Abstract
Objectives: To determine if there are clinical or anatomical differences between patients with grade II-IV obesity without obstructive sleep apnea (OSA) or mild OSA and patients with moderate or severe OSA and to assess whether any of these factors are predictive of moderate/severe OSA. Methods: Observational case-control study with consecutive sampling including patients between 18 and 65 years of age with grade II-IV obesity who were candidates for bariatric surgery. An anamnesis regarding OSA symptoms, a physical examination of the upper airway and a cardiorespiratory polygraphy were performed. Results: A total of 124 patients were included in the study, of whom 61.3% did not have OSA or had mild OSA and 38.7% had moderate or severe OSA. Age over 48 years was the only independent factor associated with moderate or severe OSA. Other factors showed a relation with moderate/severe OSA after multivariate analysis: male sex, STOP-BANG questionnaire ≥ 3, weight ≥ 105 kg, thick neck, neck circumference ≥ 41.25 cm, flaccid palate, Mallampati III-IV index, Friedman tongue position III-IV and retropalatal narrowing. Conclusions: The only independent predictive factor related to moderate or severe OSA in patients with morbid obesity was age over 48 years, therefore a sleep study remains essential for its diagnosis.
Supplementary Information
The online version contains supplementary material available at 10.1007/s12070-024-04908-0.
Keywords: Obstructive Sleep Apnea, Bariatric Surgery, Morbid Obesity, Upper Airway
Introduction
Obstructive sleep apnea (OSA) is the most prevalent sleep breathing disorder in the general population, affecting 4-30% of the population between 30 and 69 years of age worldwide [1]. Obesity is its main risk factor [2]. OSA prevalence is estimated in around 63 and 83% of obese patients [3, 4] and for every 10% increase in body weight, the risk of suffering OSA increases six-fold [5]. Individuals with central or visceral obesity, in which fat is deposited in the trunk and neck regions, are at higher risk. In addition, OSA patients develop more sedentary lifestyles due to daytime sleepiness, thus perpetuating this close relationship between OSA and obesity.
Despite its high prevalence, the pathophysiology of OSA in obese patients is still not clearly established. Obesity is thought to contribute to airway collapse by a multifactorial mechanism [6]. Apart from hormonal and metabolic factors [7–9], the local deposit of fat at the neck, pharynx and tongue [10, 11] is one of the factors responsible for OSA in obese patients by reducing the caliber of the upper airway (UA) and increasing its collapsibility [12]. However, there are very few studies in the literature that have studied the anatomy of the upper airway in these patients. Therefore, the main purpose of this study is to determine whether there are clinical or anatomical differences between patients without OSA or mild OSA and those with moderate or severe OSA, and to assess whether any of these factors are predictive of moderate/severe OSA.
Materials and Methods
This study was approved by the Research Ethics Committee (CEIm) at the Research Unit of the Hospital on March 25th, 2020 (CEIm code: 38/20).
Data Sources
Observational case-control study with consecutive sampling including patients aged 18–65 years with obesity grade II (body mass index (BMI) ≥ 35 kg/m2) and hypertension, type 2 diabetes, metabolic syndrome or OSA or obesity grade III or IV (BMI ≥ 40 kg/m2) elective for bariatric surgery (laparoscopic Roux-en-Y gastric bypass (RYGB) or vertical sleeve gastrectomy (VSG)) at the General Surgery department. Patients had to have lost at least 10% of their maximum weight and present a favorable psychiatric evaluation in order to be considered for bariatric surgery. In addition, patients had to voluntarily agree to be part of the study and sign the informed consent form.
As part of the preoperative study, patients were evaluated at the Otolaryngology department with an anamnesis regarding OSA and a physical examination of the UA. A cardiorespiratory polygraphy (CRP) was also requested. The following data were collected in the anamnesis: age, sex, smoking or drinking habits, cardiovascular risk factors, previous diagnosis of OSA, Epworth sleepiness scale [13] and STOP-BANG questionnaire [14]. Features included in the physical examination were: weight (kg), height (m), BMI (kg/m2), neck length and thickness, neck circumference, uvula thickness and length, narrowing at the posterior pharyngeal pillars and the pharyngeal lateral walls, palatal shape, tongue scalloping, Mallampati index (MI) [15], Friedman tongue position (FTP) [16] and the tonsillar size based on Brodsky classification [17]. A flexible fibre-optic endoscopy was also performed, assessing retropalatal or tongue base obstruction, and lingual tonsil size [18]. From the CRP, the following were recorded: number of apneas and hypopneas, apnea hypopnea index (AHI), oxygen desaturation index (ODI), minimum oxygen saturation (SatO2) and time with SatO2 below 90%.
Patients under 18 or over 65 years of age were excluded, as well as those who refused to participate in the study, pregnant women, patients with a score equal to or greater than IV on the American Society of Anesthesiologists (ASA) scale, those who did not attend the pre- or post-surgical Otorhinolaryngology visit or patients that did not undergo the pre or post-surgical CRP or it was not valid (less than 6 h of recording).
Statistical Analysis
Patients were divided in two groups based on the CRP results: no OSA or mild OSA (AHI < 15/h) and moderate or severe OSA (AHI≥15/h). Continuous variables were expressed by mean, median, range and standard deviation and categorical parameters by their frequencies.
ROC curves were used to determine the cut-off value with the highest sensitivity and specificity for predicting success of bariatric surgery in the treatment of OSA, dichotomizing continuous variables. A simple binary logistic regression analysis was performed to analyze factors related a higher risk of moderate/severe OSA (AHI≥15/h), determining the OR and 95% confidence intervals (CI) for non-adjusted association. Most relevant variables (p < 0.05) and possible confounders were selected for a multivariate model and adjusted ORs.
The Statistical Package for the Social Sciences (SPSS Inc., Chicago, IL, USA), 24.0.0.0 version, was used for the analysis. A p value < 0.05 was considered statistically significant.
Results
An anamnesis regarding OSA and a physical examination of the UA were performed on 169 patients. Of these, 45 patients refused to undergo CRP or it was not valid, therefore a total of 124 patients were included in the study.
CRP Metrics
Of the total, 25.8% (n = 32) did not suffer from OSA, 35.5% (n = 44) had mild OSA, 21% (n = 26) moderate, and 17.7% (n = 22) severe OSA.
In the non-OSA or mild OSA group, 76 patients (61.3%) were included, and in the moderate or severe OSA group, 48 patients (38.7%). The results of the CRP in both groups are shown in Table 1.
Table 1.
CRP results of patients without OSA/mild OSA (n = 76) and moderate/severe OSA (n = 48)
| No OSA/mild OSA | Moderate/severe OSA | |
|---|---|---|
| AHI (events/h) | 6.25 ± 4.33 | 34.44 ± 16.87 |
| ODI (events/h) | 39.29 ± 4.46 | 41.39 ± 4.96 |
| Minimum SatO 2 (%) | 94.597 ± 2.39 | 92.99 ± 2.65 |
| TSatO2 < 90% (min) | 26.53 ± 68.24 | 70.16 ± 74.61 |
| TSatO2 < 90% (%) | 6.28 ± 15.47 | 16.61 ± 19.31 |
| Number of Apneas | 3.42 ± 6.72 | 68.9 ± 78.05 |
| Number of Hypopneas | 39.45 ± 27.21 | 143.8 ± 77.96 |
AHI: apnea hypopnea index, CRP: cardiorespiratory polygraphy, ODI: oxygen desaturation index, OSA: obstructive sleep apnea, SatO2 minimum oxygen saturation, TSatO2 < 90%: time with SatO2 below 90%
Demographics
The mean age of patients without OSA or mild OSA was 46.17 ± 10.52 years (range = 19–64 years, median = 47 years), whereas for patients with moderate and severe OSA the mean age was 52.94 ± 7.93 years (range = 35–64 years, median = 54.5 years) (p = 0.000). Individuals over 48 years old had a sensitivity of 77.1% and a specificity of 53.9% for the detection of moderate and severe OSA (AUC = 0.693 (0.6–0.787)).
In the group of patients with moderate and severe OSA there were more men, a higher mean age and higher scores on the STOP-BANG questionnaire (Table 2).
Table 2.
Association between moderate/severe OSA and the patient’s clinical profile: Chi2and the simple binary logistic regression model
| Category | No OSA/mild OSA | Moderate/severe OSA | p-value | OR (95% CI) | p-value | |
|---|---|---|---|---|---|---|
| Sex | Female | 68 (67.3%) | 33 (32.7%) | 0.004 | ||
| Male | 8 (34.8%) | 15 (65.2%) | 3.86 (1.49–10.03) | 0.005 | ||
| Age | < 48 years old | 41 (78.8%) | 11 (21.2%) | 0.001 | ||
| ≥ 48 years old | 35 (48.6%) | 37 (51.4%) | 3.94 (1.75–8.86) | 0.001 | ||
| Epworth Sleepiness Scale | < 12 | 67 (64.4%) | 37 (35.6%) | 0.216 | ||
| ≥ 12 | 5 (45.4%) | 6 (54.5%) | 2.17 (0.62–7.61) | 0.225 | ||
| STOP-BANG | Low risk | 25 (89.3%) | 3 (10.7%) | 0.001 | ||
| Moderate-severe risk | 49 (53.8%) | 42 (46.2%) | 7.14 (2.01–25.35) | 0.002 | ||
CI: confidence interval, OSA: obstructive sleep apnea, OR: odds ratio
In the preoperative physical examination, differences in mean weight, BMI, and neck circumference were observed among patients without OSA or mild OSA and those with moderate or severe OSA (Table 3). A weight of 105 kg at the ENT visit had a sensitivity of 65.2% and a specificity of 54% for the detection of moderate or severe OSA (AUC = 0.538 (0.426–0.650). A body mass index (BMI) of 39.3 kg/m2 had a sensitivity of 58.7% and a specificity of 53.6% for the detection of moderate or severe OSA (AUC = 0.619 (0.515–0.723)). A neck circumference greater than 41.25 cm had a sensitivity of 66.7% and a specificity of 65.8% for the detection of moderate and severe OSA (AUC = 0.74 (0.653–0.826)).
Table 3.
Weight, BMI, and mean neck circumference of the non-OSA/mild OSA group vs. moderate/severe OSA: Student’s t-test for independent samples
| No OSA/mild OSA | Moderate/severe OSA | p-value | |
|---|---|---|---|
| Weight (kg) | 105.14 ± 15.44 | 113.29 ± 16.19 | 0.006 |
| BMI (kg/m 2 ) | 39.29 ± 4.46 | 41.39 ± 4.96 | 0.017 |
| Neck circumference (cm) | 40.67 ± 4.07 | 44.32 ± 4.16 | 0.000 |
BMI: body mass index, OSA: obstructive sleep apnea
Of all the anatomical features examined, significant differences were observed in the parameters shown in Table 4. The rest of the features explored are shown in the complementary material.
Table 4.
Association between moderate/severe obstructive sleep apnea and upper airway examination: Chi2and simple binary logistic regression model
| Category | No OSA/mild OSA | Moderate/severe OSA | p-value | OR (95% CI) | p-value | |
|---|---|---|---|---|---|---|
| Weight | < 105 kg | 41 (71.9%) | 16 (28.1%) | 0.025 | ||
| ≥ 105 kg | 35 (52.2%) | 32 (47.8%) | 2.34 (1.11–4.96) | 0.026 | ||
| Neck thickness | Normal | 27 (87.1%) | 4 (12.9%) | 0.001 | ||
| Thick | 49 (53.8%) | 42 (46.2%) | 5.79 (1.87–17.88) | 0.002 | ||
| Neck circumference | < 41.25 cm | 50 (76.9%) | 15 (23.1%) | 0.000 | ||
| ≥ 41.25 cm | 26 (44.1%) | 33 (55.9%) | 4.23 (1.95–9.16) | 0.000 | ||
| Flaccid soft palate | No | 39 (73.6%) | 14 (26.4%) | 0.024 | ||
| Yes | 37 (53.6%) | 32 (46.4%) | 2.41 (1.11–5.22) | 0.026 | ||
| Mallampati Index | I-II | 50 (70.4%) | 21 (29.6%) | 0.004 | ||
| III-IV | 15 (41.7%) | 21 (58.3%) | 3.33 (1.45–7.7) | 0.005 | ||
| Friedman tongue position | I-II | 28 (75.7%) | 9 (24.3%) | 0.044 | ||
| III-IV | 48 (56.5%) | 37 (43.5%) | 2.4 (1.01–5.7) | 0.047 | ||
| Retropalatal space | Normal | 59 (68.6%) | 27 (31.4%) | 0.042 | ||
| Narrow | 16 (48.5%) | 17 (51.5%) | 2.32 (1.02–5.28) | 0.044 | ||
CI: confidence interval, OSA: obstructive sleep apnea, OR: odds ratio
Risk Factors for Moderate/Severe OSA
Age over 48 years was the only variable that showed a significant association with the development of moderate/severe OSA in the multivariate analysis (Table 5).
Table 5.
Association between moderate/severe OSA and clinical-anatomical characteristics: multivariate regression
| Category | OR | CI 95% | p-value |
|---|---|---|---|
| Sex: male | 0.065 | 0.003–1.67 | 0.095 |
| Age ≥ 48 years old | 33.64 | 1.2–944.44 | 0.039 |
| STOP-BANG: moderate-high risk | 0.426 | 0.02–9.52 | 0.59 |
| Weight ≥ 105 kg | 4.62 | 0.33–65.86 | 0.258 |
| Neck: thick | 3.79 | 0.25–57.76 | 0.338 |
| Neck circumference ≥ 41.25 cm | 6.61 | 0.29–149.13 | 0.235 |
| Flaccid palate: yes | 2.31 | 0.22–24.04 | 0.483 |
| Mallampati index III-IV | 1.16 | 0.07–18.32 | 0.92 |
| Friedman Tongue position III-IV | 3.07 | 0.21–45.11 | 0.413 |
| Retropalatal space: narrow | 0.73 | 0.06–8.46 | 0.803 |
CI: confidence interval, OR: odds ratio
Discussion
In recent years, several studies have investigated the factors associated with the development of OSA in obese patients, mainly related to male gender, age and BMI [19–23].
In our study, in order to analyze the factors associated with the development of OSA, two groups were differentiated on the basis of pre-surgical CRP: no OSA/mild OSA (AHI < 15/h) and moderate/severe OSA (AHI ≥ 15/h), since AHI ≥ 15/h indicates a clinically significant level of disease [23].
Age over 48 years was the only independent predictor of moderate/severe OSA. The studies of Duarte et al. and Khan et al. also associated age with an increased risk of OSA (OR = 1.078 and OR = 1.4, respectively) [21, 22]. Carneiro et al. [19]. and Dixon et al. [20]. established an age over 36 and 38 years, respectively, as a risk factor for developing OSA, an age lower than that of our study, being this difference probably due to the lower mean age of the population in both studies. However, for Lee et al. age did not prove to be a predictor of OSA [23], also probably due to the fact that their study population had a lower mean age than ours (35.69 ± 9.6 years vs. 48.79 ± 10.12 years). In the general population, age has also been defined as a risk factor for the development of OSA due to its association with increased upper airway resistance, neck adiposity deposit, impaired pharyngeal muscle reflexes, and narrowing of the upper airway of the pharynx [24].
In the simple regression analysis, other factors related to the development of moderate/severe OSA were identified. Male gender was a simple predictor of moderate or severe OSA [4, 20–22]. Several studies have previously noted male gender as a risk factor for OSA [4, 21, 22] or severe OSA [20]. This association of OSA with male sex is probably due to different hormonal and physical factors, including the higher predisposition to fat deposition in the parapharyngeal space in men and the fact that men have a longer and more collapsible upper airway [25], in addition to the fact that testosterone favors the development of OSA whereas estrogens and progesterone are protective factors [26]. In our study, sex was no longer a risk factor for moderate/severe OSA after adjusting for confounding factors such as the difference in age and weight between both sexes. Men had higher weight than women (122.32 ± 16.13 kg vs. 104.53 ± 13.25 kg, p = 0.000), although there were no differences in BMI (40.32 ± 4.9 kg/m2 vs. 39.71 ± 4.61 kg/m2, p = 0.497). Women were younger than men (47.54 ± 10.24 years vs. 53.56 ± 7.44 years, p = 0.000).
The Epworth Sleepiness Scale score was normal in most cases, unrelated to the presence of moderate/severe OSA, as in previous studies [20, 27, 28]. This low sensitivity of the Epworth scale and the lack of association with OSA are possibly due to its subjectivity and low reproducibility.
A score of ≥ 3 on the STOP-BANG scale was associated with moderate/severe OSA. Kositanurit et al. obtained an OR = 16 (95% CI: 6.67–43.49, p < 0.001) for the STOP-BANG score ≥ 3 and the presence of OSA [30]. In the study by Glazer et al. the STOP-BANG questionnaire was the best predictor of moderate and severe OSA [27]. Despite not being a clearly validated questionnaire in obese patients, previous studies have demonstrated it to be a suitable tool for the detection of moderate and severe OSA in this group of patients [28, 29], with greater efficiency in the female gender among severely obese patients (sensitivity and specificity of 71% and 80%, respectively, in women vs. 90% and 12% in men) [28].
After our review of the literature, no studies evaluating the exploration of the upper airway in obese patients with OSA in the Otolaryngology clinic beyond the measurement of the neck circumference have been found, although there are studies that have assessed the upper airway in these patients using measurements obtained on plain lateral radiography [30], magnetic resonance imaging (MRI) [31–33] or computed tomography (CT) [34, 35].
In the present study, a large number of UA characteristics were evaluated in patients with morbid obesity. Significant differences between non-OSA/mild OSA and moderate/severe OSA were observed in weight, cervical thickness, presence of a flaccid palate, Mallampati index (MI), Friedman Tongue Position (FTP) and retropalatal space, with differences mainly observed in weight, cervical thickness and tongue size, consistent with the differences most frequently obtained in previous studies.
Weight was 8.14 kg higher in subjects with moderate/severe OSA, with a weight of 105 kg being the cut-off point with the highest sensitivity and specificity for its detection. Schafer et al. also observed a relationship between weight and AHI, but it was not an independent factor to predict OSA either, same as in our study [36].
In this study, the BMI was 2.1 kg/m2 higher in patients with moderate/severe OSA, but it was not a predictive factor, as in previous studies [19, 22, 23]. In other studies, it has been considered a risk factor for OSA in general [21, 37] and for severe OSA [37, 38], but of all the factors found, it was the least important [37]. This difference in the association of BMI and OSA among the variety of studies may be due to the fact that BMI might not be a good predictor of OSA, since this disease is more associated with central fat distribution and BMI does not reflect such distribution [39]. Proof of this is the study by Dixon et al., in which BMI, one of the predictors of severe OSA included in their logistic regression, was replaced by neck circumference when measures of central weight distribution were added to the analysis [20]. In addition, the mean BMI of our sample was lower than that of most of the compared studies [4, 19, 21–23, 37].
A thick neck was associated with the presence of moderate/severe OSA, with this group having a 3.65 cm greater cervical perimeter. The cut-off point with the highest sensitivity and specificity for the detection of moderate and severe OSA was 41.25 cm, but it was not an independent risk factor. Previous studies also observed thicker necks in patients with OSA [23, 28, 40] and pointed out the measure of 43 cm of neck perimeter as a predictor of OSA [20, 23, 28], being this characteristic an independent risk factor [20, 21, 23]. In other studies, cervical circumference was also not an independent predictor of OSA [22, 37]. Neck circumference, which is a good marker of central obesity, seems to be a good marker of OSA as well. Furthermore, it more directly reflects the accumulation of adipose tissue in the upper airway and it is more closely related to the pathophysiology of OSA than waist circumference [21, 23, 38].
In our study, the variables that evaluated macroglossia were tongue scalloping, MI and FTP, being the latter two partially dependent on the size of the tongue and related to the presence of moderate/severe OSA. Macroglossia has also been associated with OSA in obese patients in previous studies [31, 40].
The presence of a flaccid palate and the retropalatal narrowing were also associated with the presence of moderate and severe OSA, as stated by Feng et al. who observed a smaller retropalatal space measured on MRI in patients with AHI ≥ 15/h after adjusting for gender, age, BMI, and race [33]. This observation may be due to the fact that the adipose tissue in the upper airway, in addition to depositing and infiltrating tissues such as the tongue, also does so in the parapharyngeal space and the soft palate, causing this accumulation to narrow the retropalatal space [32] favoring, as a result, the collapse of the UA and finally OSA, being such reduction of the retropalatal area an important factor for the development of OSA in obese patients.
Limitations
Most of the participants in this study were women (81.5%), as occurs in other cohorts of patients undergoing bariatric surgery, which might have underestimated the real prevalence of moderate and severe OSA in the morbidly obese population, since men suffer from the disease more frequently and severely.
The sleep test performed in all cases was the CRP and not the polysomnography. The CRP test may underestimate the severity of OSA and desaturations by not taking into account actual sleep time but rather recording time.
Only the AHI was used to establish the diagnosis of OSA without considering clinical or other sleep testing criteria, as has been done in the majority of previous studies in the literature to facilitate comparison with other works.
It should be taken into account that the exploration of the UA is subjective and poorly quantifiable. In addition, examination in an awake patient does not allow evaluating parameters beyond anatomy, therefore this work does not analyze how these elements behave during sleep causing the collapse of the UA [41].
Other confounding factors that could be related to the development of OSA in obese patients, such as genetic [40], hormonal, neuromuscular factors [26, 40, 42] or the osseous structural variables of the UA, were not evaluated.
Conclusion
The only independent predictor of moderate or severe OSA in this study was age over 48 years, although this group of patients presented a higher deposit of fat in the neck, tongue, and soft palate, coinciding with previous studies. It is to presume that the anatomical factor is not the only one involved in the development of OSA in patients with morbid obesity and that other characteristics such as neuromuscular, hormonal or genetic factors are probably related and have not been analyzed in the present study. Therefore, with the current knowledge, we believe that there is no reliable predictive factor for diagnosing OSA in patients who are candidates for bariatric surgery, maintaining the sleep study essential for its diagnosis.
Electronic Supplementary Material
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Funding
This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.
Declarations
Conflict of Interest
The authors have no conflicts of interest to declare.
Footnotes
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