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First published online August 18, 2005
Journal of Experimental Biology 208, 3331-3339 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01758

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

Suzanne L. Munns^*, Lynn K. Hartzler, Albert F. Bennett and James W. Hicks

Department of Ecology and Evolutionary Biology, University of California, 321 Steinhaus Hall, Irvine, CA 92697, USA

View larger version (28K): [in a new window]   Fig. 1. A sample recording of the variations in intra-abdominal pressure (IAP), central venous pressure (CVP) and total post caval vein blood flow (PC) during ventilation (A) at rest and (B) running at 1.0 km h–1. During expiration (Exp), IAP falls to near atmospheric pressure, and PC increases. Peak IAP and CVP and minimum PC occur at the end of inspiration (Insp). Inspired tidal volume was twofold higher during exercise (46.23 ml kg–1) compared with rest (24.68 ml kg–1). Buccal oscillations (movement of air in and out of the buccal region) occur in alligators but do not contribute to gas exchange. Data are from one alligator (mass 3.6 kg) and are representative of the trend in all alligators tested. Scale bar in A, 15 s; B, 5 s.

View larger version (21K): [in a new window]   Fig. 2. Inferior vena cava flow (PC) and intra-abdominal pressure (IAP) vary during each breathing cycle. (A) Increasing inspired tidal volumes (open diamonds) correlate with decreasing PC (r2=–0.71, P<0.0001). Expiration (filled diamonds) causes an increase in PC but the magnitude of the increase does not correlate with increasing tidal volumes (r2=–0.15, P=0.33). (B) The sum of the inspiratory and expiratory alterations results in no net change in total PC (open squares) during the breath cycle at low tidal volumes and a net decrease at high tidal volumes. As a result, increasing tidal volumes are correlated with a net decrease in total PC (r2=–0.57, P<0.0001). IAP (filled squares) is positively correlated with increments in tidal volume (r2=0.72, P<0.0001). Data presented are 50 consecutive breaths from the recovery period post-exercise in one representative alligator (mass 3.55 kg). PC was calculated as the change relative to the preceding non-ventilatory period. 1 mmHg=133.3 Pa.

View larger version (33K): [in a new window]   Fig. 3. Dynamic changes in post caval flow (PC; ml min–1 kg–1) during treadmill exercise and during the first 10 min of recovery. PC increases during treadmill exercise; however, there was no correlation between treadmill speed and magnitude of the PC change. Maximal PC was achieved 20 s after the onset of exercise at 0.75 km h–1, and 40 s after the onset at both 1.0 and 1.5 km h–1 (paired Dunnett's test). PC was still significantly elevated (relative to rest) during the 10th minute after all treadmill speeds. Data presented are means ± S.E.M. for 10 s intervals (N=5). Open symbols represent rest; black symbols represent exercise; grey symbols represent recovery from exercise.

View larger version (17K): [in a new window]   Fig. 4. Heart rate (fH), mean arterial blood pressure (MAP), central venous pressure (CVP) and intra-abdominal pressure (IAP) increase during treadmill exercise. White bars indicate rest, black bars indicate exercise and grey bars indicate recovery period (first 2 min). Data presented are means ± S.E.M. (N=5). * indicates a significant difference relative to rest (paired Dunnett's test, P<0.05). 1 mmHg=133.3 Pa.

View larger version (10K): [in a new window]   Fig. 5. The effect of exercise on inferior vena cava transmural pressure (PTRANS) and % change in inferior vena cava blood flow relative to rest (PC). Open symbols represent rest; black symbols represent exercise; grey symbols represent recovery from exercise. Data presented are means ± S.E.M. (N=5) for each treadmill speed (a, b and c represent 0.75, 1.0 and 1.5 km h–1, respectively). All exercise and recovery values for PC(*) and PTRANS() were significantly different relative to rest (paired Dunnett's test, P<0.05).

View larger version (20K): [in a new window]   Fig. 6. Inspired tidal volume, breathing frequency, minute ventilation, rate of oxygen consumption (O2) and rate of carbon dioxide production (CO2) increase in response to treadmill exercise. White bars indicate rest, black bars indicate exercise and grey bars indicate recovery period (first 2 min). Increases in both minute ventilation and inspired tidal volume correlate with increases in treadmill speed (r2=0.49, P=0.033; r2=0.47, P=0.041, respectively); however, increases in breathing frequency, O2 and CO2 did not correlate with increases in treadmill speed (r2=0.012, P=0.78; r2=0.011, P=0.78, r2=0.174, P=0.26, respectively). Data presented are means ± S.E.M. (N=5). * indicates a significant difference relative to rest (paired Dunnett's test, P<0.05).

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