Elsevier

Sleep Medicine

Volume 4, Issue 6, November 2003, Pages 523-529
Sleep Medicine

Original article
Effects of gender on upper airway collapsibility and severity of obstructive sleep apnea

https://doi.org/10.1016/S1389-9457(03)00168-0Get rights and content

Abstract

Objective

Obstructive sleep apnea (OSA) is far more common in males than females. The discrepancy between the lower prevalence of OSA, the greater frequency of obesity and the smaller airway size in women compared to men suggests that a gender difference underlies this condition. We hypothesized that due to differences in tissue linkage women have more stable and less mobile upper airway structures than men, providing protection against severe forms of OSA.

Methods

Seventy-one consecutive patients with OSA, defined as having apnea-hypopnea index ≥5 events per hour, were enrolled into the study. The median (range) apnea-hypopnea index was 20 (5–132) events/h. In addition, measurements of upper airway dimensions were made, using an acoustic reflectance method, while the lower jaw was in the resting position and during retrusive posture. Measurements of upper airway dimensions were used during wakefulness to examine whether changes in pharyngeal dimensions, resulting from retrusive movement of the mandible commonly occurring during sleep, would explain the gender differences in the characteristics of OSA.

Results

OSA was much more positional and severe in men than women as indicated by the higher apnea-hypopnea index in supine position compared with sleeping on the side (difference between supine and side apnea-hypopnea index: 43.7±5.2 (SEM) events/h in men versus 10.7±7.6 events/h in women, P=0.0015). The position dependency of OSA was most pronounced in those patients who demonstrated the largest decrease in pharyngeal cross-sectional area with retrusive movement of the mandible. There was no significant change in pharyngeal cross-sectional area as a result of retrusive movement of the mandible in women.

Conclusions

Men tend to have a larger but more collapsible airway during mandibular movement than women and this, in part, may play a role in the positional dependency and severity of OSA in men.

Introduction

Obstructive sleep apnea (OSA) is more common in men than women despite the fact that women with OSA tend to be more obese and have smaller upper airway size than men [1], [2], [3], [4]. This gender difference in the prevalence of OSA has not been adequately explained on the basis of obesity, upper airway size and neural control of upper airway muscles [5], [6], [7]. In a recent study by Pillar et al., men demonstrated more collapsibility of the upper airway during sleep than women when exposed to an external inspiratory load [8]. However, they found no gender difference in genioglossal or tensor palatini muscle activation in response to inspiratory resistive loading during sleep, suggesting differences in upper airway anatomy and mechanics rather than neural control of upper airway muscles. The current concept of the mechanism of upper airway maintenance during sleep suggests a complex interplay between intrinsic mechanical properties of the pharynx and neural regulation of pharyngeal dilator muscle activities. During sleep the neural inputs to pharyngeal dilator muscles are diminished, allowing the anatomical forces to increase pharyngeal collapsibility. Body position plays a significant role in the severity of OSA. Studies found that the number of obstructive events during sleep was much higher for the supine position than the lateral position in patients with OSA [9], [10]. The pharyngeal airway is structurally surrounded by soft tissues such as the tongue and lateral soft tissue. Watanabe and colleagues recently suggested that the balance between the size of soft tissue and the bony enclosure, such as the mandible, determines the closing pressure of the airway [11]. Gravitational force is considered to be one significant determinant of the closing pressure [11]. The larger mass of the soft tissues, such as the tongue, located anterior to the pharynx, can exert greater gravitational force on the anterior pharyngeal airway wall while the patient is in the supine position, whereas the relatively smaller amount of the soft tissues located laterally may exert less pressure onto the lateral pharyngeal airway wall while the patient in the lateral position [11]. The mandible tends to move inferiorly and posteriorly during sleep in the supine position [12], a movement associated with decreased pharyngeal diameter and an increase in upper airway resistance [13], [14]. We hypothesized that women might be protected from developing severe OSA because of the intrinsic stability of the pharynx and limited changes in upper airway caliber during inferior-posterior mandibular movement. The present study examines the relationship between changes in upper airway size and the severity and position-dependency of OSA in men and women.

Section snippets

Subjects

Among the consecutive patients referred to the sleep center for assessment, 71 patients were enrolled in the study after being diagnosed with OSA, as defined by a respiratory disturbance index (RDI, sum of apneas and hypopneas) ≥5 events per hour sleep. The current cohort is a subsample of a previously reported population that met the inclusion criteria for the present study [15]. Patients with a prior uvulopalatopharyngoplasty or clinically evident maxillofacial abnormalities such as

Results

The study population consisted of 53 men and 18 women, with mean ages of 52.0±1.5 and 48.6±3.2 years, respectively. The anthropometric data and respiratory indices are shown in Table 1. The men and women were obese with body mass indexes (BMI) of 33.5±0.7 and 39.5±3.0 kg m−2 (P=NS), respectively. The degree of daytime sleepiness, based on Epworth sleepiness scale, was comparable in men and women. Mean awake and minimum arterial oxygen saturations (SaO2) during sleep were also similar. However,

Discussion

The present study shows that: (1) OSA is more position-dependent in men than women; and (2) men have a greater reductions in upper airway dimensions with retrusive movement of the mandible than women and the worsening of sleep apnea in supine position appears, in part, be related to the degree of reduction in airway caliber with retrusive movement of the mandible.

Although there are lines of evidence to suggest the role of pharyngeal muscle tone, airway compliance and anatomic variables in

Acknowledgements

The author thanks Lauren Pollio and Wendy Stegina for their valuable technical assistance. The author has no financial relationship with the equipment manufacturers mentioned in this study. This research was supported, in part, by the departmental fund from the Yale University School of Medicine.

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