Effect of calf muscle electrical stimulation on rostral fluid shift, snoring and obstructive sleep apnea

Abstract

Study objectives

Overnight fluid shift from the legs into the neck may contribute to the pathogenesis of snoring and obstructive sleep apnea (OSA). The present study investigates the effects of calf muscle electrical stimulation (ES) on reducing leg fluid accumulation while seated, subsequent rostral fluid shift on lying down, and the impact on snoring and OSA.

Methods

Sixteen non-obese, normotensive men with OSA participated in the study. On the first study day, participants sat for 150 min receiving either active or sham ES through random allocation, then lied supine for 60 min. While seated and supine, leg and neck fluid volumes were measured using bioelectrical impedance to determine the magnitude of fluid shift. On the night of the study day, participants wore a portable sleep apnea diagnostic device overnight to measure snoring and sleep apnea severity. One week later, participants crossed over to the other study condition.

Results

Active calf muscle ES reduced leg fluid accumulation by 46% while seated. Upon lying supine, active ES reduced fluid shift out of the legs by 17% and reduced neck fluid accumulation by 31%. This led to a 15% reduction in snoring index, but did not alleviate OSA.

Conclusions

One session of calf muscle ES was effective at reducing leg fluid accumulation and rostral fluid shift, which led to a modest reduction in the snoring index, but not OSA. Despite this lack of effect of calf muscle ES in attenuating OSA severity, the reduction in the snoring index suggests that it did have an effect, albeit mild, on upper-airway mechanics.

Introduction

Obstructive sleep apnea (OSA) is a common disorder that occurs in 10% of the population [1] and is characterized by intermittent narrowing or collapse of the pharynx during sleep. Pharyngeal collapse can occur due to multiple interacting pathophysiological mechanisms, which can vary across individuals [2]. Among the components predisposing to OSA, anatomical factors that narrow the airway (eg, craniofacial abnormalities, enlarged peripharyngeal tissues, or excessive neck fat deposition), are well understood to interact with various other mechanisms and contribute to pharyngeal collapse. Through this same mechanism, nocturnal fluid shift from the legs to the neck can also contribute to pharyngeal narrowing and predispose to OSA. Specifically, overnight fluid shift increases mucosal water content in the peripharyngeal tissues [3], which can apply pressure to the pharynx, leading to pharyngeal narrowing [4], increased pharyngeal resistance [5] and collapsibility [6], as well as increased OSA severity [7].

Rostral fluid shift and its association with OSA present avenues for new therapies to treat OSA that target the fluid shift mechanism. Alternative therapies for OSA are of particular importance given that the most common therapy, continuous positive airway pressure, is poorly tolerated by patients [8]. Therapies aimed at reducing fluid retention and/or fluid accumulation in legs have been shown to reduce pharyngeal narrowing and OSA. For example, daily walking, wearing compression stockings during the day, ultrafiltration, and diuretics, reduce overnight rostral fluid shift in association with a 16–34% reduction in OSA severity [9], [10], [11], [12]. Among these therapies, compression stockings and exercise are most practical for the general population, although both are associated with low adherence [13], [14], [15].

An alternative method for reducing leg fluid is involuntary activation of the calf muscle via electrical stimulation (ES) [16], [17]. As a device-based therapeutic approach, calf muscle ES can be especially useful for individuals that are sedentary due to their occupation, aging, or mobility impairment. Calf muscle contractions via ES reduces leg fluid by activating the skeletal muscle pump, moving blood back to the heart, reducing hydrostatic pressure in the capillaries of the legs, and counteracting the filtration of fluid out of the capillaries into the interstitium [18], [19]. Indeed, calf muscle ES has been shown to reduce leg fluid accumulation while seated [16], [17]. However, to the best of our knowledge the effect of calf muscle ES on rostral fluid shift and the pharyngeal airway has never been investigated.

The present study is an observational trial that tests the hypothesis that calf muscle ES will reduce the rostral shift of fluid out of the legs and into the neck, reduce snoring and alleviate OSA. Therefore, the primary objective of this study was to examine the effect of calf muscle ES on leg fluid accumulation while seated, and its impact on rostral fluid shift when lying supine and subsequent snoring and OSA.