Heart rate variability and daytime
functioning in insomniacs and normal sleepers: preliminary results.
Fang SC, Huang CJ, Yang TT, Tsai PS.
College of Nursing, Taipei Medical University, Taipei, Taiwan.
OBJECTIVES: This study examined the differences in heart rate variability (HRV) and daytime functioning between insomniacs and normal sleepers. METHODS: All
participants underwent an interview, a medical examination, and a sleep measurement protocol during which they wore an actigraph and logged a sleep diary for a 7-day period to verify their eligibility. Included in the study were 18 insomniacs and 21 normal sleepers.
During a laboratory session, these participants completed four paper-pencil tests of sleepiness, anxiety, fatigue, and concentration difficulty and the Wisconsin Card Sorting Test. Resting HRV was recorded under paced breathing. RESULTS: Neither did
insomniacs experience cognitive impairment nor did they experience excessive daytime sleepiness compared with normal sleepers. However, insomniacs experienced higher frequency of fatigue [effect size (ES)=1.14, P=.002] compared with normal sleepers. There was also a trend toward higher trait anxiety score (ES=0.62) and concentration difficulty (ES=0.59) in insomniacs than in normal sleepers. Although a tendency toward lower resting high- frequency (HF) HRV (ES=-0.57) in insomniacs than in normal sleepers was noted, neither the resting low-frequency (LF) HRV nor the LF/HF ratio were different between groups. Subjective sleep estimates correlated to self-reported daytime
consequences such as fatigue and concentration difficulty but not cognitive function. On the contrary, objective sleep estimates correlated to problem-solving/conceptualization and learning but not self-reported daytime consequences. CONCLUSIONS: Insomniacs are not sleepier during the day than normal sleepers. However, they may experience such a
daytime symptom as fatigue although cognitive function remains unimpaired.
