Professional shift-work drivers who adopt prophylactic naps can reduce the risk of car accidents during night work.
OBJECTIVE
Night work can be dangerous because both circadian sleep propensity (process C) and sleep pressure due to the prolonged wakefulness (process S) contribute to the reduction of vigilance levels. As naps are a countermeasure to sleepiness, this study evaluates the role they play in preventing sleep-related accidents in Italian shift-working police drivers.


METHODS
The study concerns highway car accidents that occurred to Italian shift-working police drivers; it was performed in 2 steps: a retrospective analysis of the overall number of accidents that occurred during the years 1993--1997 (n, 1195), followed by a validation analysis of a smaller cohort of accidents prospectively collected during 2003 (n, 84).


METHODS
N/A.


RESULTS
RETROSPECTIVE ANALYSIS: The influence of process S, process C, driver characteristics, and context conditions on accident risk, estimated by means of Cox hazard regression, revealed that nighttime accident risk was mainly influenced by process S levels. Consequently, an experimental mathematical model linking the hourly observed number of accidents to process S levels was designed. Its generalization to the theoretical case of drivers omitting naps showed an increase of about 38% of accidents. PROSPECTIVE ANALYSIS: In order to validate our results, we compared retrospective and prospective sleep patterns: no statistical difference was found. Again, the hourly number of accidents increased with homeostatic sleep pressure; the theoretical efficacy of napping was quantified in 48% accidents decrease.


CONCLUSIONS
Our data seem to confirm that napping before working a night shift is an effective countermeasure to alertness and performance deterioration associated with night work. Moreover, this self-initiated behavior could have a prophylactic efficacy in reducing the number of car accidents.
Garbarino
Sergio
S
Center of Sleep Medicine, University of Genoa, Italy.
Mascialino
Barbara
B
Penco
Maria Antonietta
MA
Squarcia
Sandro
S
De Carli
Fabrizio
F
Nobili
Lino
L
Beelke
Manolo
M
Cuomo
Gianni
G
Ferrillo
Franco
F
D000062:Accidents, Occupational / Q000517:prevention & control* / Q000706:statistics & numerical data; D000063:Accidents, Traffic / Q000517:prevention & control* / Q000706:statistics & numerical data; D000328:Adult; D001143:Arousal; D002940:Circadian Rhythm; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007558:Italy; D008297:Male; D016495:Police; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012189:Retrospective Studies; D012890:Sleep; D012892:Sleep Deprivation / Q000150:complications / Q000453:epidemiology; D020178:Sleep Disorders, Circadian Rhythm / Q000453:epidemiology / Q000517:prevention & control*; D014851:Wakefulness