Plasma renin activity and aldosterone: correlations with moderate hypohydration.

Area of Science:

• Environmental Physiology
• Human Performance
• Protective Equipment Research

Background:

• Military personnel and first responders often operate in demanding environments requiring protective clothing.
• Understanding the physiological impact of wearing impermeable protective garments during physical exertion is crucial for safety and performance.

Purpose of the Study:

• To investigate the physiological effects of different clothing configurations, including impermeable chemical protective garments and masks, on fluid-electrolyte regulatory hormones during prolonged exercise.
• To evaluate the efficacy of different through-mask drinking systems under these conditions.

Main Methods:

• Sixteen adult males performed a 6-hour treadmill exercise protocol in a moderate environment (WBGT 23°C) wearing three different clothing setups.
• Blood samples were analyzed for plasma renin activity (PRA) and aldosterone levels (PA) pre- and post-exercise.
• Hypohydration was assessed via body weight loss, and two drinking systems were tested with masks.

Main Results:

• Chemical protective garments significantly elevated PRA and PA post-exercise compared to fatigues alone.
• Hypohydration levels ranged from 0.84% to 4.04% body weight loss.
• PRA and PA showed significant correlations with hypohydration (body weight loss).
• Masks reduced fluid intake, increasing hypohydration and exacerbating PRA and PA elevations.

Conclusions:

• Impermeable protective garments increase physiological stress, elevating PRA and PA in moderate environments due to heat, sweat, and dehydration.
• Challenges in fluid delivery through protective masks worsen hypohydration and hormonal stress responses.
• Optimizing fluid intake systems is critical for personnel operating in protective gear.