Reply from Zeljko Dujic

After careful reading of the Letter by Dr Marabotti and colleagues we agree with the major part of the critique of the method that is employed for evaluation of the right heart. Although we were aware of the other methods that are available we had several constraints that prevented us from using them. Fist, we decided to perform a field study. In some of our previous experiments we carried out simulated diving studies and found that diving in a hyperbaric chamber produces less venous gas bubbles than diving in real conditions. However maximal amount of venous bubbles occurred around 40 min after surfacing, which prevented us from using any equipment beside a transportable ultrasound device. We needed to perform measurements on multiple time points after dive, and tested divers are very reluctant to undergo invasive procedures. Although, radionuclide angiography is still considered the most reliable method for evaluating right ventricular volumes and function, the current literature shows no data to suggest that one method is an obligatory golden standard for volumetric evaluation of right ventricle, and most of the methods that are now widely used for estimation of volume and performance of right ventricle are semiquantitative (Kovalova, 2005). Volumetric measurements of the right heart represented only one of the observed parameters, and in all cases we were looking for the relative changes in the same subject. However, the point that has been made in the Letter is correct, and it may be that the best way to interpret these results would be to represent them as relative numbers since this was the main goal of this part of investigation. In our further studies we shall try to implement 3D and 4D volumetric quantification of left and right cavities both for absolute and relative numbers.