Respiratory and cardiovascular responses to spinal cord cooling at thermoneutral, low and high ambient temperatures in the chicken

Abstract

1. Respiratory and cardiovascular responses of six chickens to spinal cord cooling (temperature of vertebral canal =34±0.8°C) were measured during thermoneutral (23°C), low (9°C) and high (34°C) ambient temperatures (Ta). 2. Spinal cord cooling at 23°CTa caused immediate increases compared to resting values in O2 consumption (128%), CO2 production (112%), minute volume (\(\dot V_E \); 125%), heart rate (HR; 113%) and cardiac output (CO; 127%). Similar responses, of greater magnitude, were found compared to resting values at 9°CTa when the spinal cord was cooled during thatTa: O2 consumption=139%; CO2 production=136%;\(\dot V_E \)=156%; HR=126%; and CO=157%. 3. In contrast, spinal cord cooling at 34°CTa caused no significant changes in O2 consumption or CO2 production compared to resting values, while\(\dot V_E \) and CO decreased. 4. There were no major changes in\(P_{O_2 } \),\(P_{CO_2 } \) or pH of the blood produced by spinal cord cooling, but a significant arterial hypocapnia and increased arterial and venous\(P_{O_2 } \) occurred at highTa. 5. Both CO and\(\dot V_E \) were linearly related to oxygen consumption among all the groups studied. However, some independence of respiration from O2 consumption, presumably because of thermoregulatory demand to increase respiratory evaporative water loss, was observed at the high ambient temperature.