Use of Echocardiography Under Hypoxic Stress Without Exercise to Assess Right to Left Shunting

Acute exposure to hypoxia will induce right ventricular (RV) hemodynamic changes and may increase the degree of right-to-left shunting, which can contribute to dyspnea at altitude. In this retrospective study, 125 patients (median age 66 years; 50.4% women) with unexplained dyspnea at altitude underwent hypoxic simulation testing (HST) with transthoracic echocardiography (TTE). During simulated hypoxia (mode (Min-Max) altitude: 8000 (6000-18,000) ft, were observed a significant decrease in oxygen saturation (97% (95-98) vs. 88% (82-92), p < 0.001) and RV free wall longitudinal strain (-19.6 ± 3.99% vs. -17.3 ± 4.17%, p < 0.01), an increase in RV systolic pressure (RVSP: 26 (23-30.5) vs. 29 (25-36.5) mmHg, p < 0.001). No significant changes were observed in TAPSE (20 (18-23) vs. 20 (19-24) mm) or S wave (0.12 (0.11-0.14) vs. 0.13 (0.12-0.14) m/s). Right-to-left shunting was present in 47.2% of patients and 11.9% exhibited inducible shunting only under hypoxia. However, under hypoxia, there were no significant differences in RV hemodynamic parameters or saturation between those with and without shunting. TTE with HST is useful to characterize both cardiopulmonary response and the dynamic changes in right-to-left shunt behavior under hypoxic stress.