Effect of Local Heat Stress Via Leg Bath on Artery Function
Condition: Endothelial Dysfunction
MeSH terms: Heat Stress Disorders
Study type: Interventional

Summary: 
      Arteries are flexible in their structure and function and change in response to a variety of
      factors. Endothelial cells, are the skin type cells that form a layer inside arteries, and
      they are very important for arterial health. When they work properly, they produce substances
      that make the artery enlarge and support a healthy environment; but when they do not work
      properly, they produce substances that make the artery constrict and lead to a harmful
      environment. We can measure the function of these cells using an ultrasound machine and a
      quick test. The application of heat has been shown to change the structure and function of
      arteries, but we need to understand how these changes happen before we can effectively use
      heat as a therapy. Limb heating protocols (e.g., leg bath), in contrast with whole-body
      heating modes (e.g., sauna), are appealing as therapies because they generally cost less and
      are easier to use; but evidence is needed to demonstrate that they work before widespread use
      can be considered. Imagine soaking your legs in a bathtub filled with warm water becoming
      part of the options you have for staying healthy. Clearly, there is a lot of potential for
      heat to be used as a therapy, particularly for people who are unable to, or have difficulty
      participating in other health interventions that are known to improve arterial, but we need
      to do this type of research before we are able to recommend warm foot baths for therapeutic
      purposes.
    

Detailed description: 
      A within-subjects interventional design will be used in a cohort of 16 young, healthy males
      and females between the ages of 18-35 years old. Interested individuals will be invited to
      the lab for a screening and familiarization visit, in which the brachial artery (BA) and
      superficial femoral artery (SFA) will be scanned to vet for ultrasound image quality and BA
      and SFA flow-mediated dilation tests will be performed to ensure participant tolerance during
      collection visits. According to current FMD guidelines, all qualified participants will be
      instructed to refrain from vigorous physical activity > 24 hours, alcohol and caffeine > 8
      hours, and food > 6 hours prior to each of the two experimental visits. Participants will
      also be asked to ingest a wireless telemetry pill 2 hours prior to each of the two
      experimental visits. Upon arrival, basic anthropometric measures will be collected and
      hematocrit will be measured in duplicate with a finger prick blood sample equivalent to two
      70 µl capillary tubes. Experimental visits will begin with 10 minutes of supine rest, while
      the participant is instrumented with skin temperature probes on the foot, calf, thigh, chest,
      and arm for measurement of skin temperature; single-lead ECG (Powerlab model ML795,
      ADInstruments, Colorado Springs, CO, USA) and non-invasive finger cuff (Finometer MIDI,
      Finapres, The Netherlands) for continuous heart rate and blood pressure monitoring. Following
      rest, BA and SFA FMD tests will be conducted to assess baseline endothelial function.
      Afterwards, single-point laser Doppler flowmetry focused on the forearm will be used to track
      skin blood flow continuously throughout heating. The heating protocol will involve
      participants immersing their lower limbs either up to the ankles or the knees in a 42 °C
      water bath for 45 minutes, in separate conditions. The order by which participants undergo
      these interventions will be randomized. Five minutes after the conclusion of the
      intervention, BA and SFA FMD tests will be conducted to assess endothelial function in the
      acute phase. BA and SFA blood velocities, blood flow turbulence, endothelial shear rate, and
      oscillatory shear index will be assessed before and during each of the interventions; and
      arterial stiffness defined as carotid-femoral pulse wave velocity (PWV) and common carotid
      artery (CCA) distensibility will be assessed before and after each of the interventions as
      additional outcomes. Participants will provide written informed consent prior to beginning
      any portion of the study.
    

Intervention name(s): Lower limb hot water immersion
Intervention type(s): Other
Intervention description(s): Participants will undergo two interventions in separate visits: lower limb hot water (42 deg C) immersion up to the (1) ankles or (2) knees.
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: heat stress; endothelial function; hot water immersion; arterial stiffness