The Effects of Environmental Temperature, Hypoxia, and Hypercapnia on the Breathing Pattern of Saltwater Crocodiles (<i>Crocodylus porosus</i>)

Munns, Suzanne L.; Frappell, Peter B.; Evans, Barbara K.

doi:10.1086/515913

Cited by 21 publications

(10 citation statements)

References 3 publications

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“…Loss of diaphragmatic function disabled the hepatic piston pump, thus aspiration could only be achieved via alterations in intercostal or abdominal muscle activities. The resting breathing patterns of crocodiles in this study at both 20°C and 30°C, and in response to hypercapnia, were similar, both before and after surgery, to those previously measured in juvenile alligators and crocodiles under similar conditions (Farmer and Carrier, 2000c;Hartzler et al, 2006a;Munns et al, 1998;Munns et al, 2005). This suggests that the surgical intervention did not adversely alter the animals' breathing patterns, and the consistency of ventilatory and metabolic data both before and after surgery precluded the need for shamoperated controls.…”

Section: Discussionsupporting

confidence: 80%

“…similar magnitude were supported solely by increases in T I . Increases in T I reflect a delay in the centrally integrated inspiratory 'off switch' (Munns et al, 1998) and as such are unlikely to be altered by the transection of the diaphragmaticus muscle. However, increases in VT I /T I likely reflect an increase in respiratory muscle recruitment, thus increasing the rate of inspiratory airflow.…”

Section: Discussionmentioning

confidence: 99%

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

Munns

Owerkowicz

Andrewartha

et al. 2012

Journal of Experimental Biology

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SUMMARYCrocodilians 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.

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Section: Discussionsupporting

confidence: 80%

Section: Discussionmentioning

confidence: 99%

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

Munns

Owerkowicz

Andrewartha

et al. 2012

Journal of Experimental Biology

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“…In contrast to mammals, changes in breathing pattern do not appear to mediate surfactant release in lizards (69). Given that the saltwater crocodile can experience long and variable nonventilatory periods (35), breathing parameters may not be an appropriate regulator of surfactant secretion in this species.…”

Section: Development Of Surfactant Pls In Crocodilesmentioning

confidence: 97%

Control of the development of the pulmonary surfactant system in the saltwater crocodile,Crocodylus porosus

Sullivan

Orgeig

Daniels

2002

American Journal of Physiology-Regulatory, Integrative and Comp

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. Control of the development of the pulmonary surfactant system in the saltwater crocodile, Crocodylus porosus. Am J Physiol Regul Integr Comp Physiol 283: R1164-R1176, 2002. First published July 25, 2002 10.1152/ ajpregu.00009.2002.-Pulmonary surfactant is a mixture of lipids and proteins that controls the surface tension of the fluid lining the inner lung. Its composition is conserved among the vertebrates. Here we hypothesize that the in ovo administration of glucocorticoids and thyroid hormones during late incubation will accelerate surfactant development in the saltwater crocodile, Crocodylus porosus. We also hypothesize that the increased maturation of the type II cells in response to hormone pretreatment will result in enhanced responsiveness of the cells to surfactant secretagogues. We sampled embryos at days 60, 68, and 75 of incubation and after hatching. We administered dexamethasone (Dex), 3,5,3Ј-triiodothyronine (T3), or a combination of both hormones (Dex ϩ T3), 48 and 24 h before each prehatching time point. Lavage analysis indicated that the maturation of the phospholipids (PL) in the lungs of embryonic crocodiles occurs rapidly. Only T3 and Dex ϩ T3 increased total PL in lavage at embryonic day 60, but Dex, T3, and Dex ϩ T3 increased PL at day 75. The saturation of the PLs was increased by T3 and Dex ϩ T3 at day 68. Swimming exercise did not increase the amount or alter the saturation of the surfactant PLs. Pretreatment of embryos with Dex, T3, or Dex ϩ T3 changed the secretion profiles of the isolated type II cells. Dex ϩ T3 increased the response of the cells to agonists at days 60 and 68. Therefore, glucocorticoids and thyroid hormones regulate surfactant maturation in the crocodile.

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“…On the other hand, hypoxia-temperature response was described for other land vertebrates (Jackson, 1973;Kruhøffer et al, 1987;Munns et al, 1998). Little information is available on the physiological background of L. paradoxa's ability to survive different environmental conditions.…”

Section: Introductionmentioning

confidence: 99%

Combined ventilatory responses to aerial hypoxia and temperature in the South American lungfish Lepidosiren paradoxa

Silva

Giusti

Branco

et al. 2011

Journal of Thermal Biology

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The Effects of Environmental Temperature, Hypoxia, and Hypercapnia on the Breathing Pattern of Saltwater Crocodiles (Crocodylus porosus)

Cited by 21 publications

References 3 publications

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

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

Control of the development of the pulmonary surfactant system in the saltwater crocodile,Crocodylus porosus

Combined ventilatory responses to aerial hypoxia and temperature in the South American lungfish Lepidosiren paradoxa

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