Mechanical Ventilator for Delivery of (17)O(2) in Brief Pulses

The (17)O nucleus has been used recently by several groups for magnetic resonance (MR) imaging of cerebral metabolism. Inhalational delivery of (17)O(2) in very brief pulses could, in theory, have significant advantages for determination of the cerebral metabolic rate for oxygen (CMRO(2)) with MR imaging. Mechanical ventilators, however, are not typically capable of creating step changes in gas concentration at the airway. We designed a ventilator for large animal and human studies that provides mechanical ventilation to a subject inside an MR scanner through 25 feet of small-bore connecting tubing, and tested its capabilities using helium as a surrogate for (17)O(2). After switching the source gas from oxygen to helium, the 0-90% response time for helium concentration changes at the airway was 2.4 seconds. The capability for creating rapid step changes in gas concentration at the airway in large animal and human studies should facilitate the experimental testing of the delivery (17)O(2) in brief pulses, and its potential use in imaging CMRO(2).