Like many mammalian heterotherms, the big brown bat, Eptesicus fuscus, breathes intermittently during torpor. By exploiting this bat's preference to roost in crevices, we could separately measure O2 uptake during ventilatory bouts and apneic periods using a flow-through metabolic chamber with a small dead space volume and short time constant. Oxygen uptake was measured during apneas ranging from 10 to 150 min duration at body temperatures of 20, 10 and 5 degrees C. The fraction of total O2 uptake acquired during apnea was 0.26 +/- 0.03 (9), 0.54 +/- 0.10 (5) and 0.35 +/- 0.04 (3) for body temperatures of 20, 10 and 5 degrees C, respectively. Cardiogenic pulsations during apnea visible on plethysmographic pressure traces and theoretical calculations of airway and cutaneous diffusion potentials support the notion that apneic O2 uptake occurs down an open airway by both diffusion and bulk convection.

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