Deconditioning in patients with orthostatic intolerance

Objective: To study the frequency and degree of deconditioning, clinical features, and relationship between deconditioning and autonomic parameters in patients with orthostatic intolerance. Methods: We retrospectively studied all patients seen for orthostatic intolerance at Mayo Clinic between January 2006 and June 2011, who underwent both standardized autonomic and exercise testing. Results: A total of 184 patients (84 with postural orthostatic tachycardia syndrome [POTS] and 100 without orthostatic tachycardia) fulfilled the inclusion criteria. Of these, 89% were women, and median age was 27.5 years (interquartile range [IQR] 22-37 years). Symptom duration was 4 years (IQR 2-7.8). Of the patients, 90% had deconditioning (reduced maximum oxygen uptake [VO_2max%] <85%) during exercise. This finding was unrelated to age, gender, or duration of illness. The prevalence of deconditioning was similar between those with POTS (95%) and those with orthostatic intolerance (91%). VO_2max% had a weak correlation with a few autonomic and laboratory parameters but adequate predictors of VO_2max%could not be identified. Conclusion: Reduced VO_2max% consistent with deconditioning is present in almost all patients with orthostatic intolerance and may play a central role in pathophysiology. This finding provides a strong rationale for retraining in the treatment of orthostatic intolerance. None of the autonomic indices are reliable predictors of deconditioning.