Weight Loss See Also Chapter

The importance of obesity in OSA patients has been discussed in prior sections of this chapter. Several predominantly uncontrolled studies have been performed to investigate the effect of various methods of nonsurgical weight loss (diet, behavior, and activity) on sleep apnea (53,145-147). In general, such studies have shown that significant weight loss (approximately 10%) is associated with varying degrees of improvement in sleep apnea (53,145). Importantly, weight loss is challenging to sustain and therefore re-emergence of apnea may occur. Examining the effect of weight loss on airway properties, investigators have reported that OSA patients who achieved a mean reduction of 17% in body weight demonstrated significant decreases in airway collapsibility [i.e., critical closing pressure (Pcrit)] and, in turn, significant decreases (greater than a 50% decrement) in disordered breathing (74). Three-dimensional MRI in obese normal women (AHI < 5 events per hour) has demonstrated that a 17.7% weight loss increased the volume of the upper airway and significantly decreased the volume of the lateral pharyngeal walls and para-pharyngeal fat pads (148) (Figs. 9 and 10). The volume of the soft palate and tongue also decreased but these changes did not achieve statistical significance. The explanation of these upper airway geometry changes with weight loss has not been completely elucidated. It is possible that decrements in fat pad volume could lead to a lateral traction effect upon the lateral pharyngeal walls. In addition, adipose tissue within the lateral pharyngeal walls, tongue, uvula, and under the mandible could decrease with weight loss and hence contribute to the overall increase in volume of the upper airway. Finally, weight loss may affect the muscular tissue surrounding the airway thereby altering airway biomechanical properties. It is well documented that weight gain in obese patients is not solely due to increased fat but also muscle (107,109). Further investigation is required to clarify the anatomic

FIGURE 9 Axial retropalatal magnetic resonance imaging of a normal woman, before and after a 17% weight loss. Airway area and lateral airway dimensions increase and the thickness of lateral pharyngeal walls and the size of the parapharyngeal fat pads decrease with weight loss.

FIGURE 10 (See color insert.) Upper airway soft tissue [soft palate (purple), the tongue (orange/ rust), the lateral pharyngeal walls (green), parapharyngeal fat pads (yellow)] and craniofacial [mandible (gray)] magnetic resonance imaging reconstructions before and after a 17% weight loss in a normal woman. The size of the upper airway increases with weight loss. The largest reductions in the size of the upper airway soft tissue structures with weight loss were in the lateral pharyngeal walls and the parapharyngeal fat pads. Source: From Ref. 148.

FIGURE 10 (See color insert.) Upper airway soft tissue [soft palate (purple), the tongue (orange/ rust), the lateral pharyngeal walls (green), parapharyngeal fat pads (yellow)] and craniofacial [mandible (gray)] magnetic resonance imaging reconstructions before and after a 17% weight loss in a normal woman. The size of the upper airway increases with weight loss. The largest reductions in the size of the upper airway soft tissue structures with weight loss were in the lateral pharyngeal walls and the parapharyngeal fat pads. Source: From Ref. 148.

relationship between weight loss and sleep apnea. The extent of weight loss required for improved outcomes in patients with sleep apnea and the effects on the airway configuration require more study.

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