The purpose of the study was to analyze the ultrasound lung comets (ULCs) 
variation, which are a sign of extra-vascular lung water. Forty-two healthy 
individuals performed breath-hold diving in different conditions: dynamic 
surface apnea; deep variable-weight apnea and shallow, face immersed without 
effort (static maximal and non-maximal). The number of ULCs was evaluated by 
means of an ultrasound scan of the chest, before and after breath-hold diving 
sessions. The ULC score increased significantly from baseline after dynamic 
surface apnea (p = 0.0068), after deep breath-hold sessions (p = 0.0018), and 
after static maximal apnea (p = 0.031). There was no statistically significant 
difference between the average increase of ULC scores after dynamic surface 
apnea and deep breath-hold diving. We, therefore, postulate that extravascular 
lung water accumulation may be due to other factors than (deep) immersion alone, 
because it occurs during dynamic surface apnea as well. Three mechanisms may be 
responsible for this. First, the immersion-induced hydrostatic pressure gradient 
applied on the body causes a shift of peripheral venous blood towards the 
thorax. Second, the blood pooling effect found during the diving response 
Redistributes blood to the pulmonary vascular bed. Third, it is possible that 
the intense involuntary diaphragmatic contractions occurring during the 
"struggle phase" of the breath-hold can also produce a blood shift from the 
pulmonary capillaries to the pulmonary alveoli. A combination of these factors 
may explain the observed increase in ULC scores in deep, shallow maximal and 
shallow dynamic apneas, whereas shallow non-maximal apneas seem to be not "ULC 
provoking".