Relationship of autonomic nervous system activity to daytime sleepiness and prior sleep

Autonomic nervous system (ANS) measures have been used frequently as measures of activation or arousal. However, their relationship to standard measures of alertness--the Multiple Sleep Latency Test (MSLT) and Stanford Sleepiness Scale (SSS)--and to the quantity and quality of prior sleep has not been determined. In this study, the direct pupil light reflex (PLR) was measured with the MSLT and SSS to determine how ANS activity varies with daytime sleepiness and how all three measures were related to prior nocturnal sleep in a group of patients with obstructive sleep apnea. When the effects of age and time of day were partialed out, PLR data suggest that increased sleepiness as measured by MSLT is significantly correlated with increased parasympathetic activity (r = -0.60, p less than 0.01) and not with decreased sympathetic activity (r = -0.24, not significant). These partial correlations were significantly different (p less than 0.05). Increased sleepiness as measured by the SSS was significantly correlated with decreased sympathetic activity (r = -0.46, p less than 0.05) and not with increased parasympathetic activity (r = -0.00, not significant). These partial correlations were significantly different (p less than 0.02). In the group of sleep apnea patients, the PLR suggests that increased number of apneas and hypopneas (sleep fragmentation) was significantly correlated with both decreased sympathetic activity and increased parasympathetic activity. These findings suggest that ANS activity is related to daytime sleepiness and to the quality of prior sleep.