Scaling respiratory pattern and respiratory ‘drive’

Abstract

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 Te ∝ BW 1.0 (Stahl, 1967), if Te and Ti are ∝ BW 0.28 (Bennett and Tenney, 1982), and if Vt/ Ti is an index of respiratory ‘drive’ should be ∝ BW 0.72, following the same proportionality with body size as does basal metabolic rate (V̇ O 2 ). Data for the same eleven species gave the relationship Vt/ Ti ∝ BW 0.74. Testing further the notion that ‘drive’, on a weight specific basis, is proportional to BW −0.26, we studied the response, %ΔV̇ i, in eleven species to approximately 12% inspired O 2. 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.