1. Obstructive Sleep Apnea (OSA) in Obese Patients
OSA, primarily defined as an anatomical abnormality concomitant with obesity, now has a well-established position as a manifestation of a metabolic syndrome with a rather molecular than strictly anatomical mechanism of development 
. Insulin resistance and an increased leptin level are independent of obesity associated with OSA. One of the considered mechanisms of leptin’s impact on OSA is its direct influence on the respiratory center in the central nervous system 
. OSA and obesity coexist with elevated levels of proinflammatory cytokines. Obesity facilitates low-grade inflammation in many complex molecular pathways. Remittent hypoxia episodes, which are a fundamental pathology caused by OSA, also favor inflammation. Obesity and OSA may aggravate each other by the exacerbation of an inflammatory state 
. Importantly, in the context of bariatric surgery, Tirado et al. proved a statistically highly significant (p
< 0.01) decrease in inflammation-associated molecules (CRP, HO-1, IL-6, IL-1β, TNF-α) after the procedure with no statistically significant differences between the Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy 
. Regarding how respiratory drive leptin is recognized as an essential stimulant of ventilation, increased leptin levels in obese patients reflect leptin resistance, with a decreased respiratory drive as one presentation of central leptin resistance 
. These listed facts are proof of the molecular origin of OSA 
. There are numerous risk factors independently associated with an increased likelihood of OSA, including male sex, BMI > 35 kg/m2
, smoking, gastroesophageal reflux disease (GERD), hypothyroidism, acromegaly, and benzodiapine use 
The necessity of effective treatment for OSA arises from severe, recognized complications of OSA, including poor control of hypertension, other cardiovascular comorbidities, and premature mortality 
. OSA is an important risk factor for the most common arrhythmia—atrial fibrillation. Evidence strongly suggests that appropriate OSA management can improve atrial fibrillation control 
. Positive airway pressure (PAP) in different modes, preferably continuous positive airway pressure (CPAP), is a gold standard for OSA treatment with proven effectiveness in reducing OSA symptoms, complications and improving the quality of sleep 
. Although CPAP is the “golden method” for OSA treatment, there are other methods in OSA therapy. Mandibular advancement devices (MADs) are anti-snoring mouthpieces designed to physically move the jaw forward and expand the airway. There are also some new methods, including Lin oral appliances or even transoral robotic surgery 
. In the context of considered bariatric surgery, preoperative CPAP improves the safety of general anesthesia and the procedure itself 
Though a decrease in body mass is an advantageous strategy in patients with OSA, it leads rather to a reduction in symptoms than to the resolution of OSA 
. Another common difficulty is the fact that no more than 10% of patients with obesity treated only with dietary or behavioral regimes maintain weight loss in the long-term perspective 
. Due to the temporary effect of behavioral strategies, AASM proposes bariatric surgery as the leading adjunctive therapy for OSA in obese patients. The remission rate of OSA after bariatric surgery was estimated by AASM to be 40%. Sustainable weight loss seems to contribute to the success of invasive strategies.
2. Effect of Bariatric Surgery on OSA Treatment in Obese Patients
In compliance with the current guidelines, bariatric surgery has been indicated in patients with a BMI > 40 independently of coexisting comorbidities or in patients with BMI > 35 with a history of comorbidities, including diabetes mellitus type 2, heart failure, hypertension, or OSA 
. Though numerous studies have been conducted in recent years to define the impact of bariatric surgery on OSA, there remains a need to gather further information, especially in RCTs.
Furlan et al. randomly assigned patients into groups that were treated with Usual Care (nutritional, psychological intervention, physical activity) or RYGB 
. The follow-up lasted for 3 years. Compared to UC, RYGB was related to a significant improvement in numerous parameters, including BMI, EDS, and neck and waist circumference. Importantly, a median increase in AHI was observed in the UC group, while the RYGB group showed a significant decrease in AHI. Bariatric surgery gave an incomparably better chance to cure OSA than UC. The obtained differences between groups were statistically significant with p
Nastalek et al. included obese patients who were diagnosed with OSA using screening tools 
. In addition to sleep questionnaires, each patient was assessed with polysomnography preoperatively and 12 months after the procedure. In total, 44 patients diagnosed with OSA were treated with bariatric surgery (sleeve gastrectomy (31/44) or RYBG (13/44)), underwent follow-up hospitalization, and were included in the final analysis. After CPAP titration and continuation, a significant improvement in numerous parameters, including AHI, ODI, and mean SpO2, was observed. All these listed findings were of high statistical significance with p
< 0.001. In total, 25 patients from 44 (56.8%) achieved the normalization of AHI. Though CPAP remained a gold standard to treat OSA, treatment with CPAP was burdened with a low compliance problem. CPAP was used over less than half of the days, which indicated low compliance in these patients. Compared to a preoperative assessment, post-operative polysomnography showed a significant improvement in numerous parameters, including the AHI (44.9 vs. 29.2), oxygen desaturation index (ODI) (43.6 vs. 18.3), mean hemoglobin saturation (93% vs. 95%) and snoring (21.6 vs. 4.5%). High statistical significance was obtained (p
< 0.001). A moderate correlation between the percentage loss of excess AHI and the percentage loss of excess BMI was observed. This effect of bariatric surgery on OSA is consistent with the current literature 
(Reviewer 1). Bariatric surgery resulted in an approximately low rate of normalization regarding sleeping disturbances (16%), while in 5% of cases, OSA severity increased. The most probable scenarios seem to be stabilization (39%) or a decrease in OSA severity without complete normalization (41%).
Another study comparing the effects of bariatric surgery versus non-invasive treatment was Feigel-Guiller et al. 
. Obese patients with OSA treated by non-invasive mechanical ventilation (NIV) were included. The target was to assess the differences in NIV weaning in patients treated with gastric surgery or INC at 1, 3, and 10 years of follow-up. Patients (n = 70) were randomly allocated into two groups—the first group was treated with laparoscopic adjustable gastric banding (LAGB), and the second group was treated non-invasively by intensive nutritional care (INC). Data were collected at years 1, 3, and 10 after intervention. LAGB was associated with a significantly greater weight loss than INC, with 15% vs. 6% after the first year (p
< 0.001) and 14% vs. 3% after the third year (p
< 0.001). Despite greater weight loss and a positive trend in NIV weaning in patients treated with LAGB, the difference was not statistically significant both after the first and third years. The INC group showed a decrease in AHI in years 1 and 3; however, this result was not statistically significant. The decrease in AHI in the LAGB group was statistically significant after one and three years of follow-up. Data collected after ten years of follow-up showed that a high percentage of patients in both groups required another bariatric procedure.
Auclair et al. evaluated the impact of biliopancreatic diversion with a duodenal switch (BPD-DS) on OSA and systemic hypertension 
. A 77% remission rate in OSA was achieved in a twelve-month follow-up. The molecular profile of patients who achieved resolution of OSA was similar to those who did not, with the exception of a high-sensitivity C-reactive protein. The reduction in this parameter was statistically and significantly greater in patients who were cured of OSA than in patients who did not achieve a resolution. The disadvantage is a rather small probe: from the sixty-two patients included, forty underwent a procedure. Twenty patients of twenty-six with OSA had their OSA resolved. As the effects of BPD-DS diverged from the results presented in other studies, this method requires following assessments in studies involving a bigger probe.
While the general improvement in OSA control after bariatric surgery is well-established knowledge, there is an increasing need to conduct studies that compare different techniques. Nowadays, leading techniques include LRYGB and the more conservative laparoscopic sleeve gastrectomy (LSG). Wölnerhanssen et al. conducted a study based on merged Swiss and Finnish data 
. The comparison of the results of LSG to LRYGB was conducted in all fields in relation to metabolic syndrome (MetS), including OSA. No statistically significant difference was noted between LSG and LRYGB regarding OSA’s remission rate. The OSA control was similar in both groups after five years of follow-up as well.
The results of numerous studies assessing bariatric surgery’s impact on OSA control are relatively consistent: bariatric surgery decreases OSA symptoms and can lead to OSA resolution. Yet, there is an increasing need to conduct studies assessing certain subpopulations. The prevalence of OSA and obesity is also alarmingly high among adolescents 
. Amin et al. conducted a study proving an early improvement in OSA symptoms control and laboratory findings in patients between fifteen and twenty years old 
3. Conservative Treatments for OSA
A study assessing OSA control in the long term was presented by Kuna et al. 
Two conservative regimes were compared. Intensive lifestyle intervention (ILI) gave a greater chance of reducing OSA severity compared to diabetes support and education (DSE). The improvement in the control of OSA symptoms was correlated with body mass reduction, baseline AHI and factors independent of weight change. A higher probability of OSA remission after ten years of follow-up was observed in the ILI group (34.4% vs. 22.2%).
Positive and promising effects of both invasive and conservative strategies in OSA management signalize a need to conduct studies that compare the efficiency and safety of bariatric surgery to acknowledged conservative strategies, for example, ILI. Combined behavioral, pharmacological, and surgical strategies also require studies to assess their effectiveness 
. Regarding pharmacological intervention pharmaceutics from flozins and the glucagone-like peptide 1 analog, groups should be considered that can offer supportive treatment to invasive procedures. Neeland et al. proved the beneficial effect of empagliflozin in patients with diabetes mellitus 2 and coexisting OSA 
The OSA remission rate may be increased by the avoidance of supine sleeping positions. Joosten et al. examined patients that did not meet OSA resolution criteria after significant weight loss 
. In total, 22% of them had resolved their OSA after changing their daily sleep position to non-supine.