Review Article

Cardiovascular Adaptations to Upright and Supine Prolonged Exercise: Heart Rate Modulation as a Factor of Cardiovascular Drift

Author: Luna Rizzo

The interactive effects of posture and exercise on cardiovascular drift remain controversial despite scientists have conducted extensive studies addressed to this topic. For example, changes in posture at rest are associated with significant changes in Left Ventricular (LV) filling and Stroke Volume (SV). A transition from the supine to the upright position produces a decrease in LV end-diastolic pressureand volumeand SV [1,2]. The results of previous studies of the alterations in LV end-diastolic volume during exercise in the supine position have varied [3]. There is general theory that end-systolic volume is smaller during exercise than at rest [3], most scientists have observed an exercise-induced increase in SV, although others have not [1]. LV stroke volume increases markedly during the transition from rest to exercise in the upright position and is almost as great as during supine exercise [1]. It has been found that, after exercise, the Heart Rate (HR) changes showing an initial dramatic decrease followed by a gradual decrease to a steady state level, which maintains itself elevated above the level of preexercise baseline for a period relatively extended [4]. Many studies have reported that when generally the body position changes from upright to supine, cardiac sympathetic nerve activity decreases while vagus nerve activity increases[5]. If, during recovery from exercise, a reciprocal change in the activity of the two autonomic nervous system divisions occurs, a decrease of post-exercise HR elevation would be stimulated by the supine position via a prevalence of vagus nerve activity, compared to the upright position. The gravitational force plays an important role on the transition from the supine to the upright position. In fact, the distribution of blood volume in the body is markedly influenced by this force. It has been observed that, adjustments of arterial blood pressure to compensate the postural perturbation, are achieved in a complex manner through a number of reflex mechanisms [6]. Recent studies have reported that, effects of post-exercise include a reduction in arterial blood pressure, are related to body position4. However, mechanisms involved in the post-exercise hypotension and why this event occurs, remain unclear so far. This could be addressed to body position differences, i.e. supine and sitting, during the period after exercise. To date, several studies have been conducted on this argument to ascertain and clarify what mechanisms are responsible and involved in the cardiovascular drift responses to posture changes. Certain mechanisms remain still unclear despite few attempts have been made to evaluate different theories on these. The purpose of the present manuscript is to discuss and try to clarify how a change in posture affects the cardiovascular responses during recovery from exercise