Circadian studies of autonomic nervous balance in patients with fibromyalgia (FM): a heart rate variability analysis

OBJECTIVE: To determine the accumulated 24-hour cardiovascular

autonomic modulation and its circadian variations in patients

with fibromyalgia, by means of heart rate variability


METHODS: Thirty patients with fibromyalgia and 30

age- and sex-matched controls were studied prospectively.

Assessments included a 24-hour ambulatory recording of heart

rate variability, time-domain analysis of the accumulated

24-hour R-R interval variations, and power spectral analysis

to determine the sympatho/ vagal balance at different hours

(calculated as the power spectral density of the low-frequency

[0.04- 0.15-Hz] sympathetic band divided by the power of the

high-frequency [0.15-0.50-Hz] parasympathetic band).


Fibromyalgia patients had diminished accumulated 24-hour heart

rate variability, manifested by a decreased standard deviation

of all R-R intervals (mean +/- SD 126 +/- 35 ms, versus 150

+/- 33 ms in controls; P = 0.008) and a decreased ratio of

pairs of adjacent R-R intervals differing by >50 ms (mean +/-

SD 12.0 +/- 9.0% versus 20.1 +/- 18.0%; P = 0.031). Patients

lost the circadian variations of sympatho/vagal balance, with

nocturnal values significantly higher than those of controls

at time 0 (mean +/- SD 3.5 +/- 3.2 versus 1.2 +/- 1.0; P =

0.027) and at 3 hours (3.3 +/- 3.0 versus 1.6 +/- 1.4; P =


CONCLUSION: Individuals with fibromyalgia have

diminished 24-hour heart rate variability due to an increased

nocturnal predominance of the low-frequency band oscillations

consistent with an exaggerated sympathetic modulation of the

sinus node. This abnormal chronobiology could explain the

sleep disturbances and fatigue that occur in this syndrome.

Spectral analysis of heart rate variability may be a useful

test to identify fibromyalgia patients who have dysautonomia.

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