|
Abstract
|
A Commentary on
The Circulatory Effects of Increased Hydrostatic Pressure Due to Immersion and Submersion
by Weenink, R. P., and Wingelaar, T. T. (2021). Front. Physiol. 12:699493. doi: 10.3389/fphys.2021.699493
We noted with interest the article by Weenink and Wingelaar published last July in Frontiers in Physiology (Weenink and Wingelaar, 2021). However, reading the abstract and the article was largely disappointing. We cannot agree with many statements made by the authors. In our opinion, their analysis of the physiological responses to immersion lacks precision in physical and physiological evidence presented, and cannot support the actual mechanisms underlying their findings.
One cannot assert with certainty that buoyancy reduces movement of fluid from the vascular to extracellular compartment. Also, the authors suggest that the hydrostatic force does not exert a compressive force on the body and this is not correct. In a fluid (liquid or gas), hydrostatic pressure acts in every direction on the sheath of the immersed object (or body). Buoyancy results from the upward force experienced by the whole object according to both the volume of fluid displaced and the difference between densities of the object/body and the fluid. For example, a hot air balloon gets buoyancy from the atmospheric (hydrostatic) pressure due to the lower density of the inner volume than the same atmospheric volume outside.
However, the "Archimedes principle" operating on the entire immersed human body does not exert any buoyancy effect inside the vascular network where gravity still acts on blood exactly as when outside water. In an upright position an immersed subjects' pulmonary tissue is still less distended in the base of the lungs which supports the whole lung weight than in the apex...
Language: en |