DAYTIME CARDIAC AUTONOMIC ACTIVITY DURING ONE WEEK OF CONTINUOUS NIGHT SHIFT

Abstract

Shift workers encounter an increased risk of cardiovascular disease compared to their day working counterparts. To explore this phenomenon, the effects of one week of simulated night shift on cardiac sympathetic (SNS) and parasympathetic (PNS) activity were assessed. Ten (5m; 5f) healthy subjects aged 18-29 years attended an adaptation and baseline night before commencing one week of night shift (2300-0700h). Sleep was recorded using a standard polysomnogram and circadian phase was tracked using salivary melatonin data. During sleep, heart rate (HR), cardiac PNS activity (RMSSD) and cardiac SNS activity (pre-ejection period) were recorded. Night shift did not influence seep quality, but reduced sleep duration by a mean of 52±29 min. One week of night shift evoked a small chronic sleep debt of 5h 14±56 min and a cumulative circadian phase delay of 5h±14 min. Night shift had no significant effect on mean HR, but mean cardiac SNS activity during sleep was consistently higher and mean cardiac PNS activity during sleep declined gradually across the week. These results suggest that shiftwork has direct and unfavourableeffects on cardiac autonomic activity and that this might be one mechanism via which shiftwork increases the risk of cardiovascular disease. It is postulated that sleep losscould be one mediator of the association between shiftwork and cardiovascular health.