Abstract
During walking and running in human, evidence for the synchronization between cardiac and locomotor rhythm (CLS) has been demonstrated, but direct evidence showing the functional significance of such coordination has not yet been presented. One of explanations for the functional significance of CLS is enhancing cardiovascular efficiency. During locomotion, increased muscle tension produces an elevation of intramuscular pressure (IMP), and this often exceeds systolic pressures. Therefore, it is likely that the locomotor activity periodically occludes blood flow through active muscles. If the peak of IMP during locomotor activity were not to occur when the arterial pressure was highest the reduction of cardiac afterload and therefore ensuring of blood flow for active muscles would be expected. In the present investigation, I tested this hypothesis in nine healthy subjects by simulating the rhythmic IMP change using computer-controlled dynamic thigh cuff occlusion device. Alternate dynamic occlusions of bilateral thigh cuff administered at the frequency of mean heart rate produced the significant phase synchronization between heartbeat and occlusion rhythm. Heartbeats were most likely to occur at phases where the peak systolic pressure was not overlapped with the elevation of cuff pressure. These locking phases were comparable to those observed when walking cadence was voluntarily synchronized with mean heart rate. The results suggest that CLS may be associated with improving perfusion from heart to exercising muscles. [Jpn J Physiol 54 Suppl:S238 (2004)]
