Determinants of the apnea index in a sleep center population.

We hypothesized that the increased apnea-hypopnea index (AHI) in men compared to women was secondary to an increased proportion of apneas in men as measured by the ratio of the apnea index to the apnea-hypopnea index (AI/AHI ratio), and that the influence of gender was independent of other demographic factors such as body mass index (BMI) and neck circumference (NC). Database analysis of 501 patients (218 men and 283 women) who underwent polysomnography between August 2001 and June 2003 and who were found to have an AHI of at least five events per hour was performed. Respiratory parameters were compared between genders. To correct for differences in demographic parameters, correlations were made between AHI and the AI/AHI ratio and age, BMI, NC, and the percentage time spent in the supine position (%TST-supine) followed by a regression analysis to determine which factors independently predicted these parameters. AHI [women, 26.8 (interquartile range 13.9, 57.0) events per hour vs men, 58.9 (interquartile range 27.7, 105.7) events per hour, p<0.001] and AI/AHI ratio [women, 0.58 (0.36, 0.80) vs men, 0.80 (0.51, 0.95), p<0.001) were higher in men compared to women. The independent predictors of the AHI were male gender, BMI, NC, and the %TST-supine. Independent predictors of the AI/AHI ratio were male gender, BMI, NC, and the percentage of time spent in the supine position. The increased AHI in men is secondary to an increased proportion of apneas in men compared to women and is independent of other potential determinants such as age, BMI, and NC.