Measurement of nonlinear pO₂ decay in mouse lungs using ³He‐MRI

Spatial and temporal variations in oxygen partial pressure (pO(2)) during breath-hold can be exploited to obtain important regional parameters of lung function. In the course of apnea, the oxygen concentration is known to decay exponentially. Therefore, the initial pO(2) (p(0)) can be used to represent local ventilation, and the oxygen depletion time constant can characterize perfusion. The protocol, based on a nonlinear model of pO(2) decay, was validated in six healthy mice. Parametric maps of p(0) and oxygen depletion time constant were obtained for pure (3)He and (3)He/air mixture. The mean measured values of p(0) were 77 +/- 9 mbar for the pure (3)He insufflation and 107 +/- 5 mbar for (3)He/air mixture, in agreement with the predefined p(0) values: 75 +/- 15 mbar and 123 +/- 15 mbar, respectively. The mean measured oxygen depletion time constants were 6.5 +/- 0.2 s for pure (3)He and 7.1 +/- 0.8 s for the (3)He/air mixture, in agreement with physiology.