Topographical distribution of VA/Q in elderly subjects using Krypton-81m.

The topography of ventilation-perfusion (VA/Q) ratios was measured in seven elderly (aged 58--69) subjects, seated erect, using the short-life (t1/2 = 13 sec) radioisotope Krypton-81m. 81mKr was inhaled (for ventilation) or infused intravenously (for perfusion) continuously for 1--2 min periods, during spontaneous ventilation, while radio-activity was recorded on a large-field gamma camera interfaced to a computer. The VA/Q ratio was computed for 15 horizontal slices of the left lung. VA/Q distribution was similar to that of young subjects. No decrease of basal VA/Q was seen; thus, if there are any changes of ventilation in the lower part of the lung in the elderly, they are matched by equal alterations of perfusion. There was no significant change when 60% oxygen was breathed. The progressive fall in arterial oxygen tension which occurs in erect subjects with increasing age does not appear to be caused by inter-regional differences of ventilation and perfusion.