The relationship between body mass and ventilation rate in mammals.

The resting, specific metabolic rate (rate per unit mass) and rate of oxygen consumption increase with decreasing body mass in mammals (see SchmidtNielson, 1984, for a review). Since lung volume is linearly related to body mass (Tenney and Remmers, 1963), the increased demand for oxygen in small mammals is met by an increase in ventilation rate, rather than by an increase in respiratory volume. The study most frequently cited which relates resting ventilation rate to body mass is that of Stahl (1967). In the course of completing an earlier project (Altringham and Young, 1991), we had reason to look at Stahl's paper in some detail, and identified a number of potential problems, which cast some doubt on the value of the results. Stahl used data from the literature in determining this relationship, and a study of the source material shows that the physiological state of the animals is very variable. The measurements are incidental to other studies, some animals are restrained, in others breathing was measured by invasive methods, and the variation in resting ventilation rate is often very large. No graph is provided, few raw data are included, and it is unclear what size range of mammals was investigated. We felt that it would be worthwhile to determine specifically the relationship between resting ventilation rate and body mass in as wide a size range of mammals as possible (tree shrew to elephant) using the same, non-invasive technique on all animals. A VHS camcorder, powered by rechargeable batteries, was used to film respiratory movements of resting animals. Ventilation rates were determined by timing respiratory movements during playback of the tapes at normal or reduced speeds. To check the consistency of recording and playback, a stop-watch was filmed over a period of 50min. The discrepancy on playback was never greater than ± l s over the 50-min period. The work was carried out largely on mammals at Chester Zoo, and a number of pets and laboratory mammals. AU test animals were healthy adults, both males and females. Animals were filmed, with minimal disturbance, mainly when standing, but occasionally when sitting or lying upright. No significant differences