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NPPV: Samuel L. Krachman, Joseph Crocetti, Thomas J. Berger, Wissam Chatila, Howard J. Eisen, and Gilbert E. D’Alonzo Effects of Nasal Continuous Positive Airway Pressure on Oxygen Body Stores in Patients With Cheyne-Stokes Respiration and Congestive Heart Failure Chest 2003; 123: 59-66 [Abstract] [Full text] [PDF]

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SPO2 slope and instability

Lawrence A Lynn DO FCCP   (6 February 2003)

SPO2 slope and instability 6 February 2003
Lawrence A Lynn DO FCCP Send letter to journal: Re: SPO2 slope and instability lyntek{at}iwaynet.net Lawrence A Lynn DO FCCP	Really Smart and forward looking article Joel Some respectful comments. You suggest "repetitive nature" of the apneas did not affect oxygen stores. Since CSR generally has robust recovery times you are probably right here but you did not measure apnea duration in relation to the intervening recovery times between aopneas so your ability to exclude a relationship is limited since recovery times and apnea lenghts may vary with different patients and at different times in the night. Also the 5-7 sec. averaging interval with the oximeter would markedly affect and limit the slope ranges even when used only for comparison. This would make differencesin slope more difficult to identify --this type of averaging is not required with modern oximeters and it makes it impossible for you to see the biphasic slopes typical of apneaas in the presence of very low SVO2s. (see Wilkinson et. al) I assume you only measured 10 slopes per patient and used the simple OSA definitions of apneas to quantify the CSR because of the limited the software tools available. For this reason the primary limitations of the study may be the limited samples measured in these pateints and the use of the arbitary 1976 simple threshold based count-and-add definition of OSA as an application to a complex and dynamic breathing arrhythmia. This count-and-add definition is becoming progressively discredited as a research metric for OSA (so much that it was recently described as "worthless" in a pro-con session at the ATS last year.) It seems to be a further strech to apply the simple count-and-add OSA metric to CSR. The AHI was simply made up as a best guess 25 years ago as a metric for OSA. The reason for its widespread application to CSR is, of course, pragmatic and software driven (thats all the PSG software can do). However the physiologic relavance of the application of this simple arbitary metric to CSR in research is particulary problematic. Neverthe less despite the limited tools the study is quite clever in its derivation with an intriguing findings. The study has potential relevance to OSA since we now know that in OSA similar mechanisms of overshoot and afferent attenuation are driving the propagation of OSA reentry clusters. Thank you for writing this study Larry