Original ArticleImpact of different hypopnea definitions on obstructive sleep apnea severity and cardiovascular mortality risk in women and elderly individuals
Introduction
Obstructive sleep apnea (OSA) is a highly prevalent disorder characterized by repetitive episodes of complete or partial upper airway obstruction during sleep. The apnea–hypopnea index (AHI), that is, the sum of apneas plus hypopneas per hour of sleep, is the conventional metric used to diagnose and to classify the severity of OSA. A precise definition of the events that compose this index is therefore of the utmost importance. Although the definition of apnea is clear and has not changed over the years, the scoring of hypopneas depends on several factors, such as the degree of the accompanying oxyhemoglobin desaturation (SaO2), the degree of airflow reduction, and the occurrence of an arousal. Furthermore, the criteria for scoring hypopneas have varied with successive updates from the American Academy of Sleep Medicine (AASM) [1], [2]. These modified criteria may lead to significant changes in estimates of the AHI, which, in turn, will alter disease prevalence and possibly even therapeutic decisions. Specifically, less stringent criteria would result in a higher prevalence of moderate-to-severe OSA and increase the potential number of patients requiring active treatment, particularly in the presence of associated symptoms. For example, the use of the 2012 AASM criterion for hypopnea, which requires at least a 30% decrease in oro-nasal airflow accompanied by either a three percent decrease in SaO2 or an event-related arousal, implies that almost one-third of the subjects analyzed in a recent study could be reclassified between non-OSA and OSA categories, compared to former, more restrictive criteria (AASM 2007) [3], [4]. Recent studies conducted in either population-based or small clinical cohorts have confirmed that these changes in the hypopnea definition have led to a higher prevalence of OSA [3], [5], [6], [7], [8]. However, the impact of different hypopnea metrics on population subsets is unknown. Another concern is that variability in defining hypopneas could influence the association with cardiovascular outcomes [6]. The aim of this study was to investigate the impact of three different definitions of hypopnea on the classification of OSA severity and its association with cardiovascular mortality risk in two large clinical cohorts of women and elderly individuals.
Section snippets
Design, settings, and patients
We have analyzed two large clinical cohorts composed of 1116 women and 939 elderly individuals (≥65 years of age) who were consecutively studied for suspicion of OSA between 1998 and 2007 in two Spanish sleep clinics and were followed up until December 2009. The two cohorts were originally assembled to investigate the association between OSA and cardiovascular mortality, as well as the effect of continuous positive airway pressure (CPAP) on this association. Exclusion criteria were age <18
Results
The two clinical cohorts were composed of 1116 female and 939 elderly individuals, respectively. Baseline characteristics for each cohort are shown in Table 1. The female cohort was followed up for a median of 72 months (IQR, 52–88 months) and the elderly cohort was followed for 69 months (IQR, 49–87 months). The average AHI was within the severe range with any of the hypopnea definitions used, for both cohorts, but it was significantly higher with the AHI3%a and AHI3%, compared to the AHI4%
Discussion
In two large clinical cohorts of women and elderly individuals referred for suspicion of OSA, classification of disease severity varied substantially based on the criteria used to define hypopneas. Accordingly, adopting one or other hypopnea definition would lead to marked difference in OSA prevalence and, perhaps more importantly, the therapeutic decision. Not surprisingly, different hypopnea definitions also have an impact on the association between AHI and cardiovascular outcomes. If the
Conclusions
In summary, the findings presented herein suggest that in two clinical cohorts of women and elderly individuals referred for OSA suspicion, the use of different hypopnea criteria may substantially change the severity classification of OSA in the highest-severity group in both cohorts and also in the lowest category in female patients. An AHI ≥30 events/h was independently associated with increased cardiovascular mortality risk regardless of the hypopnea definition in both groups, except in
Acknowledgment
The authors thank Dr. Valentina Isetta for her help in data analysis.
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