A similarly designed study by Gawron and colleagues (1990) of 21 healthy male pilots found no significant decrements in performance in a flight simulator aircraft after standard treatment with PB. Pilots were unable to subjectively determine whether they received PB or placebo. However, another study of similar design (Brooks et al., 1992) of 24 A-10 pilots performing complex maneuvers in a flight simulator did not reveal a significant difference except in regard to one task. In a simulation of low-level penetration into a target area, pilots on PB were “killed” by surface-to-air missiles (SAMs) 25 percent more frequently; this finding was statistically significant. The authors attributed this effect to the “simulation factor” without explaining why simulation would preferentially exert nonpharmacological effects on PB-treated subjects.

Other investigators addressed the issue of PB effects on performance in combination with other physiological stressors. Forster and colleagues (1994) studied the effects of gravitational acceleration (G-force) stress and the usual CW pre-exposure PB regimen on overall performance in five healthy male volunteers (average age 26). This placebo-controlled, double-blind study assessed physiological and cognitive parameters. No statistically significant difference between PB- and placebo-treated subjects was noted for pulmonary function, heart rate, QT intervals,9 PR intervals,10 handgrip strength, or tolerance for acceleration. Cognitive performance was not systematically statistically affected by PB. Likewise, a similarly designed study of 10 Navy divers examining exercise, immersion, and warm temperature stresses (Doubt et al., 1991), showed no drug-related changes in heart rate, minute respiration, oxygen consumption, tidal volume, handgrip strength, or perceived exertion. Another study of like design measured the effects of standard doses of PB combined with heat–exercise stress and wearing CW protective clothing on eight healthy male volunteers (Arad et al., 1992b). PB had no significant effect on cognitive and physiological parameters but a statistically significant increase was found in “shortness of breath” (p < .005) in the PB-treated group. The authors concluded that in light of the absence of objective changes in respiratory function, this symptom is not likely to be of clinical significance. Cook and colleagues (1992) studied the simultaneous effects of heat, exercise, and standard PB doses for 7 days on seven healthy male subjects (mean age 21.4 years). PB was associated with a 4-mm decrease in resting diastolic blood pressure, a 0.050-mm decrease in pupillary diameter, a 3 percent decrease in handgrip strength, and a 0.1°C higher final rectal temperature. Although statistically significant, effects of this magnitude are unlikely to be clinically important. Subjects were unable to distinguish between days on placebo and days on PB.

In summary, the preponderance of evidence in studies reviewed above supports minimal effects of PB on overall motor, physiological, and cognitive functioning when normal healthy subjects are tested with complex tasks or physical

9  

QT is the time interval that reflects the duration of ventricular depolarization and repolarization.

10  

PR is the time interval between atrial and ventricular depolarizations.



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