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Short-term cardiovascular responses to rapid whole-body tilting during exercise
P Sundblad1, Y Haruna, B Tedner
1Section of Environmental Physiology, Department of Physiology and Pharmacology, Karolinska Institute, SE-17177 Stockholm, Sweden. Patrik.Sundblad@fyfa.ki.se
European Journal of Applied Physiology
|February 9, 2000
Summary
Dynamic leg exercise and posture changes significantly alter heart rate and blood pressure. Baroreflex responses to these changes are modulated by exercise intensity, impacting cardiovascular regulation during physical activity.
Area of Science:
- Cardiovascular Physiology
- Exercise Physiology
Background:
- Understanding cardiovascular responses to postural changes during exercise is crucial for assessing physiological limits.
- Dynamic leg exercise combined with tilting challenges the body's autonomic regulation systems.
Purpose of the Study:
- To characterize heart rate (HR) and arterial blood pressure (BP) responses during combined dynamic leg exercise and postural changes (tilting).
- To investigate the influence of exercise intensity on these cardiovascular adjustments.
Main Methods:
- Ten healthy men performed dynamic leg exercise at 50, 100, and 150 W.
- Participants were repeatedly tilted between supine and 80° upright positions at 2-minute intervals.
- Continuous BP, HR, and central blood volume (via transthoracic impedance) were recorded.
Main Results:
- Short-lasting BP transients occurred with tilting (increases on down-tilt, decreases on up-tilt), influenced by exercise intensity.
- HR transients, opposite to BP changes, were larger during down-tilt and increased with work intensity.
- HR fluctuations were modeled as a baroreflex response with varying vagal and sympathetic contributions.
Conclusions:
- Tilt-induced BP transients are primarily due to changes in total peripheral resistance, likely mediated by the venous muscle pump.
- The baroreflex system modulates HR responses to postural stress during exercise, with intensity-dependent effects.
- Exercise attenuates the tachycardic response to hypotensive stimuli via baroreflex adjustments.