The Authors' Reply Pulmonary Artery Pressure and Right-to-Left Shunting Through Foramen Ovale after Diving

Abstract

Dear Editor, We are aware of the letter submitted to you by Dr. Alain Boussuges regarding our above mentioned manuscript by Valic et al (9). We support the view that a right to left shunting can occur through a patent foramen ovale during certain phases of cardiac cycle (during early diastole and during isovolumetric contraction of the right ventricle of each cardiac cycle) even in normal state (7). Increase in pulmonary artery pressure (PAP), coughing or Valsalva maneuver can make this passage even greater. Moreover, we have recently found by two non-invasive ultrasonic techniques (AcT/RVET and tricuspid jet regurgitation) that mean and systolic PAP are increased for about 30% after field dives to 30 msw for 30 minutes with the mild exercise during the bottom phase of the dive (3). Therefore, real field diving causes different changes in pulmonary hemodynamics after diving when compared with simulated chamber diving. This is caused by added stressors such as reduced water temperature, exercise, resistance of the breathing apparatus, dehydration, centralization of the blood volume, psychological effects, etc. Thus, we think that reversal of the right-to-left pressure gradient is possible after field diving. Unfortunately, we did not measure nor estimate left atrial pressure (LAP) in our study. Recently, a new non-invasive ultrasonic method for measurement of LAP and LA compliance was published (6). Invasive measurement of LAP could not be performed outside hospital environment, and our participants would be very unlikely to give informed consent for such study. We agree that additional studies are needed in order to address this topic. We propose to perform animal studies first which can give us initial data on LAP. Only if such studies show reversal of the right to left pressure gradient, invasive and risky studies on human subjects can be proposed. The other possibility for arterialization of venous gas bubbles is passage through intra-pulmonary vascular shunts. Recently, Eldridge et al (5) have shown that during high intensity post-dive exercise contrast bubbles cross through the intra-pulmonary shunts. This suggested that post-dive exercise should be avoided. However, we have shown with the same level, type and duration of post-dive exercise that no bubbles crossed to the left side though intra-pulmonary shunts (4). We also agree with dr Boussuges about the possibility of unequal pressures in the right and left atrium after diving due not only to reduced venous return (1, 2) and pulmonary vascular vasoreactivity (8), but also to reduced right and left ventricle function after field diving (3). Thus, we think that future studies have to be conducted to assess the risk of righ-to-left shunting after diving due to changes in inter-atrial pressure gradient.