1
|
Welch JF, Mitchell GS. Inaugural Review Prize 2023: The exercise hyperpnoea dilemma: A 21st-century perspective. Exp Physiol 2024; 109:1217-1237. [PMID: 38551996 PMCID: PMC11291877 DOI: 10.1113/ep091506] [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] [Received: 01/28/2024] [Accepted: 03/12/2024] [Indexed: 08/02/2024]
Abstract
During mild or moderate exercise, alveolar ventilation increases in direct proportion to metabolic rate, regulating arterial CO2 pressure near resting levels. Mechanisms giving rise to the hyperpnoea of exercise are unsettled despite over a century of investigation. In the past three decades, neuroscience has advanced tremendously, raising optimism that the 'exercise hyperpnoea dilemma' can finally be solved. In this review, new perspectives are offered in the hope of stimulating original ideas based on modern neuroscience methods and current understanding. We first describe the ventilatory control system and the challenge exercise places upon blood-gas regulation. We highlight relevant system properties, including feedforward, feedback and adaptive (i.e., plasticity) control of breathing. We then elaborate a seldom explored hypothesis that the exercise ventilatory response continuously adapts (learns and relearns) throughout life and ponder if the memory 'engram' encoding the feedforward exercise ventilatory stimulus could reside within the cerebellum. Our hypotheses are based on accumulating evidence supporting the cerebellum's role in motor learning and the numerous direct and indirect projections from deep cerebellar nuclei to brainstem respiratory neurons. We propose that cerebellar learning may be obligatory for the accurate and adjustable exercise hyperpnoea capable of tracking changes in life conditions/experiences, and that learning arises from specific cerebellar microcircuits that can be interrogated using powerful techniques such as optogenetics and chemogenetics. Although this review is speculative, we consider it essential to reframe our perspective if we are to solve the till-now intractable exercise hyperpnoea dilemma.
Collapse
Affiliation(s)
- Joseph F. Welch
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental SciencesUniversity of BirminghamEdgbastonBirminghamUK
| | - Gordon S. Mitchell
- Breathing Research and Therapeutics Centre, Department of Physical Therapy, McKnight Brain InstituteUniversity of FloridaGainesvilleFloridaUSA
| |
Collapse
|
2
|
Ito G, Feeley M, Sawai T, Nakata H, Otsuki S, Nakahara H, Miyamoto T. High-intensity interval training improves respiratory and cardiovascular adjustments before and after initiation of exercise. Front Physiol 2024; 15:1227316. [PMID: 38529482 PMCID: PMC10961378 DOI: 10.3389/fphys.2024.1227316] [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: 05/23/2023] [Accepted: 02/26/2024] [Indexed: 03/27/2024] Open
Abstract
Purpose: High-intensity interval training (HIIT) may induce training-specific physiological adaptations such as improved respiratory and cardiovascular adjustments before and after the onset of high-intensity exercise, leading to improved exercise performance during high-intensity exercise. The present study investigated the effects of HIIT on time-dependent cardiorespiratory adjustment during maximal exercise and before and after initiation of high-intensity exercise, as well as on maximal exercise performance. Methods: 21 healthy male college students were randomly assigned to HIIT group (n = 11) or control group (n = 10). HIIT group performed training on a cycle ergometer once a week for 8 weeks. The training consisted of three bouts of exercise at 95% maximal work rate (WRmax) until exhaustion. Before and after the HIIT program, dynamic cardiorespiratory function was investigated by ramp and step exercise tests, and HIIT-induced cardiac morphological changes were assessed using echocardiography. Results: HIIT significantly improved not only maximal oxygen uptake and minute ventilation, but also maximal heart rate (HR), systolic blood pressure (SBP), and time to exhaustion in both exercise tests (p < 0.05). Time-dependent increases in minute ventilation (VE) and HR before and at the start of exercise were significantly enhanced after HIIT. During high-intensity exercise, there was a strong correlation between percent change (from before to after HIIT program) in time to exhaustion and percent change in HRmax (r = 0.932, p < 0.001). Furthermore, HIIT-induced cardiac morphological changes such as ventricular wall hypertrophy was observed (p < 0.001). Conclusion: We have demonstrated that HIIT at 95% WRmax induces training-specific adaptations such as improved cardiorespiratory adjustments, not only during maximal exercise but also before and after the onset of high-intensity exercise, improvement of exercise performance mainly associated with circulatory systems.
Collapse
Affiliation(s)
- Go Ito
- Graduate School of Human Environment, Osaka Sangyo University, Daito City, Osaka, Japan
| | - Marina Feeley
- Graduate School of Human Environment, Osaka Sangyo University, Daito City, Osaka, Japan
| | - Toru Sawai
- Department of Sport and Health Sciences, Faculty of Sport and Health Sciences, Osaka Sangyo University, Daito City, Osaka, Japan
| | - Hideomi Nakata
- Graduate School of Human Environment, Osaka Sangyo University, Daito City, Osaka, Japan
- Department of Sport and Health Sciences, Faculty of Sport and Health Sciences, Osaka Sangyo University, Daito City, Osaka, Japan
| | - Shingo Otsuki
- Graduate School of Human Environment, Osaka Sangyo University, Daito City, Osaka, Japan
- Department of Sport and Health Sciences, Faculty of Sport and Health Sciences, Osaka Sangyo University, Daito City, Osaka, Japan
| | - Hidehiro Nakahara
- Graduate School of Health Sciences, Morinomiya University of Medical Sciences, Osaka City, Osaka, Japan
| | - Tadayoshi Miyamoto
- Graduate School of Human Environment, Osaka Sangyo University, Daito City, Osaka, Japan
- Department of Sport and Health Sciences, Faculty of Sport and Health Sciences, Osaka Sangyo University, Daito City, Osaka, Japan
| |
Collapse
|
3
|
Yamashiro SM, Kato T, Matsumoto T. Modeling Long-Term Facilitation of Respiration During Interval Exercise in Humans. Ann Biomed Eng 2024; 52:250-258. [PMID: 37752293 PMCID: PMC11255076 DOI: 10.1007/s10439-023-03366-z] [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: 05/04/2023] [Accepted: 09/06/2023] [Indexed: 09/28/2023]
Abstract
Long-term facilitation (LTF) of respiration has been mainly initiated by intermittent hypoxia and resultant chemoreceptor stimulation in humans. Comparable levels of chemoreceptor stimulation can occur in combined exercise and carbon dioxide (CO2) inhalation and lead to LTF. This possibility was supported by data collected during combined interval exercise and 3% inhaled CO2 in seven normal subjects. These data were further analyzed based on the dynamics involved using mathematical models in this study. Previously estimated peripheral chemoreceptor sensitivity during light exercise (40 W) with air or 3% inhaled CO2 approximately doubled resting sensitivity. Ventilation after a delay increased by 17.0 ± 2.48 L/min (p < 0.001) during recovery following 45% maximal oxygen uptake ([Formula: see text] ) exercise consistent with LTF which exceeded what can be achieved with intermittent hypoxia. Model fitting of the dynamic responses was used to separate neural from chemoreceptor-mediated CO2 responses. Exercise of 45% [Formula: see text] was followed by ventilation augmentation following initial recovery. Augmentation of LTF developed slowly according to second-order dynamics in accordance with plasticity involving a balance between self-excitatory and self-inhibitory neuronal pools.
Collapse
Affiliation(s)
- Stanley M Yamashiro
- Biomedical Engineering Department, University of Southern California, Los Angeles, CA, 90089-1111, USA.
- Biomedical Engineering Department, University of Southern California, 1042 Downey Way, Denny Research Center, Room 140, Los Angeles, CA, 90089-1111, USA.
| | - Takahide Kato
- Department of General Education, National Institute of Technology, Toyota College, Toyota, 471-8525, Japan
| | - Takaaki Matsumoto
- School of Health and Sport Sciences, Chukyo University, Toyota, 470-0393, Japan
| |
Collapse
|
4
|
Dempsey JA, Welch JF. Control of Breathing. Semin Respir Crit Care Med 2023; 44:627-649. [PMID: 37494141 DOI: 10.1055/s-0043-1770342] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/28/2023]
Abstract
Substantial advances have been made recently into the discovery of fundamental mechanisms underlying the neural control of breathing and even some inroads into translating these findings to treating breathing disorders. Here, we review several of these advances, starting with an appreciation of the importance of V̇A:V̇CO2:PaCO2 relationships, then summarizing our current understanding of the mechanisms and neural pathways for central rhythm generation, chemoreception, exercise hyperpnea, plasticity, and sleep-state effects on ventilatory control. We apply these fundamental principles to consider the pathophysiology of ventilatory control attending hypersensitized chemoreception in select cardiorespiratory diseases, the pathogenesis of sleep-disordered breathing, and the exertional hyperventilation and dyspnea associated with aging and chronic diseases. These examples underscore the critical importance that many ventilatory control issues play in disease pathogenesis, diagnosis, and treatment.
Collapse
Affiliation(s)
- Jerome A Dempsey
- John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, University of Wisconsin, Madison, Wisconsin
| | - Joseph F Welch
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
| |
Collapse
|
5
|
Apicella R, Taccola G. Passive limb training modulates respiratory rhythmic bursts. Sci Rep 2023; 13:7226. [PMID: 37142670 PMCID: PMC10160044 DOI: 10.1038/s41598-023-34422-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 04/29/2023] [Indexed: 05/06/2023] Open
Abstract
Exercise modifies respiratory functions mainly through the afferent feedback provided by exercising limbs and the descending input from suprapontine areas, two contributions that are still underestimated in vitro. To better characterize the role of limb afferents in modulating respiration during physical activity, we designed a novel experimental in vitro platform. The whole central nervous system was isolated from neonatal rodents and kept with hindlimbs attached to an ad-hoc robot (Bipedal Induced Kinetic Exercise, BIKE) driving passive pedaling at calibrated speeds. This setting allowed extracellular recordings of a stable spontaneous respiratory rhythm for more than 4 h, from all cervical ventral roots. BIKE reversibly reduced the duration of single respiratory bursts even at lower pedaling speeds (2 Hz), though only an intense exercise (3.5 Hz) modulated the frequency of breathing. Moreover, brief sessions (5 min) of BIKE at 3.5 Hz augmented the respiratory rate of preparations with slow bursting in control (slower breathers) but did not change the speed of faster breathers. When spontaneous breathing was accelerated by high concentrations of potassium, BIKE reduced bursting frequency. Regardless of the baseline respiratory rhythm, BIKE at 3.5 Hz always decreased duration of single bursts. Surgical ablation of suprapontine structures completely prevented modulation of breathing after intense training. Albeit the variability in baseline breathing rates, intense passive cyclic movement tuned fictive respiration toward a common frequency range and shortened all respiratory events through the involvement of suprapontine areas. These observations contribute to better define how the respiratory system integrates sensory input from moving limbs during development, opening new rehabilitation perspectives.
Collapse
Affiliation(s)
- Rosamaria Apicella
- Neuroscience Department, International School for Advanced Studies (SISSA), Via Bonomea 265, Trieste, Italy
- Applied Neurophysiology and Neuropharmacology Lab, Istituto Di Medicina Fisica E Riabilitazione (IMFR), Via Gervasutta 48, Udine, UD, Italy
| | - Giuliano Taccola
- Neuroscience Department, International School for Advanced Studies (SISSA), Via Bonomea 265, Trieste, Italy.
- Applied Neurophysiology and Neuropharmacology Lab, Istituto Di Medicina Fisica E Riabilitazione (IMFR), Via Gervasutta 48, Udine, UD, Italy.
| |
Collapse
|
6
|
Miyamoto T, Sotobayashi D, Ito G, Kawai E, Nakahara H, Ueda S, Toyama T, Saku K, Nakanishi Y, Kinoshita H. Physiological role of anticipatory cardiorespiratory responses to exercise. Physiol Rep 2022; 10:e15210. [PMID: 35246949 PMCID: PMC8897741 DOI: 10.14814/phy2.15210] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Accepted: 02/08/2022] [Indexed: 06/14/2023] Open
Abstract
This study aimed to investigate whether anticipatory cardiorespiratory responses vary depending on the intensity of the subsequent exercise bout, and whether anticipatory cardiorespiratory adjustments contribute importantly to enhancing exercise performance during high-intensity exercise. Eleven healthy men were provided advance notice of the exercise intensity and a countdown to generate anticipation during 10 min prior to exercise at 0, 50, 80 or 95% maximal work-rate (Experiment 1). A different group of subjects (n = 15) performed a time to exhaustion trial with or without anticipatory countdown (Experiment 2). In Experiment 1, heart rate (HR), oxygen uptake (VO2 ) and minute ventilation (VE ) during pre-exercise resting period increased over time and depended on the subsequent exercise intensity. Specifically, there was already a 7.4% increase in HR from more than 5 min prior to the start of exercise at 95% maximal work-rate, followed by progressively augmented increases of 12.5% between 2 and 3 min before exercise, 24.4% between 0 and 1 min before exercise. In Experiment 2, the initial HR for the first 10 s of exercise in the task with anticipation was 11.4% larger compared to without anticipation (p < 0.01), and the difference in HR between the two conditions decreased in a time-dependent manner. In contrast, the initial increases in VO2 and VE were significantly lower in the task with anticipation than that without anticipation. The time to exhaustion during high-intensity exercise was 14.6% longer under anticipation condition compared to no anticipation (135 ± 26 s vs. 119 ± 26 s, p = 0.003). In addition, the enhanced exercise performance correlated positively with increased HR response just before and immediately after exercise onset (p < 0.01). These results showed that anticipatory cardiorespiratory adjustments (feedforward control) via the higher brain that operate before starting exercise may play an important role in minimizing the time delay of circulatory response and enhancing performance after onset of high-intensity exercise in man.
Collapse
Affiliation(s)
- Tadayoshi Miyamoto
- Division of Human EnvironmentGraduate School of Human EnvironmentOsaka Sangyo UniversityDaito CityOsakaJapan
- Department of Sport and Health SciencesFaculty of Sport and Health SciencesOsaka Sangyo UniversityDaito CityOsakaJapan
- Department of Cardiovascular DynamicsNational Cerebral and Cardiovascular Center Research InstituteSuita CityOsakaJapan
| | - Daisuke Sotobayashi
- Department of EducationFaculty of EducationOsaka Seikei UniversityOsaka CityOsakaJapan
| | - Go Ito
- Division of Human EnvironmentGraduate School of Human EnvironmentOsaka Sangyo UniversityDaito CityOsakaJapan
| | - Eriko Kawai
- Laboratory for Pathophysiological and Health ScienceRIKEN Center for Biosystems Dynamics ResearchKobe CityHyogoJapan
| | - Hidehiro Nakahara
- Graduate School of Health SciencesMorinomiya University of Medical SciencesOsaka CityOsakaJapan
| | - Shinya Ueda
- Department of Physical EducationFaculty of EducationGifu UniversityGifu CityGifuJapan
| | - Takeshi Toyama
- Faculty of Medical SciencesKyushu UniversityFukuoka CityFukuokaJapan
| | - Keita Saku
- Department of Cardiovascular DynamicsNational Cerebral and Cardiovascular Center Research InstituteSuita CityOsakaJapan
| | - Yasuto Nakanishi
- Department of Sport and Health SciencesFaculty of Sport and Health SciencesOsaka Sangyo UniversityDaito CityOsakaJapan
| | - Hiroshi Kinoshita
- Center for Common EducationOsaka Aoyama UniversityMinoh CityOsakaJapan
| |
Collapse
|
7
|
Mitchell GS, Baker TL. Respiratory neuroplasticity: Mechanisms and translational implications of phrenic motor plasticity. HANDBOOK OF CLINICAL NEUROLOGY 2022; 188:409-432. [PMID: 35965036 DOI: 10.1016/b978-0-323-91534-2.00016-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Widespread appreciation that neuroplasticity is an essential feature of the neural system controlling breathing has emerged only in recent years. In this chapter, we focus on respiratory motor plasticity, with emphasis on the phrenic motor system. First, we define related but distinct concepts: neuromodulation and neuroplasticity. We then focus on mechanisms underlying two well-studied models of phrenic motor plasticity: (1) phrenic long-term facilitation following brief exposure to acute intermittent hypoxia; and (2) phrenic motor facilitation after prolonged or recurrent bouts of diminished respiratory neural activity. Advances in our understanding of these novel and important forms of plasticity have been rapid and have already inspired translation in multiple respects: (1) development of novel therapeutic strategies to preserve/restore breathing function in humans with severe neurological disorders, such as spinal cord injury and amyotrophic lateral sclerosis; and (2) the discovery that similar plasticity also occurs in nonrespiratory motor systems. Indeed, the realization that similar plasticity occurs in respiratory and nonrespiratory motor neurons inspired clinical trials to restore leg/walking and hand/arm function in people living with chronic, incomplete spinal cord injury. Similar application may be possible to other clinical disorders that compromise respiratory and non-respiratory movements.
Collapse
Affiliation(s)
- Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL, United States.
| | - Tracy L Baker
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI, United States
| |
Collapse
|
8
|
Dempsey JA, Neder JA, Phillips DB, O'Donnell DE. The physiology and pathophysiology of exercise hyperpnea. HANDBOOK OF CLINICAL NEUROLOGY 2022; 188:201-232. [PMID: 35965027 DOI: 10.1016/b978-0-323-91534-2.00001-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
In health, the near-eucapnic, highly efficient hyperpnea during mild-to-moderate intensity exercise is driven by three obligatory contributions, namely, feedforward central command from supra-medullary locomotor centers, feedback from limb muscle afferents, and respiratory CO2 exchange (V̇CO2). Inhibiting each of these stimuli during exercise elicits a reduction in hyperpnea even in the continuing presence of the other major stimuli. However, the relative contribution of each stimulus to the hyperpnea remains unknown as does the means by which V̇CO2 is sensed. Mediation of the hyperventilatory response to exercise in health is attributed to the multiple feedback and feedforward stimuli resulting from muscle fatigue. In patients with COPD, diaphragm EMG amplitude and its relation to ventilatory output are used to decipher mechanisms underlying the patients' abnormal ventilatory responses, dynamic lung hyperinflation and dyspnea during exercise. Key contributions to these exercise-limiting responses across the spectrum of COPD severity include high dead space ventilation, an excessive neural drive to breathe and highly fatigable limb muscles, together with mechanical constraints on ventilation. Major controversies concerning control of exercise hyperpnea are discussed along with the need for innovative research to uncover the link of metabolism to breathing in health and disease.
Collapse
Affiliation(s)
- Jerome A Dempsey
- John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, University of Wisconsin-Madison, Madison, WI, United States.
| | - J Alberto Neder
- Respiratory Investigation Unit, Department of Medicine, Queen's University and Kingston Health Sciences Centre Kingston General Hospital Campus, Kingston, ON, Canada
| | - Devin B Phillips
- Respiratory Investigation Unit, Department of Medicine, Queen's University and Kingston Health Sciences Centre Kingston General Hospital Campus, Kingston, ON, Canada
| | - Denis E O'Donnell
- Respiratory Investigation Unit, Department of Medicine, Queen's University and Kingston Health Sciences Centre Kingston General Hospital Campus, Kingston, ON, Canada
| |
Collapse
|
9
|
Hsieh YH, Litvin DG, Zaylor AR, Nethery DE, Dick TE, Jacono FJ. Brainstem inflammation modulates the ventilatory pattern and its variability after acute lung injury in rodents. J Physiol 2020; 598:2791-2811. [PMID: 32378188 DOI: 10.1113/jp279177] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Accepted: 04/21/2020] [Indexed: 01/20/2023] Open
Abstract
KEY POINTS Compared with sham rats, rats a week after acute lung injury (ALI) express more pro-inflammatory cytokines in their brainstem respiratory control nuclei, exhibit a higher respiratory frequency (fR) and breathe with a more predictable pattern. These characteristics of the respiratory pattern persist in in situ preparations even after minimizing pulmonary and chemo-afferent inputs. Interleukin (IL)-1β microinjected in the nucleus tractus solitarii increases fR and the predictability of the ventilatory pattern similar to rats with ALI. Intracerebroventricular infusion of indomethacin, an anti-inflammatory drug, mitigates the effect of ALI on fR and ventilatory pattern variability. We conclude that changes in the ventilatory pattern after ALI result not only from sensory input due to pulmonary damage and dysfunction but also from neuro-inflammation. ABSTRACT Acute lung injury (ALI) increases respiratory rate (fR) and ventilatory pattern variability (VPV), but also evokes peripheral and central inflammation. We hypothesized that central inflammation has a role in determining the ventilatory pattern after ALI. In rat pups, we intratracheally injected either bleomycin to induce ALI or saline as a sham control. One week later, we recorded the ventilatory pattern of the rat pups using flow-through plethysmography, then formed in situ preparations from these pups and recorded their 'fictive' patterns from respiratory motor nerves. Compared with the ventilatory pattern of the sham rat pups, injured rat pups had increased fR and predictability. Surprisingly, the fictive patterns of the in situ preparations from ALI pups retained these characteristics despite removing their lungs to eliminate pulmonary sensory inputs and perfusing them with hyperoxic artificial cerebral spinal fluid to minimize peripheral chemoreceptor input. Histological processing revealed increased immunoreactivity of the pro-inflammatory cytokine Interleukin-1β (IL-1β) in the nucleus tractus solitarii (nTS) from ALI but not sham rats. In subsequent experiments, we microinjected IL-1β in the nTS bilaterally in anaesthetized naïve adult rats, which increased fR and predictability of ventilatory pattern variability (VPV) after 2 h. Finally, we infused indomethacin intracerebroventricularly during the week of survival after ALI. This did not affect sham rats, but mitigated changes in fR and VPV in ALI rats. We conclude that neuro-inflammation has an essential role in determining the ventilatory pattern of ALI rats.
Collapse
Affiliation(s)
- Yee-Hsee Hsieh
- Division of Pulmonary, Critical Care and Sleep Medicine, Case Western Reserve University, Cleveland, Ohio, United States
| | - David G Litvin
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States.,Department of Fundamental Neuroscience, University of Lausanne, Lausanne, 1005, Switzerland
| | - Abigail R Zaylor
- Division of Pulmonary, Critical Care and Sleep Medicine, Case Western Reserve University, Cleveland, Ohio, United States.,Division of Pulmonary, Critical Care and Sleep Medicine, Louis Stokes VA Medical Center, Cleveland, Ohio, United States
| | - David E Nethery
- Division of Pulmonary, Critical Care and Sleep Medicine, Case Western Reserve University, Cleveland, Ohio, United States
| | - Thomas E Dick
- Division of Pulmonary, Critical Care and Sleep Medicine, Case Western Reserve University, Cleveland, Ohio, United States.,Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio, United States
| | - Frank J Jacono
- Division of Pulmonary, Critical Care and Sleep Medicine, Case Western Reserve University, Cleveland, Ohio, United States.,Division of Pulmonary, Critical Care and Sleep Medicine, Louis Stokes VA Medical Center, Cleveland, Ohio, United States
| |
Collapse
|
10
|
Lindheimer JB, Cook DB, Klein-Adams JC, Qian W, Hill HZ, Lange G, Ndirangu DS, Wylie GR, Falvo MJ. Veterans with Gulf War Illness exhibit distinct respiratory patterns during maximal cardiopulmonary exercise. PLoS One 2019; 14:e0224833. [PMID: 31714907 PMCID: PMC6850551 DOI: 10.1371/journal.pone.0224833] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 10/22/2019] [Indexed: 11/18/2022] Open
Abstract
INTRODUCTION The components of minute ventilation, respiratory frequency and tidal volume, appear differentially regulated and thereby afford unique insight into the ventilatory response to exercise. However, respiratory frequency and tidal volume are infrequently reported, and have not previously been considered among military veterans with Gulf War Illness. Our purpose was to evaluate respiratory frequency and tidal volume in response to a maximal cardiopulmonary exercise test in individuals with and without Gulf War Illness. MATERIALS AND METHODS 20 cases with Gulf War Illness and 14 controls participated in this study and performed maximal cardiopulmonary exercise test on a cycle ergometer. Ventilatory variables (minute ventilation, respiratory frequency and tidal volume) were obtained and normalized to peak exercise capacity. Using mixed-design analysis of variance models, with group and time as factors, we analyzed exercise ventilatory patterns for the entire sample and for 11 subjects from each group matched for race, age, sex, and height. RESULTS Despite similar minute ventilation (p = 0.57, η2p = 0.01), tidal volume was greater (p = 0.02, η2p = 0.16) and respiratory frequency was lower (p = 0.004, η2p = 0.24) in Veterans with Gulf War Illness than controls. The findings for respiratory frequency remained significant in the matched subgroup (p = 0.004, η2p = 0.35). CONCLUSION In our sample, veterans with Gulf War Illness adopt a unique exercise ventilatory pattern characterized by reduced respiratory frequency, despite similar ventilation relative to controls. Although the mechanism(s) by which this pattern is achieved remains unresolved, our findings suggest that the components of ventilation should be considered when evaluating clinical conditions with unexplained exertional symptoms.
Collapse
Affiliation(s)
- Jacob B. Lindheimer
- War Related Illness and Injury Study Center, Department of Veterans Affairs New Jersey Health Care System, East Orange, New Jersey, United States of America
- William S. Middleton Memorial Veterans Hospital, Madison, Wisconsin, United States of America
- Department of Kinesiology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Dane B. Cook
- William S. Middleton Memorial Veterans Hospital, Madison, Wisconsin, United States of America
- Department of Kinesiology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Jacquelyn C. Klein-Adams
- War Related Illness and Injury Study Center, Department of Veterans Affairs New Jersey Health Care System, East Orange, New Jersey, United States of America
| | - Wei Qian
- War Related Illness and Injury Study Center, Department of Veterans Affairs New Jersey Health Care System, East Orange, New Jersey, United States of America
- New Jersey Medical School, Rutgers Biomedical and Health Sciences, Newark, New Jersey, United States of America
| | - Helene Z. Hill
- New Jersey Medical School, Rutgers Biomedical and Health Sciences, Newark, New Jersey, United States of America
| | - Gudrun Lange
- Department of Neurology, Mount Sinai Beth Israel, New York, New York, Unites States of America
| | - Duncan S. Ndirangu
- War Related Illness and Injury Study Center, Department of Veterans Affairs New Jersey Health Care System, East Orange, New Jersey, United States of America
| | - Glenn R. Wylie
- War Related Illness and Injury Study Center, Department of Veterans Affairs New Jersey Health Care System, East Orange, New Jersey, United States of America
- Kessler Foundation, West Orange, New Jersey, United States of America
| | - Michael J. Falvo
- War Related Illness and Injury Study Center, Department of Veterans Affairs New Jersey Health Care System, East Orange, New Jersey, United States of America
- New Jersey Medical School, Rutgers Biomedical and Health Sciences, Newark, New Jersey, United States of America
| |
Collapse
|
11
|
Bruce RM. The control of ventilation during exercise: a lesson in critical thinking. ADVANCES IN PHYSIOLOGY EDUCATION 2017; 41:539-547. [PMID: 29066604 DOI: 10.1152/advan.00086.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 09/11/2017] [Accepted: 09/15/2017] [Indexed: 06/07/2023]
Abstract
Learning the basic competencies of critical thinking are very important in the education of any young scientist, and teachers must be prepared to help students develop a valuable set of analytic tools. In my experience, this is best achieved by encouraging students to study areas with little scientific consensus, such as the control mechanisms of the exercise ventilatory response, as it can allow greater objectivity when evaluating evidence, while also giving students the freedom to think independently and problem solve. In this article, I discuss teaching strategies by which physiology, biomedical science, and sport science students can simultaneously develop their understanding of respiratory control mechanisms and learn to critically analyze evidence thoroughly. This can be best achieved by utilizing both teacher-led and student-led learning environments, the latter of which encourages the development of learner autonomy and independent problem solving. In this article, I also aim to demonstrate a systematic approach of critical assessment that students can be taught, adapt, and apply independently. Among other things, this strategy involves: 1) defining the precise phenomenon in question; 2) understanding what investigations must demonstrate to explain the phenomenon and its underlying mechanisms; 3) evaluating the explanations/mechanisms of the phenomenon and the evidence for them; and 4) forming strategies to produce strong evidence, if none exists.
Collapse
Affiliation(s)
- Richard M Bruce
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
| |
Collapse
|
12
|
Zaman J, Van den Bergh O, Fannes S, Van Diest I. Reprint of "Learning to breathe? Feedforward regulation of the inspiratory motor drive". Respir Physiol Neurobiol 2014; 204:93-8. [PMID: 25288353 DOI: 10.1016/j.resp.2014.09.017] [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: 11/18/2022]
Abstract
Claims have been made that breathing is in part controlled by feedforward regulation. In a classical conditioning paradigm, we investigated anticipatory increases in the inspiratory motor drive as measured by inspiratory occlusion pressure (P100). In an acquisition phase, an experimental group (N = 13) received a low-intensity resistive load (5 cmH2O/l/s) for three consecutive inspirations as Conditioned Stimulus (CS), preceding a load of a stronger intensity (20 cmH2O/l/s) for three subsequent inspirations as unconditioned stimulus (US). The control group (N = 11) received the low-intensity load for six consecutive inspirations. In a post-acquisition phase both groups received the low-intensity load for six consecutive inspirations. Responses to the CS-load only differed between groups during the first acquisition trials and a strong increase in P100 during the US-loads was observed, which habituated across the experiment. Our results suggest that the disruption caused by adding low to moderate resistive loads to three consecutive inspirations results in a short-lasting anticipatory increase in inspiratory motor drive.
Collapse
Affiliation(s)
- Jonas Zaman
- Research Group on Health Psychology University of Leuven, Tiensestraat 102, Box 3726, B-3000 Leuven, Belgium
| | - Omer Van den Bergh
- Research Group on Health Psychology University of Leuven, Tiensestraat 102, Box 3726, B-3000 Leuven, Belgium
| | - Stien Fannes
- Research Group on Health Psychology University of Leuven, Tiensestraat 102, Box 3726, B-3000 Leuven, Belgium
| | - Ilse Van Diest
- Research Group on Health Psychology University of Leuven, Tiensestraat 102, Box 3726, B-3000 Leuven, Belgium.
| |
Collapse
|
13
|
Zaman J, Van den Bergh O, Fannes S, Van Diest I. Learning to breathe? Feedforward regulation of the inspiratory motor drive. Respir Physiol Neurobiol 2014; 201:1-6. [DOI: 10.1016/j.resp.2014.05.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Revised: 05/23/2014] [Accepted: 05/26/2014] [Indexed: 11/25/2022]
|
14
|
Divers revisited: The ventilatory response to carbon dioxide in experienced scuba divers. Respir Med 2014; 108:758-65. [DOI: 10.1016/j.rmed.2014.02.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 02/10/2014] [Accepted: 02/12/2014] [Indexed: 11/18/2022]
|
15
|
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.
Collapse
Affiliation(s)
- Andrew William Sheel
- The School of Kinesiology, The University of British Columbia, Vancouver, Canada.
| | | |
Collapse
|
16
|
Abstract
During exercise by healthy mammals, alveolar ventilation and alveolar-capillary diffusion increase in proportion to the increase in metabolic rate to prevent PaCO2 from increasing and PaO2 from decreasing. There is no known mechanism capable of directly sensing the rate of gas exchange in the muscles or the lungs; thus, for over a century there has been intense interest in elucidating how respiratory neurons adjust their output to variables which can not be directly monitored. Several hypotheses have been tested and supportive data were obtained, but for each hypothesis, there are contradictory data or reasons to question the validity of each hypothesis. Herein, we report a critique of the major hypotheses which has led to the following conclusions. First, a single stimulus or combination of stimuli that convincingly and entirely explains the hyperpnea has not been identified. Second, the coupling of the hyperpnea to metabolic rate is not causal but is due to of these variables each resulting from a common factor which link the circulatory and ventilatory responses to exercise. Third, stimuli postulated to act at pulmonary or cardiac receptors or carotid and intracranial chemoreceptors are not primary mediators of the hyperpnea. Fourth, stimuli originating in exercising limbs and conveyed to the brain by spinal afferents contribute to the exercise hyperpnea. Fifth, the hyperventilation during heavy exercise is not primarily due to lactacidosis stimulation of carotid chemoreceptors. Finally, since volitional exercise requires activation of the CNS, neural feed-forward (central command) mediation of the exercise hyperpnea seems intuitive and is supported by data from several studies. However, there is no compelling evidence to accept this concept as an indisputable fact.
Collapse
Affiliation(s)
- Hubert V Forster
- Medical College of Wisconsin, Department of Physiology, Milwaukee, Wisconsin, USA.
| | | | | |
Collapse
|
17
|
Evaluating the importance of the carotid chemoreceptors in controlling breathing during exercise in man. BIOMED RESEARCH INTERNATIONAL 2013; 2013:893506. [PMID: 24236297 PMCID: PMC3819889 DOI: 10.1155/2013/893506] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/25/2013] [Accepted: 07/08/2013] [Indexed: 01/24/2023]
Abstract
Only the carotid chemoreceptors stimulate breathing during hypoxia in Man. They are also ideally located to warn if the brain's oxygen supply falls, or if hypercapnia occurs. Since their discovery ~80 years ago stimulation, ablation, and recording experiments still leave 3 substantial difficulties in establishing how important the carotid chemoreceptors are in controlling breathing during exercise in Man: (i) they are in the wrong location to measure metabolic rate (but are ideally located to measure any mismatch), (ii) they receive no known signal during exercise linking them with metabolic rate and no overt mismatch signals occur and (iii) their denervation in Man fails to prevent breathing matching metabolic rate in exercise. New research is needed to enable recording from carotid chemoreceptors in Man to establish whether there is any factor that rises with metabolic rate and greatly increases carotid chemoreceptor activity during exercise. Available evidence so far in Man indicates that carotid chemoreceptors are either one of two mechanisms that explain breathing matching metabolic rate or have no importance. We still lack key experimental evidence to distinguish between these two possibilities.
Collapse
|
18
|
Babb TG. Obesity: challenges to ventilatory control during exercise--a brief review. Respir Physiol Neurobiol 2013; 189:364-70. [PMID: 23707540 DOI: 10.1016/j.resp.2013.05.019] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Revised: 05/14/2013] [Accepted: 05/15/2013] [Indexed: 10/26/2022]
Abstract
Obesity is a national health issue in the US. Among the many physiological changes induced by obesity, it also presents a unique challenge to ventilatory control during exercise due to increased metabolic demand of moving larger limbs, increased work of breathing due to extra weight on the chest wall, and changes in breathing mechanics. These challenges to ventilatory control in obesity can be inconspicuous or overt among obese adults but for the most part adaptation of ventilatory control during exercise in obesity appears remarkably unnoticed in the majority of obese people. In this brief review, the changes to ventilatory control required for maintaining normal ventilation during exercise will be examined, especially the interaction between respiratory neural drive and ventilation. Also, gaps in our current knowledge will be discussed.
Collapse
Affiliation(s)
- Tony G Babb
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75231, United States.
| |
Collapse
|
19
|
Ermolao A, Bergamin M, Rossi AC, Dalle Carbonare L, Zaccaria M. Cardiopulmonary response and body composition changes after prolonged high altitude exposure in women. High Alt Med Biol 2012; 12:357-69. [PMID: 22206562 DOI: 10.1089/ham.2010.1098] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Weight loss in men is commonly observed during prolonged high altitude exposure as a result of a daily negative energy balance. Its amount depends mainly on duration of exposure, altitude reached, and level of physical activity. This reduction in body weight often comes with a loss of muscular mass, likely contributing to the decreased physical performance generally reported. Limited data is, however, available on body composition, functional capacity, and cardiopulmonary response to exercise after high altitude exposure in women. The aim of this study was to evaluate the effects of prolonged high altitude exposure on body composition and on cardiopulmonary response to maximal exercise in a group of young, moderately active women. Twelve female subjects, aged 21.5 ± 3.1 (mean ± SD), BMI 22.1 ± 1.9 kg · m(-2) and Vo(2max) 33.8 ± 3.5 mL · kg(-1) · min(-1), participated in this study, by residing for 21 days at high altitude (5050 m, Pyramid, EV-K(2)-CNR laboratory). Before and after high altitude exposure, all subjects underwent both a body composition evaluation using two methods (bioimpedance analysis and DEXA) and a functional evaluation based on a maximal exercise test on a cycle ergometer with breath-by-breath gas analysis. After high altitude exposure, data showed a slight, nonsignificant reduction in body weight, with an average 3:2 reduction ratio between fat and fat-free mass evaluated by DEXA, in addition to a significant decrease in Vo(2max) on the cycle ergometer test (p<0.01). Changes in Vo(2max) correlated to changes of leg muscle mass, evaluated by DEXA (r(2) = 0.72; p<0.0001). No changes were observed in the maximal heart rate, work capacity, and ventilatory thresholds, while the Vo(2)/W slope was significantly reduced (p<0.05). Finally, Ve/Vo(2) and VE/Vco(2max) slopes were increased (p<0.01), suggesting a possible long-term modulation of the exercise ventilatory response after prolonged high altitude exposure.
Collapse
Affiliation(s)
- Andrea Ermolao
- Department of Medical and Surgical Sciences, Sports Medicine Unit, University of Padova, Padova, Italy
| | | | | | | | | |
Collapse
|
20
|
Poon CS. Evolving paradigms in H+ control of breathing: from homeostatic regulation to homeostatic competition. Respir Physiol Neurobiol 2011; 179:122-6. [PMID: 21864724 DOI: 10.1016/j.resp.2011.08.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Accepted: 08/01/2011] [Indexed: 11/25/2022]
Affiliation(s)
- Chi-Sang Poon
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| |
Collapse
|
21
|
Miyamoto T, Inagaki M, Takaki H, Kawada T, Shishido T, Kamiya A, Sugimachi M. Adaptation of the respiratory controller contributes to the attenuation of exercise hyperpnea in endurance-trained athletes. Eur J Appl Physiol 2011; 112:237-51. [DOI: 10.1007/s00421-011-1968-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Accepted: 04/09/2011] [Indexed: 10/18/2022]
|
22
|
Babb TG, Wood HE, Mitchell GS. Short- and long-term modulation of the exercise ventilatory response. Med Sci Sports Exerc 2010; 42:1681-7. [PMID: 20164813 DOI: 10.1249/mss.0b013e3181d7b212] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The importance of adaptive control strategies (modulation and plasticity) in the control of breathing during exercise has become recognized only in recent years. In this review, we discuss new evidence for modulation of the exercise ventilatory response in humans, specifically, short- and long-term modulation. Short-term modulation is proposed to be an important regulatory mechanism that helps maintain blood gas homeostasis during exercise.
Collapse
Affiliation(s)
- Tony G Babb
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, 7232 Greenville Ave, Dallas, TX 75231, USA.
| | | | | |
Collapse
|
23
|
Effects of Deconditioning on the Initial Ventilatory and Circulatory Responses at the Onset of Exercise in Man. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 669:319-22. [DOI: 10.1007/978-1-4419-5692-7_65] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
|
24
|
Wood HE, Mitchell GS, Babb TG. Short-term modulation of the exercise ventilatory response in young men. J Appl Physiol (1985) 2007; 104:244-52. [PMID: 17991790 DOI: 10.1152/japplphysiol.00820.2007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Arterial isocapnia is a hallmark of moderate exercise in humans and is maintained even when resting arterial Pco(2) (Pa(CO(2))) is raised or lowered from its normal level, e.g., with chronic acid-base changes or acute increases in respiratory dead space. When resting ventilation and/or Pa(CO(2)) are altered, maintenance of isocapnia requires active adjustments of the exercise ventilatory response [slope of the ventilation (Ve)-CO(2) production (Vco(2)) relationship, DeltaVe/DeltaVco(2)]. On the basis of animal studies, it has been proposed that a central neural mechanism links the exercise ventilatory response to the resting ventilatory drive without need for changes in chemoreceptor feedback from rest to exercise, a mechanism referred to as short-term modulation (STM). We tested the hypothesis that STM is elicited by increased resting ventilatory drive associated with added external dead space (DS) in humans. Twelve young men were studied in control conditions and with added DS (200, 400, and 600 ml; randomized) at rest and during mild-to-moderate cycle exercise. DeltaVe/DeltaVco(2) increased progressively as DS volume increased (P < 0.0001). While resting end-tidal Pco(2) (Pet(CO(2))) increased with DS, the change in Pet(CO(2)) from rest to exercise was not increased, indicating that increased chemoreceptor feedback from rest to exercise cannot account for the greater exercise ventilatory response. We conclude that STM of the exercise ventilatory response is induced in young men when resting ventilatory drive is increased with external DS, confirming the existence of STM in humans.
Collapse
Affiliation(s)
- Helen E Wood
- Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, and University of Texas Southwestern Medical Center-Dallas, Dallas, Texas 75231, USA
| | | | | |
Collapse
|
25
|
Poon CS, Tin C, Yu Y. Homeostasis of exercise hyperpnea and optimal sensorimotor integration: the internal model paradigm. Respir Physiol Neurobiol 2007; 159:1-13; discussion 14-20. [PMID: 17416554 PMCID: PMC2225386 DOI: 10.1016/j.resp.2007.02.020] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2007] [Revised: 02/28/2007] [Accepted: 02/28/2007] [Indexed: 11/16/2022]
Abstract
Homeostasis is a basic tenet of biomedicine and an open problem for many physiological control systems. Among them, none has been more extensively studied and intensely debated than the dilemma of exercise hyperpnea - a paradoxical homeostatic increase of respiratory ventilation that is geared to metabolic demands instead of the normal chemoreflex mechanism. Classical control theory has led to a plethora of "feedback/feedforward control" or "set point" hypotheses for homeostatic regulation, yet so far none of them has proved satisfactory in explaining exercise hyperpnea and its interactions with other respiratory inputs. Instead, the available evidence points to a far more sophisticated respiratory controller capable of integrating multiple afferent and efferent signals in adapting the ventilatory pattern toward optimality relative to conflicting homeostatic, energetic and other objectives. This optimality principle parsimoniously mimics exercise hyperpnea, chemoreflex and a host of characteristic respiratory responses to abnormal gas exchange or mechanical loading/unloading in health and in cardiopulmonary diseases - all without resorting to a feedforward "exercise stimulus". Rather, an emergent controller signal encoding the projected metabolic level is predicted by the principle as an exercise-induced 'mental percept' or 'internal model', presumably engendered by associative learning (operant conditioning or classical conditioning) which achieves optimality through continuous identification of, and adaptation to, the causal relationship between respiratory motor output and resultant chemical-mechanical afferent feedbacks. This internal model self-tuning adaptive control paradigm opens a new challenge and exciting opportunity for experimental and theoretical elucidations of the mechanisms of respiratory control - and of homeostatic regulation and sensorimotor integration in general.
Collapse
Affiliation(s)
- Chi-Sang Poon
- Harvard-MIT Division of Health Sciences and Technology, Bldg. 56-046, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
| | | | | |
Collapse
|
26
|
Herigstad M, Balanos GM, Robbins PA. Can human cardiovascular regulation during exercise be learnt from feedback from arterial baroreceptors? Exp Physiol 2007; 92:695-704. [PMID: 17449541 PMCID: PMC1974819 DOI: 10.1113/expphysiol.2007.037879] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
During dynamic exercise, a large fall in systemic vascular resistance occurs. Arterial pressure (AP) is, however, maintained through a combination of central command and neural activity from muscle afferents that adjust the autonomic outflow to the circulation. How these signals are calibrated to provide accurate regulation of AP remains unclear. This study tests the hypothesis that the calibration can be 'learnt' through feedback from the arterial baroreceptors arising over multiple trials of exercise. Eight healthy subjects undertook three different protocols in random order. The test protocol consisted of 7 days' training, when subjects were exposed on 70 occasions to 4 min of exercise (50% of maximal oxygen uptake capacity) paired with neck suction (-40 mmHg) to mimic an excessive rise in AP at the carotid baroreceptors with exercise. Two control protocols involved training with either exercise or neck suction alone. No significant changes in mean AP, diastolic AP or heart rate during normal exercise were detected following training with any protocol. However, the rise in systolic AP with exercise was attenuated by an average of 7.3 +/- 2.0 mmHg (mean +/- s.e.m., P < 0.01) on the first and second days following training with the test protocol, but not with either control protocol (P < 0.05 for difference between protocols, ANOVA). In conclusion, this study failed to show that mean AP during normal exercise could be reduced through prior conditioning by overstimulation of the baroreceptors during exercise. However, a reduction in systolic AP was observed that suggests the presence of some plasticity within the autonomic response, consistent with our hypothesis.
Collapse
Affiliation(s)
- Mari Herigstad
- Department of Physiology, Anatomy and Genetics, Parks Road, Oxford OX1 3PT, UK
| | | | | |
Collapse
|
27
|
Bell HJ. Respiratory control at exercise onset: an integrated systems perspective. Respir Physiol Neurobiol 2006; 152:1-15. [PMID: 16531126 DOI: 10.1016/j.resp.2006.02.005] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2006] [Revised: 02/06/2006] [Accepted: 02/06/2006] [Indexed: 10/24/2022]
Abstract
The near-immediate increase in breathing that accompanies the onset of constant load, dynamic exercise has remained a topic of interest to respiratory physiologists for the better part of a century. During this time, several theories have been proposed and tested in an attempt to explain what has been called the phase I response of exercise hyperpnoea, or the fast neural drive to breathe, and much controversy still remains as to what mediates this response. 'Central motor command' and 'afferent feedback' mechanisms, as described in animal models, have been centre stage in the debate, with much supportive evidence for their involvement. This review presents three relatively recent and controversial mechanisms and examines the increasing evidence for their involvement in the initial phase of exercise hyperpnoea: (1) the vascular distension hypothesis, (2) the vestibular feedback hypothesis and (3) the behavioral state hypothesis. Some outstanding fundamental questions and directions for future research are presented throughout, always with a focus on mechanistic efficacy in the integrated system response.
Collapse
Affiliation(s)
- Harold J Bell
- Department of Cell Biology and Anatomy, University of Calgary, Heritage Medical Research Building, Room 202, 3330 Hospital Dr. NW, Calgary, Alta., Canada, T2N 4N1.
| |
Collapse
|
28
|
Mitchell GS, Babb TG. Layers of exercise hyperpnea: modulation and plasticity. Respir Physiol Neurobiol 2006; 151:251-66. [PMID: 16530024 DOI: 10.1016/j.resp.2006.02.003] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2005] [Revised: 02/02/2006] [Accepted: 02/03/2006] [Indexed: 11/23/2022]
Abstract
Despite the fundamental biological significance of the ventilatory response to mild or moderate physical activity (the exercise hyperpnea), we still know remarkably little concerning its underlying mechanisms. Part of the difficulty in revealing those mechanisms may arise due to confusion between multiple mechanistic layers, each contributing to the impressive degree of regulation achieved. The primary, feedforward exercise stimulus or stimuli increase ventilation in approximate proportion to changes in metabolic rate. Chemoreceptor feedback then minimizes deviations from optimal blood gas regulation, most often preventing excessive hypocapnia in non-human mammals. Recent evidence has accumulated, suggesting that adaptive control strategies including modulation and plasticity may adjust the feedforward and/or feedback contributions when blood gas homeostasis proves inadequate. In this review, we present evidence from a goat model of exercise hyperpnea concerning the existence of modulation and plasticity, and specifically mechanisms known as short-term and long-term modulation of the exercise ventilatory response. Throughout the review, we consider available evidence concerning the relevance of these mechanisms to humans. Plasticity is a property only recently recognized in the neural system subserving respiratory control, and the application of these concepts to the exercise ventilatory response in humans is in its infancy. Modulation and plasticity may confer an ability of individuals to adapt their exercise ventilatory response so that it remains appropriate in the face of life-long changes in endogenous (e.g. development, aging, onset of disease) or exogenous (e.g. altitude, wearing a breathing apparatus during physical exertion) physiological conditions.
Collapse
Affiliation(s)
- Gordon S Mitchell
- Department of Comparative Biosciences, University of Wisconsin, 2015 Linden Drive, Madison, WI 53706, USA.
| | | |
Collapse
|
29
|
Turner D, Stewart JD. Associative conditioning with leg cycling and inspiratory resistance enhances the early exercise ventilatory response in humans. Eur J Appl Physiol 2005; 93:333-9. [PMID: 15375661 DOI: 10.1007/s00421-004-1194-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Repeated trials of hypercapnic exercise [deltaPET CO2 = 7 (1) mmHg] augment the increase in inspired minute ventilation and tidal volume (V(T)) in the early phase of subsequent trials of unencumbered exercise alone. The increase in V(T) in the first 20 s of exercise was correlated to the increase in V(T) evoked during hypercapnic exercise trials, suggesting that the evoked increase in V(T) during conditioning may be a factor in mediating associative conditioning. To test this hypothesis, inspiratory resistive loading (IRL) was employed to evoke an increase in V(T) [deltaV(T) = 0.4 (0.1) I(BTPS)] during conditioning exercise trials [IRL + EX; deltaP(ET)CO2 = 2 (l) mmHg]. IRL + EX associative conditioning elicited a significant augmentation of the early minute ventilation (+46%) and V(T) (+100%) responses to subsequent unencumbered exercise. The latter was correlated to the evoked increase in V(T) during associative conditioning with IRL + EX. The results support the hypothesis that an evoked increase in V(T) during associative conditioning could be a factor in eliciting long-term modulation of minute ventilation in subsequent unencumbered exercise. The results further indicated that the modulation of ventilation early in exercise is not due to sensitisation to repeated trials of either IRL or exercise alone. Associative conditioning may shape the ventilatory response to exercise through a process of motor learning. Data are presented as mean (SEM) unless otherwise stated.
Collapse
Affiliation(s)
- Duncan Turner
- School of Life and Sport Sciences, University of Surrey Roehampton, London SW15 3SN, UK.
| | | |
Collapse
|
30
|
Cathcart AJ, Herrold N, Turner AP, Wilson J, Ward SA. Absence of long-term modulation of ventilation by dead-space loading during moderate exercise in humans. Eur J Appl Physiol 2004; 93:411-20. [PMID: 15490221 DOI: 10.1007/s00421-004-1218-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/23/2004] [Indexed: 10/26/2022]
Abstract
The stability of arterial PCO(2) (P(a)CO(2)) during moderate exercise in humans suggests a CO(2)-linked control that matches ventilation (V(E)) to pulmonary CO(2) clearance (VCO(2)). An alternative view is that V(E) is subject to long-term modulation (LTM) induced by "hyperpnoeic history". LTM has been reported with associative conditioning via dead-space (V(D)) loading in exercising goats (Martin and Mitchell 1993). Whether this prevails in humans is less clear, which may reflect differences in study design (e.g. subject familiarisation; V(D) load; whether or not V(E) is expressed relative to VCO(2); choice of P(a)CO(2) estimator). After familiarisation, nine healthy males performed moderate constant-load cycle-ergometry (20 W-80 W-20 W; <lactate threshold, theta;(L)): day 1, pre-conditioning, n=3; day 2, conditioning (V(D)=1.59 l, doubling V(E) at 20 W and 80 W), n=8 with 10 min rest between tests; and, after 1 h rest, post-conditioning, n=3. Gas exchange was determined breath-by-breath. Post-conditioning, neither the transient [phase 1, phase 2 (capital EF, Cyrillic1, capital EF, Cyrillic2)] nor steady-state V(E) exercise responses, nor their proportionality to VCO(2), differed from pre-conditioning. For post-conditioning trial 1, steady-state V(E) was 28.1 (4.7) l min(-1) versus 29.1 (3.8) l min(-1) pre-conditioning, and mean-alveolar PCO(2) (a validated P(a)CO(2) estimator) was 5.53 (0.48) kPa [41.5 (3.6) mmHg] versus 5.59 (0.49) kPa [41.9 (3.7) mmHg]; the capital EF, Cyrillic1 V(E) increment was 4.2 (2.9) l min(-1) versus 5.2 (1.9) l min(-1); the capital EF, Cyrillic2 V(E) time-constant (tau) was 64.4 (24.1) s versus 64.1 (25.3) s; tauV(E)/tauVCO(2) was 1.12 (0.04) versus 1.10 (0.04); and the V(E)-VCO(2) slope was 21.7 (3.4) versus 21.2 (3.2). In conclusion, we could find no evidence to support ventilatory control during moderate exercise being influenced by hyperpnoeic history associated with dead-space loading in humans.
Collapse
Affiliation(s)
- A J Cathcart
- School of Sport and Exercise Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | | | | | | | | |
Collapse
|
31
|
Bin-Jaliah I, Maskell PD, Kumar P. Indirect sensing of insulin-induced hypoglycaemia by the carotid body in the rat. J Physiol 2004; 556:255-66. [PMID: 14742728 PMCID: PMC1664881 DOI: 10.1113/jphysiol.2003.058321] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The most physiologically important sensors for systemic glucoregulation are located in extra-cranial sites. Recent evidence suggests that the carotid body may be one such site. We assessed rat carotid body afferent neural output in response to lowered glucose, indirectly by measurement of ventilation, and directly by recording single or few-fibre chemoafferent discharge, in vitro. Insulin (0.4 Ukg(-1)min(-1))-induced hypoglycaemia (blood glucose reduced by ca 50% to 3.4 +/- 0.1 mmoll(-1)) significantly increased spontaneous ventilation in sham-operated animals but not in bilateral carotid sinus nerve sectioned (CSNX) animals. In both groups, metabolic rate (measured as ) was almost doubled during hypoglycaemia. The ventilatory equivalent was unchanged in the sham group leading to a maintained control level of P(a, CO(2)), but was significantly reduced in the CSNX group, giving rise to an elevation of 6.0 +/- 1.3 mmHg in P(a, CO(2)). When pulmonary ventilation in sham animals was controlled and maintained, phrenic neural activity increased during hypoglycaemia and was associated with a significant increase in P(a, CO(2)) of 5.1 +/- 0.5 mmHg. Baseline chemoreceptor discharge frequency, recorded in vitro, was not affected, and did not increase when the superfusate [glucose] was lowered from 10 mm to 2 mm by substitution with sucrose: 0.40 +/- 0.20 Hz to 0.27 +/- 0.15 Hz, respectively (P > 0.20). We suggest therefore that any potential role of the carotid bodies in glucose homeostasis in vivo is mediated through its transduction of some other metabolically derived blood-borne factor rather than glucose per se and that this may also provide the link between exercise, metabolic rate and ventilation.
Collapse
Affiliation(s)
- I Bin-Jaliah
- Department of Physiology, Division of Medical Sciences, The Medical School, University of Birmingham, Birmingham B15 2TT, UK
| | | | | |
Collapse
|