Splenectomy impairs diffusive oxygen transport in the lung of dogs.

The research article explores how removing the spleen (splenectomy) in dogs can negatively affect their lungs’ ability to transport oxygen. The study finds that the spleen helps distribute oxygen, particularly during exercise, and its removal can reduce oxygen uptake by 30%.

Research Context

• The study begins by discussing how some species, notably dogs and horses, use their spleens as an ‘erythrocyte reservoir’. Erythrocytes, or red blood cells, are responsible for carrying oxygen in the bloodstream.
• The authors explain that during exercise, the spleen contracts (a process driven by the sympathetic nervous system) which increases hematocrit (the proportion of blood that is made up of red blood cells), blood volume, and overall oxygen-carrying capacity.

Hypothesis

• Based on prior studies, the researchers form the hypothesis that spleenic contraction does not only enhance ‘convective’ oxygen transport (i.e., the direct movement of oxygen-carrying blood from the heart to the rest of the body) but also assists ‘diffusive’ transport. ‘Diffusive’ transport involves the movement of oxygen from the bloodstream into body tissues and cells.

Methodology

• To test their hypothesis, the researchers turned to a breed of hunting dog known as a foxhound. The team compared the dogs’ lung diffusing capacity (DL(CO)) during exercise both before and after splenectomy. DL(CO) refers to how efficiently the lungs can transfer oxygen from the air into the bloodstream.

Findings

• The post-splenectomy dogs showed a significant reduction in DL(CO) at any given level of pulmonary blood flow. This lower capacity was due to a reduced ‘membrane diffusing capacity’ (the ability of the lung’s cell membranes to allow oxygen to pass through), Albeit, the pulmonary capillary blood volume changed variably.
• Removing the spleen also lowered the degree of ‘microvascular recruitment’. This term refers to the body’s ability to increase the number of small blood vessels that are actively supplying oxygen to tissues during periods of high demand, such as during exercise.

Conclusions

• The study concludes that the contraction of the spleen enhances both convective and diffusive oxygen transport. Furthermore, this function represents a compensatory mechanism for maintaining alveolar O2 transport when facing restrictive lung disease or ambient hypoxia.