The measurement of regional ventilation in man: a new method of quantitation

Regional ventilation has been measured in 20 healthy subjects as the fractional exchange of air per breath using radioactive xenon and a gamma scintillation camera interfaced to a small digital computer. Because xenon is slightly soluble in blood and more soluble in fat, a tissue background correction has been incorporated into the calculation so that regional ventilation can be determined from a washout procedure after a washin lasting several minutes. Regional ventilation is determined as the mean fractional exchange of air per breath using the Stewart Hamilton equation. Figures are obtained for the fractional exchange of air per breath for upper, mid, and lower zones in each lung, and images are produced showing the functional relationships within and between regions. Ventilation in the upright position increased from apex to base in the expected fashion and was slightly more efficient in the left lung than the right, particularly at the left base. No lateral gradient was observed. A good correlation was obtained between tidal volume and the fractional exchange of air per breath (r = 0.83). Allowing for differences in tidal volume between the washin and washout parts of the procedure, figures for the regional fractional exchange of air were similar for each part of the study. Thus the tissue background correction allows the washout curves to be used to measure ventilation, and these are a more sensitive indication of impaired ventilation than washin curves.