Exercise in the postural orthostatic tachycardia syndrome

Abstract

Patients with the Postural Orthostatic Tachycardia Syndrome (POTS) have orthostatic intolerance, as well as exercise intolerance. Peak oxygen uptake (VO2peak) is generally lower in these patients compared with healthy sedentary individuals, suggesting a lower physical fitness level. During acute exercise, POTS patients have an excessive increase in heart rate and reduced stroke volume for each level of absolute workload; however, when expressed at relative workload (%VO2peak), there is no difference in the heart rate response between patients and healthy individuals. The relationship between cardiac output and VO2 is similar between POTS patients and healthy individuals. Short-term (i.e., 3 months) exercise training increases cardiac size and mass, blood volume, and VO2peak in POTS patients. Exercise performance is improved after training. Specifically, stroke volume is greater and heart rate is lower at any given VO2 during exercise after training versus before training. Peak heart rate is the same but peak stroke volume and cardiac output are greater after training. Heart rate recovery from peak exercise is significantly faster after training, indicating an improvement in autonomic circulatory control. These results suggest that patients with POTS have no intrinsic abnormality of heart rate regulation during exercise. The tachycardia in POTS is due to a reduced stroke volume. Cardiac remodeling and blood volume expansion associated with exercise training increase physical fitness and improve exercise performance in these patients.

Keywords: Cardiovascular response; Chronic orthostatic intolerance; Exercise intolerance; Non-drug therapy; Physical activity.

Figure 1

Changes of stroke volume (SV, A), heart rate (HR, B), cardiac output (Qc, C), arterio-venous oxygen content difference (A-vDO₂, D), mean arterial pressure (MAP, E), and total peripheral resistance (TPR, F) in relation to changes of oxygen uptake (VO₂) during upright treadmill exercise in healthy sedentary individuals and patients with POTS before and after 3-month endurance training. Adapted with permission from Shibata et al (Shibata et al., 2012).

Figure 2

Heart rate (HR) responses, when expressed at percent of peak oxygen uptake (VO_2peak), between POTS patients and healthy sedentary individuals. Data from our laboratory (Robin et al., 2007 abstract).