Respiration Physiolog); 89 (1992) 147-155 O 1992 Elsevier Science Publishers B.V. All rights reserved. 0034-5687/92/$05.00 147 RESP 01931 Respiratory mechanics of the coatimundi and woodchuck Dona F. Boggs a and Charles G. Irvin b aDi~,ision of Biological Sciences. Uni~,ersiO, of Montana. Missoula. Monmm~. and b Di~,isio, of Pulmonary Sciences. Departme, t of Medic#w. National Jewish Centerfor bm,tmology a,d Respiratory Medici~w a,d U, iversiO, of Colorado Health Science Center. Dem,er. Colorado. USA (Accepted 13 April 1992) Abstract. The coatimundi breathes with a large tidal volume and relatively short TE/TTOT while the wood- chuck has a relatively long TE/TTOT compared to other mammals. Hence, the respiratory mechanics of the coatimundi and woodchuck were studied to determine whether mechanics play any role in the differences in breathing pattern observed in these two mammals of similar body size. Although static respiratory sys- tem compliance was less and lower airway resistance was greater in the woodchuck compared to the coati there was no significant difference in deflationary time constant that could contribute to the difference in expiratory time. Both species exhibit less compliant chest walls than would be predicted for animals this size (4.5 and 5 kg) and the coati lung compliance is greater than that of the woodchuck or the prediction. The large tidal volume in the coati may be attributed in part to the large lung volume of this species (2.2 times the allometric prediction). The differences in breathing pattern are more likely related to differences in the control of breathing (i.e. regulation of expiratory airflow and inspiratory onset) than to differences in res- piratory mechanics. Mammals, coatimundi: Mammals, woodchuck: Mechanics of breathing, coatimundi t,s woodchuck; Pattern of breathing, respiratory mechanics (coatimundi t:~, woodchuck) The pattern of the respiratory cycle of a given animal is the result of a complex interaction of the integrated output of the central control network directing the respi- ratory pump, and the mechanical characteristics of that pump. Bennett and Tenney (1982) suggested that passive respiratory mechanics play a major role in determining expiratory time (TE) and total breath time (TTOT) during quiet breathing. Boggs and Tenney (1984)subsequently demonstrated that the ratio of TE/TTOT is, as predicted from mechanical considerations, an interspecific constant with a value of 0.65 during awake quiet breathing in eleven species ranging in size from 0.03 to 520 kg. However, quiet expiration is not strictly a passive relaxation, but may be slowed by laryngeal and diaphragmatic 'braking' mechanisms, as observed in the cat and human (Gautier et al., Correspondence to: D. F. Boggs, Division of Biological Sciences, University of Montana, Missoula, Montana 59812, USA.