Local Heat Stress in Autonomic Failure Patients With Supine Hypertension
Condition: Hypertension; Pure Autonomic Failure; Multiple System Atrophy; Autonomic Failure
MeSH terms: Multiple System Atrophy; Shy-Drager Syndrome; Pure Autonomic Failure; Hypertension; Heat Stress Disorders
Study type: Interventional

Summary: 
      Patients with autonomic failure are characterized by disabling orthostatic hypotension (low
      blood pressure on standing), and at least half of them also have high blood pressure while
      lying down (supine hypertension). Exposure to heat, such as in hot environments, often
      worsens their orthostatic hypotension. The causes of this are not fully understood. The
      purpose of this study is to evaluate whether applying local heat over the abdomen of patients
      with autonomic failure and supine hypertension would decrease their high blood pressure while
      lying down. This will help us better understand the mechanisms underlying this phenomenon,
      and may be of use in the treatment of supine hypertension.
    

Detailed description: 
      Primary autonomic failure is a neurodegenerative condition characterized by severe impairment
      of the autonomic nervous system. The clinical hallmark of autonomic failure is disabling
      orthostatic hypotension, but at least half of patients are also hypertensive while lying
      down. This supine hypertension can be severe and associated with end-organ damage and
      worsening of orthostatic hypotension due to increased pressure natriuresis. It also
      complicates the management of these patients by limiting the use of daytime pressor agents
      for the treatment of orthostatic hypotension.

      It is well known that heat exposure (e.g. hot weather or a hot bath or shower) produces an
      acute and temporary worsening of orthostatic hypotension in autonomic failure patients.
      However, the mechanisms underlying this phenomenon are completely unexplored. Factors that
      may predispose autonomic failure patients to the acute lowering blood pressure effects of
      heat stress include 1) impaired heat dissipation due to inability to sweat, 2) preserved
      heat-mediated skin vasodilation, and 3) blunted sympathetic hemodynamic responses to maintain
      blood pressure. In this study, we test the hypothesis that moderate levels of local
      (abdominal) passive heat stress will lower blood pressure in autonomic failure patients with
      supine hypertension.

      To test this hypothesis, we propose this pilot study with the following specific aims:

        1. To evaluate the acute blood pressure effects of local passive heat stress in autonomic
           failure patients with supine hypertension, we will compare changes in BP between
           controlled local heat stress (~44ºC) using a commercial heating pad that covers the
           abdomen and part of the torso, and a control (non-heating) study day using the same
           heating pad but turned off.

        2. To evaluate the mechanisms underlying BP changes during local heat stress, we will
           compare changes in hemodynamic parameters (cardiac output, stroke volume and peripheral
           vascular resistance), segmental fluid shifts (measured by segmental bioimpedance), skin
           blood flow and skin temperature between the heat and non-heating study days.
    

Intervention name(s): Passive heat stress; Control (non-heating)
Intervention type(s): Other; Other
Intervention description(s): Passive heat stress will be applied with a commercial heating pad that covers all the abdomen and part of the torso to provide local heating at ~44ºC continuously for 2 hr.; Heating pad will be applied over the abdomen and part of the torso but it will be turned off.
Other intervention name(s): Heating pad; sham
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: randomized, 2-arm crossover study (heat vs. sham)
Masking: Single (Participant)
Primary purpose: Other
Keywords: Supine hypertension; Autonomic failure; Heat intolerance; Orthostatic hypotension; Heat stress