Hemodynamic and respiratory concomitants of learned heart rate control during exercise

Each of three monkeys was trained to slow its heart, to exercise (lift weights), and to attenuate the tachycardia of exercise by combining these two skills. During all experiments, heart rate, stroke volume, intra-arterial blood pressure, O2 consumption, and CO2 production were recorded on a beat-to-beat basis. All animals reliably attenuated the tachycardia of exercise, indicating that this expression of central command is, at least in part, a learned motor skill. Double-product (heart rate X systolic pressure) was attenuated during combined sessions relative to exercise only sessions, and heart rate was always lower at similar levels of cardiac output, indicating that under the combined conditions, animals were performing with better cardiac efficiency at comparable levels of mechanical effort. Analyses of O2 consumption, CO2 production, and respiratory quotient (the ratio of CO2 production to O2 consumption) suggested that the animals also might have been delivering more O2 to their working muscles during combined sessions.