Am. J. Respir. Crit. Care Med., Volume 159, Number 1, January 1999, 43-48

A Comparison of Apnea-Hypopnea Indices Derived from Different Definitions of Hypopnea

WILLIS H. TSAI, W. WARD FLEMONS, WILLIAM A. WHITELAW, and JOHN E. REMMERS

Division of Respiratory Medicine, Department of Medicine, University of Calgary, Calgary, Alberta, Canada

We examined the effects of arousal- and desaturation-based scoring criteria on the apnea-hypopnea index (AHI) and on the measured prevalence of obstructive sleep apnea (OSA). Ninety-four randomly selected patients underwent overnight polysomnography. Studies were scored according to three different criteria for hypopnea, as defined by a  10 s discernible reduction in thoracoabdominal movement associated with: (1)  4% decrease in oxygen saturation (Sa_O2) (Type A); (2) either a  4% decrease in Sa_O2 or an arousal (Type B); or (3) electroencephalographically based arousal alone (Type C). Excellent correlation existed between AHI-A, AHI-B, and the oxygen desaturation index (ODI) (r > 0.98). AHI-A and AHI-B differed by only 2.04 ± 1.72/h (2 SD). AHI-A and AHI-B differed from the ODI by 1.04 ± 4.07/h and 3.07 ± 4.30/h, respectively. Despite these small differences, use of the Type B rather than Type A definition resulted in an extra case of OSA being diagnosed for every 14 to 31 patients tested, depending on the definition of OSA (AHI:  5, 10, 15, or 20/h). The addition of arousal-based scoring criteria for hypopnea causes only small changes in the AHI, but if OSA is defined solely by an AHI value, the measured prevalence of OSA will increase.

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