Lung function and breathing pattern in subjects developing high altitude pulmonary edema

Abstract

Introduction: The purpose of the study was to comprehensively evaluate physiologic changes associated with development of high altitude pulmonary edema (HAPE). We tested whether changes in pulmonary function and breathing pattern would herald clinically overt HAPE at an early stage.

Methods: In 18 mountaineers, spirometry, diffusing capacity, nitrogen washout, nocturnal ventilation and pulse oximetry were recorded at 490 m and during 3 days after rapid ascent to 4559 m. Findings were compared among subjects developing HAPE and those remaining well (controls).

Results: In 8 subjects subsequently developing radiographically documented HAPE at 4559 m, median FVC declined to 82% of low altitude baseline while closing volume increased to 164% of baseline (P<0.05, both instances). In 10 controls, FVC decreased slightly (to 93% baseline, P<0.05) but significantly less than in subjects with HAPE and closing volume remained unchanged. Sniff nasal pressure was reduced in both subjects with and without subsequent HAPE. During nights at 4559 m, mean nocturnal oxygen saturation dropped to lower values while minute ventilation, the number of periodic breathing cycles and heart rate were higher (60%; 8.6 L/min; 97 cycles/h; 94 beats/min, respectively) in subjects subsequently developing HAPE than in controls (73%; 5.1 L/min; 48 cycles/h; 79 beats/min; P<0.05 vs. HAPE, all instances).

Conclusion: The results comprehensively represent the pattern of physiologic alterations that precede overt HAPE. The changes in lung function are consistent with reduced lung compliance and impaired gas exchange. Pronounced nocturnal hypoxemia, ventilatory control instability and sympathetic stimulation are further signs of subsequent overt HAPE.

Trial registration: ClinicalTrials.gov NCT00274430.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Changes in lung function in subjects developing HAPE and in healthy controls.

FVC (upper panel), closing volume above RV (middle panel) and DLCO adjusted for PIO2 (lower panel), all expressed in percent of the value at 490 m. HAPE  =  subjects subsequently developing HAPE, controls  =  subjects not developing HAPE; first and last day at 4559 m  =  values measured on the day of arrival and either on the last day before clinically overt HAPE occurred, or on day 3 in controls. *P<0.05 vs. 490 m. **P<0.05 vs. controls.