Effects Of Ischemic Conditioning On Pulmonary Artery Pressure And Oxygen Saturation

Abstract

Purpose: Hypoxic pulmonary vasoconstriction occurs at high altitude (HA) with resultant pulmonary hypertension. Pulmonary vasodilator medications are useful in acutely lowering pulmonary artery pressure (PAP) at HA. Ischemic conditioning of the extremity (ICE) induces systemic cardio-protective effects via multiple mechanisms including increased nitric oxide (NO) and HIF-1alpha activation. The purpose of this study was to evaluate the effects of ICE on PAP at HA. Method(s): PAP was measured using transthoracic echocardiography in 13 healthy runners after 5 days of daily ICE or sham-ICE at sea-level (SL) and immediately after a 12.8km competitive run to the summit of White Mountain, CA, (altitude = 4342m). Each subject completed the course twice (once following ICE and once following sham-ICE) separated by 6 weeks in a randomized cross-over design. ICE was administered using a blood pressure (BP) cuff around the thigh inflated to 200mmHg for 5 minutes, deflated for 5 minutes and this sequence repeated for 4 cycles. The cuff was inflated to 40mmHg for sham-ICE. Pulmonary artery systolic pressure (PASP) was calculated from peak continuous-wave Doppler tricuspid regurgitation (TR) velocity and mean PAP (mPAP) from pulsed-wave Doppler right ventricular outflow tract acceleration time. Echocardiographic measurements were made offline and Doppler data were graded for quality by observers blinded to the randomization. Oxygen saturation was measured continuously during echocardiography and averaged over 10 minutes. Exercise performance times were recorded. Result(s): Poor quality echocardiograhic data were excluded from the analysis. At HA, ICE significantly reduced PASP (38 +/- 8 mmHg sham-ICE vs. 36 +/- 6 mmHg ICE, p< 0.03, n=8) and mPAP (24 +/- 7 mmHg sham-ICE vs. 17 +/- 6 mmHg ICE, p<0.004, n=13). ICE did not significantly change PASP or mPAP at SL. ICE significantly improved average oxygen saturation at HA (75 +/- 9% sham-ICE vs. 80 +/- 8% ICE, p <0.001). ICE was associated with significantly improved exercise performance (128 +/- 27 minutes ICE vs. 137 +/- 33 minutes sham-ICE, p<0.03). Conclusion(s): At high altitude, ischemic conditioning of the extremity induces systemic effects that are associated with decreased pulmonary artery pressure, increased oxygen saturation and possibly, improved exercise performance.