The effect of weight loss on obstructive sleep apn

Authors: Sophia E Schiza Charalampos Mermigkis Izolde Bouloukaki

Publish Date: 2014/03/18

Volume: 18, Issue: 4, Pages: 679-681

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Abstract

Obstructive sleep apnea OSA is a common chronic disorder whose severity and duration predisposes to neurocognitive and medical sequelae development and varies among individuals Obstructive respiratory events can be more severe and frequent in the supine sleeping position indeed more than half of all patients with obstructive sleep apnea OSA can be classified as supinerelated OSA The anatomical and physiological mechanisms for this phenomenon have not been well explained yet In the supine posture due to the unfavourable gravitational effects the upper airway calibre could be reduced resistance is likely to be increased and therefore the tendency for the upper airway to collapse is worsening compared to lateral positionSince the first large study of Oksenberg et al of 574 OSA patients who found that 559  had positional OSA POSA and the prevalence was higher in mild to moderate OSA patients ranging from 65–69  than in severe OSA 1 several studies with similar findings were published These patients tend to have less severe OSA to be less obese and to be younger 2 Even in those patients in whom the apnea hypopnea index AHI is not influenced by body position the duration of apnea/hypopnea and the degree of associated desaturations seems to be worse in the supine position 3Avoidance of the supine posture is efficacious and most studies report a positive effect of positional therapy PT on the AHI Additionally conservative treatment of OSA including weight reduction can be just as crucial Improvement could be accomplished even by a modest weight loss however the compliance with this form of treatment is often very low With this in mind bariatric surgical procedures according to body mass index BMI stratification are preferred achieving substantial weight loss and far exceeding the effectiveness of nonsurgical weight loss programmes In terms of longterm effectiveness a recent study showed that patients have achieved and maintained a loss of nearly half of their excess weight for as long as 15 years after bariatric surgery 4In this issue of Sleep and Breathing Dr Morong and colleagues tried to determine the prevalence of POSA in patients undergoing bariatric surgery and to evaluate the influence of bariatric surgery on POSA Furthermore based on previous studies they choose four predictors for POSA BMI neck circumference AHI and age The study was performed on 162 patients and 91 of them were finally analyzed The authors found that the prevalence of POSA in patients undergoing bariatric surgery was significantly lower 34  than the prevalence noted in the general population and a low AHI was shown to be the only significant independent predictor for the presence of POSA Their principal finding was that weight loss following bariatric surgery to a magnitude of 9 kg/m2 with a concomitant reduction in AHI about 19 events/h and an improvement in desaturation indices was related to the transition from nonpositional OSA into positional OSA ~65  of patients Although in retrospective this study extends previous observations of interaction between changes in body weight and its association with changes in positional dominance in nontreated patients with OSA 5 However the use of a bariatric surgery group in this study where magnitude of weight loss is greater than in clinical OSA groups has allowed the authors to state that nonpositional OSA can switch to mild positional OSA following weight lossKnowledge of positional dependency might be of importance in diagnosis as well as in the evaluation of treatment efficacy of OSA patients The high prevalence of positional OSA in the less severe forms of OSA have several implications in both clinical practice and research as mild OSA patients which are the vast majority of OSA patients 6 that might be good candidates for positional therapy Furthermore severe nonpositional OSA patients who cannot adhere to CPAP could use PT after losing weight allowing them to have an improved quality of sleep and life On the other hand POSA patients using successfully PT should be warned that increasing weight may convert them into nonpositional OSA who no longer benefit from PT and therefore for them CPAP is the treatment of choiceNevertheless it is worth noting that patients whose OSA improves or resolves after weight loss should strive to maintain their weight loss since weight gain is associated with worsening of OSA Although data addressing weight loss in OSA patients are somewhat limited the data available suggest that weight loss can be a highly effective treatment in the short term 7 Such patients should also be followed closely because OSA may recur even in patients who maintain their weight loss 8 Because of this clinicians remain sceptical of the overall efficacy of weight loss in these patients Counselling regarding ongoing diet modification and exercise as well as referral to a nutritionist may be beneficialIn the literature an increasing amount of studies has been published on the role of sleep position in OSA and PT Positional therapy can be defined as preventing patients to sleep in the worst sleeping position which is usually but not always the supine position When this is the case forcing a change to the nonsupine position during sleep may be an effective treatment So far due to the usage of bulky masses placed in the back compliance with PT was an issue Poor compliance and the subsequent disappointing longterm results of PT were reported attributed to backache discomfort and no improvement in sleep quality or daytime alertness However various techniques have developed such as positional alarms verbal instructions vests “shark fins” or special pillows which look promising Although the effectiveness of PT in positional OSA has been tested since the 1980s longterm compliance data and wellpowered randomized controlled trials are lacking In the metaanalysis by Ha et al 9 of the only three randomized trials comparing PT vs continuous positive airway pressure CPAP it was found that patients with mild positional OSA may benefit more from PT than those with severe OSA Furthermore in this group of patients with mild disease PT appeared to be almost as effective as CPAP therapy 10 Thus PT would appear to be a reasonable choice in patients with a mild disease with a positional component leading to a powerful therapeutic effect and thus helping avoid the deleterious health and behavioural consequences of OSAOne could ask why this kind of therapy remains largely ignored and has not been investigated more thoroughly into the daily OSA diagnosis and treatment Unfortunately the records of body position changes during all polysomnography PSG evaluations although being mentioned in the PSG report are not being used further Furthermore findings of PSG studies should be interpreted with caution as there are data suggesting that patients spend more time in the supine posture during PSG study compared to home sleep Therefore considering that the overall AHI is affected by the relative proportion of each of the different sleeping positions the severity of OSA may be overestimated in the laboratory settings In fact a significant nighttonight AHI variability has been reported As a consequence sleep study centres need to recognize that and advise their patients to occupy their natural sleep postures during the PSG study Likewise PT although a minimally invasive treatment modality is mostly reported in a superficial way or not mentioned at all in the PSG reportsThe main limitation of the study of Morong et al was the retrospective nature of the study leading to the possibility of underestimation of problems residing in the studied population owing to bias in subject selection and interpretation of the data recall bias Moreover as the authors explain another limitation of this study is that other pathophysiological mechanisms that influence positional dependency apart from weight change such as alcohol consumption and sedative use during the study period were not taken into account In addition accuracy in recording of sleep posture should be considered as direct review of videotape recordings of the patient and realtime posture scoring by the nighttime technicians appears to yield more consistent records of sleep posture than that of various digital position monitors Lastly in terms of sleep architecture sleep efficiency improved significantly after bariatric surgery however although the patients underwent full polysomnography there are no information on sleep variables such as arousal index per hour of sleep and percentage of total sleep time spent in each sleep stageIn conclusion significant improvement and even remission was noted in obese patients diagnosed with OSA undergoing bariatric surgery Therefore clinicians should consider this kind of treatment for patients with severe OSA and obesity alongside with the CPAP Most of the studies in this area are small nonrandomized uncontrolled and short term In order to find out the causality between changes in body weight and its effect on positional OSA it is imperative to carry out a large prospective longitudinal study Still positional data are not always used in clinical practice to aid in treatment choices

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