Minor redistribution of ventilation and perfusion within the lung during exercise in sheep

Considerable heterogeneity unrelated to the effect of gravity has been demo nstrated for both local ventilation ((V) over dot) and perfusion ((Q) over dot) in the lung. Local ventilation and perfusion are well matched, so that the heterogeneity of the (V) over dot / (Q) over dot ratio is less than fo r ventilation or perfusion alone (Melsom et al. 1997). We are searching for the mechanisms responsible for the coordinate heterogeneity of ventilation and perfusion. Here, we ask how and to what extent physical exercise induc es changes in the distribution of ventilation and perfusion. We measured lo cal (approximate to 1.5 cm(3) tissue volume) pulmonary ventilation and perf usion simultaneously in six sheep before. during and after running on a tre admill. Local ventilation was determined from the deposition of labelled ae rosol particles and local perfusion from trapping of radioactive microspher es. Cardiac output increased approximate to 2.5-fold during exercise, (V) o ver dot / (Q) over dot-ratios were not normally distributed and we therefor e present the heterogeneity as the interquartile range. At rest, the averag e interquartile ranges for local ventilation, perfusion and (V) over dot / (Q) over dot-ratio were 0.48, 0.51 and 0.39, respectively. During exercise, the corresponding values were 0.44. 0.40 and 0.32. Thus, the distribution of local (V) over dot / (Q) over dot-ratio was narrower than for ventilatio n and perfusion also during exercise. We found a moderate redistribution of relative flow towards the dorsal parts of the lungs when perfusion increas ed, but the increase in total perfusion and ventilation was for the most pa rt throughout the lung. The results indicate that the coupling between loca l ventilation and perfusion is at least as potent during exercise as at res t. The correlation (r) between paired values in the two resting periods was 0.93 for ventilation and 0.91 for perfusion and thus indicates time stabil ity for the two variables.