Actn Pctdiatr Scand 64: 57-68, 1975
T H E INFLUENCE O F DIFFERENT ENVIRONMENTAL TEMPERATURES ON PULMONARY GAS EXCHANGE AND BLOOD GAS CHANGES AFTER BIRTH RAGNAR ‘TUNELL From the Department of’Purdiutrics, Kurolinsku Sjukhuset, Stochholm. SxIedvn
ABSTRACT. Tunell, R. (Department of Paediatrics, Karolinska Sjukhuset, Stockholm, Sweden). The influence of different environmental temperatures on pulmonary gas exchange and blood gas changes after birth. Acta Paediatr Scand, 64:57, 1975.-The oxygen uptake (VOJ and respiratory exchange ratio ( R ) was determined during the first 20 min and at one and at 2 hours after birth in 16 healthy full-term newborn infants studied in different environmental temperatures. Arterial blood gases and acid-base balance were determined on repeated blood samples from the abdominal aorta. The infants were grouped in a “warm” group (n=lO) where efforts were made to avoid cooling after birth, and a “cold” group ( n = 6 ) where a decrease in rectal temperature to a mean value of 354°C a t 2 hours occurred. Irrespective of environmental temperature, VO, was approximately 10 ml/kg min during the first 8 min after birth, thereafter decreasing to about 6-7 ml/kg min. During the first 8 min the main increase in Pa,, occurred and about 2 ml/kg min of the VOs was accounted for by changes in oxygen stores after birth. At 16-20 min and at 60 min after birth a negative relationship was found between V,, and Pa%. During the period 8-120 min after birth a close relationship was found between VO, and the degree of muscular activity. Within &16 min after birth, R values above 1.0 were regularly found simultaneously with the main decrease in Paco2. In infants kept “cold” a tendency to hyperventilate was found, probably elicited by cold stimuli. The rapid drop in deep body temperature regularly seen after birth could thus not be explained by a limited ability to increase pulmonary gas exchange. A high degree of evaporative heat loss, a relatively low “basal” metabolic rate and a limited response in “non-shivering thermogenesis” seem to be the main reasons for the heat loss after birth. KEY WORDS: Newborn infants, oxygen consumption, carbon dioxide production, environrnental temperature, blood gases
Immediately after birth, the human newborn infant has a rapid decrease in skin temperature (10, 1 1 ) and within the first hour after birth the rectal temperature decreases by about 2-3°C (2, 7, 10, 28). The reason for this rapid cooling is mainly a high degree of evaporative heat loss from the relatively large skin surface area of the newborn infant (10, 18). It has been suggested that the hypoxemia, normally present a t birth, may
-
The study was supported by grants from the Swedish Research Council (project K 68-19x1035-03 and B 71-13 P-3268-01) and Semper Fund of Nutrition, Stockholm, Sweden.
lead t o a depression in the metabolic response to cold and thus may contribute to the rapid decrease in body temperature (10, 28). This statement has not been based on direct measurements of oxygen consumption and blood gases, but on results achieved in studies of newborn infants a few days old, breathing gas mixtures with ,low oxygen content (8, 33). However, this ‘experimental situation differs in several respects from the situation a t birth. Furthermore, Cross et al. failed to confirm these reports (9). In the present investigation a group of full-term healthy newborn infants were studActa Pizdiatr Scand 64
58
R . Tunell
ied during the first 2 hours after birth a t controlled environmental temperatures with serial determinations of pulmonary gas exchange and arterial blood gases and acidbase status. Simultaneously the arterial blood concentrations of free fatty acids, glycerol, glucose, lactate and p-hydroxybutyrate were determined. The results of these biochemical measurements have been previously published (34). The object of the present investigation was to determine the oxygen uptake during the period of hypoxemia immediately after birth and to see if differences in environmental temperature would influence the degree of pulmonary gas exchange and blood gas changes after birth. MATERIAL AND METHODS The nature and the aim of the investigation was explained to the parents and all gave theis. consent. Sixteen healthy full-term infants were investigated. Clinical data on the infants and their mother are given in Figs. I , 2 and 3. Procedurc,
At birth the infants were placed on an open infant bed consisting of a box (40x50 cm) with a 3 cm thick waterfilled mattress and a sterile towel. When infants were to
be studied in a "warm" environmental temperature the mattress and the towel were prewarmed to 38°C using an electric pad. A heating lamp (150 W) was placed 70 cm above the mattress. In investigations with "cold" environmental conditions the bed was kept at room temperature and no heating lamp was used. All infants were carefully dried. After suction of the oro-pharynx and as soon as spontaneous breathing had started, a face mask was placed over the face of the infants and measurements of oxygen consumption, VO2,and carbon dioxide elimination, V,,, were started using an apparatus described earlier (45). The measurements were performed continuously for 4 min periods during the first 20 min after birth and subsequently in two more periods of 4 min at one and at 2 hours after birth. As soon as possible after birth a cetheter was introduced into an umbilical artery and blood samples were withdrawn at predetermined intervals (for details see ref. 34). Within 5-10 min after birth the infants were transferred to a thermocontrolled chamber (45). The temperature of the chamber was set at four different levels: 343°C ( n = S ) , 33.5"C ( n = 5 ) , 32°C ( n = 3 ) and 28.9"C ( n = 3 ) . During the complete investigation period of 2 hours the infants were carefully watched and the degree of muscular activity assessed using a four-point scale (45). Acta Pediatr Scand 64
Temperuticrr recordings
Within 3 min after birth the rectal temperature was measured using an electric thermometer (45). In the chamber rectal temperature and abdominal skin temperature were recorded every minute. Five additional skin temperatures were measured every 20 min. In order to get information about the mean skin temperature, each skin temperature was weighted according to the surface area (in percent) that they represented (6). The skin temperatures were determined from (with weighting factor F ) : The xiphoid process ( F : 0.33). the abdorninal skin in the mid-line above the umbilical region (F: 0.7-3), the lateral side of the left hand ( F : 0.05), the lateral side of the left upper leg ( F : 0.29) and the dorsal side of the left foot ( F : 0.05). Arterial blood gus and acid determinutions
base balunce
The blood samples (0.5 ml) were transferred to a heparinized and siliconiced glass syringe with a mercury lock. The Po, determinations were performed with an open Clark electrode (19). The pH, P,,,, and acid-base determinations were performed by the Astrup microequilibration technique (4 I ) . The blood gas deterrnindtions were made as soon a s possible after ,sampling (always within 60 min). The results were corrected to the actual rectal temperature (40). All determinations were done in duplicate. The error of Po, determination was 1.6 mmHg ( n = 1 8 5 ) and of pH determination 0.005 units (n=200).
RESULTS Temperature The 10 infants handled immediately in a "warm" environment and subsequently studied in an environmental temperature of 34.8"C and 33.5"C had rectal temperatures which in no infant fell below 36.7"C. After an initid drop in skin temperature, the ternperature gradient between mean skin ternperature and environmental temperature was 2.1-2.2"C (Table 1). As the changes in rectal temperature and skin temperature were similar in all 10 infants, these infants were grouped together in group 1 . The 6 infants immediately taken care of in room temperature and subsequently studied in an environmental temperature of 32°C and 28.9"c, showed a heat loss with decreasing rectal temperatures, and at 120 min all 6 infants had rectal temperatures below 36.5"C. These 6 infants were grouped together in group 2 . The 3 infants s'tudied in an environmental temperature of 28.9T
Injluence of temperature on pulnzonar?, gas exchange
59
15 Vn2 ml / ~ gmin
10
5
15
v co2 ml / ~ gm i n
10
5
’”.
,
,
.
,
,
I
Activity score
3lT-7
B.E.
2 1
\\w
04 0
-
\w
1
W
10
5
A
,
-
-10;
20
15
D
0
5
0
10
15
-
20
min
30
Fig. I . Sampling times and results of parameters measured in five “warm” infants. Analgesia Duration of Case no.
Parity
labour (hours)
2nd stage (min) 40 5 20
10
7 12 17
I 111
12 2.5 6
26 28
I1 IV
3 5
I11
5
Pud. nerve block
+
Pethidina
+ + +
Mode of delivery presentation Vertex Vertex Occiput post Vertex Vertex
Birth weight
(€9
T, (“C)
4 255 3 580 2 770.
34.8 34.7 34.8
2 960 3 120
33.2 33.5
Pethidin 50-100 mg administered 1-3.5 hours before delivery. All infants had a similar postnatal course with an initial high degree of activity and pulmonary gas exchange followed by a rapid drop in activity and pulmonary gas exchange values. Rapid “normalization” of blood gases and acid-base balance was present in all infants:
Acta Pzdiatr S c a d 64
60
R . Tunell Pa o2 mm Hg
I001
....
40
1
1
51
0.4
/
4I
Activity
score
Fig.2. Sampling times and results of parameters measured,in five "warm" infants. Analgesia Duration of Case no.
Parity
3
I1
19
111
23 25 29
I I1 111
labour (hours)
2nd stage (min)
3 7 6 3
5 50 5 5
Pud . nerve block
Pethidin"
+
Mode of delivery presentation
Birth weight (g)
T, ("C)
Ces. sect.b Vertex Vertex Vertex Vertex
3 050 3 580 3 200 3 820 4 040
34.6 34.7 33.5 33.4 33.3
Symbol 0
+0 0
Pethidin 75 mg given 2 hours before delivery. Ces. section because ofnarrow pelvis. Spinal anaesthesia. Case no. 23 was clinically uneventful, but during the first 4 min, a low degree of pulmonary gas exchange was found. The arterial Po, at 5 min of 17 mmHg indicates ineffective pulmonary gas exchange. A persistently high degree of activity was found in cases 19, 25 and 29. High f', and low Pa& values were found in these three cases. Case 19 had a tendency to hyperventilate.
*
Arta Pediatr Scand 64
Injluence of temperature on pulmonary gas exchange
61
Fig. 3. Sampling times and results of the parameters measured in “cold” infants. _
_
_
_
_
_
Analgesia Duration of Case
labour (hours)
no.
Panty
9 13
V
3
11
5
16
IV I
4 1 4.5
18 20 21
111
I
17
2nd stage (min) 5 10 10 20 10
60
Pud . nerve block
+ +
Pethidin
+ +
Mode of delivery presentation Vertex Vertex Vertex Vertex Occiput post Vertex
Birth weight (g)
T,
(“0
Symbol
3 370 3 320, 4080 2 930’ 2 660
32.0 31.7 32.0 28.8 28.1
0 A
3 030
29.8
V
0 0 W
Pethidin 100 mg given more than 3.5 hours before delivery. The pattern of changes in all parameters were the same as found in infants kept “warm”. Infants with high Vo2values 16-20 rnin after birth had low Pas values. a
Acto Padiatr Scand 64
p
~
62
R. Tunell
Table 1. Meun I-dues and range in the temprratitrr mrusurrments in groitp I ( ‘ h ~ a r m ”und ) group 2 (“cold”) infants Minutes after birth ~~
Measurement
Group
2
40
120
Rectal temperature (“0
I
38.0 37.8-3 8.2 38.1 37.9-38.5
37.2 36.9-37.5 36. I 35.4-36.9
37.3 36.7-37.9 35.4 34.3-36.4
I
1.1
I1
0.61.3 I .6 0.3-2. I
0.6 0.4-1.4 1.3 I . 1-1.6
2.1 1.3-3.0 4.0 2.84.8
2.2 I.62.9 3.6 2.54.8
I1 Rectal-skin temperature gradient (“C)
Skinxnvironmental temperature gradient (“C)
I
were, in contrast to the infants studied at 3 2 T , restless and very active during the examination period and meconium passage occurred. Infants in group 2 had a significantly greater skin-environmental temperature gradient than infants in group 1 (Table I ).
Blood gus und acid base balance de term ina tions The results of Pa,,,, PaCo2,pH and base excess (BE) determinations are given in Table 3. The results from individual infants during the period 0-20 min after birth are given in Figs. 1, 3 and 3. The pattern of changes in these parameters was similar in all infants irrespective of Pulnionary gas exchange and rnusculur environmental temperature. activity The results of the determinations of V o z , The main increase in Pa,,? took place 1Vicoz,the respiratory exchange ratio R (Vco,/ 10 rnin after birth. After that period PaOz Vo,), and the degree of muscular activity increased slowly but the values showed are given in Table 2. The results from indi- great variation. A close relationship was vidual infants during the period 0-20 min found between the values a t 16-20 rnin after birth and the values at 60 and 120 rnin after after birth are given in Figs. 1, 2 and 3. The pattern of changes in Voz and Vco2 birth respectively. (r=0.76, p < O . O O l , n=16 was similar in all infants irrespective of en- and r=0.79, p
T H E INFLUENCE O F DIFFERENT ENVIRONMENTAL TEMPERATURES ON PULMONARY GAS EXCHANGE AND BLOOD GAS CHANGES AFTER BIRTH RAGNAR ‘TUNELL From the Department of’Purdiutrics, Kurolinsku Sjukhuset, Stochholm. SxIedvn
ABSTRACT. Tunell, R. (Department of Paediatrics, Karolinska Sjukhuset, Stockholm, Sweden). The influence of different environmental temperatures on pulmonary gas exchange and blood gas changes after birth. Acta Paediatr Scand, 64:57, 1975.-The oxygen uptake (VOJ and respiratory exchange ratio ( R ) was determined during the first 20 min and at one and at 2 hours after birth in 16 healthy full-term newborn infants studied in different environmental temperatures. Arterial blood gases and acid-base balance were determined on repeated blood samples from the abdominal aorta. The infants were grouped in a “warm” group (n=lO) where efforts were made to avoid cooling after birth, and a “cold” group ( n = 6 ) where a decrease in rectal temperature to a mean value of 354°C a t 2 hours occurred. Irrespective of environmental temperature, VO, was approximately 10 ml/kg min during the first 8 min after birth, thereafter decreasing to about 6-7 ml/kg min. During the first 8 min the main increase in Pa,, occurred and about 2 ml/kg min of the VOs was accounted for by changes in oxygen stores after birth. At 16-20 min and at 60 min after birth a negative relationship was found between V,, and Pa%. During the period 8-120 min after birth a close relationship was found between VO, and the degree of muscular activity. Within &16 min after birth, R values above 1.0 were regularly found simultaneously with the main decrease in Paco2. In infants kept “cold” a tendency to hyperventilate was found, probably elicited by cold stimuli. The rapid drop in deep body temperature regularly seen after birth could thus not be explained by a limited ability to increase pulmonary gas exchange. A high degree of evaporative heat loss, a relatively low “basal” metabolic rate and a limited response in “non-shivering thermogenesis” seem to be the main reasons for the heat loss after birth. KEY WORDS: Newborn infants, oxygen consumption, carbon dioxide production, environrnental temperature, blood gases
Immediately after birth, the human newborn infant has a rapid decrease in skin temperature (10, 1 1 ) and within the first hour after birth the rectal temperature decreases by about 2-3°C (2, 7, 10, 28). The reason for this rapid cooling is mainly a high degree of evaporative heat loss from the relatively large skin surface area of the newborn infant (10, 18). It has been suggested that the hypoxemia, normally present a t birth, may
-
The study was supported by grants from the Swedish Research Council (project K 68-19x1035-03 and B 71-13 P-3268-01) and Semper Fund of Nutrition, Stockholm, Sweden.
lead t o a depression in the metabolic response to cold and thus may contribute to the rapid decrease in body temperature (10, 28). This statement has not been based on direct measurements of oxygen consumption and blood gases, but on results achieved in studies of newborn infants a few days old, breathing gas mixtures with ,low oxygen content (8, 33). However, this ‘experimental situation differs in several respects from the situation a t birth. Furthermore, Cross et al. failed to confirm these reports (9). In the present investigation a group of full-term healthy newborn infants were studActa Pizdiatr Scand 64
58
R . Tunell
ied during the first 2 hours after birth a t controlled environmental temperatures with serial determinations of pulmonary gas exchange and arterial blood gases and acidbase status. Simultaneously the arterial blood concentrations of free fatty acids, glycerol, glucose, lactate and p-hydroxybutyrate were determined. The results of these biochemical measurements have been previously published (34). The object of the present investigation was to determine the oxygen uptake during the period of hypoxemia immediately after birth and to see if differences in environmental temperature would influence the degree of pulmonary gas exchange and blood gas changes after birth. MATERIAL AND METHODS The nature and the aim of the investigation was explained to the parents and all gave theis. consent. Sixteen healthy full-term infants were investigated. Clinical data on the infants and their mother are given in Figs. I , 2 and 3. Procedurc,
At birth the infants were placed on an open infant bed consisting of a box (40x50 cm) with a 3 cm thick waterfilled mattress and a sterile towel. When infants were to
be studied in a "warm" environmental temperature the mattress and the towel were prewarmed to 38°C using an electric pad. A heating lamp (150 W) was placed 70 cm above the mattress. In investigations with "cold" environmental conditions the bed was kept at room temperature and no heating lamp was used. All infants were carefully dried. After suction of the oro-pharynx and as soon as spontaneous breathing had started, a face mask was placed over the face of the infants and measurements of oxygen consumption, VO2,and carbon dioxide elimination, V,,, were started using an apparatus described earlier (45). The measurements were performed continuously for 4 min periods during the first 20 min after birth and subsequently in two more periods of 4 min at one and at 2 hours after birth. As soon as possible after birth a cetheter was introduced into an umbilical artery and blood samples were withdrawn at predetermined intervals (for details see ref. 34). Within 5-10 min after birth the infants were transferred to a thermocontrolled chamber (45). The temperature of the chamber was set at four different levels: 343°C ( n = S ) , 33.5"C ( n = 5 ) , 32°C ( n = 3 ) and 28.9"C ( n = 3 ) . During the complete investigation period of 2 hours the infants were carefully watched and the degree of muscular activity assessed using a four-point scale (45). Acta Pediatr Scand 64
Temperuticrr recordings
Within 3 min after birth the rectal temperature was measured using an electric thermometer (45). In the chamber rectal temperature and abdominal skin temperature were recorded every minute. Five additional skin temperatures were measured every 20 min. In order to get information about the mean skin temperature, each skin temperature was weighted according to the surface area (in percent) that they represented (6). The skin temperatures were determined from (with weighting factor F ) : The xiphoid process ( F : 0.33). the abdorninal skin in the mid-line above the umbilical region (F: 0.7-3), the lateral side of the left hand ( F : 0.05), the lateral side of the left upper leg ( F : 0.29) and the dorsal side of the left foot ( F : 0.05). Arterial blood gus and acid determinutions
base balunce
The blood samples (0.5 ml) were transferred to a heparinized and siliconiced glass syringe with a mercury lock. The Po, determinations were performed with an open Clark electrode (19). The pH, P,,,, and acid-base determinations were performed by the Astrup microequilibration technique (4 I ) . The blood gas deterrnindtions were made as soon a s possible after ,sampling (always within 60 min). The results were corrected to the actual rectal temperature (40). All determinations were done in duplicate. The error of Po, determination was 1.6 mmHg ( n = 1 8 5 ) and of pH determination 0.005 units (n=200).
RESULTS Temperature The 10 infants handled immediately in a "warm" environment and subsequently studied in an environmental temperature of 34.8"C and 33.5"C had rectal temperatures which in no infant fell below 36.7"C. After an initid drop in skin temperature, the ternperature gradient between mean skin ternperature and environmental temperature was 2.1-2.2"C (Table 1). As the changes in rectal temperature and skin temperature were similar in all 10 infants, these infants were grouped together in group 1 . The 6 infants immediately taken care of in room temperature and subsequently studied in an environmental temperature of 32°C and 28.9"c, showed a heat loss with decreasing rectal temperatures, and at 120 min all 6 infants had rectal temperatures below 36.5"C. These 6 infants were grouped together in group 2 . The 3 infants s'tudied in an environmental temperature of 28.9T
Injluence of temperature on pulnzonar?, gas exchange
59
15 Vn2 ml / ~ gmin
10
5
15
v co2 ml / ~ gm i n
10
5
’”.
,
,
.
,
,
I
Activity score
3lT-7
B.E.
2 1
\\w
04 0
-
\w
1
W
10
5
A
,
-
-10;
20
15
D
0
5
0
10
15
-
20
min
30
Fig. I . Sampling times and results of parameters measured in five “warm” infants. Analgesia Duration of Case no.
Parity
labour (hours)
2nd stage (min) 40 5 20
10
7 12 17
I 111
12 2.5 6
26 28
I1 IV
3 5
I11
5
Pud. nerve block
+
Pethidina
+ + +
Mode of delivery presentation Vertex Vertex Occiput post Vertex Vertex
Birth weight
(€9
T, (“C)
4 255 3 580 2 770.
34.8 34.7 34.8
2 960 3 120
33.2 33.5
Pethidin 50-100 mg administered 1-3.5 hours before delivery. All infants had a similar postnatal course with an initial high degree of activity and pulmonary gas exchange followed by a rapid drop in activity and pulmonary gas exchange values. Rapid “normalization” of blood gases and acid-base balance was present in all infants:
Acta Pzdiatr S c a d 64
60
R . Tunell Pa o2 mm Hg
I001
....
40
1
1
51
0.4
/
4I
Activity
score
Fig.2. Sampling times and results of parameters measured,in five "warm" infants. Analgesia Duration of Case no.
Parity
3
I1
19
111
23 25 29
I I1 111
labour (hours)
2nd stage (min)
3 7 6 3
5 50 5 5
Pud . nerve block
Pethidin"
+
Mode of delivery presentation
Birth weight (g)
T, ("C)
Ces. sect.b Vertex Vertex Vertex Vertex
3 050 3 580 3 200 3 820 4 040
34.6 34.7 33.5 33.4 33.3
Symbol 0
+0 0
Pethidin 75 mg given 2 hours before delivery. Ces. section because ofnarrow pelvis. Spinal anaesthesia. Case no. 23 was clinically uneventful, but during the first 4 min, a low degree of pulmonary gas exchange was found. The arterial Po, at 5 min of 17 mmHg indicates ineffective pulmonary gas exchange. A persistently high degree of activity was found in cases 19, 25 and 29. High f', and low Pa& values were found in these three cases. Case 19 had a tendency to hyperventilate.
*
Arta Pediatr Scand 64
Injluence of temperature on pulmonary gas exchange
61
Fig. 3. Sampling times and results of the parameters measured in “cold” infants. _
_
_
_
_
_
Analgesia Duration of Case
labour (hours)
no.
Panty
9 13
V
3
11
5
16
IV I
4 1 4.5
18 20 21
111
I
17
2nd stage (min) 5 10 10 20 10
60
Pud . nerve block
+ +
Pethidin
+ +
Mode of delivery presentation Vertex Vertex Vertex Vertex Occiput post Vertex
Birth weight (g)
T,
(“0
Symbol
3 370 3 320, 4080 2 930’ 2 660
32.0 31.7 32.0 28.8 28.1
0 A
3 030
29.8
V
0 0 W
Pethidin 100 mg given more than 3.5 hours before delivery. The pattern of changes in all parameters were the same as found in infants kept “warm”. Infants with high Vo2values 16-20 rnin after birth had low Pas values. a
Acto Padiatr Scand 64
p
~
62
R. Tunell
Table 1. Meun I-dues and range in the temprratitrr mrusurrments in groitp I ( ‘ h ~ a r m ”und ) group 2 (“cold”) infants Minutes after birth ~~
Measurement
Group
2
40
120
Rectal temperature (“0
I
38.0 37.8-3 8.2 38.1 37.9-38.5
37.2 36.9-37.5 36. I 35.4-36.9
37.3 36.7-37.9 35.4 34.3-36.4
I
1.1
I1
0.61.3 I .6 0.3-2. I
0.6 0.4-1.4 1.3 I . 1-1.6
2.1 1.3-3.0 4.0 2.84.8
2.2 I.62.9 3.6 2.54.8
I1 Rectal-skin temperature gradient (“C)
Skinxnvironmental temperature gradient (“C)
I
were, in contrast to the infants studied at 3 2 T , restless and very active during the examination period and meconium passage occurred. Infants in group 2 had a significantly greater skin-environmental temperature gradient than infants in group 1 (Table I ).
Blood gus und acid base balance de term ina tions The results of Pa,,,, PaCo2,pH and base excess (BE) determinations are given in Table 3. The results from individual infants during the period 0-20 min after birth are given in Figs. 1, 3 and 3. The pattern of changes in these parameters was similar in all infants irrespective of Pulnionary gas exchange and rnusculur environmental temperature. activity The results of the determinations of V o z , The main increase in Pa,,? took place 1Vicoz,the respiratory exchange ratio R (Vco,/ 10 rnin after birth. After that period PaOz Vo,), and the degree of muscular activity increased slowly but the values showed are given in Table 2. The results from indi- great variation. A close relationship was vidual infants during the period 0-20 min found between the values a t 16-20 rnin after birth and the values at 60 and 120 rnin after after birth are given in Figs. 1, 2 and 3. The pattern of changes in Voz and Vco2 birth respectively. (r=0.76, p < O . O O l , n=16 was similar in all infants irrespective of en- and r=0.79, p
