Cardiodynamic adaptive mechanisms of two kinds of stress in right and left ventricles of rat heart

definition of stress according to Selye is, ...the rate of wear and tear in the body " (42). Selye's ideas are expressed in a model of a general adaptation to the environment mediated by individual organs, particularly those of the nervous and endocrine systems. Adaptation is defined in the context of acclimatization; that is, an individual organism exhibits physiological and/or anatomical adjustments to a change in its immediate environment. Three levels of the stress syndrome are the alarm reaction, resistance, and exhaustion. Couched in different terminology, Ursin, Evind, and Seymour (49) view stress as a type of coping which is defined as advantageous changes in behavior or physiological responses to noxious or adverse stimulation. In their model, stress is viewed in the context of problem solving. Two kinds of adverse stimulation that have been studied at length are exposure to hypoxia and exercise. In both situations, the circulatory system demonstrates adaptation to the stressors.

In the case of chronic adaptation to hypoxia, well described changes include increases in hematocrit, hemoglobin, RBC coimt, O2 carrying capacity and specific gravity of the blood, and total blood volume (50). Pulmonary hypertension and right ventricular hypertrophy also develop. Chronic adaptation to exercise, on the other hand, has been observed to result in an increased capillary density in skeletal and cardiac muscle, increased heart volume and weight, increased blood volume and cardiac output during maximal work, and increased stroke volume during rest, submaximal, and maximal work (5). Other increases have been observed in maximal oxygen uptake and blood lactate tolerance during maximal work. Decreases have been noted in heart rate at rest and during submaximal work. Other decreases have been found in oxygen uptake and blood lactate at given submaximal work loads.