Shining light on dolphin physiology
Dear MarMamers We would like to share our new open-access publication that investigated the use of Near Infrared Spectroscopy as a non-invasive tool to study physiology in the bottlenose dolphin. We report preliminary data which indicate that this technology allows us to measure blood flow and tissue and blood oxygenation in this dolphins. The details about the paper can be found below, and please send me or Alex Ruesch (aruesch@andrew.cmu.edu) an email if you have any questions. Sincerely, Andreas Title: Evaluating feasibility of functional near-infrared spectroscopy in dolphins Authors: Ruesch, A., Acharya, D., Bulger, E., Cao, J., McKnight, J. C., Manley, M., Fahlman, A., Shinn-Cunningham, B. G. and Kainerstorfer, J. M. Journal: Journal of Biomedical Optics doi: 10.1117/1.JBO.28.7.075001 Abstract: Significance: Using functional near-infrared spectroscopy (fNIRS) in bottlenose dolphins (Tursiops truncatus) could help to understand how echolocating animals perceive their environment and how they focus on specific auditory objects, such as fish, in noisy marine settings. Aim: To test the feasibility of near-infrared spectroscopy (NIRS) in medium-sized marine mammals, such as dolphins, we modeled the light propagation with computational tools to determine the wavelengths, optode locations, and separation distances that maximize sensitivity to brain tissue. Approach: Using frequency-domain NIRS, we measured the absorption and reduced scattering coefficient of dolphin sculp. We assigned muscle, bone, and brain optical properties from the literature and modeled light propagation in a spatially accurate and biologically relevant model of a dolphin head, using finite-element modeling. We assessed tissue sensitivities for a range of wavelengths (600 to 1700 nm), source-detector distances (50 to 120 mm), and animal sizes (juvenile model 25% smaller than adult). Results: We found that the wavelengths most suitable for imaging the brain fell into two ranges: 700 to 900 nm and 1100 to 1150 nm. The optimal location for brain sensing positioned the center point between source and detector 30 to 50 mm caudal of the blowhole and at an angle 45 deg to 90 deg lateral off the midsagittal plane. Brain tissue sensitivity comparable to human measurements appears achievable only for smaller animals, such as juvenile bottlenose dolphins or smaller species of cetaceans, such as porpoises, or with source-detector separations ≫100 mm in adult dolphins. Conclusions: Brain measurements in juvenile or subadult dolphins, or smaller dolphin species, may be possible using specialized fNIRS devices that support optode separations of >100 mm. We speculate that many measurement repetitions will be required to overcome hemodynamic signals originating predominantly from the muscle layer above the skull. NIRS measurements of muscle tissue are feasible today with source-detector separations of 50 mm, or even less..
Dear MarMamers We would like to share our new open-access publication that investigated how breathing is affecting heart rate. The details about the paper can be found below, and please send me an email if you have any questions. Sincerely, Andreas Title Cardiorespiratory coupling in the bottlenose dolphin (Tursiops truncatus) Authors: A. Fahlman, J. C. Mcknight, A. M. Blawas, N. West, A. G. Torrente, K. Aoki Journal: Frontiers Physiology doi: https://doi.org/10.3389/fphys.2023.1234432 Abstract: Introduction: The bottlenose dolphin (Tursiops truncatus) is an intermittent breather, where the breath begins with an exhalation followed by inhalation and an extended inter-breath interval ranging from 10 to 40 s. Breathing has been shown to alter both the instantaneous heart rate (ifH) and stroke volume (iSV) in the bottlenose dolphin, with a transitory ventilatory tachycardia following the breath, and an exponential decrease to a stable ifH around 40 beats • min−1 during the inter-breath period. As the total breath duration in the dolphin is around 1 s, it is not possible to assess the contribution of exhalation and inhalation to these changes in cardiac function during normal breathing. Methods: In the current study, we evaluated the ifH response by separating expiration and inspiration of a breath, which allowed us to distinguish their respective contribution to the changes in ifH. We studied 3 individual male bottlenose dolphins trained to hold their breath between the different respiratory phases (expiration and inhalation). Results: Our data show that inspiration causes an increase in ifH, while expiration appears to result in a decrease in ifH. Discussion: These data provide improved understanding of the cardiorespiratory coupling in dolphins, and show how both exhalation and inhalation alters ifH.
Dear MarMamers We would like to share our new open-access publication that measured the resting/basal metabolism, the cost of digestion (heat increment of feeding), and lung function in the rough toothed dolphin. The details about the paper can be found below, and please send me an email if you have any questions or cannot get access to this open access paper.. Sincerely, Andreas Title: Resting metabolic rate and lung function in fasted and fed rough-toothed dolphins, Steno bredanensis Authors: Andreas Fahlman, Kaylee Rhieu, Brie Alessi, Shelly Marquardt, Michelle B. Schisa, Guillermo J. Sanchez-Contreras, Josefin Larsson Journal: Marine Mammal Science doi: https://doi.org/10.1111/mms.13068 Abstract: We measured resting metabolic rate (RMR), tidal volume (VT), breathing frequency (fR), respiratory flow, and end-expired gases in rough-toothed dolphins (Steno bredanensis) housed in managed care after an overnight fast and 1–2 hr following a meal. The measured average (± standard deviation) VT (4.0 ± 1.3 L) and fR (1.9 ± 1.0 breaths/min) were higher and lower, respectively, as compared with estimated values from both terrestrial and aquatic mammals, and the average VT was 43% of the estimated total lung capacity. The end-expired gas levels suggested that this species keep alveolar O2 (10.6% or 80 mmHg) and CO2 (7.6% or 57 mmHg), and likely arterial gas tensions, low and high, respectively, to maximize efficiency of gas exchange. We show that following an overnight fast, the RMR (566 ± 158 ml O2/min) was 1.8 times the estimated value predicted by Kleiber for terrestrial mammals of the same size. We also show that between 1 and 2 hr after ingestion of a meal, the metabolic rate increases an average of 29% (709 ± 126 ml O2/min). Both body mass (Mb) and fR significantly altered the measured RMR and we propose that both these variables should be measured when estimating energy use in cetaceans.
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@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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Andreas Fahlman