Effects of High Altitude on Sleep and Respiratory System

Sex-related Differences in Loop Gain during High-Altitude Sleep-disordered Breathing

Rationale: Central sleep apnea (CSA) is pervasive during sleep at high altitude, disproportionately impacting men and associated with increased peripheral chemosensitivity. Objectives: We aimed to assess whether biological sex affects loop gain (LGn) and CSA severity during sleep over 9-10 days of acclimatization to 3,800 m. We hypothesized that CSA severity would worsen with acclimatization in men but not in women because of greater increases in LGn in men. Methods: Sleep studies were collected from 20 (12 male) healthy participants at low altitude (1,130 m, baseline) and after ascent to (nights 2/3, acute) and residence at high altitude (nights 9/10, prolonged). CSA severity was quantified as the respiratory event index (REI) as a surrogate of the apnea-hypopnea index. LGn, a measure of ventilatory control instability, was quantified using a ventilatory control model fit to nasal flow. Linear mixed models evaluated effects of time at altitude and sex on respiratory event index and LGn. Data are presented as contrast means with 95% confidence intervals. Results: REI was comparable between men and women at acute altitude (4.1 [-9.3, 17.5] events/h; P = 0.54) but significantly greater in men at prolonged altitude (23.7 [10.3, 37.1] events/h; P = 0.0008). Men had greater LGn than did women for acute (0.08 [0.001, 0.15]; P = 0.047) and prolonged (0.17 [0.10, 0.25]; P < 0.0001) altitude. The change in REI per change in LGn was significantly greater in men than in women (107 ± 46 events/h/LGn; P = 0.02). Conclusions: The LGn response to high altitude differed between sexes and contributed to worsening of CSA over time in men but not in women. This sex difference in acclimatization appears to protect females from high altitude-related CSA. These data provide fundamental sex-specific physiological insight into high-altitude acclimatization in healthy individuals and may help to inform sex differences in sleep-disordered breathing pathogenesis in patients with cardiorespiratory disease.

Oxygen saturation thresholds for bronchiolitis at high altitudes: a cost-effectiveness analysis

BACKGROUND

There is evidence suggesting that exaggerated reliance on pulse oximetry (SpO2) and the use of arbitrary/inadequate thresholds of SpO2 might drive unnecessary hospitalizations for viral bronchiolitis, especially among high-altitude residents. The aim of the present study was to compare the cost-effectiveness of two oxygen SpO2 thresholds for deciding whether infants with viral bronchiolitis living at high altitudes need hospital admission or can be discharged home.

METHODS

A cost-effectiveness study was performed to compare the cost and clinical outcomes of two oxygen SpO2 thresholds, adjusted or not, to an altitude above the sea level of Bogota, Colombia (2640 m), for deciding whether infants with viral bronchiolitis need hospitalization or can be discharged home. The principal outcome was avoidance of hospital admission.

RESULTS

Compared to the use of an SpO2 threshold of 90%, using an SpO2 threshold of 85% in infants with viral bronchiolitis was associated with lower overall costs (US$130.4 vs. US$194.0 average cost per patient) and a higher probability of hospitalization avoided (0.7500 vs. 0.5900), thus leading to dominance.

CONCLUSIONS

The use of an SpO2 threshold below 90% for deciding on hospitalization in infants with viral bronchiolitis living at high altitudes appears to be logical, secure, and cost-effective.

Comparison of two oxygen saturation targets to decide on hospital discharge of infants with viral bronchiolitis living at high altitudes: a cost-effectiveness analysis

OBJECTIVES

The objective of the current study was to evaluate the cost-effectiveness of two pulse oximetry (SpO2) thresholds to decide on hospital discharge when all other discharge criteria are met, in infants with viral bronchiolitis living at high altitudes.

METHODS

A decision analysis model was developed to estimate the cost-effectiveness of the use of an SpO2 threshold of 90% versus one of 85% for deciding whether infants hospitalized for viral bronchiolitis can be safely discharged to home, from a third-party payer's perspective. The main outcome was discharge to home at day 4 of the initial hospitalization. The time horizon was 28 days after discharge from hospital. We performed deterministic sensitivity analyses and probabilistic sensitivity analyses.

RESULTS

Compared to the use of an SpO2 threshold of 90%, treating infants with viral bronchiolitis with the use of an SpO2 threshold of 85% resulted in lower total costs (US$119.39 vs. US$188.357 mean cost per patient) and a greater probability of discharge to home at day 4 of the initial hospitalization (0.8400 vs. 0.7600), therefore being a dominant strategy. Sensitivity analyses were in line with base case results.

CONCLUSIONS

In Bogota, a high-altitude city, in infants admitted for viral bronchiolitis, the use of an SpO2 threshold of 85% to decide on hospital discharge when all other discharge criteria are met is dominant because it entails a greater probability of discharge to home at day 4 of the initial hospitalization and generates fewer costs than the use of an SpO2 threshold of 90%.