Abstract
Introduction: In humans and other mammals, sustained isocapnic hypoxia for 20-60 minutes elicits a biphasic ventilatory response (roll-off), with initial peak ventilation followed by decline to a plateau. The activities of the respiratory muscles during the sustained hypoxic response are not known.
Aim: To study ventilation and actions of the chest wall muscles, specifically Parasternal Intercostal (PARA) during sustained hypoxia in awake canines.
Methods: After implantation of sonomicrometry transducers and EMG electrodes in PARA, and complete recovery, we measured airflow, oxygen saturation, end tidal CO2, moving average EMG and shortening (SHORT) of PARA, during room air ventilation (BASE), followed by 25 minutes of isocapnic hypoxia (mean 78% SpO2). The canines were awake, breathing through a snout mask. We report results 2-3 min after reaching SpO2 80% (PEAK) and final 5 min (PLATEAU) of sustained hypoxia, then room air breathing (RECOVERY).
Results: For N=7 (mean 28.9 kg, 28 days post implant), minute ventilation (VI) and tidal volume (VT) increased significantly from BASE to PEAK, then decreased to an intermediate PLATEAU (p<0.001). Concurrently, mean EMG and SHORT of the PARA increased significantly from BASE to PEAK, then attenuated to PLATEAU (p<0.01).
Conclusion: As minute ventilation “rolls off” during sustained isocapnic hypoxia, there is a concurrent decline in shortening and EMG activity of the chest wall muscle, the Parasternal Intercostal.
- © 2011 ERS
