Echocardiographic changes induced by moderate to marked hypobaric hypoxia in dogs.

Hypobaric (high-altitude) hypoxia is a physiologic cause of pulmonary hypertension, and alters left ventricular (LV) systolic and diastolic function. In the presence of tricuspid regurgitation, systolic pulmonary artery pressure can be measured noninvasively using the peak tricuspid regurgitation velocity and the Bernoulli equation. In the absence of measurable tricuspid regurgitation, severity of pulmonary hypertension may be estimated using two-dimensional, M-mode, and Doppler-derived parameters. To evaluate the usefulness of echocardiographic parameters for detecting mild-to-moderate pulmonary hypertension caused by moderate-to-marked hypoxia and to study the effect of high-altitude hypoxia on systolic and diastolic LV function in dogs, 19 Greenland dogs were examined at moderate altitude (2300 m) and high altitude (3500 m), and 10 Greenland control dogs were examined at 700-900 m. Evaluated parameters were pulmonary flow profile (shape, right ventricular acceleration time (RVAT), ejection time (RVET), RVAT/ET), peak mitral inflow velocities (LVE, LVA, LVE/A-ratio), LV % fractional shortening (FS), systolic time intervals (LVPEP, LVPEP/ET), and stroke volume index (SVI). Notching during deceleration was common in dogs at high altitude and in the control dogs, but not in dogs at moderate altitude. RVAT was shorter in dogs at high altitude compared with moderate altitude, but not compared with control dogs. Peak A-velocity was higher and E/A-ratio was lower in dogs at high altitude compared with moderate altitude and control dogs. FS was increased in dogs at high altitude compared with moderate altitude, and LVPEP and LVPEP/ET were shorter in the dogs at high altitude compared with moderate altitude and control dogs. In conclusion, significant differences in pulmonary flow profiles and systolic and diastolic parameters can be observed echocardiographically in dogs at different degrees of hypobaric hypoxia. However, overlap between the groups compromises their usefulness for diagnosing and estimating the degree of mild-to-moderate pulmonary hypertension in individual dogs.