Doppler assessment of hypoxic pulmonary vasoconstriction and susceptibility to high altitude pulmonary oedema

Abstract

Background - Subjects with previous high altitude pulmonary oedema may have stronger than normal hypotic pulmonary vasoconstriction. Susceptibility to high altitude pulmonary oedema may be detectable by echo Doppler assessment of the pulmonary vascular reactivity to breathing a hypoxic gas mixture at sea level. Methods - The study included 20 healthy controls, seven subjects with a previous episode of high altitude pulmonary oedema, and nine who had successfully climbed to altitudes of 6000-8842 m during the 40th anniversary British expedition to Mount Everest. Echo Doppler measurements of pulmonary blood flow acceleration time (AT) and ejection time (ET), and of the peak velocity of the tricuspid regurgitation jet (TR), were obtained under normobaric conditions of normoxia (fraction of inspired oxygen, FIO2, 0.21), of hyperoxia (FIO2 1.0), and of hypoxia (FIO2 0.125). Results - Hypoxia decreased AT/ET by mean (SE) 0.06 (0.01) in the control subjects, by 0.11 (0.01) in those susceptible to high altitude pulmonary oedema, and by 0.02 (0.02) in the successful high altitude climbers. Hypoxia increased TR in the three groups by 0.22 (0.06) (n = 14), 0.56 (0.13) (n = 5), and 0.18 (0.1) (n = 7) m/s, respectively. However, AT/ET and/or TR measurements outside the normal range, defined as mean ± 2 SD of measurements obtained in the controls under hypoxia, were observed in only two of the subjects susceptible to high altitude pulmonary oedema and in five of the successful high altitude climbers. Conclusions - Pulmonary vascular reactivity to hypoxia is enhanced in subjects with previous high altitude pulmonary oedema and decreased in successful high altitude climbers. However, echo Doppler estimates of hypoxic pulmonary vasoconstriction at sea level cannot reliably identify subjects susceptible to high altitude pulmonary oedema or successful high altitude climbers from a normal control population.