Depression of ventilatory responses after daily, cyclic hypercapnic hypoxia in piglets

Departments of Medicine and Paediatrics and Child Health, University of Sydney, Sydney, New South Wales 2006, Australia Ventilatory responses (VRs) were measured via a sealed face mask and pneumotachograph in 30 unsedated, mixed-breed miniature piglets at 12.6 ± 2.3 days of age ( day 1 ) and then repeated after seven daily 24-min exposures to 10% O 2 -6% CO 2 [hypercapnic hypoxia (HH)]. Arterial blood was sampled at baseline, after 10 min of exposure, and after 10 min of recovery. VRs included hypoxia (10% O 2 in N 2 ), hypercapnia (6% CO 2 in air), and HH (10% O 2 -6% CO 2 -balance N 2 ). Treatment groups ( n = 10 each) were exposed to 24 min of HH from day 2 to 8 as sustained HH (24 min of HH and then 24 min of air) or cyclic HH (4 min of HH alternating with 4 min of air). Day 1 and 9 data were compared in treatment and control groups. After cyclic HH, respiratory responses to CO 2 were reduced during hypercapnia and during HH ( P