In 135 asymptomatic newborn infants, 1–53 days of age, body weight 1,820–4,120 g, indirect calometry was performed. According to the state of wakefulness the infants showed during the testing procedure, they were divided into four groups of vigilance (V₁–V₄). Metabolic rate and oxygen consumption showed similar results between groups V₁, V₂ and V₃ (deep sleep; REM sleep; wakefulness with no muscular activity). V₄ infants (with muscular activity) had a higher metabolic rate and O₂ consumption. Correlation between metabolic rate and body surface area is similar in V₂ and V₃ but shows a steeper slope in the V₁ group. It is speculated that central regulatory mechanisms may account for this difference.

Arterial oxygen tension measurements were performed simultaneously using two different techniques: (1) the conventional method of analyzing a blood sample obtained from the radial artery by means of a Clark electrode and (2) a new method of transcutaneous oxygen tension recording using a newly developed surface electrode containing a built-in heating device to ensure optimal cutaneous perfusion at the site of measurement. Two groups of newborn infants were used as subjects: (1) 70 clinically healthy babies who were tested during normoxia and hyperoxia (breathing 80% to 100% oxygen) and (2) 20 sick preterm and term infants receiving inspired oxygen concentrations of between 21% and 100% during the measurement. Our results indicate a satisfactory accuracy for the transcutaneous oxygen tension measurements in normoxia and hyperoxia (percentage coefficient of variation, 15.9% and 24.1%, respectively). In hypoxia agreement between the two methods varies depending on the degree of circulatory derangement. Overall correlation coefficients were greater than 0.85 in each group.

In a randomly selected group of asymptomatic neonatal and postneonatal infants, acid-base parameters and oxygen tension measurements in arterial blood (radial artery) were carried out during air and oxygen breathing. Acid-base results showed a mild, partially compensated metabolic acidosis, indicating adequate pulmonary function. Arterial oxygen tension was in the normal range for this age group. Calculated alveolar oxygen tension levels demonstrated alveolar-arterial gradients of about 30 mm Hg during air breathing and 320 mm Hg during O2 breathing. Volumes of R-L shunts calculated from these gradients, were in the order of magnitude commonly found at this age, i.e., about 20% of right cardiac output. No differences were discernible between infants of appropriate weight for gestational age and small-for-date infants.

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