One session of remote ischemic preconditioning does not improve vascular function in acute normobaric and chronic hypobaric hypoxia

Application of repeated short duration bouts of ischemia to the limbs, termed remote ischemic preconditioning (RIPC), is a novel technique that may have protective effects on vascular function during hypoxic exposures. In separate parallel-design studies, at sea-level (SL; n=16), and after 8-12 days at high-altitude (HA; n=12; White Mountain, 3800m), participants underwent either a sham protocol or one session of 4x5 minutes of dual-thigh cuff occlusion with 5-minutes recovery. Brachial artery flow-mediated dilation (FMD; ultrasound), pulmonary artery systolic pressure (PASP; echocardiography), and internal carotid artery flow (ICA; ultrasound) were measured at SL in normoxia and isocapnic hypoxia [end-tidal PO (PETO ) maintained to 50mmHg], and during normal breathing at HA. The hypoxic ventilatory response (HVR) was measured at each location. All measures at SL and HA were obtained at baseline (BL), 1 hour, 24 hours, and 48 hours post-RIPC or sham. At SL, RIPC produced no changes in FMD, PASP, ICA flow, end-tidal gases or HVR in normoxia or hypoxia. At HA, although HVR increased 24 hours post RIPC compared to BL (2.05{plus minus}1.4 vs. 3.21{plus minus}1.2 L•min-1•%SaO2-1, p<0.01), there were no significant differences in FMD, PASP, ICA flow, resting end-tidal gases. Accordingly, a single session of RIPC is insufficient to evoke changes in peripheral, pulmonary, and cerebral vascular function in healthy adults. Although chemosensitivity may increase following RIPC at HA, this did not confer any vascular changes. The utility of a single RIPC session seems unremarkable during acute and chronic hypoxia

EFFECT OF LUNG-INFLATION ON ACTIVE AND PASSIVE LIQUID CLEARANCE FROM IN-VIVO RABBIT LUNG

Active sodium transport contributes to liquid clearance from the alveoli. We hypothesized that the magnitude of active transport of alveolar liquid depends on the extent to which the alveolar epithelium is stretched and, consequently, on the degree of alveolar inflation. In a study on 38 adult rabbits, the left lung was filled in vivo with a solution of glucose (10 mmol/l) made isosmotic with plasma, using sodium chloride, and held at a constant airway pressure of 3, 6, or 9 cmH2O for 6 h. Alveolar liquid clearance was measured directly as a flow into a left main bronchial catheter. Control animals were compared with animals in which active epithelial sodium transport was inhibited by adding amiloride and phloridzin (both 1 mmol/l) to the instillate. At low inflation, active sodium transport reversed a secretion of liquid into the alveoli; at high inflation, active sodium transport made little or no contribution to transepithelial flow. Hydraulic conductance of the left lung was 1.57 microliters.min-1.cmH2O-1.kg body wt-1. The experiments suggest that pulmonary inflation renders active liquid clearance ineffective