Medicine & Science in Sports & Exercise:
Pathogenesis, Pathobiology and Treatment of Exertional Heat Injury/Stroke
1U.S. Army Res. Inst. Environmental Med., Natick, MA 01760 and Naval Hospital, Beaufort, SC 29902
Since E in the absence of EHI induces ISD, the relevance of ISD to EHI pathogenesis is unclear.
To determine if ISD with EHI could be distinguished from those due to E alone, lymphocyte responses were studied in military recruits training (U.S. Marine Corp Recruit Depot, Parris Island, SC) in warm weather (June-September, 2000).
Recruits (age = 18.5 ± 0.3 yrs; mean ± S.E.) were briefed prior to the start of military training and those providing informed consent identified in a database. When a recruit presented with EHI, this database was queried for consent compliance (10 males; 1 female). Consenting exercise controls, (E, 3 males; 3 females) performed similar military training (1.75–2 mile run) as those with EHI. Blood was collected at 0 (EHI onset or E completion), 2 and 24h. Samples were processed for flow cytometric analysis of peripheral lymphocyte subpopulation (PLSP) distribution and phytohemagglutinin (PHA)-stimulated CD69 mitogen response.
EHI peak body temperature (40.4 ± 0.3°C) was significantly (p < 0.05) elevated compared to E (38.6 ± 0.2°C). One EHI patient was delirious and diagnosed with heat stroke. All others suffered, at most only slow mentation and thus were classified as exertional heat exhaustion or injury. For EHI vs. E at 0h, natural killer cell percentage was significantly elevated, helper T cell percentage and helper: suppressor ratio were significantly depressed, while other PLSPs were similar. By 2h, all EHI PLSPs were similar to E. From 0 to 24h all EHI PLSPs, except B-lymphocytes revealed a significantly reduced PHA response compared to E.
EHI ISD were distinguished from E to suggest ISD pertain to EHI pathogenesis. Since heat stroke also induces ISD, similar findings in heat exhaustion or injury indicated EHI of varying severity may represent parts of a continuum, sharing pathophysiological processes. Supported by the Bureau of Medicine and Surgery Clinical Investigation and the USA MRMC grant to the H. M. Jackson Foundation.