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Sleep Study Predictors of Prevalent Cardiovascular Disease

In their article, Dr. Punjabi and colleagues have explored the relative predictive value of several different sleep study respiratory event indices for prevalent cardiovascular disease (CVD) (1). This is an extremely valuable contribution to the literature and uses the large database generated through the Sleep Heart Health Study. It is becoming increasingly clear that the older indices quantifying sleep disordered breathing (apneas and hypopneas) are poorly predictive of symptoms and overdue for replacement. Punjabi and coworkers also suggest that hypopneas, as classically defined, are not the best predictor of prevalent cardiovascular risk. Interestingly, the authors showed that hypopneas, defined using associated hypoxic dips of 4% or more, correlated better with prevalent CVD than hypopneas defined with less, or no, hypoxic dips. What is even more interesting, if I have interpreted Punjabi and colleagues' data correctly, is that using greater than 4% hypoxic dips alone, uncontaminated with a measure of hypopneas (their Table 3 versus their Table 2), correlates with prevalent CVD even better.

The conclusion one could draw from this is that using greater than 4% hypoxic dips alone would be better than persisting with any flow-based event definitions, at least if cardiovascular issues are the endpoint of interest. However, researchers working in other areas have suggested that arousals, rather than hypoxic dipping, might be more important to the development of hypertension, which seems to suggest something different from these new data. Do the authors have the data to explore the hypothesis that hypoxic dips might be better predictors than hypopneas of prevalent CVD simply because hypoxic dips also happen to be more robust markers of arousals than flow-based events?

John R. Stradling

University of Oxford
Oxford, United Kingdom

FOOTNOTES

Conflict of Interest Statement: In 2006, ResMed donated 200 CPAP machines for an RCT sponsored by the British Heart Foundation to the Oxford Sleep Unit; in 2008, ResMed donated £30,000 unconditionally towards a research fellow in sleep apnea in the Oxford Sleep Unit (J.R.S. is the director of this unit).

REFERENCES

1. Punjabi NM, Newman AB, Young TB, Resnick HE, Sanders MH. Sleep-disordered breathing and cardiovascular disease: an outcome-based definition of hypopneas. Am J Respir Crit Care Med 2008;177:1150–1155.[Abstract/Free Full Text]

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