Shunt volume

Question

Dear expert team,

Is it possible that the shunt volume does have an influence on Cystic Fibrosis?

I have been diagnosed with an increased shunt volume but so far the therapy has not been changed. Was does “increased shunt volume” mean exactly? (...) How has an increased shunt volume to be treated? Which possibilities do I have once it is clear that the reason is not a cardiac one?

Many thanks

Answer

Hello,

Let me start with explaining what an increased shunt volume is: In the so called pulmonary (small) circulation the blood circulates from the right heart via the lungs back to the left heart. In the lung tissue the vascular distribution is branching out microscopically (the so called capillary bed) in order to facilitate the gas exchange with the aeriferous pulmonary alveoli. Only if all capillaries had contact with the alveoli, all blood could be saturated with oxygen. However, this assumption is not even true for healthy persons.

In a resting state about 20% of the blood volume circulates in the pulmonary (small) circulation without having contact to the ventilated lungs, the so called “physiological shunt volume”. In case of sick lungs the shunt can be expanded functionally in a considerable way if either ventilated lung areas are not supplied with blood (so called dead space volume) or if areas supplied with blood are not ventilated. Alternatively, the blood can also arrive via a shunt from the right heart directly to the left heart (outside of the lungs), e.g. in case of a cardiac defect or vascular anomaly. While the latter (anatomical shunts) are frequently congenital, the functional shunts are usually acquired, e.g. by lung diseases or diseases of the vascular bed. The amount of different diseases which cause shunts is pretty high so that your question about the reason of your shunt cannot be answered easily. In CF we often find an emphysema, not ventilated lung areas (so called atelectases) or inflamed tissue as a reason. If a relevant shunt was assumed in your case the reason can be found out by several functional methods (e.g. pure O2 respiration, right heart catheterisation) or imaging methods (e.g. computer tomography, angiography) – however, these methods differ what invasiveness is concerned. Your doctors have to decide which methods should be applied in your case. It also depends on the results if and how you can be treated. Further to causal therapies the treatment of the symptoms (e.g. providing additional oxygen) is often more in the foreground.

Best regards,
TO Hirche

22.03.2010