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Peters CM, Dempsey JA, Hopkins SR, Sheel AW. Is the Lung Built for Exercise? Advances and Unresolved Questions. Med Sci Sports Exerc 2023; 55:2143-2159. [PMID: 37443459 PMCID: PMC11186580 DOI: 10.1249/mss.0000000000003255] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/15/2023]
Abstract
ABSTRACT Nearly 40 yr ago, Professor Dempsey delivered the 1985 ACSM Joseph B. Wolffe Memorial Lecture titled: "Is the lung built for exercise?" Since then, much experimental work has been directed at enhancing our understanding of the functional capacity of the respiratory system by applying complex methodologies to the study of exercise. This review summarizes a symposium entitled: "Revisiting 'Is the lung built for exercise?'" presented at the 2022 American College of Sports Medicine annual meeting, highlighting the progress made in the last three-plus decades and acknowledging new research questions that have arisen. We have chosen to subdivide our topic into four areas of active study: (i) the adaptability of lung structure to exercise training, (ii) the utilization of airway imaging to better understand how airway anatomy relates to exercising lung mechanics, (iii) measurement techniques of pulmonary gas exchange and their importance, and (iv) the interactions of the respiratory and cardiovascular system during exercise. Each of the four sections highlights gaps in our knowledge of the exercising lung. Addressing these areas that would benefit from further study will help us comprehend the intricacies of the lung that allow it to meet and adapt to the acute and chronic demands of exercise in health, aging, and disease.
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Affiliation(s)
| | - Jerome A Dempsey
- Population Health Science, John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin-Madison, Madison, WI
| | - Susan R Hopkins
- Department of Radiology, University of California San Diego, La Jolla, CA
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2
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Ramsook AH, Dominelli PB, Angus SA, Senefeld JW, Wiggins CC, Joyner MJ. The oxygen transport cascade and exercise: Lessons from comparative physiology. Comp Biochem Physiol A Mol Integr Physiol 2023; 282:111442. [PMID: 37182787 DOI: 10.1016/j.cbpa.2023.111442] [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: 02/24/2023] [Revised: 05/09/2023] [Accepted: 05/11/2023] [Indexed: 05/16/2023]
Abstract
Studies of animal physiology not only provide valuable knowledge for the species in question, but also offer insights into human physiology. This thought is best highlighted by the 'Krogh Principle', which states "for many problems there is an animal on which it can be most conveniently studied". This graphical review focuses on three distinct stages of the oxygen transport cascade in which human exercise physiology knowledge has been enhanced by studies carried out in animal models. We begin by exploring ventilation, and the detrimental effects of cold, dry air on the airways in two sets of elite athletes, the cross-country skier and the racing sled dog. We then discuss the transport of oxygen via hemoglobin and the shifts in humans and deer mice with relatively shifted oxygen dissociation curves. Finally, we consider the technical difficulties of measuring respiratory muscle blood flow in exercising humans and how an equine model can provide an understanding of the distribution of blood flow during exercise. These cases illustrate the complementary nature of physiological studies across species.
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Affiliation(s)
- Andrew H Ramsook
- Department of Anesthesia and Perioperative Medicine, Mayo Clinic, Rochester, USA
| | - Paolo B Dominelli
- Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, ON, Canada
| | - Sarah A Angus
- Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, ON, Canada
| | - Jonathon W Senefeld
- Department of Anesthesia and Perioperative Medicine, Mayo Clinic, Rochester, USA; Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, MN, USA
| | - Chad C Wiggins
- Department of Anesthesia and Perioperative Medicine, Mayo Clinic, Rochester, USA; Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, MN, USA
| | - Michael J Joyner
- Department of Anesthesia and Perioperative Medicine, Mayo Clinic, Rochester, USA; Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, MN, USA.
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Gerson EAM, Dominelli PB, Leahy MG, Kipp S, Guenette JA, Archiza B, Sheel AW. The effect of proportional assist ventilation on the electrical activity of the human diaphragm during exercise. Exp Physiol 2023; 108:296-306. [PMID: 36420595 PMCID: PMC10103863 DOI: 10.1113/ep090808] [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: 09/01/2022] [Accepted: 11/10/2022] [Indexed: 11/25/2022]
Abstract
NEW FINDINGS What is the central question of this study? What is the effect of lowering the normally occurring work of breathing on the electrical activity and pressure generated by the diaphragm during submaximal exercise in healthy humans? What is the main finding and its importance? Ventilatory assist during exercise elicits a proportional lowering of both the work performed by the diaphragm and diaphragm electrical activity. These findings have implications for exercise training studies using proportional assist ventilation to reduce diaphragm work in patients with cardiopulmonary disease. ABSTRACT We hypothesized that when a proportional assist ventilator (PAV) is applied in order to reduce the pressure generated by the diaphragm, there would be a corresponding reduction in electrical activity of the diaphragm. Healthy participants (five male and four female) completed an incremental cycle exercise test to exhaustion in order to calculate workloads for subsequent trials. On the experimental day, participants performed submaximal cycling, and three levels of assisted ventilation were applied (low, medium and high). Ventilatory parameters, pulmonary pressures and EMG of the diaphragm (EMGdi ) were obtained. To compare the PAV conditions with spontaneous breathing intervals, ANOVA procedures were used, and significant effects were evaluated with a Tukey-Kramer test. Significance was set at P < 0.05. The work of breathing was not different between the lowest level of unloading and spontaneous breathing (P = 0.151) but was significantly lower during medium (25%, P = 0.02) and high (36%, P < 0.001) levels of PAV. The pressure-time product of the diaphragm (PTPdi ) was lower across PAV unloading conditions (P < 0.05). The EMGdi was significantly lower in medium and high PAV conditions (P = 0.035 and P < 0.001, respectively). The mean reductions of EMGdi with PAV unloading were 14, 22 and 39%, respectively. The change in EMGdi for a given lowering of PTPdi with the PAV was significantly correlated (r = 0.61, P = 0.01). Ventilatory assist during exercise elicits a reduction in the electrical activity of the diaphragm, and there is a proportional lowering of the work of breathing. Our findings have implications for exercise training studies using assisted ventilation to reduce diaphragm work in patients with cardiopulmonary disease.
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Affiliation(s)
- Emily A. M. Gerson
- School of KinesiologyThe University of British ColumbiaVancouverBritish ColumbiaCanada
| | | | - Michael G. Leahy
- School of KinesiologyThe University of British ColumbiaVancouverBritish ColumbiaCanada
| | - Shalaya Kipp
- School of KinesiologyThe University of British ColumbiaVancouverBritish ColumbiaCanada
| | - Jordan A. Guenette
- School of KinesiologyThe University of British ColumbiaVancouverBritish ColumbiaCanada
- Centre for Heart Lung InnovationProvidence ResearchThe University of British Columbia, St. Paul's HospitalVancouverBritish ColumbiaCanada
- Department of Physical TherapyFaculty of MedicineThe University of British ColumbiaVancouverBritish ColumbiaCanada
| | - Bruno Archiza
- School of KinesiologyThe University of British ColumbiaVancouverBritish ColumbiaCanada
- Department of PhysiotherapyCardiopulmonary Physiotherapy LaboratoryNucleus of Research in Physical Exercise, Federal University of Sao CarlosSao CarlosBrazil
| | - Andrew William Sheel
- School of KinesiologyThe University of British ColumbiaVancouverBritish ColumbiaCanada
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Dempsey JA, La Gerche A, Hull JH. Is the healthy respiratory system built just right, overbuilt, or underbuilt to meet the demands imposed by exercise? J Appl Physiol (1985) 2020; 129:1235-1256. [PMID: 32790594 DOI: 10.1152/japplphysiol.00444.2020] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
In the healthy, untrained young adult, a case is made for a respiratory system (airways, pulmonary vasculature, lung parenchyma, respiratory muscles, and neural ventilatory control system) that is near ideally designed to ensure a highly efficient, homeostatic response to exercise of varying intensities and durations. Our aim was then to consider circumstances in which the intra/extrathoracic airways, pulmonary vasculature, respiratory muscles, and/or blood-gas distribution are underbuilt or inadequately regulated relative to the demands imposed by the cardiovascular system. In these instances, the respiratory system presents a significant limitation to O2 transport and contributes to the occurrence of locomotor muscle fatigue, inhibition of central locomotor output, and exercise performance. Most prominent in these examples of an "underbuilt" respiratory system are highly trained endurance athletes, with additional influences of sex, aging, hypoxic environments, and the highly inbred equine. We summarize by evaluating the relative influences of these respiratory system limitations on exercise performance and their impact on pathophysiology and provide recommendations for future investigation.
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Affiliation(s)
- Jerome A Dempsey
- John Robert Sutton Professor of Population Health Sciences, John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin-Madison, Madison, Wisconsin
| | - Andre La Gerche
- Clinical Research Domain, Baker Heart and Diabetes Institute, Melbourne, Australia.,National Center for Sports Cardiology, St. Vincent's Hospital, Melbourne, Fitzroy, Australia
| | - James H Hull
- Department of Respiratory Medicine, Royal Brompton Hospital, London, United Kingdom.,Institute of Sport, Exercise and Health (ISEH), University College London, United Kingdom
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Dempsey JA. Respiratory Determinants of Exercise Limitation: Focus on Phrenic Afferents and the Lung Vasculature. Clin Chest Med 2019; 40:331-342. [PMID: 31078213 DOI: 10.1016/j.ccm.2019.02.002] [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] [Indexed: 01/10/2023]
Abstract
We examine 2 means by which the healthy respiratory system contributes to exercise limitation. These include the activation of respiratory and locomotor muscle afferent reflexes, which constrain blood flow and hasten fatigue in both sets of muscles, and the excessive increases in pulmonary vascular pressures at high cardiac outputs, which constrain O2 transport and precipitate maladaptive right ventricular remodeling in endurance-trained subjects.
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Affiliation(s)
- Jerome A Dempsey
- Department Population Health Sciences, University of Wisconsin-Madison, 707 WARF Building, 610 N. Walnut Street, WI 53726, USA.
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Dominelli PB, Katayama K, Vermeulen TD, Stuckless TJ, Brown CV, Foster GE, Sheel AW. Work of breathing influences muscle sympathetic nerve activity during semi-recumbent cycle exercise. Acta Physiol (Oxf) 2019; 225:e13212. [PMID: 30358142 DOI: 10.1111/apha.13212] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Revised: 10/17/2018] [Accepted: 10/18/2018] [Indexed: 02/06/2023]
Abstract
Reducing the work of breathing during exercise improves locomotor muscle blood flow and reduces diaphragm and locomotor muscle fatigue and is thought to be the result of a sympathetically mediated reflex. AIM The aim of this study was to assess muscle sympathetic nerve activity (MSNA) when the work of breathing is experimentally lowered during dynamic exercise. METHODS Healthy subjects (n = 12; age = 29 ± 9 years) performed semi-recumbent cycling trials at 40%, 60%, and 80% of peak workload. Exercise trials consisted of spontaneous breathing, reduced work of breathing (proportional assist ventilator), followed by further spontaneous breathing (post-ventilator). MSNA was recorded from the median nerve. RESULTS There was no difference in work of breathing between PAV and post-PAV at 40% peak work. At 60% peak work, the ventilator significantly (P < 0.05) reduced work of breathing (103 ± 39 vs 144 ± 47 J min-1 ), sympathetic nerve activity (35 ± 5 vs 42 ± 8 burst min-1 ), and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:mover><mml:mi>V</mml:mi> <mml:mo>˙</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:math> (2.4 ± 0.5 vs 2.6 ± 0.5 L min-1 ) without influencing ventilation (86 ± 9 vs 82 ± 10 L min-1 ; P > 0.05), for PAV and post-PAV respectively. During 80% peak work (n = 8), the ventilator significantly (P < 0.05) reduced work of breathing (235 ± 110 vs. 361 ± 150 J min-1 ), MSNA (48 ± 7 vs 54 ± 11 burst min-1 ), and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:mover><mml:mi>V</mml:mi> <mml:mo>˙</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:math> (2.9 ± 0.6 vs 3.2 ± 0.7 L min-1 ) but not ventilation (121 ± 20 vs 123 ± 20 L min-1 ; P > 0.05), for PAV and post-PAV respectively. There was a significant relationship between MSNA and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:mover><mml:mi>V</mml:mi> <mml:mo>˙</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:math> (P < 0.0001) with a significant interaction due to the ventilator (P < 0.05). CONCLUSION Lowering the normally occurring work of breathing during exercise results in commensurate reductions in MSNA. Our findings provide evidence of a sympathetically mediated vasoconstrictor effect emanating from respiratory muscles during exercise.
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Affiliation(s)
- Paolo B. Dominelli
- School of Kinesiology University of British Columbia Vancouver British Columbia Canada
- Department of Anaesthesiology Mayo Clinic Rochester Minnesota
| | - Keisho Katayama
- Research Center of Health, Physical Fitness and Sports, Graduate School of Medicine Nagoya University Nagoya Japan
| | - Tyler D. Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences University of British Columbia Kelowna British Columbia Canada
| | - Troy J.R. Stuckless
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences University of British Columbia Kelowna British Columbia Canada
| | - Courtney V. Brown
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences University of British Columbia Kelowna British Columbia Canada
| | - Glen E. Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences University of British Columbia Kelowna British Columbia Canada
| | - Andrew William Sheel
- School of Kinesiology University of British Columbia Vancouver British Columbia Canada
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Intercostal muscle blood flow is elevated in old rats during submaximal exercise. Respir Physiol Neurobiol 2019; 263:26-30. [PMID: 30825527 DOI: 10.1016/j.resp.2019.02.003] [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: 11/23/2018] [Revised: 02/11/2019] [Accepted: 02/13/2019] [Indexed: 11/24/2022]
Abstract
BACKGROUND Respiratory muscle blood flows (BF) increase substantially during exercise in younger adult rats. As aging is associated with altered pulmonary function, we hypothesized that old rats will have greater intercostal muscle BF and vascular conductances (VC) than young rats during submaximal exercise. METHODS Mean arterial pressure and respiratory muscle BFs (via carotid artery catheter and radiolabeled microspheres, respectively) were measured at rest and during submaximal exercise in young (n = 9) and old (n = 7) Fischer 344 X Brown Norway rats. RESULTS At rest, diaphragm, intercostal, and transversus abdominis BFs and VCs were not different between groups (all, p > 0.10). During submaximal exercise, old compared to young rats had greater intercostal BF (40 ± 6 vs 25 ± 2 mL/min/100 g) and VC (0.30 ± 0.05 vs 0.18 ± 0.02 mL/min/mmHg/100 g) (both, p ≤ 0.01). Diaphragm and transversus abdominis BFs and VCs were not different between groups during exercise (all, p > 0.24). CONCLUSIONS These data demonstrate that intercostal muscle BF and VC are increased in old compared to young rats during submaximal exercise.
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8
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Sheel AW, Boushel R, Dempsey JA. Competition for blood flow distribution between respiratory and locomotor muscles: implications for muscle fatigue. J Appl Physiol (1985) 2018; 125:820-831. [PMID: 29878876 DOI: 10.1152/japplphysiol.00189.2018] [Citation(s) in RCA: 76] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Sympathetically induced vasoconstrictor modulation of local vasodilation occurs in contracting skeletal muscle during exercise to ensure appropriate perfusion of a large active muscle mass and to maintain also arterial blood pressure. In this synthesis, we discuss the contribution of group III-IV muscle afferents to the sympathetic modulation of blood flow distribution to locomotor and respiratory muscles during exercise. This is followed by an examination of the conditions under which diaphragm and locomotor muscle fatigue occur. Emphasis is given to those studies in humans and animal models that experimentally changed respiratory muscle work to evaluate blood flow redistribution and its effects on locomotor muscle fatigue, and conversely, those that evaluated the influence of coincident limb muscle contraction on respiratory muscle blood flow and fatigue. We propose the concept of a "two-way street of sympathetic vasoconstrictor activity" emanating from both limb and respiratory muscle metaboreceptors during exercise, which constrains blood flow and O2 transport thereby promoting fatigue of both sets of muscles. We end with considerations of a hierarchy of blood flow distribution during exercise between respiratory versus locomotor musculatures and the clinical implications of muscle afferent feedback influences on muscle perfusion, fatigue, and exercise tolerance.
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Affiliation(s)
- A William Sheel
- School of Kinesiology, University of British Columbia , Vancouver, British Columbia , Canada
| | - Robert Boushel
- School of Kinesiology, University of British Columbia , Vancouver, British Columbia , Canada
| | - Jerome A Dempsey
- Department of Population Health Sciences, John Rankin Laboratory of Pulmonary Medicine, School of Medicine and Public Health, University of Wisconsin , Madison, Wisconsin
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9
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Smith JR, Ferguson SK, Hageman KS, Harms CA, Poole DC, Musch TI. Dietary nitrate supplementation opposes the elevated diaphragm blood flow in chronic heart failure during submaximal exercise. Respir Physiol Neurobiol 2017; 247:140-145. [PMID: 29037770 DOI: 10.1016/j.resp.2017.09.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Revised: 09/13/2017] [Accepted: 09/29/2017] [Indexed: 02/05/2023]
Abstract
Chronic heart failure (CHF) results in a greater cost of breathing and necessitates an elevated diaphragm blood flow (BF). Dietary nitrate (NO3‾) supplementation lowers the cost of exercise. We hypothesized that dietary NO3‾ supplementation would attenuate the CHF-induced greater cost of breathing and thus the heightened diaphragm BF during exercise. CHF rats received either 5days of NO3‾-rich beetroot (BR) juice (CHF+BR, n=10) or a placebo (CHF, n=10). Respiratory muscle BFs (radiolabeled microspheres) were measured at rest and during submaximal exercise (20m/min, 5% grade). Infarcted left ventricular area and normalized lung weight were not significantly different between groups. During submaximal exercise, diaphragm BF was markedly lower for CHF+BR than CHF (CHF+BR: 195±28; CHF: 309±71mL/min/100g, p=0.04). The change in diaphragm BF from rest to exercise was less (p=0.047) for CHF+BR than CHF. These findings demonstrate that dietary NO3‾ supplementation reduces the elevated diaphragm BF during exercise in CHF rats thus providing additional support for this therapeutic intervention in CHF.
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Affiliation(s)
- Joshua R Smith
- Department of Kinesiology, Kansas State University, Manhattan, KS 66506, USA.
| | - Scott K Ferguson
- Department of Kinesiology, Kansas State University, Manhattan, KS 66506, USA; Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA
| | - K Sue Hageman
- Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA
| | - Craig A Harms
- Department of Kinesiology, Kansas State University, Manhattan, KS 66506, USA
| | - David C Poole
- Department of Kinesiology, Kansas State University, Manhattan, KS 66506, USA; Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA
| | - Timothy I Musch
- Department of Kinesiology, Kansas State University, Manhattan, KS 66506, USA; Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA
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10
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Dominelli PB, Archiza B, Ramsook AH, Mitchell RA, Peters CM, Molgat-Seon Y, Henderson WR, Koehle MS, Boushel R, Sheel AW. Effects of respiratory muscle work on respiratory and locomotor blood flow during exercise. Exp Physiol 2017; 102:1535-1547. [DOI: 10.1113/ep086566] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2017] [Accepted: 08/21/2017] [Indexed: 12/31/2022]
Affiliation(s)
- Paolo B. Dominelli
- School of Kinesiology; University of British Columbia; Vancouver BC Canada
| | - Bruno Archiza
- School of Kinesiology; University of British Columbia; Vancouver BC Canada
- Department of Physical Therapy; Federal University of São Carlos; São Carlos São Paulo Brazil
| | - Andrew H. Ramsook
- Centre for Heart Lung Innovation, Providence Health Care Research Institute; University of British Columbia; Vancouver BC Canada
| | - Reid A. Mitchell
- Centre for Heart Lung Innovation, Providence Health Care Research Institute; University of British Columbia; Vancouver BC Canada
| | - Carli M. Peters
- School of Kinesiology; University of British Columbia; Vancouver BC Canada
| | | | | | - Michael S. Koehle
- School of Kinesiology; University of British Columbia; Vancouver BC Canada
- Faculty of Medicine; University of British Columbia; Vancouver BC Canada
| | - Robert Boushel
- School of Kinesiology; University of British Columbia; Vancouver BC Canada
| | - A. William Sheel
- School of Kinesiology; University of British Columbia; Vancouver BC Canada
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11
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Smith JR, Hageman KS, Harms CA, Poole DC, Musch TI. Effect of chronic heart failure in older rats on respiratory muscle and hindlimb blood flow during submaximal exercise. Respir Physiol Neurobiol 2017; 243:20-26. [PMID: 28495570 DOI: 10.1016/j.resp.2017.05.002] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2017] [Revised: 05/04/2017] [Accepted: 05/04/2017] [Indexed: 11/18/2022]
Abstract
Submaximal exercise diaphragm blood flow (BF) is elevated in young chronic heart failure (CHF) rats, while it is unknown if this occurs in older animals. Respiratory and hindlimb muscle BFs (radiolabeled microspheres) were measured at rest and during submaximal exercise (20m/min, 5% grade) in older healthy (n=7) and CHF (n=6) Fischer 344X Brown Norway rats (27-29 mo old). Older CHF, compared to healthy, rats had greater (p<0.01) left ventricular end-diastolic pressure and right ventricle and lung weight (normalized to body weight). During submaximal exercise, respiratory and hindlimb muscle BFs increased (p<0.02) in both groups, while diaphragm BF was higher (CHF: 257±32; healthy: 121±9mL/min/100g, p<0.01) and hindlimb BF lower (CHF: 111±10; healthy: 133±12mL/min/100g, p=0.04) in older CHF compared to healthy rats. Submaximal exercise hindlimb BF was negatively related (r=-0.93; p=0.03) to diaphragm BF in older CHF rats. During submaximal exercise, diaphragm BF is elevated in older CHF compared to healthy rats in proportion to the compromised hindlimb BF.
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Affiliation(s)
- Joshua R Smith
- Department of Kinesiology, Kansas State University, Manhattan, KS, 66506, USA.
| | - K Sue Hageman
- Department of Anatomy and Physiology, Kansas State University, Manhattan, KS, 66506, USA
| | - Craig A Harms
- Department of Kinesiology, Kansas State University, Manhattan, KS, 66506, USA
| | - David C Poole
- Department of Kinesiology, Kansas State University, Manhattan, KS, 66506, USA; Department of Anatomy and Physiology, Kansas State University, Manhattan, KS, 66506, USA
| | - Timothy I Musch
- Department of Kinesiology, Kansas State University, Manhattan, KS, 66506, USA; Department of Anatomy and Physiology, Kansas State University, Manhattan, KS, 66506, USA
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12
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Smith JR, Hageman KS, Harms CA, Poole DC, Musch TI. Respiratory muscle blood flow during exercise: Effects of sex and ovarian cycle. J Appl Physiol (1985) 2017; 122:918-924. [PMID: 28126910 DOI: 10.1152/japplphysiol.01007.2016] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Revised: 01/11/2017] [Accepted: 01/23/2017] [Indexed: 11/22/2022] Open
Abstract
Sex and ovarian cycle have been speculated to modify respiratory muscle blood flow control during exercise, but the findings are inconclusive. We tested the hypotheses that females would have higher respiratory muscle blood flow and vascular conductance (VC) compared with males during exercise and that this difference would be accentuated in proestrus vs. ovariectomized (OVA) females. Mean arterial pressure (carotid artery catheter) and respiratory muscle blood flow (radiolabeled microspheres) were measured during moderate-intensity (24 m/min, 10% grade) exercise in male (n = 9), female (n = 9), and OVA female (n = 7) rats and near-maximal (60 m/min, 5% grade) exercise in male (n = 5) and female (n = 7) rats. At rest, diaphragm, intercostal, and transversus abdominis blood flow were not different (P = 0.33) among groups. During moderate-intensity exercise, diaphragm (M: 124 ± 16; F: 140 ± 14; OVA: 140 ± 20 ml·min-1·100 g-1), intercostal (M: 33 ± 5; F: 34 ± 5; OVA: 30 ± 5 ml·min-1·100 g-1), and transversus abdominis blood flow (M: 24 ± 4; F: 35 ± 7; OVA: 35 ± 9 ml·min-1·100 g-1) significantly increased in all groups compared with rest but were not different (P = 0.12) among groups. From rest to moderate-intensity exercise, diaphragm (P < 0.03) and transversus abdominis (P < 0.04) VC increased in all groups, whereas intercostal VC increased only for males and females (P = 0.01). No differences (P > 0.13) existed in VC among groups. During near-maximal exercise, diaphragm (M: 304 ± 62; F: 283 ± 17 ml·min-1·100 g-1), intercostal (M: 29 ± 8; F: 40 ± 6 ml·min-1·100 g-1), and transversus abdominis (M: 85 ± 14; F: 86 ± 9 ml·min-1·100 g-1) blood flow and VC were not different (P > 0.27) between males and females. These data demonstrate that respiratory muscle blood flow and vascular conductance at rest and during exercise are not affected by sex or ovarian cycle in rats.NEW & NOTEWORTHY It has been proposed that sex and ovarian cycle modulate respiratory muscle blood flow control during exercise. We demonstrate herein that neither sex nor ovarian cycle influences respiratory muscle blood flow or vascular conductance at rest or during exercise in rats.
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Affiliation(s)
- Joshua R Smith
- Department of Kinesiology, Kansas State University, Manhattan, Kansas; and
| | - K Sue Hageman
- Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas
| | - Craig A Harms
- Department of Kinesiology, Kansas State University, Manhattan, Kansas; and
| | - David C Poole
- Department of Kinesiology, Kansas State University, Manhattan, Kansas; and.,Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas
| | - Timothy I Musch
- Department of Kinesiology, Kansas State University, Manhattan, Kansas; and.,Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas
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13
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Joyner MJ, Casey DP. Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs. Physiol Rev 2015; 95:549-601. [PMID: 25834232 DOI: 10.1152/physrev.00035.2013] [Citation(s) in RCA: 415] [Impact Index Per Article: 46.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This review focuses on how blood flow to contracting skeletal muscles is regulated during exercise in humans. The idea is that blood flow to the contracting muscles links oxygen in the atmosphere with the contracting muscles where it is consumed. In this context, we take a top down approach and review the basics of oxygen consumption at rest and during exercise in humans, how these values change with training, and the systemic hemodynamic adaptations that support them. We highlight the very high muscle blood flow responses to exercise discovered in the 1980s. We also discuss the vasodilating factors in the contracting muscles responsible for these very high flows. Finally, the competition between demand for blood flow by contracting muscles and maximum systemic cardiac output is discussed as a potential challenge to blood pressure regulation during heavy large muscle mass or whole body exercise in humans. At this time, no one dominant dilator mechanism accounts for exercise hyperemia. Additionally, complex interactions between the sympathetic nervous system and the microcirculation facilitate high levels of systemic oxygen extraction and permit just enough sympathetic control of blood flow to contracting muscles to regulate blood pressure during large muscle mass exercise in humans.
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Affiliation(s)
- Michael J Joyner
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota; and Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, Iowa
| | - Darren P Casey
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota; and Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, Iowa
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Dominelli PB, Render JN, Molgat-Seon Y, Foster GE, Romer LM, Sheel AW. Oxygen cost of exercise hyperpnoea is greater in women compared with men. J Physiol 2015; 593:1965-79. [PMID: 25652549 DOI: 10.1113/jphysiol.2014.285965] [Citation(s) in RCA: 97] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Accepted: 01/20/2015] [Indexed: 12/15/2022] Open
Abstract
KEY POINTS The oxygen cost of breathing represents a significant fraction of total oxygen uptake during intense exercise. At a given ventilation, women have a greater work of breathing compared with men, and because work is linearly related to oxygen uptake we hypothesized that their oxygen cost of breathing would also be greater. For a given ventilation, women had a greater absolute oxygen cost of breathing, and this represented a greater fraction of total oxygen uptake. Regardless of sex, those who developed expiratory flow limitation had a greater oxygen cost of breathing at maximal exercise. The greater oxygen cost of breathing in women indicates that a greater fraction of total oxygen uptake (and possibly cardiac output) is directed to the respiratory muscles, which may influence blood flow distribution during exercise. ABSTRACT We compared the oxygen cost of breathing (V̇O2 RM ) in healthy men and women over a wide range of exercise ventilations (V̇E). Eighteen subjects (nine women) completed 4 days of testing. First, a step-wise maximal cycle exercise test was completed for the assessment of spontaneous breathing patterns. Next, subjects were familiarized with the voluntary hyperpnoea protocol used to estimate V̇O2 RM . During the final two visits, subjects mimicked multiple times (four to six) the breathing patterns associated with five or six different exercise stages. Each trial lasted 5 min, and on-line pressure-volume and flow-volume loops were superimposed on target loops obtained during exercise to replicate the work of breathing accurately. At ∼55 l min(-1) V̇E, V̇O2 RM was significantly greater in women. At maximal ventilation, the absolute V̇O2 RM was not different (P > 0.05) between the sexes, but represented a significantly greater fraction of whole-body V̇O2 in women (13.8 ± 1.5 vs. 9.4 ± 1.1% V̇O2). During heavy exercise at 92 and 100% V̇O2max, the unit cost of V̇E was +0.7 and +1.1 ml O2 l(-1) greater in women (P < 0.05). At V̇O2max, men and women who developed expiratory flow limitation had a significantly greater V̇O2 RM than those who did not (435 ± 44 vs. 331 ± 30 ml O2 min(-1) ). In conclusion, women have a greater V̇O2 RM for a given V̇E, and this represents a greater fraction of whole-body V̇O2. The greater V̇O2 RM in women may have implications for the integrated physiological response to exercise.
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Affiliation(s)
- Paolo B Dominelli
- School of Kinesiology, University of British Columbia, Vancouver, BC, Canada
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Abstract
During dynamic exercise, the healthy pulmonary system faces several major challenges, including decreases in mixed venous oxygen content and increases in mixed venous carbon dioxide. As such, the ventilatory demand is increased, while the rising cardiac output means that blood will have considerably less time in the pulmonary capillaries to accomplish gas exchange. Blood gas homeostasis must be accomplished by precise regulation of alveolar ventilation via medullary neural networks and sensory reflex mechanisms. It is equally important that cardiovascular and pulmonary system responses to exercise be precisely matched to the increase in metabolic requirements, and that the substantial gas transport needs of both respiratory and locomotor muscles be considered. Our article addresses each of these topics with emphasis on the healthy, young adult exercising in normoxia. We review recent evidence concerning how exercise hyperpnea influences sympathetic vasoconstrictor outflow and the effect this might have on the ability to perform muscular work. We also review sex-based differences in lung mechanics.
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Affiliation(s)
- Andrew William Sheel
- The School of Kinesiology, The University of British Columbia, Vancouver, Canada.
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16
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Abstract
Evolutionary forces drive beneficial adaptations in response to a complex array of environmental conditions. In contrast, over several millennia, humans have been so enamored by the running/athletic prowess of horses and dogs that they have sculpted their anatomy and physiology based solely upon running speed. Thus, through hundreds of generations, those structural and functional traits crucial for running fast have been optimized. Central among these traits is the capacity to uptake, transport and utilize oxygen at spectacular rates. Moreover, the coupling of the key systems--pulmonary-cardiovascular-muscular is so exquisitely tuned in horses and dogs that oxygen uptake response kinetics evidence little inertia as the animal transitions from rest to exercise. These fast oxygen uptake kinetics minimize Intramyocyte perturbations that can limit exercise tolerance. For the physiologist, study of horses and dogs allows investigation not only of a broader range of oxidative function than available in humans, but explores the very limits of mammalian biological adaptability. Specifically, the unparalleled equine cardiovascular and muscular systems can transport and utilize more oxygen than the lungs can supply. Two consequences of this situation, particularly in the horse, are profound exercise-induced arterial hypoxemia and hypercapnia as well as structural failure of the delicate blood-gas barrier causing pulmonary hemorrhage and, in the extreme, overt epistaxis. This chapter compares and contrasts horses and dogs with humans with respect to the structural and functional features that enable these extraordinary mammals to support their prodigious oxidative and therefore athletic capabilities.
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Affiliation(s)
- David C Poole
- Departments of Kinesiology, Anatomy and Physiology, Kansas State University, Manhattan, KS, USA.
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Franklin SH, Van Erck-Westergren E, Bayly WM. Respiratory responses to exercise in the horse. Equine Vet J 2012; 44:726-32. [DOI: 10.1111/j.2042-3306.2012.00666.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- S. H. Franklin
- School of Animal and Veterinary Sciences; University of Adelaide; South Australia; Australia
| | | | - W. M. Bayly
- Office of the Provost; Washington State University; Washington; USA
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18
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Guenette JA, Henderson WR, Dominelli PB, Querido JS, Brasher PM, Griesdale DEG, Boushel R, Sheel AW. Blood flow index using near-infrared spectroscopy and indocyanine green as a minimally invasive tool to assess respiratory muscle blood flow in humans. Am J Physiol Regul Integr Comp Physiol 2011; 300:R984-92. [DOI: 10.1152/ajpregu.00739.2010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Near-infrared spectroscopy (NIRS) in combination with indocyanine green (ICG) dye has recently been used to measure respiratory muscle blood flow (RMBF) in humans. This method is based on the Fick principle and is determined by measuring ICG in the respiratory muscles using transcutaneous NIRS in relation to the [ICG] in arterial blood as measured using photodensitometry. This method is invasive since it requires arterial cannulation, repeated blood withdrawals, and reinfusions. A less invasive alternative is to calculate a relative measure of blood flow known as the blood flow index (BFI), which is based solely on the NIRS ICG curve, thus negating the need for arterial cannulation. Accordingly, the purpose of this study was to determine whether BFI can be used to measure RMBF at rest and during voluntary isocapnic hyperpnea at 25, 40, 55, and 70% of maximal voluntary ventilation in seven healthy humans. BFI was calculated as the change in maximal [ICG] divided by the rise time of the NIRS-derived ICG curve. Intercostal and sternocleidomastoid muscle BFI were correlated with simultaneously measured work of breathing and electromyography (EMG) data from the same muscles. BFI showed strong relationships with the work of breathing and EMG for both respiratory muscles. The coefficients of determination ( R2) comparing BFI vs. the work of breathing for the intercostal and sternocleidomastoid muscles were 0.887 ( P < 0.001) and 0.863 ( P < 0.001), respectively, whereas the R2 for BFI vs. EMG for the intercostal and sternocleidomastoid muscles were 0.879 ( P < 0.001) and 0.930 ( P < 0.001), respectively. These data suggest that the BFI closely reflects RMBF in conscious humans across a wide range of ventilations and provides a less invasive and less technically demanding alternative to measuring RMBF.
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Affiliation(s)
- Jordan A. Guenette
- School of Human Kinetics, University of British Columbia, Vancouver, British Columbia, Canada
| | - William R. Henderson
- School of Human Kinetics, University of British Columbia, Vancouver, British Columbia, Canada
- UBC Program of Critical Care Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Paolo B. Dominelli
- School of Human Kinetics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Jordan S. Querido
- School of Human Kinetics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Penelope M. Brasher
- Centre for Clinical Epidemiology and Evaluation, Vancouver Coastal Health Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Donald E. G. Griesdale
- UBC Program of Critical Care Medicine, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada; and
| | - Robert Boushel
- Center for Healthy Aging, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | - A. William Sheel
- School of Human Kinetics, University of British Columbia, Vancouver, British Columbia, Canada
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Guenette JA, Vogiatzis I, Zakynthinos S, Athanasopoulos D, Koskolou M, Golemati S, Vasilopoulou M, Wagner HE, Roussos C, Wagner PD, Boushel R. Human respiratory muscle blood flow measured by near-infrared spectroscopy and indocyanine green. J Appl Physiol (1985) 2008; 104:1202-10. [DOI: 10.1152/japplphysiol.01160.2007] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Measurement of respiratory muscle blood flow (RMBF) in humans has important implications for understanding patterns of blood flow distribution during exercise in healthy individuals and those with chronic disease. Previous studies examining RMBF in humans have required invasive methods on anesthetized subjects. To assess RMBF in awake subjects, we applied an indicator-dilution method using near-infrared spectroscopy (NIRS) and the light-absorbing tracer indocyanine green dye (ICG). NIRS optodes were placed on the left seventh intercostal space at the apposition of the costal diaphragm and on an inactive control muscle (vastus lateralis). The primary respiratory muscles within view of the NIRS optodes include the internal and external intercostals. Intravenous bolus injection of ICG allowed for cardiac output (by the conventional dye-dilution method with arterial sampling), RMBF, and vastus lateralis blood flow to be quantified simultaneously. Esophageal and gastric pressures were also measured to calculate the work of breathing and transdiaphragmatic pressure. Measurements were obtained in five conscious humans during both resting breathing and three separate 5-min bouts of constant isocapnic hyperpnea at 27.1 ± 3.2, 56.0 ± 6.1, and 75.9 ± 5.7% of maximum minute ventilation as determined on a previous maximal exercise test. RMBF progressively increased (9.9 ± 0.6, 14.8 ± 2.7, 29.9 ± 5.8, and 50.1 ± 12.5 ml·100 ml−1·min−1, respectively) with increasing levels of ventilation while blood flow to the inactive control muscle remained constant (10.4 ± 1.4, 8.7 ± 0.7, 12.9 ± 1.7, and 12.2 ± 1.8 ml·100 ml−1·min−1, respectively). As ventilation rose, RMBF was closely and significantly correlated with 1) cardiac output ( r = 0.994, P = 0.006), 2) the work of breathing ( r = 0.995, P = 0.005), and 3) transdiaphragmatic pressure ( r = 0.998, P = 0.002). These data suggest that the NIRS-ICG technique provides a feasible and sensitive index of RMBF at different levels of ventilation in humans.
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20
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Romer LM, Polkey MI. Exercise-induced respiratory muscle fatigue: implications for performance. J Appl Physiol (1985) 2008; 104:879-88. [DOI: 10.1152/japplphysiol.01157.2007] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
It is commonly held that the respiratory system has ample capacity relative to the demand for maximal O2and CO2transport in healthy humans exercising near sea level. However, this situation may not apply during heavy-intensity, sustained exercise where exercise may encroach on the capacity of the respiratory system. Nerve stimulation techniques have provided objective evidence that the diaphragm and abdominal muscles are susceptible to fatigue with heavy, sustained exercise. The fatigue appears to be due to elevated levels of respiratory muscle work combined with an increased competition for blood flow with limb locomotor muscles. When respiratory muscles are prefatigued using voluntary respiratory maneuvers, time to exhaustion during subsequent exercise is decreased. Partially unloading the respiratory muscles during heavy exercise using low-density gas mixtures or mechanical ventilation can prevent exercise-induced diaphragm fatigue and increase exercise time to exhaustion. Collectively, these findings suggest that respiratory muscle fatigue may be involved in limiting exercise tolerance or that other factors, including alterations in the sensation of dyspnea or mechanical load, may be important. The major consequence of respiratory muscle fatigue is an increased sympathetic vasoconstrictor outflow to working skeletal muscle through a respiratory muscle metaboreflex, thereby reducing limb blood flow and increasing the severity of exercise-induced locomotor muscle fatigue. An increase in limb locomotor muscle fatigue may play a pivotal role in determining exercise tolerance through a direct effect on muscle force output and a feedback effect on effort perception, causing reduced motor output to the working limb muscles.
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21
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Manohar M, Goetz TE. Intrapulmonary arteriovenous shunts of >15 microm in diameter probably do not contribute to arterial hypoxemia in maximally exercising Thoroughbred horses. J Appl Physiol (1985) 2005; 99:224-9. [PMID: 15774703 DOI: 10.1152/japplphysiol.01230.2004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The present study examined whether Thoroughbred horses performing strenuous exercise exhibit intrapulmonary arteriovenous shunting that may contribute to the observed arterial hypoxemia. Experiments were carried out on seven healthy, exercise-trained Thoroughbreds at rest, maximal exercise (galloping at 14 m/s on a 3.5% uphill grade for 120 s), and submaximal exertion (8 m/s on a 3.5% uphill grade for 150 s). Along with blood gas/hemodynamic parameters, intrapulmonary arteriovenous shunting was studied by injecting 15-microm-diameter microspheres, labeled with different stable isotopes, into the right atrium while simultaneous blood samples were being withdrawn at a constant rate from the pulmonary artery and the aorta. Arterial hypoxemia was observed only during maximal exercise. Also, despite significant pulmonary arterial hypertension during submaximal and maximal exertion, 15-microm microspheres did not traverse the pulmonary microcirculation to appear in the aortic blood. Thus our findings did not support a role for intrapulmonary arteriovenous shunts of >15 microm in diameter in the exercise-induced arterial hypoxemia in racehorses. Interestingly, our observation that, in going from 30 to 120 s of maximal exertion, arterial O2 tension had remained unchanged despite significant reductions in mixed venous blood O2 tension, hemoglobin-O2 saturation, and O2 content also discounts the importance of intrapulmonary arteriovenous shunts in causing arterial hypoxemia. This is because, assuming that a constant fraction of total pulmonary blood flow bypasses the gas-exchange areas of the equine lungs via intrapulmonary arteriovenous shunts during 30-120 s of maximal exertion, the observed significant reductions in mixed venous blood oxygenation should cause a significant reduction in arterial O2 tension, which was not the case in our horses. Thus it is suggested that intrapulmonary arteriovenous shunting probably does not contribute to the exercise-induced arterial hypoxemia in racehorses.
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Affiliation(s)
- Murli Manohar
- Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61802, USA.
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22
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Poole DC, Petrisko RN, Anderson L, Fedde MR, Erickson HH. Structural and oxidative enzyme characteristics of the diaphragm. Equine Vet J 2002:459-63. [PMID: 12405734 DOI: 10.1111/j.2042-3306.2002.tb05466.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
During exercise, the horse can achieve oxygen uptakes and ventilations in excess of 200 ml/kg/min and 1800 l/min, respectively. Whether the diaphragm has the capacity to contribute substantially to inspiratory effort in the exercising horse is not known. To investigate the potential for the horse diaphragm to generate tension, lung displacement and sustain ventilatory function, we measured diaphragm thickness, muscle length and oxidative enzyme activity (citrate synthase) within the ventral, medial and dorsal costal and crural diaphragm. In the diaphragms of 6 mature horses (5 Thoroughbreds, one Quarter Horse; body mass (mean +/- s.e.) 475 +/- 14 kg, age 4 +/- 1 years), the mass of the freshly-excised diaphragm was 4.54 +/- 0.19 kg of which 79% was the costal diaphragm, 17% the crural diaphragm and 4% the central tendon. The medial costal region (2.1 +/- 0.1 cm) was significantly thicker (P<0.05) than either the ventral (1.4 +/- 0.1 cm) or dorsal (1.2 +/- 0.2 cm) costal regions and the crural diaphragm was significantly thicker (>3.2 +/- 0.3 cm, P<0.05) than any costal diaphragm region. With respect to the costal diaphragm, excised muscle length was greatest (P<0.05) in the medial costal (17.2 +/- 1.0 cm) than either the ventral costal (<12.6 +/- 1.5 cm) or dorsal costal (<13.9 +/- 1.8 cm) regions and therefore the medial region would be expected to exhibit the greatest absolute length change on inspiration. Citrate synthase activity was high throughout the diaphragm (40.8 +/- 113 to 55.3 +/- 9.7 micromol/g/min), but was not significantly different among regions. These structural characteristics and the oxidative potential of the horse diaphragm are consistent with the diaphragm providing a significant and substantial contribution to the inspiratory effort during exercise in the horse. Consequently, clinical and physiological investigations of exercise performance should not ignore the potentially crucial importance of the diaphragm.
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Affiliation(s)
- D C Poole
- Department of Kinesiology, Kansas State University, Manhattan 66506-5802, USA
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23
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Poole DC, Kindig CA, Fenton G, Ferguson L, Rush BR, Erickson HH. Effects of external nasal support on pulmonary gas exchange and EIPH in the horse. J Equine Vet Sci 2000. [DOI: 10.1016/s0737-0806(00)70266-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Rafferty GF, Lou Harris M, Polkey MI, Greenough A, Moxham J. Effect of hypercapnia on maximal voluntary ventilation and diaphragm fatigue in normal humans. Am J Respir Crit Care Med 1999; 160:1567-71. [PMID: 10556122 DOI: 10.1164/ajrccm.160.5.9801114] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Relatively little is known about the combined effects of hypercapnia and fatigue on the human diaphragm. We examined the effects of acute hypercapnia and fatigue in seven subjects by measuring changes in transdiaphragmatic pressure (Pdi) elicited by cervical magnetic stimulation after 2 min maximal voluntary ventilation (MVV) while breathing air and also with the inspired PCO(2) increased to 8% for 12 min before and during the MVV. Diaphragm strength was assessed before and at 0, 20, 40, 60, and 90 min after the MVV in both studies with the subjects breathing air. There was no difference in the level of ventilation for each run. Mean (+/- SD) twitch Pdi (TwPdi) fell significantly (p < 0.01) at 20 min after the control and hypercapnic MVV; (30.4 [7.8] to 27.0 [8.1] cm H(2)O control and 30.3 [4.1] to 27.3 [5.0] cm H(2)O CO(2)) and remained significantly (p < 0.01) below baseline. The changes in TwPdi at 20 to 90 min were not significantly different between the control and CO(2) runs. The decrease in TwPdi at 0 min after MVV, however, was greater (15%) in the hypercapnic run than in the control run (8.1%) (p < 0.05) when compared with baseline valves. Hypercapnia does not intensify long lasting fatigue but may reduce diaphragm contractility immediately after MVV.
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Affiliation(s)
- G F Rafferty
- Department of Child Health, Guy's, King's and St. Thomas' School of Medicine, London, United Kingdom
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25
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Manohar M, Goetz TE. Pulmonary vascular resistance of horses decreases with moderate exercise and remains unchanged as workload is increased to maximal exercise. Equine Vet J 1999:117-21. [PMID: 10659234 DOI: 10.1111/j.2042-3306.1999.tb05200.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
This study was carried out to examine changes in pulmonary vascular resistance (PVR) induced by moderate and strenuous exercise; the objective being to understand why pulmonary artery blood pressure of exercising horses increases progressively as work intensity increases. Pulmonary arterial and wedge pressures (referenced at the point of the left shoulder) were determined simultaneously with cardiac output in 2 groups of healthy, sound, exercise-trained horses. Horses in Group 1 (n = 8) were studied at rest and during exercise performed at 8 and 13 m/s; the latter workload eliciting maximal heart rate (mean +/- s.e. 212 +/- 3 beats/min). Horses in Group 2 (n = 7 Thoroughbreds) were studied at rest and during galloping at 14.5 m/s on 5% uphill grade, a workload which elicited maximal heart rate (217 +/- 3 beats/min) and could not be sustained for > 90 s. Pulmonary vascular resistance was calculated by dividing pulmonary perfusion pressure gradient (i.e. mean pulmonary arterial pressure minus mean pulmonary wedge pressure) with cardiac output. Pulmonary arterial and wedge pressures, pulmonary perfusion pressure gradient and cardiac output increased significantly (P < 0.05) with exercise in both groups. There were no differences in PVR between the 2 groups of horses at rest. In Group 1 horses PVR decreased significantly (P < 0.05) with exercise at 8 m/s, but further pulmonary vasodilation did not occur as workload increased to 13 m/s. During exercise at 14.5 m/s on 5% grade, PVR of Group 2 horses also decreased significantly and was not different from values for 8 or 13 m/s in Group 1 horses. It is concluded that PVR reaches its nadir during moderate exercise, presumably due to upper limit of recruitment and distension having been reached. Therefore, in accordance with Ohm's law (P alpha Q x PVR), in going to higher workloads pulmonary blood flow (Q) remained the sole determinant of the rise in pulmonary arterial blood pressure (P). Our data also indicate that pulmonary artery wedge pressure is another variable that is important in determining the absolute value of pulmonary arterial blood pressure.
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Affiliation(s)
- M Manohar
- Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign 61801, USA
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26
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Ainsworth DM, Eicker SW, Nalevanko ME, Ducharme NG, Hackett RP, Snedden K. The effect of exercise on diaphragmatic activation in horses. RESPIRATION PHYSIOLOGY 1996; 106:35-46. [PMID: 8946575 DOI: 10.1016/0034-5687(96)00058-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Horses chronically-instrumented with costal diaphragmatic electromyographic electrodes were studied during exercise while unencumbered by a breathing mask. Exercise-associated changes in esophageal (Pes), gastric (Pga) and transdiaphragmatic (Pdi) pressures were measured and related to diaphragmatic electromyographic activity (CS EMG) and to left forelimb impact. In all breaths examined, CS EMG always coincided with decrements in Pes. For all exercise trials, linear increases in CS EMG, Pga and Pdi and linear decreases in Pes, as a function of exercise intensity, always occurred. During all gaits, breathing frequency (fR) was entrained with stride frequency (fS) one for one. However, a constant phase-coupling relationship between fR and fS, observed when horses cantered and galloped, was absent when horses walked or trotted. We conclude that biomechanical forces contribute minimally to ventilation in exercising horses, that the diaphragm is always phasically active during each breath and its total electrical activity and mechanical output are proportional to the exercise hyperpnea.
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Affiliation(s)
- D M Ainsworth
- Department of Clinical Sciences College of Veterinary Medicine, Cornell University, Ithaca, NY 14850, USA
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Uribe JM, Stump CS, Tipton CM, Fregosi RF. Influence of exercise training on the oxidative capacity of rat abdominal muscles. RESPIRATION PHYSIOLOGY 1992; 88:171-80. [PMID: 1626136 DOI: 10.1016/0034-5687(92)90038-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Our purpose was to determine if endurance exercise training would increase the oxidative capacity of the abdominal expiratory muscles of the rat. Accordingly, 9 male rats were subjected to an endurance training protocol (1 h/day, 6 days/week, 9 weeks) and 9 litter-mates served as controls. Citrate synthase (CS) activity was used as an index of oxidative capacity, and was determined in the following muscles: soleus, plantaris, costal diaphragm, crural diaphragm, and in all four abdominal muscles: rectus abdominis, transversus abdominis, external oblique, and internal oblique. Compared to their non-trained litter-mates, the trained rats had higher peak whole body oxygen consumption rates (+ 16%) and CS activities in plantaris (+34%) and soleus (+36%) muscles. Thus, the training program caused substantial systemic and locomotor muscle adaptations. The CS activity of costal diaphragm was 20% greater in the trained animals, but no difference was observed in crural diaphragm. The CS activity in the abdominal muscles was less than one-half of that in locomotor and diaphragm muscles, and there were no significant changes with training except in the rectus abdominis where a 26% increase was observed. The increase in rectus abdominis CS activity may reflect its role in postural support and/or locomotion, as none of the primary expiratory pumping muscles adapted to the training protocol. The relatively low levels of CS activity in the abdominal muscles suggests that they are not recruited frequently at rest, and the lack of an increase with training indicates that these muscles do not contribute significantly to the increased ventilatory activity accompanying exercise in the rat.
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Affiliation(s)
- J M Uribe
- Department of Exercise and Sports Sciences, Arizona Health Sciences Center, University of Arizona, Tucson 85721
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