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Reduced stroke volume during exercise in postural tachycardia syndrome
Shizue Masuki1, John H Eisenach, William G Schrage
1Department of Anesthesiology, Mayo Clinic Foundation, Rochester, MN 55905, USA.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 14, 2007
Summary
Postural tachycardia syndrome (POTS) patients exhibit reduced stroke volume during exercise, particularly upright. This compensatory increase in heart rate contributes to their exercise intolerance.
Area of Science:
- Cardiology
- Exercise Physiology
- Autonomic Dysfunction
Background:
- Postural tachycardia syndrome (POTS) is a condition characterized by excessive heart rate increase without a drop in blood pressure upon standing.
- POTS is frequently associated with exercise intolerance, impacting patients' quality of life.
Purpose of the Study:
- To investigate the cardiovascular regulatory mechanisms during graded exercise in POTS patients compared to healthy controls.
- To determine the relationship between stroke volume, heart rate, and exercise capacity in POTS.
Main Methods:
- 13 POTS patients and 10 healthy controls underwent graded cycle ergometry (25, 50, 75 W) in supine and upright positions.
- Measurements included arterial pressure, heart rate (ECG), and cardiac output (acetylene rebreathing).
Main Results:
- POTS patients showed significantly lower stroke volume (SV) and higher heart rate (HR) than controls, especially in the upright position during exercise.
- Mean arterial pressure, cardiac output, and total peripheral resistance were similar between groups.
- Reduced upright SV was inversely correlated with increased HR, suggesting a compensatory mechanism.
Conclusions:
- The increased HR observed in POTS patients during exercise, particularly upright, is secondary to reduced stroke volume.
- This compensatory mechanism is linked to the exercise intolerance experienced by POTS patients.
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