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The accessory role of the diaphragmaticus muscle in lung ventilation in the estuarine crocodile Crocodylus porosus

journal contribution
posted on 2023-05-17, 10:46 authored by Munns, SL, Owerkowicz, T, Sarah AndrewarthaSarah Andrewartha, Peter FrappellPeter Frappell
Crocodilians use a combination of three muscular mechanisms to effect lung ventilation: the intercostal muscles producing thoracic movement, the abdominal muscles producing pelvic rotation and gastralial translation, and the diaphragmaticus muscle producing visceral displacement. Earlier studies suggested that the diaphragmaticus is a primary muscle of inspiration in crocodilians, but direct measurements of the diaphragmatic contribution to lung ventilation and gas exchange have not been made to date. In this study, ventilation, metabolic rate and arterial blood gases were measured from juvenile estuarine crocodiles under three conditions: (i) while resting at 30°C and 20°C; (ii) while breathing hypercapnic gases; and (iii) during immediate recovery from treadmill exercise. The relative contribution of the diaphragmaticus was then determined by obtaining measurements before and after transection of the muscle. The diaphragmaticus was found to make only a limited contribution to lung ventilation while crocodiles were resting at 30°C and 20°C, and during increased respiratory drive induced by hypercapnic gas. However, the diaphragmaticus muscle was found to play a significant role in facilitating a higher rate of inspiratory airflow in response to exercise. Transection of the diaphragmaticus decreased the exercise-induced increase in the rate of inspiration (with no compensatory increases in the duration of inspiration), thus compromising the exercise-induced increases in tidal volume and minute ventilation. These results suggest that, in C. porosus, costal ventilation alone is able to support metabolic demands at rest, and the diaphragmaticus is largely an accessory muscle used at times of elevated metabolic demand.

History

Publication title

Journal of Experimental Biology

Volume

215

Issue

5

Pagination

845-852

ISSN

0022-0949

Department/School

Tasmanian Institute of Agriculture (TIA)

Publisher

Company Of Biologists Ltd

Place of publication

140 Cowley Rd, Cambridge, CB4 0DL, UK

Rights statement

Copyright 2012 The Company of Biologists Ltd.

Repository Status

  • Restricted

Socio-economic Objectives

Coastal or estuarine biodiversity

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