Hemodynamic Effects of Compression in POTS

Postural Tachycardia Syndrome (POTS) is a chronic form of orthostatic intolerance marked by a significant and sustained increase in heart rate (HR) upon positional change from supine to standing (>30 beats/min [bpm]) in the absence of orthostatic hypotension (\<20/10 mmHg decrease). Symptoms must be present for >6 months and other causes of orthostatic tachycardia must be ruled out. Individuals with POTS report orthostatic symptoms including palpitations, lightheadedness, and mental clouding, which improve on recumbence. The vast majority of individuals diagnosed with POTS are women age 13-50 years.

Upon standing, approximately 500 mL of blood immediately redistributes from the thorax down to the abdomen, buttocks and legs. This leads to sympathetic activation as the baroreceptors sense less pressure. In a healthy individual, HR initially increases 10-20 bpm, and the systolic blood pressure (BP) decreases by approximately 5 mmHg. However, in an individual with POTS, this compensatory mechanism is impaired and HR will increase by >30 bpm and remain at this elevated rate for the duration of standing. In some individuals with POTS, upon standing cerebral blood flow velocity decreases. In other individuals, oscillation of cerebral blood flow due to failure of cerebral autoregulatory mechanisms is observed.

Current treatment of POTS involves pharmacological and non-pharmacological intervention including salt and fluid loading, exercise, and physical countermanuevers. There are no approved medications for use in POTS and all use is off label. Compression garments are also often prescribed. Abdominal/lower extremity compression garments provide pressure to the blood vessels in the legs, thighs and abdomen which can minimize blood pooling and lead to improved blood return to the heart. One such garment is the Lifewrap Non-pneumatic AntiShock garment (NASG), indicated in post-partum hypovolemia.

A pediatric study (n=20) found that orthostatic tachycardia and symptoms were decreased during head up tilt (HUT), with the use of a different NASG compression garment vs. no compression. However, there is no data to validate the efficacy of compression in adults POTS, and also no data to determine which type of compression is most beneficial (e.g. lower leg only, abdomen only, combination).

The investigators hypothesize that the use of the Lifewrap NASG compression garment in a fully applied configuration will decrease orthostatic tachycardia and orthostatic symptoms during a 10 minute HUT vs. no compression garment. The investigators will complete a 4-way randomized crossover study of HUTs with compression applied by the LifeWrap NSAG in at attempt to demonstrate decreased orthostatic tachycardia and increased orthostatic tolerance in individuals with POTS. If successful, this study could provide needed evidence that compression in POTS is a successful non-pharmacological treatment modality, and as well, what type of compression is the most beneficial to patients with this syndrome. These findings could rapidly translate to the clinical setting and improve patient care.

The study participant will complete 4x 10min HUTs during a single study day. There will be 4 compression conditions based on strap configuration of the Lifewrap garment: (1) full abdominal and lower extremity compression, (2) abdominal only compression, (3) lower extremity only compression and (4) no compression. A pressure sensor will used to measure the magnitude of compression pressure applied. The study will be conducted on a tilt table in a human physiology research and procedure room. Each intervention phase in the protocol will involve a supine baseline assessment period of 10 minutes followed by a 10 min HUT (80 degrees). There will be a 20 min recovery periods between each HUT. The study will take approximately 4 hours.

The study participant will be instrumented in a fasting state and on an empty bladder. The investigators will apply skin electrodes to continuously monitor heart rate and record an ECG. BP will be monitored continuously using a finger volume clamp method (Nexfin, Edwards Lifesciences) and calibrated with intermittent brachial cuff measurements (Vital-Guard 450C Patient Care Monitor, IVY Medical). From the continuous BP waveform, the investigators can obtain an estimate of stroke volume, cardiac output, and systemic vascular resistance (Modelflow). Middle cerebral blood flow velocity will be assessed using transcranial doppler.