DOPPLER ASSESSMENT OF HYPOXIC PULMONARY VASOCONSTRICTION AND SUSCEPTIBILITY TO HIGH-ALTITUDE PULMONARY-EDEMA

Background - Subjects with previous high altitude pulmonary oedema may have stronger than normal hypoxic pulmonary vasoconstriction. Suscept ibility to high altitude pulmonary oedema may be detectable by echo Do ppler assessment of the pulmonary vascular reactivity to breathing a h ypoxic gas mixture at sea level.Methods - The study included 20 health y controls, seven subjects with a previous episode of high altitude pu lmonary oedema, and nine who had successfully climbed to altitudes of 6000-8842 m during the 40th anniversary British expedition to Mount Ev erest. Echo Doppler measurements of pulmonary blood flow acceleration time (AT) and ejection time (ET), and of the peak velocity of the tric uspid regurgitation jet (TR), were obtained under normobaric condition s 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 i n the three groups by 0.22 (0.06) (n=14), 0.56 Cardiology (0.13) (n=5) , and 0.18 (0.1) (n=7) mis, respectively. However, AT/ET and/or TR Dep artment of measurements outside the normal range, defined as mean +/- 2 SD of measurements obtained in the controls under hypoxia, were obse rved in only two of the subjects susceptible to high altitude pulmonar y oedema and in five of the successful high altitude climbers. Conclus ions - Pulmonary vascular reactivity to hypoxia is enhanced in subject s with previous high altitude pulmonary oedema and decreased in succes sful high altitude climbers. However, echo Doppler estimates of hypoxi c pulmonary vasoconstriction at sea level cannot reliably identify sub jects susceptible to high altitude pulmonary oedema or successful high altitude climbers from a normal control population.