[MARMAM] The selective gas exchange hypothesis, a mechanism how cetaceans avoids the bends?!

Andreas Fahlman afahlman at whoi.edu
Thu Nov 16 02:18:47 PST 2023


Dear MarMamers
A new review on the cardiorespiratory physiology in cetaceans is published in Experimental Physiology and summarizes the current knowledge on cardiorespiratory physiology and how a combination of anatomy and physiology allows cetaceans to manage gases while diving. This mechanism, the selective gas exchange hypothesis, was proposed to explain how cetaceans avoid excessive uptake of N2 while also being able to exchange O2 and CO2 while diving. This article is open access and can be downloaded at: https://physoc.onlinelibrary.wiley.com/doi/10.1113/EP091095 (doi: 10.1113/EP091095), and if you have any questions, please contact me at: gdrsl16 at gmail.com
Sincerely,
Andreas

Title: Cardiorespiratory adaptations in small cetaceans and marine mammals
Author: Fahlman, A.
Journal: Experimental Physiology
doi: 10.1113/EP091095
ABSTRACT
The dive response, or the “master switch of life”, is probably the most studied physiological trait in marine mammals and is generally thought to conserve the available O2 for the heart and brain. Although generally thought to be an autonomic reflex, several studies indicate that the cardiovascular changes during diving can also be conditioned. The respiratory adaptations, where the aquatic breathing pattern resemble intermittent breathing in land mammals, with expiratory flow exceeding 160 l · sec-1 has been measured in cetaceans, and where exposure to extreme pressures result in alveolar collapse (atelectasis) and recruitment upon ascent. Cardiorespiratory coupling, where breathing results in changes in heart rate, has been proposed to improve gas exchange. This cardiorespiratory coupling has also been reported in marine mammals, and in the bottlenose dolphin, where it alters both heart rate and stroke volume. When accounting for this respiratory dependence on cardiac function, several studies have reported an absence of a diving related bradycardia except during dives that exceed the duration that appears to be fuelled by aerobic metabolism. In this review, the attempt is made to summarize what is known about the respiratory physiology in marine mammals, with a special focus on cetaceans. The cardiorespiratory coupling is reviewed, and the selective gas exchange hypothesis is summarized, which provides a testable mechanism how breath-hold diving vertebrates may actively prevent uptake of N2 during routine dives and how stress results in failure of this mechanism which results in diving related gas emboli.
NEW FINDINGS:
1. What is the topic of this review?
This review summarizes the current knowledge of the respiratory physiology in small cetaceans and its influence of cardiac function.

2. What advances does it highlight?
The review presents the selective gas exchange hypothesis, which is a framework how marine mammals manage gases during diving and based upon the current understanding of cardiorespiratory coupling in breath-hold diving vertebrates.

KEYWORDS: diving physiology, marine mammal, cetacean, heart rate, perfusion
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