Understanding standing in Postural Orthostatic Tachycardia Syndrome (POTS)

This is a non-therapeutic mechanistic physiological study. The study consists of a 1 hour familiarisation and two experimental visits (1.5 hours and 3 hours). Studies will be conducted in Human Cardiorespiratory Physiology Laboratory within the Clinical Research Centre, Faculty of Health and Medical Science, University of Auckland. The following physiological measures will be made in the POTS participant group and matched healthy control group. All assessments will be one-on-one. Assessments: Screening visit- Health Screening Questionnaires (EQ-5D-5L, IPAQ, COMPASS-31, MAPS, Beighton Joint Hypermobility) Delivered by a trained investigator. Delivered face-to-face. Delivered once. Takes 10-15 min to complete these forms. Height, weight, hip and waist circumference Delivered by a trained investigator. Delivered face-to-face. Delivered once. Takes 5-10 min to complete this assessment. Experimental visit 1- The following tests will each be separated by a ~10 minute break. Arterial stiffness Measured by the placement of a pen-shaped probe over arteries at the participants neck, wrist, and ankle. A cuff will be placed around the participants upper thigh that will inflate for a couple of minutes. Delivered by a trained investigator. Delivered face-to-face. Delivered once. Takes 10-15 min to complete this assessment. Flow mediated dilatation While brachial artery is imaged with ultrasound a cuff around the upper arm will be inflated [for 5 minutes] and then deflated [5 minutes]. Delivered by a trained investigator. Delivered face-to-face. Delivered once. Takes 10-15 min to complete this assessment. Venous function Measured by a cuff placed around the thigh, above the knee and a lightweight elastic band or sensor cuff placed around the widest portion of the calf. The cuff will be inflated for 8 minutes and then slowly deflated over 60 seconds. Delivered by a trained investigator. Delivered face-to-face. Delivered once. Takes 10-15 min to complete this assessment. Experimental visit 2- The following tests will each be separated by a ~10 minute break. Slow deep breathing The participant will be asked to take slow deep breaths for 5 minutes with the guidance of an investigator. Delivered by a trained investigator. Delivered face-to-face. Delivered once. Takes 10-15 min to complete this assessment. Handgrip test The participant will be asked to hold a device that measures the force of the handgrip. The participant will do some short handgrip trials to establish the maximum grip strength, then hold ~30% of this for 2 min. Delivered by a trained investigator. Delivered face-to-face. Delivered once. Takes 10-15 min to complete this assessment. Valsalva’s manoeuvre The participant will forcefully breathe out against a resistance (breathing out whilst you are wearing a mouthpiece) for around 15 seconds. Delivered by a trained investigator. Delivered face-to-face. Delivered three times. Takes 5-10 min to complete this assessment. Cold pressor test The participant will be asked to place a hand in cold water for 2 minutes. Delivered by a trained investigator. Delivered face-to-face. Delivered three times. Takes 5-10 min to complete this assessment. The devices/instruments used for study visits are novel devices supplied for human research purposes (e.g., by ADInstruments).