CARDIOVASCULAR AND RESPIRATORY CONSEQUENCES OF BODY WARMING DURING HYPOXIA IN CONSCIOUS NEWBORN CATS

Acute hypoxia in newborns of various species including humans is assoc iated with decreased thermogenesis and a fall in body temperature. We have investigated the cardiorespiratory consequences of correcting the fall in colonic temperature (Tc) during acute hypoxia in newborn cats . Experiments were conducted on 21 unanesthetized kittens (12 +/- 1 d SEM, 244 +/- 8 g) instrumented with catheters in the left common carot id artery and superior vena cava for measurements of systemic arterial pressure, central venous pressure, heart rate, arterial blood gases, arterial O-2 saturation (Sao(2)) and mixed venous O-2 saturation. Oxyg en consumption (Vo(2)) and CO2 production (Vco(2)) were also measured. Alveolar ventilation (VA), cardiac index (CI), and systemic vascular resistance index (SVRI) were calculated. These determinations were mad e in 21% O-2 at an ambient temperature (Tamb) of 25 degrees C, and aft er 80 min of exposure to Fio(2) = 0.10. In one group Tamb was maintain ed at 25 degrees C (n = 8) during hypoxia and Tc fell by 2.7 +/- 0.4 d egrees C whereas in a second group Tamb was increased to 35 degrees C for the second 40 min of hypoxia to raise Tc to the prehypoxic level ( n = 13). Vo(2), Vco(2), VA, Sao(2), and systemic arterial pressure dur ing hypoxia did not differ between the animals which were warmed and t hose which were not. However, CI and heart rate were greater (452 +/- 23 versus 346 +/- 30 mL . min(-1). kg(-1) p < 0.05, 279 +/- 8 versus 2 28 +/- 12 beats . min(-1) p < 0.05) and SVRI lower (0.115 +/- 0.022 ve rsus 0.153 +/- 0.014 mm Hg . mL(-1). min . kg, p < 0.05) during hypoxi a in the warmed animals compared with the unwarmed group. Thus, artifi cially raising Tc during hypoxia resulted in peripheral vasodilatation , whereas systemic arterial pressure was maintained by the increase in cardiac output. We conclude that, in the hypoxic kitten, raising Tc t o normoxic values elicits a response that may reflect a condition of r elative hyperthermia.