Effects of Dehydration on Neuromuscular Performance and Sympathetic Control of Cardiovascular Function
Condition: Dehydration Hypertonic; Isotonic Dehydration
MeSH terms: Dehydration
Study type: Interventional

Summary: 
      The mechanism(s) by which dehydration (both intra- and extracellular) impairs performance are
      still poorly described. A loss of volume results in increased occurrence of orthostatic
      intolerance, including dizziness, fatigue, headaches and related symptoms with upright
      posture. Any of these symptoms can contribute to decreased performance in maneuvers performed
      in the upright posture, which includes many military tasks. Thus, loss of volume challenges
      the cardiovascular and blood pressure responses to systemic whole body endurance exercise,
      while osmolality is the stimulus for intracellular dehydration that may impair local muscle
      force production by impairing contractile function, neural signaling, or both. In this study,
      we will compare how both types of dehydration affect MSNA and CAC.

      The results of this study will provide mechanistic insight for how dehydration (intra- or
      extracellular) impairs systemic whole body and local small muscle performance in vivo. This
      Basic Science study seeks to understand how volume and osmolality impact MSNA and CAC as a
      basis for improving potential countermeasures, such as a more optimally formulated
      rehydration beverage. Therefore, this study directly complements Task Area T10 (Hot Weather
      Operations and Hydration: Injury and Performance Optimization) and impacts virtually all 14
      Military Operational Medicine Research Program Drivers.
    

Detailed description: 
      Study Objectives and Hypotheses

      Primary Objective

      The primary objectives of this study are to understand the in vivo effects of dehydration on:

        1. Sympathetic neural control of cardiovascular function (MSNA), and

        2. Neuromuscular function (CAC) via the IT Test

      The primary hypotheses of this study are:

        1. Baseline MSNA, and MSNA responses to tilt, will be higher in response to extracellular
           dehydration due to larger intravascular volume losses and greater baroreceptor
           unloading.

        2. Neuromuscular function (CAC) via the IT Test will a) be more impaired by intracellular
           dehydration (cell stress) and b) CAC will show a greater performance reduction than CAR
           because it reduces the emphasis placed on the voluntary portion of performance (i.e.,
           MVC).

      Ancillary Questions/Sub Studies

        1. The collection of blood and urine before and after exercise-heat stress and dehydration
           provides an opportunity to measure and characterize cytokine and intestinal barrier
           integrity marker (I-FAB, claudin-3) responses (blood) and renal stress biomarkers
           (urine) in humans. This descriptive research 'sub-study' directly complements Task Area
           T10 (Hot Weather Operations and Hydration: Injury and Performance Optimization) near and
           mid-term research goals of identifying biomarkers of heat stress for protection against
           heat injury. There are no hypotheses associated with this sub-study.

        2. The study of dehydration requires rehydration for recovery. Rehydration provides an
           opportunity for a novel comparison of renal water retention (urine volume) when
           consuming equal volumes of two different commercial beverages (Gatorade® or
           Enterade-S®). Unlike Gatorade®, which is a carbohydrate-based beverage containing
           electrolytes, Enterade-S® is an amino acid-based beverage containing electrolytes. We
           hypothesize that the unique formulation of Enterade-S® will improve the rate of fluid
           absorption and fluid retention compared to Gatorade® in both intracellular and
           extracellular dehydration trials.
    

Intervention name(s): Gatorade or Enterade
Intervention type(s): Other
Intervention description(s): Commercially available oral rehydration therapies
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: Between groups design
Masking: None (Open Label)
Primary purpose: Treatment