THE PATTERN OF RESPIRATION WITH INCREASING METABOLISM IN A SMALL DASYURID MARSUPIAL

Previous studies have indicated that the pattern of respiration in mar supial and placental mammals may be different. Some marsupials have la rger tidal volumes and slower respiratory rates under basal conditions . This study examined the respiratory responses of a small marsupial, Dasyuroides byrnei, to increasing metabolic demand. The highest metabo lic rate elicited by cold exposure in a helium-oxygen atmosphere was 1 0.4 times the basal metabolic rate. Basal tidal volumes and respirator y rates were 138% and 46% respectively of the values predicted for pla cental mammals. The increasing oxygen demands of metabolism were met b y increases in ventilation rather than by changes in oxygen extraction . Initially, tidal volume increased until it reached a maximum value 2 .6 times that of basal tidal volume. Subsequently, ventilation was aug mented by an increase in respiratory frequency. Ventilatory accommodat ion to an increasing oxygen demand indicated that D. byrnei has an exc ellent respiratory capacity to deal with the thermogenic demands of a cold environment.