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

Summary

• 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 (T _a).

• 2. Spinal cord cooling at 23°CT _a 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°CT _a when the spinal cord was cooled during thatT _a: O₂ consumption=139%; CO₂ production=136%;$\dot V_E$=156%; HR=126%; and CO=157%.

• 3. In contrast, spinal cord cooling at 34°CT _a 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 highT _a.

• 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.