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Abstract
The sensation that develops as a long breath hold continues is what this article is about. We term this sensation of an urge to breathe "air hunger." Air hunger, a primal sensation, alerts us to a failure to meet an urgent homeostatic need maintaining gas exchange. Anxiety, frustration, and fear evoked by air hunger motivate behavioral actions to address the failure. The unpleasantness and emotional consequences of air hunger make it the most debilitating component of clinical dyspnea, a symptom associated with respiratory, cardiovascular, and metabolic diseases. In most clinical populations studied, air hunger is the predominant form of dyspnea (colloquially, shortness of breath). Most experimental subjects can reliably quantify air hunger using rating scales, that is, there is a consistent relationship between stimulus and rating. Stimuli that increase air hunger include hypercapnia, hypoxia, exercise, and acidosis; tidal expansion of the lungs reduces air hunger. Thus, the defining experimental paradigm to evoke air hunger is to elevate the drive to breathe while mechanically restricting ventilation. Functional brain imaging studies have shown that air hunger activates the insular cortex (an integration center for perceptions related to homeostasis, including pain, food hunger, and thirst), as well as limbic structures involved with anxiety and fear. Although much has been learned about air hunger in the past few decades, much remains to be discovered, such as an accepted method to quantify air hunger in nonhuman animals, fundamental questions about neural mechanisms, and adequate and safe methods to mitigate air hunger in clinical situations. © 2021 American Physiological Society. Compr Physiol 11:1449-1483, 2021.
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Affiliation(s)
- Robert B Banzett
- Division of Pulmonary, Critical Care, and Sleep Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA
- Department of Medicine, Harvard Medical School, Boston, Massachusetts, USA
| | - Robert W Lansing
- Division of Pulmonary, Critical Care, and Sleep Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA
| | - Andrew P Binks
- Department of Basic Science Education, Virginia Tech Carilion School of Medicine, Roanoke, Virginia, USA
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Natusch DJD, Aust PW, Khadiejah S, Ithnin H, Isa A, Zamzuri CK, Ganswindt A, DeNardo DF. Behavioral and corticosterone responses to carbon dioxide exposure in reptiles. PLoS One 2020; 15:e0240176. [PMID: 33022690 PMCID: PMC7538201 DOI: 10.1371/journal.pone.0240176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 09/21/2020] [Indexed: 11/19/2022] Open
Abstract
The use of carbon dioxide (CO2) exposure as a means of animal euthanasia has received considerable attention in mammals and birds but remains virtually untested in reptiles. We measured the behavioral responses of four squamate reptile species (Homalopsis buccata, Malayopython reticulatus, Python bivitattus, and Varanus salvator) to exposure to 99.5% CO2 for durations of 15, 30, or 90 minutes. We also examined alterations in plasma corticosterone levels of M. reticulatus and V. salvator before and after 15 minutes of CO2 exposure relative to control individuals. The four reptile taxa showed consistent behavioral responses to CO2 exposure characterized by gaping and minor movements. The time taken to lose responsiveness to stimuli and cessation of movements varied between 240–4260 seconds (4–71 minutes), with considerable intra- and inter-specific variation. Duration of CO2 exposure influenced the likelihood of recovery, which also varied among species (e.g., from 0–100% recovery after 30-min exposure). Plasma corticosterone concentrations increased after CO2 exposure in both V. salvator (18%) and M. reticulatus (14%), but only significantly in the former species. Based on our results, CO2 appears to be a mild stressor for reptiles, but the relatively minor responses to CO2 suggest it may not cause considerable distress or pain. However, our results are preliminary, and further testing is required to understand optimal CO2 delivery mechanisms and interspecific responses to CO2 exposure before endorsing this method for reptile euthanasia.
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Affiliation(s)
- Daniel J. D. Natusch
- Department of Biological Sciences, Macquarie University, North Ryde, NSW, Australia
- EPIC Biodiversity, Frogs Hollow, NSW, Australia
- * E-mail:
| | - Patrick W. Aust
- Department of Zoology, University of Oxford, Oxford, United Kingdom
- Bushtick Environmental Services, Grantham, Lincolnshire, United Kingdom
| | - Syarifah Khadiejah
- Department of Wildlife and National Parks, Peninsular Malaysia, Kuala Lumpur, Malaysia
| | - Hartini Ithnin
- Department of Wildlife and National Parks, Peninsular Malaysia, Kuala Lumpur, Malaysia
| | - Ain Isa
- Department of Wildlife and National Parks, Peninsular Malaysia, Kuala Lumpur, Malaysia
| | - Che Ku Zamzuri
- Department of Wildlife and National Parks, Peninsular Malaysia, Kuala Lumpur, Malaysia
| | - Andre Ganswindt
- Endocrine Research Laboratory, Mammal Research Institute, Department of Zoology and Entomology, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria, South Africa
- Centre of Veterinary Wildlife Studies, Faculty of Veterinary Science, University of Pretoria, Pretoria, Onderstepoort, South Africa
| | - Dale F. DeNardo
- School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
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Evaluation of Low versus High Volume per Minute Displacement CO₂ Methods of Euthanasia in the Induction and Duration of Panic-Associated Behavior and Physiology. Animals (Basel) 2016; 6:ani6080045. [PMID: 27490573 PMCID: PMC4997270 DOI: 10.3390/ani6080045] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 06/21/2016] [Accepted: 07/12/2016] [Indexed: 11/17/2022] Open
Abstract
Current recommendations for the use of CO ₂ as a euthanasia agent for rats require the use of gradual fill protocols (such as 10% to 30% volume displacement per minute) in order to render the animal insensible prior to exposure to levels of CO ₂ that are associated with pain. However, exposing rats to CO ₂ , concentrations as low as 7% CO ₂ are reported to cause distress and 10%-20% CO ₂ induces panic-associated behavior and physiology, but loss of consciousness does not occur until CO ₂ concentrations are at least 40%. This suggests that the use of the currently recommended low flow volume per minute displacement rates create a situation where rats are exposed to concentrations of CO ₂ that induce anxiety, panic, and distress for prolonged periods of time. This study first characterized the response of male rats exposed to normoxic 20% CO ₂ for a prolonged period of time as compared to room air controls. It demonstrated that rats exposed to this experimental condition displayed clinical signs consistent with significantly increased panic-associated behavior and physiology during CO ₂ exposure. When atmospheric air was then again delivered, there was a robust increase in respiration rate that coincided with rats moving to the air intake. The rats exposed to CO ₂ also displayed behaviors consistent with increased anxiety in the behavioral testing that followed the exposure. Next, this study assessed the behavioral and physiologic responses of rats that were euthanized with 100% CO ₂ infused at 10%, 30%, or 100% volume per minute displacement rates. Analysis of the concentrations of CO ₂ and oxygen in the euthanasia chamber and the behavioral responses of the rats suggest that the use of the very low flow volume per minute displacement rate (10%) may prolong the duration of panicogenic ranges of ambient CO ₂ , while the use of the higher flow volume per minute displacement rate (100%) increases agitation. Therefore, of the volume displacement per minute rates evaluated, this study suggests that 30% minimizes the potential pain and distress experienced by the animal.
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Behavioural responses of rats to gradual-fill carbon dioxide euthanasia and reduced oxygen concentrations. Appl Anim Behav Sci 2006. [DOI: 10.1016/j.applanim.2005.12.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Koppers RJH, Vos PJE, Folgering HTM. Tube breathing as a new potential method to perform respiratory muscle training: Safety in healthy volunteers. Respir Med 2006; 100:714-20. [PMID: 16126382 DOI: 10.1016/j.rmed.2005.07.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2005] [Accepted: 07/20/2005] [Indexed: 11/16/2022]
Abstract
Normocapnic hyperpnea has been established as a method of respiratory muscle endurance training (RMET). This technique has not been applied on a large scale because complicated and expensive equipment is needed to maintain CO(2)-homeostasis during hyperpnea. This CO(2)-homeostasis can be preserved during hyperpnea by enlarging the dead space of the ventilatory system. One of the possibilities to enlarge dead space is breathing through a tube. If tube breathing is safe and feasible, it may be a new and inexpensive method for RMET, enabling its widespread use. The aim of this study was to evaluate the safety of tube breathing and investigate the effect on CO(2)-homeostasis in healthy subjects. A total of 20 healthy volunteers performed 10 min of tube breathing (dead space 60% of vital capacity). Oxygen-saturation, PaCO(2), respiratory muscle function, hypercapnic ventilatory response and dyspnea (Borg-score) were measured. Tube breathing did not lead to severe complaints, adverse events or oxygen desaturations. A total of 14 out of 20 subjects became hypercapnic (PaCO(2)>6.0 kPa) during tube breathing. There were no significant correlations between PaCO(2) and respiratory muscle function or hypercapnic ventilatory responses. The normocapnic versus hypercapnic subjects showed no significant differences between decrease in oxygen saturation (-0.7% versus -0.2%, respectively, P=0.6), Borg score (4.3 versus 4.7, P=0.9), respiratory muscle function nor hypercapnic ventilatory responses. Our results show that tube breathing is well tolerated amongst healthy subjects. No complaints, nor desaturations occurred. Hypercapnia developed in a substantial number of subjects. When tube breathing will be applied as respiratory muscle training modality, this potential development of hypercapnia must be considered.
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Affiliation(s)
- Ralph J H Koppers
- Department of Pulmonology, Medical Center Leeuwarden, Postbus 888, 8901 BR Leeuwarden, The Netherlands.
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Cohen ER, Rostrup E, Sidaros K, Lund TE, Paulson OB, Ugurbil K, Kim SG. Hypercapnic normalization of BOLD fMRI: comparison across field strengths and pulse sequences. Neuroimage 2004; 23:613-24. [PMID: 15488411 DOI: 10.1016/j.neuroimage.2004.06.021] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2004] [Revised: 04/29/2004] [Accepted: 06/18/2004] [Indexed: 11/24/2022] Open
Abstract
The blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signal response to neural stimulation is influenced by many factors that are unrelated to the stimulus. These factors are physiological, such as the resting venous cerebral blood volume (CBV(v)) and vessel size, as well as experimental, such as pulse sequence and static magnetic field strength (B(0)). Thus, it is difficult to compare task-induced fMRI signals across subjects, field strengths, and pulse sequences. This problem can be overcome by normalizing the neural activity-induced BOLD fMRI response by a global hypercapnia-induced BOLD signal. To demonstrate the effectiveness of the BOLD normalization approach, gradient-echo BOLD fMRI at 1.5, 4, and 7 T and spin-echo BOLD fMRI at 4 T were performed in human subjects. For neural stimulation, subjects performed sequential finger movements at 2 Hz, while for global stimulation, subjects breathed a 5% CO(2) gas mixture. Under all conditions, voxels containing primarily large veins and those containing primarily active tissue (i.e., capillaries and small veins) showed distinguishable behavior after hypercapnic normalization. This allowed functional activity to be more accurately localized and quantified based on changes in venous blood oxygenation alone. The normalized BOLD signal induced by the motor task was consistent across different magnetic fields and pulse sequences, and corresponded well with cerebral blood flow measurements. Our data suggest that the hypercapnic normalization approach can improve the spatial specificity and interpretation of BOLD signals, allowing comparison of BOLD signals across subjects, field strengths, and pulse sequences. A theoretical framework for this method is provided.
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Affiliation(s)
- Eric R Cohen
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 15260, USA
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Rohrbach M, Perret C, Kayser B, Boutellier U, Spengler CM. Task failure from inspiratory resistive loaded breathing: a role for inspiratory muscle fatigue? Eur J Appl Physiol 2003; 90:405-10. [PMID: 12827367 DOI: 10.1007/s00421-003-0871-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/16/2003] [Indexed: 10/22/2022]
Abstract
The use of non-invasive resistive breathing to task failure to assess inspiratory muscle performance remains a matter of debate. CO2 retention rather than diaphragmatic fatigue was suggested to limit endurance during inspiratory resistive breathing. Cervical magnetic stimulation (CMS) allows discrimination between diaphragmatic and rib cage muscle fatigue. We tested a new protocol with respect to the extent and the partitioning of inspiratory muscle fatigue at task failure. Nine healthy subjects performed two runs of inspiratory resistive breathing at 67 (12)% of their maximal inspiratory mouth pressure, respiratory rate (fR), paced at 18 min(-1), with a 15-min pause between runs. Diaphragm and rib cage muscle contractility were assessed from CMS-induced esophageal (P(es,tw)), gastric (P(ga,tw)), and transdiaphragmatic (P(di,tw)) twitch pressures. Average endurance times of the first and second runs were similar [9.1 (6.7) and 8.4 (3.5) min]. P(di,tw) significantly decreased from 33.1 to 25.9 cmH2O in the first run, partially recovered (27.6 cmH2O), and decreased further in the second run (23.4 cmH2O). P(es,tw) also decreased significantly (-5.1 and -2.4 cmH2O), while P(ga,tw) did not change significantly (-2.0 and -1.9 cmH2O), indicating more pronounced rib cage rather than diaphragmatic fatigue. End-tidal partial pressure of CO2 ( PETCO2) rose from 37.2 to 44.0 and 45.3 mmHg, and arterial oxygen saturation (SaO2) decreased in both runs from 98% to 94%. Thus, task failure in mouth-pressure-targeted, inspiratory resistive breathing is associated with both diaphragmatic and rib cage muscle fatigue. Similar endurance times despite different degrees of muscle fatigue at the start of the runs indicate that other factors, e.g. increases in PETCO2, and/or decreases in SaO2, probably contributed to task-failure.
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Affiliation(s)
- Markus Rohrbach
- Exercise Physiology, Institute for Human Movement Sciences, Swiss Federal Institute of Technology, and Institute of Physiology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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Lansing RW, Im BS, Thwing JI, Legedza AT, Banzett RB. The perception of respiratory work and effort can be independent of the perception of air hunger. Am J Respir Crit Care Med 2000; 162:1690-6. [PMID: 11069798 DOI: 10.1164/ajrccm.162.5.9907096] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Dyspnea in patients could arise from both an urge to breathe and increased effort of breathing. Two qualitatively different sensations, "air hunger" and "respiratory work and effort," arising from different afferent sources are hypothesized. In the laboratory, breathing below the spontaneous level may produce an uncomfortable sensation of air hunger, and breathing above it a sensation of work or effort. Measurement of a single sensory dimension cannot distinguish these as separate sensations; we therefore measured two sensory dimensions and attempted to vary them independently. In five normal subjects we obtained simultaneous ratings of air hunger and of work and effort while independently varying PCO(2) or the level of targeted voluntary breathing. We found a difference in response to the two stimulus dimensions: air hunger ratings changed more steeply when PCO(2) was altered and ventilation was constant; work or effort ratings changed more steeply when ventilation was altered and PCO(2) was constant. We conclude that "air hunger" is qualitatively different from "work and effort" and arises from different afferent sources.
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Affiliation(s)
- R W Lansing
- Physiology Program and Department of Biostatistics, Harvard School of Public Health, Boston, Massachusetts 02115, USA
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Banzett RB, Mulnier HE, Murphy K, Rosen SD, Wise RJ, Adams L. Breathlessness in humans activates insular cortex. Neuroreport 2000; 11:2117-20. [PMID: 10923655 DOI: 10.1097/00001756-200007140-00012] [Citation(s) in RCA: 238] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Dyspnea (shortness of breath, breathlessness) is a major and disabling symptom of heart and lung disease. The representation of dyspnea in the cerebral cortex is unknown. In the first study designed to explore the central neural structures underlying perception of dyspnea, we evoked the perception of severe 'air hunger' in healthy subjects by restraining ventilation below spontaneous levels while holding arterial oxygen and carbon dioxide levels constant. PET revealed that air hunger activated the insular cortex. The insula is a limbic structure also activated by visceral stimuli, temperature, taste, nausea and pain. Like dyspnea, such perceptions underlie behaviors essential to homeostasis and survival.
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Affiliation(s)
- R B Banzett
- Department of Medicine, Harvard Medical School, Harvard School of Public Health, Boston, MA, USA
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Bloch-Salisbury E, Spengler CM, Brown R, Banzett RB. Self-control and external control of mechanical ventilation give equal air hunger relief. Am J Respir Crit Care Med 1998; 157:415-20. [PMID: 9476852 DOI: 10.1164/ajrccm.157.2.9701024] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Elevated end-tidal partial pressure of CO2 (PET(CO2)) causes air hunger; this sensation becomes intense with a relatively small rise in PET(CO2) if ventilation is held constant. Spontaneously breathing subjects increase ventilation in response to CO2, thereby greatly diminishing air hunger. In healthy subjects and ventilator-dependent patients, experimenter-induced increases in ventilator tidal volume (VT) relieve air hunger even if PET(CO2) is kept elevated. We addressed two questions: (1) Can paralyzed, ventilator-dependent patients use the sensation of air hunger to effectively control ventilator VT using nonrespiratory motor pathways; and (2) Do subjects obtain more relief when in control of their own ventilator? Four subjects were trained to increase ventilator VT using a mouth-operated switch. Subjects' ratings of air hunger intensity in response to elevated PET(CO2) were compared during three conditions: (1) constant VT; (2) subject-controlled VT; and (3) experimenter-controlled VT. When given control of their ventilator, all subjects increased VT in response to increased PET(CO2), thereby relieving air hunger. Air hunger relief was similar when the experimenter mimicked these VT changes. These results suggest that: (1) ventilator-dependent patients can use sensation, conscious decisions, and nonrespiratory motor pathways to achieve an appropriate respiratory response to increased PCO2 and (2) control of one's own ventilation is unimportant in these circumstances.
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Affiliation(s)
- E Bloch-Salisbury
- Physiology Program, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
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