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Article #35

One form of sleep-disordered breathing, closely related to Sleep Apnea, is that of heavy snoring without actual apneas/hypopneas or oxygen saturations, but with increases of upper airway resistancethat lead to arousals, sleep fragmentation, and excessive daytime sleepiness.This has been termed the "Upper Airway Resistance Syndrome."It has been measured with instruments such as the esophageal catheter, which involves a tube with an attached balloon inserted into the airway, and the pneumotachograph, which involves a tight-fitting face mask. Both of these instruments may disturb sleep. The authors of this paper used a different instrument designed to be less disruptive of sleep, the "respiratory inductive plethysmograph," which is used externally on the body to measure changes in the size of the chest and abdomen related to breathing. These changes can be analyzed to measure airflow and respiratory effort to describe breathing patterns in 10 snorers compared with seven non-snorers. In the snorers, the presence of non-apneic snoring was previously documented by standard all-night polysomnography. Their average age was 53 years (SD=9) and their average Body Mass Index or BMI was 28 (SD=3), whereas the non-snorers were younger at an average age of 38 (SD=5) and an average BMI of 23 (SD=2) indicating less obesity. Among the snorers, the investigators looked specifically at breathing during (1) non-REM (NREM) sleep with snoring and without arousals; (2) NREM sleep with snoring and with arousals; and (3) wakefulness. In the nonsnorers, they looked at NREM sleep and wakefulness. I will omit describing the procedures by which the authors calibrated their equipment or analyzed their measures, which is quite complex. I will mention their use of thermistors to measure oral and nasal airflow, and both a miniature microphone and a vibratophone taped to the skin above the larynx, to measure snoring. Those periods mentioned just above were analyzed with reference to overall breathing for 50-75 breaths (3-5 minutes) and close examination of the five breaths before and five breaths immediately after arousals when these were present. For the ten snorers, the average time in bed was 448 minutes (SD=53) and the average total sleep time (TST) was 338 mins (SD=70). They spent 71% (SD=12%) of their TST in light stages I and II of sleep, 14% (SD=9%) in deep stages III and IV, and 15% (SD=8%) in Rapid Eye Movement (REM) sleep.For comparison, the nonsnorers spent about the same time in bed (422 mins SD=30) but slept longer (TST=421 SD=31). They had a similar distribution proportion of sleep time spent in different stages: 69% (SD=8) in stages I and II, 16% (SD=6%) in stages III and IV, and 15% (SD=6%) in REM.In the case of patients with full-blown Obstructive Sleep Apnea (OSA) one would expect decreases of time spent in stages III, IV, and REM, which were not found for these non-apneic snorers. However, the snorers had an increased average Arousal Index or AI (24/hr, SD=15) and an increased average respiratory disturbance index or RDI (19 episodes/hr, SD=15) similar to what one might see in mild OSA--but note the large standard deviations indicating that some snorers had no elevation of AI or RDI whatsoever, whereas others had levels consist with quite severe OSA. In fact, the authors note that two snorers had no associated arousals, while another patient had arousals with every episode of snoring. The nonsnorers had significantly lower AIs (13/hr, SD=4) and significantly lower RDIs (6/hr, SD=4). Among the snorers, breathing patterns during snoring sleep without arousals were "very regular," but consistent with inspiratory flow limitation. During snoring sleep with arousals, breathing patterns were more variable in timing, amplitude, and flow. Abnormalities of breathing pattern were most evident just before the arousal, most normal during and just after the arousal, and then progressively more abnormal until the following arousal. In their discussion of their findings the authors emphasized that their analyses of plethysmographic data--routinely available in all sleep studies--showed that it could be used as an alternative to the more invasive techniques, like esophageal catheters, in assessing upper airway resistance. In addition, their data serve to confirm prior findings that patients with obstructive sleep apnea and habitual nonapneic snorers with sleep fragmentation show similar abnormalities in breathing patterns indicating large changes in airway resistance, inspiratory flow limitations, and increasing lung pressure swings leading up to arousals. 

I have omitted the authors' impressively complex description of detailed abnormalities in breathing pattern in sleep-disrupted snorers, as of limited interest to a lay audience presumably consisting of people already diagnosed with sleep apnea and therefore less personally interested in the entity of upper airway resistance syndrome. However, it is still of value for us to keep this condition in mind, to realize that a key mechanism in the symptoms of sleep apnea--sleep fragmentation--can occur as a result of breathing difficulty without any apneas, hypopneas, or oxygen desaturation, but with perhaps only snoring as an outward sign of difficulty. One reason for us to remain aware of this condition is that we have good evidence that first-degree relatives of sleep apneics not only have a substantially increased risk of sleep apnea itself, but also of other sleep-related respiratory disorders short of apnea, such as that under study here. It seems quite possible--though it will need confirmation from long-term follow-up studies--that this entity represents an early stage of full-blown sleep apnea, in which no actual apneas or hypopneas can be documented but the symptoms of sleep fragmentation are already present.     For individuals with such easily-overlooked yet quite significant afflictions, who may after all be our own children--it could be very important that the syndrome can be detected with computer analyses of routinely available plethysmographic data, without requiring the rather intimidating prospect of esophageal catheterization!

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