Two Experiments In Animal Physiology Involving The Use Of The Treadmill: A Comparison Of The Rectal And Internal Carotid Temperatures Measured Simultaneously At Ambient Temperatures Of 25C And 35C And Evaporative Heat Loss In Exercising Dogs: The Effects Of Ambient Temperature, Workload, And Dehydration

In recent years, the use of the treadmill to simulate exercise for diagnostic purposes has increased along with the interest in physical activity for many Americans. The treadmill is very useful equipment because the experimenter can conveniently gather data. Both speed and slope can be changed to provide varying work loads. It is relatively inexpensive and uses little space. This thesis reports two separate experiments involving the use of the treadmill. Dogs were used as the subjects. In many studies a change in rectal temperature is used as a measure of the animal\u27s response to varying physical conditions. Rectal temperature is most often used because it is so easy to obtain. The value of rectal temperature versus deep body temperature as an indicator of the dog\u27s physiological response is the subject of the first experiment It would seem that temperatures measured in the deep body would be of greater value to scientists studying physiological responses of the body to exercise but are much more difficult to obtain. The second experiment showed the relationship of the amount of heat lost due to evaporation by panting in exercising dogs in normal and dehydrated states. For effective body temperature regulation, heat loss must equal heat production. The main source of heat is the result of metabolism, and physical exercise can increase the basal metabolic rate over 24 times (3). Of the four main avenues for heat dissipation (conduction, convection, radiation, and evaporation), evaporation is the most efficient during exercise. In man, the evaporation is carried out by the sweating mechanism, while the dog\u27s main avenue of heat dissipation is through the respiratory system (panting) and not by sweating. In man, equilibrium levels of rectal temperature (T ) during exercise are significantly correlated with concomitant plasma (Na+) and osmotic concentrations, but they are apparently unrelated to variations in plasma volume by inference from changes in plasma colloid osmotic pressure (14) , from plasma protein concentrations (4), or calculated from the hematocrit (6). This ion-osmotic factor appears to act by influencing sweating; the sweat rate is inversely proportional * to the serum osmotic concentrations (5) and to the change in osmolality (16). Neilsen (13) suggests that the hyperthermic effect of increased plasma osmolality is due to the sodium ion. However, in experiments carried out on human subjects, it is difficult to determine whether the postulated ion osmotic effect acts peripherally on the sweat glands (5), on the central nervous system temperature centers (13), or at both sites. It has been shown that regulatory sweating is a linear function of mean skin and body core temperatures when exercise is performed continuously in the upright position and equilibrium conditions are attained (3). The failure of skin and core temperatures to predict sweating during intermittent exercise (1), work in the supine position (8), at altitude (7), during negative work-walking downhill (12, 17), and during thermal transients suggests that there are factors other than skin or core temperatures important in this control system. It has been shown that sodium and calcium ions injected into cerebral ventricles can change body temperature (11). Greenleaf et al. (9) infused NaCl solutions of various concentrations in dogs at rest and during moderate exercise on a treadmill. They found that infusions of hypertonic solutions either before or during exercise resulted in elevated plasma Na+ and osmotic concentrations and produced higher equilibrium levels of T during exercise but not at rest. Water consumption during exercise decreased plasma \u27 Na+ concentration, osmolality, and the equilibrium level of Tr to control levels. From this study it was concluded that the exercise T^ responses of the dog respond quantitatively like man to elevated plasma Na+ concentration and osmolality but it is not related to changes in plasma volume. Also, water intake significantly reduced the ion-osmotic hyperthermia. In a study by Grande (2), it was shown that the elevation of T^ during exercise above the control value begins only after a certain negative water balance has been reached. The sweat rate appeared to decrease in a linear way as soon as the negative water balance develops. Thus, it appears that the response of the sweating mechanism decreases as dehydration progresses. The problem focused on the measurement of the change in relative humidity. The difference between atmospheric air and the expired air from the exercising dog was used as a measure of evaporative heat loss. If the difference in dehydrated animals was less than that of normally hydrated animals, this would support the observations stated above. That is, with loss of water, the Na+ concentration and osmolality increase and the sweat rate decreases