Arrhythmic breathing in torpid pipistrelle bats, Pipistrellus pipistrellus

Abstract

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 of 11 individuals over 17 experiments, during which time 974 apneic intervals were monitored, over ambient temperatures (Ta, °C) ranging from −1 to 14 °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 °C intervals, was best described by the least squares fit regression equation: ln (apneic length in s) = 7.07−0.811 ln (Ta + 1), ( r 2 = 0.96, P < 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 °C intervals, was best described by the least squares fit regression equation: ƒ = 0.812 + 0.499 Ta ( r 2 = 0.92, P < 0.01). Using previously published values for O 2 consumption (V̇ O 2 ) in torpid pipistrelles, and tidal volume and O 2 extraction efficiency at 4 °C in torpid bats of the same mean size (6.2 g), we calculated that at 4 °C ventilation would, on average, supply only 14.2–21.3% of V̇ O 2 . This suggests that in torpid pipistrelles the glottis may remain open during apnea, allowing a significant diffusive influx of O 2 into the lungs.