The measurement of myocardial tissue gas tensions by mass spectrometry.

The mass spectrometer is a well established tool for the measurement of the partial pressures of gases in respiratory gas mixtures and in flowing blood. Only recently has mass spectrometry been applied to the measurement of gas tensions in tissue. Both blood and tissue gas tension measurements by mass spectrometry were made possible by the development of a special sampling catheter surrounded at its tip by a gas--but not liquid--permeable membrane. The partial pressure of each gas at the external surface of the membrane determines the flow of that gas across the membrane which, in turn, is measured by the mass spectrometer. The use of a Teflon membrane permits tissue measurements because its low permeability to gases reduces the sampling rate of gas molecules with the result that the depletion of gas molecules in the tissue surrounding the membrane is minimal. Mass spectrometry is the only technique whereby it is possible to measure regional tissue pO2 and pCO2 and other gas tensions simultaneously and continuously. One application of mass spectrometric tissue gas tension measurements is the monitoring of myocardial ischemia through measurements of myocardial tissue pO2 and pCO2. We have reviewed the work of others and ourselves in this field.