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Aalkjær C, Wang T. The cardiovascular challenges in giraffes. J Muscle Res Cell Motil 2023; 44:53-60. [PMID: 35879488 DOI: 10.1007/s10974-022-09626-0] [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: 05/10/2022] [Accepted: 07/10/2022] [Indexed: 11/30/2022]
Abstract
Giraffes are the highest living animals on Earth and therefore are challenged by gravity more than any other species. In particular the cardiovascular system needs to adapt to this challenge. Giraffes have a mean blood pressure around 200 mmHg, which ensures a mean arterial pressure near the head of 100 mmHg when the giraffe is standing with the neck in a near vertical position. This immediately raises several questions. How do giraffes avoid edema in the legs where the arterial pressure is 300 mmHg or higher? How does the heart produce a pressure of 200 mmHg, and what is the energy required for this endeavor? How can the kidney tolerate a pressure of about 200 mmHg and does this mean that giraffes have a high glomerular filtration rate? What is the arterial pressure in the head of giraffes when they drink, and how is perfusion of the brain maintained when they lift their head after drinking? In this short review, we present some answers to these questions.
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Affiliation(s)
- Christian Aalkjær
- Department of Biomedicine, Aarhus University, 8000, Aarhus C, Denmark.
- Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark.
| | - Tobias Wang
- Zoophysiology, Department of Biological Sciences, Aarhus University, 8000, Aarhus C, Denmark
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2
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A Preliminary Study on the Siphon Mechanism in Giraffe ( Giraffa camelopardalis). Animals (Basel) 2022; 12:ani12233348. [PMID: 36496868 PMCID: PMC9740075 DOI: 10.3390/ani12233348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2022] [Revised: 11/23/2022] [Accepted: 11/26/2022] [Indexed: 12/04/2022] Open
Abstract
Adult giraffes reach heights of 4.5 m with a heart-to-head distance of over 2 m, making cranial blood supply challenging. Ultrasound confirmed that the giraffe jugular vein collapses during head movement from ground level to fully erect, negating the possibility of a siphon mechanism in the neck. We showed that a short-length siphon structure over a simulated head-to-heart distance for a giraffe significantly influences flow in a collapsible tube. The siphon structure is determined according to brain case measurements. The short-length siphon structure in a shorter-necked ostrich showed no significant increase in flow. The shorter head-to-heart distance might be the reason for the lack of effect in ostriches. A siphon mechanism situated in the cranium is certainly possible, with a significant effect exerted on the amount of pressure the heart must generate to allow adequate cranial blood perfusion in a long-necked giraffe. The study validated that a cranial-bound siphon structure can operate and will be of significant value for adequate cranial blood perfusion in long-necked species such as giraffes and might also have existed in extinct species of long-necked dinosaurs.
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Eiken O, Keramidas ME, Sköldefors H, Kölegård R. Human cardiovascular adaptation to hypergravity. Am J Physiol Regul Integr Comp Physiol 2022; 322:R597-R608. [PMID: 35470711 DOI: 10.1152/ajpregu.00043.2022] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Despite decades of experience from high-G exposures in aircraft and centrifuges, information is scarce regarding primary cardiovascular adaptations to +Gz loads in relaxed humans. Thus, effects of G-training are typically evaluated after regimens that are confounded by concomitant use of anti-G straining maneuvers, anti-G suits and pressure breathing. Accordingly, the aim was to evaluate cardiovascular adaptations to repeated +Gz exposures in the relaxed state. Eleven men underwent 5 weeks of centrifuge G training, consisting of 15 × 40 min +Gz exposures at G levels close to their individual relaxed G-level tolerance. Before and after the training regimen, relaxed G-level tolerance was investigated during rapid (ROR) and gradual (GOR) onset-rate G exposures, and cardiovascular responses were investigated during orthostatic provocation and vascular pressure-distension tests. The G training resulted in: (i) a 13% increase in relaxed ROR G tolerance (P < 0.001), but no change in GOR G tolerance, (ii) increased pressure resistance in the arteries and arterioles of the legs (P < 0.001), but not the arms, (iii) a reduced initial drop in arterial pressure upon ROR high G, but no change in arterial pressure under basal resting conditions or during GOR G loading, or orthostatic provocation. The results suggest +Gz adaptation via enhanced pressure resistance in dependent arteries/arterioles. Presumably this reflects local adaptations to high transmural pressures, resulting from the +Gz-induced exaggeration of the intravascular hydrostatic pressure gradients.
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Affiliation(s)
- Ola Eiken
- Division of Environmental Physiology, Swedish Aerospace Physiology Centre, School of Chemistry, Bioengineering and Health, Royal Institute of Technology, KTH, Stockholm, Sweden
| | - Michail E Keramidas
- Division of Environmental Physiology, Swedish Aerospace Physiology Centre, School of Chemistry, Bioengineering and Health, Royal Institute of Technology, KTH, Stockholm, Sweden
| | | | - Roger Kölegård
- Division of Environmental Physiology, Swedish Aerospace Physiology Centre, School of Chemistry, Bioengineering and Health, Royal Institute of Technology, KTH, Stockholm, Sweden
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The effects of gravity and compression on interstitial fluid transport in the lower limb. Sci Rep 2022; 12:4890. [PMID: 35318426 PMCID: PMC8941011 DOI: 10.1038/s41598-022-09028-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Accepted: 03/14/2022] [Indexed: 11/13/2022] Open
Abstract
Edema in the limbs can arise from pathologies such as elevated capillary pressures due to failure of venous valves, elevated capillary permeability from local inflammation, and insufficient fluid clearance by the lymphatic system. The most common treatments include elevation of the limb, compression wraps and manual lymphatic drainage therapy. To better understand these clinical situations, we have developed a comprehensive model of the solid and fluid mechanics of a lower limb that includes the effects of gravity. The local fluid balance in the interstitial space includes a source from the capillaries, a sink due to lymphatic clearance, and movement through the interstitial space due to both gravity and gradients in interstitial fluid pressure (IFP). From dimensional analysis and numerical solutions of the governing equations we have identified several parameter groups that determine the essential length and time scales involved. We find that gravity can have dramatic effects on the fluid balance in the limb with the possibility that a positive feedback loop can develop that facilitates chronic edema. This process involves localized tissue swelling which increases the hydraulic conductivity, thus allowing the movement of interstitial fluid vertically throughout the limb due to gravity and causing further swelling. The presence of a compression wrap can interrupt this feedback loop. We find that only by modeling the complex interplay between the solid and fluid mechanics can we adequately investigate edema development and treatment in a gravity dependent limb.
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Horrell HD, Lindeque A, Farrell AP, Seymour RS, White CR, Kruger KM, Snelling EP. Relationship between capillaries, mitochondria and maximum power of the heart: a meta-study from shrew to elephant. Proc Biol Sci 2022; 289:20212461. [PMID: 35135343 PMCID: PMC8825986 DOI: 10.1098/rspb.2021.2461] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
This meta-study uses phylogenetic scaling models across more than 30 species, spanning five orders of magnitude in body mass, to show that cardiac capillary numerical density and mitochondrial volume density decrease with body mass raised to the -0.07 ± 0.03 and -0.04 ± 0.01 exponents, respectively. Thus, while an average 10 g mammal has a cardiac capillary density of approximately 4150 mm-2 and a mitochondrial density of 33%, a 1 t mammal has considerably lower corresponding values of 1850 mm-2 and 21%. These similar scaling trajectories suggest quantitative matching for the primary oxygen supply and oxygen consuming structures of the heart, supporting economic design at the cellular level of the oxygen cascade in this aerobic organ. These scaling trajectories are nonetheless somewhat shallower than the exponent of -0.11 calculated for the maximum external mechanical power of the cardiac tissue, under conditions of heavy exercise, when oxygen flow between capillaries and mitochondria is probably fully exploited. This mismatch, if substantiated, implies a declining external mechanical efficiency of the heart with increasing body mass, whereby larger individuals put more energy in but get less energy out, a scenario with implications for cardiovascular design, aerobic capacity and limits of body size.
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Affiliation(s)
- Heidi D. Horrell
- Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa,Department of Companion Animal Clinical Studies, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
| | - Anika Lindeque
- Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
| | - Anthony P. Farrell
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada,Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada
| | - Roger S. Seymour
- School of Biological Sciences, Faculty of Sciences, University of Adelaide, Adelaide, South Australia, Australia
| | - Craig R. White
- Centre for Geometric Biology, School of Biological Sciences, Faculty of Science, Monash University, Clayton, Victoria, Australia
| | - Kayla M. Kruger
- Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
| | - Edward P. Snelling
- Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa,Centre for Veterinary Wildlife Research, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
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Natterson-Horowitz B, Baccouche BM, Mary J, Shivkumar T, Bertelsen MF, Aalkjær C, Smerup MH, Ajijola OA, Hadaya J, Wang T. Did giraffe cardiovascular evolution solve the problem of heart failure with preserved ejection fraction? EVOLUTION MEDICINE AND PUBLIC HEALTH 2021; 9:248-255. [PMID: 34447575 PMCID: PMC8385250 DOI: 10.1093/emph/eoab016] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Accepted: 06/04/2021] [Indexed: 11/18/2022]
Abstract
The evolved adaptations of other species can be a source of insight for novel biomedical innovation. Limitations of traditional animal models for the study of some pathologies are fueling efforts to find new approaches to biomedical investigation. One emerging approach recognizes the evolved adaptations in other species as possible solutions to human pathology. The giraffe heart, for example, appears resistant to pathology related to heart failure with preserved ejection fraction (HFpEF)—a leading form of hypertension-associated cardiovascular disease in humans. Here, we postulate that the physiological pressure-induced left ventricular thickening in giraffes does not result in the pathological cardiovascular changes observed in humans with hypertension. The mechanisms underlying this cardiovascular adaptation to high blood pressure in the giraffe may be a bioinspired roadmap for preventive and therapeutic strategies for human HFpEF.
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Affiliation(s)
- Barbara Natterson-Horowitz
- Department of Medicine, Harvard Medical School, Boston, MA, USA.,Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, USA.,Division of Cardiology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Basil M Baccouche
- Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, USA.,Department of Public Health and Primary Care, University of Cambridge, Cambridge, UK
| | - Jennifer Mary
- Zoobiquity Research Initiative at UCLA, Los Angeles, CA 90024, USA
| | | | | | | | - Morten H Smerup
- Department of Cardiothoracic Surgery, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark
| | - Olujimi A Ajijola
- UCLA Cardiac Arrhythmia Center, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Joseph Hadaya
- UCLA Cardiac Arrhythmia Center, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.,Molecular, Cellular and Integrative Physiology Program, UCLA, Los Angeles, CA, USA
| | - Tobias Wang
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
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Pandya SK. Letter from Mumbai. THE NATIONAL MEDICAL JOURNAL OF INDIA 2021; 34:183-184. [PMID: 34825534 DOI: 10.25259/nmji_34_3_183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
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Armelin VA, Braga VHDS, Teixeira MT, Guagnoni IN, Wang T, Florindo LH. The baroreflex in aquatic and amphibious teleosts: Does terrestriality represent a significant driving force for the evolution of a more effective baroreflex in vertebrates? Comp Biochem Physiol A Mol Integr Physiol 2021; 255:110916. [PMID: 33545361 DOI: 10.1016/j.cbpa.2021.110916] [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: 09/26/2020] [Revised: 01/24/2021] [Accepted: 01/25/2021] [Indexed: 10/22/2022]
Abstract
All vertebrates have baroreflexes that provide fast regulation of arterial blood pressure (PA) to maintain adequate tissue perfusion and avoid vascular lesions from excessive pressures. The baroreflex is a negative feedback loop, where altered PA results in reciprocal changes in heart rate (fH) and systemic vascular conductance to restore pressure. In terrestrial environments, gravity usually leads to blood pooling in the lower body reducing venous return, cardiac filling, cardiac output and PA. Conversely, in aquatic environments, the hydrostatic pressure of surrounding water mitigates blood pooling and prevents vascular distensions. In this context, we aimed to test the hypothesis that vertebrate species that were exposed to gravity-induced hemodynamic disturbances throughout their evolutionary histories have a more effective barostatic reflex than those that were not. We examined the cardiac baroreflex of fish that perform (Clarias gariepinus and Hoplerythrinus unitaeniatus) and do not perform (Hoplias malabaricus and Oreochromis niloticus) voluntary terrestrial sojourns, using pharmacological manipulations of PA to characterize reflex changes in fH using a four-variable sigmoidal logistic function (i.e. the "Oxford technique"). Our results revealed that amphibious fish exhibit higher baroreflex gain and responsiveness to hypotension than strictly aquatic fish, suggesting that terrestriality and the gravitational circulatory stresses constitute a relevant driving force for the evolution of a more effective baroreflex in vertebrates. We also demonstrate that strictly aquatic teleosts have considerable baroreflex gain, supporting the view that the baroreflex is an ancient cardiovascular trait that appeared before vertebrates colonized the gravity-dominated realm of land.
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Affiliation(s)
- Vinicius Araújo Armelin
- Department of Physiology, Institute of Biosciences, University of São Paulo (USP), Rua do Matão, Travessa 14, 321, São Paulo, SP, 05508-090, Brazil; Department of Zoology and Botany, São Paulo State University (UNESP), Rua Cristóvão Colombo 2265, São José do Rio Preto, SP, 15054-000, Brazil; National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil.
| | - Victor Hugo da Silva Braga
- Department of Zoology and Botany, São Paulo State University (UNESP), Rua Cristóvão Colombo 2265, São José do Rio Preto, SP, 15054-000, Brazil; National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil
| | - Mariana Teodoro Teixeira
- Department of Zoology and Botany, São Paulo State University (UNESP), Rua Cristóvão Colombo 2265, São José do Rio Preto, SP, 15054-000, Brazil; National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil
| | - Igor Noll Guagnoni
- Department of Zoology and Botany, São Paulo State University (UNESP), Rua Cristóvão Colombo 2265, São José do Rio Preto, SP, 15054-000, Brazil; National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil
| | - Tobias Wang
- Section for Zoophysiology, Department of Bioscience, Aarhus University (AU), C. F. Møllers Allé 3, Aarhus, 8000 Aarhus C, Denmark; National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil
| | - Luiz Henrique Florindo
- Department of Zoology and Botany, São Paulo State University (UNESP), Rua Cristóvão Colombo 2265, São José do Rio Preto, SP, 15054-000, Brazil; Aquaculture Center (CAUNESP), São Paulo State University (UNESP), Rodovia Prof. Paulo Donato Castellane n/n, Jaboticabal, SP, 14884-900, Brazil; National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, Brazil
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