Study
Counter-current heat exchange in the respiratory passages
Schmidt-Nielsen, Knut; Hainsworth, F. Reed; Murrish, David E.
Respiration Physiology, 1970
Measured the temperature of exhaled air in desert rodents and other species, comparing it with body temperature and with ambient temperature, and calculated the water recovered by the difference.
- Studied in
- Dipodomys, Mammalia, Aves
- Sample size
- measurements of exhaled air temperature in several species
Exhaled air leaves at well below body temperature because the nasal passages, cooled during inhalation, condense water out of the outgoing breath. In kangaroo rats this recovers a large fraction of the water that would otherwise be lost by breathing.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
The nasal passages operate as a countercurrent heat exchanger, and the water saving is a direct consequence of the temperature drop.
How NatureHQ reads it
The mechanism NatureHQ uses to introduce countercurrent exchange, because it is the version with the most immediate everyday hook: breathing costs water, and a nose can get most of it back.
- Exhaled air temperature is sensitive to ambient humidity, so the saving varies with conditions.
- Quantified in a small number of species.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Kangaroo rat
A kangaroo rat can live its whole life without drinking, on water released by metabolising dry seed. It manages it by losing almost none — including by cooling its own exhaled breath to condense the water back out.
Countercurrent exchange
Run two flows past each other in opposite directions and whatever is being exchanged transfers almost completely. The same arrangement retains heat in a bird’s legs and recovers water from a desert rat’s breath.
Countercurrent exchange
A countercurrent exchanger is not always on. An animal that needs to lose heat can send blood around it instead of through it, which turns the same limb from a heat conserver into a radiator.
Published by: Elsevier journalsPublished in an Elsevier journal.
doi.org/10.1016/0034-5687(70)90075-7
Checked against Crossref on 2026-09-28, and they agree on the title, the authors and the year.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-09-03.