Effect of Exercise in OI
Condition: Orthostatic Intolerance; Postural Tachycardia Syndrome
MeSH terms: Postural Orthostatic Tachycardia Syndrome; Orthostatic Intolerance; Tachycardia
Study type: Interventional

Summary: 
      The main limitation patients with orthostatic intolerance (OI, or postural tachycardia
      syndrome, POTS) have to exercise is related to their increase in heart rate when standing.
      Main pharmacological treatment today is aimed at reducing heart rate with the use of
      betablockers (propanolol), this theoretically could also improve their exercise capacity; if
      their heart rate do not increase as much with the medication, they could exercise more. In
      addition, it has been suggested that in healthy volunteers subjected to head down tilt for 2
      weeks (situation that produces a "simulated" transient POTS-like state) a single bout of
      intense exercise can improve orthostatic tolerance the day after exercising. The mechanisms
      involved in such response are not that clear but could be an increase in plasma volume
      already diminished in POTS patients. It seems likely that the same could be true for POTS
      patients.

      The purpose of the present study are to pharmacologically improve the amount of exercise POTS
      patients can perform by reducing their baseline heart rate (specific aim 1) and to evaluate
      next day heart responses to an acute bout of intense exercise.

      Therefore, the specific aims of this study are:

        1. To test the hypothesis that lowering heart rate response with propanolol will result in
           an increase in exercise capacity.

        2. To test the hypothesis that a single bout of exercise will result in an improvement in
           orthostatic tolerance the day after exercising.
    

Detailed description: 
      -  Subjects will be studied twice, once after receiving placebo and in a second occasion
           after receiving propanolol.

        -  An exercise capacity test with estimation of maximal oxygen consumption (VO2 max) will
           be done within 1 hour of receiving a pill containing placebo and that will be in
           appearance identical to the one for propanolol. This test will be conducted on a
           stationary bicycle and the effort will be gradually increased while expired air is
           measured during exhaustive physical work. The test will last approximately 30 minutes
           and be conducted in Vanderbilt's Clinical Trial Center.

        -  The day before and the day after the exercise test subjects will be asked to collect
           urine for 12 hours each time and to keep a record of how much liquid they ingest.

        -  Posture study tests (measurements of heart rate and blood pressure taken while lying
           down and at intervals for up to 30 minutes while standing) will be done the day before
           and the day after the exercise test.
    

Intervention name(s): Propranolol then Placebo; Placebo then Propranolol
Intervention type(s): Drug; Drug
Intervention description(s): Propanolol 20 mg, given orally within 1 hour prior to exercising; Placebo, matching pill given orally within 1 hour prior to exercising
Other intervention name(s): Active; Inactive
Intervention MeSH terms: Propranolol
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Participant, Investigator)
Primary purpose: Treatment
Keywords: Exercise; Propanolol; Beta blockers