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Ventilatory and metabolic responses to acute hyperoxia in newborns
J P Mortola1, P B Frappell, A Dotta
1Department of Physiology, McGill University, Montreal, Quebec, Canada.
Insights
In newborn infants, breathing 100% oxygen increases metabolic rate, oxygen consumption, and carbon dioxide production. This suggests oxygen availability limits metabolic rate in newborns.
Area of Science:
- Neonatal Physiology
- Respiratory Medicine
- Metabolic Studies
Background:
- Hyperoxia is known to elevate metabolic rate in newborn mammals.
- The effect of hyperoxia on metabolic rate in newborn infants remains less understood.
Purpose of the Study:
- To investigate whether breathing pure oxygen increases metabolic rate in newborn infants.
- To determine the impact of hyperoxia on oxygen consumption (VO2) and carbon dioxide production (VCO2) in neonates.
Main Methods:
- Studied 25 full-term infants (1-2 days old) using a pneumotachograph and face mask.
- Measured breathing pattern, VO2, and VCO2 during normoxia (21% O2) and hyperoxia (100% O2).
- Calculated VO2 and VCO2 from ventilation and gas concentrations, ensuring accurate measurements with bias flow.
Main Results:
- Hyperoxia significantly increased minute ventilation (VE) by 18% in 22 out of 25 infants.
- Alveolar ventilation (VA) increased by 58% due to increased tidal volume and decreased breathing rate.
- Oxygen consumption (VO2) rose by 25% and carbon dioxide production (VCO2) by 17% during hyperoxia.
Conclusions:
- Newborn infants exhibit increased metabolic rate, VO2, and VCO2 when breathing pure oxygen.
- The observed increase in VO2 suggests that oxygen availability may limit metabolic rate in healthy newborns.
- Findings align with previous observations in other newborn mammal species.
Abstract:
Hyperoxia has previously been found to increase metabolic rate (oxygen consumption [VO2] and CO2 production [VCO2]) in newborn mammals. We asked whether the same occurs in the newborn infant. Breathing pattern was measured in 25 full-term infants, 1 to 2 days of age, from the spirometric record obtained with a pneumotachograph attached to a face mask. Concentrations of O2 and CO2 were continuously measured at the mouth; VO2 and VCO2 were computed as the product of VE and the difference between inspired and expired concentration of the respective gases, 5 min of air (FIO2 = 0.21) and 5 min of O2 (FIO2 = 1). A bias flow through the mask and pneumotachograph delivered the inspired gas and eliminated the effects of the instrumental dead space. In neither case did measurements at 1 min significantly differ from those taken at 5 min. In hyperoxia VE increased in 22 of the 25 infants, in average +18% (p less than 0.001, paired two-tailed t test). Because of a rise in tidal volume (+35%, p less than 0.001) and a decrease in breathing rate (-11%, p less than 0.005) alveolar ventilation (VA) increased by about 58% (p less than 0.001). VO2 and VCO2 increased by 25% and 17%, respectively (p less than 0.001). The rise in VO2 was too large to be explained by the greater respiratory work of the hyperventilation, whereas that of VCO2 was not large enough to fully explain the increase in VA. We conclude that in newborn humans, as in other newborn species, the normoxic metabolic rate seems to be limited by the availability of O2.(ABSTRACT TRUNCATED AT 250 WORDS)