diving physiology, energetics, field metabolic rate, lung mechanics, marine mammals, pulmonary function test, spirometry, total lung capacity

We measured resting metabolic rate (RMR), tidal volume (V-T), breathing frequency (f(R)), respiratory flow, and endexpired gases in rough-toothed dolphins (Steno bredanensis) housed in managed care after an overnight fast and 1-2 hr following a meal. The measured average (+/- standard deviation) V-T (4.0 +/- 1.3 L) and f(R) (1.9 +/- 1.0 breaths/min) were higher and lower, respectively, as compared with estimated values from both terrestrial and aquatic mammals, and the average V-T was 43% of the estimated total lung capacity. The end-expired gas levels suggested that this species keep alveolar O-2 (10.6% or 80 mmHg) and CO2 (7.6% or 57 mmHg), and likely arterial gas tensions, low and high, respectively, to maximize efficiency of gas exchange. We show that following an overnight fast, the RMR (566 +/- 158 ml O-2/min) was 1.8 times the estimated value predicted by Kleiber for terrestrial mammals of the same size. We also show that between 1 and 2 hr after ingestion of a meal, the metabolic rate increases an average of 29% (709 +/- 126 ml O-2/min). Both body mass (M-b) and f(R) significantly altered the measured RMR and we propose that both these variables should be measured when estimating energy use in cetaceans.