Obstructive sleep apnea (OSA) is a prevalent sleep disorder characterized by recurrent episodes of complete or partial upper airway collapse during sleep. This leads to disrupted sleep architecture, intermittent hypoxia, and significant cardiovascular and metabolic consequences [1]. It affects approximately 936 million adults aged 30–69 worldwide, with about 425 million suffering from moderate to severe cases [2]. The primary risk factors for OSA include obesity, age, male gender, and craniofacial abnormalities [3]. Among these, obesity is considered the most significant modifiable risk factor, with evidence showing a direct link between increased body weight and the severity of OSA [4].

Obesity contributes to the development and severity of OSA by increasing adipose tissue in the upper airway, which can narrow the airway and make it more likely to collapse during sleep, obstructing airflow. Additionally, obesity is linked to systemic inflammation, which may lead to airway remodeling and increased collapsibility [5]. Given the substantial relationship between obesity and OSA severity, weight loss is commonly recommended as a therapeutic strategy for OSA patients [6]. Weight loss has been shown to reduce the severity of OSA, enhance clinical outcomes, and decrease the need for medical interventions such as positive airway pressure (PAP) therapy, considered the gold standard treatment for OSA [7].

PAP therapy acts as a pneumatic splint, delivering a continuous stream of air to keep the upper airway open during sleep [8]. It effectively prevents apnea episodes, improves oxygen saturation, and restores normal sleep architecture [9]. However, a significant challenge in managing OSA with PAP is determining the optimal PAP level to prevent upper airway obstruction. Optimal PAP levels greatly vary among individuals and depend on several factors including body mass index (BMI), age, neck circumference, and severity of airway obstruction, indicated by metrics such as the apnea-hypopnea index (AHI), arousal index, and minimal oxygen saturation [10,11]. Therefore, changes in body weight, especially weight loss, can influence the required PAP levels for effective therapy in OSA patients.

The optimal PAP level is defined as the lowest pressure setting that effectively prevents airway collapse during sleep. It is crucial for maximizing therapeutic outcomes and preventing upper airway collapse. Using inappropriate pressure settings can result in various negative outcomes and diminished therapeutic efficacy [9]. If the PAP level is lower than optimal, respiratory disturbances may increase, and symptoms may persist. Conversely, if the PAP level is higher than necessary, it may lead to adverse effects such as air leakage, upper airway dryness, and frequent arousals, consequently reducing adherence to PAP therapy [9,12].

Understanding the relationship between weight loss and changes in optimal PAP levels is essential for improving OSA management. However, the specifics of this relationship are currently poorly understood. Thus, as a pilot study to explore the potential relationship between weight reduction and alterations in optimal PAP levels, the objectives of this study were to investigate the association between weight loss and changes in optimal PAP levels required for effective OSA treatment.

The study included a total of 20 patients with OSA, comprising 18 males and 2 females. Baseline demographic data are displayed in Table 1. The subjects had a mean age (±SD) of 42.2± 9.3 years, a height of 1.72±0.07 m, a weight of 100.6±15.6 kg, and a BMI of 34.2±5.1 kg/m². The average tonsil size grade was 1.1±0.6 and all high palate-tongue positions were observed. Two patients had previously undergone uvulopalatopharyngoplasty, and one had a tonsillectomy. The average Epworth sleepiness scale was 13.3±4.5, and the average STOP-BANG questionnaire score was 5.1±1.1.

Baseline polysomnographic data are shown in Table 2. The total recording time was 410.8±34.2 minutes, total sleep time (TST) was 351.9±48.6 minutes, sleep efficiency was 85.9%±11.8%, and the arousal index was 55.6±26.1 events per hour of TST. Sleep stage durations, as percentages of TST, were as follows: Stage N1, 39.3%±25.0%; Stage N2, 33.5%±18.9%; Stage N3 (slow-wave sleep), 2.9%±6.4%; and Stage R (rapid eye movement sleep), 14.2%±7.5%. The AHI was 61.2±31.1 events per hour of TST, the respiratory disturbance index was 65.1±27.8 events per hour of TST, minimum oxygen saturation was 71.4%±10.7%, and the snoring duration, as a percentage of TST, was reported in 55.1%±22.5% of the study.

Changes in optimal PAP levels before and after weight loss are summarized in Table 3. Patients who achieved substantial weight loss, from 100.6±15.6 to 86.5±12.9 kg (p<0.001), experienced a significant reduction in their optimal PAP levels, from 12.0±1.6 to 9.9±1.2 cm H₂O (p<0.001).

Simple linear regression analysis illustrates the association between weight loss and changes in optimal PAP levels in Fig. 1. A scatterplot visualizes this relationship, and the analysis shows a positive correlation between weight loss and decreased optimal PAP levels (r=0.428, p=0.0596). However, this correlation did not reach statistical significance at the 0.05 level. The regression equation, y (decrease in optimal PAP levels, cm H₂O)= 0.820+0.093x (weight loss, kg), indicates that for every 1 kg reduction in body weight, the optimal PAP level is estimated to decrease by 0.093 cm H₂O (95% confidence interval: -0.0042, 0.1986).

This study investigates the relationship between weight loss and changes in optimal PAP levels among patients with OSA. Consequently, subjects who experienced significant weight loss (≥5 kg) observed considerably lower optimal PAP levels. The regression equation (y=0.820+0.093x) implies that for each kilogram of weight lost, the optimal PAP level is estimated to decrease by 0.093 cm H₂O. To our knowledge, this is the first study to specifically explore how optimal PAP levels decrease in proportion to weight loss.

In this study, optimal PAP levels significantly decreased in OSA patients who achieved significant weight loss (≥5 kg), with the following mechanism proposed. Excessive weight, particularly around the neck and tongue, leads to upper airway obstruction by increasing pressure on the respiratory tract [5,6]. As weight is lost, fat deposits around the upper airway diminish, resulting in reduced collapse and overall improved breathing during sleep [5,6]. Understanding this relationship elucidates how weight loss decreases the need for high optimal PAP levels as the upper airway becomes more naturally open.

Numerous studies have explored the correlation between weight change and the severity of OSA [4,7]. In a population-based, prospective cohort study, Peppard et al. [4] assessed the independent longitudinal association between weight alterations and OSA severity. They demonstrated a significant correlation whereby, compared to stable weight, a 10% decrease in body weight correlated with a 26% reduction in AHI, whereas a 10% increase in body weight corresponded to approximately a 32% rise in AHI. Malhotra et al. [7], through a meta-analysis of 27 studies and 32 treatment arms, quantified the relationship between weight loss and AHI changes. They found that weight loss in individuals with both OSA and obesity was significantly associated with reductions in OSA severity. Specifically, a 10% drop in BMI corresponded to a 36% decrease in AHI, a 20% drop resulted in a 57% decrease, and a 30% decrease in BMI linked with a 69% reduction in AHI. The study also noted a 0.093 cm H₂O decrease in the optimal PAP level for every 1 kg of weight loss, indicating that a patient losing 1 kg of weight can expect a 0.093 cm H₂O decrease in their optimal PAP level.

Several approaches to weight loss for managing overweight and obesity include dietary interventions, behavioral modifications, physical activities, pharmacological therapies, and surgical procedures [15]. Diet, behavioral changes, and exercise are typically considered the first-line management strategies for obesity, although their effectiveness can be limited. In severe cases, especially for patients with obesity and OSA, pharmacotherapy and bariatric surgery are usually recommended. In Western countries, surgical management, like bariatric surgery, is advised for individuals with a BMI of ≥40 kg/m² or for those with a BMI between 35 and 40 kg/m² who have significant comorbidities such as cardiovascular disease, diabetes, or OSA [16,17]. The consensus statement for Asian populations suggests surgical intervention for individuals with a BMI of ≥35 kg/m² who also have type 2 diabetes, or a BMI of ≥30 kg/m² in cases of uncontrolled type 2 diabetes or metabolic syndrome [16,17]. In the study, one of the 20 participants underwent bariatric surgery, while the remaining 19 employed non-surgical strategies including dietary changes, physical activity, behavioral interventions, or medication to achieve weight loss.

Elucidating the connection between weight loss and changes in optimal PAP levels is crucial for several reasons. A primary benefit of predicting these changes is the ability to tailor PAP therapy, enhancing patient compliance. PAP therapy should be customized to each patient’s needs, with optimal pressure settings calculated to maintain their upper airways open during sleep. When weight loss occurs, the collapse of a patient’s upper airway during sleep often reduces, which may decrease the required pressure level to maintain airway patency. Investigating the relationship between weight loss and optimal PAP levels allows for accurate adjustment of PAP settings over time, avoiding excessive levels that can cause discomfort and side effects such as mask leaks, eye irritation, headaches, difficulty falling asleep, increased awakenings, and dry nose and mouth.

In patients with OSA undergoing PAP therapy, several factors including age, anthropometric measurements, polysomnographic parameters, and upper airway anatomy influence the optimal PAP level [10,11]. Choi et al. [10] evaluated these factors in 202 patients with OSA, considering demographic and polysomnographic variables. The study identified significant correlations between optimal PAP levels and AHI (r=0.595, p<0.001), arousal index (r=0.542, p<0.001), BMI (r=0.494, p<0.001), neck circumference (r=0.265, p<0.001), minimum oxygen saturation (r=-0.502, p<0.001), and age (r=-0.164, p=0.019). Wang et al. [11] conducted a study identifying independent predictors of optimal PAP levels and developed a predictive equation for determining the optimal PAP value in patients with OSA. They used correlation analysis and multiple stepwise regression analysis to establish that BMI, AHI, minimum percutaneous oxygen saturation, and longest apnea duration were significant independent predictors of optimal PAP level.

The current study has several limitations. It is a retrospective medical record review and involves a relatively small number of subjects. The study did not include a control group and did not address the association between weight gain and optimal PAP levels. Moreover, the findings may not be generalizable to all patients with OSA. Considering these limitations, further research is needed to explore these areas more thoroughly.

In conclusion, the study highlights an association between weight loss and reduced optimal PAP levels in patients with OSA. Patients who achieved substantial weight loss (≥5 kg) experienced a clinically meaningful decrease in their optimal PAP level. Predicting changes in optimal PAP levels due to weight loss enables the personalization of PAP therapy, improving patient compliance. However, the study has several limitations, including its retrospective design and small sample size, highlighting the need for further research to bridge these gaps. Ultimately, this study enhances the understanding of the relationship between weight loss and alterations in optimal PAP levels, contributing to the optimization of PAP therapy for effective clinical outcomes in patients with OSA, and laying the groundwork for more targeted interventions in future studies.