Central Sleep Apnea at High Altitude

Expedition 5300: limits of human adaptations in the highest city in the world

Exposure to chronic hypobaric hypoxia imposes a significant physiological burden to more than 80 million humans living above 2500 m throughout the world. Among them, 50 000 live in the world's highest city, La Rinconada, located at 5000-5300 m in southern Peru. Expedition 5300 is the first scientific and medical programme led in La Rinconada to investigate the physiological adaptations and altitude-related health issues in this unique population. Dwellers from La Rinconada have very high haemoglobin concentration (20.3 ± 2.4 g/dL; n = 57) and those with chronic mountain sickness (CMS) exhibit even higher concentrations (23.1 ± 1.7 g/dL; n = 150). These values are associated with large total haemoglobin mass and blood volume, without an associated iron deficit. These changes in intravascular volumes lead to a substantial increase in blood viscosity, which is even larger in CMS patients. Despite these large haematological changes, 24 h blood pressure monitoring is essentially normal in La Rinconada, but some results suggest impaired vascular reactivity. Echocardiography revealed large right heart dilatation and high pulmonary arterial pressure as well as left ventricle concentric remodelling and grade I diastolic dysfunction. These changes in heart dimension and function tend to be more severe in highlanders with CMS. Polygraphy evaluations revealed a large reduction in nocturnal pulse oxygen saturation (median SpO2 = 79%), which is even more severe in CMS patients who also tended to show a higher oxygen desaturation index. The population of La Rinconada offers a unique opportunity to investigate the human responses to chronic severe hypoxia, at an altitude that is probably close to the maximum altitude human beings can permanently tolerate without presenting major health issues.

Intermittent Versus Sustained Hypoxemia from Sleep-disordered Breathing: Outcomes in Patients with Chronic Lung Disease and High Altitude

In a variety of physiologic and pathologic states, people may experience both chronic sustained hypoxemia and intermittent hypoxemia ("combined" or "overlap" hypoxemia). In general, hypoxemia in such instances predicts a variety of maladaptive outcomes, including excess cardiovascular disease or mortality. However, hypoxemia may be one of the myriad phenotypic effects in such states, making it difficult to ascertain whether adverse outcomes are primarily driven by hypoxemia, and if so, whether these effects are due to intermittent versus sustained hypoxemia.

High Altitude

With ascent to high altitude, barometric pressure declines, leading to a reduction in the partial pressure of oxygen at every point along the oxygen transport chain from the ambient air to tissue mitochondria. This leads, in turn, to a series of changes over varying time frames across multiple organ systems that serve to maintain tissue oxygen delivery at levels sufficient to prevent acute altitude illness and preserve cognitive and locomotor function. This review focuses primarily on the physiological adjustments and acclimatization processes that occur in the lungs of healthy individuals, including alterations in control of breathing, ventilation, gas exchange, lung mechanics and dynamics, and pulmonary vascular physiology. Because other organ systems, including the cardiovascular, hematologic and renal systems, contribute to acclimatization, the responses seen in these systems, as well as changes in common activities such as sleep and exercise, are also addressed. While the pattern of the responses highlighted in this review are similar across individuals, the magnitude of such responses often demonstrates significant interindividual variability which accounts for subsequent differences in tolerance of the low oxygen conditions in this environment.

Central sleep apnea: pathophysiologic classification

Central sleep apnea is not a single disorder; it can present as an isolated disorder or as a part of other clinical syndromes. In some conditions, such as heart failure, central apneic events are due to transient inhibition of ventilatory motor output during sleep, owing to the overlapping influences of sleep and hypocapnia. Specifically, the sleep state is associated with removal of wakefulness drive to breathe; thus, rendering ventilatory motor output dependent on the metabolic ventilatory control system, principally PaCO2. Accordingly, central apnea occurs when PaCO2 is reduced below the "apneic threshold". Our understanding of the pathophysiology of central sleep apnea has evolved appreciably over the past decade; accordingly, in disorders such as heart failure, central apnea is viewed as a form of breathing instability, manifesting as recurrent cycles of apnea/hypopnea, alternating with hyperpnea. In other words, ventilatory control operates as a negative-feedback closed-loop system to maintain homeostasis of blood gas tensions within a relatively narrow physiologic range, principally PaCO2. Therefore, many authors have adopted the engineering concept of "loop gain" (LG) as a measure of ventilatory instability and susceptibility to central apnea. Increased LG promotes breathing instabilities in a number of medical disorders. In some other conditions, such as with use of opioids, central apnea occurs due to inhibition of rhythm generation within the brainstem. This review will address the pathogenesis, pathophysiologic classification, and the multitude of clinical conditions that are associated with central apnea, and highlight areas of uncertainty.

Altitude and Breathing during Sleep in Healthy Persons and Sleep Disordered Patients: A Systematic Review

Objetive  The aim of this systematic review is to analyze the recent scientific evidence of the clinical effects of altitude on breathing during sleep in healthy persons and sleep disordered patients. Material and Methods  A search was carried out in PubMed and Scopus looking for articles published between January 1, 2010 and December 31, 2021, in English and Spanish, with the following search terms: "sleep disorders breathing and altitude". Investigations in adults and carried out at an altitude of 2000 meters above mean sea level (MAMSL) or higher were included. The correlation between altitude, apnea hypopnea index (AHI) and mean SpO2 during sleep was calculated. Results  18 articles of the 112 identified were included. A good correlation was found between altitude and AHI (Rs = 0.66 P = 0.001), at the expense of an increase in the central apnea index. Altitude is inversely proportional to oxygenation during sleep (Rs = -0.93 P = 0.001), and an increase in the desaturation index was observed (3% and 4%). On the treatment of respiratory disorders of sleeping at altitude, oxygen is better than servoventilation to correct oxygenation during sleep in healthy subjects and acetazolamide controlled respiratory events and oxygenation during sleep in patients with obstructive sleep apnea under treatment with CPAP. Conclusions  Altitude increases AHI and decreases oxygenation during sleep; oxygen and acetazolamide could be an effective treatment for sleep-disordered breathing at altitude above 2000 MAMSL.

High Altitude as a Risk Factor for the Development of Nonarteritic Anterior Ischemic Optic Neuropathy

BACKGROUND

Episodic high-altitude exposure leads to optic disc edema and retinopathy. It is uncertain whether high-altitude exposure is a risk factor for nonarteritic anterior ischemic optic neuropathy (NAION).

METHODS

We performed a single-center, retrospective, cross-sectional case study of 5 patients with high-altitude-associated NAION (HA-NAION) from April 2014 to April 2019. Main study parameters included known vascular risk factors for NAION, evolution of visual acuity, visual field, optic disc, and macula measurements.

RESULTS

We studied 5 eyes of 5 patients with HA-NAION that occurred at 7,000-9,000 ft above sea level, 28 patients with classic NAION that developed at sea level (normal altitude NAION or NA-NAION), and 40 controls. All 5 patients with HA-NAION had clinically confirmed NAION by a neuro-ophthalmologist within 3-21 days of onset and comprehensive follow-up evaluations (average follow-up of 23 months). Other than high-altitude exposure, 4 of 5 patients had undiagnosed obstructive sleep apnea (OSA, apnea-hypopnea index 5.4-22.2) and 1 had systemic vascular risk factors. All patients had disc-at-risk in the contralateral eye. The best-corrected distance visual acuity was 20/20 to 20/70 (median logMAR 0) at presentation and 20/70 to counting finger (median logMAR 0) at ≥6 months. Automated static perimetry revealed average mean deviation of -18.6 dB at presentation and -22.1 dB at ≥6 months. The average retinal nerve fiber layer was 244 µm (80-348 µm) at onset and 59 µm (55-80 µm) at ≥6 months. The average ganglion cell complex thickness was 50 µm (43-54 µm) at onset and 52 µm (50-55 µm) at ≥6 months. The patients with OSA were started on home continuous positive airway pressure treatment. Visual outcomes were similar in patients with HA-NAION and NA-NAION. - After addressing all NAION risk factors, no new events occurred in the HA-NAION group within 2-8 years with or without repeat high-altitude exposure.

CONCLUSIONS

NAION can occur under high-altitude conditions. HA-NAION is associated with relatively younger age at onset, disc-at-risk, and OSA. These patients exhibit a relatively progressive course of vision loss after initial onset and severe thinning of optic nerves on optical coherence tomography. Treatment for OSA is recommended, especially with repeated high-altitude exposure.

Time Domains of Hypoxia Responses and -Omics Insights

The ability to respond rapidly to changes in oxygen tension is critical for many forms of life. Challenges to oxygen homeostasis, specifically in the contexts of evolutionary biology and biomedicine, provide important insights into mechanisms of hypoxia adaptation and tolerance. Here we synthesize findings across varying time domains of hypoxia in terms of oxygen delivery, ranging from early animal to modern human evolution and examine the potential impacts of environmental and clinical challenges through emerging multi-omics approaches. We discuss how diverse animal species have adapted to hypoxic environments, how humans vary in their responses to hypoxia (i.e., in the context of high-altitude exposure, cardiopulmonary disease, and sleep apnea), and how findings from each of these fields inform the other and lead to promising new directions in basic and clinical hypoxia research.

Altitude-Induced Sleep Apnea Is Highly Dependent on Ethnic Background (Sherpa Vs. Tamang)

Heiniger, Grégory, Simon Walbaum, Claudio Sartori, Alban Lovis, Marco Sazzini, Andrew Wellman, and Raphael Heinzer. Altitude-Induced Sleep Apnea Is Highly Dependent on Ethnic Background (Sherpa Vs. Tamang). High Alt Med Biol. 23:165-172, 2022. Rationale: High altitude-induced hypocapnic alkalosis generates central sleep apnea (CSA). In Nepal, two ethnic groups live at medium-to-high altitude: Tamangs originate from low-altitude Tibeto-Burman populations, whereas Sherpas descend from high-altitude Tibetans. Objective: To compare apnea severity at low and high altitude between Sherpas and Tamangs. Methods: Polygraphy recordings, including airflow and oxygen saturation, were performed in Nepal at "low" (2,030 m) and "high" (4,380 m) altitudes. Resting ventilation (V̇E) and mixed-exhaled CO₂ (F_ECO₂) were also measured at the same altitudes. Differences in apnea-hypopnea index (AHI), oxygen desaturation index (ODI), and % of nocturnal periodic breathing (NPB) at the two altitudes were compared between ethnicities. Measurements and Main Results: Twenty Sherpas and 20 Tamangs were included (males, median [interquartile range] age: 24.5 [21.5-27.8] years vs. 26.0 [21.5-39.8] years, body mass index: 23.9 [22.1-26.1] kg/m² vs. 25.21 [20.6-27.6] kg/m²). Compared with Tamangs, Sherpas showed a lower increase in AHI (+7.5 [2.6-17.2]/h vs. +31.5 [18.2-57.3]/h, p < 0.001), ODI (+13.8 [5.5-28.2]/h vs. +42.0 [22.6-77.6]/h, p < 0.001), and NPB proportion (+0.9 [0-3.5]% vs. +12.8 [3.1-27.4]%, p < 0.001) from low to high altitude. Resting V̇E was higher in Sherpas versus Tamangs at both low (8.45 [6.89-10.70] l/min vs. 6.3 [4.9-8.3] l/min, p = 0.005) and high (9.7 [8.5-11] l/min vs. 8.74 [7.39-9.73] l/min, p = 0.020) altitudes, whereas the mean ± standard deviation F_ECO₂ decrease between low and high altitude was greater in Tamangs versus Sherpas (-0.50% ± 0.44% vs. -0.80% ± 0.33%, p < 0.023). Conclusion: Overall, altitude-adapted Sherpas showed a 3.2-times smaller increase in sleep-disordered breathing between low and high altitude compared with Tamangs, and higher ventilation and a smaller drop in F_ECO₂ at high altitude. These data suggest that genetic differences in breathing control can be protective against CSA.

Algorithm for automatic detection of self-similarity and prediction of residual central respiratory events during continuous positive airway pressure

Study Objectives

Sleep-disordered breathing is a significant risk factor for cardiometabolic and neurodegenerative diseases. High loop gain (HLG) is a driving mechanism of central sleep apnea or periodic breathing. This study presents a computational approach that identifies “expressed/manifest” HLG via a cyclical self-similarity feature in effort-based respiration signals.

Methods

Working under the assumption that HLG increases the risk of residual central respiratory events during continuous positive airway pressure (CPAP), the full night similarity, computed during diagnostic non-CPAP polysomnography (PSG), was used to predict residual central events during CPAP (REC), which we defined as central apnea index (CAI) higher than 10. Central apnea labels are obtained both from manual scoring by sleep technologists and from an automated algorithm developed for this study. The Massachusetts General Hospital sleep database was used, including 2466 PSG pairs of diagnostic and CPAP titration PSG recordings.

Results

Diagnostic CAI based on technologist labels predicted REC with an area under the curve (AUC) of 0.82 ± 0.03. Based on automatically generated labels, the combination of full night similarity and automatically generated CAI resulted in an AUC of 0.85 ± 0.02. A subanalysis was performed on a population with technologist-labeled diagnostic CAI higher than 5. Full night similarity predicted REC with an AUC of 0.57 ± 0.07 for manual and 0.65 ± 0.06 for automated labels.

Conclusions

The proposed self-similarity feature, as a surrogate estimate of expressed respiratory HLG and computed from easily accessible effort signals, can detect periodic breathing regardless of admixed obstructive features such as flow limitation and can aid the prediction of REC.

High flow nasal cannula treatment for obstructive sleep apnea in infants and young children

BACKGROUND

Continuous positive airway pressure (CPAP) is the nonsurgical treatment of choice for children with obstructive sleep apnea (OSA). However, CPAP limitations include difficulty with adherence and midface hypoplasia risk. We, therefore, sought to assess the effect of warm humidified air delivered via open nasal cannula (HFNC) on OSA in children in the sleep laboratory and at home.

METHODS

A retrospective review was performed among children recommended treatment of OSA with HFNC. Reasons for HFNC recommendation included poor surgical candidacy, residual OSA following surgery, and CPAP intolerance. Children underwent both diagnostic and HFNC titration sleep studies and were prescribed HFNC for home use. Standard sleep architecture, arousals, and apnea-hypopnea indices (AHI) were assessed with the evaluation of reported adherence and complications over 12 months of treatment.

RESULTS

Twenty-two children (average 12.8 months, 95% confidence interval [95% CI: 7.0, 18.6]) with OSA (obstructive AHI [OAHI] range: 4.8-89.2 events/h) underwent HFNC titration with significant reduction in OAHI (28.9 events/h [17.6, 40.2] vs 2.6 [1.1, 4.0]; P < .001) (mean [95% CI]). Nineteen patients received home HFNC treatment. By 12 months, four patients were lost to follow-up and OSA resolved in three patients (16%). Of 12 remaining patients, 7 (58%) continued therapy while 5 (42%) discontinued due to intolerance. The most common treatment complication was cannula dislodgement. Additional complications included skin irritation, dry mucus membranes, restlessness, oxygen desaturation, and increased central apneas.

CONCLUSION

HFNC offers a treatment alternative to CPAP in infants and young children with OSA and was well tolerated at home in our study.

Multimorbidity in COPD, does sleep matter?

A good night's sleep is a prerequisite for sustainable mental and physical health. Sleep disorders, including sleep disordered breathing, insomnia and sleep related motor dysfunction (e.g., restless legs syndrome), are common in patients with chronic obstructive pulmonary disease (COPD), especially in more severe disease. COPD is commonly associated with multimorbidity, and sleep disorders as a component of this multimorbidity spectrum have a further negative impact on COPD-related comorbidities. Indeed, concomitant diseases in COPD and in obstructive sleep apnea (OSA) are similar, suggesting that the combination of COPD and OSA, the so called OSA-COPD overlap syndrome (OVS), affects patient outcomes. Potential clinically important interactions of OVS exist in cardiovascular and metabolic disease, arthritis, anxiety, depression, neurocognitive disorder and the fatigue syndrome. Correct diagnosis for recognition and treatment of sleep-related disorders in COPD is recommended. However, surprisingly limited information is available and further research and improved diagnostic tools are needed. In the absence of clear evidence, we agree with the recommendation of the Global Initiative on Chronic Obstructive Lung Disease that sleep disorders should be actively searched for and treated in patients with COPD. We believe that both aspects are important components of the holistic approach required in patients with chronic multimorbid conditions.

More than Heart Failure: Central Sleep Apnea and Sleep-Related Hypoventilation

Central sleep apnea (CSA) comprises a variety of breathing patterns and clinical entities. They can be classified into 2 categories based on the partial pressure of carbon dioxide in the arterial blood. Nonhypercapnic CSA is usually characterized by a periodic breathing pattern, while hypercapnic CSA is based on hypoventilation. The latter CSA form is associated with central nervous, neuromuscular, and rib cage disorders as well as obesity and certain medication or substance intake. In contrast, nonhypercapnic CSA is typically accompanied by an overshoot of the ventilation and often associated with heart failure, cerebrovascular diseases, and stay in high altitude. CSA and hypoventilation syndromes are often considered separately, but pathophysiological aspects frequently overlap. An integrative approach helps to recognize underlying pathophysiological mechanisms and to choose adequate therapeutic strategies. Research in the last decades improved our insights; nevertheless, diagnostic tools are not always appropriately chosen to perform comprehensive sleep studies. This supports misinterpretation and misclassification of sleep disordered breathing. The purpose of this article is to highlight unresolved problems, raise awareness for different pathophysiological components and to discuss the evidence for targeted therapeutic strategies.

Diagnosis and management of central sleep apnea syndrome

Introduction: Central sleep apnea (CSA) syndrome has gained a considerable interest in the sleep field within the last 10 years. It is overrepresented in particular subpopulations such as patients with stroke or heart failure. Early detection and diagnosis, as well as appropriate treatment of central breathing disturbances during sleep remain challenging. Areas covered: Based on a systematic review of CSA in adults the clinical evidence and polysomnographic patterns useful for discerning central from obstructive events are discussed. Current therapeutic indications of CSA and perspectives are presented, according to the type of respiratory disturbances during sleep, alterations in blood gases and ventilatory control. Expert opinion: The precise identification of central events during polysomnographic recording is mandatory. Therapeutic choices for CSA depend on the typology of respiratory disturbances observed by polysomnography, changes in blood gases and ventilatory control. In CSA with normocapnia and ventilatory instability, adaptive servo-ventilation is recommended. In CSA with hypercapnia and/or rapid-eye movement sleep hypoventilation, non-invasive ventilation is required. Further studies are required as strong evidence is lacking regarding the long-term consequences of CSA and the long-term impact of current treatment strategies.

Linking sleep disturbance to idiopathic male infertility

Recently published data suggests that male fertility has declined over the past four decades. The reasons for the decline are unclear with up to 50% of cases of male infertility remaining unexplained (idiopathic male infertility). Whilst environmental factors and rising rates of obesity have been implicated, there is now growing evidence that sleep disturbance may be an independent causative factor. Indeed, the prevalence of sleep disturbance appears to be increasing in parallel with deterioration in population sperm quality, a commonly used surrogate marker of male fertility. Although there is some understanding of the relationship between sleep, gonadal hormone secretion and sexual function, it remains to be seen whether sleep disturbance is implicated in idiopathic male infertility. This review will detail the current evidence supporting a link between sleep disturbance and male infertility. Potential mechanistic pathways will be proposed and evidence supporting these pathways will be discussed. Further research is needed in clarifying links between sleep disturbance and idiopathic male infertility. At present the only available treatment option for men with idiopathic infertility is assisted reproductive technology. Demonstration of a causative link between sleep disturbance and idiopathic male infertility may in the future lead to additional treatment options in selected cases.

High Altitude Affects Nocturnal Non-linear Heart Rate Variability: PATCH-HA Study

Background: High altitude (HA) exposure can lead to changes in resting heart rate variability (HRV), which may be linked to acute mountain sickness (AMS) development. Compared with traditional HRV measures, non-linear HRV appears to offer incremental and prognostic data, yet its utility and relationship to AMS have been barely examined at HA. This study sought to examine this relationship at terrestrial HA. Methods: Sixteen healthy British military servicemen were studied at baseline (800 m, first night) and over eight consecutive nights, at a sleeping altitude of up to 3600 m. A disposable cardiac patch monitor was used, to record the nocturnal cardiac inter-beat interval data, over 1 h (0200-0300 h), for offline HRV assessment. Non-linear HRV measures included Sample entropy (SampEn), the short (α1, 4-12 beats) and long-term (α2, 13-64 beats) detrend fluctuation analysis slope and the correlation dimension (D2). The maximal rating of perceived exertion (RPE), during daily exercise, was assessed using the Borg 6-20 RPE scale. Results: All subjects completed the HA exposure. The average age of included subjects was 31.4 ± 8.1 years. HA led to a significant fall in SpO₂ and increase in heart rate, LLS and RPE. There were no significant changes in the ECG-derived respiratory rate or in any of the time domain measures of HRV during sleep. The only notable changes in frequency domain measures of HRV were an increase in LF and fall in HFnu power at the highest altitude. Conversely, SampEn, SD1/SD2 and D2 all fell, whereas α1 and α2 increased (p < 0.05). RPE inversely correlated with SD1/SD2 (r = -0.31; p = 0.002), SampEn (r = -0.22; p = 0.03), HFnu (r = -0.27; p = 0.007) and positively correlated with LF (r = 0.24; p = 0.02), LF/HF (r = 0.24; p = 0.02), α1 (r = 0.32; p = 0.002) and α2 (r = 0.21; p = 0.04). AMS occurred in 7/16 subjects (43.8%) and was very mild in 85.7% of cases. HRV failed to predict AMS. Conclusion: Non-linear HRV is more sensitive to the effects of HA than time and frequency domain indices. HA leads to a compensatory decrease in nocturnal HRV and complexity, which is influenced by the RPE measured at the end of the previous day. HRV failed to predict AMS development.

Chemoreflex mediated arrhythmia during apnea at 5,050 m in low- but not high-altitude natives

Peripheral chemoreflex mediated increases in both parasympathetic and sympathetic drive under chronic hypoxia may evoke bradyarrhythmias during apneic periods. We determined whether 1) voluntary apnea unmasks arrhythmia at low (344 m) and high (5,050 m) altitude, 2) high-altitude natives (Nepalese Sherpa) exhibit similar cardiovagal responses at altitude, and 3) bradyarrhythmias at altitude are partially chemoreflex mediated. Participants were grouped as Lowlanders ( n = 14; age = 27 ± 6 yr) and Nepalese Sherpa ( n = 8; age = 32 ± 11 yr). Lowlanders were assessed at 344 and 5,050 m, whereas Sherpa were assessed at 5,050 m. Heart rate (HR) and rhythm (lead II ECG) were recorded during rest and voluntary end-expiratory apnea. Peripheral chemoreflex contributions were assessed in Lowlanders ( n = 7) at altitude after 100% oxygen. Lowlanders had higher resting HR at altitude (70 ± 15 vs. 61 ± 15 beats/min; P < 0.01) that was similar to Sherpa (71 ± 5 beats/min; P = 0.94). High-altitude apnea caused arrhythmias in 11 of 14 Lowlanders [junctional rhythm ( n = 4), 3° atrioventricular block ( n = 3), sinus pause ( n = 4)] not present at low altitude and larger marked bradycardia (nadir -39 ± 18 beats/min; P < 0.001). Sherpa exhibited a reduced bradycardia response during apnea compared with Lowlanders ( P < 0.001) and did not develop arrhythmias. Hyperoxia blunted bradycardia (nadir -10 ± 14 beats/min; P < 0.001 compared with hypoxic state) and reduced arrhythmia incidence (3 of 7 Lowlanders). Degree of bradycardia was significantly related to hypoxic ventilatory response (HVR) at altitude and predictive of arrhythmias ( P < 0.05). Our data demonstrate apnea-induced bradyarrhythmias in Lowlanders at altitude but not in Sherpa (potentially through cardioprotective phenotypes). The chemoreflex is an important mechanism in genesis of bradyarrhythmias, and the HVR may be predictive for identifying individual susceptibility to events at altitude. NEW & NOTEWORTHY The peripheral chemoreflex increases both parasympathetic and sympathetic drive under chronic hypoxia. We found that this evoked bradyarrhythmias when combined with apneic periods in Lowlanders at altitude, which become relieved through supplemental oxygen. In contrast, high-altitude residents (Nepalese Sherpa) do not exhibit bradyarrhythmias during apnea at altitude through potential cardioprotective adaptations. The degree of bradycardia and bradyarrhythmias was related to the hypoxic ventilatory response, demonstrating that the chemoreflex plays an important role in these findings.

Sleep respiratory disturbances during the ascent to Mount Aconcagua

Introduction

Mountaineers exposed to hypobaric hypoxia (HH) show high-altitude periodic breathing (PB).

Objective

To analyze high-altitude PB during the ascent of Mount Aconcagua (Argentina).

Materials and Methods

Descriptive study in healthy volunteers using respiratory polygraphy (RP) at different altitudes.

Results

We studied 8 andinist, mean age: 36 years old (25-51), body mass index (BMI) of 23.6 (20.9-28.7) and 22.77 (20.9-27.7) upon return, p<0.01. RP without PB showed a lower Oxygen Desaturation Index (ODI) and a lower Apnea-Hypopnea-Index (AHI); 5.43 (0 - 20) versus 45.95 (2-122) p<0.001 and 3.9 (0-15.5) versus 44.35 (4-115) p<0.001. AHI increased with altitude at the expense of central apneas and hypopneas: p<0.05.

Conclusion

High-altitude PB is frequent above 2,581m.a.s.l. And it is characterized by short cycles. None of the mountaineers showed PB at baseline; however, high-altitude PB occurred in all subjects above 4,900 m.a.s.l

Positive Airway Pressure Therapy for Hyperventilatory Central Sleep Apnea: Idiopathic, Heart Failure, Cerebrovascular Disease, and High Altitude

Central sleep apnea (CSA) and Hunter-Cheyne-Stokes breathing (HCSB) are caused by failure of the pontomedullary pacemaker generating breathing rhythm. CSA/HCSB may complicate several disorders causing recurrent arousals and desaturations. Common causes of CSA in adults are congestive heart failure, stroke, and chronic use of opioids; opioids have hypoventilatory effects. Diagnosis and treatment of hyperventilatory CSA may improve quality of life, and, when associated with heart failure or cerebrovascular disease, reduce morbidity and perhaps mortality.