Splenectomy impairs diffusive oxygen transport in the lung of dogs

The spleen acts as an erythrocyte reservoir in highly aerobic species such as the dog and horse. Sympathetic-mediated splenic contraction during exercise reversibly enhances convective O₂ transport by increasing hematocrit, blood volume, and O₂-carrying capacity. Based on theoretical interactions between erythrocytes and capillary membrane (Hsia CCW, Johnson RL Jr, and Shah D. J Appl Physiol 86: 1460-1467, 1999) and experimental findings in horses of a postsplenectomy reduction in peripheral O₂-diffusing capacity (Wagner PD, Erickson BK, Kubo K, Hiraga A, Kai M, Yamaya Y, Richardson R, and Seaman J. Equine Vet J 18, Suppl: 82-89, 1995), we hypothesized that splenic contraction also augments diffusive O₂ transport in the lung. Therefore, we have measured lung diffusing capacity (DL_CO) and its components during exercise by a rebreathing technique in six adult foxhounds before and after splenectomy. Splenectomy eliminated exercise-induced polycythemia, associated with a 30% reduction in maximal O₂ uptake. At any given pulmonary blood flow, DL_CO was significantly lower after splenectomy owing to a lower membrane diffusing capacity, whereas pulmonary capillary blood volume changed variably; microvascular recruitment, indicated by the slope of the increase in DL_CO with respect to pulmonary blood flow, was also reduced. We conclude that splenic contraction enhances both convective and diffusive O₂ transport and provides another compensatory mechanism for maintaining alveolar O₂ transport in the presence of restrictive lung disease or ambient hypoxia.