Effect of hydration on whole blood viscosity in firefighters

Cardiovascular disease (CVD) is the leading cause of on-duty death among firefighters, totaling 45% of on-duty fatalities. Heat stress and fluid losses can result in decreases in cardiac output of firefighters, despite sustained tachycardia and maximally elevated heart rate during emergencies. Measurements of whole blood viscosity (WBV) may serve as an independent biomarker of the hydration and dehydration states of on-duty firefighters.

The current pilot study investigates the effects of a strenuous firefighting simulation and subsequent rehydration on WBV and other biological metrics in nine healthy, nonsmoking firefighters to (1) determine whether dehydration and rehydration result in detectable changes in WBV and (2) compare WBV with the results from a range of conventional medical tests.

The research team designed a single-center, unblinded pilot study.

Fire Training Division, 1900 Lind Ave SW, Renton, WA, 98057.

Participants were 9 healthy, nonsmoking firefighters who were volunteers.

Vital signs, traditional medical blood tests, and WBV were measured for each firefighter (1) at baseline, (2) after exercise but before rehydration with alkaline water, and (3) postexercise and after rehydration. Hematocrit (HCT), hemoglobin (Hb), and WBV increased after exercise and before rehydration.

Dehydration during the mock fire drill resulted in elevated WBV at both low- and high-shear rates. HCT and Hb increased due to dehydration and hemoconcentration. Hb and HCT returned to baseline values after exercise and rehydration, and while WBV improved, baseline values were not restored. After exercise but before rehydration, WBV changes were significantly larger than HCT and Hb changes, suggesting the profound influence of hydration states on WBV.

WBV measurements were better determinants of hydration states than HCT or Hb and should be performed to monitor the cardiovascular health of at-risk firefighters.