- Email: [email protected]
The nasal resistance of newborn infants
T h e J o u r n a l of P E D I A T R I C S
557
The nasal resistance of newborn infants The resistance o[ the nasal air passages, which is an important [actor in the mechanics of respiration in newborn infants, was found to be about one [ourth of the total lung resistance. I t would appear that the nasal passages contribute a relatively smaller part (slightly less than hall) o[ the airway resistance than in adults. The reason for "obligatory" nose breathing in newborn in[ants may be found in the pattern o[ phylogenetic development o[ oropharyngeal and nasal structures.
George Polgar, M.D.,* and Glen P. Kong, M.D.** PHILADELPHIAj PA., AND VANCOUVER, B. C., CANADA
M E A S U R E t) values for total pulmonary resistance in newborn infants have been obtained by various methods?, 2, a, 4 In all methods the babies breathed through their noses, so that the results included the resistance of the nasal air passages; newborn infants do not naturally breathe through their mouths. They are "obligatory" nose-breathers, except when they cry. Thus, it is not possible to compare published values for total pulmonary resistance, or airway resistance s of infants with similar measurements made on older subjects who were studied while breathing through their mouths with their noses occluded. The correlation between airway resistance From the Departments o[ Physiology and Pediatrics, Schools of Medicine, University of Pennsylvania, Philadelphia, and the Department of Otolaryngology, School of Medicine, University of British Columbia, Vancouver, B. C., Canada. This study was supported by a United States Public Health Service Research Career Program Award (No. HE-K3-9471) and a United States Public Health Service Research Grant (No. HD-00236). *Address, Department of Physiology, Graduate School of Medicine, University o[ Pennsylvania, Philadelphia 4, Pa. "~*R. Samuel McLaughlin Fellow, present position, Clinical Instructor, University o] British Columbia Medical School, Vancouver, B.C., Canada.
and lung volume in various age groups ~' 7 suggests a disproportionate growth of the flow-resistive air passages and the other aircontaining spaces of the lungs during childhood and adolescence, s However, since the partition of the measured airway resistance between the various parts of the airways in the newborn is not known, no definite information about this functlonal-anatomical relationship in the earliest period after the onset of respiration could be obtained. The purpose of the present investigation was to measure air flow resistance through the nose in newborn infants and to compare this with the resistance of the other airways. MATERIAL
AND
METHODS
The technical difficulties involved in adapting methods for the measurement of resistance, i.e., the pressure/flow ratio through the nose in subjects of this age were considerable, so that it was necessary to derive the values of nasal resistance by subtraction from two separate measurements of total pulmonary resistance. The total pulmonary resistance was measured with the subject in a supine position during quiet breathing. Simultaneous record-
5 5 8 Polgar and Kong
October 1965
Fig. 1. Photograph of pneumotachograph and attached face mask. Over-all length: 105 mm.
Fig. 2. Photograph of pneumotachograph and attached plastic oral airway. Over-all length: 135 mm. ings were made of variations in intraesophageal pressure, 9 monitored via an approximately 5 cm. long and 5 mm. wide, thin latex balloon filled with about 0.5 ml. of air, attached to a plastic tube (I.D. 0.055 inch), and of the flow rate of air monitored via a wire mesh-screen pneumotachograph. ~5 Recordings were obtained under two different conditions: first the pneumotachograph was attached to a modified Bennett No. 3 face mask (Fig. 1) which was placed around the "X'The pneumotachograph was made in the machine shop of the Moore School of Electrical Engineering, University of Pennsylvania, J. Pedley and Robert J. Titherlngton. The differential pressure from the flowmeter was measured with a Grass Model PT 5 strain gauge, esophageal pressure with a Statham Model P23DC strain gauge. Signals were recorded on a Grass Model 7 polygraph.
baby's mouth and nose so that no obstruction of the latter should occur. Thus, the newborn was breathing quietly through his nose. Immediately thereafter, the same pneumotaehograph was connected to a Sierra No. 0 plastic oral airway (Fig. 2), and the latter was placed into the newborn infant's oral cavity with great care in order to maintain a relatively normal respiratory pattern. The airway has a single opening on its distal end. According to careful measurements and direct inspection, when in position for measurements, this opening was situated in the air space between the root of the tongue, the epiglottis, and the posterior pharyngeal wall. T h e baby's lips were closed against the collar of the air-
Volume 67 Number 4
Nasal resistance of newborn infants
way and the nostrils gently occluded with two fingers. Thus, the infants were made to breathe through the artificial airway, and after a short period of adaptation, a relatively quiet breathing pattern could be established for about one minute or long enough to obtain satisfactory recordings of esophageal pressure and airflow. T h e flow resistance of both the pneumotachograph and the oral airway had been estimated previously by measuring the differential pressure between their two ends at different rates of air flow over a range which included the flow rates observed in newborns at quiet respiration. T h e pressure/flow ratio of the flowmeter alone and that of the flowmeter and plastic airway together is shown in Figs. 3 and 4. T h e average resistance of the p n e u m o t a c h o g r a p h over the longer linear part of the pressure/flow curve (approximately between 0.05 and 0.15 L. per second flow rates) was 0.5 cm. H 2 0 per liter per second and the average combined resistance of the flowmeter and oral airway between RESISTANCE
approximately identical limits of linearity was 3.2 cm. H 2 0 per liter per second. The calculated resistance of the oral airway alone was 2.7 cm. H~O per liter per second. T h e nasal resistance of the babies was calculated as the difference between the total lung resistance measured during nasal breathing and as measured when the nose was occluded and the infants breathed through the plastic airway. Both values were corrected before subtraction for the resistance of the p n e u m o t a c h o g r a p h and the artificial airway, respectively. The total lung resistance can be obtained from simultaneously recorded tracings of esophageal pressure and air flow by various techniques. A common preliminary step in such calculations is to separate the pressure needed to overcome the elastic recoil of the lung from the frictional flow resistive pressure. For this the method of Frank, Mead, and Ferris TM was used, with a minor modification (Fig. 5). The intraesophageal pressure difference was measured on the recorded pressure
OF
PNEUMOTACHOGRAPH
FLOW RATE L/u* 0-15
/r 0-10
/,,~t J /
f
f
7
f
J
J
f
f
J
J
J
J
Ir
0.06
0 O
! 0.01
I 0.02
I 0 03
5 59
i 0-04
I 0.05
I 0-06
I O,OT
I 0 - 0 8 NHsO PREISURE
Fig. 3. Pressure/flow relationship measured through the pneumotachograph. The slope of the longer linear part of the curve between approximately 0.05 and 0.15 L. per second flow is 0.5 cm. H20 per liter per second. The dependent variable is plotted on the abscissa in order to conform with the customary pressure/flow diagrams such as in Fig. 6.
5 60
Polgar and Kong
October 1965 GONBINEO
RESISTANGE
OF
PNEUMOTAGHOGRAPH AND ORAL AIRWAY
FLOW RA 1"E L/-,o O-15
/
/
/
/
/,
/ O-IO
/ /
/
/
O'OS
/r
0
0
I
I
t
I
O'l
O,Z
0'5
0 4.
I
--
O-S o-, PRESSURE
Fig. 4. Pressure/flow relationship measured through the pneumotachograph and attached oral airway. The slope of the longer linear part of the curve between approximately 0.05 and 0.15 L. per second flow is 3.2 cm. H20 per liter per second. The dependent variable is plotted on the abscissa in order to conform with the customary pressure/flow diagrarm such as in Fig. 6. curve between two points at equal lung volumes during the inspiratory and expiratory phase of a complete respiratory cycle. The elastic forces being volume dependent, they are assumed to be identical at these equal volume points, and, therefore, the remaining pressure difference represents the frictional, i.e., nonelastic resistive pressure. The equal volumes were found by dividing the area underneath the inspiratory and expiratory air flow recordings into equal parts. The rate of air flow at equal volumes was then measured from the flow curve, and the pressure difference between the points of equal volume in centimeters of water was divided by the sum of the inspiratory and expiratory flow in liters per second. For each determination at least 5 breaths were analyzed from parts of the recording where the breathing pattern was the most regular. Successful measurements of the nasal resistance with this method were accomplished in 5 full-term newborn infants, 3 males and 2 females, at 2 hours to 3 days of age; their body weights ranglng from 2,580 grams to 4,050 grams; 2 were Caucasians and 3 were Negroes.
RESULTS Results of the measurements are given in Table I. T h e average total lung resistance when breathing through the nose, and corrected for the resistance of the pneumotachograph, was 47.5 cm. H 2 0 per liter per second (with a range of 38.0 to 53.0 cm. H 2 0 per liter per second). O n the other hand, when breathing through the plastic airway, and after correction for the combined resistance of the p n e u m o t a c h o g r a p h and oral airway, this value was 35.4 cm. H 2 0 per liter per second (with a range of 28.1 to 47.4 cm. H 2 0 per liter per second). T h e difference between the two, i.e., the average nasal resistance was 12.1 cm. H 2 0 per liter per second (with a range of 5.6-19.9 cm. H 2 0 per liter per second). T h e relative magnitude of the nasal resistance as compared with the average total lung resistance was 26 per cent (with a range of 11 to 41 per cent). It is evident that both the absolute and relative values in individual babies varied
Volume 67 Number 4
Nasal resistance o[ newborn in[ants
561
CALCULATION OF TOTAL LUNG RESISTANCE (SGHEMATIG DIAGRAM}
AIR FLOW *'tt
~..::..:tL r
/~!il[ "~
O
EXPIRATION '
\
Expm.
\
IS~176
~
." LUME 'SO'~/O
:~:
J
Vz~V s "
i i
NO FLOW I
NO FLOW z
NO FLOW~}
EXPIRATION
ESOPHAGEAL PRESSURE (P)
~ : - - " / h
"''ikr-.. ; p. " ~ i ' ~ " ~*T "~I
/'A?'E*~ """ it;l~l' J}A I~' * AF~E TIME
>_
Fig. 5. Schematic demonstration of the method for calculating total lung resistance from simultaneous recordings of air flow (top curve) and intraesophageal pressure (bottom curve). The stippled areas under the inspiratory and expiratory flow curves are equal and represent equal volumes (because L./sec. x sec. = L.). Vz and VE are inspiratory and expiratory flow rates at the points of equal volumes. The projections of no-flow points 1, 2, and 3 on the pressure curve represent pressures at the beginning and end points of inspiration and expiration, respectively. The lines connecting these points represent changes of elastic pressure related to volume changes. Pel I and Pe~E are the points where the elastic pressure is equal in the course of inspiration and expiration respectively. P~I is the total elastic pressure difference between end-expiratory and maximal inspiratory volume. A PtI and A PtE are the inspiratory and expiratory frictional resistive pressures, respectively, at the times of equal volumes. considerably. T h e 2 Caucasian infants h a d a nasal resistance close to the average value, while in the 3 Negroes, both high a n d low resistances were found. T h e r e was no a p p a r ent relationship between the infant to infant variations of the nasal resistance a n d that of the total nonelastic resistance. COMMENT T h e simplest a n d most s t r a i g h t f o r w a r d m e t h o d for measuring nasal resistance in adults a n d cooperative older children is posterior rhinometry, n A n e w b o r n infant would only by chance keep a tube or a balloon in its m o u t h without p r o d u c i n g pressure artifacts, u n r e l a t e d to nasal resistance, by m a n i p u l a t i n g the pressure transmitting device
with his tongue or by occluding holes on a tube with saliva. I t was for this reason that the m e t h o d described above was developed. However, d u r i n g attempts to employ posterior rhinometry a single successful measurem e n t was made. A plastic tube (I.D. 0.55 inch) was passed into the esophagus of a Negro male b a b y through the mouth. Its distal end h a d been occluded a n d several small holes h a d been m a d e in its side at a p r e m e a s u r e d distance from the lips, so that they would be within the p h a r y n g e a l airpocket. By repeatedly passing air through the tube from a syringe to clear the holes of mucus, pressure could be recorded from the a t t a c h e d strain gauge d u r i n g a few breaths. T h e air flow rate was simultaneously re-
562
Polgar and Kon~
October 1965
T a b l e I. Nasal resistance in 5 n e w b o r n infants calculated from the total lung resistance when
Subject~ No.
Sex
Race
1 2 3 4 5
M F F M M
Negro Caucasian Caucasian Negro Negro
Age 2 5 3 2 2
Hours Hours Days Days Days
Weight (grams) 4,050 3,680 3,680 2,580 3,640
Total lung Breathing through nose (~) crn, H,O/L./sec. t S.D.'~ 48.1 38.0 50.2 53.0 48.0 Average 47.5 S.E. 2.6
11.9 9.8 14.5 7.4 3.4
"~Correeted for the resistance of the pneumotachograph (0.5 cm. H~O/L./sec.) when breathing through the nose and for the combined resistance of the pneumotachog~aphand plastic airway (3.2 em HzO/L./sec.) when breathing through the latter. tS.D. of the means of 5 breaths. ++S.E. of the difference of means. w of the mean diffe,ences. corded through the pneumotachograph. T h e average nasal resistance as calculated from the corresponding points on the pressure and flow rate curves was 12.2 cm. H 2 0 per liter per second. A plot of pressure versus flow values of one respiratory cycle from this infant is shown in Fig. 6. A large variability of the absolute values for nasal resistance a n d also for its m a g n i t u d e relative to the airway resistance has been observed in adults? 2, ~:'~ T h e reason for this is probably the highly variable state of congestion of the nasal nmcosa, which might be d e p e n d e n t on various factors such as body position, e n v i r o n m e n t a l temperature, emotional state, 1~ etc. Butler ~2 measured nasal resistance in 5 adults by posterior rhinometry a n d by subtracting plethysmographic airway resistance estimated during m o u t h breathing from that measured d u r i n g nose breathing; their nasal resistance varied from 1.09 to 4.26 cm. H 2 0 per liter per second with an average value of 2.18 cm. H 2 0 per liter per second. T h e average percentage of nasal resistance was 63 per cent of the airway resistance d u r i n g nasal breathing with a range of 46.3 per cent to 76.0 per cent. Such large variations on a small n u m b e r of subjects render the accuracy of average values relatively insignificant. However. the variability seems to be more a physiologic one than one related to the accuracy of the methods of measurements.
T h e relationship of nasal resistance in newborns to the resistance of the rest of their conductive airways c a n n o t be assessed by using the total lung resistance for comparison, because the latter includes the lung tissue resistance. For an approximate comparison, data were used which have been obtained on a series of 14 newborns by plethysmographic measurements of the airway resistance d u r i n g nasal breathing. T h e method employed for these measurements has been described elsewherea; it is basically a n adaptation of the method of DuBois, Botelho, and Comroe 1'~ to n e w b o r n infants. I n Fig. 7 a plot of airway conductance (which is the reciprocal of airway resistance), against lung volume in these 14 n e w b o r n infants is shown. Their average airway conductance was 0.0351 L. per second per centimeter H 2 0 which corresponds with a n average airway resistance of 28.5 era. H 2 0 per liter per second. ~" A short comment is necessary to explain the discrepancy between this value and the one originally published.~ In the plethysmograph first used for the measmements of airway resistance, a manipulator rod entered the plastic body-box through a ntbber stopper in its top. When, in order to measure lung volume, the baby was forced to breathe *These values were obtained with tbe cooperation of Robert A. Ersek, member of the Student Research Program at the Universityof Pennsylvania,1961-1962.
Volume 67 Number 4
breathing
through
Nasal resistance of newborn infants
the nose a n d
when
b r e a t h i n g t h r o u g h an artificial a i r w a y
resistance (corrected*) Breathing through oralairway (b) cm. HeO/L./see.
S.E.
28.2 28.1 40.2 47.4 33.3 35.4 3.8
I
S.D.t 8.2 5.3 5.9 3.9 7.3
563
Nasal resistance (.~
(a-b = c) cm. H~O/L./sec.
I
19.9 9.9 10.0 5.6 14.7 12.1 S.D. 5.5 s.g. 2.5.~ p ~ 0.10
against a mechanical shutter occluding the airway, alternating positive and negative pressure was transmitted by dry friction to the flexible plastic top of the plethysmograph. This resulted in the over-estimation of lung volume and of the corresponding airway conductance (i.e., underestimation of airway resistance). Before making the second series of measurements this source of error was eliminated. The corrected average lung vohtme is in close agreement with results reported by Geubelle and co-workers, 16 and by KIaus and associates. 17 I f the average nasal resistance from the present study, 12.1 cm. H 2 0 p e r liter per second, is subtracted from the average value for airway resistance in the other 14 newborns, one obtains the calculated resistance of the airways as they would be when the babies b r e a t h e d through their mouths, 16.4 cm. H 2 0 p e r liter p e r second. Considering the wide variations of nasal resistance between individual infants, the range of the calculated a i r w a y resistance (excluding nasal resistance) w o u l d be 8.6 to 22.9 cm. H 2 0 per liter p e r second. Using the same n u m bers, the average nasal resistance is about 42 p e r cent of the airway resistance when b r e a t h i n g t h r o u g h the nose, with a range of 19.6 p e r cent to 70.0 p e r cent. A p p l y i n g the two-sample ranks test TM to the comparison of percentages of nasal resistance relative to airway resistance when b r e a t h i n g t h r o u g h the nose, in the 5 newb o r n infants from this study a n d in 5 adults
.100
S.E.~
(%)
1.4 1.0 1.6 0.8 0.8
41 26 20 11 31 26
)
of Butler ( T a b l e I I ) , the level of significance for the difference of the means was p > 0.10. Therefore, it cannot be stated with certainty that the relative nasal resistance in newborns is significantly smaller t h a n in adults. H o w ever, it should be concluded that such a tendency is noticeable, a n d that the resistance of the nasal air passages in newborn infants is neither a m a j o r nor a negligible p a r t of the total airway resistance. I t is a r e m a r k a b l e fact t h a t the absolute m a g n i t u d e of nasal resistance in newborn infants is only 5.5 times as large as that of the aduhs. This, a n d the similarly small ratio
II. C o m p a r i s o n of p e r c e n t a g e nasal resistance to total a i r w a y resistance in 5 n e w b o r n infants a n d 5 adults
Table
Newborn infants* .. % I Rank 70.0 34.6 35.0 19.6 51.5 Sum of ranks "~Percentages
calculated
8 2 3 1 6 20:~ from
%
Adultst I Rank
46.3 48.0 52.5 75.0 76.0 the nasal
4 5 7 9 10 35:~ resistance mea-
sured in 5 newborn infants (Table I) as related to the average airway resistance measured in 14 newborn infants (Fig. 7). ~'Percentages
calculated
from
data of Butler. a2
~Extreme sums of ranks for p = 0.10 are 19:3678 The extreme sums in the present comparison, 20:35 are just outside these limits indicating a level of significance slightly
larger than p = 0.10.
564
Polgar and Kon.~
October 1965
0'08' F L O W RATE L/=,= 0.06
,/J
0.04 9
/.O"
/
0"02EXPIRATION
-,!o
-0:8
-d6
-o'. 4
o~r o!2
-oz~ r
INSPIRATION
jW,O/
o!.
o?6
o~a
1.0
PHARYNGEAL P R E S S U R E ;u I'llO
-0"02
-0.04
-0.06
-0.01 Fig. 6. Plots of pharyngeal pressure versus flow from two breaths (-x--~, and -o--)) in posterior rhinometry. The points represent nasal resistance and their average is 12.2 cm. H~O per liter per second.
of airway resistance (when breathing through the nose) in newborns versus adults (8.2), suggests that the airway dimensions in general are relatively larger in infants than in adults. For details on the relationship of dimensions, shape, and structure of the airways on one hand, and their resistance to air flow on the other, the review of the subject by Mead s may be consulted. Mead postulated that tile rate of growth and the relationship of airway conductance airway resistance/ 1
and lun/ wdume is
/
not the same for all age groups. If the simplified relationship of: Conductance (L./sec./cm. H 2 0 ) = 0.24 Lung Volume (L), found by Briscoe and DuBois: were typical for the neonate as well as for older subjects, the predicted airway resistance
of a newborn when breathing through the mouth would be about 50 times larger than in an adult. However, the value of 16.4 tin. H 2 0 per liter per second obtained here in newborns is only about 14 times larger than that of adults. Minute ventilation of adults is approximately 12 times larger than that of newborns~; it seems that the relationship between the airway resistance in newborn infants and in adults is in good agreement with this number. It is this remarkably efficient coincidence which makes it possible that a normal newborn infant breathes with a work output of less than 10 per cent of that of an adult 2 and by producing total intrathoraeie pressure changes during respiration which are not greater than those in adults, z' ~ In spite of the relatively favorable parti-
Volume 67 Number 4
Nasal resistance o[ newborn in[ants
565
AIRWAY GONDUGTANGs L / H e l o " NtO
~A " 0 . 0 5 5 1 .t 0 . 0 1 0 5 ( 0 " 0 5 5 1 It: 0 " 0 1 6 ) 0,06 , , 0 " 0 7 0 4. 0 " 0 1 7 7 (0" 1 9 0 It: 0 . 0 6 ) 0.05
0.04
9
~
..--.tg""~ "~':- .....
o.o3
0.02
0.01
0
i 0
O'Ol
~ 0`02
1 0'03
! 0'04
! 0"05
,, !
I
0"06
0"07
1 0.08
! 0"09
!
;
0"I0 LUNG
0"II
VOLUME
Fig. 7. Airway conductance and corresponding lung volume in 14 normal newborn infants. Each point represents the average of several measurements on one baby. The solid regression line has been calculated for these 14 newborn infants. The broken regression line has been calculated for the obsolete values measured before correction of the method. 5 Values in the box are the mean airway conductance (CA) in L./sec./cm. H~O and mean lung volume (V) in L for these infants. Values in parentheses are those measured before correction of the method.
tion of airway resistance in newborns, their nasal air passages do represent a sizeable resistance to air flow and are prone to become easily obstructed; it takes very little narrowing of the conductive channels to increase the resistance and consequently respiratory work exponentially. While a newborn infant during the first weeks of life is unable to change spontaneously from nose breathing to m o u t h breathing, an adult can voluntarily lower his airway resistance by more than 60 per cent of its normal value by changing to mouth breathing; the adult is able to use this device for counteracting an increase of the lower airway resistance or for completely eliminating an increased respiratory workload due to nasal obstruction. T h e "obligatory" nose breathing tendency of newborns on one hand, and the ease with
which obstruction of the nasal airways occurs in this age on the other, is clearly in contradiction to the usual principles of physiological reserves and adaptive mechanisms protecting the vital functions. An explanation for this transient stage of relatively high vulnerability of airway patency may be found in a peculiar situation of phylogenetic development. I n most mammals, especially in the herbivora, the nasopharyngeal anatomy renders them obligatory nose breathers. 19 Their larynx is positioned high, opposite to the base of the skull, and their large epiglottis is in close contact with the soft palate so that the nasopharyngeal and laryngeal airways form an uninterrupted channel. This prevents olfactory function, from being interrupted when feeding. Also, since their life is dependent on a highly developed sense of smell, they have wide
5 66
Polgar and Kong
nostrils a n d nasal air passages which do not easily become obstructed. T h e a d u l t human, on the other hand, has a wide open comm u n i c a t i o n between his oral a n d nasopharyngeal cavities a n d his small nostrils. W h e n e v e r m a n opens his mouth, breathing must automatically occur through this p a t h of lower resistance rather than through the nose. I n h u m a n newborns, the larynx and epiglottis, while continuously descending d u r i n g fetal life are still positioned relatively high. T h e epiglottis is close to the palate, similar to the more primitive m a m m a l s , ~9 a n d the tongue is in contact with the palateS~ for these reasons they are practically unable to breathe through their mouths. At the same time the intranasal structures of the neonate, although reminiscent of an earlier stage of development, are, in fact, further ahead in the phylogenetie degeneration of tile olfactory apparatus. It a p p a r e n t l y takes a period of some weeks of extrauterine development for the pharyngolaryngeal a n a t o m y to catch up with the nasal structures. D u r i n g this period, nasal obstruction can cause severe respiratory distress and suffocation. SUMMARY
T h e nasal resistance of 5 newborn infants was d e t e r m i n e d by an indirect m e t h o d calculated from measurements of total lung resistance during nasal breathing and while breathing through a plastic oral airway. T h e average nasal resistance was 12.1 cm. H~O per liter p e r second (5.6 to 19.9 era. H.,O per liter per second) or 26 per cent (11 to 41 per cent) of the total hmg resistance. Relative to an average value of total airway resistance measured on other newborns who were breathing through their noses, this nasal resistance represents an average of 42 per cent (19.6 to 70.0 per cent) of the total resistance. I t would a p p e a r that the nasal passages contribute a relatively smaller p a r t of the airway resistance in newborn infants than in adults. Still, the newborn infant is at a disadvantage because he cannot spontaneously breathe through his m o u t h during the first few weeks of life. T h e reason for this m a y be found in the peculiar p a t t e r n of
October 1965
phylogenetic d e v e l o p m e n t of o r o p h a r y n g e a l a n d nasal structures. REFERENCES
1. McIlroy, M. B., and Tomlinson, E. S.: The mechanics of breathing in newly born babies, Thorax 10: 58, 1955. 2. Cook, C. D., Sutherland, J. M., Segal, S., Cherry, R. B., Mead, J., McIlroy, M. B., and Smith, C. A.: Studies of respiratory physiology in the newborn infant. III. Measurements of mechanics of respiration, J. Clin. Invest. 36: 440, 1957. 3. Karlberg, P., Cherry, R. B., Escardo, F. E., and Koch, G.: Respiratory studies in newborn infants. I. Apparatus and methods for studies of pulmonary ventilation and the mechanics of breathing. Principles of analysis in Mechanics of Breathing, Acta paediat. 49: 345, 1960. 4. Swyer, P. R., Reiman, R. C., and Wright, J. J.: Ventilation and ventilatory mechanics in the newborn, J. PEDIAT. 56" 612, 1960. 5. Polgar, G.: Airway resistance in the newborn infant, J. PEDIAT. 59" 915, 1961. 6. Cook, C. D., Helliesen, P. J., and Agathon, S.: Relation between mechanics of respiration, lung size and body size from birth to young adulthood, J. Appl. Physiol. 13: 349, 1958. 7. Briscoe, W. A., and DuBois, A. B.: The relationship between airway resistance and lung volume in subjects of different age and body size, J. Clin. Invest. 37: 1279, 1958. 8. Mead, J.: Mechanical properties of hmgs, Physiol. Rev, 41: 281, 1961. 9. Fry, D. L., Stead, W, W., Ebert, R. V., Lubin, R. I., and Wells, H. S.: Measurement of intraesophageal pressure and its relationship to intrathoracic pressure, J. Lab. & Clin. Med. 40: 664, 1952. 10. Frank, N. R., Mead, J., and Ferris, B. G., Jr.: The mechanical behavior of the lungs in healthy elderly persons, J. Clin. Invest. 36: 1680, 1957. 11. Spiess, G.: Die Untersuchungsmetoden der Nase und ihrer Nebenh6hlen, Handb. d. Laryngol. u. Rhinol., Wien 3: 2159, 1900. (Referred to by Butler. 12) 12. Butler, J.: The work of breathing through the nose, Clin. Se. 19: 55, 1960. 13. Cottle, M.: Concepts of nasal physiology as related to corrective nasal surgery, Arch. Otolaryng. 72: 11, 1960. 14. Uddstr6mer, M.: Nasal respiration. A critical survey of some current physiological and clinical aspects of the respiratory mechanism with a description of a new method of diagnosis, Acta oto-laryng. Suppl. 42, 1940. 15. DuBois, A. B., Botelho, S. Y., and Comroe, J. H., Jr.: A new method of measuring airway resistance in man using a body plethysmograph: Values in normal subjects and in patients with respiratory disease, J. Clin. Invest. 35: 327, 1956. 16. Geubelle, F., Karlberg, P., Koch, G., Lind, J., WaUgren, G., and Wegelius, C.: L'a6ration
Volume 67 Number 4
17. 18. 19.
20.
du poumon chez le nouveau-n~, Biol. Neonat. 1" 169, 1959. Klaus, M., Tooley, W. H., Weaver, K. H., and Clements, J. A.: Lung volume in the newborn infant, Pediatrics 30: 111, 1962. Mainland, D.: Elementary medical statistics, ed. 2, Philadelphia-London, 1963, W. B. Saunders Company, p. 283. Negus, V. E.: Comparative anatomy and physiology of the larynx, New York-London, 1949, Hafner Publishing Company, (repr. 1962). Birrell, J. F.: The ear, nose and throat diseases of children, Philadelphia, 1960, F. A. Davis Company, p. 3.
APPENDIX
Terminology as used in this article for describing physiological variables. I. Total pulmonary-, or lung resistance (in cm. H~O/L./sec.), the sum of: A. Airway resistance the frictional resistance of air flowing in and out through the conductive airways. Can be subdivided into: a. nasal resistance b. pharyngolaryngeal resistance c. lower airway resistance
Nasal resistance of newborn infants
(Airway conductance =
56 7
1
airway resistance
)
B. Lung tissue resistance the frictional resistance of tissues against the motion of the lung during inflation and deflation. II. Pressures (in era. H20 ) opposing the motions of the lung: A. Elastic pressure developed by the recoil of the elastic tissues and by the surface pressure on the alveolar air-liquid interface (static component) B. Frictional resistive gas pressure in the airways (dynamic component) C. Frictional resistive tissue pressure (dynamic component) II[. Lung volume (in L.), as related to airway resistance is the actual volume at which the airway resistance is determined; usually identical with the functional residual capacity (the lung volume at the end of a normal expiration). IV. Minute ventilation (in L./min.), the total volume of air breathed in and out during one minute.
557
The nasal resistance of newborn infants The resistance o[ the nasal air passages, which is an important [actor in the mechanics of respiration in newborn infants, was found to be about one [ourth of the total lung resistance. I t would appear that the nasal passages contribute a relatively smaller part (slightly less than hall) o[ the airway resistance than in adults. The reason for "obligatory" nose breathing in newborn in[ants may be found in the pattern o[ phylogenetic development o[ oropharyngeal and nasal structures.
George Polgar, M.D.,* and Glen P. Kong, M.D.** PHILADELPHIAj PA., AND VANCOUVER, B. C., CANADA
M E A S U R E t) values for total pulmonary resistance in newborn infants have been obtained by various methods?, 2, a, 4 In all methods the babies breathed through their noses, so that the results included the resistance of the nasal air passages; newborn infants do not naturally breathe through their mouths. They are "obligatory" nose-breathers, except when they cry. Thus, it is not possible to compare published values for total pulmonary resistance, or airway resistance s of infants with similar measurements made on older subjects who were studied while breathing through their mouths with their noses occluded. The correlation between airway resistance From the Departments o[ Physiology and Pediatrics, Schools of Medicine, University of Pennsylvania, Philadelphia, and the Department of Otolaryngology, School of Medicine, University of British Columbia, Vancouver, B. C., Canada. This study was supported by a United States Public Health Service Research Career Program Award (No. HE-K3-9471) and a United States Public Health Service Research Grant (No. HD-00236). *Address, Department of Physiology, Graduate School of Medicine, University o[ Pennsylvania, Philadelphia 4, Pa. "~*R. Samuel McLaughlin Fellow, present position, Clinical Instructor, University o] British Columbia Medical School, Vancouver, B.C., Canada.
and lung volume in various age groups ~' 7 suggests a disproportionate growth of the flow-resistive air passages and the other aircontaining spaces of the lungs during childhood and adolescence, s However, since the partition of the measured airway resistance between the various parts of the airways in the newborn is not known, no definite information about this functlonal-anatomical relationship in the earliest period after the onset of respiration could be obtained. The purpose of the present investigation was to measure air flow resistance through the nose in newborn infants and to compare this with the resistance of the other airways. MATERIAL
AND
METHODS
The technical difficulties involved in adapting methods for the measurement of resistance, i.e., the pressure/flow ratio through the nose in subjects of this age were considerable, so that it was necessary to derive the values of nasal resistance by subtraction from two separate measurements of total pulmonary resistance. The total pulmonary resistance was measured with the subject in a supine position during quiet breathing. Simultaneous record-
5 5 8 Polgar and Kong
October 1965
Fig. 1. Photograph of pneumotachograph and attached face mask. Over-all length: 105 mm.
Fig. 2. Photograph of pneumotachograph and attached plastic oral airway. Over-all length: 135 mm. ings were made of variations in intraesophageal pressure, 9 monitored via an approximately 5 cm. long and 5 mm. wide, thin latex balloon filled with about 0.5 ml. of air, attached to a plastic tube (I.D. 0.055 inch), and of the flow rate of air monitored via a wire mesh-screen pneumotachograph. ~5 Recordings were obtained under two different conditions: first the pneumotachograph was attached to a modified Bennett No. 3 face mask (Fig. 1) which was placed around the "X'The pneumotachograph was made in the machine shop of the Moore School of Electrical Engineering, University of Pennsylvania, J. Pedley and Robert J. Titherlngton. The differential pressure from the flowmeter was measured with a Grass Model PT 5 strain gauge, esophageal pressure with a Statham Model P23DC strain gauge. Signals were recorded on a Grass Model 7 polygraph.
baby's mouth and nose so that no obstruction of the latter should occur. Thus, the newborn was breathing quietly through his nose. Immediately thereafter, the same pneumotaehograph was connected to a Sierra No. 0 plastic oral airway (Fig. 2), and the latter was placed into the newborn infant's oral cavity with great care in order to maintain a relatively normal respiratory pattern. The airway has a single opening on its distal end. According to careful measurements and direct inspection, when in position for measurements, this opening was situated in the air space between the root of the tongue, the epiglottis, and the posterior pharyngeal wall. T h e baby's lips were closed against the collar of the air-
Volume 67 Number 4
Nasal resistance of newborn infants
way and the nostrils gently occluded with two fingers. Thus, the infants were made to breathe through the artificial airway, and after a short period of adaptation, a relatively quiet breathing pattern could be established for about one minute or long enough to obtain satisfactory recordings of esophageal pressure and airflow. T h e flow resistance of both the pneumotachograph and the oral airway had been estimated previously by measuring the differential pressure between their two ends at different rates of air flow over a range which included the flow rates observed in newborns at quiet respiration. T h e pressure/flow ratio of the flowmeter alone and that of the flowmeter and plastic airway together is shown in Figs. 3 and 4. T h e average resistance of the p n e u m o t a c h o g r a p h over the longer linear part of the pressure/flow curve (approximately between 0.05 and 0.15 L. per second flow rates) was 0.5 cm. H 2 0 per liter per second and the average combined resistance of the flowmeter and oral airway between RESISTANCE
approximately identical limits of linearity was 3.2 cm. H 2 0 per liter per second. The calculated resistance of the oral airway alone was 2.7 cm. H~O per liter per second. T h e nasal resistance of the babies was calculated as the difference between the total lung resistance measured during nasal breathing and as measured when the nose was occluded and the infants breathed through the plastic airway. Both values were corrected before subtraction for the resistance of the p n e u m o t a c h o g r a p h and the artificial airway, respectively. The total lung resistance can be obtained from simultaneously recorded tracings of esophageal pressure and air flow by various techniques. A common preliminary step in such calculations is to separate the pressure needed to overcome the elastic recoil of the lung from the frictional flow resistive pressure. For this the method of Frank, Mead, and Ferris TM was used, with a minor modification (Fig. 5). The intraesophageal pressure difference was measured on the recorded pressure
OF
PNEUMOTACHOGRAPH
FLOW RATE L/u* 0-15
/r 0-10
/,,~t J /
f
f
7
f
J
J
f
f
J
J
J
J
Ir
0.06
0 O
! 0.01
I 0.02
I 0 03
5 59
i 0-04
I 0.05
I 0-06
I O,OT
I 0 - 0 8 NHsO PREISURE
Fig. 3. Pressure/flow relationship measured through the pneumotachograph. The slope of the longer linear part of the curve between approximately 0.05 and 0.15 L. per second flow is 0.5 cm. H20 per liter per second. The dependent variable is plotted on the abscissa in order to conform with the customary pressure/flow diagrams such as in Fig. 6.
5 60
Polgar and Kong
October 1965 GONBINEO
RESISTANGE
OF
PNEUMOTAGHOGRAPH AND ORAL AIRWAY
FLOW RA 1"E L/-,o O-15
/
/
/
/
/,
/ O-IO
/ /
/
/
O'OS
/r
0
0
I
I
t
I
O'l
O,Z
0'5
0 4.
I
--
O-S o-, PRESSURE
Fig. 4. Pressure/flow relationship measured through the pneumotachograph and attached oral airway. The slope of the longer linear part of the curve between approximately 0.05 and 0.15 L. per second flow is 3.2 cm. H20 per liter per second. The dependent variable is plotted on the abscissa in order to conform with the customary pressure/flow diagrarm such as in Fig. 6. curve between two points at equal lung volumes during the inspiratory and expiratory phase of a complete respiratory cycle. The elastic forces being volume dependent, they are assumed to be identical at these equal volume points, and, therefore, the remaining pressure difference represents the frictional, i.e., nonelastic resistive pressure. The equal volumes were found by dividing the area underneath the inspiratory and expiratory air flow recordings into equal parts. The rate of air flow at equal volumes was then measured from the flow curve, and the pressure difference between the points of equal volume in centimeters of water was divided by the sum of the inspiratory and expiratory flow in liters per second. For each determination at least 5 breaths were analyzed from parts of the recording where the breathing pattern was the most regular. Successful measurements of the nasal resistance with this method were accomplished in 5 full-term newborn infants, 3 males and 2 females, at 2 hours to 3 days of age; their body weights ranglng from 2,580 grams to 4,050 grams; 2 were Caucasians and 3 were Negroes.
RESULTS Results of the measurements are given in Table I. T h e average total lung resistance when breathing through the nose, and corrected for the resistance of the pneumotachograph, was 47.5 cm. H 2 0 per liter per second (with a range of 38.0 to 53.0 cm. H 2 0 per liter per second). O n the other hand, when breathing through the plastic airway, and after correction for the combined resistance of the p n e u m o t a c h o g r a p h and oral airway, this value was 35.4 cm. H 2 0 per liter per second (with a range of 28.1 to 47.4 cm. H 2 0 per liter per second). T h e difference between the two, i.e., the average nasal resistance was 12.1 cm. H 2 0 per liter per second (with a range of 5.6-19.9 cm. H 2 0 per liter per second). T h e relative magnitude of the nasal resistance as compared with the average total lung resistance was 26 per cent (with a range of 11 to 41 per cent). It is evident that both the absolute and relative values in individual babies varied
Volume 67 Number 4
Nasal resistance o[ newborn in[ants
561
CALCULATION OF TOTAL LUNG RESISTANCE (SGHEMATIG DIAGRAM}
AIR FLOW *'tt
~..::..:tL r
/~!il[ "~
O
EXPIRATION '
\
Expm.
\
IS~176
~
." LUME 'SO'~/O
:~:
J
Vz~V s "
i i
NO FLOW I
NO FLOW z
NO FLOW~}
EXPIRATION
ESOPHAGEAL PRESSURE (P)
~ : - - " / h
"''ikr-.. ; p. " ~ i ' ~ " ~*T "~I
/'A?'E*~ """ it;l~l' J}A I~' * AF~E TIME
>_
Fig. 5. Schematic demonstration of the method for calculating total lung resistance from simultaneous recordings of air flow (top curve) and intraesophageal pressure (bottom curve). The stippled areas under the inspiratory and expiratory flow curves are equal and represent equal volumes (because L./sec. x sec. = L.). Vz and VE are inspiratory and expiratory flow rates at the points of equal volumes. The projections of no-flow points 1, 2, and 3 on the pressure curve represent pressures at the beginning and end points of inspiration and expiration, respectively. The lines connecting these points represent changes of elastic pressure related to volume changes. Pel I and Pe~E are the points where the elastic pressure is equal in the course of inspiration and expiration respectively. P~I is the total elastic pressure difference between end-expiratory and maximal inspiratory volume. A PtI and A PtE are the inspiratory and expiratory frictional resistive pressures, respectively, at the times of equal volumes. considerably. T h e 2 Caucasian infants h a d a nasal resistance close to the average value, while in the 3 Negroes, both high a n d low resistances were found. T h e r e was no a p p a r ent relationship between the infant to infant variations of the nasal resistance a n d that of the total nonelastic resistance. COMMENT T h e simplest a n d most s t r a i g h t f o r w a r d m e t h o d for measuring nasal resistance in adults a n d cooperative older children is posterior rhinometry, n A n e w b o r n infant would only by chance keep a tube or a balloon in its m o u t h without p r o d u c i n g pressure artifacts, u n r e l a t e d to nasal resistance, by m a n i p u l a t i n g the pressure transmitting device
with his tongue or by occluding holes on a tube with saliva. I t was for this reason that the m e t h o d described above was developed. However, d u r i n g attempts to employ posterior rhinometry a single successful measurem e n t was made. A plastic tube (I.D. 0.55 inch) was passed into the esophagus of a Negro male b a b y through the mouth. Its distal end h a d been occluded a n d several small holes h a d been m a d e in its side at a p r e m e a s u r e d distance from the lips, so that they would be within the p h a r y n g e a l airpocket. By repeatedly passing air through the tube from a syringe to clear the holes of mucus, pressure could be recorded from the a t t a c h e d strain gauge d u r i n g a few breaths. T h e air flow rate was simultaneously re-
562
Polgar and Kon~
October 1965
T a b l e I. Nasal resistance in 5 n e w b o r n infants calculated from the total lung resistance when
Subject~ No.
Sex
Race
1 2 3 4 5
M F F M M
Negro Caucasian Caucasian Negro Negro
Age 2 5 3 2 2
Hours Hours Days Days Days
Weight (grams) 4,050 3,680 3,680 2,580 3,640
Total lung Breathing through nose (~) crn, H,O/L./sec. t S.D.'~ 48.1 38.0 50.2 53.0 48.0 Average 47.5 S.E. 2.6
11.9 9.8 14.5 7.4 3.4
"~Correeted for the resistance of the pneumotachograph (0.5 cm. H~O/L./sec.) when breathing through the nose and for the combined resistance of the pneumotachog~aphand plastic airway (3.2 em HzO/L./sec.) when breathing through the latter. tS.D. of the means of 5 breaths. ++S.E. of the difference of means. w of the mean diffe,ences. corded through the pneumotachograph. T h e average nasal resistance as calculated from the corresponding points on the pressure and flow rate curves was 12.2 cm. H 2 0 per liter per second. A plot of pressure versus flow values of one respiratory cycle from this infant is shown in Fig. 6. A large variability of the absolute values for nasal resistance a n d also for its m a g n i t u d e relative to the airway resistance has been observed in adults? 2, ~:'~ T h e reason for this is probably the highly variable state of congestion of the nasal nmcosa, which might be d e p e n d e n t on various factors such as body position, e n v i r o n m e n t a l temperature, emotional state, 1~ etc. Butler ~2 measured nasal resistance in 5 adults by posterior rhinometry a n d by subtracting plethysmographic airway resistance estimated during m o u t h breathing from that measured d u r i n g nose breathing; their nasal resistance varied from 1.09 to 4.26 cm. H 2 0 per liter per second with an average value of 2.18 cm. H 2 0 per liter per second. T h e average percentage of nasal resistance was 63 per cent of the airway resistance d u r i n g nasal breathing with a range of 46.3 per cent to 76.0 per cent. Such large variations on a small n u m b e r of subjects render the accuracy of average values relatively insignificant. However. the variability seems to be more a physiologic one than one related to the accuracy of the methods of measurements.
T h e relationship of nasal resistance in newborns to the resistance of the rest of their conductive airways c a n n o t be assessed by using the total lung resistance for comparison, because the latter includes the lung tissue resistance. For an approximate comparison, data were used which have been obtained on a series of 14 newborns by plethysmographic measurements of the airway resistance d u r i n g nasal breathing. T h e method employed for these measurements has been described elsewherea; it is basically a n adaptation of the method of DuBois, Botelho, and Comroe 1'~ to n e w b o r n infants. I n Fig. 7 a plot of airway conductance (which is the reciprocal of airway resistance), against lung volume in these 14 n e w b o r n infants is shown. Their average airway conductance was 0.0351 L. per second per centimeter H 2 0 which corresponds with a n average airway resistance of 28.5 era. H 2 0 per liter per second. ~" A short comment is necessary to explain the discrepancy between this value and the one originally published.~ In the plethysmograph first used for the measmements of airway resistance, a manipulator rod entered the plastic body-box through a ntbber stopper in its top. When, in order to measure lung volume, the baby was forced to breathe *These values were obtained with tbe cooperation of Robert A. Ersek, member of the Student Research Program at the Universityof Pennsylvania,1961-1962.
Volume 67 Number 4
breathing
through
Nasal resistance of newborn infants
the nose a n d
when
b r e a t h i n g t h r o u g h an artificial a i r w a y
resistance (corrected*) Breathing through oralairway (b) cm. HeO/L./see.
S.E.
28.2 28.1 40.2 47.4 33.3 35.4 3.8
I
S.D.t 8.2 5.3 5.9 3.9 7.3
563
Nasal resistance (.~
(a-b = c) cm. H~O/L./sec.
I
19.9 9.9 10.0 5.6 14.7 12.1 S.D. 5.5 s.g. 2.5.~ p ~ 0.10
against a mechanical shutter occluding the airway, alternating positive and negative pressure was transmitted by dry friction to the flexible plastic top of the plethysmograph. This resulted in the over-estimation of lung volume and of the corresponding airway conductance (i.e., underestimation of airway resistance). Before making the second series of measurements this source of error was eliminated. The corrected average lung vohtme is in close agreement with results reported by Geubelle and co-workers, 16 and by KIaus and associates. 17 I f the average nasal resistance from the present study, 12.1 cm. H 2 0 p e r liter per second, is subtracted from the average value for airway resistance in the other 14 newborns, one obtains the calculated resistance of the airways as they would be when the babies b r e a t h e d through their mouths, 16.4 cm. H 2 0 p e r liter p e r second. Considering the wide variations of nasal resistance between individual infants, the range of the calculated a i r w a y resistance (excluding nasal resistance) w o u l d be 8.6 to 22.9 cm. H 2 0 per liter p e r second. Using the same n u m bers, the average nasal resistance is about 42 p e r cent of the airway resistance when b r e a t h i n g t h r o u g h the nose, with a range of 19.6 p e r cent to 70.0 p e r cent. A p p l y i n g the two-sample ranks test TM to the comparison of percentages of nasal resistance relative to airway resistance when b r e a t h i n g t h r o u g h the nose, in the 5 newb o r n infants from this study a n d in 5 adults
.100
S.E.~
(%)
1.4 1.0 1.6 0.8 0.8
41 26 20 11 31 26
)
of Butler ( T a b l e I I ) , the level of significance for the difference of the means was p > 0.10. Therefore, it cannot be stated with certainty that the relative nasal resistance in newborns is significantly smaller t h a n in adults. H o w ever, it should be concluded that such a tendency is noticeable, a n d that the resistance of the nasal air passages in newborn infants is neither a m a j o r nor a negligible p a r t of the total airway resistance. I t is a r e m a r k a b l e fact t h a t the absolute m a g n i t u d e of nasal resistance in newborn infants is only 5.5 times as large as that of the aduhs. This, a n d the similarly small ratio
II. C o m p a r i s o n of p e r c e n t a g e nasal resistance to total a i r w a y resistance in 5 n e w b o r n infants a n d 5 adults
Table
Newborn infants* .. % I Rank 70.0 34.6 35.0 19.6 51.5 Sum of ranks "~Percentages
calculated
8 2 3 1 6 20:~ from
%
Adultst I Rank
46.3 48.0 52.5 75.0 76.0 the nasal
4 5 7 9 10 35:~ resistance mea-
sured in 5 newborn infants (Table I) as related to the average airway resistance measured in 14 newborn infants (Fig. 7). ~'Percentages
calculated
from
data of Butler. a2
~Extreme sums of ranks for p = 0.10 are 19:3678 The extreme sums in the present comparison, 20:35 are just outside these limits indicating a level of significance slightly
larger than p = 0.10.
564
Polgar and Kon.~
October 1965
0'08' F L O W RATE L/=,= 0.06
,/J
0.04 9
/.O"
/
0"02EXPIRATION
-,!o
-0:8
-d6
-o'. 4
o~r o!2
-oz~ r
INSPIRATION
jW,O/
o!.
o?6
o~a
1.0
PHARYNGEAL P R E S S U R E ;u I'llO
-0"02
-0.04
-0.06
-0.01 Fig. 6. Plots of pharyngeal pressure versus flow from two breaths (-x--~, and -o--)) in posterior rhinometry. The points represent nasal resistance and their average is 12.2 cm. H~O per liter per second.
of airway resistance (when breathing through the nose) in newborns versus adults (8.2), suggests that the airway dimensions in general are relatively larger in infants than in adults. For details on the relationship of dimensions, shape, and structure of the airways on one hand, and their resistance to air flow on the other, the review of the subject by Mead s may be consulted. Mead postulated that tile rate of growth and the relationship of airway conductance airway resistance/ 1
and lun/ wdume is
/
not the same for all age groups. If the simplified relationship of: Conductance (L./sec./cm. H 2 0 ) = 0.24 Lung Volume (L), found by Briscoe and DuBois: were typical for the neonate as well as for older subjects, the predicted airway resistance
of a newborn when breathing through the mouth would be about 50 times larger than in an adult. However, the value of 16.4 tin. H 2 0 per liter per second obtained here in newborns is only about 14 times larger than that of adults. Minute ventilation of adults is approximately 12 times larger than that of newborns~; it seems that the relationship between the airway resistance in newborn infants and in adults is in good agreement with this number. It is this remarkably efficient coincidence which makes it possible that a normal newborn infant breathes with a work output of less than 10 per cent of that of an adult 2 and by producing total intrathoraeie pressure changes during respiration which are not greater than those in adults, z' ~ In spite of the relatively favorable parti-
Volume 67 Number 4
Nasal resistance o[ newborn in[ants
565
AIRWAY GONDUGTANGs L / H e l o " NtO
~A " 0 . 0 5 5 1 .t 0 . 0 1 0 5 ( 0 " 0 5 5 1 It: 0 " 0 1 6 ) 0,06 , , 0 " 0 7 0 4. 0 " 0 1 7 7 (0" 1 9 0 It: 0 . 0 6 ) 0.05
0.04
9
~
..--.tg""~ "~':- .....
o.o3
0.02
0.01
0
i 0
O'Ol
~ 0`02
1 0'03
! 0'04
! 0"05
,, !
I
0"06
0"07
1 0.08
! 0"09
!
;
0"I0 LUNG
0"II
VOLUME
Fig. 7. Airway conductance and corresponding lung volume in 14 normal newborn infants. Each point represents the average of several measurements on one baby. The solid regression line has been calculated for these 14 newborn infants. The broken regression line has been calculated for the obsolete values measured before correction of the method. 5 Values in the box are the mean airway conductance (CA) in L./sec./cm. H~O and mean lung volume (V) in L for these infants. Values in parentheses are those measured before correction of the method.
tion of airway resistance in newborns, their nasal air passages do represent a sizeable resistance to air flow and are prone to become easily obstructed; it takes very little narrowing of the conductive channels to increase the resistance and consequently respiratory work exponentially. While a newborn infant during the first weeks of life is unable to change spontaneously from nose breathing to m o u t h breathing, an adult can voluntarily lower his airway resistance by more than 60 per cent of its normal value by changing to mouth breathing; the adult is able to use this device for counteracting an increase of the lower airway resistance or for completely eliminating an increased respiratory workload due to nasal obstruction. T h e "obligatory" nose breathing tendency of newborns on one hand, and the ease with
which obstruction of the nasal airways occurs in this age on the other, is clearly in contradiction to the usual principles of physiological reserves and adaptive mechanisms protecting the vital functions. An explanation for this transient stage of relatively high vulnerability of airway patency may be found in a peculiar situation of phylogenetic development. I n most mammals, especially in the herbivora, the nasopharyngeal anatomy renders them obligatory nose breathers. 19 Their larynx is positioned high, opposite to the base of the skull, and their large epiglottis is in close contact with the soft palate so that the nasopharyngeal and laryngeal airways form an uninterrupted channel. This prevents olfactory function, from being interrupted when feeding. Also, since their life is dependent on a highly developed sense of smell, they have wide
5 66
Polgar and Kong
nostrils a n d nasal air passages which do not easily become obstructed. T h e a d u l t human, on the other hand, has a wide open comm u n i c a t i o n between his oral a n d nasopharyngeal cavities a n d his small nostrils. W h e n e v e r m a n opens his mouth, breathing must automatically occur through this p a t h of lower resistance rather than through the nose. I n h u m a n newborns, the larynx and epiglottis, while continuously descending d u r i n g fetal life are still positioned relatively high. T h e epiglottis is close to the palate, similar to the more primitive m a m m a l s , ~9 a n d the tongue is in contact with the palateS~ for these reasons they are practically unable to breathe through their mouths. At the same time the intranasal structures of the neonate, although reminiscent of an earlier stage of development, are, in fact, further ahead in the phylogenetie degeneration of tile olfactory apparatus. It a p p a r e n t l y takes a period of some weeks of extrauterine development for the pharyngolaryngeal a n a t o m y to catch up with the nasal structures. D u r i n g this period, nasal obstruction can cause severe respiratory distress and suffocation. SUMMARY
T h e nasal resistance of 5 newborn infants was d e t e r m i n e d by an indirect m e t h o d calculated from measurements of total lung resistance during nasal breathing and while breathing through a plastic oral airway. T h e average nasal resistance was 12.1 cm. H~O per liter p e r second (5.6 to 19.9 era. H.,O per liter per second) or 26 per cent (11 to 41 per cent) of the total hmg resistance. Relative to an average value of total airway resistance measured on other newborns who were breathing through their noses, this nasal resistance represents an average of 42 per cent (19.6 to 70.0 per cent) of the total resistance. I t would a p p e a r that the nasal passages contribute a relatively smaller p a r t of the airway resistance in newborn infants than in adults. Still, the newborn infant is at a disadvantage because he cannot spontaneously breathe through his m o u t h during the first few weeks of life. T h e reason for this m a y be found in the peculiar p a t t e r n of
October 1965
phylogenetic d e v e l o p m e n t of o r o p h a r y n g e a l a n d nasal structures. REFERENCES
1. McIlroy, M. B., and Tomlinson, E. S.: The mechanics of breathing in newly born babies, Thorax 10: 58, 1955. 2. Cook, C. D., Sutherland, J. M., Segal, S., Cherry, R. B., Mead, J., McIlroy, M. B., and Smith, C. A.: Studies of respiratory physiology in the newborn infant. III. Measurements of mechanics of respiration, J. Clin. Invest. 36: 440, 1957. 3. Karlberg, P., Cherry, R. B., Escardo, F. E., and Koch, G.: Respiratory studies in newborn infants. I. Apparatus and methods for studies of pulmonary ventilation and the mechanics of breathing. Principles of analysis in Mechanics of Breathing, Acta paediat. 49: 345, 1960. 4. Swyer, P. R., Reiman, R. C., and Wright, J. J.: Ventilation and ventilatory mechanics in the newborn, J. PEDIAT. 56" 612, 1960. 5. Polgar, G.: Airway resistance in the newborn infant, J. PEDIAT. 59" 915, 1961. 6. Cook, C. D., Helliesen, P. J., and Agathon, S.: Relation between mechanics of respiration, lung size and body size from birth to young adulthood, J. Appl. Physiol. 13: 349, 1958. 7. Briscoe, W. A., and DuBois, A. B.: The relationship between airway resistance and lung volume in subjects of different age and body size, J. Clin. Invest. 37: 1279, 1958. 8. Mead, J.: Mechanical properties of hmgs, Physiol. Rev, 41: 281, 1961. 9. Fry, D. L., Stead, W, W., Ebert, R. V., Lubin, R. I., and Wells, H. S.: Measurement of intraesophageal pressure and its relationship to intrathoracic pressure, J. Lab. & Clin. Med. 40: 664, 1952. 10. Frank, N. R., Mead, J., and Ferris, B. G., Jr.: The mechanical behavior of the lungs in healthy elderly persons, J. Clin. Invest. 36: 1680, 1957. 11. Spiess, G.: Die Untersuchungsmetoden der Nase und ihrer Nebenh6hlen, Handb. d. Laryngol. u. Rhinol., Wien 3: 2159, 1900. (Referred to by Butler. 12) 12. Butler, J.: The work of breathing through the nose, Clin. Se. 19: 55, 1960. 13. Cottle, M.: Concepts of nasal physiology as related to corrective nasal surgery, Arch. Otolaryng. 72: 11, 1960. 14. Uddstr6mer, M.: Nasal respiration. A critical survey of some current physiological and clinical aspects of the respiratory mechanism with a description of a new method of diagnosis, Acta oto-laryng. Suppl. 42, 1940. 15. DuBois, A. B., Botelho, S. Y., and Comroe, J. H., Jr.: A new method of measuring airway resistance in man using a body plethysmograph: Values in normal subjects and in patients with respiratory disease, J. Clin. Invest. 35: 327, 1956. 16. Geubelle, F., Karlberg, P., Koch, G., Lind, J., WaUgren, G., and Wegelius, C.: L'a6ration
Volume 67 Number 4
17. 18. 19.
20.
du poumon chez le nouveau-n~, Biol. Neonat. 1" 169, 1959. Klaus, M., Tooley, W. H., Weaver, K. H., and Clements, J. A.: Lung volume in the newborn infant, Pediatrics 30: 111, 1962. Mainland, D.: Elementary medical statistics, ed. 2, Philadelphia-London, 1963, W. B. Saunders Company, p. 283. Negus, V. E.: Comparative anatomy and physiology of the larynx, New York-London, 1949, Hafner Publishing Company, (repr. 1962). Birrell, J. F.: The ear, nose and throat diseases of children, Philadelphia, 1960, F. A. Davis Company, p. 3.
APPENDIX
Terminology as used in this article for describing physiological variables. I. Total pulmonary-, or lung resistance (in cm. H~O/L./sec.), the sum of: A. Airway resistance the frictional resistance of air flowing in and out through the conductive airways. Can be subdivided into: a. nasal resistance b. pharyngolaryngeal resistance c. lower airway resistance
Nasal resistance of newborn infants
(Airway conductance =
56 7
1
airway resistance
)
B. Lung tissue resistance the frictional resistance of tissues against the motion of the lung during inflation and deflation. II. Pressures (in era. H20 ) opposing the motions of the lung: A. Elastic pressure developed by the recoil of the elastic tissues and by the surface pressure on the alveolar air-liquid interface (static component) B. Frictional resistive gas pressure in the airways (dynamic component) C. Frictional resistive tissue pressure (dynamic component) II[. Lung volume (in L.), as related to airway resistance is the actual volume at which the airway resistance is determined; usually identical with the functional residual capacity (the lung volume at the end of a normal expiration). IV. Minute ventilation (in L./min.), the total volume of air breathed in and out during one minute.