Scaling respiratory pattern and respiratory 'drive'.

We tested three predictions regarding the relationship between body size and respiratory 'drive' and timing in mammals. Mechanical considerations had led to the prediction that TE/TTOT and probably TI/TTOT would be interspecific constants. In eleven species of mammals, ranging in size from 0.033 kg to 520 kg, TE/TTOT during awake quiet breathing was an interspecific constant with a value of 0.65 (+/- 0.004); TI/TTOT was 0.345 (+/- 0.004). Given that VT is directly proportional to BW1.0 (Stahl, 1967), if TE and TI are directly proportional to BW0.28 (Bennett and Tenney, 1982), and if VT/TI is an index of respiratory 'drive', then 'drive' should be directly proportional to BW0.72, following the same proportionality with body size as does basal metabolic rate (VO2). Data for the same eleven species gave the relationship VT/TI BW0.74. Testing further the notion that 'drive', on a weight specific basis, is proportional to BW-0.26, we studied the response, % delta VI, in eleven species to approximately 12% inspired O2. This 'output' of the system in response to a hypoxic stimulus was found to scale with BW-0.27. The question whether this reflects a higher set 'gain' of the respiratory controller of smaller animals and/or some feature of the innervation, or intrinsic properties of the respiratory muscles that varies with body size is discussed.