Got this info from a nuclear medicine website :

133Xe-gas is a noble gas which decays by emitting 81 keV gamma
rays. Its half-life is 5.3 days. In order to measure
ventilation, the patient is connected to a closed circuit spirometer
containing 133Xe-gas in air. The examination consists of three
phases:

     Wash-in: During tidal breathing the wash-in of activity in
different regions is recorded. The slope of the wash-in
     time-activity curve is a measure of regional ventilation.
     Equilibrium: After approximately 3 to 5 minutes the alveolar gas
has a uniform xenon concentration and the regional
     activity is a measure of regional alveolar volume.
     Wash-out: After the patient is disconnected from the spirometer
circuit, the wash-out of activity is recorded. Similar to
     the wash-in procedure, the slope of the wash-out time-activity
curve is a measure of regional ventilation.

Hope this helps
Fiona


Fiona Coombes MBBS IBCLC               [log in to unmask]
Lactation Consultant, Family Physician
Perth Western Australia