MAXIMAL EXERCISE PERFORMANCE-IMPAIRING EFFECTS OF SIMULATED BLAST OVERPRESSURE IN SHEEP

Lung contusion has been identified as a primary blast injury. These ex periments addressed a fundamental and overt endpoint of primary blast injury, incapacitation (performance decrement). Respiration, hemodynam ics, and blood gases were measured in sheep undergoing incremental exe rcise challenge before and 1 h after simulated blast exposure of the t horax. Pathologic examination of lung tissue was performed after expos ure and exercise testing. Blast overpressure was simulated in the labo ratory using a compressed air-driven shock tube. Three levels of lung injury (Levels 1-3,'Trivial', 'Slight', and 'Moderate' injury, respect ively) were examined for effects on maximal oxygen consumption ((V) ov er dot O-2max), an index of cardiorespiratory fitness. Resting hemodyn amics and blood gases were relatively normal an hour after exposure, i mmediately before exercise. However, Levels 1-3 lung injury were assoc iated with average 4.8, 29.9 and 49.3% (V) over dot O-2max decreases, respectively. These performance decrements for Levels 2 and 3 were sig nificantly different from respective controls (non-exposed). Exercise caused significant hemoconcentration in sheep under control conditions , before exposure (resting 9.5 +/- 0.9, end-exercise 11.8 +/- 0.9 g/10 0 mi). Blast exposure resulted in average decreases of 4.9 +/- 3.4, 12 .8 +/- 4.0, and 12.6 +/- 3.3% in exercise-induced hemoconcentration fo r Levels 1-3 injury, respectively. Normal exercise-induced hemodynamic increases were also attenuated after exposure. Levels 2 and 3 injury resulted in average 22.6 +/- 2.9 and 18.5 +/- 11.2% stroke volume decr eases, and also 22.3 +/- 8,4 and 29.0 +/- 14.2% cardiac output decreas es, respectively, during exercise. While blast lung pathology and pulm onary function changes could account for post-blast performance decrem ents, these experiments suggest that in sheep, early after exposure, d iminished hemoconcentration and cardiac disfunction may also contribut e to decreased exercise performance. (C) 1997 Elsevier Science Ireland Ltd.