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Burggren W, Fahlman A, Milsom W. Breathing patterns and associated cardiovascular changes in intermittently breathing animals: (Partially) correcting a semantic quagmire. Exp Physiol 2024; 109:1051-1065. [PMID: 38502538 PMCID: PMC11215480 DOI: 10.1113/ep091784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Accepted: 02/29/2024] [Indexed: 03/21/2024]
Abstract
Many animal species do not breathe in a continuous, rhythmic fashion, but rather display a variety of breathing patterns characterized by prolonged periods between breaths (inter-breath intervals), during which the heart continues to beat. Examples of intermittent breathing abound across the animal kingdom, from crustaceans to cetaceans. With respect to human physiology, intermittent breathing-also termed 'periodic' or 'episodic' breathing-is associated with a variety of pathologies. Cardiovascular phenomena associated with intermittent breathing in diving species have been termed 'diving bradycardia', 'submersion bradycardia', 'immersion bradycardia', 'ventilation tachycardia', 'respiratory sinus arrhythmia' and so forth. An examination across the literature of terminology applied to these physiological phenomena indicates, unfortunately, no attempt at standardization. This might be viewed as an esoteric semantic problem except for the fact that many of the terms variously used by different authors carry with them implicit or explicit suggestions of underlying physiological mechanisms and even human-associated pathologies. In this article, we review several phenomena associated with diving and intermittent breathing, indicate the semantic issues arising from the use of each term, and make recommendations for best practice when applying specific terms to particular cardiorespiratory patterns. Ultimately, we emphasize that the biology-not the semantics-is what is important, but also stress that confusion surrounding underlying mechanisms can be avoided by more careful attention to terms describing physiological changes during intermittent breathing and diving.
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Affiliation(s)
- Warren Burggren
- Developmental Integrative Biology Group, Department of Biological SciencesUniversity of North TexasDentonTexasUSA
| | - Andreas Fahlman
- Fundación OceanogràficValenciaSpain
- Kolmården Wildlife ParkKolmårdenSweden
- IFMLinkoping UniversityLinkopingSweden
| | - William Milsom
- Department of ZoologyUniversity of British ColumbiaVancouverBritish ColumbiaCanada
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2
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Kristensen L, Zardo JQ, Hansen SM, Bertelsen MF, Alstrup AKO, Wang T, Williams CJA. Effect of atropine and propofol on the minimum anaesthetic concentration of isoflurane in the freshwater turtle Trachemys scripta (yellow-bellied slider). Vet Anaesth Analg 2023; 50:180-187. [PMID: 36739261 DOI: 10.1016/j.vaa.2021.10.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 10/06/2021] [Accepted: 10/27/2021] [Indexed: 12/05/2022]
Abstract
OBJECTIVE To determine if the administration of atropine would reduce the measured minimum anaesthetic concentration of isoflurane (MACisoflurane) in freshwater turtles - the yellow-bellied slider (Trachemys scripta scripta). STUDY DESIGN Paired, blinded, randomized, prospective studies of 1) the effect of atropine in isoflurane anaesthetized freshwater turtles (T. scripta scripta) and 2) the effect of atropine in yellow-bellied sliders in which anaesthesia was induced with propofol and maintained with isoflurane. ANIMALS T. scripta scripta (n = 8), female, adult. METHODS Atropine (2 mg kg-1) or an isovolumetric control injection of saline was administered intraperitoneally 15 minutes prior to induction of anaesthesia with isoflurane. Individual MACisoflurane was then determined by end-tidal gas analysis in a bracketing design by an experimenter blinded to the administered drug, with a 2 week washout period. The experiment was repeated, with atropine (2 mg kg-1) or saline administered intravascularly in combination with propofol for anaesthetic induction. Linear mixed modelling was used to determine the effects of atropine and propofol on the individual MACisoflurane. Data are presented as mean ± standard deviation. RESULTS Premedication with atropine significantly reduced MACisoflurane (p = 0.0039). In isoflurane-induced T. scripta scripta, MACisoflurane decreased from 4.2 ± 0.4% to 3.3 ± 0.8% when atropine had been administered. Propofol as an induction agent had a MAC-sparing effect (p < 0.001) such that MACisoflurane following propofol and a control injection of saline was 2.3 ± 1.0%, which decreased further to 1.5 ± 0.8% when propofol was combined with atropine. CONCLUSIONS AND CLINICAL RELEVANCE Atropine, presumably by inhibiting parasympathetically mediated pulmonary artery constriction, decreases right-to-left cardiac shunting and the MACisoflurane in yellow-bellied sliders, and thereby may facilitate control of inhalant anaesthesia. Propofol can be used for induction of anaesthesia and reduces the required concentration of inhaled anaesthesia assessed 1.5 hours following induction.
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Affiliation(s)
- Line Kristensen
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Juliana Q Zardo
- School of Veterinary Medicine and Animal Science, Copenhagen University, Copenhagen, Denmark
| | - Sofie M Hansen
- School of Veterinary Medicine and Animal Science, Copenhagen University, Copenhagen, Denmark
| | - Mads F Bertelsen
- Center for Zoo and Wild Animal Health, Copenhagen Zoo, Frederiksberg, Denmark
| | - Aage K O Alstrup
- Department of Nuclear Medicine & PET, Aarhus University Hospital, Aarhus, Denmark; Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Tobias Wang
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Catherine J A Williams
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark; Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada.
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3
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Joyce W, Wang T. Regulation of heart rate in vertebrates during hypoxia: A comparative overview. Acta Physiol (Oxf) 2022; 234:e13779. [PMID: 34995393 DOI: 10.1111/apha.13779] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 11/12/2021] [Accepted: 01/01/2022] [Indexed: 12/18/2022]
Abstract
Acute exposure to low oxygen (hypoxia) places conflicting demands on the heart. Whilst an increase in heart rate (tachycardia) may compensate systemic oxygen delivery as arterial oxygenation falls, the heart itself is an energetically expensive organ that may benefit from slowing (bradycardia) to reduce work when oxygen is limited. Both strategies are apparent in vertebrates, with tetrapods (mammals, birds, reptiles, and amphibians) classically exhibiting hypoxic tachycardia and fishes displaying characteristic hypoxic bradycardia. With a richer understanding of the ontogeny and evolution of the responses, however, we see similarities in the underlying mechanisms between vertebrate groups. For example, in adult mammals, primary bradycardia results from the hypoxic stimulation of carotid body chemoreceptors that are overwhelmed by mechano-sensory feedback from the lung associated with hyperpnoea. Fish-like bradycardia prevails in the mammalian foetus (which, at this stage, is incapable of pulmonary ventilation), and in fish and foetus alike, the bradycardia ensues despite an elevation of circulating catecholamines. In both cases, the reduced heart rate may primarily serve to protect the heart. Thus, the comparative perspective offers fundamental insight into how and why different vertebrates regulate heart rate in different ways during periods of hypoxia.
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Affiliation(s)
- William Joyce
- Department of Biology—Zoophysiology Aarhus University Aarhus C Denmark
| | - Tobias Wang
- Department of Biology—Zoophysiology Aarhus University Aarhus C Denmark
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4
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Smith B, Crossley DA, Wang T, Joyce W. No evidence for pericardial restraint in the snapping turtle (Chelydra serpentina) following pharmacologically-induced bradycardia at rest or during exercise. Am J Physiol Regul Integr Comp Physiol 2022; 322:R389-R399. [PMID: 35200048 PMCID: PMC9018006 DOI: 10.1152/ajpregu.00004.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Most animals elevate cardiac output during exercise through a rise in heart rate (fH), whilst stroke volume (VS) remains relatively unchanged. Cardiac pacing reveals that elevating fH alone does not alter cardiac output, which is instead largely regulated by the peripheral vasculature. In terms of myocardial oxygen demand, an increase in fH is more costly than that which would incur if VS instead were to increase. We hypothesized that fH must increase because any substantial rise in VS would be constrained by the pericardium. To investigate this hypothesis, we explored the effects of pharmacologically-induced bradycardia, with ivabradine treatment, on VS at rest and during exercise in the common snapping turtle (Chelydra serpentina) with intact or opened pericardium. We first showed that, in isolated myocardial preparations, ivabradine exerted a pronounced positive inotropic effect on atrial tissue, but only minor effects on ventricle. Ivabradine reduced fH in vivo, such that exercise tachycardia was attenuated. Pulmonary and systemic VS rose in response to ivabradine. The rise in pulmonary VS largely compensated for the bradycardia at rest, leaving total pulmonary flow unchanged by ivabradine, although ivabradine reduced pulmonary blood flow during swimming (exercise x ivabradine interaction, P<0.05). Although systemic VS increased, systemic blood flow was reduced by ivabradine both at rest and during exercise, in spite of ivabradine's potential to increase cardiac contractility. Opening the pericardium had no effect on fH, VS or blood flows before or after ivabradine, indicating that the pericardium does not constrain VS in turtles, even during pharmacologically-induced bradycardia.
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Affiliation(s)
- Brandt Smith
- Department of Biological Sciences, University of North Texas, Denton, TX, United States
| | - Dane A Crossley
- Department of Biological Sciences, University of North Texas, Denton, TX, United States
| | - Tobias Wang
- Department of Biology- Zoophysiology, Aarhus University, Aarhus C, Denmark
| | - William Joyce
- Department of Biology- Zoophysiology, Aarhus University, Aarhus C, Denmark
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5
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Williams CJA, Hansen K, Williams N, Jakobsen SR, Pedersen CCE, Bertelsen MF, Wang T. The influence of assisted ventilation and recumbency on cardiorespiratory physiology in the anesthetized freshwater turtle Trachemys scripta scripta. Comp Biochem Physiol A Mol Integr Physiol 2021; 260:111036. [PMID: 34256130 DOI: 10.1016/j.cbpa.2021.111036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Revised: 06/15/2021] [Accepted: 07/08/2021] [Indexed: 11/18/2022]
Abstract
The use of assisted ventilation is required in anesthetized reptiles as their respiratory drive is lost at surgical depths of anesthesia. The minute volume of the assisted ventilation influences arterial blood gases and acid-base regulation. Meanwhile, the ventilatory pattern may also affect hemodynamics in chelonians, which, given their large capacity for cardiac shunts, may impact the efficacy of the ventilation in terms of gas exchange. Hence, there is a need for primary information on the influence of assisted ventilation on chelonian physiology, and we, therefore, performed a randomized study into the effects of recumbency and maximum airway pressure on pressure-cycled ventilation in nine female Trachemys scripta scripta. Pronounced effects of ventilation pressure on arterial PCO2 and pH regardless of recumbency were revealed, whilst dorsal recumbency led to a larger Arterial-alveolar (A-a) O2 difference, suggesting compromised pulmonary gas exchange. Plasma [Na+] and [K+] balance was also significantly correlated with maximum airway pressure. Computed tomography (CT) scanning at a range of end-inspiratory pressures and ventral and dorsal recumbencies in eight T. scripta scripta showed that lung volumes increase with maximum ventilatory pressure, while recumbency did not influence volume at pressures above 5 cmH2O. Static compliance of the lungs was influenced by recumbency at neutral pressures. In conclusion, dorsal recumbency reduces pulmonary efficacy during positive pressure ventilation and tends to lower lung volume when ventilation is not provided. However, lung volumes and function - even in dorsal recumbency - can be adequately supported by assisted ventilation, and an end inspiratory pressure of 10 cmH2O at 4 breaths min-1 provided the most physiologically appropriate ventilation of anesthetized T. scripta scripta.
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Affiliation(s)
- Catherine J A Williams
- Zoophysiology, Department of Biology, Aarhus University, Denmark; Department of Biomedical Sciences, University of Guelph, Canada.
| | - Kasper Hansen
- Zoophysiology, Department of Biology, Aarhus University, Denmark; Department of Forensic Medicine, Aarhus University, Denmark; Department of Clinical Medicine (Comparative Medicine Lab), Aarhus University, Denmark
| | - Natasha Williams
- Zoophysiology, Department of Biology, Aarhus University, Denmark
| | | | | | | | - Tobias Wang
- Zoophysiology, Department of Biology, Aarhus University, Denmark
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6
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Joyce W, Wang T. How cardiac output is regulated: August Krogh's proto-Guytonian understanding of the importance of venous return. Comp Biochem Physiol A Mol Integr Physiol 2021; 253:110861. [DOI: 10.1016/j.cbpa.2020.110861] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 11/25/2020] [Accepted: 11/25/2020] [Indexed: 12/20/2022]
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Affiliation(s)
- William Joyce
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark .,Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada
| | - Tobias Wang
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark
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Abstract
In the 1950s, Arthur C. Guyton removed the heart from its pedestal in cardiovascular physiology by arguing that cardiac output is primarily regulated by the peripheral vasculature. This is counterintuitive, as modulating heart rate would appear to be the most obvious means of regulating cardiac output. In this Review, we visit recent and classic advances in comparative physiology in light of this concept. Although most vertebrates increase heart rate when oxygen demands rise (e.g. during activity or warming), experimental evidence suggests that this tachycardia is neither necessary nor sufficient to drive a change in cardiac output (i.e. systemic blood flow, Q̇ sys) under most circumstances. Instead, Q̇ sys is determined by the interplay between vascular conductance (resistance) and capacitance (which is mainly determined by the venous circulation), with a limited and variable contribution from heart function (myocardial inotropy). This pattern prevails across vertebrates; however, we also highlight the unique adaptations that have evolved in certain vertebrate groups to regulate venous return during diving bradycardia (i.e. inferior caval sphincters in diving mammals and atrial smooth muscle in turtles). Going forward, future investigation of cardiovascular responses to altered metabolic rate should pay equal consideration to the factors influencing venous return and cardiac filling as to the factors dictating cardiac function and heart rate.
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Affiliation(s)
- William Joyce
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark .,Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada
| | - Tobias Wang
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark
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9
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Williams CJA, Greunz EM, Ringgaard S, Hansen K, Bertelsen MF, Wang T. Magnetic resonance imaging (MRI) reveals high cardiac ejection fractions in red-footed tortoises ( Chelonoidis carbonarius). ACTA ACUST UNITED AC 2019; 222:jeb.206714. [PMID: 31439654 DOI: 10.1242/jeb.206714] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 08/14/2019] [Indexed: 12/28/2022]
Abstract
The ejection fraction of the trabeculated cardiac ventricle of reptiles has not previously been measured. Here, we used the gold standard clinical methodology - electrocardiogram-gated flow magnetic resonance imaging (MRI) - to validate stroke volume measurements and end diastolic ventricular blood volume. This produced an estimate of ejection fraction in our study species, the red footed tortoise Chelonoidis carbonarius (n=5), under isoflurane anaesthesia of 88±11%. After reduction of the prevailing right-to-left intraventricular shunt through the action of atropine, the ejection fraction was 96±6%. This methodology opens new avenues for studying the complex hearts of ectotherms, and validating hypotheses on the function of a more highly trabeculated heart than that of endotherms, which have lower ejection fractions.
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Affiliation(s)
- Catherine J A Williams
- Section of Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark .,Center for Zoo and Wild Animal Health, Copenhagen Zoo, Roskildevej 38, 2000 Frederiksberg, Denmark
| | - Eva M Greunz
- Center for Zoo and Wild Animal Health, Copenhagen Zoo, Roskildevej 38, 2000 Frederiksberg, Denmark
| | - Steffen Ringgaard
- MR Research Center, Department of Clinical Medicine, Aarhus University, Palle Juul-Jensens Blv. 99, 8200 Aarhus N, Denmark
| | - Kasper Hansen
- Section of Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.,Comparative Medicine Lab, Department of Clinical Medicine, Aarhus University, Palle Juul-Jensens Blv. 99, 8200 Aarhus N, Denmark.,Department of Forensic Medicine, Aarhus University Hospital, Palle Juul-Jensens Blv. 99, 8200 Aarhus N, Denmark
| | - Mads F Bertelsen
- Center for Zoo and Wild Animal Health, Copenhagen Zoo, Roskildevej 38, 2000 Frederiksberg, Denmark
| | - Tobias Wang
- Section of Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.,Aarhus Institute of Advanced Sciences, Aarhus University, 8000 Aarhus C, Denmark
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Joyce W, Crossley DA, Wang T, Jensen B. Smooth Muscle in Cardiac Chambers is Common in Turtles and Extensive in the Emydid Turtle, Trachemys scripta. Anat Rec (Hoboken) 2019; 303:1327-1336. [PMID: 31509333 PMCID: PMC7216914 DOI: 10.1002/ar.24257] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 06/24/2019] [Accepted: 06/28/2019] [Indexed: 02/03/2023]
Abstract
A prominent layer of smooth muscle lining the luminal side of the atria of freshwater turtles (Emydidae) was described more than a century ago. We recently demonstrated that this smooth muscle provides a previously unrecognized mechanism to change cardiac output in the emydid red-eared slider (Trachemys scripta) that possibly contributes to their tremendous diving capacity. The purpose of the present immunohistochemical study was firstly to screen major groups of vertebrates for the presence of cardiac smooth muscle. Secondly, we investigated the phylogenetic distribution of cardiac smooth muscle within the turtle order (Testudines), including terrestrial and aquatic species. Atrial smooth muscle was not detected in a range of vertebrates, including Xenopus laevis, Alligator mississippiensis, and Caiman crocodilus, all of which have pronounced diving capacities. However, we confirmed earlier reports that traces of smooth muscle are found in human atrial tissue. Only within the turtles (eight species) was there substantial amounts of nonvascular smooth muscle in the heart. This amount was greatest in the atria, while the amount in proportion to cardiac muscle was greater in the sinus venosus than in other chambers. T. scripta had more smooth muscle in the sinus venosus and atria than the other turtles. In some specimens, there was some smooth muscle in the ventricle and the pulmonary vein. Our study demonstrates that cardiac smooth muscle likely appeared early in turtle evolution and has become extensive within the Emydidae family, possibly in association with diving. Across other tetrapod clades, cardiac smooth muscle might not associate with diving. Anat Rec, 303:1327-1336, 2020. © 2019 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association for Anatomy.
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Affiliation(s)
- William Joyce
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark
| | - Dane A Crossley
- Department of Medical Biology, Amsterdam UMC, University of Amsterdam, Amsterdam 1105AZ, the Netherlands
| | - Tobias Wang
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.,Aarhus Institute of Advanced Studies, Aarhus University, Aarhus, Denmark
| | - Bjarke Jensen
- Department of Medical Biology, University Medical Center Amsterdam, Amsterdam, The Netherlands
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Joyce W, White DW, Raven PB, Wang T. Weighing the evidence for using vascular conductance, not resistance, in comparative cardiovascular physiology. J Exp Biol 2019; 222:222/6/jeb197426. [DOI: 10.1242/jeb.197426] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
ABSTRACT
Vascular resistance and conductance are reciprocal indices of vascular tone that are often assumed to be interchangeable. However, in most animals in vivo, blood flow (i.e. cardiac output) typically varies much more than arterial blood pressure. When blood flow changes at a constant pressure, the relationship between conductance and blood flow is linear, whereas the relationship between resistance and blood flow is non-linear. Thus, for a given change in blood flow, the change in resistance depends on the starting point, whereas the attendant change in conductance is proportional to the change in blood flow regardless of the starting conditions. By comparing the effects of physical activity at different temperatures or between species – concepts at the heart of comparative cardiovascular physiology – we demonstrate that the difference between choosing resistance or conductance can be marked. We also explain here how the ratio of conductance in the pulmonary and systemic circulations provides a more intuitive description of cardiac shunt patterns in the reptilian cardiovascular system than the more commonly used ratio of resistance. Finally, we posit that, although the decision to use conductance or resistance should be made on a case-by-case basis, in most circumstances, conductance is a more faithful portrayal of cardiovascular regulation in vertebrates.
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Affiliation(s)
- William Joyce
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
| | - Daniel W. White
- School of Arts & Sciences, University of Houston-Victoria, Victoria, TX 77901, USA
| | - Peter B. Raven
- Department of Physiology and Anatomy, UNT Health Science Center, Fort Worth, TX 76107, USA
| | - Tobias Wang
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
- Aarhus Institute of Advanced Sciences (AIAS), Aarhus University, 8000 Aarhus C, Denmark
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Joyce W, Axelsson M, Wang T. Contraction of atrial smooth muscle reduces cardiac output in perfused turtle hearts. ACTA ACUST UNITED AC 2019; 222:jeb.199828. [PMID: 30787139 DOI: 10.1242/jeb.199828] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Accepted: 02/18/2019] [Indexed: 11/20/2022]
Abstract
Unusual undulations in resting tension (tonus waves) were described in isolated atria from freshwater turtles more than a century ago. These tonus waves were soon after married with the histological demonstration of a rich layer of smooth muscle on the luminal side of the atrial wall. Research thereafter waned and the functional significance of this smooth muscle has remained obscure. Here, we provide evidence that contraction of the smooth muscle in the atria may be able to change cardiac output in turtle hearts. In in situ perfused hearts of the red-eared slider turtle (Trachemys scripta elegans), we demonstrated that activation of smooth muscle contraction with histamine (100 nmol kg-1 bolus injected into perfusate) reduced cardiac output by decreasing stroke volume (>50% decrease in both parameters). Conversely, inhibition of smooth muscle contraction with wortmannin (10 µmol l-1 perfusion) approximately doubled baseline stroke volume and cardiac output. We suggest that atrial smooth muscle provides a unique mechanism to control cardiac filling that could be involved in the regulation of stroke volume during diving.
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Affiliation(s)
- William Joyce
- Department of Bioscience, Section for Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
| | - Michael Axelsson
- Department of Biological and Environmental Sciences, University of Gothenburg, SE 405 30 Gothenburg, Sweden
| | - Tobias Wang
- Department of Bioscience, Section for Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark.,Aarhus Institute of Advanced Studies, Aarhus University, 8000 Aarhus C, Denmark
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Joyce W, Elsey RM, Wang T, Crossley DA. Maximum heart rate does not limit cardiac output at rest or during exercise in the American alligator (Alligator mississippiensis). Am J Physiol Regul Integr Comp Physiol 2018; 315:R296-R302. [DOI: 10.1152/ajpregu.00027.2018] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
In most vertebrates, increases in cardiac output result from increases in heart rate (fH) with little or no change in stroke volume (Vs), and maximum cardiac output (Q̇) is typically attained at or close to maximum fH. We therefore tested the hypothesis that increasing maximum fH may increase maximum Q̇. To this end, we investigated the effects of elevating fH with right atrial pacing on Q̇ in the American alligator ( Alligator mississippiensis) at rest and while swimming. During normal swimming, Q̇ increased entirely by virtue of a tachycardia (29 ± 1 to 40 ± 3 beats/min), whereas Vs remained stable. In both resting and swimming alligators, increasing fH with right atrial pacing resulted in a parallel decline in Vs that resulted in an unchanged cardiac output. In swimming animals, this reciprocal relationship extended to supraphysiological fH (up to ~72 beats/min), which suggests that maximum fH does not limit maximum cardiac output and that fH changes are secondary to the peripheral factors (for example vascular capacitance) that determine venous return at rest and during exercise.
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Affiliation(s)
- William Joyce
- Department of Zoophysiology, Aarhus University, Aarhus, Denmark
| | - Ruth M. Elsey
- Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, Louisiana
| | - Tobias Wang
- Department of Zoophysiology, Aarhus University, Aarhus, Denmark
- Aarhus Institute of Advanced Studies, Aarhus University, Aarhus, Denmark
| | - Dane A. Crossley
- Department of Biological Sciences, Developmental Integrative Biology Cluster, University of North Texas, Denton, Texas
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Joyce W, Crossley J, Elsey RM, Wang T, Crossley DA. Contribution of active atrial contraction to cardiac output in anesthetized American alligators ( Alligator mississippiensis). ACTA ACUST UNITED AC 2018; 221:jeb.178194. [PMID: 29615521 DOI: 10.1242/jeb.178194] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 03/21/2018] [Indexed: 12/30/2022]
Abstract
Ventricular filling may occur directly from the venous circulation during early diastole or via atrial contraction in late diastole. The contribution of atrial contraction to ventricular filling is typically small in mammals (10-40%), but has been suggested to predominate in reptiles. We investigated the importance of atrial contraction in filling of the ventricle in American alligators (Alligator mississippiensis) by bypassing both atria (with the use of ligatures to prevent atrial filling) and measuring the resultant effects on cardiac output in anesthetized animals. Atrial ligation had no significant effects on total systemic blood flow before or after adrenaline injection. Unexpectedly, pulmonary flow was increased following atrial ligation prior to adrenaline treatment, but was unaffected after it. These findings suggest that the atria are non-essential (i.e. redundant) for ventricular filling in alligators, at least under anesthesia, but may serve as important volume reservoirs.
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Affiliation(s)
- William Joyce
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
| | - Janna Crossley
- Department of Biological Sciences, Developmental Integrative Biology Cluster, University of North Texas, Denton, TX 76203-5017, USA
| | - Ruth M Elsey
- Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, LA 70643, USA
| | - Tobias Wang
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark.,Aarhus Institute of Advanced Studies, Aarhus University, 8000 Aarhus C, Denmark
| | - Dane A Crossley
- Department of Biological Sciences, Developmental Integrative Biology Cluster, University of North Texas, Denton, TX 76203-5017, USA
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