Individual changes in systolic tricuspid pressure gradient (ΔPmax) in response to sixteen combinations of end-tidal gas composition.

Volunteers were exposed to each combination of end-tidal PO2 and PCO2 for 10 min, preceded by 5 min baseline breathing with end-tidal gases held close to baseline values (100 mmHg end-tidal PO2 and the measured baseline end-tidal PCO2). The change in peak systolic tricuspid pressure gradient (ΔPmax) was calculated as the difference between the mean baseline ΔPmax and the mean ΔPmax during the last 6 minutes of each protocol. Gas control was achieved by means of end-tidal forcing.