Comparison Of Resting Pilocarpine-induced Sweat Sodium Concentration And Exercise-induced Sweat Sodium Concentration

INTRODUCTION: Physiological and environmental factors such as heart rate, sweat rate, temperature and relative humidity can affect the rate and composition at which sodium is excreted through sweat during exercise. One of the most common and accessible ways for one to determine their sweat Na+ composition is through a pilocarpine-induced collection of a resting sweat sample which is then tested using a sweat sodium analyzer (SSA). Changes in sweat Na+ concentration over time during exercise can be estimated by measuring resting concentrations using pilocarpine iontophoresis, and comparing with measured exercise-induced concentrations. PURPOSE: To compare Na+ concentration between pilocarpine-induced (resting sweat) sweat and exercise-induced sweat. METHODS: Thirty-two (n = 32) subjects ages 18-64 yrs volunteered for this study. Before the start of exercise, a resting Na+ concentration was collected using pilocarpine iontophoresis to induce sweating. The subjects then ran on a treadmill at a moderate intensity (~ 65% heart rate reserve) for 90 minutes. Sweat collectors were removed every 15-30 minutes and samples were analyzed using a commercial SSA. RESULTS: The average pilocarpine-induced resting Na+ concentration was 51 mM +/- 16 mM. After 15-30 minutes, the average Na+ concentration was 52 mM +/- 18 mM. The last sweat sample, taken at 90 minutes, averaged 57 mM +/- 27 mM. Of the total number subjects, 22 (69%) had a greater than 5 mM deviation between their exercise and pilocarpine resting Na+ sweat concentration with an average deviation of 10 mM. After 90 minutes of exercise, 20 (63%) had a greater than 5 mM deviation between their exercise and pilocarpine resting Na+ sweat concentration with an average difference of 8 mM with a p = 0.01 and a Cohen’s d of 0.4. The data also showed the difference between male and females. More females (65%) did not match the pilocarpine measurement after 90 minutes, compared to males (35%) with a p = 0.1 and a Cohen’s d of 0.4. CONCLUSION: The overall results showed a statistically-significant difference between exercise-induced sweat Na+ concentration compared to resting sweat Na+ concentration. A difference was also found between genders. These differences should be taken into consideration when determining measure methods. This work was supported by NSF [grant number 2111983]