POTS versus deconditioning: the same or different?

Abstract

The 2007 Streeten Lecture focused on the idea that physical deconditioning plays a key role in the symptomology and pathophysiology of POTS. Parallels were drawn between the physiological responses to orthostatic stress seen in POTS patients and the physiological responses seen in "normal" humans after prolonged periods of bedrest, deconditioning, or space flight. Additionally, the idea that endurance exercise training might ameliorate some of these symptoms was also advanced. Finally, potential parallels between POTS, chronic fatigue syndrome, and fibromyalgia were also drawn and the potential role of exercise training as a "therapeutic intervention" in all three conditions was raised. The conceptual model for the lecture was that after some "initiating event" chronic deconditioning plays a significant role in the pathophysiology of these conditions, and these physiological changes in conjunction with "somatic hypervigilence" explain many of the complaints that this diverse group of patients have. Additionally, the idea that systematic endurance exercise training might be helpful was advanced, and data supportive of this idea was reviewed. The main conclusion is that the medical community must retain their empathy for patients with unusual conditions but at the same time send a firm but empowering message about physical activity. As always, we must also ask what do the ideas about physical activity and inactivity and the conditions mentioned above not explain?

Fig. 1

Individual records of the arterial pressure (AP) and heart rate (HR) responses to the upright posture. The record includes 120 seconds of supine rest followed by 120 seconds of upright posture. In addition to having a more marked rise in heart rate during the upright posture, the POTS patient also showed much more variability in their heart rate and arterial pressure responses

Fig. 2

The upper panels (a) show heart rate (HR) and mean arterial pressure (MAP) responses to standard lower body negative pressure (left upper panels), HR and mean arterial pressure MAP responses to sham-LBNP with MAST trouser inflation to prevent venous pooling (middle upper panels), and HR and MAP responses to the vacuum sound only (right upper panels). These are representative tracings from an individual control subject and a POTS patient. The bottom bar graphs (b) demonstrate the group responses. A key point from this slide is that the excessive heart rate response in POTS only occurred during real venous pooling. Figure from reference [13]

Fig. 3

Differences between control subjects and POTS patients on psychological markers associated with their tendency to report physiological responses as more intensely experienced than control subjects. Figure from reference [13]

Fig. 4

Heart rate responses to upright tilting 72 and 23 days before space flight and on the landing day. The responses to upright tilt appear “POTS-like” after space flight. Since space flight is associated with cardiac atrophy and a reduction in blood volume which can also be seen in POTS, this and related data raises questions about the role of deconditioning in the pathophysiology of POTS. Figure from reference [10]

Fig. 5

Heart rate, arterial pressure, and pulse pressure responses to graded exercise in the supine and upright position in POTS patients. The cardiac output responses were similar in both groups during exercise, indicating that stroke volume was lower in the POTS patients. Increased heart rate responses on a lower stroke volume are also suggestive of deconditioning. Figure from reference [15]

Fig. 6

Relationship between stroke volume and muscle sympathetic nerve activity before and after space flight. This figure makes the point that the relationship between stroke volume and MNSA is constant before and after space flight but that the changes in cardiac size and blood volume shift the responses to the left on the curve. This data suggests that the responses seen in POTS might be due to the fact that the patients are simply on different parts of the stimulus response curves that relate afferent signals from barosensitive areas in the cardiovascular system to heart rate, and MSNA responses. Figure from reference [10]

Fig. 7

Oxygen uptake (a), heart rate (b), and readings of perceived exertion (c) in patients with chronic fatigue syndrome. This figure demonstrates that there is a mismatch between the perception of effort and the physiological responses to graded exercise in these patients that is conceptually similar to the somatic hypervigilence concept advanced in POTS. Figure from reference [23]