The purpose of this study was to describe an animal model to test the relationships among the cardiovascular, pulmonary, and somatomotor command systems during exercise. Using operant conditioning, three chronically chaired monkeys (Macaca mulatta) were trained to exercise (to lift weights repeatedly), to attenuate their heart rate responses, and finally, both conditions were combined so that the animals were required to exercise and attenuate their heart rates. Heart rate, systolic and diastolic blood pressure, rate-pressure product, O2 and CO2 concentration in expired air, and number of weight lifts were recorded and compared between the two conditions, i.e., exercise only and combined exercise and heart rate slowing. In all animals heart rate increases in response to exercise were significantly less (P less than 0.05) during combined conditions than during exercise only: the mean heart rate increase was 41 beats/min less during combined sessions than during exercise only sessions for monkey 1, 13.5 beats/min less for monkey 2, and 9 beats/min less for monkey 3. Rate-pressure product showed a consistent difference across animals paralleling the heart rate differences. This acquired response did not involve other cardiovascular and pulmonary parameters, which did not change systematically across animals. However, the pattern of cardiovascular reactivity in relation to O2 consumption (linear regression of heart rate and systolic or diastolic blood pressure on change in O2 consumption over many experiments) was attenuated during combined sessions relative to exercise only experiments. The relative attenuation of heart rate during combined sessions also remained significant when both experimental conditions were equated on the basis of work done. Therefore, this animal model shows a dissociation of cardiovascular, somatomotor, and pulmonary effects of central command.
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ABSTRACT This paper discusses the inherent discrepancy between the mean heart rate computed from a series of cardiotachometer data points and the true average heart rate. A mathematical proof that the mean cardiotachometer rate always exceeds the true when individual beats are sampled in the presence of variability is given. Examples which illustrate the magnitude of the discrepancy also are presented.
To identify the brain areas involved in central command, four monkeys were trained to attenuate the tachycardia of exercise while different brain sites affecting heart rate (HR) were simultaneously stimulated electrically. Among 24 brain sites located mostly in the limbic structures, we have identified four types of control systems that mediate cardiovascular and motor behavior during exercise. One system increases HR equivalently during both exercise and operantly controlled HR, whereas another increases HR during both tasks and abolishes operant HR control. In the third system, the effect of brain stimulation on HR is attenuated during exercise and during exercise with operantly controlled HR. The fourth system increases HR in both tasks, but its effect is significantly attenuated during operant HR control. We believe that this last system, which includes the mediodorsal nucleus, nucleus ventralis anterior, and cingulate cortex, plays a significant role in central command.
Beat-to-beat heart periods and intra-arterial blood pressures were monitored continuously for 18 h in each of six monkeys over periods of several weeks. Means, based on 128-s averages of these functions, were highly correlated during early evening and daytime periods; however, heart period was poorly correlated with blood pressure during the evening hours, although systolic and diastolic pressures were highly correlated, and the standard deviations of heart period also were highly correlated with the pressures. These shifts in cardiovascular integration were unexpected and suggest that the circulation is relatively sensitive to the conditions under which it is being assessed, and they suggest further that response relationships observed under one set of conditions may not be comparable to those measured under another set of conditions.
