Circulatory response evoked by a 3 s bout of dynamic leg exercise in humans.

1. The mechanisms underlying the pronounced transient fall in arterial blood pressure evoked by a 3 s bout of bicycle exercise were investigated in twenty healthy young adults and four patients with hypoadrenergic orthostatic hypotension. 2. In healthy subjects a 3 s bout of upright cycling induced a 28 +/‐ 3 mmHg fall in mean arterial pressure at 12 s. The fall in mean arterial pressure was preceded by a 12 +/‐ 2 mmHg rise in right atrial pressure at 3 s and accompanied by a 54 +/‐ 7% increase in left ventricle stroke volume at 6 s. Systemic vascular resistance dropped 48 +/‐ 2% at 7 s after the start of the manoeuvre to remain at that level for approximately 5 s. The total response lasted about 20 s. During sustained upright cycling the initial fall in mean arterial pressure was also present, but less pronounced (17 +/‐ 2 vs. 26 +/‐ 3 mmHg). A 3 s bout of supine cycling in four patients with hypoadrenergic orthostatic hypotension also elicited a pronounced fall in mean arterial pressure (22 +/‐ 4 mmHg) and in systemic vascular resistance (38 +/‐ 4%). 3. A bout of exercise with a large muscle mass induces two main effects. First, it mechanically increases filling of the heart due to activation of the muscle pump, resulting in an increase in cardiac output. Second, it induces a drop in systemic vascular resistance. The increase in cardiac output is not sufficient to compensate fully for the pronounced fall in systemic vascular resistance and the result is a transient fall in arterial pressure at the onset of whole‐body exercise. The rise in right atrial pressure evoked by 3 s cycling is abrupt and large, but the almost immediate onset and rapid fall of the systemic vascular resistance is too fast for sympathetically mediated reflex effects due to stimulation of the cardiopulmonary afferents. An important factor involved in the drop in systemic vascular resistance appears to be local, non‐autonomically mediated vasodilatation in exercising muscles, since it also occurs in patients with autonomic failure.

[1]  H. Sparks,et al.  Myogenic hyperemia following brief tetanus of canine skeletal muscle. , 1974, The American journal of physiology.

[2]  J. Taylor,et al.  Differential control of forearm and calf vascular resistance during one-leg exercise. , 1989, Journal of applied physiology.

[3]  S. Segal,et al.  Cell-to-cell communication coordinates blood flow control. , 1994, Hypertension.

[4]  J. V. van Lieshout,et al.  Spectrum of orthostatic disorders: classification based on an analysis of the short-term circulatory response upon standing. , 1991, Clinical science.

[5]  J R Jansen,et al.  Continuous cardiac output monitoring by pulse contour during cardiac surgery. , 1994, European heart journal.

[6]  M. H. Laughlin,et al.  Skeletal muscle blood flow capacity: role of muscle pump in exercise hyperemia. , 1987, The American journal of physiology.

[7]  N. T. Smith,et al.  A simple device for the continuous measurement of cardiac output. Its model basis and experimental verification , 1983 .

[8]  J. E. Hansen,et al.  Abrupt changes in mixed venous blood gas composition after the onset of exercise. , 1989, Journal of applied physiology.

[9]  L. Rowell,et al.  Disparities Between Aortic and Peripheral Pulse Pressures Induced by Upright Exercise and Vasomotor Changes in Man , 1968, Circulation.

[10]  A HOLMGREN,et al.  Circulatory changes during muscular work in man; with special reference to arterial and central venous pressures in the systemic circulation. , 1956, Scandinavian journal of clinical and laboratory investigation.

[11]  J. T. Shepherd,et al.  Reflex changes in vasoconstrictor tone in human skeletal muscle in response to stimulation of receptors in a low‐pressure area of the intrathoracic vascular bed , 1957, The Journal of physiology.

[12]  J. T. Shepherd,et al.  EFFECT OF A BRIEF CONTRACTION OF FOREARM MUSCLES ON FOREARM BLOOD FLOW. , 1964, Journal of applied physiology.

[13]  P. Vanhoutte,et al.  Flow-induced release of endothelium-derived relaxing factor. , 1986, The American journal of physiology.

[14]  Short-term cardiovascular responses to a step decrease in peripheral conductance in humans. , 1994, The American journal of physiology.

[15]  J. Marshall,et al.  Direct observations of muscle arterioles and venules following contraction of skeletal muscle fibres in the rat. , 1984, The Journal of physiology.

[16]  K H Wesseling,et al.  Initial blood pressure fall on stand up and exercise explained by changes in total peripheral resistance. , 1991, Journal of applied physiology.

[17]  J. Karemaker,et al.  Continuous non-invasive blood pressure monitoring: reliability of Finapres device during the Valsalva manoeuvre. , 1988, Cardiovascular research.

[18]  A. J. Dunning,et al.  Mechanisms of initial heart rate response to postural change. , 1982, The American journal of physiology.

[19]  A. Mark,et al.  Muscle sympathetic nerve responses to dynamic one-legged exercise: effect of body posture. , 1993, The American journal of physiology.

[20]  A. Ng,et al.  Arm muscle sympathetic nerve activity during preparation for and initiation of leg-cycling exercise in humans. , 1994, Journal of applied physiology.

[21]  J. Wesche.  The time course and magnitude of blood flow changes in the human quadriceps muscles following isometric contraction. , 1986, The Journal of physiology.

[22]  B. Imholz,et al.  Disparities in circulatory adjustment to standing between young and elderly subjects explained by pulse contour analysis. , 1992, Clinical science.

[23]  J T Shepherd,et al.  Reaction in man of resistance and capacity vessels in forearm and hand to leg exercise. , 1966, Journal of applied physiology.

[24]  L. Rowell,et al.  Is rapid rise in vascular conductance at onset of dynamic exercise due to muscle pump? , 1993, The American journal of physiology.

[25]  P. O'Brien,et al.  Statistical considerations for performing multiple tests in a single experiment. 3. Repeated measures over time. , 1988, Mayo Clinic proceedings.