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 × 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.