Short-term exercise training improves the cardiovascular response to exercise in the postural orthostatic tachycardia syndrome

Abstract

Recent studies have suggested the presence of cardiac atrophy as a key component of the pathogenesis of the postural orthostatic tachycardia syndrome (POTS), similar to physical deconditioning. It has also been shown that exercise intolerance is associated with a reduced stroke volume (SV) in POTS, and that the high heart rate (HR) observed at rest and during exercise in these patients is due to this low SV. We tested the hypotheses that (a) circulatory control during exercise is normal in POTS; and (b) that physical ‘reconditioning' with exercise training improves exercise performance in patients with POTS. Nineteen (18 women) POTS patients completed a 3 month training programme. Cardiovascular responses during maximal exercise testing were assessed in the upright position before and after training. Resting left ventricular diastolic function was evaluated by Doppler echocardiography. Results were compared with those of 10 well-matched healthy sedentary controls. A lower SV resulted in a higher HR in POTS at any given oxygen uptake (V(O(2))) during exercise while the cardiac output (Q(c))-V(O(2)) relationship was normal. V(O(2peak)) was lower in POTS than controls (26.1 ± 1.0 (SEM) vs. 36.3 ± 0.9 ml kg-1 min-1; P < 0.001) due to a lower peak SV (65 ± 3 vs. 80 ± 5 ml; P = 0.009). After training in POTS, HR became lower at any given due to increased SV without changes in the – relationship. V(O(2peak)) increased by 11% (P < 0.001) due to increased peak SV (P = 0.021) and was proportional to total blood volume. Peak HR was similar, but HR recovery from exercise was faster after training than before training (P = 0.036 for training and 0.009 for interaction). Resting diastolic function was mostly normal in POTS before training, though diastolic suction was impaired (P = 0.023). There were no changes in any Doppler index after training. These results suggest that short-term exercise training improves physical fitness and cardiovascular responses during exercise in patients with POTS.

Figures

Figure 1. Changes in stroke volume (SV, A), heart rate (HR, B), cardiac output (, C), arterio-venous oxygen content difference (a-v, D), mean arterial pressure (MAP, E), and total peripheral resistance (TPR, F) in relation to changes in oxygen uptake () during upright treadmill exercise before and after 3 months of exercise training in patients with POTS (n = 19) and healthy sedentary controls (n = 7)

Values are means ± SEM. *P < 0.05, pre-training compared with post-training in POTS. ††P < 0.01, patients compared with controls.

Figure 2

Peak oxygen uptake () as a function of blood volume (A) and plasma volume (B) in healthy controls and patients with POTS before and after 3 months of exercise training

Figure 3. Heart rate (HR) recovery from exercise in POTS patients before and after exercise training. Peak EX, maximal exercise

Values are means ± SEM. **P < 0.01 compared with pre-training in POTS.