1253A THE PATTERN OF BREATHING OF KITTENS DURING HYPOXIA

Abstract

The reduction in (F,I,O2) in preterm infants and in anaesthetized kittens less than 35 days of age produces an increase in ventilation which is not sustained. This has been widely interpreted as respiratory failure. We studied the pattern of breathing during hypoxia in 16, pentobarbitone anaesthetized kittens 5-30 days of age, and have related it to oesophageal pressure, diaphragm (Dia) e.m.g., phrenic activity (PA) carotid chemoreceptor discharge, arterial pressure, expired FCO2 and FO2 PaCO2, PaO2, PHa and rectal temp. F1O2 was reduced from 0.21 to 0.06- 0.12, sometimes adding CO2. Respiratory frequency (f) and tidal volume (VT) was increased within 30 sec. Over 5 min f fell to up to 60% below control and arterial pressure fell in 22 of 43 trials in 9 kittens , sometimes preceding the fall in f. Even when f and VT fell CO2 was always below control. Adding CO2 did not prevent this fall. Hypoxia did not change the relationship between VT and oesophageal pressure or Dia. The ratio of high to low frequencies in the Dia. did not change. PA did not always correlate well with DIA,but this was not altered by hypoxia. Carotid chemoreceptor discharge increased within 15 sec of lowering FI,O2 and at 5 min. it was still much above control. Since the decrease in ventilation was not accompanied by hypercapnia nor muscle fatigue it is not respiratory ‘failure’. A specific central effect modulating breathing pattern must be considered. The Wellcome Trust (Grant 9594/1.5).