HOW STIFF IS THE ARMADILLO - A COMPARISON WITH THE ALLOMETRICS OF MAMMALIAN RESPIRATORY MECHANICS

Static respiratory mechanics were examined in the armadillo (Dasypus n ovemcinctus) and compared with allometric relationships newly derived for adult mammals from values in the literature. Normalised by body we ight, chest wall compliance (Cw) in the armadillo is lower than predic ted. Lung compliance (Cl) is also low in the armadillo, however it is appropriately matched to the resting lung volume (Vr) (ie. Cl/Vr propo rtional to Mass(0.0)) and the ratio of Cw/Cl is appropriate for the si ze of the animal. Respiratory system resistance is high in the armadil lo, presumably because of smaller airways associated with the small lu ng. The power of breathing in the armadillo is comparatively high, mai nly due to the high resistive forces. Indeed, the oxidative cost of br eathing is approximately double that of a mammal with similar Vr. Hypo xia or hypercapnia are known to invoke an attenuated ventilatory respo nse in the armadillo and one that relies more on changes in frequency rather than volume. While such a breathing pattern helps to reduce the power of breathing it also compromises the degree of hyperventilation achieved. (C) 1998 Elsevier Science B.V. All rights reserved.