Journal of Applied Physiology, Vol 65, Issue 6 2648-2655, Copyright © 1988 by American Physiological Society
Interpretation of the krypton-81m dynamic series: the distribution of a tidal breath
B. E. Shykoff, L. Cinotti, M. Meignan, A. Harf and H. K. Chang
Biomedical Engineering Unit, McGill University, Montreal, Quebec, Canada.
Lung scans during cyclic breathing of krypton-81m, an isotope with a 13-s
half-life, were acquired in "list mode," where both temporal and spatial
information are preserved. Subjects in the left lateral decubitus position
breathed with two tidal volumes at each of two frequencies. Profiles of
total activity over the acquisition period were examined. They showed
little effect of frequency or tidal volume on the distribution of air
between dependent and non-dependent regions. Dynamic series for
ensemble-averaged breaths were constructed. The regional flow per unit
volume was shown to correspond to the time derivative of the regional
activity of the dynamic series divided by the corresponding activity. Both
the relative timing of the gas flow to different lung regions and the flow
per unit volume as a function of time were obtained from the dynamic
series. The dependent lung was seen to be better ventilated throughout the
respiratory cycle except for brief periods at the start of inspiration and
the end of expiration. Most of the dead-space gas can be construed to enter
and leave the dependent lung.
