Oxygen Transport by the Circulatory System of the Green Iguana (Iguana Iguana) at Different Body Temperatures

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Abstract
Oxygen consumption, stroke volume, heart rate and the difference in oxygen contents of arterial and venous blood (AV difference) were measured in the resting iguana at body temperatures of 20, 30 and 38° C. Oxygen consumption increased by a factor of 4·4 as temperature changed from 20 to 38° C. This increase was accomplished by a decrease in stroke volume by a factor of 0·5, and increases in heart rate and A V difference by factors of 4-1 and 2-2, respectively. During activity increases in oxygen consumption at a given temperature were accompanied by increases in heart rate and A V difference, but stroke volume did not change consistently. The percentage saturation of arterial blood with oxygen in the iguana may differ in the right and left systemic arches. In some lizards, both arches carried equally saturated blood, but in others the left arch carried blood containing less oxygen than the right arch. An hypothesis is presented concerning the function of the double systemic arches and incompletely divided ventricles of lizards. These structures may be a device for permitting increased cardiac output associated with thermoregulation to bypass the lungs while maintaining a supply of well-oxygenated blood to the head. Data on oxygen capacity, percentage saturation of blood with oxygen, haematocrit and pH of iguana blood are included in this study. This study was supported by a National Science Foundation Postdoctoral Fellowship. I am indebted to Prof. W. R. Dawson, who provided laboratory facilities and advice to make this study possible.