Cardiovascular effects of hypoxia/hypercarbia and tension pneumothorax in newborn piglets.

OBJECTIVES: To test the hypothesis that, in newborn piglets, the presence of a tension pneumothorax modifies the cardiovascular responses to hypoxia/hypercarbia. DESIGN: Prospective laboratory study. SETTING: Perinatal cardiovascular research laboratory at a university school of medicine. SUBJECTS: Seven newborn piglets. INTERVENTIONS: We sequentially exposed the piglets to a baseline (control I) measure, hypoxia/hypercarbia, tension pneumothorax with normoxia/normocarbia, and tension pneumothorax with hypoxia/hypercarbia added. MEASUREMENTS AND MAIN RESULTS: Brain and systemic blood pressures and blood flow (radionuclide-microspheres) were measured. Hypoxia/hypercarbia resulted in increased brain perfusion (207 +/- 61% of control, mean +/- SEM, p < .05) and heart perfusion (176 +/- 58% of control, p < .05) and decreased gastrointestinal perfusion (-37 +/- 9% of control, p < .05). Tension pneumothorax with normoxia/normocarbia reduced the cardiac output (-70 +/- 8% of control, p < .05), which was redistributed toward the brain (p < .05) at the expense of the gastrointestinal tract (p < .05). Although this redistribution in cardiac output persisted during tension pneumothorax with hypoxia/hypercarbia added, sustained reductions in cardiac output (-57 +/- 11%, of control, p < .01) were associated with smaller increases in perfusion to brain (55 +/- 54 vs. 207 +/- 61% of control, tension pneumothorax with hypoxia/hypercarbia added, and hypoxia/hypercarbia time periods, respectively, p < .05) and heart (65 +/- 49 vs. 176 +/- 58% of control, tension pneumothorax with hypoxia/hypercarbia added, and hypoxia/hypercarbia time periods, respectively, p < .05) and larger decreases in blood flow to gastrointestinal tract, pancreas, and kidneys (p < .05) than with hypoxia/hypercarbia alone. CONCLUSIONS: Tension pneumothorax-induced reductions in cardiac output limit the hypoxia/hypercarbia-mediated increases in perfusion to brain and heart and accentuate the hypoxia/hypercarbia-related decreases in perfusion to kidneys and splanchnic organs.

Body composition of low-birth-weight infants determined by using bioelectrical resistance and reactance.

We tested the hypothesis that bioelectrical resistance and reactance are indices of total body water (TBW) and extracellular water (ECW), respectively. Infants less than 2500 g in birth weight were studied while less than 24 h old and at 4-7 d of age. TBW (n = 32) was measured by H2(18)O dilution and ECW (n = 34), by bromide dilution. Measurements were made by using an impedance plethysmograph from each of four electrode pairs. Bioelectrical resistance correlated inversely with TBW (r = -0.683). When body weight and crown-heel length were factored into the equation, the correlation improved (r = 0.953). Bioelectrical reactance correlated inversely with ECW (r = -0.707). When body weight and surface area were factored into the equation the correlation improved (r = 0.882). We conclude that bioelectrical resistance and reactance are good indices of TBW and ECW, respectively. However, the ability to resolve small changes in body-water compartments when confined to the intraluminal or other third spaces remains questionable, particularly for single subjects.

Technical and clinical testing of a computerized indirect calorimeter for use in mechanically ventilated neonates.

Testing of a proprietary indirect calorimeter (MGM, Jr.) was performed by using nitrogen displacement and added carbon dioxide to simulate oxygen consumption (VO2), carbon dioxide production (VCO2), and the respiratory quotient (RQ; VCO2/VO2). Errors in measured VO2, VCO2, and RQ were less than or equal to 2.5% when VO2 and VCO2 were 4-43 mL/min and flow rate was 100-2000 mL/min. The relative error in predicted VO2 was increased as the inspired oxygen concentration (FiO2) was raised but the error was less than 4% when the value of FiO2 minus expired oxygen concentration (FeO2) was greater than or equal to 0.015 and the FiO2 was less than or equal to 0.6. Sixteen studies were performed on seven very-low-birth-weight (VLBW), mechanically ventilated infants aged less than or equal to 11 d. VO2 was 8.37 +/- 1.81 mL.kg-1.min-1, VCO2 was 8.15 +/- 2.03 mL.kg-1.min-1, and RQ was 0.969 +/- 0.061 (means +/- SD). The MGM, Jr. is accurate for studies of low-birth-weight infants on mechanical ventilators when VO2 and VCO2 are greater than or equal to 4 mL/min, flow rate is less than or equal to 3000 mL/min, and FiO2 is less than or equal to 0.6. Clinical testing resulted in values similar to previously published data but the variability was higher.

Gastrointestinal blood flow and oxygen delivery during environmental cold stress: effect of anaemia.

We studied the effect of environmental cold stress with and without isovolaemic anaemia on blood flow and oxygen delivery to the stomach, small intestine, and colon. The purpose of the study was to investigate the independent and combined effects of an increased oxygen demand (cold stress) and decreased oxygen availability (anaemia). Six, 3-4 days-old, awake piglets having normal haematocrit (26%), were studied in a warm environment (31.7 +/- 0.4 degrees C) and 30 min after reaching the nadir of cold stress (19.9 +/- 0.4 degrees C). Subsequently, a warm environment was reestablished and a partial volume, plasma exchange transfusion was done to lower the haematocrit to approximately 15%. Piglets were then studied as before in warm (32 +/- 0.5 degrees C) and cold (19.3 +/- 0.3 degrees C) environments. In the non-anaemic study phase, cold stress provoked a decrease in blood flow (ml.100g-1.min-1) to the small intestine (226 +/- 22 vs. 134 +/- 22) while oxygen delivery (ml O2.100g-1.min-1) was decreased to the stomach (13.6 +/- 1.4 vs 9.3 +/- 1.7), small intestine (19.6 +/- 0.6 vs. 11.2 +/- 1.1) and colon (9.6 +/- 1.7 vs. 6.1 +/- 1.0). Following plasma exchange transfusion (anaemic study phase), warm environment values for gastrointestinal blood flow did not differ from non-anaemic warm environment values. However, mean oxygen delivery while in a warm environment was decreased to the stomach (-45%), small intestine (-49%) and colon (-42%). Among anaemic piglets, cold stress provoked a further decrease in oxygen delivery to the small intestine (9.9 +/- 1.2 vs. 6.5 +/- 0.9).(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma catecholamine concentrations of newborn piglets in thermoneutral and cold environments.

Plasma epinephrine and norepinephrine concentrations were measured in seventeen unanaesthetized 3 to 4 days-old piglets while in a thermoneutral environment (31.3 degrees C) and 30, 45 and 60 min after induction of environmental cold stress (19.9-23.1 degrees C). Plasma epinephrine and norepinephrine concentrations in a warm environment were 142 +/- 26 pg/ml, and 456 +/- 44 pg/ml respectively. Environmental cold stress evoked significant increases in norepinephrine values after 30 (624 +/- 58 pg/ml), 45 (626 +/- 60 pg/ml) and 60 (626 +/- 54 pg/ml) min of cold stress. Plasma epinephrine concentrations did not significantly change during environmental cold stress. Post-hoc stratification of piglets into normothermic (deep rectal temperature 38.6 degrees C-38.8 degrees C, n = 9) and hypothermic (deep rectal temperature 37.1 degrees C-37.7 degrees C, n = 7) subgroups revealed significant increases in plasma norepinephrine concentrations only in the hypothermic subgroup. We conclude that plasma norepinephrine, but not epinephrine, is increased in newborn piglets during environmental cold stress and that the changes in norepinephrine concentrations are related to body core hypothermia. We speculate that hypothermia-mediated reductions in peripheral norepinephrine breakdown and re-uptake contribute to the rise in circulating levels.

Behavioral characteristics and early temperament of premature infants with intracranial hemorrhage.

Behavioral characteristics of 12 full-term and 44 premature infants with and without intracranial hemorrhage (ICH) were studied. Cranial ultrasonography prospectively documented Grade I-II ICH in 14, Grade III-IV in 19 and no ICH in 11 premature infants. Examination at corrected age of 40 +/- 2 weeks using the Neonatal Behavioral Assessment Scale showed that infants in the ICH groups had lower levels of arousal and more abnormal reflexes than full-terms. Infants with ICH III-IV displayed less optimal motor responses than full-term infants and diminished orientation responses, especially to visual stimuli. Thus, lower level of arousal, immature motoric processes, and poor visual orientation differentiated premature with ICH from full-term infants, although premature infants without these sequelae, did not differ significantly from full-term infants. The above may represent early manifestations of visual-perceptual and motor problems noted in the follow-up of ICH infants. Further, neonatal behavior was found to affect parent ratings of infant temperament (via the Bates Infant Characteristics Questionnaire) at 3 months corrected age, and the relationships between neonatal behavior and parental ratings differed depending upon the infant's gestational age and severity of hemorrhage. We conclude that neonatal behaviors are less optimal in premature infants, and least optimal in premature infants with severe intracranial hemorrhage when compared to fullterm infants.

Postprandial gastrointestinal blood flow and oxygen consumption during environmental cold stress.

We studied the independent and combined effects of feeding and environmental cold stress by measuring pre- and postprandial gastrointestinal blood flow (QGI), oxygen consumption (GIVO2), and oxygen extraction (GIO2ex) in seven awake 3- to 4-day-old piglets while in a thermoneutral environment (control phase, 31 degrees C) and during environmental cold stress (experimental phase, 20.5 degrees C). Each animal consecutively completed both the control and experimental phases. In the control phase, measurements were made before and 30 min after feeding. In the experimental phase, measurements were made before and 30 min after induction of cold stress. A feeding was then given and measurements repeated 30 min later during continued cold stress. QGI (ml.100 g-1.min-1) increased postprandially while in a thermoneutral environment (130 +/- 11 to 152 +/- 12) but not while in a cold environment (126 +/- 15 to 121 +/- 8). Postprandial GIVO2 (ml O2.100 g-1.min-1) increased from 2.1 +/- 0.2 to 3.7 +/- 0.5 while in a warm environment. During preprandial cold stress, an unexpected increase in GIVO2 was observed (1.7 +/- 0.2 to 3.1 +/- 0.5). Feeding while in a cold environment provoked a further significant increase in GIVO2 (3.1 +/- 0.5 to 4.2 +/- 0.4). All increases in GIVO2 were associated with increased GIO2ex. This study has demonstrated that 1) postprandial GIVO2 is appropriately increased during cold stress as a function of GIO2ex and 2) that fasting GIVO2 is increased during cold stress, demonstrating an intestinal metabolic contribution to cold-induced systemic thermogenesis.

Behavioral responsiveness in preterm infants with intraventricular hemorrhage.

Preterm infants with varying degrees of intraventricular hemorrhage (none, n = 21; grade I to II, n = 22; grade II to IV, n = 24) and a group of full-term infants (n = 21) were compared with regard to behavioral responsiveness and parental reports of the infant's temperament. Behavioral responsiveness was assessed during the presentation of 15 visual, auditory, and tactile stimuli at 3 months of age (corrected age for preterm infants). Summary scores for positive and negative responsiveness, as well as sociability, soothability, and overall activity levels, were derived from behavioral observations by coders who were unaware of the infant's characteristics. The Bates Infant Characteristic Questionnaire was completed by the main care giver and scored on four summary variables: fussy-difficult, unadaptable, dull, and unpredictable. Preterm infants, regardless of the presence or severity of intraventricular hemorrhage, showed less positive responses and less overall activity in response to stimulation. Infants with grade I to II intraventricular hemorrhage were less sociable and more difficult to soothe than full-term control infants. Individual differences in positive, negative, sociability, and soothability were related to the questionnaire scores of fussy-difficult and unadaptability. Both prematurity and degree of intraventricular hemorrhage affect behavioral responsiveness and these individual differences are related to parental reports of the infant's temperament.

Anemia blunts the thermogenic response to environmental cold stress in newborn piglets.

We tested the hypothesis that isovolemic anemia blunts the thermogenic response to environmental cold stress in 3 to 4-day-old newborn piglets. Eight animals were studied in both thermoneutral (31.6-32.8 degrees C) and cold (19.6-20.2 degrees C) environments, before and after an isovolemic, partial volume exchange transfusion which reduced the hematocrit from 26 to 15%. In the nonanemic phase of study, deep rectal temperatures declined but had plateaued by 30 minutes after onset of cold stress and remained within normal limits for newborn piglets. In the anemic phase of study, deep rectal temperature declined continuously throughout cold stress with true body core hypothermia (less than 38 degrees C) observed at all measurement points beyond 15 min of cold stress. Baseline oxygen consumption did not differ between the two study phases (17.6 +/- 1.8 versus 16.7 +/- 2.1 ml/kg-1/min-1, mean +/- SEM). However, during environmental cold stress, oxygen consumption increased by 64% over baseline in the nonanemic phase of study (p less than 0.05) whereas 21% increase over baseline was observed in the anemic phase (p NS). We conclude that isovolemic anemia limited oxygen consumption and heat production during environmental cold stress, resulting in body core hypothermia.

Postprandial gastrointestinal blood flow and oxygen consumption: effects of hypoxemia in neonatal piglets.

The effects of feeding on gastrointestinal (GI) perfusion and oxygen transport in hypoxemic neonates is unknown. We evaluated these effects in unanesthetized, spontaneously breathing newborn piglets by comparing three experimental groups: nine hypoxemic piglets (mean PaO2 26 torr) which were fed with formula, six hypoxemic piglets (mean PaO2 27 torr) which were not fed, and four normoxemic piglets (mean PaO2 79 torr) which were fed and served as controls. The control-fed group exhibited an increase in stomach and small intestinal mucosal-submucosal blood flow within 30 min following feeding which was significantly greater than that observed in the hypoxemic fed piglets. GI O2 delivery and O2 uptake rose significantly (p less than 0.05) following a meal secondary to increases in total GI blood flow. Oxygen extraction was unchanged postprandially in the control group. In the hypoxemic nonfed piglets, total and regional GI blood flow was unaltered during hypoxemia. Reductions in arterial O2 content led to significant decreases in GI O2 delivery. Gastrointestinal oxygen uptake remained stable with a compensatory increase in GI O2 extraction. In the hypoxemic-fed piglets, hypoxia significantly decreased stomach blood flow and led to unchanged blood flow in the remainder of the GI tract. Significant reductions in arterial O2 content and GI O2 delivery were observed, accompanied by significant increases in O2 extraction. Hypoxemic fed animals did not exhibit the expected increase in O2 uptake to meet postprandial metabolic demands. When the hypoxemic insult was terminated, fed piglets demonstrated significant total and regional GI hyperemia leading to increased GI O2 uptake when compared with hypoxemic nonfed piglets.(ABSTRACT TRUNCATED AT 250 WORDS)

The Apgar score revisited: influence of gestational age.

We tested the hypothesis that Apgar scores are in part related to the newborn infant's level of maturity. Seventy-three pregnant women with normal fetuses of gestational age 22 to 42 weeks were studied. Fetal well-being was documented by a prospectively designed recording of pregnancy history, labor complications, and birth outcome, including cord blood pH and base deficit measurements. The 1- and 5-minute Apgar scores were directly related to gestational age. Respiratory efforts, muscle tone, and reflex were the major determinants for a decreasing Apgar score with declining gestational age. We conclude that the 1- and 5-minute Apgar scores are influenced by the infant's level of maturity and that our data may be useful in evaluating the true value of Apgar scores in assessing the fetal and neonatal condition of low birth weight infants.

Regional blood flow in newborn piglets during environmental cold stress.

Regional blood flow, oxygen delivery, and vascular resistance were determined in newborn piglets during a successful homeothermic response to environmental cold stress. Eight 3- to 4-day-old awake piglets were studied in a thermoneutral environment and 30, 45, and 60 min after onset of environmental cold stress. During cold stress, blood flow was significantly increased to skeletal muscle, the thermogenic organ, and decreased to the small intestine (P less than 0.05). Because arterial oxygen content (CaO2) was stable during the study, changes in oxygen delivery (CaO2 X blood flow) paralleled blood flow. Vascular resistance during cold stress was significantly decreased in skeletal muscle and increased in both the adrenals and the small intestine (P less than 0.05). We conclude that, during successful thermogenesis, the redistribution of cardiac output toward the thermogenic organ (skeletal muscle) is associated with a significant decrease in intestinal blood flow and oxygen delivery. This is not a passive process as evidenced by the coincident observation of increased intestinal vascular resistance.

Tympanic membrane temperature of term and preterm neonates.

Deep body temperatures of 70 term and 24 preterm newborn infants were measured at two sites: deep rectum (5 cm beyond the anus) and tympanic membrane. A significant correlation was found between deep rectal and tympanic membrane temperatures in both term and preterm infants. Mean deep rectal and tympanic membrane temperatures in term infants were 37.01 degrees C and 36.83 degrees C, respectively. Mean deep rectal and tympanic membrane temperatures in preterm infants were both 36.69 degrees C.

Temperature measurement in term and preterm neonates.

Body temperatures of 99 term and 44 preterm infants were measured at four sites: core (5 cm beyond the anus, with an electronic telethermometer), rectum (2 cm, with a mercury-in-glass thermometer), axilla, and between the skin and mattress. Temperatures measured at the four sites agreed closely in this group of largely normothermic infants. However, five of seven term infants with abnormal core temperature (greater than 1.5 SD below or above the mean) would have been judged to be normothermic by each of the three other measurements. The temperatures in preterm infants were lower and varied less with the site of measurement, indicating a smaller core-surface temperature gradient because of their relative lack of thermal insulation by body fat. Axillary temperature was as reliable as rectal temperature measured in the usual way with a mercury-in-glass thermometer. Measurement of the temperature between the skin and mattress was nearly as accurate as the other more frequently used methods. Ninety percent of temperatures were within 0.1 degree C of their final stabilization readings by 5 minutes for each type of thermometer and measurement site.