Cardiac autonomic function and vasomotor symptoms: too much break and not enough accelerator?
In this issue of Menopause, Gibson et al21 conducted a study to examine the relationship between resting cardiac autonomic function, and the frequency and severity of VMS during menopause transition. Women were recruited from the Menopausal Treatment Using Relaxation Exercises (MaTURE) trial,22 who were perimenopausal or postmenopausal (n = 121, ages 40-59 years), with at least four hot flashes per day, and randomized to paced respiration or music-listening control intervention for 12 weeks. Cardiac impedance derived pre-ejection period (PEP), as a measure of cardiac sympathetic activity, and respiratory sinus arrhythmia (RSA), a marker of parasympathetic activity, were measured at baseline and at 12 weeks, along with VMS frequency and severity.
The main findings from the study indicate that cardiac sympathetic activity is not significantly associated with hot flash frequency or severity at baseline or over 12 weeks. In contrast, there was a trend of higher frequency of moderate-to-severe hot flashes in those with parasympathetic predominance (as measured by RSA) at baseline. Increase in RSA was positively associated with frequency of moderate-to-severe VMS over 12 weeks. Authors suggested that increased parasympathetic tone may reflect increased sensitivity to perceiving VMS. Paced respiration intervention did not result in sympathetic or parasympathetic predominance change over 12 weeks compared with music listening control.
Gibson et al should be congratulated for a well-conducted randomized study on the complex topic of autonomic function and VMS, with a slow-paced respiration intervention. Nearly 90% of subjects were retained at 12 weeks, and intervention was practiced at least 15 minutes per day per their design. Teasing apart autonomic components to assess contributions of each branch to VMS is not easy, because many things influence autonomic activity such as sound, noise, temperature, food intake, stress, and sleep.23 Similarly, VMS are impacted by emotions, stress, food, alcohol, and temperature. In this study, instead of measuring time or frequency domain heart rate variability as a global, integrative measure of autonomic function,24 PEP was used as a more specific measure of cardiac sympathetic activity, which is under beta-adrenergic influence.25 RSA was used as a measure of parasympathetic function (amplitude of high frequency oscillations of R-R interval); the ANS plays an important role in synchronizing heart rate with respiration, and fluctuations of the R-R interval by respiration represents efficiency of cardio-pulmonary interaction.