Abstract
To test the ability to increase O2 extraction when cardiac output is decreased, we assessed total body O2 delivery before and after ß adrenergic blockade during the early postnatal period. 8 lambs were studied chronically over the first 2 month of life. Cardiac output (CO), heart rate (HR), hemoglobin (Hb), Hb 02 affinity and 2,3-DPG, oxygen consumption (VO2), systemic O2 transport (SOT), and arteriovenous O2 content difference were measured while the lambs were resting and unsedated, and again after intravenous propanolol (PROP), 1mg/kg. After birth CO, HR and VO2 at rest decreased steadily while fractional O2 extraction (VO2/SOT) remained constant. After PROP CO was consistently reduced by 10 - 20 %, and there were no significant differences with age. Most of the decrease in CO was explained by the reduction in HR.Upon this decline in CO there were significant decreases in VO2 after PROP during the first postnatal week, and at 4 weeks. This was when O2Hb affinity was greatest (≤1 wk) or Hb was lowest (3-4 wk). Moreover, only when resting mixed venous Po2 was less than 29 torr was VO2 consistently and predictably decreased after PROP.
Compared to the lamb in human infants P50 after birth is lower, and Hb is decreasing relatively more. We conclude that in the human infant like in the lamb there is very little reserve to increase O2 extraction or arterialvenous O2 content difference early in infancy when P50 or Hb is low.
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Versmold, H., Lister, G., Dallman, P. et al. Limits of 02 Delivery during Propanolol-Induced Reduction of Cardiac Output in Lambs after Birth: A Longitudinal Study: 67. Pediatr Res 14, 176 (1980). https://doi.org/10.1203/00006450-198002000-00094
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DOI: https://doi.org/10.1203/00006450-198002000-00094
