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Preponderance of Hypopneas Over Apneas in Morbid Obesity FREE TO VIEW

Reeba Mathew, MD; Richard Castriotta, MD
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University of Texas Medical School at Houston, Houston, TX

Chest. 2011;140(4_MeetingAbstracts):942A. doi:10.1378/chest.1106170
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PURPOSE: Complete upper airway collapse is generally expected to occur in obese subjects with obstructive sleep apnea-hypopnea syndrome (OSAHS), resulting in more apneas over hypopneas. Observations with polysomnography (PSG) led us to hypothesize that extremely obese patients manifest OSAHS with a preponderance of hypopneas over apneas.

METHODS: Retrospective review of 96 consecutive adult patients with OSAHS by PSG, comparing 2 groups: Group A with BMI < 35 and group B with BMI ≥ 45. Exclusion criteria: age <18 years, pregnancy, central apnea >5/hr and BMI between 35 and 45. Primary outcome measure: hypopnea-apnea ratio (HAR); secondary measures: obstructive (OAI) and central apnea indices (CAI), hypopnea index (HI), SpO2 nadir, PetCO2 (baseline, peak) and % sleep time with PetCO2 > 50 torr (%PetCO2>50). Statistical methods included the 2-tailed student t-test and Wilcoxon signed-rank test. Results are expressed as group mean ± standard deviation and p < 0.05 was considered significant.

RESULTS: Group A (n = 48): age = 55±12.5 yrs, BMI = 29±3.6, AHI = 20.7±16.5. Group B (n = 48): age = 44.4±12.2, BMI = 55.9±8.1, AHI = 36.9±40. Group B had more women (60% vs 31%, p = 0.004). HAR was significantly higher in B (53.7±54 vs 17.5±30 in A, p = 0.0001), as was the HI (32±35 in B vs 14.6±10.3 in A, p = 0.0017). Significant differences were also noted between the 2 groups in age, BMI, SpO2 nadir (lower in B, p = 0.003) and %PetCO2>50 (higher in B, p = 0.03). A post-hoc analysis was performed after the groups were age and gender matched. The HAR was again significantly higher in B (41.3±51.6 in B vs 10.6 ±16.6 in A, p = 0.0002) along with HI (p = 0.0003).

CONCLUSIONS: Very obese patients manifest OSAHS with a higher ratio of hypopneas to apneas, even when matched for age and gender.

CLINICAL IMPLICATIONS: Different mechanisms may underlie generation of apneas (static obstruction) and hypopneas (dynamic obstruction), with a distinct pathophysiology in the very obese.

DISCLOSURE: The following authors have nothing to disclose: Reeba Mathew, Richard Castriotta

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