High Hypopnea/Apnea Ratio (HAR) in Extreme Obesity

Abstract

Study Objectives:The study was performed to evaluate the hypothesis that the extremely obese manifest sleep disordered breathing with a preponderance of hypopneas and relative paucity of obstructive apneas. Methods: Retrospective review of 90 adults with obstructive sleep apnea-hypopnea syndrome (OSAHS) matched for age and gender, comparing two groups, Group A: body mass index (BMI) < 35, Group B: BMI ≥ 45. Exclusion criteria: age < 18 years, pregnancy, ≥ 5 central apneas/hour, BMI ≥ 35 < 45. Primary Outcome Measure: Hypopnea/apnea ratio (HAR); secondary measures: obstructive apnea-hypopnea index (AHI), obstructive and central apnea indices, hypopnea index (HI), oxygen saturation (SpO 2 ) nadir, end-tidal carbon dioxide tension (PetCO 2 ), and presence of obesity-hypoventilation syndrome (OHS). Statistical methods: t-test for independent samples; Mann-Whitney, linear regression with natural log transformation, and Kruskal-Wallis χ 2 . Descriptive statistics were expressed as interquartile range, median and mean ± standard deviation, p < 0.05 considered signifi cant.Results: Group A (n = 45): age = 50.6 ± 11.5 years, BMI = 28.9 ± 4 kg/m 2 ; Group B (n = 45): age = 47.4 ± 12.7 years, BMI = 54.5 ± 8 kg/m 2 . HAR was signifi cantly higher in Group B (38.8 ± 50.7) than Group A (10.6 ± 16.5), p = 0.0006, as was HI (28.7 ± 28.6 in B vs 12.6 ± 8.4 in A, p = 0.0005) and AHI (35.5 ± 33.8 vs 22 ± 23, p = 0.03), but not apnea index. HAR was signifi cantly higher in Group B regardless of race, gender, or presence of OHS. The BMI was the only signifi cant predictor of HAR (adjusted r 2 = 0.138; p = 0.002) in a linear regression model with natural log transformation of the HAR performed for age, gender, race, BMI, and PetCO 2 . Conclusion: Extremely obese patients manifest OSAHS with a preponderance of hypopneas. Keywords: Obesity, obstructive sleep apnea, hypopnea, obesity-hypoventilation syndrome, gender differences, sleepdisordered breathing, hypopnea/apnea ratio. Citation: Mathew R; Castriotta RJ. High hypopnea/apnea ratio (HAR) in extreme obesity. J Clin Sleep Med 2014;10(4):391-396.http://dx.doi.org/10.5664/jcsm.3612 S C I E N T I F I C I N V E S T I G A T I O N SO besity is one of the major risk factors for obstructive sleep apnea-hypopnea syndrome (OSAHS), 1 which may be defi ned as an apnea-hypopnea index (AHI) ≥ 5 apneas+ hypopneas/hour of sleep, accompanied by symptoms of excessive sleepiness, diffi culty sleeping, or non-refreshing sleep. The prevalence of obesity in the USA has increased by 33% during the last decade, with 40% of men and 55% of women aged 25 years or older being overweight or obese.2 OSAHS has a higher prevalence among obese subjects than among the general population.3 The prevalence of OSAHS (AHI ≥ 15) in obese (body mass index [BMI] ≥ 32-59 kg/m 2 ) adults is 32% 4 and is signifi cantly higher in men with morbid obesity (BMI ≥ 39 kg/ m 2 ) with 40% having an apnea index > 20 apneas/hour. 5 The prevalence of OSAHS among hospitalized patients has been reported to be 60% in the morbidly obese.6 Com...

Increase in Body Mass Index Decreases Duration of Apneas and Hypopneas in Obstructive Sleep Apnea

“…24 In contrast, the occurrence of hypopneas is more dependent on upstream resistance, 24 which may indicate different mechanisms behind the pathogenesis of apneas and hypopneas. 23 In addition, increased genioglossal fatigability has been reported in non-obese OSA patients, whereas, in obese OSA patients, the performance of the genioglossus muscle did not differ from that of obese controls not having OSA. 25 Therefore, it can be speculated that, if obese patients with OSA have better performance of genioglossus muscle compared with patients with OSA and who are not obese, this could lead to a higher occurrence of hypopneas and reduce the number of apneas.…”

“…These findings are in line with a previous study in which very obese (BMI Ն 45 kg/m 2 ) OSA patients were compared with OSA patients having a BMI Ͻ35 kg/m 2 . 23 It has been reported that the minimum intraluminal airway pressure that is needed to keep the upper airway open is one of the most important factors in the pathogenesis of apneas. 24 In contrast, the occurrence of hypopneas is more dependent on upstream resistance, 24 which may indicate different mechanisms behind the pathogenesis of apneas and hypopneas.…”

“…Also, increase in hypopnea index and decrease in apnea index along with increasing BMI might be due to increased amount of adipose tissue in the upper airway but also increased muscle mass. 23 Because the increased amount of adipose tissue in the upper airway leads to reduction in upper-airway size, it could be assumed that the upper airway is more prone for partial occlusions (ie, hypopneas).…”

Hypopnea definitions, determinants and dilemmas: a focused review

“…In a retrospective study of 90 adults with OSA, comparing two groups with body mass indices (BMI) ≥45 vs. BMI < 35, matched for age and gender, the hypopnea-toapnea ratio (HAR) was significantly higher in the BMI ≥45 group (38.8 ± 50.7) compared to the BMI < 35 group (10.6 ± 16.5), p = 0.0006. (Mathew & Castriotta, 2014) The hypopnea index, but not the apnea index, was also higher in the BMI ≥45 vs. BMI < 35 group (28.7 ± 28.6 vs 12.6 ± 8.4, p = 0.0005), as was the AHI (35.5 ± 33.8 vs 22 ± 23, p = 0.03). In addition, the end-tidal CO2 was higher in the higher BMI group.…”

“…However, the hypopnea-to-apnea ratio did not appear to be influenced by the presence or absence of hypoventilation and was similar for those with or without obesity hypoventilation syndrome. (Mathew & Castriotta, 2014) In fact, BMI was the only significant predictor of HAR (adjusted r2 = 0.138; p = 0.002) when adjusting for age, gender, race, and ETCO2. Of note, a small sample size may have confounded the study findings.…”