Gaps in Sleep Medical Knowledge: Part II (Normal Breathing)

Normal sleep breathing. No surprise, in juxtaposition to not establishing the definition of normal sleep, we do not possess a definition for normal sleep breathing, at least in so far as it would be used in treating sleep-disordered breathing patients. The closest we come to normal is in the directive written by the American Academy of Sleep Medicine in their guidelines to titrate pressures in treating OSA/UARS. The specific and mandated treatment steps are that all breathing events—apneas, hypopneas, and flow limitation events must all be virtually eliminated. A reminder the term “flow limitation event” or FLE is a common clinical term used in place of the technical term, “respiratory effort-related arousal” or RERA, and both terms denote the specific type of breathing event in UARS.

Now, these instructions would appear to be straightforward: if we strive to eliminate all breathing events, then the absence of abnormal breathing should be normal breathing, right? Not to get too Orwellian, but there are two caveats that frequently preclude achieving this objective. The first of course is numerous sleep centers and labs ignore flow limitation events. Unfortunately, we know this point to be true, because you can discuss the issue with sleep technologists who report their sleep doctors instructed them only to titrate away the apneas and hypopneas. Some sleep professionals might contest this point by declaring that the more recent liberal definitions of hypopneas should account for most if not all RERAs. To be sure, more RERAs than ever before are probably being treated, but the concept of an aggressive titration on the first go-round or the concept of retitrations to revise pressures to aggressively resolved RERAs are simply not the standard approach taken by most sleep centers and labs. 

And, this lack of precision in titration procedures brings us to the second caveat: it is inaccurate to declare elimination of all breathing events equates to a normal airflow curve when no one has declared the morphology (shape) of a normal airflow signal. When we opened our private sleep center in 2002, this question repeatedly arose, originally because we were perplexed by the consistently mediocre responses we were seeing in most CPAP users. When we switched to BPAP therapy, and the airflow curve appeared to be more rounded on inspiration and expiration, we wondered whether these distinctions between CPAP and BPAP were real. Subjectively, we knew the answer, because so many previous CPAP users were now reporting markedly better responses with BPAP. As our curiosity piqued, we realized we needed to find truly normal sleepers with normal breathing to compared their airflow signal with patients using various types of PAP devices.

Remarkably, as described in the prior post of normal sleepers, we found a small number of patients who fit our criteria for both normal sleep and what seemed to be normal sleep breathing. When these folks were tested in the sleep lab, there airflow signal was perfectly rounded on both inspiration and expiration most of the night. All them suffered some exceedingly small amounts of flow limitation, but what we observed with great interest was how these flow limitations rarely were sustained for more than a few seconds or a few minutes and often were not linked to arousal activity. After these brief periods of flow limitation, the airflow signal reverted to normal again, that is, perfect rounding of the inspiratory and expiratory curves.

Since then, we have used this metric to confirm that a patient’s airflow signal during a titration study has achieved what we perceive to be normal or nearly normal sleep breathing. In the first paper we published on this specific topic, we demonstrated this phenomenon in insomnia patients with OSA/UARS who had failed CPAP therapy and were being tested on ASV. In addition to achieving the morphology of a rounded airflow signal, we also showed that the use of ASV was associated with various parameters of improved sleep quality compared to the patient’s previous use of CPAP, including significantly more Stage 3 NREM sleep and less Stage 1 NREM sleep, more time spent in REM sleep, lower AHI and RDI, fewer arousals, awakenings and sleep stage shifts, and less time awake at night as well as greater consolidation of REM sleep and overall sleep efficiency.

It should be appreciated that many sleep facilities and sleep professionals do not view normal breathing in this precise fashion, so from their perspectives they believe that non-normal breathing fits their conceptualization of normal breathing. Should I say that again? Because most sleep professionals do not show much interest in RERAs, let alone rounding the airflow curve, they have by default created a definition for normal breathing that we would argue reflects a non-normal breathing state as best we can determine from the scientific evidence. As you can imagine, this distinction reflects an enormous gap in sleep knowledge, because it means only a small proportion of sleep professionals are attending to efforts to normalize the airflow signal in their treatment of OSA/UARS patients. Of course, forgetting for the moment this definitional question, the good news is there may still be a large contingency of sleep technologists and sleep physicians who are attempting to normalize the airflow curve through perfected rounding of the inspiratory and expiratory limbs. For whatever reasons, however, we can assume these professionals are not so vocal on the topic, because they have not attempted to comment or publish on this issue.

Regardless of how many sleep labs and sleep physicians are moving in this direction, the bad news is that among those who adhere to the non-normal version of “normal” breathing, we can feel quite certain in suggesting that the vast majority are not going to consider advanced PAP technologies for their patients. If as we are surmising these professionals and their labs are not aggressively treating RERAs or FLEs, then they are much more likely to be confident in titrating away the apneas and hypopneas and as such imagining they have met standard of care criteria for successful treatment. In such circumstances, there would be less indications for the use of APAP, BPAP, ABPAP and so on, because pressurized air settings will always be lower than when trying to aggressively titrate the discrete breathing events of UARS.

Worse, from the diagnostic angle, this gap indicates that a sizeable proportion of cases of UARS or mild OSA with a larger UARS component would not be diagnosed and therefore often not treated. Sleep labs and sleep docs who do not titrated RERAs/FLEs are often the same institutions and personnel who do not diagnose these more subtle cases of sleep-disordered breathing. Thus, the gap in knowledge affects both diagnostic and treatment aspects of OSA/UARS patients and therefore clearly leads to underestimating the prevalence of these conditions and underserving them in so far as the use of PAP therapy would otherwise be recommended. As we have seen repeatedly in our center, even sub-threshold cases of UARS response very favorably to PAP therapy, especially when delivered in advanced forms such as ABPAP or ASV. 

Finally, this same gap cripples the field of sleep medicine when it attempts to argue with insurance carriers and government regulators who only accept AHI criteria for their diagnostic cut-offs and pay no heed to the respiratory disturbance index (RDI), which comprises the AHI plus the RERA or FLE index. In ways that pack more of a punch than expected, this gap sets the stage for how non-medical institutions, namely insurance and government, can elect to control the field of sleep medicine by routinely re-defining criteria on how to diagnosis OSA/UARS, which will no doubt eventually tempt them to define how to treat it. Such points bring us to our next post where we will delve deeper into how sleep medicine has played defense for at various points in time in its relationships with insurance carriers and government regulators.


Read more from this series:

Gaps in Sleep Medical Knowledge: Part I (Normal Sleep)
Gaps in Sleep Medical Knowledge: Part II (Normal Breathing)
Gaps in Sleep Medical Knowledge: Part III (The Medicare Hypopnea Scoring Maze)
Gaps in Sleep Medical Knowledge: Part IV (The Unsolved Puzzle of UARS)
Gaps in Sleep Medical Knowledge: Part V (Coding Issues for Billing and Reimbursement)
Gaps in Sleep Medical Knowledge: Part VI (Prior Authorizations and Atypical Patients)
Gaps in Sleep Medical Knowledge: Part VII (Confusing Compliance with Outcomes)
Gaps in Sleep Medical Knowledge: Part VIII (Comorbid Sleep Disorders)
Gaps in Sleep Medical Knowledge: Part IX (Miscellaneous Topics)


Barry Krakow MD


Dr Krakow’s 27 years of sleep research have focused on the complex relationship between physiological and psychological sleep disorders. Dr Krakow currently operates private sleep medical center, Maimonides Sleep Arts & Sciences, Ltd., and serves as Classic SleepCare’s paid Medical Director.

Leave a comment

Comments have to be approved before showing up.