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Editorials: Point and Counterpoint |

Rebuttal From Dr Punjabi FREE TO VIEW

Naresh M. Punjabi, MD, PhD, FCCP
Author and Funding Information

FINANCIAL/NONFINANCIAL DISCLOSURES: N. M. P. has received grant support from ResMed and Philips Respironics.

FUNDING/SUPPORT: This work was supported by National Institutes of Health [Grant HL07578].

CORRESPONDENCE TO: Naresh M. Punjabi, MD, PhD, FCCP, Division of Pulmonary and Critical Care Medicine, Johns Hopkins Asthma and Allergy Center, 5501 Hopkins Bayview Cir, Baltimore, MD 21224


Copyright 2016, American College of Chest Physicians. All Rights Reserved.


Chest. 2016;149(1):20-21. doi:10.1378/chest.15-1321
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It is reasonable to advocate that the apnea-hypopnea index (AHI) is a clinically valuable metric for OSA because patients with a high AHI have a higher prevalence of excessive daytime sleepiness, hypertension, and cardiovascular disease than those with a lower AHI. Moreover, the contention that the AHI is a marker of disease is also sound given that clinical symptoms improve or resolve when the AHI decreases with treatment. However, these arguments only suggest that the AHI is, at best, a crude metric for OSA. Indeed, Dr Rapoport’s conclusion that the AHI is useful in defining the presence of OSA if severely elevated and that the risk of OSA is moderately increased indicates that the AHI is not a metric with high fidelity. A high-fidelity index of disease can identify the presence of that disease and exhibit a dose-response association with relevant health outcomes. The lack of a strong association between increasing AHI and clinical consequences, such as daytime sleepiness and hypertension, points to its relatively crude nature, and rigorous consideration of alternative or complementary measures that can correlate more precisely with end points than the AHI is required.

Furthermore, the fact that the AHI is “most used” is a mere reflection of the underlying inertia common when an index of disease is adapted early in clinical practice and, thus, becomes embedded widely. Absolutely little doubt exists that part of the challenge in sleep medicine is understanding the heterogeneity in susceptibility to the clinical effects of airway obstruction during sleep. However, that is not a unique phenomenon in OSA but a common feature in many chronic disorders. It may well be that unraveling that variability in clinical effects necessitates a better delineation of measures that not only depict the full spectrum of upper-airway collapse during sleep but also accurately predict the occurrence of adverse events. The field should not be satisfied with an isolated measure that can just define the disorder. It is now time that we look beyond that initial milestone of using the AHI and embrace the complexity of OSA with better measures that will help to probe the science of differential susceptibility. There certainly is no scarcity of alternatives.

Why not consider additional measures of nocturnal hypoxemia and sleep disruption in characterizing OSA? Perhaps a combination of number of sleep-disordered breathing events, average oxygen saturation during sleep, frequency of arousals, and number of sleep stage transitions can provide a more-encompassing view of OSA. Why not quantify the number of flow-limited breaths to delineate the burden of respiratory effort during sleep? Automated methods are now readily available that can easily differentiate flow-limited from non-flow-limited breaths from an overnight polysomnogram. Such analyses will help to reinvigorate additional research into defining the ramifications of the increased work of breathing associated with airway obstruction, an area that remains neglected. If the AHI remains the “holy grail” in sleep and respiratory medicine, the science will certainly not advance, which in turn will retard the clinical and public health response to this disease.

References

Rapoport D.M. . Point: is the apnea-hypopnea index the best way to quantify the severity of sleep-disordered breathing? Yes. Chest. 2016;149:14-16 [PubMed]journal
 

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References

Rapoport D.M. . Point: is the apnea-hypopnea index the best way to quantify the severity of sleep-disordered breathing? Yes. Chest. 2016;149:14-16 [PubMed]journal
 
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