Persistent autonomic dysfunction and bladder sensitivity in primary dysmenorrhea

Abstract

Menstrual pain, also known as dysmenorrhea, is a leading risk factor for bladder pain syndrome (BPS). A better understanding of the mechanisms that predispose dysmenorrheic women to BPS is needed to develop prophylactic strategies. Abnormal autonomic regulation, a key factor implicated in BPS and chronic pain, has not been adequately characterized in women with dysmenorrhea. Thus, we examined heart rate variability (HRV) in healthy (n = 34), dysmenorrheic (n = 103), and BPS participants (n = 23) in their luteal phase across a bladder-filling task. Both dysmenorrheic and BPS participants reported increased bladder pain sensitivity when compared to controls (p's < 0.001). Similarly, dysmenorrheic and BPS participants had increased heart rate (p's < 0.01), increased diastolic blood pressure (p's < 0.01), and reduced HRV (p's < 0.05) when compared to controls. Dysmenorrheic participants also exhibited little change in heart rate between maximum bladder capacity and after micturition when compared to controls (p = 0.013). Our findings demonstrate menstrual pain's association with abnormal autonomic activity and bladder sensitivity, even two weeks after menses. Our findings of autonomic dysfunction in both early episodic and chronic visceral pain states points to an urgent need to elucidate the development of such imbalance, perhaps beginning in adolescence.

Figure 1

The three cohorts have distinct baseline HRV characteristics. (a) Heart rate, (b) RMSSD, (c) LF-HRV, and (d) HF-HRV were collected during rest prior to water ingestion. Data are represented as mean ± SEM. Data related to panels B–D were log₁₀ transformed for normal distribution. *p < 0.05, **p < 0.01, and ***p < 0.005.

Figure 2

The three cohorts have different bladder pain sensitivities during bladder filling. Participants reported bladder pain sensitivity at baseline and at first sensation (FS), first urge (FU), and maximum capacity (MC) during bladder filling. Data are represented as mean ± SEM. *p < 0.05, **p < 0.01, and ***p < 0.005 (Dysmenorrhea vs Healthy Controls), ^#p < 0.05, ^##p < 0.01, ^###p < 0.005 (BPS vs Healthy Controls).

Figure 3

The effects of bladder filling on HRV characteristics. (a) Bladder filling did not significantly impact heart rate across the three cohorts expect following micturition (or void; V). When compared to MC, healthy controls at V display a decrease in heart rate; this drop in heart rate is not observed in dysmenorrheic or BPS participants. (b,d) Bladder filling did not significantly impact RMSSD or HF-HRV across all three cohorts. (c) Bladder filling had a dynamic effect on LF-HRV in all groups. Both healthy controls and dysmenorrhea participants display a similar pattern during the bladder fill. In contrast, BPS participants have a lower and distinct LF-HRV pattern during bladder fill. Data are represented as mean ± SEM. Data related to panels B–D were log₁₀ transformed for normal distribution. *p < 0.05, **p < 0.01, and ***p < 0.005 (Dysmenorrhea vs Healthy Controls). ^#p < 0.05, ^##p < 0.01, ^###p < 0.005 (BPS vs Healthy Controls).

Figure 4

Dysmenorrheic and BPS participants fail to show post-void drop in heart rate. The difference in heart rate between after voiding and maximum capacity was calculated [ΔHR(V-M)] for all participants. Unlike healthy controls, dysmenorrheic and BPS participants did not display a drop in heart rate following micturition. Data are represented as mean ± SEM. *p < 0.05, **p < 0.01, and ***p < 0.005.