Arrhythmic breathing in torpid pipistrelle bats, Pipistrellus pipistrellus

The arrhythmic breathing pattern of torpid female pipistrelle bats (Pipistrellus pipistrellus) was monitored using Doppler radar. A total of 98 h of radar measurements were made on 11 individuals over 17 experiments, during which time 974 apneic intervals were monitored, over ambient temperatures (Ta, degrees C) ranging from -1 to 14 degrees C, and body masses ranging from 4.6 to 7.4 g. As Ta declined, a greater proportion of all breaths occurred in discrete breathing bouts. Apneic intervals lengthened at lower Ta, but were not related to body mass. Mean apneic length, averaged over 1 degree C intervals, was best described by the least squares fit regression equation: ln (apneic length in s) = 7.07-0.811 ln (Ta + 1), (r2 = 0.96, P less than 0.01). Ventilation frequency (breaths.min-1), averaged over a breathing bout and the subsequent apnea, increased as Ta increased, and was not related to body mass. Mean ventilation frequency (f), averaged over 1 degree C intervals, was best described by the least squares fit regression equation: f = 0.812 + 0.499 Ta (r2 = 0.92, P less than 0.01). Using previously published values for O2 consumption (VO2) in torpid pipistrelles, and tidal volume and O2 extraction efficiency at 4 degrees C in torpid bats of the same mean size (6.2 g), we calculated that at 4 degrees C ventilation would, on average, supply only 14.2-21.3% of VO2. This suggests that in torpid pipistrelles the glottis may remain open during apnea, allowing a significant diffusive influx of O2 into the lungs.