Abstract
CAP falls rapidly after birth with a concurrent increase in P50 (PO2 at 50% Hgb saturation, pH 7.4, pCO2 40 torr, 39° C). However, it is not known whether there is also an increase in CO to maintain O2 delivery to the tissues while CAP is low. To investigate this question we studied 7 lambs during the first 8 weeks after birth. Catheters were placed in the right atrium and carotid artery. We measured VO2, CAP, arterial and mixed venous O2 content and blood gases, Hgb, P50, 2,3-DPG, and fetal and adult Hgb in quiet unsedated lambs. CO was calculated from the Pick equation. Means ± SEM were:
There was an increase in CO/kg and VO2/kg in all lambs during the first 1 to 2 weeks followed by a steady, parallel decline to near adult values. Both peaked prior to the nadir of the anemia; thus CO/kg was decreasing when CAP was at a minimum. A rising P50 contributed to maintaining relatively constant arteriovenous O2 content differences (AVDO2) despite changes in CAP. We conclude that variations in CO are not a result of a decreased CAP, but occur primarily in response to changing metabolic needs after birth.
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Lister, G., Walter, T., Rudolph, A. et al. POSTNATAL CHANGES IN OXYGEN TRANSPORT: RELATIONSHIP BETWEEN CARDIAC OUTPUT (CO), O2 CONSUMPTION, AND O2 CARRYING CAPACITY (CAP). Pediatr Res 11, 408 (1977). https://doi.org/10.1203/00006450-197704000-00235
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DOI: https://doi.org/10.1203/00006450-197704000-00235