Hypothalamus and respiratory minute volume

¹ Department of Physiology, Western Reserve University School of Medicine, Cleveland, Ohio

Minute volume of respiration was measured in 21 cats. Hypodermic tubing and electrodes were implanted in the hypothalamus. Minute volume of respiration was measured before and after depression of the hypothalamus by coagulation with high frequency current or by microinjection of 4% thiopental into sites in the hypothalamus. Depression of the hypothalamus was followed by a 20–30% decrease in minute volume. The results were statistically significant. Depression of the thalamus by coagulation or microinjection of thiopental was not followed by a significant change in minute volume. Intravenous injection of the amount of thiopental injected into the hypothalamus did not alter minute volume. Minute volume decrease was often associated with blood pressure and muscle tone decreases, but in several cases, minute volume decreases were independent of blood pressure and muscle tone. The evidence supports the argument that tonic discharges from the hypothalamus increase the excitability of respiratory reflex pathways and effect increased minute volume.