Cardiac cycle-synchronized electrical muscle stimulator for lower limb training with the potential to reduce the heart's pumping workload

Abstract

BackgroundThe lower limb muscle may play an important role in decreasing the heart’s pumping workload. Aging and inactivity cause atrophy and weakness of the muscle, leading to a loss of the heart-assisting role. An electrical lower limb muscle stimulator can prevent atrophy and weakness more effectively than conventional resistance training; however, it has been reported to increase the heart’s pumping workload in some situations. Therefore, more effective tools should be developed.MethodsWe newly developed a cardiac cycle-synchronized electrical lower limb muscle stimulator by combining a commercially available electrocardiogram monitor and belt electrode skeletal muscle electrical stimulator, making it possible to achieve strong and wide but not painful muscle contractions. Then, we tested the stimulator in 11 healthy volunteers to determine whether the special equipment enabled lower limb muscle training without harming the hemodynamics using plethysmography and a percutaneous cardiac output analyzer.ResultsIn 9 of 11 subjects, the stimulator generated diastolic augmentation waves on the dicrotic notches and end-diastolic pressure reduction waves on the plethysmogram waveforms of the brachial artery, showing analogous waveforms in the intra-aortic balloon pumping heart-assisting therapy. The heart rate, stroke volume, and cardiac output significantly increased during the stimulation. There was no change in the systolic or diastolic blood pressure during the stimulation.ConclusionCardiac cycle-synchronized electrical muscle stimulation for the lower limbs may enable muscle training without harmfully influencing the hemodynamics and with a potential to reduce the heart’s pumping workload, suggesting a promising tool for effectively treating both locomotor and cardiovascular disorders.

Association between skeletal muscle and left ventricular mass in patients with hyperthyroidism

“…The muscles in the lower limbs, for example, help propel deoxygenated blood towards the heart and assist in the dilation and filling of capillaries, thereby enhancing cardiac pumping capacity. Therefore, sarcopenia and muscle weakness caused by hyperthyroidism may increase the workload on the heart and worsen the condition of cardiovascular diseases ( 19 ). Additionally, another study has shown that treatment methods involving electrical stimulation of the lower limbs to induce muscle contractions can effectively improve flow-mediated dilation in patients with chronic heart failure ( 20 ).…”

“…The muscles in the lower limbs, for example, help propel deoxygenated blood towards the heart and assist in the dilation and filling of capillaries, thereby enhancing cardiac pumping capacity. Therefore, sarcopenia and muscle weakness caused by hyperthyroidism may increase the workload on the heart and worsen the condition of cardiovascular diseases (19).…”