Dan came across a research paper the other day that was all about measuring respiratory function in dolphins – and it turns out that dolphins have pretty fascinating respiratory systems so we thought it worth sharing. Obviously measuring lung function in any animal is tricky, but when they live in water… We’re pretty impressed with the data these researchers managed to get, given that we often struggle with adult humans. One good thing is that dolphins are so smart that the research team were actually able to train them to perform specific respiratory manoeuvres (“chuffs”) so that they could compare normal dolphin breathing to these effortful breaths. The researchers also emphasised that the dolphins were free to swim away or resist the measurements if they wished, so actually they ‘gave consent’ for the study in their own way (tricky to sign a consent form when you’ve only got flippers).
Dolphins’ lungs get exposed to a much wider range of pressures than animals who live on the ground, as they have to be able to breathe at the surface but also cope with the increasing pressure as they dive. It has been thought for some time that diving mammals probably have much floppier small airways and alveoli in order to allow these parts of the lungs to collapse when under pressure during dives, and then re-expand easily when they re-surface. In this study, the researchers passed small tubes with pressure sensors down into the dolphins’ stomachs so that they could measure the pressure being generated by the dolphins’ respiratory muscles. This is the same as we do in our studies – though probably a bit harder to do… This showed that dolphins’ lungs are about four times ‘stretchier’ than human lungs, in line with the researchers’ hypothesis.
The researchers also used a very large flow sensor over the dolphins’ blowholes to measure how much and how fast they were breathing, along with the concentrations of oxygen and carbon dioxide in the air. Dolphins only breathe about 3 or 4 times per minute (compared to 12-15 breaths per minute in an adult human), but when they do take a breath they have to exchange a huge amount of air very quickly (their total time to breathe in and out is only about 0.7 seconds). This study showed that even during a normal breath, air moves out of the blowhole at a rate of over 2,600 litres per minute, which is almost four times higher than the fastest human cough we’ve ever measured in our lab! During a “chuff”, the highest flow recorded in this study was 8,400 litres per minute – that would be 84 bathtubs full of air over a minute! During a normal breath the dolphins tended to take breaths of about 5-6 litres (which is about the total lung size in adult humans), but this went up as high as 18 litres during chuffs. They also absorb more oxygen than humans do from the air they breathe – air contains 21% oxygen. Exhaled breath from a human is normally about 17% oxygen, but dolphins get quite a lot more from it and breathe out gas at only 12.3% oxygen. They also breathe out a bit more carbon dioxide than us (7% compared to 5% for humans).
So, in summary… Dolphins: big lungs, fast lungs, effective lungs. We are in awe of the research team for what looks like an exceptionally challenging study, with fascinating results!