Michael B. Russo

Patterns of performance degradation and restoration during sleep restriction and subsequent recovery: a sleep dose-response study

Daytime performance changes were examined during chronic sleep restriction or augmentation and following subsequent recovery sleep. Sixty‐six normal volunteers spent either 3 (n = 18), 5 (n= 16), 7 (n = 16), or 9 h (n = 16) daily time in bed (TIB) for 7 days (restriction/augmentation) followed by 3 days with 8 h daily TIB (recovery). In the 3‐h group, speed (mean and fastest 10% of responses) on the psychomotor vigilance task (PVT) declined, and PVT lapses (reaction times greater than 500 ms) increased steadily across the 7 days of sleep restriction. In the 7‐ and 5‐h groups speed initially declined, then appeared to stabilize at a reduced level; lapses were increased only in the 5‐h group. In the 9‐h group, speed and lapses remained at baseline levels. During recovery, PVT speed in the 7‐ and 5‐h groups (and lapses in the 5‐h group) remained at the stable, but reduced levels seen during the last days of the experimental phase, with no evidence of recovery. Speed and lapses in the 3‐h group recovered rapidly following the first night of recovery sleep; however, recovery was incomplete with speed and lapses stabilizing at a level comparable with the 7‐ and 5‐h groups. Performance in the 9‐h group remained at baseline levels during the recovery phase. These results suggest that the brain adapts to chronic sleep restriction. In mild to moderate sleep restriction this adaptation is sufficient to stabilize performance, although at a reduced level. These adaptive changes are hypothesized to restrict brain operational capacity and to persist for several days after normal sleep duration is restored, delaying recovery.

Comparative utility of instruments for monitoring sleepiness- related performance decrements in the operational environment

As both military and commercial operations increasingly become continuous, 24‐h‐per‐day enterprises, the likelihood of operator errors or inefficiencies caused by sleep loss and/or circadian desynchrony also increases. Avoidance of such incidents requires the timely application of appropriate interventions – which, in turn, depend on the ability to measure and monitor the performance capacity of individuals in the operational environment. Several factors determine the potential suitability of candidate measures, including their relative sensitivity, reliability, content validity, intrusiveness and cumbersomeness/fieldability. In the present study, the relative sensitivity (defined as the ratio of effect size to 95% confidence interval) of several measures to the effects of sleep loss was compared in a sleep restriction experiment, in which groups were allowed 3, 5, 7, or 9 h time in bed (TIB) across seven consecutive nights. Of the measures compared, the Psychomotor Vigilance Test was among the most sensitive to sleep restriction, was among the most reliable with no evidence of learning over repeated administrations, and possesses characteristics that make it among the most practical for use in the operational environment.

Oculomotor impairment during chronic partial sleep deprivation

OBJECTIVE The effects of chronic partial sleep (sleep deprivation) and extended sleep (sleep augmentation) followed by recovery sleep on oculomotor function were evaluated in normal subjects to explore the usefulness of oculomotor assessment for alertness monitoring in fitness-for-duty testing. METHODS Sixty-six commercial drivers (24-62 years, 50m/16f) participated in a 15 day study composed of 3 training days with 8h time in bed per night, 7 experimental days with subjects randomly assigned to either 3, 5, 7, or 9h time in bed, and 3 recovery nights with 8h time in bed. Data from 57 subjects were used. Saccadic velocity (SV), initial pupil diameter (IPD), latency to pupil constriction (CL), and amplitude of pupil constriction (CA) were assessed and correlated with the sleep latency test (SLT), the Stanford sleepiness scale (SSS), and simulated driving performance. RESULTS Regression analyses showed that SV slowed significantly in the 3 and 5h groups, IPD decreased significantly in the 9h group, and CL increased significantly in the 3h group. SLT and SSS significantly correlated with SV, IPD, CL, and driving accidents for the 3h group, and with CL for the 5h group. Analyses also showed a significant negative correlation between decreasing SV and increasing driving accidents in the 3h group and a significant negative correlation between IPD and driving accidents for the 7h group. CONCLUSIONS The results demonstrate a sensitivity primarily of SV to sleepiness, and a correlation of SV and IPD to impaired simulated driving performance, providing evidence for the potential utility of oculomotor indicators in the detection of excessive sleepiness and deterioration of complex motor performance with chronic partial sleep restriction. SIGNIFICANCE This paper shows a relationship between sleep deprivation and oculomotor measures, and suggests a potential utility for oculometrics in assessing operational performance readiness under sleep restricted conditions.

Electroencephalogram of asymptomatic adult subjects

OBJECTIVES The objective of this study is to investigate the incidence of epileptiform activity, focal or generalized slowing, patterns of uncertain significance and the effects of hyperventilation, photic stimulation and sleep on the electroencephalogram of asymptomatic adult subjects. METHODS The studied group consisted of 100 male subjects with a mean age of 34 years (range 18-45 years). Each subject was screened closely for personal or family history of seizures, HIV, head trauma and drug abuse. Half of the subjects had a magnetic resonance imaging scan (MRI). RESULTS In no subject resting or activated EEG showed any epileptiform activity or excessive slowing (focal or generalized). One subject demonstrated an H-response, one disclosed an alpha asymmetry of more than 50% and one showed slow alpha variant. Fourteen and 6 positive burst (12%) and small sharp spikes (11%) were the two most common patterns of uncertain significance. CONCLUSION In a carefully screened population of young and middle age adults, the incidence of epileptiform activity, photoparoxysmal response or excessive slowing is less than 1%.

Operational implications of varying ambient light levels and time‐of‐day effects on saccadic velocity and pupillary light reflex

Changes in maximal saccadic velocity (SV), initial pupil diameter (IPD), constriction latency (CL) and constriction amplitude (CA) determined by the pupillary light reflex have been found to be sensitive indicators of impairment as a result of drugs, sleepiness, and/or fatigue. Ambient illuminance and time of day are controlled when these indices are applied as repeated measures in fitness‐for‐duty determinations. The application of oculometrics in unrestricted operational environments, where ambient illuminance and time‐of‐day testing are not constant, requires understanding of, and potential compensation for, the effects of, and interactions among, these multiple uncontrolled variables. SV, IPD, CL, and CA were evaluated in the morning and evening on two consecutive days following adequate nightly sleep under one baseline ambient illuminance and seven test ambient illuminances. Sixteen healthy volunteers (21–38 years, eight females/eight males) participated. Within and across days, SV was unaffected by decreasing ambient light or time‐of‐day effects. With the increase of ambient light from 670 to 3300 lx, CL decreased by 1%, while IPD and CA decreased by 17% and 20%, respectively. IPD increased with time of day by 1–10% (IPD was smaller in the morning). The results show that SV and CL are essentially resistant to changes in ambient light and time‐of‐day effects, simplifying their application in uncontrolled operational environments.