The study, led by Liz E. Lezama Oropeza, with colleagues Elisa Basora-Rovira and Aarti Shakkottai, reviewed polysomnographic data from fifteen infants between zero and twelve months of age who were born at term and had no identified syndromes. The mean gestational age of the cohort was 38.4 weeks, with a narrow spread of plus or minus 0.6 weeks, and eighty percent of the infants were male. The average age at the first sleep study was 7.5 months, with a standard deviation of 3.6 months, meaning the group spanned early infancy through the first birthday.

Polysomnography, the gold-standard overnight sleep test, records brain waves, breathing effort, airflow, oxygen saturation, carbon dioxide levels, and body movements to quantify how often breathing is disrupted during sleep. In this cohort, the average apnea-hypopnea index, or AHI, which counts the number of apneas and hypopneas per hour of sleep, was 23.1 events per hour. The mean obstructive AHI, which isolates events caused by physical blockage of the upper airway, was 20 events per hour, while the mean central apnea index, reflecting pauses in breathing driven by immature or irregular brainstem signaling rather than airway obstruction, was 3.1 events per hour. For context, an obstructive AHI above 5 events per hour is generally considered moderate sleep apnea in pediatric populations, so the average infant in this series fell well into the moderate-to-severe range.

Oxygenation data added another layer of concern. Mean oxygen saturation during sleep was 97.5 percent, but the mean nadir, the lowest saturation reached during any single desaturation event, was 81.0 percent, with a wide standard deviation of 9.9 percent. Six of the fifteen infants met formal criteria for sleep-related hypoxemia, defined in this study as oxygen saturation below 90 percent for at least five minutes during the recording. Carbon dioxide measurements told a different story: mean and peak carbon dioxide levels were 35 and 48.6 millimeters of mercury, respectively, and none of the patients met criteria for sleep-related hypoventilation, which would require elevated carbon dioxide above 50 millimeters of mercury for more than a quarter of total sleep time. The pattern suggests that in these otherwise healthy infants, the dominant problem was intermittent airway obstruction causing repeated oxygen dips rather than sustained underventilation.

The clinical picture preceding referral was often subtle. Only a third of the infants had documented snoring, the symptom most parents and clinicians associate with sleep apnea, and nearly half, forty-seven percent, carried a diagnosis of gastroesophageal reflux, a condition that has been linked to airway inflammation and laryngeal hypersensitivity in infants. Seventy-three percent of the infants underwent some form of upper airway evaluation, such as flexible laryngoscopy, and seven of those evaluations revealed abnormal findings. Laryngomalacia, a condition in which immature, floppy supraglottic tissue collapses inward during inspiration, is the most common congenital cause of stridor and obstructive events in infants and featured among the abnormal findings in this series.

Follow-up polysomnography, obtained in ten of the fifteen infants at an average age of around 13.4 months, provided the study’s most striking finding. Four of the ten infants showed complete resolution of their sleep-disordered breathing without any surgical or device-based intervention. One infant achieved resolution while using continuous positive airway pressure, or CPAP, a machine that delivers a steady stream of pressurized air through a mask to splint the airway open during sleep, but was subsequently lost to follow-up. In the remaining five infants, sleep-disordered breathing persisted but improved. The researchers also examined whether disease severity tracked with age, finding a weak negative correlation between AHI and age, with a Spearman rho of minus 0.31 and a p-value of 0.26, which did not reach statistical significance in this small sample but pointed in the direction of decreasing severity as infants matured.

The authors emphasize that the frequency of moderate-to-severe obstructive sleep apnea in this population is high, but that the clinical implications remain unclear. Diagnostic thresholds for sleep-disordered breathing in infants are poorly standardized, and much of the pediatric literature derives normative values from older children or from high-risk infant populations whose airway physiology differs substantially. The infant upper airway is anatomically distinct: narrow cartilaginous structures, predominantly nasal breathing, high airway compliance, and immature neuromuscular control of the pharyngeal dilator muscles all predispose to collapse during sleep, particularly during active or rapid eye movement sleep when muscle tone falls. As infants grow, the airway enlarges, adenoid and tonsillar tissue relative to the airway changes, and neuromuscular control matures, which may explain why many infants in this series appeared to outgrow their disease.

The study has clear limitations that the authors acknowledge. As a single-center case series of fifteen infants, it cannot establish prevalence in the broader population of healthy term infants, since all participants were referred for suspected sleep-disordered breathing at a tertiary care center. The weak correlation between age and AHI did not reach statistical significance, and the follow-up cohort was small, with five of fifteen infants lacking repeat sleep studies. The authors also note that there is limited data on effective treatment strategies for this group, and that the natural history of untreated moderate-to-severe disease in otherwise healthy infants remains poorly characterized.

Nevertheless, the findings carry practical weight for parents and clinicians. Snoring in a full-term baby without a syndrome is not a reliable screening sign, appearing in only a third of this cohort, and reflux may be a more common companion diagnosis than previously appreciated. The authors conclude that further research is warranted to refine diagnostic thresholds and standardize the diagnostic evaluation and interventions for sleep-disordered breathing in this unique population. Until larger, prospective studies establish normative infant polysomnography values and clarify which infants need intervention versus watchful waiting, the study suggests that clinicians evaluating otherwise healthy infants for suspected sleep-disordered breathing should maintain a low threshold for overnight testing, while recognizing that a substantial share of these babies may simply grow out of it.

Subject of Research: A case series of fifteen term, non-syndromic infants referred for suspected sleep-disordered breathing found high rates of moderate-to-severe obstructive sleep apnea on polysomnography, with many infants outgrowing the condition by follow-up.

Article Title: Correlation between phenotype and polysomnography findings of sleep-disordered breathing in term, non-syndromic infants: a case series study

Article References: Lezama, L., Basora-Rovira, E., & Shakkottai, A. (2026). Correlation between phenotype and polysomnography findings of sleep-disordered breathing in term, non-syndromic infants: a case series study. Frontiers in Sleep, 5, Article 1877709. https://doi.org/10.3389/frsle.2026.1877709

Image Credits: AI Generated

DOI: 10.3389/frsle.2026.1877709

Keywords: infant sleep apnea, sleep-disordered breathing, polysomnography, apnea-hypopnea index, laryngomalacia, gastroesophageal reflux, oxygen saturation, hypoxemia, CPAP, term infants, Frontiers in Sleep, pediatric sleep

The study, led by Nadja Deflorin and Tsogyal Daniela Latshang of the Cantonal Hospital of Grisons in Chur, Switzerland, enrolled 44 healthy adults, half of them women, with a median age of 47 years. All participants lived above 1000 meters, at a median home altitude of 1230 meters, and none had spent a night below 1000 meters in the four weeks before testing. Each volunteer underwent polysomnography for two consecutive nights at home and, after a two-week washout period, two consecutive nights at the sleep laboratory in Chur at 590 meters. The order of testing was randomized with a computer-generated sequence, and the trial was registered at clinicaltrials.gov under identifier NCT05826808. Of 176 planned recordings, 174 were completed successfully, a remarkably high data completion rate for portable sleep studies.

The primary outcome was T90, the amount of time spent during sleep with blood oxygen saturation below 90 percent, a measure that previous research has linked to cardiovascular mortality. At home altitude, participants spent an average of 5 minutes per night below this threshold, compared with just 1 minute at 590 meters, a mean difference of 4 minutes that reached statistical significance. Nocturnal oxygen saturation rose from an average of 93.8 percent at moderate altitude to 95.2 percent at low altitude. More striking were the breathing metrics: the apnea-hypopnea index, which counts the number of breathing interruptions per hour, fell from 14.2 events per hour at home to 9.2 events per hour at 590 meters, while the oxygen desaturation index dropped from 10.0 to 6.0 events per hour.

The reduction in overall apnea-hypopnea index was driven almost entirely by obstructive events rather than central ones. Obstructive apneas and hypopneas, in which the upper airway collapses or narrows despite continuing respiratory effort, fell from 13.4 to 8.6 events per hour at the lower altitude, while central events showed no significant change. This pattern aligns with earlier observations that long-term high-altitude residents are prone to obstructive rather than periodic central breathing disturbances, because their physiological adaptations to chronic hypoxia, including larger lung volumes and greater tolerance of low oxygen, prolong the time it takes for falling saturation to trigger an arousal. The authors also point to anatomical factors, noting that highland populations often show larger neck circumferences and higher waist-hip ratios, potentially related to diets rich in salt, meat, and fat, all of which favor airway collapse during sleep.

Sleep architecture itself shifted only modestly with descent. Slow wave sleep, the deep restorative stage, was significantly higher on the second night at 590 meters, reaching 10 percent of total sleep time compared with 8 percent at home altitude, likely because fewer breathing disturbances meant fewer micro-arousals fragmenting the night. Transcutaneous carbon dioxide levels were slightly higher at low altitude during the first night, particularly during non-REM sleep, reflecting the reduced ventilatory drive that comes with richer inspired oxygen. Morning systolic blood pressure was also lower at 590 meters, averaging 115 millimeters of mercury compared with 120 at home, though values remained within the normal range. Questionnaires told a different story: participants rated their subjective sleep quality, sleepiness, and insomnia symptoms identically at both altitudes, unaware that their bodies were behaving differently.

One of the most clinically consequential findings concerned disease classification. At home altitude, six of the 44 participants, or 13.6 percent, crossed the threshold for severe obstructive sleep apnea with an apnea-hypopnea index above 30 events per hour. At 590 meters, only one participant, or 2.3 percent, met that criterion, a statistically significant difference. In other words, a diagnostic study performed at a lower-altitude laboratory would have labeled five people as not having severe sleep apnea who, sleeping in their own beds, clearly did. The authors conclude that sleep-disordered breathing assessments conducted at lower-than-living altitude may systematically underestimate the severity of the condition in patients who permanently reside at moderate elevation.

The trial also uncovered a pronounced sex difference. In male participants, descent to low altitude produced a larger effect on T90, with a mean difference of 7 minutes, and on REM sleep, which increased by 4 percent of total sleep time at the lower elevation. Regression analyses identified male sex as a significant predictor of both T90 and the oxygen desaturation index, with age also predicting desaturation frequency. Among males, 27.3 percent showed severe sleep apnea at home altitude versus essentially none at 590 meters, while no females crossed the severe threshold at either altitude. The researchers suggest that women may regulate breathing better at moderate altitude, consistent with prior studies at 3270 and 3800 meters showing sex-specific differences in hypoxic ventilatory response, loop gain, upper airway anatomy, and carbon dioxide reserve.

The physiological logic behind these results rests on the interplay between inspired oxygen pressure and ventilatory control. At 1230 meters, the partial pressure of inspired oxygen is low enough to destabilize breathing during sleep, particularly in REM stages when the ventilatory response to both hypoxia and hypercapnia naturally wanes and respiratory effort after airway occlusion diminishes. Descending to 590 meters raises inspired oxygen pressure, stabilizes the control system, and shortens the duration of each obstructive event because arterial saturation falls below arousal-triggering thresholds more quickly. The effect appeared within a single night, indicating that even brief exposure to lower altitude is sufficient to alter the diagnostic picture, and the two-week washout at home altitude confirmed the changes were reversible and altitude-dependent.

The authors recommend that polysomnography for patients living above 1000 meters be performed at their individual home elevations whenever possible, especially for male patients in whom the altitude effect on oxygenation, REM sleep, and apnea severity was most pronounced. They caution that their findings come from healthy volunteers and may not extend directly to patients with severe comorbidities or to those living at substantially higher elevations, and they call for further studies in people with diagnosed obstructive sleep apnea and for deeper investigation of sex differences. Still, the message for the millions of highlanders worldwide is clear: where you sleep when the sensors are attached matters, and a valley-floor clinic may paint a deceptively rosy picture of what happens in a mountain bedroom.

Subject of Research: The effect of short-term descent to low altitude on sleep-disordered breathing in healthy moderate-altitude residents

Article Title: The effect of short-term descent to low altitude in healthy residents at moderate altitude — a randomized crossover trial

Article References: Deflorin, N., Furian, M., Vontobel, J., Niederseer, D., & Latshang, T. D. (2026). The effect of short-term descent to low altitude in healthy residents at moderate altitude — a randomized crossover trial. Journal of Clinical Sleep Medicine, 22(1), Article 122. https://doi.org/10.1007/s44470-026-00128-1

Image Credits: AI Generated

DOI: 10.1007/s44470-026-00128-1

Keywords: sleep apnea, polysomnography, altitude, hypoxemia, sleep-disordered breathing, apnea-hypopnea index, oxygen saturation, REM sleep, slow wave sleep, randomized crossover trial, high-altitude residents, sex differences