Elevated intra-abdominal pressure limits venous return during exercise in Varanus exanthematicus

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High gestational loads have been associated with a range of ecological costs, such as decreased locomotor ability; however, the physiological mechanisms that underpin these changes are poorly understood. In this study, breathing patterns, metabolic rates, lung volume and lung diffusing capacity were measured at rest and during exercise in the pregnant skink Tiliqua nigrolutea. Breathing patterns were largely unaffected by gestation; however, decreases in metabolic rate (rate of oxygen consumption) in the late stages of pregnancy induced a relative hyperventilation. The reductions in metabolic rate during late pregnancy prevent the calculation of the maintenance cost of pregnancy based on post-partum and neonatal metabolic rates. Despite the high relative litter mass of 38.9±5.3%, lung diffusing capacity was maintained during all stages of pregnancy, suggesting that alterations in diffusion at the alveolar capillary membrane were not responsible for the relative hyperventilation. Lung volume was increased during pregnancy compared with non-pregnant females, but lung volume was significantly lower during pregnancy compared with post-partum lung volume. Pregnant females were unable to produce the same metabolic and ventilatory changes induced by exercise in nonpregnant females. This lack of ability to respond to increased respiratory drive during exercise may underpin the locomotor impairment measured during gestation in previous studies.

Section: Discussionsupporting

confidence: 72%

Section: Measurement Of Lung Ventilation and Gas Exchangementioning

confidence: 99%

Pregnancy limits lung function during exercise and depresses metabolic rate in the skink Tiliqua nigrolutea

Munns

Edwards

Nicol

et al. 2015

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“…Surgical procedure, blood flow, intra-abdominal pressure and blood pressure The surgical procedures used in this study are presented in detail for Savannah monitor lizards (Varanus exanthematicus) in Munns et al (2004) and are briefly described below. Alligators were lightly anesthetized by placing them in a sealed container with gauze dampened with isofluorane (Isoflo; Abbott Laboratories, North Chicago, IL, USA).…”

Section: Methodsmentioning

confidence: 99%

Terrestrial locomotion does not constrain venous return in the American alligator,Alligator mississippiensis

Munns

Hartzler

Bennett

et al. 2005

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SUMMARY The effects of treadmill exercise on components of the cardiovascular(heart rate, mean arterial blood pressure, central venous pressure, venous return) and respiratory (minute ventilation, tidal volume, breathing frequency, rate of oxygen consumption, rate of carbon dioxide production)systems and on intra-abdominal pressure were measured in the American alligator, Alligator mississippiensis, at 30°C. Alligators show speed-dependent increases in tidal volume and minute ventilation,demonstrating that the inhibition of ventilation during locomotion that is present in some varanid and iguanid lizards was not present in alligators. Exercise significantly increases intra-abdominal pressure; however,concomitant elevations in central venous pressure acted to increase the transmural pressure of the post caval vein and thus increased venous return. Therefore, despite elevated intra-abdominal pressure, venous return was not limited during exercise in alligators, as was the case in Varanus exanthematicus and Iguana iguana. Respiratory cycle variations in intra-abdominal pressure, central venous pressure and venous return indicate that, at high tidal volumes, inspiration causes a net reduction in venous return during active ventilation and thus may act to limit venous return during exercise. These results suggest that, while tonically elevated intra-abdominal pressure induced by exercise does not inhibit venous return,phasic fluctuations during each breath cycle may contribute to venous flow limitation during exercise.

“…More specifically, regions of the lung may be compressed or collapse as a result of the expansion of the ovarian follicles during reproduction and the distention of the stomach following ingestion, thereby limiting tidal volume and hence the respiratory fraction of fresh, oxygen-rich air in contact with the respiratory surfaces (Munns and Daniels, 2007). In addition to altered ventilation patterns, the combination of intense physical activity, enlarged ovarian follicles and the distention of the stomach may increase intra-abdominal pressure in T. marcianus sufficiently to reduce blood flow through the inferior vena cava, thereby limiting venous return and constraining maximal levels of cardiac output (Farmer and Hicks, 2000;Munns et al, 2004).…”

Section: Post-prandial Exhaustive Activitymentioning

confidence: 99%

Patterns of oxygen consumption during simultaneously occurring elevated metabolic states in the viviparous snake,Thamnophis marcianus

Jackson

Leu

Ford

et al. 2015

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Snakes exhibit large factorial increments in oxygen consumption during digestion and physical activity, and long-lasting sub-maximal increments during reproduction. Under natural conditions, all three physiological states may occur simultaneously, but the integrated response is not well understood. Adult male and female checkered gartersnakes (Thamnophis marcianus) were used to examine increments in oxygen consumption (i.e. V O2 ) and carbon dioxide production (i.e. V CO2 ) associated with activity (Act), digestion (Dig) and post-prandial activity (Act+Dig). For females, we carried out these trials in the non-reproductive state, and also during the vitellogenic (V) and embryogenic (E) phases of a reproductive cycle. Endurance time (i.e. time to exhaustion, TTE) was recorded for all groups during Act and Act +Dig trials. Our results indicate that male and non-reproductive female T. marcianus exhibit significant increments in V O2 during digestion (∼5-fold) and activity (∼9-fold), and that Act+Dig results in a similar increment in V O2 (∼9-to 10-fold). During reproduction, resting V O2 increased by 1.6-to 1.7-fold, and peak increments during digestion were elevated by 30-50% above non-reproductive values, but values associated with Act and Act+Dig were not significantly different from non-reproductive values. During Act+Dig, endurance time remained similar for all of the groups in the present study. Overall, our results indicate that prioritization is the primary pattern of interaction in oxygen delivery exhibited by this species. We propose that the metabolic processes associated with digestion, and perhaps reproduction, are temporarily compromised during activity.