Non-invasive positive pressure ventilation during sleep at 3800 m: Relationship to acute mountain sickness and sleeping oxyhaemoglobin saturation

Positive expiratory pressure improves arterial and cerebral oxygenation in acute normobaric and hypobaric hypoxia

Positive expiratory pressure (PEP) has been shown to limit hypoxia-induced reduction in arterial oxygen saturation, but its effectiveness on systemic and cerebral adaptations, depending on the type of hypoxic exposure [normobaric (NH) versus hypobaric (HH)], remains unknown. Thirteen healthy volunteers completed three randomized sessions consisting of 24-h exposure to either normobaric normoxia (NN), NH (inspiratory oxygen fraction, FiO2 = 13.6%; barometric pressure, BP = 716 mmHg; inspired oxygen partial pressure, PiO2 = 90.9 ± 1.0 mmHg), or HH (3,450 m, FiO2 = 20.9%, BP = 482 mmHg, PiO2 = 91.0 ± 0.6 mmHg). After the 6th and the 22nd hours, participants breathed quietly through a facemask with a 10-cmH₂O PEP for 2 × 5 min interspaced with 5 min of free breathing. Arterial (SpO2, pulse oximetry), quadriceps, and cerebral (near-infrared spectroscopy) oxygenation, middle cerebral artery blood velocity (MCAv; transcranial Doppler), ventilation, and cardiovascular responses were recorded continuously. SpO2without PEP was significantly lower in HH (87 ± 4% on average for both time points, P < 0.001) compared with NH (91 ± 3%) and NN (97 ± 1%). PEP breathing did not change SpO2 in NN but increased it similarly in NH and HH (+4.3 ± 2.5 and +4.7 ± 4.1% after 6h; +3.5 ± 2.2 and +4.1 ± 2.9% after 22h, both P < 0.001). Although MCAv was reduced by PEP (in all sessions and at all time points, -6.0 ± 4.2 cm/s on average, P < 0.001), the cerebral oxygenation was significantly improved (P < 0.05) with PEP in both NH and HH, with no difference between conditions. These data indicate that PEP could be an attractive nonpharmacological means to improve arterial and cerebral oxygenation under both normobaric and hypobaric mild hypoxic conditions in healthy participants.

The Effect of an Expiratory Resistance Mask with Dead Space on Sleep, Acute Mountain Sickness, Cognition, and Ventilatory Acclimatization in Normobaric Hypoxia

We examined the hypothesis that an expiratory resistance mask containing a small amount of dead space (ER/DS) would reduce the apnea-hypopnea index (AHI) during sleep, attenuate the severity of acute mountain sickness (AMS), and offset decrements in cognitive function compared with a sham mask. In a double-blinded, randomized, sham-controlled, crossover design, 19 volunteers were exposed to two nights of normobaric hypoxia (F_IO_{2 =} 0.125), using a ER/DS mask (3.5 mm restrictive expiratory orifice; 125 mL DS volume) and sham mask (zero-flow resistance; 50 mL DS volume). Cognitive function, AMS, and ventilatory acclimatization were assessed before and after the 12-hour normobaric hypoxia exposure. Polysomnography was conducted during sleep. AHI was reduced using the ER/DS sleep mask compared with the sham (30.1 ± 23.9 events·hr^-1 vs. 58.9 ± 34.4 events·hr^-1, respectively; p = 0.01). Likewise, oxygen desaturation index and headache severity were reduced (both p < 0.05). There were also benefits on limiting the hypoxia-induced reductions in select measures of reaction speed and attention (p < 0.05). Our study indicates that a simple noninvasive and portable ER/DS mask resulted in reductions (49%) in AHI, and reduced headache severity and aspects of cognitive decline. The field applications of this ER/DS mask should be investigated before recommendations can be made to support its benefit for travel to high altitude.

Adaptive Servoventilation as Treatment for Central Sleep Apnea Due to High-Altitude Periodic Breathing in Nonacclimatized Healthy Individuals

Orr, Jeremy E., Erica C. Heinrich, Matea Djokic, Dillon Gilbertson, Pamela N. Deyoung, Cecilia Anza-Ramirez, Francisco C. Villafuerte, Frank L. Powell, Atul Malhotra, and Tatum Simonson. Adaptive servoventilation as treatment for central sleep apnea due to high-altitude periodic breathing in nonacclimatized healthy individuals. High Alt Med Biol. 19:178-184, 2018.

AIMS

Central sleep apnea (CSA) is common at high altitude, leading to desaturation and sleep disruption. We hypothesized that noninvasive ventilation using adaptive servoventilation (ASV) would be effective at stabilizing CSA at altitude. Supplemental oxygen was evaluated for comparison.

METHODS

Healthy subjects were brought from sea level to 3800 m and underwent polysomnography on three consecutive nights. Subjects underwent each condition-No treatment, ASV, and supplemental oxygen-in random order. The primary outcome was the effect of ASV on oxygen desaturation index (ODI). Secondary outcomes included oxygen saturation, arousals, symptoms, and comparison to supplemental oxygen.

RESULTS

Eighteen subjects underwent at least two treatment conditions. There was a significant difference in ODI across the three treatments. There was no statistical difference in ODI between no treatment and ASV (17.1 ± 4.2 vs. 10.7 ± 2.9 events/hour; p > 0.17) and no difference in saturation or arousal index. Compared with no treatment, oxygen improved the ODI (16.5 ± 4.5 events/hour vs. 0.5 ± 0.2 events/hour; p < 0.003), in addition to saturation and arousal index.

CONCLUSIONS

We found that ASV was not clearly efficacious at controlling CSA in persons traveling to 3800 m, whereas supplemental oxygen resolved CSA. Adjustment in the ASV algorithm may improve efficacy. ASV may have utility in acclimatized persons or at more modest altitudes.

Wearable physiological sensors and real-time algorithms for detection of acute mountain sickness

This is a minireview of potential wearable physiological sensors and algorithms (process and equations) for detection of acute mountain sickness (AMS). Given the emerging status of this effort, the focus of the review is on the current clinical assessment of AMS, known risk factors (environmental, demographic, and physiological), and current understanding of AMS pathophysiology. Studies that have examined a range of physiological variables to develop AMS prediction and/or detection algorithms are reviewed to provide insight and potential technological roadmaps for future development of real-time physiological sensors and algorithms to detect AMS. Given the lack of signs and nonspecific symptoms associated with AMS, development of wearable physiological sensors and embedded algorithms to predict in the near term or detect established AMS will be challenging. Prior work using [Formula: see text], HR, or HRv has not provided the sensitivity and specificity for useful application to predict or detect AMS. Rather than using spot checks as most prior studies have, wearable systems that continuously measure SpO2 and HR are commercially available. Employing other statistical modeling approaches such as general linear and logistic mixed models or time series analysis to these continuously measured variables is the most promising approach for developing algorithms that are sensitive and specific for physiological prediction or detection of AMS.

No effect of acute normobaric hypoxia on plasma triglyceride levels in fasting healthy men

Circulating fatty acids are a major systemic energy source in the fasting state as well as a determinant of hepatic triglycerides (TG)-rich very-low-density lipoprotein production. Upon acute hypoxia, sympathetic arousal induces adipose tissue lipolysis, resulting in an increase in circulating nonesterified fatty acids (NEFA). Animal studies suggest that TG clearance may also be strongly reduced under hypoxia, though this effect has been shown to be dependent on temperature. Whether the hypoxia-induced rise in blood fatty acid concentrations affects fasting TG levels in humans under thermoneutral conditions remains unknown. TG, NEFA, and glycerol levels were measured in fasted healthy young men (n = 10) exposed for 6 h to either normoxia (ambient air) or acute hypoxia (fraction of inspired oxygen = 0.12) in a randomized, crossover design. Participants were casually clothed and rested in front of a fan in an environmental chamber maintained at 28 °C during each trial. Under hypoxia, a significantly greater increase in NEFA occurred (condition × time interaction, p = 0.049) and glycerol levels tended to be higher (condition × time, p = 0.104), suggesting an increase in adipose tissue lipolysis. However, plasma TG levels did not change over time and did not differ between the normoxia and hypoxia conditions. In conclusion, acute exposure to normobaric hypoxia under thermoneutral condition in healthy men during fasting state increased lipolysis without affecting circulating TG.

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.

Acute Mountain Sickness Symptoms Depend on Normobaric versus Hypobaric Hypoxia

Acute mountain sickness (AMS), characterized by headache, nausea, fatigue, and dizziness when unacclimatized individuals rapidly ascend to high altitude, is exacerbated by exercise and can be disabling. Although AMS is observed in both normobaric (NH) and hypobaric hypoxia (HH), recent evidence suggests that NH and HH produce different physiological responses. We evaluated whether AMS symptoms were different in NH and HH during the initial stages of exposure and if the assessment tool mattered. Seventy-two 8 h exposures to normobaric normoxia (NN), NH, or HH were experienced by 36 subjects. The Environmental Symptoms Questionnaire (ESQ) and Lake Louise Self-report (LLS) were administered, resulting in a total of 360 assessments, with each subject answering the questionnaire 5 times during each of their 2 exposure days. Classification tree analysis indicated that symptoms contributing most to AMS were different in NH (namely, feeling sick and shortness of breath) compared to HH (characterized most by feeling faint, appetite loss, light headedness, and dim vision). However, the differences were not detected using the LLS. These results suggest that during the initial hours of exposure (1) AMS in HH may be a qualitatively different experience than in NH and (2) NH and HH may not be interchangeable environments.

Association of arterial oxygen saturation and acute mountain sickness susceptibility: a meta-analysis

Acute mountain sickness (AMS) is the most common high altitude illnesses experienced during rapid ascent to a higher altitude without prior acclimation. It is mainly characterized by a headache which may be accompanied with nausea, vomiting, anorexia, dizziness, lethargy, fatigue, and sleep disturbance. If not diagnosed and treated in a timely manner, AMS can develop into deadly high altitude pulmonary edema or high altitude cerebral edema. In the previous studies of individual variation in susceptibility to AMS, arterial oxygen saturation (SO2) was identified as being associated with AMS. However, other studies have reported no association between AMS and arterial oxygen saturation. In this study, the association between SO2 and AMS was assessed through a meta-analysis of published data. The literature databases PubMed, Web of Science, LWW, Science Direct, and Embase were queried for papers published before 15 April 2014. A fixed-effects model and a random-effects model were applied (Revman 5.0) on the basis of heterogeneity, and the study quality was assessed in duplicate. Twelve studies with 614 AMS patients and 1,025 control subjects were analyzed. There was a significant association with differences in SO2 and the risk of developing AMS. SO2 values are associated with AMS incidence.

Common High Altitudes Illnesses a Primer for Healthcare Provider

Exposure to high altitude imposes significant strain on cardiopulmonary system and the brain. As a consequence, sojourners to high altitude frequently experience sleep disturbances, often reporting restless and sleepless nights.

At altitudes above 3,000 meters (9,800 ft) almost all healthy subjects develop periodic breathing especially during NREM sleep.

Sleep architecture gradually improves with increased NREM and REM sleep despite persistence of periodic breathing.

The primary reason for periodic breathing at high altitude is a hypoxic-induced increase in chemoreceptor sensitivity to changes in PaCO₂ – both above and below eupnea, leading to periods of apnea and hyperpnea.

Acetazolamide improves sleep by reducing the periodic breathing through development of metabolic acidosis and induced hyperventilation decreasing the plant gain and widening the PCO₂ reserve. This widening of the PCO₂ reserve impedes development of central apneas during sleep. Benzodiazepines and GABA receptor antagonist such as zolpidem improve sleep without affecting breathing pattern or cognitive functions.

Continuous positive airway pressure treatment for acute mountain sickness at 4240 m in the Nepal Himalaya

Acute mountain sickness (AMS) is very common at altitudes above 2500 m. There are few treatment options in the field where electricity availability is limited, and medical assistance or oxygen is unavailable or difficult to access. Positive airway pressure has been used to treat AMS at 3800 m. We hypothesized that continuous positive airway pressure (CPAP) could be used under field conditions powered by small rechargeable batteries. Methods Part 1. 5 subjects trekked to 3500 m from 2800 m in one day and slept there for one night, ascending in the late afternoon to 3840 m, where they slept using CPAP 6-7 cm via mask. The next morning they descended to 3500 m, spent the day there, ascended in late afternoon to 3840 m, and slept the night without CPAP. Continuous overnight oximetry was recorded and the Lake Louise questionnaire for AMS administered both mornings. Methods Part 2. 14 trekkers with symptoms of AMS were recruited at 4240 m. All took acetazolamide. The Lake Louise questionnaire was administered, oximetry recorded, and CPAP 6-7 cm was applied for 10-15 min. CPAP was used overnight and oximetry recorded continuously. In the morning the Lake Louise questionnaire was administered, and oximetry recorded for 10-15 min. The equipment used in both parts was heated, humidified Respironics RemStar® machines powered by Novuscell™ rechargeable lithium ion batteries. Oximetry was recorded using Embletta™ PDS. Results Part 1. CPAP improved overnight Sao2 and eliminated AMS symptoms in the one subject who developed AMS. CPAP was used for 7-9 h and the machines operated for >8 h using the battery. Results Part 2. CPAP use improved Sao2 when used for 10-15 min at the time of recruitment and overnight CPAP use resulted in significantly reduced AMS symptoms. Conclusion. CPAP with rechargeable battery may be a useful treatment option for trekkers and climbers who develop AMS.