significant determinants of sucking. The earlier observations led to the prediction that the differences found between nonnutritive sucking and sucking for small amounts of dextrose would become more marked during a feed. Secondary aims were to provide data on the regulation of food intake by the newborn, the effects of fatigue and satiation on nutritive sucking, and changes in heart rate during feeding. METHOD
Sucking was measured under three conditions: first, nonnutritive sucking when no fluid was given to the baby; second, when small amounts of dextrose fluid were delivered; and third, throughout a bottle feed. The order of nonnutritive and dextrose conditions was not varied as it has been shown that the order of trials has no significant effect on the sucking elicited in each condition (Dubignon and Campbell, 1968b). Subjects. Twenty-four full-term babies (12 male, 12 female) were seen during the third or fourth days of life (mean age: 70 hours; SD 12.1). All the babies were bottle-fed infants of multiparous mothers, and had no known or suspected pathological condition. Apparatus. The apparatus gave measures of sucking behavior and heart rate from infants held in the ordinary feeding position. The device used to measure sucking (Fig. 1) was designed to record two components of sucking behavior: expression, or the positive pressure created when the baby approximates his gums and elevates his tongue, and suction, or negative pressure produced when the baby lowers his tongue and bottom jaw. Pressure changes produced by suction and expression were monitored by two pressure transducers and written out on two channels of a polygraph using DC preamplifiers. Before each experimental session, the apparatus was calibrated by applying standard negative and positive pressures to the nipple. During the feed a rotary pump moved the milk along the delivery tube. The action of the pump was controlled by a trigger circuit fired by the polygraph; for half of the group (12 infants) the pump was triggered by expression responses and for the other half by suction responses. The aim of the experiment was to record normal sucking behavior during a feed that closely resembled a natural bottle feed. Accordingly, the
284
btJkIGNON
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minimum pressures that triggered the pump (-20 mm Hg for suction and 4 mm Hg for expression) were set very low to avoid influencing normal suction or expression pressures by reinforcement contingencies. The pump delivered 0.16 cc of milk each time it moved so that the infant had to suck 190 times in order to get 1 ounce of milk. Sucking was also recorded by counting the movements of the mouth and jaw made by the baby. An observer signalled every tenth count with an event marker on the polygraph. An EKG was taken from electrodes on the baby’s chest and back. These led to two channels of the polygraph that recorded both the electrocardiogram and a t,achograph tracing of heart rate. TUBE
FOR
DELIVERY
OF MILK 2 CHANNEL
FOLEY CATHETER
NIPPLE GLUED TO PLASTIC DISC TUBE TO RECORD CHANGES WITHIN [EXPRESSION]
PRESSURE NIPPLE
TUBE TO RECORD INTRA-ORAL PRESSURE CHANGES [SUCTION] FIQ. 1. Diagram of nipple adapted to deliver fluid and to measure the suction and expression components of sucking.
Procedure. At a normal feeding hour the subject was brought to the research room. The nursery regimen called for a feed every 4 hours. Diapers were changed in the nursery to provide a standard rousing procedure. The baby was weighed, heart rate electrodes were applied, and the baby was bundled in a carrying blanket and given to the first experimenter (El). El held the baby in the normal feeding position, i.e., in the crook of the left arm with the head resting against the experimenter’s chest. El was responsible for giving the baby the nipple, signalling: (i) the different phases of the experiment and, (ii) every tenth suck during the sucking trials. A second experimenter (E2) operated the polygraph, timed the trials, delivered dextrose through the nipple during the second trial, and prepared the milk delivery system for the feed. At the start of the experiment, the baby was held by El in the feeding
SUCKING
IN
THE
NEWBORN
285
position for.2 minutes. During this time only a heart-rate ‘record was made. Immediately afterwards the baby was given a nipple, and once this had been accepted, 2 minutes of nonnutritive sucking were recorded. After this first trial, a syringe filled with a 5% dextrose solution (temperature approximately 35°C) was attached to the delivery tube of the catheter so that during the second trial E2 delivered .5 cc of dextrose for every tenth suck counted by El. The dextrose trial followed the nonnutritive trial by approximately 30 seconds and also lasted 2 minutes. During the third part of the experiment, expression, suction, and heart rate, were recorded while the baby was given its usual milk feed by means of the pump. El held the baby as before and signalled: (i) presentation and acceptance of the nipple, (ii) her count of sucking and, (iii) withdrawal of the nipple when burping was necessary. During burping periods the polygraph was switched off and the length of these periods was noted on the record before the feed was resumed. When the baby rejected the nipple, the bottle was removed from the pump-delivery mechanism; the amount of milk consumed and time taken over the feed was noted. The infant was offered what remained of the feed directly from the bottle, heart rate was recorded, and El continued to count sucks if the baby sucked at all at this point. When the nipple was finally rejected, any additional amount taken was noted and heart rate was recorded during a final 2-minute rest period. The baby was weighed and returned to the nursery. Scoring and analysis. Scoring criteria were calculated for each chart so that every record could be scored in terms of a standard preamplifier sensitivity setting on the polygraph and a “standard” nipple. The minimum standards for scoring pressure changes corresponded to a pressure of -20 mm Hg for suction and 4 mm Hg for expression (cf. Dubignon, 1967). The first 2 minutes of the feed were treated as a a-minute trial comparable to the non-nutritive and dextrose trials. The last 90 seconds of each 2-minute trial were scored to avoid the initial burst of sw.&ing at the beginning of each trial. The following scores were made for both expression and suction: (i) a count of the number of responses above criterion amplitude; (ii) time spent responding during the 90 seconds (the criterion for time out from responding was any break in tbe record longer than. 1 second) ; (iii) rate (calculated from the first two measures by -dividing the time spent responding into the count) ; (iv) the amplitude of every fifth response; (v) expression/suction ratio (calculated by dividing the suction count into the expression count) ; and, (vi) the observer’s count for each a-minute trial was recorded.
286
DUBIGNON
AND
CAMPBELL
Heart rate was scored for the last 45 seconds of each 2-minute trial and heart-rate variability was measured by recording the difference between the highest and lowest point on the tachograph tracing for the same period. This measure is referred to as heart-rate range. Sucking during the whole feed was first studied by dividing each pump-feed record into four sections of equal duration (excluding burping periods). The end of the pump feed was taken as the last storable response. The last 45 seconds of each quarter section of the feed were scored for suction and expression responses and the same six measures were taken as in the three earlier trials. Heart rate and heart-rate range were scored for the same four periods with the addition of a further score for the last 45 seconds of the final rest period. The influence of fatigue on sucking during the feed was examined by scoring additional 45-second sections of the records before and after the first and last burping periods; this was done for half of the group (NE 12). The results were treated by analysis of variance and evaluated as mixed models. An arcsin transformation was applied to the time scores before analysis. Reliability of scoring. The reliability of polygraph scores was examined by having ten records scored independently by two scorers (r = 1.0 for counts, r = .99 for time spent sucking, and r = .99 for amplitude scores). The method of scoring amplitude was checked for reliability by taking ten records and scoring every response. The mean amplitudes obtained in this way were correlated with the means obtained from scoring every fifth response (r = .97). RESULTS Comparisons of p-ump feeding with natural bottle feeding. The total duration of the pump feed, the number of sucks counted by the observer, and the number of rest periods for burping were recorded for each of the 24 infants. These data were compared with equivalent figures for 20 infants given bottle feeds by their mothers in a previous experiment (Dubignon and Campbell, 1968b). No significant differences were found between pump and natural bottle feeding although a natural feed took a shorter time, required fewer burping periods, and led to a lesser number of sucks on the average. Suclcing scores. The over-all mean and range of the different measures of sucking behavior are summarized in Table 1. These scores fall within the range of scores reported by other investigators (Balint, 1948; Colley and Creamer, 1958; Halverson; 1938, 1944;‘Kron et c&,:1967; Sameroff, 1965).
SUCKING
MEAN
AND RANGE
OF
IN
THE
287
NEWBORN
TABLE 1 SCORES Pyle MEASURES
Suction count/minute Expression count/minute Suction time/minute (seconds) Expression time/minute (aeccnds) Suction rate per second of sucking time
OF SUCJXING
BEHAVIOR
Mean
Range
49.77
5-87 14-87 4-58
53.58 37.96 40.16 1.326 1.351 -82.0 23.5
Expressionrate per secondof suckingtime Suctionpressure(nun Hg) Expressionpressure(mmHg)
1%59 .951-1.976 .898-1.867 - (20-185) j-48 -
Treatment effects. The mean scores for expression and suction under each treatment for all six measures are summarized in Table 2 together with F values. Duncan’s Multiple Range tests were used to test the differences between the individual means. Sucking counts. The introduction of dextrose on the second trial led to a sharp drop in expression count followed by a return to the nonnutritive level during the feeding trial (p < .05). The same effect was found in the observer’s count (p < .05). The suction count varied in the same direction across trials but the effect was not significant. TABLE TREATMENT
MEANS
FOR EXPRESSION
2 AND SUCTION
Measure Sucking ~0unt.e (in 90 seconds) Suction count
Expression count Observer’s count (for each 2-minute trial) Sucks per second Time spent sucking (in 90 seconds) Suction time
ExpreGon time
Nonnutritive trial
79.4
85.4 ,941
50.7 54.9
ON EACH
MEASURE
Dextrose Feeding trial trial 70.3 72.7 ,814
74.2 83.0 ,901
55.8 56.3
64.3 69.5
1.26 1.30
1.16 1.21
.-
P 1.55 4.50* 3.66* 7.28** 14.06***
Sucking rate (per second of actual sucking time)
Suctionrate
1.55
Expression rate Amplitude of responding (mm) Suction amplitude Expression amplitude Expression/suction ratio (over 90 seccnds) * p < .05; ** p < .Ol;
*** p < .OOl.
1.54 9.19 9.91 1.17
10.78 11.19
1.05
10.92 8.93 1.16
7a.99***
56.94*** 10.30*** 2.50 -.
288
DUBIGNON
Tinze spenlt sucking. During
AND
CAMPBELL
the feeding trials the time spent in suction and expression was significantly higher than in either the non-nutritive or dextrose trials (p < .Ol). Sucking rate. There was a marked decline in suction and expression rates during the dextrose trial (p < .OOl) and a further significant decline during feeding (p < .Ol). Amplitude of sucking. Suction amplitude was significantly lower (p < .OOl) during non-nutritive sucking than in the dextrose and feeding trials in which the suction amplitudes did not differ. Amplitude of expression did not change significantly across trials. Expression/suction ratio. There were no significant differences in the ratio of the two components of sucking during the three trials. The ratio was always greater than 1, showing that the expression component appeared more often than the suction component. Trigger group effects. There were no significant differences on any measure between the scores obtained by the two groups for whom the pump was triggered by suction and expression respectively. Nor were any of the trigger group X treatments interactions significant. In summary, the results show that non-nutritive sucking differed from sucking when nutritive fluid was delivered. Fluid delivery was accompained by a change in the pattern of sucking, i.e., by an increase in time spent sucking, slower sucking rates, and an increase in amplitude of suction. To a lesser extent sucking during a feed differed from nutritive sucking for small amounts of dextrose. This was shown by the marked increase in time spent sucking during the feeding trial that resulted in a higher sucking count in spite of the slower sucking rate. While a change in pattern of sucking occurred when nutritive fluid was delivered, it appears that the mechanism of sucking did not change, in that the relationship between the expression and suction components of sucking remained the same. Suckitig behavior during the feed. The mean scores for expression and suction during each quarter of the feed for all six measures are summarized in Table 3 together with F values. Sucking counts. The counts of suction and expression responses were significantly lower (p < .OOl) during the last quarter of the feed than in the first three quarters in which the counts did not differ. The observer’s count made throughout each quarter of the feed revealed the same effect (p < .OOl) and also showed that the number of sucks made during the third quarter was lower than during the first quarter (p < .05). Time spent sucking. During the last quarter of the feed there was a significant drop in suction time (p < .OOl) and expression time (p <
SCORES
MEASURE
Measure
FOR EACH
OF EXPRESSION
*p < .05; **p < 605; ***p
< ml.
Suction timetime Expression Sucking rate (per second of actual sucking time) Suction rate Expression rate Amplitude of responding (mm) Suction amplitude Expression amplitude Expression/suction ratio (over 45 seconds)
Suction count Expression count Observer’s count (for duration of each quarter) Sucks per second Time spent sucking (in 45 seconds)
Sucking counts (in 45 seconds)
MEAN
TABLE SUCTION
3 THE
LAST
28.08 32.46 1.22 1.22 9.55 9.42 1.226
1.22 1.25 9.57 10.08 1.292
,817
34.29 39.41
Second quarter
DURING
30.04 34.63
,859
36.46 42.25
First quarter
AND
quarter
8.61 9.34 1.429
1.15 1.23
26.44 32.39
,759
31.87 39.46
Third
45 SECONDS QUARTER
6.60*‘* 3.61*
11.93***
1.23 6.18 6.92 1.799
1.01
1.17
10.86*** 6.01**
24.79***
12,39*** 11.24***
F
OF THE FEED
1.23
15.90 25.92
.56S
18.92 30.42
Fourth quart,er
OF EACH
E
!
3
g 9
2 8
290
DUBIGNON
AND
CAMPBELL
.005) as compared with the first three quarters in which time spent responding did not differ. Sucking rates. There were no significant differences in suction or expression rates throughout the feed. Amplitude of such&g. During the last quarter of the feed there was a sharp drop in amplitude of suction (p < 901) and expression (p < .Ol) as compared with the first three quarters in which amplitude of suction or expression did not differ significantly. Expression/suction ratio. There was an increase in the ratio of expression to suction responses in the last quarter of the feed (p < .05). Trigger group effects. Suction amplitude was slightly higher over-all in the group of subjects for whom the pump was triggered by the expression component of sucking. The mean amplitudes were: 7.21 mm for the suction trigger group and 9.75 mm for the expression trigger group (F = 4.36, dj 1,22, p < .05). There were no significant differences between the two groups on any other measure. In summary, these results show that the infants did not control their food intake by altering their sucking rate. Satiation was marked by less time spent sucking (and a consequent reduction in sucking count) and reduced amplitude of suction. In addition there appeared to be a change in the sucking mechanism with satiation as shown by the increase in expression/suction ratio. This was due to a marked drop in the frequency of the suction component during the last quarter of the feed. Sucking behavior before and after burping. The mean scores for the main effects are shown in Table 4 together with F values. There were no significant interactions. Before and after burping. The sucking counts for suction and expressions were higher after burping than before burping (p < .005), and there was a corresponding increase in suction time (p < .025) and expression time (p < 905). There were no significant differences before and after burping in suction or expression rates. First and last burp. At the time of the first burp sucking counts for both expression (p < .095) and suction (p < .025), and time spent in suction (p < .Ol) were higher than at the last burp. Time spent in expression varied in the same direction but did not reach significance. There were no significant differences between sucking rates at the first and last burping periods. In summary, these results show that after a burping period the infants increased the time spent sucking and showed a corresponding increase in sucking counts. The recovery after a rest was as great in the early part of the feed as toward the end of the feed. Toward the end of the feed (last burp) sucking counts and time spent sucking dropped off as
SUCKING
IN
THE
TABLE SUCKING
SCORES
IN RELATION
291
NEWBORN
4 TO REST
PERIODS
Mean sucking scores before and after burping periods
Suction count (45 seconds) Expression count (45 seconds) Suction time (45 seconds) Expression time (45 seconds) Suction rate (per second) Expression rate (per second)
Before
After
F
P
30.04 38.17 24.79 30.88
41.54 46.54 34.50 38.31
13.99 15.78 s.97 14.75
<.005 < ,005 C.025 <.OO.i
1,166
1.225
1.2.57
1.2’3
n-s .~
N::
Mean sucking scores at first and last burping periods
Suction count (45 seconds) Expression count (45 seconds) Suction time (45 seconds) Expression time (45 seconds) Suction rate (per second) Expression rate (per second)
First
Last
42.21 45.93 35.23 36.42 1.197 1.277
29.38 3s.79 24.06 32.77 1.194 1.204
F
9.53
P
< .o’J5
18.11
< ,005
11.29 3.11
<.Ol NS
1.50
NS i”;p
compared with the early part of the feed (first burp) but sucking rates did not change. Heart-rate changes. The mean heart rate and heart-rate ranges scored over 45-second periods under the various conditions are plotted in Figure 2. Time spent sucking (expression) is shown at the top of the figure. For the quarters of the feed, time spent sucking in 45 seconds has been doubled to give scores comparable with those for the 90-second trials. Analyses of variance were carried out on the heart-rate measures for the eight conditions (excluding the scores for the feeding trial, which were identical to those for the first quarter of the feed). Highly significant differences were found between conditions (p < .OOl) for both heart rate and heart-rate range. Multiple range tests revealed that: (i) during feeding (all four quarters) heart rate was faster than during non-nutritive sucking or initial and final rest periods; (ii) during feeding (quarters two and three), heart rate was faster than during the dextrose trial; (iii) during the first three quarters of the feed heart-rate range was lower than during either rest period ; and (iv) during the first half of the feed, heart-rate range was lower than during the last quarter of the feed or non-nutritive and dextrose trials. In summary, these results show that during nutritive sucking heart rate increased sharply and moment-to-moment variation in heart rate
DUBIGNON
FIG.
AND
CAMPBELL
2. Measures of heart rate as related to sucking and rest.
(heart-rate range) showed a corresponding decrease below the resting levels. The plot of time spent sucking, which has been superimposed on Fig. 2, makes it clear that the reduction in heart-rate range was associated with sucking per se rather than the provision of dextrose or milk. Sucking scores were studied in relation to length of labor and drugs or anesthetics given to the mother before delivery. The sucking scores bore no relation to these variables. DISCUSSION
This experiment was designed to compare sucking under conditions that were thought to represent progressive approximations to a bottle feed. Was pump feeding really like a normal feed by bottle? Although the pump feed took longer and the babies gave a greater number of sucks and had to be burped more frequently, the analyses of these data showed that the differences could have arisen by chance. Eight of the 24 pump-fed babies took some milk from the bottle when it was offered at the end of the pump feed (one-eighth to one-half oz) and in this respect their performance did not differ from that of bottle-fed babies who often take more from the bottle when it is offered them by an ex-
SUCKING
IN
THE
NEWBORN
293
perienced nurse at the end of a feed. Thus, despite a tendency to require a longer time, the pump feed provides a facsimile of bottle feeding. These findings clear the way for an examination of the first hypothesis, namely: that nutritive fluids are significant determinants of sucking. The results reinforce the conclusions drawn from an earlier experiment (Dubignon and Campbell, 1968b) : when nutritive fluid is delivered, marked changes in the pattern of sucking occur. It should be noticed that an analysis based upon sucking counts would show a significant drop in expression scores when dextrose was introduced on the second trial followed by a return to the non-nutritive level in the first 2 minutes of the pump feed. However, these shifts in count follow from a change in the over-all pattern of responding: the rate of sucking, for both expression and suction, fell when dextrose was introduced in the second trial and became even slower during the first 2 minutes of the feed. (In this context, rate means the rate of expression and suction responses per second during the intervals of time when the baby was actually sucking). The fall in rate was offset by an increase in time spent sucking when dextrose was introduced and a further increase during the feed. As predicted, during the feed the changes in pattern of sucking, which had already been observed to take place immediately on the addition of dextrose to the array of intraoral stimuli, were exaggerated. The order in which the non-nutritive, dextrose and feeding conditions were presented must be considered in interpreting these results. It has been shown previously that the order of non-nutritive and dextrose trials has no effect upon the sucking patterns elicited under each condition (Dub&on and Campbell, 1968b). In the present study it was not possible to vary the order of feeding and dextrose conditions because, after a feed, it is difficult to elicit sucking reliably. In a recent study sucking for small and equal amounts of milk and dextrose has been compared when the order of trials was counterbalanced. Milk elicited higher sucking counts and more time spent sucking and both these effects were independent of the order of trials (Dubignon and Campbell, 1968c). It is therefore improbable that the order of conditions in the present experiment contributed significantly to the changes in pattern of responding. An experiment based upon sucking counts alone would have led to the conclusion that non-nutritive sucking and sucking during a feed do not differ. One practical consequence of these results is that the study of sucking in relation to changes in stimulating conditions should be based upon measures that are more analytical than a sucking count taken over a specified length of time because a count alone does not do justice to changes in the pattern of responding. The findings agree with those of Halverson (1923). Sameroff (1965) (
294
DUBIGNON
AND
CAMPBELL
who reported lower counts during non-nutritive sucking, fed his subjects for 5 minutes before the measurement of non-nutritive sucking so that the conditions were not directly comparable with the present experiment. There were no significant changes in the ratio of expression count to suction count between the three treatments, which suggests that in both nutritive and non-nutritive conditions the mechanism of sucking is the same. However, the expression component tended to occur more frequently than the suction component. It is frequently possible to have an expression component without a matching suction component; the converse of this-suction without expression-rarely happens (cf. Sameroff, 1965).’ The amplitude of suction responses showed a significant increase across trials so that the babies used the greatest negative pressure during the pump feed. Expression amplitude, on the other hand, declined during feeding but not sufficiently to reach significance. One could argue, that the relative importance of suction and expression (as measured by the pressure exerted) shifts when a feed is given. However, this result should be checked using a variety of delivery systems since the pressure exerted in any given setting could conceivably be an artefact of the mechanism used to deliver milk. Before framing any conclusions regarding the differences found between the three treatments it is instructive to re-examine the sucking rates: Non-nutritive Suction rate Expression rate
1.55 1.54
Dextrose
Feeding
1.26 1.30
1.16 1.21
The major change in rate took place between the non-nutritive and dextrose trials and a smaller drop occurred during feeding. The average consumption of fluid during the periods scored was 3.5 cc of dextrose and 11.5 cc of milk. It is possible that the small drop in sucking rate between the dextrose and feeding trials may stem from the need to swallow three times as much fluid, rather than differences in the qualities of milk and dextrose. The fact that the large difference in intake caused only a slight drop in rate makes it clear that the much larger decrease in rate between non-nutritive and dextrose trials is not likely to be due to the need to swallow 3.5 cc during the dextrose trial. Here the change in sucking pattern is clearly due to the change in intra-oral stimulation. The changes in sucking during the feed suggest that it may be necessary to make some distinctions between the control of sucking by intraoral stimulation and the control exerted by satiation or fatigue. It should be noted that during the pump feed the significant changes in counts and time spent sucking in the last quarter of the feed are not matched by
SUCKING
IN
THE
295
NEWBORN
any change in sucking rates. Similarly, there were no changes in sucking rates before and after burping periods. It seems plausible to argue that the sucking rate is primarily under the control of intraoral stimulation while the probability of sucking is controlled by other factors as well. Thus a baby, given a feed, will react to satiation, not by sucking more slowly, but by sucking less of the time. Both fatigue and satiation must be considered in interpreting the changes in sucking behavior that occurred at the end of the feed. Studies of non-nutritive sucking over long periods (10-15 minutes) have shown that work decrements are small and that there is complete recovery of initial sucking levels given a l-minute rest period (Levin and Kaye, 1964, 1966). These findings are confirmed in the present study of feeding. Examination of time spent sucking and mean sucking counts for the first quarter of the feed and after the last burping period reveals that the infants showed almost complete recovery of initial sucking levels after rest.
First quarter of feed After last burping period
Suction count
Expression cmlnt
Suction time
Expression time
36.46 33.92
42.25 41.58
30.04 28.63
34.63 35.54
The increase in time spent sucking and sucking count after burping can be construed as recovery from fatigue. This recovery was as large in the early part of the feed as it was toward the end of the feed. On the other hand, it appears that increasing satiation is responsible for the decrease in time spent sucking and lower sucking counts at the time of the last burp as compared with the first burp. It will be remembered that during the last quarter of the feed the part of the record scored was the final 45 seconds of sucking. After a further rest the infant refused to accept the nipple. It therefore seems likely that satiation and fatigue are jointly responsible for the changes in sucking behavior that were observed at the end of the last quarter of the feed, while the refusal to accept the nipple after a further rest may be attributed to satiation alone. The uniformity of sucking performance during the first three quarters of the feed stands in contrast to decrements in non-nutritive sucking after the consumption of amounts of fluid as small as lo-20 cc (Kaye, 1966). These effects were interpreted as due to satiation. In the present study no decrement in responding was observed until 60-90 cc of fluid had been consumed. Two interpretations of these findings are possible: either small amounts of fluid in the stomach have different effects on nutritive and non-nutritive sucking, or t.he decrement found by Kaye
296
DUBIGNON
AND
CAMPBELL
(1966) was a contrast phenomenon, i.e., the dry nipple may be less effective in sustaining sucking after the infant has experienced the additional stimulation of fluid in the mouth. The change in expression/suction ratio at the end of the feed indicates that satiation or fatigue induces a change in the mechanism of sucking; the suction component tends to drop out, while the expression component appears to represent chewing or mouthing of the nipple. This finding supports the conclusion that suction is the means by which bottle-fed infants usually control their food intake from standard commercial nipples as opposed to the “stripping” action that may be the effective means of getting milk from the breast. Throughout the feed the trigger was set to fire for low-amplitude responding, so that milk was delivered for every sucking response. The mean suction and expression amplitudes recorded were in fact four times the amplitude necessary to trigger the pump. It therefore seems likely that the higher suction amplitudes recorded for the expression trigger group during the feed were a chance finding. At first sight the pattern of changes in heart rate and heart-rate range give the impression that feeding exerts a stronger influence than nonnutritive or dextrose sucking on “state” as measured by heart rate. However, examination of the sucking scores suggests that feeding has this influence because more time is spent sucking during feeding. The plot of time spent sucking under the various conditions is virtually a mirror image of the plot of heart-rate range, and this supports the conclusion that the reduction in heart-rate variability is a function of sucking per se rather than the provision of nutriment. The relation between heart rate and sucking is not quite so obvious. Nutritive sucking leads to increases in heart rate, and as sucking drops off toward the end of the feed heart rate shows a corresponding drop toward the resting level. Similar increases in heart rate during nutritive sucking have been reported in other studies, e.g., Baliassnikowa and Model (1931) ; Lipton et al. (1958). The observation that high heart rates tend to be associated with low heart-rate ranges suggests that the reduction in range may possibly be attributed to a “ceiling” effect. However, the heart rate of newborn infants can increase very considerably above the highest mean rates reported here (approximatly 147 beats per minute). To sum up, non-nutritive sucking has been shown to differ from nutritive sucking on five of the six measures of sucking investigated in this study. In most cases, the differences were shown in both the suction and expression components of sucking. The results replicate and extend earlier findings and confirm the hypothesis that the stimuli provided by
SUCKING
IN
THE
NEWBORN
297
nutritive fluids are significant determinants of sucking. The. differences between non-nutritive sucking and sucking during a feed tiidke it clear that investigations that are intended to have implications for the feeding of the newborn should be carried out in a nutritive setting. The earlier finding that non-nutritive sucking frequency is in part determined by the characteristics of the nipple cannot be generalized to infant feeding without further study. Sucking behavior throughout a feed remained fairly uniform until the end of the last quarter when a decrease in sucking counts, time spent sucking, and suction amplitude, as well as a reduction in the frequency of the suction component of sucking marked the end of the feed. No COYresponding changes in sucking rate were found, which suggests that this measure of sucking may be primarily under the control of current intraoral stimulation. REFERENCES BALIASSNIKOWA, N. J., AND MODEL, fur Kinderheilkunde., 1931-2, BALINT, M. Individual differences
M. M. Zur Neurologie des Saugens. Zeitschrifl 39, 1-16. (Cited in Halverson, 1938). of behavior in early infancy and an objective method for recording them, I: Approach and the method of recording. II: Results and conclusions. Journal of Genetic Psychology, 1948, 73, 57-79; 81-117. COI,LEY, J. R. T., AND CREAMER, B. Sucking and swallowing in infants. British Medical Journal, 1958, 2, 422423. DUBIGNON, J. Intra-oral stimulation and sucking in the newborn. Unpublished Ph.D. Thesis : Queen’s University, 1967. DUBIGNON, J., AND CAMPBELL, D. Intra-oral stimulation and sucking in the newborn. Journal of Experimental Child Psychology, 1968 (a), 6, 154-166. DUBIGNON, J., AND CAMPBELL, D. Sucking in the newborn under three conditions: non-nutritive, nutritive and a feed. Journal of Experimental Child Psychology, 1968 (b), 6, 335-350. DUBIGNON, J., AND CAMPBELL, D. Discrimination of milk and dextrose by human newborns. 1968 (c) (in preparation). HALVERSON, H. M. Infant sucking and tensional behavior. Journal of Genetic Psychology, 1938, 53, 365430. HALVERSON, H. M. Mechanisms of early infant feeding. Journal of Genetic Psychology, 1944, 64, 185-223. KAYE, H. Effects of feeding and tonal stimulation on non-nutritive sucking in the human newborn. Journal of Experimental Child Psychology, 1966, 3, 131-145. &YE, H. Infant sucking and its modification. In L. P. Lip&t and C. C. Spiker (Eds.) Advances in Child Development and Behavior, vol. 3, Academic Press, New York: 1967. KRON, R. E., STEIN, M., GODDARD, K. E., AND PHOENIX, M. D. Effect of nutrient upon the sucking behavior of newborn infants. Psychosomatic Medicine, 1967, 23, 24-32. LEVIN, G. R., AND &YE, H. Non-nutritive sucking by human neonates. Child Development, 1964, 35, 749-758. LEVIN, G. R., AND KAYE, H. Work decrement and rest recovery during non-nutritive
298
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sucking in the human neonate. Journal of Experimental Child Psychology, 1966, 3, M-154. Lrpsrrr, L., AND KAYE, H. Change in neonatal response to optimising and nonoptimising sucking stimulation. Psychonomic Science, 1965,2,221-222. LIPTON, E. L., RICHMOND, J. B., WEINBERQEE, H. L., AND HEBSHEB, L. An approach to evaluation of neonate autonomic responses. Psychosomatic Medicine, 1958, 20, 469. SANEROFF, A. J. An experimental study of the response components of sucking in the human newborn. Unpublished Ph.D. Thesis : Yale University, 1965. TINBERGEN, N. The study of instinct. London and New York: Oxford Univ. Press, 1951.
OF EXPERIMXCNTAL
Sucking JUDITH
CHILD
7, 282-298 (1969)
PSYCHOLOGY
in the
Newborn
DUBIGNON
DUGAL
AND
Queen’s University,
during
Kingston,
a Feed
CAMPBELLI
Ontario
Two components of sucking (suction and expression) were measured under three conditions: when no fluid waz available, when small amounts of dextrose were delivered, and throughout a milk feed. Significant differences in sucking rate, time spent sucking, and pressure were found between the nonnutritive and dextrose conditions; these differences were more marked during the feed. Sucking throughout the feed remained uniform until the end of the last
quarter when a reduction in frequency of sucking, time spent sucking, and sucking pressure took place. There were no changes in sucking rate. Heart rate rose during nutritive sucking and moment-to-moment variation in heart rate was reduced.
Experiments intended to identify the stimuli that control sucking have shown that intraoral stimuli are significant determinants of sucking in the newborn. For example, characteristics of the nipple, such as.& siae, shape, and compressibility, have been found to control the frequency of nonnutritive sucking (Lipsitt and Kaye, 1965; Dubignon and CamIj’bell, 1968a). These results resemble those found in ethological studies. that have shown that feeding behavior in the young of certain species is controlled by relatively specific sign-stimuli (Tinbergen, 1951). Little is known about stimulus control of sucking during feeding; however, among the stimuli that control sucking in a functional context, it is likely that those provided by nutritive fluids are relatively important, as well as other factors, such as satiation and fatigue. Until recently “there have been no reports comparing sucking for liquids and nonnutritive sucking within the same recording system” (Kaye, 1967). In one such study the data suggested that nutritive sucking during a feed is different from nonnutritive sucking. It was found that the delivery of small amounts of dextrose brought about immediate changes in pattern ‘The work reported in this paper Foundation (Grant No. 16) and the We wish to record our thanks to the and to our research assistants, Miss Elizabeth Wood.
was supported by the Ontario Mental Health Association for the Aid of Crippled Children. nursery stat7 of the Kingston General Hospital M. Henderson, Mrs. E. Stephenz, and Miss
282
SUCKING
IN
THE
NEWBORX
283
of sucking: the infants sucked more slowly and gave longer bursts of sucking. Naturalistic observations of breast and bottle feeding suggested that these changes in pattern of sucking became even more marked during feeding. In the same study significant changes in heart rate were found to accompany sucking (Dubignon and Campbell, 1968b). The present experiment was designed to examine further the hypothesis that the stimuli provided by nutritive fluids are significant determinants of sucking. The earlier observations led to the prediction that the differences found between nonnutritive sucking and sucking for small amounts of dextrose would become more marked during a feed. Secondary aims were to provide data on the regulation of food intake by the newborn, the effects of fatigue and satiation on nutritive sucking, and changes in heart rate during feeding. METHOD
Sucking was measured under three conditions: first, nonnutritive sucking when no fluid was given to the baby; second, when small amounts of dextrose fluid were delivered; and third, throughout a bottle feed. The order of nonnutritive and dextrose conditions was not varied as it has been shown that the order of trials has no significant effect on the sucking elicited in each condition (Dubignon and Campbell, 1968b). Subjects. Twenty-four full-term babies (12 male, 12 female) were seen during the third or fourth days of life (mean age: 70 hours; SD 12.1). All the babies were bottle-fed infants of multiparous mothers, and had no known or suspected pathological condition. Apparatus. The apparatus gave measures of sucking behavior and heart rate from infants held in the ordinary feeding position. The device used to measure sucking (Fig. 1) was designed to record two components of sucking behavior: expression, or the positive pressure created when the baby approximates his gums and elevates his tongue, and suction, or negative pressure produced when the baby lowers his tongue and bottom jaw. Pressure changes produced by suction and expression were monitored by two pressure transducers and written out on two channels of a polygraph using DC preamplifiers. Before each experimental session, the apparatus was calibrated by applying standard negative and positive pressures to the nipple. During the feed a rotary pump moved the milk along the delivery tube. The action of the pump was controlled by a trigger circuit fired by the polygraph; for half of the group (12 infants) the pump was triggered by expression responses and for the other half by suction responses. The aim of the experiment was to record normal sucking behavior during a feed that closely resembled a natural bottle feed. Accordingly, the
284
btJkIGNON
AND
CAMPBELL
minimum pressures that triggered the pump (-20 mm Hg for suction and 4 mm Hg for expression) were set very low to avoid influencing normal suction or expression pressures by reinforcement contingencies. The pump delivered 0.16 cc of milk each time it moved so that the infant had to suck 190 times in order to get 1 ounce of milk. Sucking was also recorded by counting the movements of the mouth and jaw made by the baby. An observer signalled every tenth count with an event marker on the polygraph. An EKG was taken from electrodes on the baby’s chest and back. These led to two channels of the polygraph that recorded both the electrocardiogram and a t,achograph tracing of heart rate. TUBE
FOR
DELIVERY
OF MILK 2 CHANNEL
FOLEY CATHETER
NIPPLE GLUED TO PLASTIC DISC TUBE TO RECORD CHANGES WITHIN [EXPRESSION]
PRESSURE NIPPLE
TUBE TO RECORD INTRA-ORAL PRESSURE CHANGES [SUCTION] FIQ. 1. Diagram of nipple adapted to deliver fluid and to measure the suction and expression components of sucking.
Procedure. At a normal feeding hour the subject was brought to the research room. The nursery regimen called for a feed every 4 hours. Diapers were changed in the nursery to provide a standard rousing procedure. The baby was weighed, heart rate electrodes were applied, and the baby was bundled in a carrying blanket and given to the first experimenter (El). El held the baby in the normal feeding position, i.e., in the crook of the left arm with the head resting against the experimenter’s chest. El was responsible for giving the baby the nipple, signalling: (i) the different phases of the experiment and, (ii) every tenth suck during the sucking trials. A second experimenter (E2) operated the polygraph, timed the trials, delivered dextrose through the nipple during the second trial, and prepared the milk delivery system for the feed. At the start of the experiment, the baby was held by El in the feeding
SUCKING
IN
THE
NEWBORN
285
position for.2 minutes. During this time only a heart-rate ‘record was made. Immediately afterwards the baby was given a nipple, and once this had been accepted, 2 minutes of nonnutritive sucking were recorded. After this first trial, a syringe filled with a 5% dextrose solution (temperature approximately 35°C) was attached to the delivery tube of the catheter so that during the second trial E2 delivered .5 cc of dextrose for every tenth suck counted by El. The dextrose trial followed the nonnutritive trial by approximately 30 seconds and also lasted 2 minutes. During the third part of the experiment, expression, suction, and heart rate, were recorded while the baby was given its usual milk feed by means of the pump. El held the baby as before and signalled: (i) presentation and acceptance of the nipple, (ii) her count of sucking and, (iii) withdrawal of the nipple when burping was necessary. During burping periods the polygraph was switched off and the length of these periods was noted on the record before the feed was resumed. When the baby rejected the nipple, the bottle was removed from the pump-delivery mechanism; the amount of milk consumed and time taken over the feed was noted. The infant was offered what remained of the feed directly from the bottle, heart rate was recorded, and El continued to count sucks if the baby sucked at all at this point. When the nipple was finally rejected, any additional amount taken was noted and heart rate was recorded during a final 2-minute rest period. The baby was weighed and returned to the nursery. Scoring and analysis. Scoring criteria were calculated for each chart so that every record could be scored in terms of a standard preamplifier sensitivity setting on the polygraph and a “standard” nipple. The minimum standards for scoring pressure changes corresponded to a pressure of -20 mm Hg for suction and 4 mm Hg for expression (cf. Dubignon, 1967). The first 2 minutes of the feed were treated as a a-minute trial comparable to the non-nutritive and dextrose trials. The last 90 seconds of each 2-minute trial were scored to avoid the initial burst of sw.&ing at the beginning of each trial. The following scores were made for both expression and suction: (i) a count of the number of responses above criterion amplitude; (ii) time spent responding during the 90 seconds (the criterion for time out from responding was any break in tbe record longer than. 1 second) ; (iii) rate (calculated from the first two measures by -dividing the time spent responding into the count) ; (iv) the amplitude of every fifth response; (v) expression/suction ratio (calculated by dividing the suction count into the expression count) ; and, (vi) the observer’s count for each a-minute trial was recorded.
286
DUBIGNON
AND
CAMPBELL
Heart rate was scored for the last 45 seconds of each 2-minute trial and heart-rate variability was measured by recording the difference between the highest and lowest point on the tachograph tracing for the same period. This measure is referred to as heart-rate range. Sucking during the whole feed was first studied by dividing each pump-feed record into four sections of equal duration (excluding burping periods). The end of the pump feed was taken as the last storable response. The last 45 seconds of each quarter section of the feed were scored for suction and expression responses and the same six measures were taken as in the three earlier trials. Heart rate and heart-rate range were scored for the same four periods with the addition of a further score for the last 45 seconds of the final rest period. The influence of fatigue on sucking during the feed was examined by scoring additional 45-second sections of the records before and after the first and last burping periods; this was done for half of the group (NE 12). The results were treated by analysis of variance and evaluated as mixed models. An arcsin transformation was applied to the time scores before analysis. Reliability of scoring. The reliability of polygraph scores was examined by having ten records scored independently by two scorers (r = 1.0 for counts, r = .99 for time spent sucking, and r = .99 for amplitude scores). The method of scoring amplitude was checked for reliability by taking ten records and scoring every response. The mean amplitudes obtained in this way were correlated with the means obtained from scoring every fifth response (r = .97). RESULTS Comparisons of p-ump feeding with natural bottle feeding. The total duration of the pump feed, the number of sucks counted by the observer, and the number of rest periods for burping were recorded for each of the 24 infants. These data were compared with equivalent figures for 20 infants given bottle feeds by their mothers in a previous experiment (Dubignon and Campbell, 1968b). No significant differences were found between pump and natural bottle feeding although a natural feed took a shorter time, required fewer burping periods, and led to a lesser number of sucks on the average. Suclcing scores. The over-all mean and range of the different measures of sucking behavior are summarized in Table 1. These scores fall within the range of scores reported by other investigators (Balint, 1948; Colley and Creamer, 1958; Halverson; 1938, 1944;‘Kron et c&,:1967; Sameroff, 1965).
SUCKING
MEAN
AND RANGE
OF
IN
THE
287
NEWBORN
TABLE 1 SCORES Pyle MEASURES
Suction count/minute Expression count/minute Suction time/minute (seconds) Expression time/minute (aeccnds) Suction rate per second of sucking time
OF SUCJXING
BEHAVIOR
Mean
Range
49.77
5-87 14-87 4-58
53.58 37.96 40.16 1.326 1.351 -82.0 23.5
Expressionrate per secondof suckingtime Suctionpressure(nun Hg) Expressionpressure(mmHg)
1%59 .951-1.976 .898-1.867 - (20-185) j-48 -
Treatment effects. The mean scores for expression and suction under each treatment for all six measures are summarized in Table 2 together with F values. Duncan’s Multiple Range tests were used to test the differences between the individual means. Sucking counts. The introduction of dextrose on the second trial led to a sharp drop in expression count followed by a return to the nonnutritive level during the feeding trial (p < .05). The same effect was found in the observer’s count (p < .05). The suction count varied in the same direction across trials but the effect was not significant. TABLE TREATMENT
MEANS
FOR EXPRESSION
2 AND SUCTION
Measure Sucking ~0unt.e (in 90 seconds) Suction count
Expression count Observer’s count (for each 2-minute trial) Sucks per second Time spent sucking (in 90 seconds) Suction time
ExpreGon time
Nonnutritive trial
79.4
85.4 ,941
50.7 54.9
ON EACH
MEASURE
Dextrose Feeding trial trial 70.3 72.7 ,814
74.2 83.0 ,901
55.8 56.3
64.3 69.5
1.26 1.30
1.16 1.21
.-
P 1.55 4.50* 3.66* 7.28** 14.06***
Sucking rate (per second of actual sucking time)
Suctionrate
1.55
Expression rate Amplitude of responding (mm) Suction amplitude Expression amplitude Expression/suction ratio (over 90 seccnds) * p < .05; ** p < .Ol;
*** p < .OOl.
1.54 9.19 9.91 1.17
10.78 11.19
1.05
10.92 8.93 1.16
7a.99***
56.94*** 10.30*** 2.50 -.
288
DUBIGNON
Tinze spenlt sucking. During
AND
CAMPBELL
the feeding trials the time spent in suction and expression was significantly higher than in either the non-nutritive or dextrose trials (p < .Ol). Sucking rate. There was a marked decline in suction and expression rates during the dextrose trial (p < .OOl) and a further significant decline during feeding (p < .Ol). Amplitude of sucking. Suction amplitude was significantly lower (p < .OOl) during non-nutritive sucking than in the dextrose and feeding trials in which the suction amplitudes did not differ. Amplitude of expression did not change significantly across trials. Expression/suction ratio. There were no significant differences in the ratio of the two components of sucking during the three trials. The ratio was always greater than 1, showing that the expression component appeared more often than the suction component. Trigger group effects. There were no significant differences on any measure between the scores obtained by the two groups for whom the pump was triggered by suction and expression respectively. Nor were any of the trigger group X treatments interactions significant. In summary, the results show that non-nutritive sucking differed from sucking when nutritive fluid was delivered. Fluid delivery was accompained by a change in the pattern of sucking, i.e., by an increase in time spent sucking, slower sucking rates, and an increase in amplitude of suction. To a lesser extent sucking during a feed differed from nutritive sucking for small amounts of dextrose. This was shown by the marked increase in time spent sucking during the feeding trial that resulted in a higher sucking count in spite of the slower sucking rate. While a change in pattern of sucking occurred when nutritive fluid was delivered, it appears that the mechanism of sucking did not change, in that the relationship between the expression and suction components of sucking remained the same. Suckitig behavior during the feed. The mean scores for expression and suction during each quarter of the feed for all six measures are summarized in Table 3 together with F values. Sucking counts. The counts of suction and expression responses were significantly lower (p < .OOl) during the last quarter of the feed than in the first three quarters in which the counts did not differ. The observer’s count made throughout each quarter of the feed revealed the same effect (p < .OOl) and also showed that the number of sucks made during the third quarter was lower than during the first quarter (p < .05). Time spent sucking. During the last quarter of the feed there was a significant drop in suction time (p < .OOl) and expression time (p <
SCORES
MEASURE
Measure
FOR EACH
OF EXPRESSION
*p < .05; **p < 605; ***p
< ml.
Suction timetime Expression Sucking rate (per second of actual sucking time) Suction rate Expression rate Amplitude of responding (mm) Suction amplitude Expression amplitude Expression/suction ratio (over 45 seconds)
Suction count Expression count Observer’s count (for duration of each quarter) Sucks per second Time spent sucking (in 45 seconds)
Sucking counts (in 45 seconds)
MEAN
TABLE SUCTION
3 THE
LAST
28.08 32.46 1.22 1.22 9.55 9.42 1.226
1.22 1.25 9.57 10.08 1.292
,817
34.29 39.41
Second quarter
DURING
30.04 34.63
,859
36.46 42.25
First quarter
AND
quarter
8.61 9.34 1.429
1.15 1.23
26.44 32.39
,759
31.87 39.46
Third
45 SECONDS QUARTER
6.60*‘* 3.61*
11.93***
1.23 6.18 6.92 1.799
1.01
1.17
10.86*** 6.01**
24.79***
12,39*** 11.24***
F
OF THE FEED
1.23
15.90 25.92
.56S
18.92 30.42
Fourth quart,er
OF EACH
E
!
3
g 9
2 8
290
DUBIGNON
AND
CAMPBELL
.005) as compared with the first three quarters in which time spent responding did not differ. Sucking rates. There were no significant differences in suction or expression rates throughout the feed. Amplitude of such&g. During the last quarter of the feed there was a sharp drop in amplitude of suction (p < 901) and expression (p < .Ol) as compared with the first three quarters in which amplitude of suction or expression did not differ significantly. Expression/suction ratio. There was an increase in the ratio of expression to suction responses in the last quarter of the feed (p < .05). Trigger group effects. Suction amplitude was slightly higher over-all in the group of subjects for whom the pump was triggered by the expression component of sucking. The mean amplitudes were: 7.21 mm for the suction trigger group and 9.75 mm for the expression trigger group (F = 4.36, dj 1,22, p < .05). There were no significant differences between the two groups on any other measure. In summary, these results show that the infants did not control their food intake by altering their sucking rate. Satiation was marked by less time spent sucking (and a consequent reduction in sucking count) and reduced amplitude of suction. In addition there appeared to be a change in the sucking mechanism with satiation as shown by the increase in expression/suction ratio. This was due to a marked drop in the frequency of the suction component during the last quarter of the feed. Sucking behavior before and after burping. The mean scores for the main effects are shown in Table 4 together with F values. There were no significant interactions. Before and after burping. The sucking counts for suction and expressions were higher after burping than before burping (p < .005), and there was a corresponding increase in suction time (p < .025) and expression time (p < 905). There were no significant differences before and after burping in suction or expression rates. First and last burp. At the time of the first burp sucking counts for both expression (p < .095) and suction (p < .025), and time spent in suction (p < .Ol) were higher than at the last burp. Time spent in expression varied in the same direction but did not reach significance. There were no significant differences between sucking rates at the first and last burping periods. In summary, these results show that after a burping period the infants increased the time spent sucking and showed a corresponding increase in sucking counts. The recovery after a rest was as great in the early part of the feed as toward the end of the feed. Toward the end of the feed (last burp) sucking counts and time spent sucking dropped off as
SUCKING
IN
THE
TABLE SUCKING
SCORES
IN RELATION
291
NEWBORN
4 TO REST
PERIODS
Mean sucking scores before and after burping periods
Suction count (45 seconds) Expression count (45 seconds) Suction time (45 seconds) Expression time (45 seconds) Suction rate (per second) Expression rate (per second)
Before
After
F
P
30.04 38.17 24.79 30.88
41.54 46.54 34.50 38.31
13.99 15.78 s.97 14.75
<.005 < ,005 C.025 <.OO.i
1,166
1.225
1.2.57
1.2’3
n-s .~
N::
Mean sucking scores at first and last burping periods
Suction count (45 seconds) Expression count (45 seconds) Suction time (45 seconds) Expression time (45 seconds) Suction rate (per second) Expression rate (per second)
First
Last
42.21 45.93 35.23 36.42 1.197 1.277
29.38 3s.79 24.06 32.77 1.194 1.204
F
9.53
P
< .o’J5
18.11
< ,005
11.29 3.11
<.Ol NS
1.50
NS i”;p
compared with the early part of the feed (first burp) but sucking rates did not change. Heart-rate changes. The mean heart rate and heart-rate ranges scored over 45-second periods under the various conditions are plotted in Figure 2. Time spent sucking (expression) is shown at the top of the figure. For the quarters of the feed, time spent sucking in 45 seconds has been doubled to give scores comparable with those for the 90-second trials. Analyses of variance were carried out on the heart-rate measures for the eight conditions (excluding the scores for the feeding trial, which were identical to those for the first quarter of the feed). Highly significant differences were found between conditions (p < .OOl) for both heart rate and heart-rate range. Multiple range tests revealed that: (i) during feeding (all four quarters) heart rate was faster than during non-nutritive sucking or initial and final rest periods; (ii) during feeding (quarters two and three), heart rate was faster than during the dextrose trial; (iii) during the first three quarters of the feed heart-rate range was lower than during either rest period ; and (iv) during the first half of the feed, heart-rate range was lower than during the last quarter of the feed or non-nutritive and dextrose trials. In summary, these results show that during nutritive sucking heart rate increased sharply and moment-to-moment variation in heart rate
DUBIGNON
FIG.
AND
CAMPBELL
2. Measures of heart rate as related to sucking and rest.
(heart-rate range) showed a corresponding decrease below the resting levels. The plot of time spent sucking, which has been superimposed on Fig. 2, makes it clear that the reduction in heart-rate range was associated with sucking per se rather than the provision of dextrose or milk. Sucking scores were studied in relation to length of labor and drugs or anesthetics given to the mother before delivery. The sucking scores bore no relation to these variables. DISCUSSION
This experiment was designed to compare sucking under conditions that were thought to represent progressive approximations to a bottle feed. Was pump feeding really like a normal feed by bottle? Although the pump feed took longer and the babies gave a greater number of sucks and had to be burped more frequently, the analyses of these data showed that the differences could have arisen by chance. Eight of the 24 pump-fed babies took some milk from the bottle when it was offered at the end of the pump feed (one-eighth to one-half oz) and in this respect their performance did not differ from that of bottle-fed babies who often take more from the bottle when it is offered them by an ex-
SUCKING
IN
THE
NEWBORN
293
perienced nurse at the end of a feed. Thus, despite a tendency to require a longer time, the pump feed provides a facsimile of bottle feeding. These findings clear the way for an examination of the first hypothesis, namely: that nutritive fluids are significant determinants of sucking. The results reinforce the conclusions drawn from an earlier experiment (Dubignon and Campbell, 1968b) : when nutritive fluid is delivered, marked changes in the pattern of sucking occur. It should be noticed that an analysis based upon sucking counts would show a significant drop in expression scores when dextrose was introduced on the second trial followed by a return to the non-nutritive level in the first 2 minutes of the pump feed. However, these shifts in count follow from a change in the over-all pattern of responding: the rate of sucking, for both expression and suction, fell when dextrose was introduced in the second trial and became even slower during the first 2 minutes of the feed. (In this context, rate means the rate of expression and suction responses per second during the intervals of time when the baby was actually sucking). The fall in rate was offset by an increase in time spent sucking when dextrose was introduced and a further increase during the feed. As predicted, during the feed the changes in pattern of sucking, which had already been observed to take place immediately on the addition of dextrose to the array of intraoral stimuli, were exaggerated. The order in which the non-nutritive, dextrose and feeding conditions were presented must be considered in interpreting these results. It has been shown previously that the order of non-nutritive and dextrose trials has no effect upon the sucking patterns elicited under each condition (Dub&on and Campbell, 1968b). In the present study it was not possible to vary the order of feeding and dextrose conditions because, after a feed, it is difficult to elicit sucking reliably. In a recent study sucking for small and equal amounts of milk and dextrose has been compared when the order of trials was counterbalanced. Milk elicited higher sucking counts and more time spent sucking and both these effects were independent of the order of trials (Dubignon and Campbell, 1968c). It is therefore improbable that the order of conditions in the present experiment contributed significantly to the changes in pattern of responding. An experiment based upon sucking counts alone would have led to the conclusion that non-nutritive sucking and sucking during a feed do not differ. One practical consequence of these results is that the study of sucking in relation to changes in stimulating conditions should be based upon measures that are more analytical than a sucking count taken over a specified length of time because a count alone does not do justice to changes in the pattern of responding. The findings agree with those of Halverson (1923). Sameroff (1965) (
294
DUBIGNON
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who reported lower counts during non-nutritive sucking, fed his subjects for 5 minutes before the measurement of non-nutritive sucking so that the conditions were not directly comparable with the present experiment. There were no significant changes in the ratio of expression count to suction count between the three treatments, which suggests that in both nutritive and non-nutritive conditions the mechanism of sucking is the same. However, the expression component tended to occur more frequently than the suction component. It is frequently possible to have an expression component without a matching suction component; the converse of this-suction without expression-rarely happens (cf. Sameroff, 1965).’ The amplitude of suction responses showed a significant increase across trials so that the babies used the greatest negative pressure during the pump feed. Expression amplitude, on the other hand, declined during feeding but not sufficiently to reach significance. One could argue, that the relative importance of suction and expression (as measured by the pressure exerted) shifts when a feed is given. However, this result should be checked using a variety of delivery systems since the pressure exerted in any given setting could conceivably be an artefact of the mechanism used to deliver milk. Before framing any conclusions regarding the differences found between the three treatments it is instructive to re-examine the sucking rates: Non-nutritive Suction rate Expression rate
1.55 1.54
Dextrose
Feeding
1.26 1.30
1.16 1.21
The major change in rate took place between the non-nutritive and dextrose trials and a smaller drop occurred during feeding. The average consumption of fluid during the periods scored was 3.5 cc of dextrose and 11.5 cc of milk. It is possible that the small drop in sucking rate between the dextrose and feeding trials may stem from the need to swallow three times as much fluid, rather than differences in the qualities of milk and dextrose. The fact that the large difference in intake caused only a slight drop in rate makes it clear that the much larger decrease in rate between non-nutritive and dextrose trials is not likely to be due to the need to swallow 3.5 cc during the dextrose trial. Here the change in sucking pattern is clearly due to the change in intra-oral stimulation. The changes in sucking during the feed suggest that it may be necessary to make some distinctions between the control of sucking by intraoral stimulation and the control exerted by satiation or fatigue. It should be noted that during the pump feed the significant changes in counts and time spent sucking in the last quarter of the feed are not matched by
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any change in sucking rates. Similarly, there were no changes in sucking rates before and after burping periods. It seems plausible to argue that the sucking rate is primarily under the control of intraoral stimulation while the probability of sucking is controlled by other factors as well. Thus a baby, given a feed, will react to satiation, not by sucking more slowly, but by sucking less of the time. Both fatigue and satiation must be considered in interpreting the changes in sucking behavior that occurred at the end of the feed. Studies of non-nutritive sucking over long periods (10-15 minutes) have shown that work decrements are small and that there is complete recovery of initial sucking levels given a l-minute rest period (Levin and Kaye, 1964, 1966). These findings are confirmed in the present study of feeding. Examination of time spent sucking and mean sucking counts for the first quarter of the feed and after the last burping period reveals that the infants showed almost complete recovery of initial sucking levels after rest.
First quarter of feed After last burping period
Suction count
Expression cmlnt
Suction time
Expression time
36.46 33.92
42.25 41.58
30.04 28.63
34.63 35.54
The increase in time spent sucking and sucking count after burping can be construed as recovery from fatigue. This recovery was as large in the early part of the feed as it was toward the end of the feed. On the other hand, it appears that increasing satiation is responsible for the decrease in time spent sucking and lower sucking counts at the time of the last burp as compared with the first burp. It will be remembered that during the last quarter of the feed the part of the record scored was the final 45 seconds of sucking. After a further rest the infant refused to accept the nipple. It therefore seems likely that satiation and fatigue are jointly responsible for the changes in sucking behavior that were observed at the end of the last quarter of the feed, while the refusal to accept the nipple after a further rest may be attributed to satiation alone. The uniformity of sucking performance during the first three quarters of the feed stands in contrast to decrements in non-nutritive sucking after the consumption of amounts of fluid as small as lo-20 cc (Kaye, 1966). These effects were interpreted as due to satiation. In the present study no decrement in responding was observed until 60-90 cc of fluid had been consumed. Two interpretations of these findings are possible: either small amounts of fluid in the stomach have different effects on nutritive and non-nutritive sucking, or t.he decrement found by Kaye
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(1966) was a contrast phenomenon, i.e., the dry nipple may be less effective in sustaining sucking after the infant has experienced the additional stimulation of fluid in the mouth. The change in expression/suction ratio at the end of the feed indicates that satiation or fatigue induces a change in the mechanism of sucking; the suction component tends to drop out, while the expression component appears to represent chewing or mouthing of the nipple. This finding supports the conclusion that suction is the means by which bottle-fed infants usually control their food intake from standard commercial nipples as opposed to the “stripping” action that may be the effective means of getting milk from the breast. Throughout the feed the trigger was set to fire for low-amplitude responding, so that milk was delivered for every sucking response. The mean suction and expression amplitudes recorded were in fact four times the amplitude necessary to trigger the pump. It therefore seems likely that the higher suction amplitudes recorded for the expression trigger group during the feed were a chance finding. At first sight the pattern of changes in heart rate and heart-rate range give the impression that feeding exerts a stronger influence than nonnutritive or dextrose sucking on “state” as measured by heart rate. However, examination of the sucking scores suggests that feeding has this influence because more time is spent sucking during feeding. The plot of time spent sucking under the various conditions is virtually a mirror image of the plot of heart-rate range, and this supports the conclusion that the reduction in heart-rate variability is a function of sucking per se rather than the provision of nutriment. The relation between heart rate and sucking is not quite so obvious. Nutritive sucking leads to increases in heart rate, and as sucking drops off toward the end of the feed heart rate shows a corresponding drop toward the resting level. Similar increases in heart rate during nutritive sucking have been reported in other studies, e.g., Baliassnikowa and Model (1931) ; Lipton et al. (1958). The observation that high heart rates tend to be associated with low heart-rate ranges suggests that the reduction in range may possibly be attributed to a “ceiling” effect. However, the heart rate of newborn infants can increase very considerably above the highest mean rates reported here (approximatly 147 beats per minute). To sum up, non-nutritive sucking has been shown to differ from nutritive sucking on five of the six measures of sucking investigated in this study. In most cases, the differences were shown in both the suction and expression components of sucking. The results replicate and extend earlier findings and confirm the hypothesis that the stimuli provided by
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nutritive fluids are significant determinants of sucking. The. differences between non-nutritive sucking and sucking during a feed tiidke it clear that investigations that are intended to have implications for the feeding of the newborn should be carried out in a nutritive setting. The earlier finding that non-nutritive sucking frequency is in part determined by the characteristics of the nipple cannot be generalized to infant feeding without further study. Sucking behavior throughout a feed remained fairly uniform until the end of the last quarter when a decrease in sucking counts, time spent sucking, and suction amplitude, as well as a reduction in the frequency of the suction component of sucking marked the end of the feed. No COYresponding changes in sucking rate were found, which suggests that this measure of sucking may be primarily under the control of current intraoral stimulation. REFERENCES BALIASSNIKOWA, N. J., AND MODEL, fur Kinderheilkunde., 1931-2, BALINT, M. Individual differences
M. M. Zur Neurologie des Saugens. Zeitschrifl 39, 1-16. (Cited in Halverson, 1938). of behavior in early infancy and an objective method for recording them, I: Approach and the method of recording. II: Results and conclusions. Journal of Genetic Psychology, 1948, 73, 57-79; 81-117. COI,LEY, J. R. T., AND CREAMER, B. Sucking and swallowing in infants. British Medical Journal, 1958, 2, 422423. DUBIGNON, J. Intra-oral stimulation and sucking in the newborn. Unpublished Ph.D. Thesis : Queen’s University, 1967. DUBIGNON, J., AND CAMPBELL, D. Intra-oral stimulation and sucking in the newborn. Journal of Experimental Child Psychology, 1968 (a), 6, 154-166. DUBIGNON, J., AND CAMPBELL, D. Sucking in the newborn under three conditions: non-nutritive, nutritive and a feed. Journal of Experimental Child Psychology, 1968 (b), 6, 335-350. DUBIGNON, J., AND CAMPBELL, D. Discrimination of milk and dextrose by human newborns. 1968 (c) (in preparation). HALVERSON, H. M. Infant sucking and tensional behavior. Journal of Genetic Psychology, 1938, 53, 365430. HALVERSON, H. M. Mechanisms of early infant feeding. Journal of Genetic Psychology, 1944, 64, 185-223. KAYE, H. Effects of feeding and tonal stimulation on non-nutritive sucking in the human newborn. Journal of Experimental Child Psychology, 1966, 3, 131-145. &YE, H. Infant sucking and its modification. In L. P. Lip&t and C. C. Spiker (Eds.) Advances in Child Development and Behavior, vol. 3, Academic Press, New York: 1967. KRON, R. E., STEIN, M., GODDARD, K. E., AND PHOENIX, M. D. Effect of nutrient upon the sucking behavior of newborn infants. Psychosomatic Medicine, 1967, 23, 24-32. LEVIN, G. R., AND &YE, H. Non-nutritive sucking by human neonates. Child Development, 1964, 35, 749-758. LEVIN, G. R., AND KAYE, H. Work decrement and rest recovery during non-nutritive
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sucking in the human neonate. Journal of Experimental Child Psychology, 1966, 3, M-154. Lrpsrrr, L., AND KAYE, H. Change in neonatal response to optimising and nonoptimising sucking stimulation. Psychonomic Science, 1965,2,221-222. LIPTON, E. L., RICHMOND, J. B., WEINBERQEE, H. L., AND HEBSHEB, L. An approach to evaluation of neonate autonomic responses. Psychosomatic Medicine, 1958, 20, 469. SANEROFF, A. J. An experimental study of the response components of sucking in the human newborn. Unpublished Ph.D. Thesis : Yale University, 1965. TINBERGEN, N. The study of instinct. London and New York: Oxford Univ. Press, 1951.