The FREEDIVING SCIENCE series explores freediving science in depth.



In March 2022 the 2nd Taiwanese Cup freediving depth competition was held off Xiao Liuqiu Island in Taiwan. During the pre-comp a group of researchers led by Andy Chi 齊英仁 studied many of the athletes using various methods including lung ultrasounds before and after their dives.

Donny was also participating in the study and in the competition. In this episode we discuss the interesting prelimenary findings which delivers much food for thought for the world’s freediving community.

There is much yet to be researched and discussed on this subject but let’s add comments between Andy Chi (Doctor of Emergency Medicine at Kaohsiung Chang Gung Memorial Hospital), who I interviewed in this episode, and Bizo Silva (Emergency Medicine physician) .

Bizo: What do you think B lines mean in lung ultrasound?
This is obviously a loaded question, but I have a strong opinion about how we are using B lines in freediving. Trust me, no one more than me would love for the answer to be as simple as “pulmonary edema”, and lung ultrasound would be absolutely incredible for the management of pulmonary barotrauma. Unfortunately I believe most people do not question this, and forgot how B lines are generated. B lines are simply the resulting artifact from the ultrasound beam reverberating inside a fluid layer which is surrounded by gas (which reflects ultrasound). There are MANY situations that create this condition, and extravascular lung water is only one of them. Freediving creates AT LEAST three other conditions that create B lines: atelectasis (compression with de-aeration of the lung tissue), increased vascular diameter (blood shift) and alveolar flooding with serum. We simply don’t know which of these conditions is causing the B lines upon surfacing. We don’t know how long it takes after a dive for the lungs to re-expand, for the alveolar arterioles to return to their baseline size, for the serum to be drained. We can’t assume the B lines are extravascular lung water. Unfortunately I see studies coming out assuming B lines are pulmonary edema, and I think we just don’t know enough about how the lung tissue behaves in freediving to assume that.


 Andy: I agree with that the result of lung ultrasound should be interpreted in caution. B line is a sign of pulmonary edema but not directly referred to it. By excluding other causes could be a method to get closer to the truth. As Bizo mentioned, atelectasis might be another possible cause, but we just don’t know the prevalence for diver’s lung failing to re-expand upon surfacing. A CT scan right after surfacing may help, but very difficult to operate. As for the “blood shift”, I don’t think it creates B line easily even still presented on surface, because the shifted blood will mostly be in the pulmonary vessels situated in the central part of lung (especially veins with better compliance), that is too deep for ultrasound to reach theoretically. Alveolar flooding with serum sounds very alike to the fact with pulmonary edema, and I feel it impossible to distinguish between them in any method. Serum in alveolar also disturbs gas exchange and causes breathing problem, maybe we don’t have to separate if from pulmonary edema?

Despite these limitations, the lung ultrasound still provides us more understanding for the lung condition right after diving. In my opinion, under the current knowledge, we should interpreted it conservatively, and correlate it to other clinical symptoms/signs and physiological changes.


Donny’s Lung Ultrasound Images (pre-dive on left, post-dive on right), can you spot the 3 B lines on the middle right image?

Donny's ultrasound images

Other athletes ultrasound images:

athletes ultrasound images