Inspiratory Muscle Training (Review): How to Get Most Benefits?

Inspiratory Muscle Training for Sports Performance,
Asthma, COPD, Cystic Fibrosis and Other Conditions

Most, but not all, clinical trials have found benefits of inspiratory muscle training on sports performance in rowers (Volianitis et al, 2001; Klusiewicz et al, 2008; Riganas et al, 2008), cyclists (Romer et al, 2002a; Romer et al, 2002b), and swimmers (Kilding et al, 2010; Wells et al, 2005; Mickleborough et al, 2008).

Clinical trials also tested the effects of inspiratory muscle training on asthma, COPD, bronchiectasis, cystic fibrosis, diabetes, pre- and postsurgery, chronic heart failure, ischaemic heart disease, stroke, ventilator weaning, and neuromuscular diseases (some references with conclusions are provided below).

Most of these studies have demonstrated the following benefits:
- reduction in dyspnea (a sensation of breathlessness) during exercise in athletes and at rest or during very light exercise in patients
- increase in the force of inspiratory muscles during intensive exercise training for athletes
- increased endurance in patients with improvements in some lung function parameters
- reduced medication and improved quality of life in people with chronic diseases.

Most of these studies have used the following respiratory trainers or devices: UltraBreathe, Powerlung, Powerbreathe, and Expand-A-Lung.

The claimed goal of respiratory and inspiratory muscle training is to improve oxygen transport. Let us consider problems with oxygen transport for sick people with dyspnea (shortness of breath) at rest.

Dyspnea and oxygen transport

Dyspnea in patients, and in some degree in competing or training athletes, is virtually always accompanied by inefficient oxygen transport and resultant tissue hypoxia. While inspiratory muscle training is focused on mechanical effects, we are going to focus on cellular effects related to the mechanism of oxygen transport.

People with heart disease, asthma, diabetes, COPD and many other conditions, have greatly elevated minute ventilation at rest: about 2-3 times more than the medical norm. (The norm is 6 L/min for a 70-kg man.) This has been known to clinical physicians for decades and proven by dozens of studies. What are the effects?

Chronic hyperventilation, and here we have even more impressive supporting evidence, causes systemic cell hypoxia. The mechanism of inefficient O2 transport and resultant tissue hypoxia depends on the presence of lung problems (ventilation-perfusion mismatch). For patients with normal lungs (e.g., most people with heart disease and diabetes), alveolar hyperventilation leads to arterial hypocapnia (lack of CO2 in the arterial blood). Since CO2 is a potent vasodilator, hypocapnia leads to constriction of arteries and arterioles causing reduced perfusion and increased systemic resistance to blood flow.

In addition, a lack of CO2 in tissues suppresses the Bohr effect causing reduced release of oxygen in cells. These two effects significantly reduce systemic oxygen delivery (Laffey & Kavanagh, 2002; Nunn, 1987). There are, however, some differences in the reduction of oxygen delivery to various muscle tissues. Lowered oxygenation of the heart muscle due to hypocapnic hyperventilation is well documented (Foëx et al, 1979; Karlsson et al, 1994; Okazaki et al, 1991; Okazaki et al, 1992; Wexels et al, 1985). Similarly, a large reduction in partial O2 pressure takes place in the smooth muscles of the colon (Guzman et al, 1999), with a more moderate decrease in striated and skeletal muscles (Gustafsson et al, 1993; Thorborg et al, 1998; Okazaki et al, 1989). Tissue hypoxia results in anaerobic cellular respiration at rest and elevated blood lactic acid levels (common for all these health conditions). These effects sharpen the sensation of fatigue in the respiratory muscles (experienced as shortness of breath) at rest in patients and during exercise in athletes.

Furthermore, since carbon dioxide is a strong dilator of airways (see links to studies below), hypocapnic bronchoconstriction increases airway resistance. In addition, cell hypoxia causes generation of free radicals, suppression of the immune system, and favors chronic inflammation. Therefore, frequent infections, airway inflammation and extra mucus production can drastically worsen the symptom of dyspnea.

Hence, dyspnea is caused by factors that all originate in chronic hyperventilation at rest.

Effects of hyperventilation on oxygen transport during exercise

During physical exercise, if alveolar CO2 levels drop (overbreathing in relation to CO2 production), the main effects on oxygen transport are the same: less oxygen is delivered to tissues due to hypocapnic vasoconstriction and the suppressed Bohr effect.

Conclusions

Training inspiratory muscles can be an independent purpose for breathing exercises. However, this type of training (improved strength of the inspiratory muscles) does not address the mechanism of reduced oxygen transport during dyspnea (breathlessness or shortness of breath). Therefore, the main physiological potential and benefit of breathing training is improved breathing patterns, VO2max and body oxygenation test results at rest (slower and lighter breathing with reduced respiratory frequency and minute ventilation rate). All these effects can be achieved with longer exhalations during inspiratory muscle training. Lifestyle corrections (see Learn here Section) will improve benefits of inspiratory muscle training as well. The best sport performance effects was found after application of the Training Mask.

This YouTube Video explains how to choose effective breathing techniques for high body-oxygen levels:

For more complete references and abstracts, visit Inspiratory muscle training studies.

Reference pages: Breathing norms and medical facts:
- Breathing norms: Parameters, graph, and description of the normal breathing pattern
- 6 breathing myths: Myths and superstitions about breathing and body oxygenation (prevalence: over 90%)
- Hyperventilation: Definitions of hyperventilation: their advantages and weak points
- Hyperventilation syndrome: Western scientific evidence about prevalence of chronic hyperventilation in patients with chronic conditions (37 medical studies)
- Normal minute ventilation: Small and slow breathing at rest is enjoyed by healthy subjects (14 studies)
- Hyperventilation prevalence: Present in over 90% of normal people (24 medical studies)
- HV and hypoxia: How and why deep breathing reduces oxygenation of cells and tissues of all vital organs
- Body-oxygen test (CP test) : How to measure your own breathing and body oxygenation (two in one) using a simple DIY test
- Body oxygen in healthy: Results for the body-oxygen test for healthy people (27 medical studies)
- Body oxygen in sick : Results for the body-oxygen test for sick people (14 medical studies)
- Buteyko Table of Health Zones: Clinical description and ranges for breathing zones: from the critically ill (severely sick) up to super healthy people with maximum possible body oxygenation
- Morning hyperventilation: Why people feel worse and critically ill people are most likely to die during early morning hours

References: pages about CO2 effect:
- Vasodilation: CO2 expands arteries and arterioles facilitating perfusion (or blood supply) to all vital organs
- The Bohr effect: How and why oxygen is released by red blood cells in tissues
- Cell oxygen levels: How alveolar CO2 influences oxygen transport
- Oxygen transport: O2 transport is controlled by vasoconstriction-vasodilation and the Bohr effects, both of which rely on CO2
- Free radical generation: Reactive oxygen species are produced within cells due to anaerobic cell respiration caused by cell hypoxia
- Inflammatory response: Chronic inflammation in fueled by the hypoxia-inducible factor 1, while normal breathing reduces and eliminates inflammation
- Nerve stabilization: People remain calm due to calmative or sedative effects of carbon dioxide in neurons or nerve cells
- Muscle relaxation: Relaxation of muscle cells is normal at high CO2, while hypocapnia causes muscular tension, poor posture and, sometimes, aggression and violence
- Bronchodilation: Dilation of airways (bronchi and bronchioles) is caused by carbon dioxide, and their constriction by hypocapnia (low CO2)
- Blood pH: Regulation of blood pH due to breathing and regulation of other bodily fluids
- CO2: lung damage: Elevated carbon dioxide prevents lung injury and promotes healing of lung tissues
- CO2: Topical carbon dioxide can heal skin and tissues
- Synthesis of glutamine in the brain, CO2 fixation, and other chemical reactions
- Deep breathing myth: Ignorant and naive people promote the idea that deep breathing and breathing more air at rest is beneficial for health
- Breathing control: How is our breathing regulated? Why hypocapnia makes breathing uneven, irregular and erratic.

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References

Sports Performance
Riganas CS, Vrabas IS, Christoulas K, Mandroukas K.
Specific inspiratory muscle training does not improve performance or VO2max levels in well trained rowers.
J Sports Med Phys Fitness. 2008 Sep;48(3):285-92.
Ergophysiology Laboratory, Department of Physical Education and Sports Sciences, Thessaloniki, Greece.
... CONCLUSION: In conclusion, six weeks of IMT increases inspiratory muscle strength by approximately 28% in highly trained rowers. However, this increase in inspiratory muscle strength does not appear to improve VO2max, dyspnea sensation during exercise, or rowing performance in well-trained rowers.

Klusiewicz A, Borkowski L, Zdanowicz R, Boros P, Wesołowski S.
The inspiratory muscle training in elite rowers.
J Sports Med Phys Fitness. 2008 Sep;48(3):279-84.
Department of Physiology, Institute of Sport, Warsaw, Poland.
... CONCLUSION: The data obtained corroborate the observations that in well-trained athletes the introduction of the principle of incremental inspiratory resistance allows to improve methodically the inspiratory muscles' strength. Once the essential period of IMT has been completed, the training volume should be reduced in order to secure the attained level of the inspiratory muscles' strength.

Volianitis S, McConnell AK, Koutedakis Y, McNaughton L, Backx K, Jones DA.
Inspiratory muscle training improves rowing performance.
Med Sci Sports Exerc. 2001 May;33(5):803-9.
School of Sport and Exercise Sciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
... CONCLUSIONS: IMT improves rowing performance on the 6-min all-out effort and the 5000-m trial.

Romer LM, McConnell AK, Jones DA.
Inspiratory muscle fatigue in trained cyclists: effects of inspiratory muscle training.
Med Sci Sports Exerc. 2002 May;34(5):785-92.
Sports Medicine and Human Performance Unit, School of Sport and Exercise Sciences, The University of Birmingham, Edgbaston, Birmingham, UK.
... CONCLUSION: These data support existing evidence that there is significant global inspiratory muscle fatigue after sustained heavy endurance exercise. Furthermore, the present study provides new evidence that performance enhancements observed after IMT are accompanied by a decrease in inspiratory muscle fatigue.

Romer LM, McConnell AK, Jones DA.
Effects of inspiratory muscle training on time-trial performance in trained cyclists.
J Sports Sci. 2002 Jul;20(7):547-62.
The Human Performance Laboratory, School of Sport and Exercise Sciences, The University of Birmingham, Edgbaston, UK.
... These results support evidence that specific inspiratory muscle training attenuates the perceptual response to maximal incremental exercise. Furthermore, they provide evidence of performance enhancements in competitive cyclists after inspiratory muscle training.

Kilding AE, Brown S, McConnell AK.
Inspiratory muscle training improves 100 and 200 m swimming performance.
Eur J Appl Physiol. 2010 Feb;108(3):505-11. Epub 2009 Oct 16.
School of Sport and Recreation, Faculty of Health and Environmental Sciences, AUT University, Auckland, New Zealand.
... In conclusion, 6 weeks of IMT [inspiratory muscle training] has a small positive effect on swimming performance in club-level trained swimmers in events shorter than 400 m.

Wells GD, Plyley M, Thomas S, Goodman L, Duffin J.
Effects of concurrent inspiratory and expiratory muscle training on respiratory and exercise performance in competitive swimmers.
Eur J Appl Physiol. 2005 Aug;94(5-6):527-40. Epub 2005 Jun 8.
Graduate Department of Exercise Sciences, University of Toronto, Toronto, Canada. greg.wells@sickkids.ca
... We concluded that although swim training results in attenuation of the ventilatory response to hypercapnia and in improvements in pulmonary function and sustainable breathing power, supplemental respiratory muscle training has no additional effect except on dynamic pulmonary function variables.

Mickleborough TD, Stager JM, Chatham K, Lindley MR, Ionescu AA.
Pulmonary adaptations to swim and inspiratory muscle training.
Eur J Appl Physiol. 2008 Aug;103(6):635-46. Epub 2008 May 14.
Human Performance Laboratory, Department of Kinesiology, Indiana University, Bloomington, IN 47405, USA. tmickleb@indiana.edu
... This study has demonstrated that there are no appreciable differences in terms of respiratory changes between elite swimmers undergoing a competitive ST program and those undergoing respiratory muscle training using the flow-resistive IMT device employed in the present study; as yet, the causal mechanisms involved are undefined.

Asthma
Ram FS, Wellington SR, Barnes NC.
Inspiratory muscle training for asthma.
Cochrane Database Syst Rev. 2003;(4):CD003792.
National Collaborating Centre for Women's and Children's Health, Royal College of Obstetricians and Gynaecologists, 27, Sussex Place, Regent's Park, London, UK, NW1 4RG.
... REVIEWER'S CONCLUSIONS: Currently there is insufficient evidence to suggest that inspiratory muscle training provides any clinical benefit to patients with asthma. Due to the limited availability of studies in this area there is a need for further trials evaluating the efficacy of inspiratory muscle training devices in patients with asthma. These studies should investigate asthmatics with a range of severity. They should investigate clinically relevant outcomes such as lung function, symptoms, exacerbation rate and concomitant medications.

Weiner P, Magadle R, Massarwa F, Beckerman M, Berar-Yanay N.
Influence of gender and inspiratory muscle training on the perception of dyspnea in patients with asthma.
Chest. 2002 Jul;122(1):197-201.
Department of Medicine A, Hillel Yaffe, Medical Center, Hadera, Israel.
... CONCLUSIONS: POD [perception of dyspnea] and mean daily beta(2)-agonist consumption in asthmatic women are significantly higher, and the P(Imax) significantly lower, than that of their male counterparts. When the P(Imax) of female subjects following training is equal to that in male subjects, the differences in POD and mean daily beta(2)-agonist consumption disappear.

Weiner P, Berar-Yanay N, Davidovich A, Magadle R, Weiner M.
Specific inspiratory muscle training in patients with mild asthma with high consumption of inhaled beta(2)-agonists.
Chest. 2000 Mar;117(3):722-7.
Department of Medicine A, Hillel-Yaffe Medical Center, Hadera, Israel.
CONCLUSIONS: We have shown that patients with mild asthma, who have a high beta(2)-agonist consumption, have a higher perception of dyspnea than those with normal consumption. In addition, SIMT [specific inspiratory muscle training] was associated with a decrease in perception of dyspnea and a decrease in beta(2)-agonist consumption.

Weiner P, Azgad Y, Ganam R, Weiner M.
Inspiratory muscle training in patients with bronchial asthma.
Chest. 1992 Nov;102(5):1357-61.
Department of Medicine A, Hillel-Yaffe Medical Center, Hadera, Israel.
... We conclude that SIMT [specific inspiratory muscle training], for six months, improves the inspiratory muscle strength and endurance, and results in improvement in asthma symptoms, hospitalizations for asthma, emergency department contact, absence from school or work, and medication consumption in patients with asthma.

Asthma - Children
Lima EV, Lima WL, Nobre A, dos Santos AM, Brito LM, Costa Mdo R.
Inspiratory muscle training and respiratory exercises in children with asthma
J Bras Pneumol. 2008 Aug;34(8):552-8.
Faculdade Santa Terezinha - CEST, Santa Terezinha College - São Luís, Brazil.
... CONCLUSIONS: Programs involving IMT [inspiratory muscle training] and respiratory exercises can increase mechanical efficiency of the respiratory muscles, as well as improving PEF and severity variables.

Asthma and COPD
McConnell AK.
The role of inspiratory muscle function and training in the genesis of dyspnoea in asthma and COPD.
Prim Care Respir J. 2005 Aug;14(4):186-94. Epub 2005 Jun 27.
Sport Sciences Department, Brunel University, Uxbridge, Middlesex UB8 3PH, UK.
... IMT [inspiratory muscle training] offers a relatively accessible non-pharmacological treatment for dyspnoea that also improves exercise tolerance and quality of life.

COPD
Decramer M.
Response of the respiratory muscles to rehabilitation in COPD.
J Appl Physiol. 2009 Sep;107(3):971-6. Epub 2009 Apr 2.
Respiratory Division, University Hospital, University of Leuven, 3000 Leuven, Belgium.
Abstract
Respiratory rehabilitation is known to improve outcomes in patients with chronic obstructive pulmonary disease (COPD)...  The final question is whether improvements in inspiratory muscle function produced by IMT [inspiratory muscle training] lead to improved outcomes in COPD. In all five studies in which training load was adequately controlled, a significant reduction of dyspnea during activities of daily living was found. Eight randomized studies examined the effects of the combination. Greater improvements in exercise capacity were only found in three studies, and none showed a greater reduction in dyspnea.

O'Brien K, Geddes EL, Reid WD, Brooks D, Crowe J.
Inspiratory muscle training compared with other rehabilitation interventions in chronic obstructive pulmonary disease: a systematic review update.
J Cardiopulm Rehabil Prev. 2008 Mar-Apr;28(2):128-41.
Department of Physical Therapy, University of Toronto, Toronto, Ontario, Canada.
... CONCLUSIONS: Performing a combination of IMT [inspiratory muscle training] plus exercise may lead to significant improvements in inspiratory muscle strength and one outcome of exercise tolerance for individuals with COPD.

Geddes EL, O'Brien K, Reid WD, Brooks D, Crowe J.
Inspiratory muscle training in adults with chronic obstructive pulmonary disease: an update of a systematic review.
Respir Med. 2008 Dec;102(12):1715-29. Epub 2008 Aug 15.
School of Rehabilitation Science, Institute of Applied Health Science, Room 403, McMaster University, 1400 Main Street West, Hamilton, ON, Canada L8S 1C7.
... Results suggest that targeted, threshold or normocapneic hyperventilation IMT [inspiratory muscle training] significantly increases inspiratory muscle strength and endurance, improves outcomes of exercise capacity and one measure of quality of life, and decreases dyspnea for adults with stable COPD.

Crowe J, Reid WD, Geddes EL, O'Brien K, Brooks D.
Inspiratory muscle training compared with other rehabilitation interventions in adults with chronic obstructive pulmonary disease: a systematic literature review and meta-analysis.
COPD. 2005 Sep;2(3):319-29.
School of Rehabilitation Science, IAHS-Room 403, McMaster University, 1400 Main Street West, Hamilton, Ontario, Canada.
The purpose of this systematic review was to determine the effect of inspiratory muscle training (IMT) (alone or combined with exercise and/or pulmonary rehabilitation) compared to other rehabilitation interventions such as: exercise, education, other breathing techniques or exercise and/or pulmonary rehabilitation among adults with chronic obstructive pulmonary disease (COPD)...  IMT results in improved inspiratory muscle strength and endurance compared to education. Further trials are required to investigate the effect of IMT (or combined IMT) compared to other rehabilitation inventions for outcomes such as dyspnea, exercise tolerance, and quality of life.

Hill K, Jenkins SC, Philippe DL, Cecins N, Shepherd KL, Green DJ, Hillman DR, Eastwood PR.
High-intensity inspiratory muscle training in COPD.
Eur Respir J. 2006 Jun;27(6):1119-28.
Dept of Pulmonary Physiology, Sir Charles Gairdner Hospital, Hospital Avenue, Nedlands, Western Australia, 6009 Australia.
... In conclusion, high-intensity inspiratory muscle training improves inspiratory muscle function in subjects with moderate-to-severe chronic obstructive pulmonary disease, yielding meaningful reductions in dyspnoea and fatigue.

Larson JL, Covey MK, Wirtz SE, Berry JK, Alex CG, Langbein WE, Edwards L.
Cycle ergometer and inspiratory muscle training in chronic obstructive pulmonary disease.
Am J Respir Crit Care Med. 1999 Aug;160(2):500-7.
University of Illinois at Chicago, Chicago, Illinois, USA.

Sánchez Riera H, Montemayor Rubio T, Ortega Ruiz F, Cejudo Ramos P, Del Castillo Otero D, Elias Hernandez T, Castillo Gomez J.
Inspiratory muscle training in patients with COPD: effect on dyspnea, exercise performance, and quality of life.
Chest. 2001 Sep;120(3):748-56.
Pneumology Service, Virgen Del Rocio University Hospital, Sevilla, Spain.
... CONCLUSIONS: We conclude that targeted IMT [inspiratory muscle training] relieves dyspnea, increases the capacity to walk, and improves HRQL [health-related quality of life] in COPD patients.

Lisboa C, Villafranca C, Leiva A, Cruz E, Pertuzé J, Borzone G.
Inspiratory muscle training in chronic airflow limitation: effect on exercise performance.
Eur Respir J. 1997 Mar;10(3):537-42.
Department of Respiratory Diseases, Catholic University of Chile, Santiago.
... We conclude that inspiratory muscle training using a load of 30% peak maximal inspiratory pressure, improves dyspnoea, increases walking capacity and reduces the metabolic cost of exercise.

Hill K, Jenkins SC, Philippe DL, Shepherd KL, Hillman DR, Eastwood PR.
Comparison of incremental and constant load tests of inspiratory muscle endurance in COPD.
Eur Respir J. 2007 Sep;30(3):479-86. Epub 2007 May 15.
Department of Pulmonary Physiology, Sir Charles Gairdner Hospital, Hospital Avenue, Nedlands, Western Australia, Australia 6009.
... When assessing inspiratory muscle function in chronic obstructive pulmonary disease via tests in which the pattern of breathing is unconstrained, the current authors recommend incremental load tests be used in preference to constant load tests. However, to attribute changes in these tests to improvements in inspiratory muscle endurance, breathing pattern should be controlled.

Garrod R, Lasserson T.
Role of physiotherapy in the management of chronic lung diseases: an overview of systematic reviews.
Respir Med. 2007 Dec;101(12):2429-36. Epub 2007 Sep 17.
School of Physiotherapy, St. George's, University of London, Faculty of Health and Social Care Sciences, Cranmer Terrace, London SW17 0RE, UK.

Others than COPD (asthma, bronchiectasis, cystic fibrosis, pre- and postsurgery, ventilator weaning, neuromuscular diseases, and chronic heart failure)
Padula CA, Yeaw E.
Inspiratory muscle training: integrative review of use in conditions other than COPD.
Res Theory Nurs Pract. 2007;21(2):98-118.
University of Rhode Island, College of Nursing, Kingston 02881, USA.
Inspiratory muscle training (IM training) is a technique that is designed to improve the performance of the respiratory muscles (RMs) that may be impaired in a variety of conditions. Interest in IM training has expanded over the past two decades, and IM training has been used in an increasingly wide range of clinical conditions. However, the benefits of IM training continue to be debated, primarily because of methodological limitations of studies conducted to date. The focus of this article is to provide a critical review of IM training research in conditions other than chronic obstructive pulmonary disease for which it has been used, including asthma, bronchiectasis, cystic fibrosis, pre- and postsurgery, ventilator weaning, neuromuscular diseases, and chronic heart failure. Emphasis is placed on what has been learned, remaining questions, future applications, and significance to practice.

Heart Disease
Laoutaris I, Dritsas A, Brown MD, Manginas A, Alivizatos PA, Cokkinos DV.
Inspiratory muscle training using an incremental endurance test alleviates dyspnea and improves functional status in patients with chronic heart failure.
Eur J Cardiovasc Prev Rehabil. 2004 Dec;11(6):489-96.
Onassis Cardiac Surgery Centre, Athens, Greece.
CONCLUSION: Inspiratory muscle training using an incremental endurance test, successfully increases both inspiratory strength and endurance, alleviates dyspnea and improves functional status in CHF [chronic heart failure].

Stein R, Chiappa GR, Güths H, Dallʼago P, Ribeiro JP.
Inspiratory Muscle Training Improves Oxygen Uptake Efficiency Slope in Patients With Chronic Heart Failure.
J Cardiopulm Rehabil Prev. 2009 Sep 22. [Epub ahead of print]
Exercise Pathophysiology Research Laboratory and Cardiology Division, Hospital de Clinicas de Porto Alegre (Drs Stein, Chiappa, and Ribeiro), School of Physical Therapy, UNILASALLE, Canoas (Mr Güths and Dr Dall'Ago), Department of Physiological Sciences, Fundação Faculdade Federal de Ciências Médicas de Porto Alegre, Porto Alegre (Dr Dall'Ago), and Department of Medicine, Federal University of Rio Grande do Sul, Porto Alegre (Dr Ribeiro), Brazil.
... CONCLUSION: In CHF patients with IMW [inspiratory muscle weakness], IMT [inspiratory muscle training] results in a significant increase in OUES [oxygen uptake efficiency slope].

Sutbeyaz ST, Koseoglu F, Inan L, Coskun O.
Respiratory muscle training improves cardiopulmonary function and exercise tolerance in subjects with subacute stroke: a randomized controlled trial.
Clin Rehabil. 2010 Mar;24(3):240-50. Epub 2010 Feb 15.
Fourth Physical Medicine & Rehabilitation Clinic, Ankara Physical Medicine and Rehabilitation Education and Research Hospital, Ankara, Turkey.
... CONCLUSIONS: Significant short-term effects of the respiratory muscle training programme on respiratory muscle function, exercise capacity and quality of life were recorded in this study.

Darnley GM, Gray AC, McClure SJ, Neary P, Petrie M, McMurray JJ, MacFarlane NG.
Effects of resistive breathing on exercise capacity and diaphragm function in patients with ischaemic heart disease.
Eur J Heart Fail. 1999 Aug;1(3):297-300.
Institute of Biomedical and Life Sciences, Glasgow University, Scotland, UK.
... Independent of the mechanisms involved, this small, uncontrolled study suggests that inspiratory muscle training may improve exercise capacity, diaphragm function and symptoms of breathlessness in patients with chronic coronary artery disease even in the absence of heart failure.

Dall'Ago P, Chiappa GR, Guths H, Stein R, Ribeiro JP.
Inspiratory muscle training in patients with heart failure and inspiratory muscle weakness: a randomized trial.
J Am Coll Cardiol. 2006 Feb 21;47(4):757-63. Epub 2006 Jan 26.
Department of Physiological Sciences, Fundação Faculdade Federal de Ciências Médicas de Porto Alegre, Porto Alegre, Brazil.
... CONCLUSIONS: In patients with CHF and inspiratory muscle weakness, IMT [inspiratory muscle training] results in marked improvement in inspiratory muscle strength, as well as improvement in functional capacity, ventilatory response to exercise, recovery oxygen uptake kinetics, and quality of life.

Winkelmann ER, Chiappa GR, Lima CO, Viecili PR, Stein R, Ribeiro JP.
Addition of inspiratory muscle training to aerobic training improves cardiorespiratory responses to exercise in patients with heart failure and inspiratory muscle weakness.
Am Heart J. 2009 Nov;158(5):768.e1-7. Epub 2009 Oct 2.
Hospital de Clinicas de Porto Alegre, RS, Brazil.
... CONCLUSION: This randomized trial demonstrates that the addition of IMT [inspiratory muscle training] to AE [aerobic exercise training] results in improvement in cardiorespiratory responses to exercise in selected patients with CHF and IMW [inspiratory muscle weakness]. The clinical significance of these findings should be addressed by larger randomized trials.

Mancini DM, Henson D, La Manca J, Donchez L, Levine S.
Benefit of selective respiratory muscle training on exercise capacity in patients with chronic congestive heart failure.
Circulation. 1995 Jan 15;91(2):320-9.
Cardiovascular and Pulmonary Sections, Philadelphia Veterans Administration Medical Center, Pa.
... CONCLUSIONS: Selective respiratory muscle training improves respiratory muscle endurance and strength, with an enhancement of submaximal and maximal exercise capacity in patients with heart failure. Dyspnea during activities of daily living was subjectively improved in the majority of trained patients.

Cystic Fibrosis
de Jong W, van Aalderen WM, Kraan J, Koëter GH, van der Schans CP.
Inspiratory muscle training in patients with cystic fibrosis.
Respir Med. 2001 Jan;95(1):31-6.
Department of Rehabilitation, University Hospital Groningen, The Netherlands.
... After training no significant differences were found in changes from baseline in pulmonary function, exercise capacity, dyspnoea and fatigue. It is concluded that low-intensity inspiratory-threshold loading at 40% of Pimax [maximal static inspiratory pressure] was sufficient to elicit an increased inspiratory-muscle endurance in patients with CF.

Reid WD, Geddes EL, O'Brien K, Brooks D, Crowe J.
Effects of inspiratory muscle training in cystic fibrosis: a systematic review.
Clin Rehabil. 2008 Oct-Nov;22(10-11):1003-13.
Department of Physical Therapy, University of British Columbia, Muscle Biophysics Laboratory, Vancouver, BC, Canada.
...CONCLUSION: The benefit of IMT [inspiratory muscle training] in adolescents and adults with cystic fibrosis for outcomes of inspiratory muscle function is supported by weak evidence. Its impact on exercise capacity, dyspnoea and quality of life is not clear. Future research should investigate the characteristics of the subgroup of people with cystic fibrosis that might benefit most from IMT.

Enright S, Chatham K, Ionescu AA, Unnithan VB, Shale DJ.
Inspiratory muscle training improves lung function and exercise capacity in adults with cystic fibrosis.
Chest. 2004 Aug;126(2):405-11.
School of Health Care Professions, University of Salford, Manchester, UK.
... CONCLUSION: An 8-week program of high-intensity IMT [inspiratory muscle training] resulted in significant benefits for CF patients, which included increased IMF and thickness of the diaphragm (during contraction), improved lung volumes, increased PWC, and improved psychosocial status.

Diabetes
ICorrêa AP, Ribeiro JP, Balzan FM, Mundstock L, Ferlin EL, Moraes RS.
Inspiratory muscle training in type 2 diabetes with inspiratory muscle weakness.
Med Sci Sports Exerc. 2010 Dec 21.
Exercise Pathophysiology Research Laboratory and Cardiovascular Division, Hospital de Clínicas de Porto Alegre. Rua Ramiro Barcelos 2350, 90035-007, Porto Alegre, RS, Brazil 2Department of Medicine, Faculty of Medicine, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
CONCLUSIONS: Patients with type 2 diabetes may frequently present inspiratory muscle weakness. In these patients, IMT [inspiratory muscle training] improves inspiratory muscle function with no consequences in functional capacity or autonomic modulation.

Muscle oxygenation and blood flow
Clark A, Coats A.
Mechanisms of exercise intolerance in cardiac failure: abnormalities of skeletal muscle and pulmonary function.
Curr Opin Cardiol. 1994 May;9(3):305-14.
Department of Cardiac Medicine, National Heart and Lung Institute, London, United Kingdom.
The syndrome of chronic heart failure is characterized by exercise intolerance. Exercise is limited by shortness of breath and fatigue, and either symptom occurs in the same patient depending on the type of exercise performed. Exercise capacity correlates poorly with indices of central hemodynamic function, but the increased ventilatory response in chronic heart failure correlates well with exercise capacity. Possible pulmonary causes have been explored, including increased dead space ventilation, abnormal airway function, and abnormal diffusion capacity. However, the finding of hypocapnia and hyperoxemia in arterial blood during exercise in patients with heart failure suggests that blood gas values reflect hyperventilation, and that any abnormality of pulmonary function is secondary to changes elsewhere. Skeletal muscle is abnormal in chronic heart failure, and shows changes in structure, bulk, exercise capacity, blood flow, and intrinsic metabolic activity...

Gustafsson U, Sjöberg F, Lewis DH, Thorborg P.
The effect of hypocapnia on skeletal muscle microcirculatory blood flow, oxygenation and pH.
Int J Microcirc Clin Exp. 1993 Apr;12(2):131-41.
Clinical Research Center, Faculty of Health Sciences, University Hospital, Linköping, Sweden.
Hypocapnia is known to decrease blood flow and tissue oxygen tension in the brain and the splanchnic organs, but there are few and contradictory results in skeletal muscle. The aim of the present study was to investigate the effect of hypocapnia on microcirculatory blood flow, local skeletal muscle PO2 (PtO2) and pH (pHt)... These results show that hypocapnia induces a 20% decrease in LDF [laser-Doppler flowmetry] flow and a 9% reduction in PtO2 with an unchanged pHt level. In this skeletal muscle model, the decrease in microcirculatory blood flow due to vasoconstriction leads to a reduction in both tissue oxygenation and in the removal of acid metabolites, which counteract a developing tissue alkalosis.

Thorborg P, Jorfeldt L, Löfström JB, Lund N.
Striated muscle tissue oxygenation and lactate levels during normo-, hyper- and hypocapnia. A study in the rabbit.
Microcirc Endothelium Lymphatics. 1988 Jun;4(3):205-29.
Department of Anesthesiology, University Hospital, Linköping, Sweden.
The relationship between striated muscle tissue oxygenation during hyper- and hypocapnia, and lactate levels and venous pO2 (pvO2) was studied in a rabbit model... A decrease in pvO2 was seen during hypocapnia...  In this study, hypercapnia influenced striated muscle tissue oxygenation only to a minor degree while hypocapnia influenced it more but not as much as expected...

Laffey JG & Kavanagh BP
Hypocapnia
New England Journal of Medicine 2002, 347(1) 43-53.
Section "Neurologic Effects of Hypocapnia"
Because both hypocapnia and alkalosis cause a leftward shift of the oxyhemoglobin dissociation curve, off-loading of oxygen at the tissue level is restricted. In addition, hypocapnia causes systemic arterial vasoconstriction, decreasing the global and regional oxygen supply and compounding the reduction in the delivery of oxygen to tissue.

Nunn JF. Applied respiratory physiology, 1987, 3rd ed. London: Butterworths.

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Effect of CO2 on the systemic and coronary circulations and on coronary sinus blood gas tensions, Bulletin of European Physiopathology and Respirology
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Central and regional blood flow during hyperventilation. An experimental study in the pig
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Okazaki K, Okutsu Y, Fukunaga A
Effect of carbon dioxide (hypocapnia and hypercapnia) on tissue blood flow and oxygenation of liver, kidneys and skeletal muscle in the dog
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