Respiration affects heart variability (HRV) by baroreflexes. HRV increases at low respiratory rates with a maximum at about .2 Hz. In 18 women with fibromyalgia, which lowers central pain treshold (F;43±10 yrs) and 18 control women (C;39±11) ECG was recorded in supine position while breathing at spontaneous rate (S=.25-.35 Hz) and .2 Hz paced rate (P). FFT spectra of HRV were obtained from RR intervals time series in S and P. Power was assessed in the bands VLF (.02-.04 Hz), LF (.04-.15), HF (.15-.4), TOT (total= .02-.4) LF/HF ratio was calculated.

Results (ln ms2; m±se): 

TOT VLF LF HF

S:C=5.9±0.2 S:C=4.0±0.2 S:C=5.1±0.2 S:C=4.6±0.2

S:F=5.1±0.3 S:F=3.5±0.2 S:F=4.3±0.3 S:F=3.7±0.3

P:C=6.4±0.3 P:C=4.0±0.2 P:C=4.9±0.2 P:C=5.6±0.3

P:F=5.3±0.3 P:F=3.1±0.3 P:F=4.0±0.3 P:F=4.6±0.4

LF/HF S:C=2.2±0.4 S:F=2.3±0.5

LF/HF P:C=0.8±0.2 P:F=0.8±0.2

At 2-ways ANOVA and Bonferroni test TOT P and HF P were greater than TOT S (<.05) and HF S (<.001) in C, but not in F. TOT P and HF P in C were greater than in F (<0.01; <.05). The LF/HF values were quite similar in C and F subjects. Slowing respiration down to 0.2 Hz failed to increase HRV in F women mainly in the HF band. These data agree with the hypothesis of an interplay between central control mechanism of baroreflexes and pain threshold.