submission - Independent Pilots Association

Fatigue, Alcohol and Perforrnance Impairment
Nature. Volume 388, July-August 1997
Reduced opportunitv for sleep and reduced sleep qualiqv are frequently
related to accidenls involving shift-workersr'3. Poor-qualiry sleep and
inadequate recovery leads to increased fatigue, decreased alertness and
impairìd performance in a variety of cognitive psychomotor testsa. However.
the risks associated with fatigue a¡e not well quantified. Here we equate the
performance impairment caused by fatigue with that due to alcohol
intoxicauon, aná show that moderate levels of fatigue produce trigher levels of
impairment than the proscribed level of alcohol intoxication.
Forty subjects participated in two counterbala¡lced oçeriments. ln one
they were irept áwake for 28 hours (from 8:0O until l2:AO tl.e following day)'
rtrá itt the other they were asked to consume lO-l5g alcohol at 3O-min
intervals from 8:OO until their mean blood alcohol concentration reached
O.lOo/0. We measured cognitive psychomotor perfolrnance at half-hourly
inten'als using a computer-administered test of hand-eye coordination (an
unpredictablekacking task). Results are expressed as a percentage of
performance at the start of the session.
performance decreased significantly in both conditjons. Between the
tenth and twenty-sixth hours of wakefubress, mean relative performance on the
tracking task decreased bl'O.71o/o per hour. Regression analvsis in the
sustainéd wakefulness condition revealed a linear correlation betrveen meart
relatir-e performance and hours of rvakefulness that accounted for roughlv 90%
of the variance (Fig. ta).
Regression analvsis in the alcohol condition indicated a significant linea¡
correlation between subject's mean blood a-lcohol concenlration and mean
relatiçe performance tfrat accounted for roughlv 7Oo/o of the variance (Fig. lb).
For each O.Ololo increase in blood alcohol. performance decreased by 1.1602ô.
Thus. at a mean blood alcohol concentration of 0.100/0. mean relative
performance on tJ.e tracking task decreased. on average b]- I L'60lo'
Equating the two rates at which performance declined (percentage
decline per hour of wakefulness and percentage decline rvith change in blood
alcohol concentration), rve calculated t-Ìrat the performance decrement for each
hour of wakefulness behveen i O and 26 hours was equivalent to the
performance decrement obsen'ed with a O.OO4o/o rise in blood alcohol
concentration. Therefore. after I7 hours of sustained rvakefulness (3:OO)
cognitive psychomotor perforrnance decreased to a level equivalent to the
p.kor-*cè impairment observed at a blood alcohol concentration of 0.050,0.
This is the proscribed level of alcohol intoxication in marl\- rvestern
industrializèd countries. After 24 hours of sustained rvakefulness (8:00)