The mechanism of respiratory arrest in inspiratory loading and hypoxemia.

Respiratory arrests occur in the clinical setting of respiratory failure, but the mechanism is unclear. We used a dog model with increased inspiratory resistance and hypoxemia to explore the cause. We hypothesized that respiratory muscle fatigue (RMF) played a role in these respiratory arrests, and that the combination of hypoxia and resistive loading would produce respiratory arrest by the mechanism of RMF. Our preparation had transdiaphragmatic pressures that were 40% of maximum (Pdimax = 46.3 +/- 10.0 cm H2O) and progressive hypoxia resulting in a final arterial PO2 of 38 +/- 9 mm Hg and a phrenic vein O2 content of 1.8 +/- 1.1 mg/dl. Instead of failure associated with carbon dioxide retention and RMF, we saw a rapid decrease in tidal volume and respiratory rate, leading to apnea over 30 to 60 s while the diaphragm still responded with significant pressure generation when externally stimulated. These results suggest that respiratory muscle fatigue may not be a major factor in respiratory arrests associated with inspiratory loading and hypoxia, but that suppression of central drive, induced by the combination of inspiratory loading and hypoxemia, may be important.