Increased Gastric–End Tidal P CO 2 Gap during Exercise at High Altitude Measured by Gastric Tonometry

Martin, Daniel, Stuart McCorkell, Andre Vercueil, Paul Gunning, Mark Cox, John Dick, Monty Mythen, and Mike Grocott. Increased gastric–end tidal P_CO2 gap during exercise at high altitude measured by gastric tonometry. High Alt. Med. Biol. 8:50–55, 2007.—Using automated air gastric tonometry, the hypothesis that gastric perfusion is reduced while exercising at high altitude was explored. This prospective observational study of 5 well acclimatized healthy volunteers was performed during a medical research expedition to Chamlang base camp (5000 m), Hongu valley, Nepal. We used gastric tonometry at rest and during graded submaximal exercise. The endtidal partial pressure of carbon dioxide was subtracted from the gastric mucosal partial pressure of carbon dioxide to calculate the P_CO2 gradient, which is a marker of gastric mucosal perfusion. When compared with rest, there was no increase in the mean P_CO2 gradient at the lower work rate (0.22 vs. 0.18, p 0.10), but an increase was seen between rest and the higher work rate (0.22 vs. 0.77, p = 0.04). We conclude that exercising while at high altitude can lead to a raised P_CO2 gradient when gastric tonometry is performed, indicating reduced perfusion. This may represent reduced gastric mucosal perfusion under these conditions.