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Respiratory movements in fetal rhesus monkeys
Respiratory movements in fetal rhesus monkeys CHESTER YUJI ROY
B.
MARTIN,
MURATA, H.
JULIAN Los Angeles,
M.D.
M.D.
PETRIE. T.
JR.,
M.D.
PARER,
PH.D.,
M.D.
California
Fetal tracheal pressure was recorded continuously for prolonged periods in awake, restrained rhesus monkeys. Other parameters recorded included fetal blood pressure, heart rate, eye movements, and EEG. Fetal arterial blood samples were obtained intermittently for determination of pH and respiratory gas tensions. The observations spanned the interval from approximately I15 days’ gestation until term. Changes in tracheal pressure representing a variety of respiratory morlements were observed. Isolated and repetitive gasping movements exceeded 30 mm. Hg negative pressure. Rhythmic and rapid irregular breathing movements of lesser intensities were also recorded. These breathing movements occupied approximately two thirds of the time in the healthy fetuses. Somatic and eye movements were more frequent and the heart rate and blood pressure more irregular during the periods of respiratory activity than during the intervening quiet times. Fetal breathing movements disappeared during fetal stress and failed to develop in fetuses which did not exhibit normal pH and respirator11 gas tensions following operation.
UNTIL THE recent demonstration by Dawes and co-workers1 of intrauterine breathing movements in healthy fetal lambs, it had been held generally that fetal respiratory movements were limited to gasping occurring in response to asphyxial stress. Subsequently, human fetal breathing movements have been described by Boddy and Kobinson,’ who observed chest wall movements by
means of ultrasonic scanning, and by Duenhoelter and Pritchard,3 who found that Cr51tagged erythrocytes were aspirated into the fetal lungs from the amniotic fluid. In this paper, we describe the occurrence of intrauterine breathing movements in rhesus monkey fetuses observed continuously for prolonged periods. Materials
From the Department of Obstetrics Gynecology, Los Angeles CountyUniversity of Southern California Medical Center. Supported in part by Grant from the National Institutes ‘Lrnited States Public Health Received 1973. Revised Accepted
for publication January January
and
These pregnant National
HD-06406 of Health, Service.
October
and
methods
experiments were carried out in rhesus monkeys obtained from the Center for Primate Biology in Davis, California. The duration of pregin some of the monkeys nancy, estimated from early rectal palpation and known in others on the basis of timed matings, ranged from 115 days to near-term ( 164 days) . The technique for establishing and maintaining the chronic monkey fetal preparation has been described previously* and will be summarized only briefly here. The initial operation was performed under phencyclidine
17,
2, 1974. 14, 1974.
Reprint requests: C. B. Martin, Jr., M.D., Department of Obstetrics and Gynecology, LAG/USC Medical Center, Women’s Hospital 5K-22, 1240 N. Mission Rd., Los Angeles, California 90033. 939
940
Martin
August 1, 1974 Am. J. Obstet. Gynecol.
et al.
Table I. Gestational duration delivery
age at operation, of observation, and fetal weight in the chronic experiments* Days observed
Monkey No. 72-2 72-3 72-4 72-5 73-3 73-4 73-10 73-11
115 126 116 130 112 123$ 125 139+
11 10
7 22 11 35
at
Fetal weight at delivery (grams) 290 370 305 430 285 480 260 385
‘Gestational age was estimated on the basis of rectal palpation in early pregnancy except for the 2 animals marked the duration of pregnancy was known (t), in which from timed matings.
and pentobarbital anesthesia. A small hysterotomy incision was placed below the inferior margin of the anterior placenta. The intended external ends of the catheters and electrode leads were passed downward between the fetal membranes and myometrium and out the cervix and vagina. The hysterotomy incision was extended, the fetal membranes opened, and the fetal head and shoulders delivered. A transverse incision was made in the skin of the fetal neck, and small polyethylene catheters (PE-50, ClayAdams Corporation) were inserted into the trachea and a carotid artery of the fetus. Both catheters were passed proximally 3 to 4 cm. from the point of insertion. The third catheter was left free in the uterine cavity to measure amniotic fluid pressure. One pair of stainless steel or silver alloy electrodes was placed beneath the skin of the fetal arms or chest wall to record ECG. Another pair of electrodes was placed at the outer canthi of the eyelids to detect eye movements (2 animals), or in the scalp (4 animals) to record EEG. The fetus was restored to the uterine cavity, the fetal membranes closed around the catheter and electrode bundle, and the myometrium sutured external to it. The monkey was placed in the left latera recumbent position in a restraining chair. The chair was not set upright until 15 to 18 hours later. The monkeys received progesterone on the day prior to operation and for
several days thereafter. In the early experimerits, the dose of progesterone was tapered beginning on the third or fourth postoperative day. In the later ones, the progesterone was stopped entirely after this time. The monkeys also received antibiotics (ampicillin or cephalothin plus kanamycin) during the entire duration of the experiment. The catheters and electrodes were connected to appropriate strain gauges and couplers and the biophysical data recorded continuously with Offner or Brush polygraphs. Fetal arterial blood samples were obtained periodically from the carotid artery catheter for determination of pH and respiratory gas tensions. In the later experiments, normal saline containing heparin, 5 to 10 units per milliliter, was infused continuously at 0.02 ml. per minute to prolong the duration of patency of this catheter. Results Seven animals with fetal tracheal catheters have been observed in good condition for prolonged periods ranging from 2yz to 35 days (Table I) . The tracheal pressure records of all but one of these animals showed negative deflections indicating fetal breathing movements. In the remaining animal (No. 72-3)) the tracheal catheter recorded breathing movements during the first 48 hours of observation, and afterward only intrauterine pressure. When this fetus was delivered 8 days later by cesarean section, the tracheal catheter was found to lie free in the amniotic cavity, presumably having become dislodged at about the time the negative deflections disappeared from the tracing. In these fetuses, respiratory movements first appeared between 6 and 12 hours after the end of operation. These early movements consisted of brief episodes of gasping or short bursts of more rapid breathing movements. The amount of fetal breathing activity increased notably during the second 24 hours following the operation, but did not reach a maximum, stable level until as late as the fourth or fifth postoperative day in some of
Respiratory
Fig. 1. The tracheal pressure record repetitive gasping movements. Short spersed. The fetal heart rate exhibits tion. Paper speed, 50 mm. per minute.
movements
in fetal
monkeys
941
shows a series of strong negative deflections representing bursts of rapid irregular breathing movements are intermoderate irregularity. Monkey 72-5, day 14 of observa-
oso-
-
IDo-
-...
..I._-
.
-_I --.-_.
,^,..
*- *
~~.^-,.
“I -. .
_._.<... L >. ._ A..;..
”
”
^
Fig. 2. This portion of record illustrates fairly regular fetal breathing movements. The fetal heart rate is relatively slow and exhibits a respiratory arrhythmia. Isolated deep negative reflections appear in the tracheal pressure record in association with fetal movements. Monkey 72-5, day 13 of observation. Paper speed, 50 mm. per minute.
Fig. 3. This section of record shows rapid irregular amplitude interspersed with deeper gasping movements. the heart rate exhibits frequent V-shaped decelerations. Paper speed, 50 mm. per minute.
respirations of varying frequency and The blood pressure is irregular, and Monkey 72-4, day 5 of observation.
942
Martin
et al.
.\ugust 1, 19x Am. J. Obstet.
Gynccol.
Fig. 4. Section of record obtained at faster paper speed (2.5 mm. per second) showing small breathing movements ranging in frequency from 1 to approximately 2.5 Hz. The EOG record contains deflections suggesting conjugate eye movement as well as motion artifact. The blood pressure record was interrupted for an arterial blood gas sample. Monkey 72-4, day 5 of observation.
Fig. 5. Transition between quiet and active phases in Monkey 72-j. During the quiet phase, there are occasional gasps accompanied by fetal movement. With the onset of fetal breathing, there is an increase in the heart rate and irregularity and also in the frequency of fetal move-
ments. Paper speed, 50 mm. per minute. the experiments. Once this stable level had been reached, breathing activity of some type was present more than half of the time (up to 80 per cent in some fetuses) as long as the fetuses remained in good condition. The tracheal pressure records of the healthy fetuses suggested a variety of respiratory movements. Abrupt negative deflections of 20 to 40 mm. Hg intensity were taken to represent fetal gasping movements. These occurred singly, often in association with deflections in other channels indicating fetal movement, and also in groups (Fig. I ) . Dur-
ing these episodes of repetitive gasping, the inspiratory lllovernents could occur as infrequently as one per minute, or as often 3s nearly one per second. Other, less intense repetitive respiratory movements \vere also observed. These exhibited great variabilit) in both amplitude and frequency. ranging from -2 to -20 mm. Hg, and from 0.5 to 3 Hz. At the lower frequencies, these movements gave the appearance of more or less regular breathing (Fig. 2). This type of respiratory activity was sometimes sustained for several minutes. The more rapid breath-
Respiratory
ing movements tended to occur in bursts lasting from a few seconds to 2 to 3 minutes, although longer continuous episodes of this rapid breathing were also recorded (Fig. 3). Finally, there were episodes of small, very rapid fluctuations in fetal tracheal pressure ranging in amplitude from 2 mm. Hg down to barely perceptible deflections, and in frequency from 1.5 to 3 Hz (Fig, 4). The variable frequency of these fluctuations and their lack of synchrony with the ECG distinguished them from transmitted cardiovascular pulsations. These fluctuations were thus taken to represent low-intensity, rapid respiratory movements. With the exception of the isolated gasping motions, which might occur at any time, the several types of respiratory movements described above tended to occur together during the same portions of the records. The various breathing patterns were frequently not separate and distinct. One pattern might be superimposed on another (for example, a burst of rapid respiration might occur during an episode of rhythmic gasping without altering the frequency of the gasping movemerits), or different patterns might follow each other sequentially, each one merging into the succeeding one (Figs. 1 and 3). The over-all picture was thus one of breathing and nonbreathing periods, with usually a variety of respiratory movements occurring during the breathing periods. Figs. 5 and 7 show portions of quiet times preceding the onset of active phases. The active breathing periods usually lasted 30 to 60 minutes and the quiet ones, 5 to 15 minutes, once the maximum level of breathing activity had been reached. Grrat variability was often observed in the duration of these active and quiet phases even in successive cycles in the same fetus, especially in prolongation of the active breathing periods. There were no differences in the pH or respiratory gas tensions of fetal arterial blood between breathing and nonbreathing periods, lvhether all samples or paired samples obtained during successive breathing and nonbreathing episodes were compared (Table II).
movements
in fetal
monkeys
943
Table II. Comparison of fetal arterial blood pH and respiratory gas tensions between active (breathing) and quiet (nonbreathing) states in unstressed fetuses* No. Active X, + S.D.
Quiet X + S.D.
of
samgles
t
+ 0.05
54
1.15
Group A PH
PO2 (mm. Hg)
7.35
f 0.05
7.34
27.0
I- 4.1
26.4
+_3.8
44
0.55
31.3
r! 5.7
30.7
k 5.8
44
0.30
15
0.17
pcor
(mm. HZ) Group B PH
p02 (mm. Hg)
7.35
t 0.05
7.342
0.05
26.5
k 3.7
26.4
f4.0
14
0.12
31.8
t 4.4
31.0
+ 6.6
14
0.54
pcor
(mm. Hz-)
*A, results from all breathing status could be B, results from paired nearly sequential active paired data. There were data set between breathing
samples for which hreathing/nonassigned. t, from the student t test. samples obtained in sequential or and quiet phases. t, from t test for no significant differences with either and nonbreathing periods.
The base-line fetal heart rate was usually more rapid during the periods in which respiratory movements were occurring than during the intervening quiet times. Moreover, the fetal heart rate exhibited increased irregularity during the breathing periods (Figs. 5 and 7). Abrupt or U-shaped fetal heart rate decelerations or brief accelerations often accompanied bursts of’ rapid respiratory movements. Small V-shaped decelerations frequently occurred with gasping movements; these were seen more often with the isolated gasps or the more infrequent repetitive gasps and tended to disappear as the frequency of gasping increased. A respiratory arrhythmia could be observed at times in association with rhythmic breathing movements. The fetal arterial blood pressure tended to be somewhat higher and was definitely more variable during the active breathing periods than during the quiet times (Fig. 7 ) Fetal movements could be deduced from the occurrence of deflections in multiple
944
Martin
August 1, 1974 Am. J. Obstet. Gynecol.
et al.
Fig. 6. Portion tracing typical
of record of conjugate
during an active eye movements.
phase
showing
frequent
deflections
in
the
EOG
Monkey 72-4, day 3 of observation. Paper speed,
2.5 mm. per second.
Fig. 7. Transition from quiet to active state in Monkey 72-4, day 4 of observation. During the quiet phase, the fetal heart rate is regular and there are few deflections in the EOG record. With the onset of breathing. the fetal heart rate becomes more irregular, blood pressure rises slightly, and EOG activity increases. Paper speed, 50 mm. per minute.
channels while the mother was observed to be still. These movements tended to occur in clusters during the portions of the record in which breathing movements were also present. When fetal movements occurred during the quiet times, they were discrete events and were usually associated with a transient deceleration or acceleration in the fetal heart rate. Although the electrooculogram (EOG) record
contained
considerable
motion
arti-
fact, deflections typical of conjugate movements could be observed (Fig. These occurred more frequently during active
breathing
periods
than
when
eye 6). the
respira-
were absent (Fig. 7). tory movements Groups of rapid eye movements (REM’s) occurred only during these times. The EEG records thus far have not shown a clear distinction in pattern between active breathing and quiet periods; however, the tracings were obtained from scalp electrodes
Volume Number
1IY 7
Respiratory
movements
in fetal monkeys
,
”
945
(,
*1-
Fig. 8. Segment of record obtained 24 hours prior to delivery in Monkey 72-4. The intraamniotic catheter had become dislodged by this time, but the frequency and intensity of the uterine contractions may be deduced from the blood pressure and tracheal pressure records. Bursts of rapid fetal breathing movements continued to occur during this period of 30 to 40 mm. Hg contractions. The V-shaped decelerations in the fetal heart rate appear to be related to the respirations rather than the uterine contractions. Paper speed, 50 mm. per minute.
Fig. 9. Deep gasping movements immediately tracing shows only motion artifact and DC speed, 50 mm. per minute.
and were clouded by motion artifact resulting from fetal movements and from maternal abdominal respiratory movements. Five of the monkeys exhibited episodes of increased uterine activity during the period 10 P.M. to 6 A.M. for 2 or 3 days prior to labor. Uterine contractions reached intensities of 30 to 40 mm. Hg during these times, then diminished greatly or disappeared during the
prior to fetal potentials
from
death in Monkey 72-4. The the myometrial contraction.
EOG Paper
following day. The fetal tracheal catheter was still working well in 3 of these animals (Nos. 72-4, 72-5, and 73-4). The fetal breathing movements persisted during this prelabor activity in all 3 animals (Fig. 8). Recordings of fetal tracheal pressure during labor were also obtained in these three animals plus one other. In this latter monrapidly progressive labor key (No. 73-IO),
946
Martin
et al.
August 1, 1974 Am. J. Obstet.
Gynecol.
Fig. 10. Acute
fetal stress experiment in Monkey 72-5. Acute fetal respiratory acidosis produced by administration of 20 per cent CO1 to the mother promptly abolished the rapid fetal breathing movements intermixed with repetitive gasping. Less frequent gasping movements occurred during the acidosis accompanied by abrupt fetal heart rate decelerations. Rapid fetal breathing movements reappeared briefly approximately 4 minutes after the end of the CO, inhalation. The maternal hyperpnea is reflected in increased positive excursions in the IUP and tracheal pressure records. Paper speed, 30 mm. per minute.
occurred unexpectedly after 2f/2 days of observation; however, the fetus had been in good condition and had established rapid breathing activity during this period. Monkeys 72-4, 72-5, and 73-4 exhibited prolonged labor with expulsion of the fetus apparently prevented by the fixation of the catheters and electrode leads at their point of exit through the fetal membranes. All 3 of these fetuses died following several hours of labor and after exhibiting evidence of distress: late deceleration fetal heart rate patterns, decreased fetal heart rate base-line variability, then bradycardia and hypotension. Fetal breathing movements persisted during early labor in these 3 fetuses, but disappeared in advance of fetal heart rate evidence of fetal distress. Forceful gasping movements recurred in these fetuses shortly before death (Fig. 9). Monkey 73-10 was found shortly after partial expulsion of the fetus. Fetal breathing movements had occurred during this short (2vz hour) labor until approximately 30 minutes before expulsion. Fetal respiratory acidosis was produced in 3 monkeys in this series (72-5, 73-3, and 73-4) by administration of 20 per cent CO, to the mother by means of a helmet. When this was done during a period of rapid fetal
breathing, the rapid breathing movements quickly disappeared, to be replaced after a short interval by strong gasps (Fig. 10). The rapid breathing movements returned 6 or more minutes after the mother resumed air breathing. In 2 monkeys (Nos. 73-4 and 73-10)) fetal hypoxia was induced by administration of 10 per cent 0, to the mother. The fetal arterial catheter had become dislodged in Monkey 73-4, but in No. 73-10, the fetal p0, had decreased from 29 to 19 mm. Hg after 45 minutes of low O,, with no fetal acidosis (initial pH 7.38, ending pH 7.43; initial pC0, 28, ending pC0, 21). Rapid fetal breathing movements continued during the short-term hypoxia in these experiments. Several animals failed to become chronic preparations for varied reasons and yet were observed for more than 18 hours following operation, a time by which all of the healthy fetuses had begun to have breathing movements. The appearance or absence of breathing movements in relation to fetal condition in these animals corresponds well with the observations during the stress experiments and labor in the healthy fetuses. In the failure group, 4 fetuses exhibited gradually worsening hypoxia and acidosis, resulting in 2 instances from
Respiratory
increasing uterine activity, in a third following severe asphyxia during the operation, and in the remaining case associated with maternal circulatory failure (suspected heat stress). None of these fetuses showed rapid respirations. One exhibited gasping during late decelerations and again immediately prior to death, and the remaining fetuses showed only agonal gasping movements. Two fetuses showed initial recovery followed by deterioration in the second 24 hours following operation in association with maternal circulatory failure (also probable heat stress) . One of these fetuses maintained normal pH values (above 7.30) with low Oz tensions (none above 18 mm. Hg) for several hours, but did not exhibit any breathing movements. The second achieved pH and ~0, comparable to those in the healthy fetuses for a time. During this period, breathing movements appeared resembling those observed at comparable times following operation in the chronic preparations. Another fetus appeared to be doing well when, at approximately 44 hours, it died suddenly after the carotid arterial catheter had been flushed. This fetus had shown normal evolution of breathing movements. Comment The breathing movements exhibited by these fetal monkeys are very similar to those reported by Dawes and associates1 in fetal lambs. The nature and pattern of the gasping movements is almost exactly the same in the two species. The other breathing movements observed in the fetal monkeys, encompassing a wide spectrum of frequencies and intensities, would seem to be the counterpart of the rapid irregular respiration exhibited by the fetal lambs. These similarities were probably expectable and, indeed, equivalent breathing movements should be anticipated in other species as a regular feature of intrauterine life. For as Dawes has pointed out, if the fetus had not exercised its breathing muscles in utero, it would not be able to initiate and sustain pulmonary ventilation during the neonatal period. The magnitude of the negative intrathoracic pres-
movements
in fetal
monkeys
947
sure obtained during intrauterine gasping is equivalent to that required to effect initial expansion of the lungs.” The intensities of other breathing movements, except for the very smallest ones, are in the range required for sustained air breathing. The breathing movements tended to occur in cycles, with longer periods of frequent (though discontinuous) respiratory activity alternating with shorter periods in which no movements or only isolated gasps occurred. There were no differences in pH or respiratory gas tensions of arterial blood between breathing and quiet periods in either the fetal monkeys or lambs. This observation, together with the increased variability in heart rate and blood pressure and clustering of somatic and eye movements during the breathing periods, suggests that the respiratory movement cycles are an expression of a more basic alternation in the functional level of the central nervous system between quiet and active states. These rest-activity cycles are observable in term newborns of several speciesfit i Although it has been reported that the cycles appear only after 32 weeks’ conceptional age in human premature infants,* there is also some evidence of their occurrrence in human fetuses as early as midpregnancy. In these experiments, definite alternation betwee:: quiet and active periods could be observed even in the youngest fetuses, approximately 115 to 120 days’ gestational age. The active state was markedly predominant after the first few days of observation in all of these fetal monkeys. This finding agrees well with the observations that, in general, the proportion of time spent by infants of several species in quiet sleep increases with increasing postnatal age. 6-S Much of the variability in cycle length observed in these experiments, and particularly the occurrence of very prolonged active periods, may have reflected the incomplete development of quiet sleep and its replacement by an intermediate or transitional activity state. In these experiments, rapid fetal breathing movements and the alternation of active and quiet states occurred only in fetuses in good
948
Martin
August 1, 1974
et al.
Am. J. Obstet.
condition, as judged from heart rate, pH, and respiratory gas tensions. Rapid respirations appeared well before clear active-quiet cycling during recovery from the initial operation, and both disappeared early in the course of fetal deterioration in labor. The distressed fetuses usually showed no breathing movements except for gasping shortly before death; however, few instances of fetal gasping during late fetal heart rate decelerations were observed. Rapid breathing movements did not develop in fetuses which remained acidotic after operation, even though they were observed past the time when all of the healthy fetuses had shown breathing movements. In a limited number of acute experiments, acute fetal respiratory acidosis
Gynecol.
inhibited the rapid breathing movements. Hypoxia for limited periods in the presence of normal pH did not abolish the rapid breathing movements, but these failed to develop following operation in a fetus with more chronic hypoxia, even though the pH remained nearly normal. The absence of rapid breathing movements in distressed monkey fetuses parallels similar findings by Dawes and associates’ in fetal sheep. It is noteworthy also, that Boddy and Robinson’ could not detect fetal chest wall movements in small-for-dates pregnancies. It appears that the occurrence of rapid fetal breathing movements and the alternation of active and quiet states may be sensitive indices of fetal well-being.
REFERENCES
1.
Dawes, G. S., Fox, H. E., Leduc, B. M., et al.: J. Physiol. 220: 119, 1972. 2. Boddy, K., and Robinson, J. S.: Lancet 2: 1231, 1971. 3. Duenhoelter, J., and Pritchard, J. A.: Obstet. Gynecol. 42: 746, 1973. 4. Martin, C. B., Jr., Murata, Y., and Parer, J. T.: AM. J. OBSTET. GYNECOL. 117: 126, 1973. 5. Uawes, G. S.: Fetal and Neonatal Physiology, Chicago, 1968, Year Book Medical Publishers, Inc., Chap. 11.
Attention
to authors:
Section
on Clinical
6.
7.
8.
Sterman, M. B., and Hoppenbrouwers, T.: In Sterman, M. B., McGinty, D. J., and Adinolfi, A. M., editors: Brain Development and Btiavior, New York, 1971, Academic Press, Inc., p. 203. McGinty. D. J.: In Sterman, M. B., McGinty, D. J., and Adinolfi, A. M., editors: Brain Development and Behavior, New York, 1971, Academic Press, Inc., p. 335. Dreyfus-Brisac, C.: Dev. Psychobiol. 3: 91, 1970.
Opinion
The editors and publisher of the AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY wish to call your attention to a new section entitled “Clinical Opinion.” The section will be devoted to the clinical diagnosis and management of certain disease entities. The section is designed to accommodate from eight to twenty typed pages with appropriate illustrative material, tables, and figures helpful in clarifying to the reader how a condition is actually managed. References need not be extensive, since the emphasis should be on the author’s actual handling of clinical problems. The objective of this section is to transmit to the reader how a clinical situation is actually handled. Manuscripts should be submitted to Frederick P. Zuspan, M.D., Editor, American Journal of Obstetrics and Gynecology, 5841 S. Maryland Ave., Chicago, Illinois 60637.
B.
MARTIN,
MURATA, H.
JULIAN Los Angeles,
M.D.
M.D.
PETRIE. T.
JR.,
M.D.
PARER,
PH.D.,
M.D.
California
Fetal tracheal pressure was recorded continuously for prolonged periods in awake, restrained rhesus monkeys. Other parameters recorded included fetal blood pressure, heart rate, eye movements, and EEG. Fetal arterial blood samples were obtained intermittently for determination of pH and respiratory gas tensions. The observations spanned the interval from approximately I15 days’ gestation until term. Changes in tracheal pressure representing a variety of respiratory morlements were observed. Isolated and repetitive gasping movements exceeded 30 mm. Hg negative pressure. Rhythmic and rapid irregular breathing movements of lesser intensities were also recorded. These breathing movements occupied approximately two thirds of the time in the healthy fetuses. Somatic and eye movements were more frequent and the heart rate and blood pressure more irregular during the periods of respiratory activity than during the intervening quiet times. Fetal breathing movements disappeared during fetal stress and failed to develop in fetuses which did not exhibit normal pH and respirator11 gas tensions following operation.
UNTIL THE recent demonstration by Dawes and co-workers1 of intrauterine breathing movements in healthy fetal lambs, it had been held generally that fetal respiratory movements were limited to gasping occurring in response to asphyxial stress. Subsequently, human fetal breathing movements have been described by Boddy and Kobinson,’ who observed chest wall movements by
means of ultrasonic scanning, and by Duenhoelter and Pritchard,3 who found that Cr51tagged erythrocytes were aspirated into the fetal lungs from the amniotic fluid. In this paper, we describe the occurrence of intrauterine breathing movements in rhesus monkey fetuses observed continuously for prolonged periods. Materials
From the Department of Obstetrics Gynecology, Los Angeles CountyUniversity of Southern California Medical Center. Supported in part by Grant from the National Institutes ‘Lrnited States Public Health Received 1973. Revised Accepted
for publication January January
and
These pregnant National
HD-06406 of Health, Service.
October
and
methods
experiments were carried out in rhesus monkeys obtained from the Center for Primate Biology in Davis, California. The duration of pregin some of the monkeys nancy, estimated from early rectal palpation and known in others on the basis of timed matings, ranged from 115 days to near-term ( 164 days) . The technique for establishing and maintaining the chronic monkey fetal preparation has been described previously* and will be summarized only briefly here. The initial operation was performed under phencyclidine
17,
2, 1974. 14, 1974.
Reprint requests: C. B. Martin, Jr., M.D., Department of Obstetrics and Gynecology, LAG/USC Medical Center, Women’s Hospital 5K-22, 1240 N. Mission Rd., Los Angeles, California 90033. 939
940
Martin
August 1, 1974 Am. J. Obstet. Gynecol.
et al.
Table I. Gestational duration delivery
age at operation, of observation, and fetal weight in the chronic experiments* Days observed
Monkey No. 72-2 72-3 72-4 72-5 73-3 73-4 73-10 73-11
115 126 116 130 112 123$ 125 139+
11 10
7 22 11 35
at
Fetal weight at delivery (grams) 290 370 305 430 285 480 260 385
‘Gestational age was estimated on the basis of rectal palpation in early pregnancy except for the 2 animals marked the duration of pregnancy was known (t), in which from timed matings.
and pentobarbital anesthesia. A small hysterotomy incision was placed below the inferior margin of the anterior placenta. The intended external ends of the catheters and electrode leads were passed downward between the fetal membranes and myometrium and out the cervix and vagina. The hysterotomy incision was extended, the fetal membranes opened, and the fetal head and shoulders delivered. A transverse incision was made in the skin of the fetal neck, and small polyethylene catheters (PE-50, ClayAdams Corporation) were inserted into the trachea and a carotid artery of the fetus. Both catheters were passed proximally 3 to 4 cm. from the point of insertion. The third catheter was left free in the uterine cavity to measure amniotic fluid pressure. One pair of stainless steel or silver alloy electrodes was placed beneath the skin of the fetal arms or chest wall to record ECG. Another pair of electrodes was placed at the outer canthi of the eyelids to detect eye movements (2 animals), or in the scalp (4 animals) to record EEG. The fetus was restored to the uterine cavity, the fetal membranes closed around the catheter and electrode bundle, and the myometrium sutured external to it. The monkey was placed in the left latera recumbent position in a restraining chair. The chair was not set upright until 15 to 18 hours later. The monkeys received progesterone on the day prior to operation and for
several days thereafter. In the early experimerits, the dose of progesterone was tapered beginning on the third or fourth postoperative day. In the later ones, the progesterone was stopped entirely after this time. The monkeys also received antibiotics (ampicillin or cephalothin plus kanamycin) during the entire duration of the experiment. The catheters and electrodes were connected to appropriate strain gauges and couplers and the biophysical data recorded continuously with Offner or Brush polygraphs. Fetal arterial blood samples were obtained periodically from the carotid artery catheter for determination of pH and respiratory gas tensions. In the later experiments, normal saline containing heparin, 5 to 10 units per milliliter, was infused continuously at 0.02 ml. per minute to prolong the duration of patency of this catheter. Results Seven animals with fetal tracheal catheters have been observed in good condition for prolonged periods ranging from 2yz to 35 days (Table I) . The tracheal pressure records of all but one of these animals showed negative deflections indicating fetal breathing movements. In the remaining animal (No. 72-3)) the tracheal catheter recorded breathing movements during the first 48 hours of observation, and afterward only intrauterine pressure. When this fetus was delivered 8 days later by cesarean section, the tracheal catheter was found to lie free in the amniotic cavity, presumably having become dislodged at about the time the negative deflections disappeared from the tracing. In these fetuses, respiratory movements first appeared between 6 and 12 hours after the end of operation. These early movements consisted of brief episodes of gasping or short bursts of more rapid breathing movements. The amount of fetal breathing activity increased notably during the second 24 hours following the operation, but did not reach a maximum, stable level until as late as the fourth or fifth postoperative day in some of
Respiratory
Fig. 1. The tracheal pressure record repetitive gasping movements. Short spersed. The fetal heart rate exhibits tion. Paper speed, 50 mm. per minute.
movements
in fetal
monkeys
941
shows a series of strong negative deflections representing bursts of rapid irregular breathing movements are intermoderate irregularity. Monkey 72-5, day 14 of observa-
oso-
-
IDo-
-...
..I._-
.
-_I --.-_.
,^,..
*- *
~~.^-,.
“I -. .
_._.<... L >. ._ A..;..
”
”
^
Fig. 2. This portion of record illustrates fairly regular fetal breathing movements. The fetal heart rate is relatively slow and exhibits a respiratory arrhythmia. Isolated deep negative reflections appear in the tracheal pressure record in association with fetal movements. Monkey 72-5, day 13 of observation. Paper speed, 50 mm. per minute.
Fig. 3. This section of record shows rapid irregular amplitude interspersed with deeper gasping movements. the heart rate exhibits frequent V-shaped decelerations. Paper speed, 50 mm. per minute.
respirations of varying frequency and The blood pressure is irregular, and Monkey 72-4, day 5 of observation.
942
Martin
et al.
.\ugust 1, 19x Am. J. Obstet.
Gynccol.
Fig. 4. Section of record obtained at faster paper speed (2.5 mm. per second) showing small breathing movements ranging in frequency from 1 to approximately 2.5 Hz. The EOG record contains deflections suggesting conjugate eye movement as well as motion artifact. The blood pressure record was interrupted for an arterial blood gas sample. Monkey 72-4, day 5 of observation.
Fig. 5. Transition between quiet and active phases in Monkey 72-j. During the quiet phase, there are occasional gasps accompanied by fetal movement. With the onset of fetal breathing, there is an increase in the heart rate and irregularity and also in the frequency of fetal move-
ments. Paper speed, 50 mm. per minute. the experiments. Once this stable level had been reached, breathing activity of some type was present more than half of the time (up to 80 per cent in some fetuses) as long as the fetuses remained in good condition. The tracheal pressure records of the healthy fetuses suggested a variety of respiratory movements. Abrupt negative deflections of 20 to 40 mm. Hg intensity were taken to represent fetal gasping movements. These occurred singly, often in association with deflections in other channels indicating fetal movement, and also in groups (Fig. I ) . Dur-
ing these episodes of repetitive gasping, the inspiratory lllovernents could occur as infrequently as one per minute, or as often 3s nearly one per second. Other, less intense repetitive respiratory movements \vere also observed. These exhibited great variabilit) in both amplitude and frequency. ranging from -2 to -20 mm. Hg, and from 0.5 to 3 Hz. At the lower frequencies, these movements gave the appearance of more or less regular breathing (Fig. 2). This type of respiratory activity was sometimes sustained for several minutes. The more rapid breath-
Respiratory
ing movements tended to occur in bursts lasting from a few seconds to 2 to 3 minutes, although longer continuous episodes of this rapid breathing were also recorded (Fig. 3). Finally, there were episodes of small, very rapid fluctuations in fetal tracheal pressure ranging in amplitude from 2 mm. Hg down to barely perceptible deflections, and in frequency from 1.5 to 3 Hz (Fig, 4). The variable frequency of these fluctuations and their lack of synchrony with the ECG distinguished them from transmitted cardiovascular pulsations. These fluctuations were thus taken to represent low-intensity, rapid respiratory movements. With the exception of the isolated gasping motions, which might occur at any time, the several types of respiratory movements described above tended to occur together during the same portions of the records. The various breathing patterns were frequently not separate and distinct. One pattern might be superimposed on another (for example, a burst of rapid respiration might occur during an episode of rhythmic gasping without altering the frequency of the gasping movemerits), or different patterns might follow each other sequentially, each one merging into the succeeding one (Figs. 1 and 3). The over-all picture was thus one of breathing and nonbreathing periods, with usually a variety of respiratory movements occurring during the breathing periods. Figs. 5 and 7 show portions of quiet times preceding the onset of active phases. The active breathing periods usually lasted 30 to 60 minutes and the quiet ones, 5 to 15 minutes, once the maximum level of breathing activity had been reached. Grrat variability was often observed in the duration of these active and quiet phases even in successive cycles in the same fetus, especially in prolongation of the active breathing periods. There were no differences in the pH or respiratory gas tensions of fetal arterial blood between breathing and nonbreathing periods, lvhether all samples or paired samples obtained during successive breathing and nonbreathing episodes were compared (Table II).
movements
in fetal
monkeys
943
Table II. Comparison of fetal arterial blood pH and respiratory gas tensions between active (breathing) and quiet (nonbreathing) states in unstressed fetuses* No. Active X, + S.D.
Quiet X + S.D.
of
samgles
t
+ 0.05
54
1.15
Group A PH
PO2 (mm. Hg)
7.35
f 0.05
7.34
27.0
I- 4.1
26.4
+_3.8
44
0.55
31.3
r! 5.7
30.7
k 5.8
44
0.30
15
0.17
pcor
(mm. HZ) Group B PH
p02 (mm. Hg)
7.35
t 0.05
7.342
0.05
26.5
k 3.7
26.4
f4.0
14
0.12
31.8
t 4.4
31.0
+ 6.6
14
0.54
pcor
(mm. Hz-)
*A, results from all breathing status could be B, results from paired nearly sequential active paired data. There were data set between breathing
samples for which hreathing/nonassigned. t, from the student t test. samples obtained in sequential or and quiet phases. t, from t test for no significant differences with either and nonbreathing periods.
The base-line fetal heart rate was usually more rapid during the periods in which respiratory movements were occurring than during the intervening quiet times. Moreover, the fetal heart rate exhibited increased irregularity during the breathing periods (Figs. 5 and 7). Abrupt or U-shaped fetal heart rate decelerations or brief accelerations often accompanied bursts of’ rapid respiratory movements. Small V-shaped decelerations frequently occurred with gasping movements; these were seen more often with the isolated gasps or the more infrequent repetitive gasps and tended to disappear as the frequency of gasping increased. A respiratory arrhythmia could be observed at times in association with rhythmic breathing movements. The fetal arterial blood pressure tended to be somewhat higher and was definitely more variable during the active breathing periods than during the quiet times (Fig. 7 ) Fetal movements could be deduced from the occurrence of deflections in multiple
944
Martin
August 1, 1974 Am. J. Obstet. Gynecol.
et al.
Fig. 6. Portion tracing typical
of record of conjugate
during an active eye movements.
phase
showing
frequent
deflections
in
the
EOG
Monkey 72-4, day 3 of observation. Paper speed,
2.5 mm. per second.
Fig. 7. Transition from quiet to active state in Monkey 72-4, day 4 of observation. During the quiet phase, the fetal heart rate is regular and there are few deflections in the EOG record. With the onset of breathing. the fetal heart rate becomes more irregular, blood pressure rises slightly, and EOG activity increases. Paper speed, 50 mm. per minute.
channels while the mother was observed to be still. These movements tended to occur in clusters during the portions of the record in which breathing movements were also present. When fetal movements occurred during the quiet times, they were discrete events and were usually associated with a transient deceleration or acceleration in the fetal heart rate. Although the electrooculogram (EOG) record
contained
considerable
motion
arti-
fact, deflections typical of conjugate movements could be observed (Fig. These occurred more frequently during active
breathing
periods
than
when
eye 6). the
respira-
were absent (Fig. 7). tory movements Groups of rapid eye movements (REM’s) occurred only during these times. The EEG records thus far have not shown a clear distinction in pattern between active breathing and quiet periods; however, the tracings were obtained from scalp electrodes
Volume Number
1IY 7
Respiratory
movements
in fetal monkeys
,
”
945
(,
*1-
Fig. 8. Segment of record obtained 24 hours prior to delivery in Monkey 72-4. The intraamniotic catheter had become dislodged by this time, but the frequency and intensity of the uterine contractions may be deduced from the blood pressure and tracheal pressure records. Bursts of rapid fetal breathing movements continued to occur during this period of 30 to 40 mm. Hg contractions. The V-shaped decelerations in the fetal heart rate appear to be related to the respirations rather than the uterine contractions. Paper speed, 50 mm. per minute.
Fig. 9. Deep gasping movements immediately tracing shows only motion artifact and DC speed, 50 mm. per minute.
and were clouded by motion artifact resulting from fetal movements and from maternal abdominal respiratory movements. Five of the monkeys exhibited episodes of increased uterine activity during the period 10 P.M. to 6 A.M. for 2 or 3 days prior to labor. Uterine contractions reached intensities of 30 to 40 mm. Hg during these times, then diminished greatly or disappeared during the
prior to fetal potentials
from
death in Monkey 72-4. The the myometrial contraction.
EOG Paper
following day. The fetal tracheal catheter was still working well in 3 of these animals (Nos. 72-4, 72-5, and 73-4). The fetal breathing movements persisted during this prelabor activity in all 3 animals (Fig. 8). Recordings of fetal tracheal pressure during labor were also obtained in these three animals plus one other. In this latter monrapidly progressive labor key (No. 73-IO),
946
Martin
et al.
August 1, 1974 Am. J. Obstet.
Gynecol.
Fig. 10. Acute
fetal stress experiment in Monkey 72-5. Acute fetal respiratory acidosis produced by administration of 20 per cent CO1 to the mother promptly abolished the rapid fetal breathing movements intermixed with repetitive gasping. Less frequent gasping movements occurred during the acidosis accompanied by abrupt fetal heart rate decelerations. Rapid fetal breathing movements reappeared briefly approximately 4 minutes after the end of the CO, inhalation. The maternal hyperpnea is reflected in increased positive excursions in the IUP and tracheal pressure records. Paper speed, 30 mm. per minute.
occurred unexpectedly after 2f/2 days of observation; however, the fetus had been in good condition and had established rapid breathing activity during this period. Monkeys 72-4, 72-5, and 73-4 exhibited prolonged labor with expulsion of the fetus apparently prevented by the fixation of the catheters and electrode leads at their point of exit through the fetal membranes. All 3 of these fetuses died following several hours of labor and after exhibiting evidence of distress: late deceleration fetal heart rate patterns, decreased fetal heart rate base-line variability, then bradycardia and hypotension. Fetal breathing movements persisted during early labor in these 3 fetuses, but disappeared in advance of fetal heart rate evidence of fetal distress. Forceful gasping movements recurred in these fetuses shortly before death (Fig. 9). Monkey 73-10 was found shortly after partial expulsion of the fetus. Fetal breathing movements had occurred during this short (2vz hour) labor until approximately 30 minutes before expulsion. Fetal respiratory acidosis was produced in 3 monkeys in this series (72-5, 73-3, and 73-4) by administration of 20 per cent CO, to the mother by means of a helmet. When this was done during a period of rapid fetal
breathing, the rapid breathing movements quickly disappeared, to be replaced after a short interval by strong gasps (Fig. 10). The rapid breathing movements returned 6 or more minutes after the mother resumed air breathing. In 2 monkeys (Nos. 73-4 and 73-10)) fetal hypoxia was induced by administration of 10 per cent 0, to the mother. The fetal arterial catheter had become dislodged in Monkey 73-4, but in No. 73-10, the fetal p0, had decreased from 29 to 19 mm. Hg after 45 minutes of low O,, with no fetal acidosis (initial pH 7.38, ending pH 7.43; initial pC0, 28, ending pC0, 21). Rapid fetal breathing movements continued during the short-term hypoxia in these experiments. Several animals failed to become chronic preparations for varied reasons and yet were observed for more than 18 hours following operation, a time by which all of the healthy fetuses had begun to have breathing movements. The appearance or absence of breathing movements in relation to fetal condition in these animals corresponds well with the observations during the stress experiments and labor in the healthy fetuses. In the failure group, 4 fetuses exhibited gradually worsening hypoxia and acidosis, resulting in 2 instances from
Respiratory
increasing uterine activity, in a third following severe asphyxia during the operation, and in the remaining case associated with maternal circulatory failure (suspected heat stress). None of these fetuses showed rapid respirations. One exhibited gasping during late decelerations and again immediately prior to death, and the remaining fetuses showed only agonal gasping movements. Two fetuses showed initial recovery followed by deterioration in the second 24 hours following operation in association with maternal circulatory failure (also probable heat stress) . One of these fetuses maintained normal pH values (above 7.30) with low Oz tensions (none above 18 mm. Hg) for several hours, but did not exhibit any breathing movements. The second achieved pH and ~0, comparable to those in the healthy fetuses for a time. During this period, breathing movements appeared resembling those observed at comparable times following operation in the chronic preparations. Another fetus appeared to be doing well when, at approximately 44 hours, it died suddenly after the carotid arterial catheter had been flushed. This fetus had shown normal evolution of breathing movements. Comment The breathing movements exhibited by these fetal monkeys are very similar to those reported by Dawes and associates1 in fetal lambs. The nature and pattern of the gasping movements is almost exactly the same in the two species. The other breathing movements observed in the fetal monkeys, encompassing a wide spectrum of frequencies and intensities, would seem to be the counterpart of the rapid irregular respiration exhibited by the fetal lambs. These similarities were probably expectable and, indeed, equivalent breathing movements should be anticipated in other species as a regular feature of intrauterine life. For as Dawes has pointed out, if the fetus had not exercised its breathing muscles in utero, it would not be able to initiate and sustain pulmonary ventilation during the neonatal period. The magnitude of the negative intrathoracic pres-
movements
in fetal
monkeys
947
sure obtained during intrauterine gasping is equivalent to that required to effect initial expansion of the lungs.” The intensities of other breathing movements, except for the very smallest ones, are in the range required for sustained air breathing. The breathing movements tended to occur in cycles, with longer periods of frequent (though discontinuous) respiratory activity alternating with shorter periods in which no movements or only isolated gasps occurred. There were no differences in pH or respiratory gas tensions of arterial blood between breathing and quiet periods in either the fetal monkeys or lambs. This observation, together with the increased variability in heart rate and blood pressure and clustering of somatic and eye movements during the breathing periods, suggests that the respiratory movement cycles are an expression of a more basic alternation in the functional level of the central nervous system between quiet and active states. These rest-activity cycles are observable in term newborns of several speciesfit i Although it has been reported that the cycles appear only after 32 weeks’ conceptional age in human premature infants,* there is also some evidence of their occurrrence in human fetuses as early as midpregnancy. In these experiments, definite alternation betwee:: quiet and active periods could be observed even in the youngest fetuses, approximately 115 to 120 days’ gestational age. The active state was markedly predominant after the first few days of observation in all of these fetal monkeys. This finding agrees well with the observations that, in general, the proportion of time spent by infants of several species in quiet sleep increases with increasing postnatal age. 6-S Much of the variability in cycle length observed in these experiments, and particularly the occurrence of very prolonged active periods, may have reflected the incomplete development of quiet sleep and its replacement by an intermediate or transitional activity state. In these experiments, rapid fetal breathing movements and the alternation of active and quiet states occurred only in fetuses in good
948
Martin
August 1, 1974
et al.
Am. J. Obstet.
condition, as judged from heart rate, pH, and respiratory gas tensions. Rapid respirations appeared well before clear active-quiet cycling during recovery from the initial operation, and both disappeared early in the course of fetal deterioration in labor. The distressed fetuses usually showed no breathing movements except for gasping shortly before death; however, few instances of fetal gasping during late fetal heart rate decelerations were observed. Rapid breathing movements did not develop in fetuses which remained acidotic after operation, even though they were observed past the time when all of the healthy fetuses had shown breathing movements. In a limited number of acute experiments, acute fetal respiratory acidosis
Gynecol.
inhibited the rapid breathing movements. Hypoxia for limited periods in the presence of normal pH did not abolish the rapid breathing movements, but these failed to develop following operation in a fetus with more chronic hypoxia, even though the pH remained nearly normal. The absence of rapid breathing movements in distressed monkey fetuses parallels similar findings by Dawes and associates’ in fetal sheep. It is noteworthy also, that Boddy and Robinson’ could not detect fetal chest wall movements in small-for-dates pregnancies. It appears that the occurrence of rapid fetal breathing movements and the alternation of active and quiet states may be sensitive indices of fetal well-being.
REFERENCES
1.
Dawes, G. S., Fox, H. E., Leduc, B. M., et al.: J. Physiol. 220: 119, 1972. 2. Boddy, K., and Robinson, J. S.: Lancet 2: 1231, 1971. 3. Duenhoelter, J., and Pritchard, J. A.: Obstet. Gynecol. 42: 746, 1973. 4. Martin, C. B., Jr., Murata, Y., and Parer, J. T.: AM. J. OBSTET. GYNECOL. 117: 126, 1973. 5. Uawes, G. S.: Fetal and Neonatal Physiology, Chicago, 1968, Year Book Medical Publishers, Inc., Chap. 11.
Attention
to authors:
Section
on Clinical
6.
7.
8.
Sterman, M. B., and Hoppenbrouwers, T.: In Sterman, M. B., McGinty, D. J., and Adinolfi, A. M., editors: Brain Development and Btiavior, New York, 1971, Academic Press, Inc., p. 203. McGinty. D. J.: In Sterman, M. B., McGinty, D. J., and Adinolfi, A. M., editors: Brain Development and Behavior, New York, 1971, Academic Press, Inc., p. 335. Dreyfus-Brisac, C.: Dev. Psychobiol. 3: 91, 1970.
Opinion
The editors and publisher of the AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY wish to call your attention to a new section entitled “Clinical Opinion.” The section will be devoted to the clinical diagnosis and management of certain disease entities. The section is designed to accommodate from eight to twenty typed pages with appropriate illustrative material, tables, and figures helpful in clarifying to the reader how a condition is actually managed. References need not be extensive, since the emphasis should be on the author’s actual handling of clinical problems. The objective of this section is to transmit to the reader how a clinical situation is actually handled. Manuscripts should be submitted to Frederick P. Zuspan, M.D., Editor, American Journal of Obstetrics and Gynecology, 5841 S. Maryland Ave., Chicago, Illinois 60637.