Doppler Assessment of Pulmonary Hypertension Induced by Hypoxic Breathing in Subjects Susceptible to High Altitude Pulmonary Edema

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To verify the abnormal pulmonary vascular response implicated in the pathogenesis of high altitude pulmonary edema (HAPE), we examined the hemodynamic responses to hypoxia in HAPE-susceptible subjects (HAPE-S) by means of both right heart catheterization and pulsed Doppler echocardiography. The HAPE-S were seven men and one woman with a history of HAPE. Six healthy volunteers who had repeated experiences of mountain climbing without any history of altitude-related problems served as control subjects. The HAPE-S showed much greater increase in pulmonary vascular resistance (PVR) than did the control subjects, resulting in a much higher level of pulmonary arterial pressure (Ppa) under acute hypoxia both of 15% O2 and 10% O2. We then evaluated the usefulness of pulsed Doppler echocardiography in the prediction of pulmonary hypertension. Acceleration time (AcT) and right ventricular ejection time (RVET) were measured from the flow velocity pattern in the right ventricular outflow tract. The ratio of AcT to RVET was correlated to invasively determined mean Ppa (Symbol) and PVR. The results were as follows: (1) AcT/RVET = 0.52 to 0.0047 (Symbol), r = −0.93, SEE = 0.017, p < 0.001 (HAPE-S); (2) AcT/RVET = 0.55 to 0.0055 (Symbol), r = −0.85, SEE = 0.020, p < 0.001 (control subjects); (3) AcT/RVET = 0.46 to 0.00027 (PVR), r = −0.70, SEE = 0.030, p < 0.001 (HAPE-S); (4) AcT/RVET = 0.52 to 0.00077 (PVR), r = −0.91, SEE = 0.016, p < 0.001 (control subjects). We conclude that HAPE-S have a constitutional abnormality in the pulmonary vascular response to hypoxia, which is a possible causative factor of HAPE, and that pulsed Doppler echocardiography may be supportive to assess the pulmonary vascular pressor response in the HAPE-S.

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