Breathing pattern of kittens during hypoxia

Abstract

In 19 pentobarbital sodium-anesthetized kittens aged 5-34 days, inspired O2 was reduced from 21 to 6-12%. Respiratory frequency (f) and tidal volume (VT) increased with 30 s. Over 5 min f fell to .apprx. 60% below control; VT usually fell but remained above control. Arterial pressure fell to 80% of trials, sometimes before f fell. Arterial CO2 was below control, but raising inspired CO2 to keep expired CO2 at control did not prevent the fall in f and VT. The relation betwen VT and esophageal pressure or diaphragm electromyogram (EMG) did not change consistently, nor was the ratio of high to low frequencies in the diaphragm EMG altered. Carotid chemoreceptor discharge increased within 15 s, and at 5 min it was much above control. The change in the breathing pattern in hypoxia is probably due to the activation of a central mechanism.