Regional V(over-dot)(A)/Q(over-dot) ratios in man using Xe-133 and single photon emission computed tomography (SPECT) corrected for attenuation

We describe a technique to obtain non-invasively regional pulmonary ventila tion-perfusion ratios ((V)over dot(A)/(Q)over dot) using single photon emis sion computed tomography (SPECT) and continuous infusion of Xe-133. Single photon transmission tomography was used for attenuation correction, for del ineation of the lungs and for (V)over dot(A)/(Q)over dot calculations. Data are presented for six normal subjects and compared to those for two patien ts with moderate chronic obstructive pulmonary disease (COPD). The mean (V) over dot(A)/(Q)over dot for the whole lung of the normal subjects ranged fr om 0.49 to 0.65, group mean 0.56 +/- 0.07 (1 SD), and there was no signific ant difference between the right and left lung. The consistently too low (V )over dot(A)/(Q)over dot values are related to the inability to measure reg ional blood volume and the low resolution of the scintillation camera, givi ng an under-estimation of tracer input. For the normal subjects, the disper sion of (V)over dot(A)/(Q)over dot, as defined by the standard deviation of the individual distribution functions, ranged from 0.12 to 0.19. One of th e patients was characterized by a low mean (V)over dot(A)/(Q)over dot of 0. 35, and the other patient had a wide dispersion (SD) of (V)over dot(A)/(Q)o ver dot of 0.37. In the normal subjects, a consistent (V)over dot(A)/(Q)ove r dot gradient was found only in the ventrodorsal direction. Xe-133 and SPE CT can be used to obtain meaningful biological information regarding ventil ation/perfusion relationships of potential clinical value.