High hypopnea/apnea ratio (HAR) in extreme obesity.

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 (SpO2) nadir, end-tidal carbon dioxide tension (PetCO2), 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 significant.

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 significantly 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 significantly higher in Group B regardless of race, gender, or presence of OHS. The BMI was the only significant 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 PetCO2.

CONCLUSION

Extremely obese patients manifest OSAHS with a preponderance of hypopneas.