We identified 184 patients who fulfilled our inclusion and exclusion criteria. Of these, 84 patients fulfilled the HR criteria for POTS, and 100 did not (OI). shows the orthostatic change in HR in both patient groups. The OI group was slightly older than the POTS group (POTS vs OI: 25 years, interquartile range [(IQR] 20–32 years) vs 32 years, IQR 24–40 years, p < 0.0001). Patients were mostly women (89%) ().
Orthostatic change in heart rate
Baseline demographic and clinical presentation of patients with orthostatic intolerancea
Onset of symptoms were acute (1 month) in 7 (4%), subacute (1–3 months) in 4 (2%), gradual (>3 months) in 155 (84%), and not specified in 18 (10%) patients. Of the patients, 181 (98%) had reduced work capability since the onset of the symptoms; 60 (33%) patients identified a preceding event as possible trigger for their symptoms, with viral illness being the most common.
Clinical presentation included orthostatic, nonorthostatic (i.e., nausea, vomiting, diarrhea, constipation, bladder, and pupillary dysfunction), and generalized (fatigue and sleep disturbances) symptoms (). Ganglionic antibodies were tested in 120 (65%) patients, and results were normal in all subjects (range 0.00–0.04 nmol/L, normal ≤0.05 nmol/L). A gastric transit study was performed in 18 patients (10%): 2 (11%) had delayed transit, 1 (6%) had rapid transit, and the rest had normal transit.
Responses to different medications () were poor in both groups. Most patients (130 [71%]) had a static course, 38 patients (21%) had mild improvement, and only 1 patient had moderate to good improvement in symptoms. The remaining 15 patients (8%) had a progressive course with continuous worsening.
Medications used for orthostatic intolerance
A total of 171 (93%) patients had evidence of cardiovascular deconditioning. The prevalence of deconditioning was similar between patients with POTS (95%) and those with OI (91%, p = 0.39) (). The severity of deconditioning was also similar between patients with POTS (mild 50%, severe 50%) and those with OI (mild 42%, severe 58%; (p = 0.28). Deconditioning was not correlated to age (r = 12, p = 0.13) or duration of illness (r = 0.003, p = 0.97). Furthermore, deconditioning was similar in both genders (p = 0.15). Effort was maximal in 70% and submaximal in 21%, and performance was considered inadequate in 9% of the subjects based on RER.
The correlation between VO2max
% and different autonomic parameters is shown in appendix e-1 on the Neurology
® Web site at www.neurology.org
. Among patients with POTS, TST anhydrosis %, ΔIIE
SBP, and 24-hour urine volume were significantly correlated with VO2max
%; however, the strength of correlation was generally weak (r
≤ 0.34). Among patients with OI, ΔIIL
DBP, VR, and supine plasma norepinephrine had significant but weak correlation with VO2max
≤ 0.32). There was no significant correlation between ΔHR and VO2max
%. Appendix e-2 describes the correlation between HR recovery at 1 minute and different autonomic parameters. For all patients, TST anhydrosis % was significantly and negatively correlated with VO2max
= –0.30, p
Overall, none of the autonomic and laboratory parameters were significant predictors of deconditioning.