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Inspiratory muscle training for managing breathlessness

Alison K McConnell
BSc MSc PhD
Professor of Applied Physiology
Department of Sport Sciences
Brunel University
London
E:alison.mcconnell@brunel.ac.uk

Breathlessness, or dyspnoea, is defined as an "uncomfortable sensation of breathing" or a "consciousness of an increased necessity for respiratory effort".(1) Patients with conditions as wide ranging as cancer and neurological disorders experience disabling bouts of breathlessness that profoundly impair their quality of life. However, the patients for whom disabling breathlessness is their primary symptom are most commonly those with asthma, chronic obstructive pulmonary disease (COPD) and heart failure. Breathlessness has proved to be a difficult "nut to crack" pharmacologically, but there is now a large body of evidence that structured programmes of physical exercise (rehabilitation) reduce breathlessness and improve quality of life. This is acknowledged in the latest NICE Guidelines for Management of COPD,(2) which state that pulmonary rehabilitation "should be made available to all appropriate patients".
A British Thoracic Society survey on pulmonary rehabilitation provision in the UK concluded that only 1.7% of the COPD patients who could benefit from pulmonary rehabilitation actually have access to it. Furthermore, in his synopsis of the latest NICE guidelines in Nursing in Practice,(3) Geoff Hall commented that, although pulmonary rehabilitation is strongly recommended for patients with COPD, it is not always practical. Many patients with COPD have co-morbidities that render them unable to walk, including recent myocardial infarction and unstable angina. These contraindications apply equally to patients with heart failure. So what can be done to reduce breathlessness in such patients, or indeed for the thousands who do not have access to pulmonary rehabilitation?
One component of a pulmonary rehabilitation programme that can be applied either in combination with physical exercise or as an independent intervention, is inspiratory muscle training (IMT). With a growing evidence base to support its efficacy as a method of improving breathlessness, exercise tolerance and quality of life, IMT offers a lifeline to many patients for whom pharmacological treatment options have been exhausted.

The neurophysiology of breathlessness
Breathlessness is essentially an increased sense of effort associated with breathing. The intensity of breathlessness is influenced by both chemical and neural feedback from the arterial blood and lungs/inspiratory muscles, respectively. While a wide range of stimuli are known to modulate breathlessness, a primary contributor to the sensation is thought to be the sense of inspiratory muscle effort.
What is often overlooked is the fact that breathing is brought about by the contraction of muscles. The primary muscle of inhalation is the diaphragm, which is assisted by the inspiratory accessory muscles of the chest wall. Breathlessness has been linked primarily to inspiratory muscle effort, not expiratory muscle effort.
The sense of effort that is associated with any muscular act is the result of a balance between the muscle's ability to supply force (its strength), and the force that is being demanded - that is, "supply vs demand". When lifting a heavy object, the sense of effort associated with lifting it is high compared with lifting a light object. However, if we increase the strength of the muscles (improve supply), then the effort of lifting a given object is reduced because the muscles' capacity to supply force has been increased. These principles apply equally well to inspiratory muscles such as the diaphragm.
In patients with asthma, COPD or heart failure, the balance between supply and demand is tilted heavily towards "demand", making the sense of effort disproportionate to the activity.

Breathlessness in asthma, COPD and heart failure
Patients with asthma and COPD have expiratory flow limitation, which leads to dynamic hyperinflation. Expiration is curtailed before the lungs reach their relaxation volume (functional residual capacity), forcing patients to inhale to higher lung volumes, where the elastic work of breathing is high. Hyperinflated patients must work harder to inflate their lungs, placing huge demands on the inspiratory muscles, especially during exercise, when hyperinflation worsens. Similarly, patients with heart failure have pulmonary oedema, a stiff lung, and correspondingly high inspiratory muscle work. The increased sense of muscle effort associated with breathing in these conditions is perceived as breathlessness.

Training the inspiratory muscles
It should be clear from the preceding discussion that a major input to the intensity of breathlessness is a mismatch in the "supply vs demand" relationship for breathing, and that in patients with breathlessness this relationship is tilted too far towards demand. Pharmacological approaches to reducing breathlessness in patients with airway obstruction focus upon reducing demand by improving lung emptying (minimising the degree of hyperinflation). However, the "supply vs demand" relationship can also be restored by improving the supply side of the equation through training of the inspiratory muscles.
Once a controversial treatment, IMT has now achieved a good evidence base, particularly in patients with COPD. The NICE COPD guidelines cite the conclusions of a meta-analysis on the effects of IMT in patients with COPD.(4) The authors of the meta-analysis concluded that: "inspiratory muscle training is an important addition to a pulmonary rehabilitation programme directed at chronic obstructive pulmonary disease patients".
The role of IMT in patients with asthma also has a growing evidence base. Well-controlled studies have demonstrated improvements in inspiratory muscle strength, breathlessness and quality of life.(5-8) In the case of asthma, patients with high levels of breathlessness and high consumption of b(2)-agonists have shown remarkable improvements in both. For example, a reduction in b(2)-agonist consumption of 40-80% is commonly reported after IMT.(5-8) IMT is therefore highly recommended for this group of asthmatic patients.
Successful outcomes with IMT have most commonly employed a technique of inspiratory muscle strength training known as pressure threshold training. There are currently two proprietary devices of this type that are supported by peer-reviewed research in scientific journals: POWERbreathe(®), manufactured by Leisure Systems International Ltd, Southam, UK; and Threshold®, manufactured by Respironics, Cedar Grove, NJ, USA. Figure 1 depicts the POWERbreathe device, which was developed and manufactured in the UK and is readily available from Lloyds Chemists and Boots. Pressure threshold devices have an excellent evidence base in patients with lung disease, and also in athletes, where training has been shown to improve performance in highly trained individuals.(9)

[[NIP20_fig1_62]]

In pressure threshold IMT, the user breathes in against a spring-loaded valve. The load (or weight) of the valve can be adjusted to accommodate a wide range of starting abilities, as well as the rapid improvements in strength that accompany training. Increases in strength of 25-40% are achievable within 4-6 weeks. The training programme is simple, can be conducted in the patient's own home and with a minimal imposition upon their daily lives. Because the intrathoracic pressures that are generated are negative, the technique is very safe, and no adverse events have been reported to date.
A typical training programme consists of 30 breaths twice daily; this takes about three minutes per session (once in the morning and once in the evening). The training load is set by trial and error; the user identifies the load at which they can successfully execute 30 breaths. This individualised load increases progressively as their inspiratory muscles become stronger, and is achieved by small adjustments every few days. After the first 4-6 weeks, patients can switch to a "maintenance" programme of training once per day every other day.

Conclusion
Patients with breathlessness often have weak breathing muscles that have very high demands placed upon them. There is now good evidence that specific training of the inspiratory muscles improves breathlessness and quality of life. Although not yet available on prescription, a growing number of patients are benefiting from IMT.
IMT represents a cost-effective management tool that every patient with breathlessness could, and arguably should, have access to.

References

  1. Meakins J. The cause and treatment of dyspnea in cardiovascular disease. BMJ 1923;1:1043-5.
  2. National Institute for Clinical Excellence. Guidelines for the ­management of COPD. London: NICE; 2004.
  3. Hall G. NICE guideline sets COPD management standards. NiP 2004;17:43-6.
  4. Lotters F, van Tol B, Kwakkel G, Gosselink R. Effects of controlled inspiratory muscle training in patients with COPD: a meta-analysis.Eur Respir J 2002;20:570-6.
  5. 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;122:197-201.
  6. Weiner P, Magadle R, Beckerman M, Berar-Yanay N. The relationship among inspiratory muscle strength, the perception of dyspnea and inhaled b2-agonist use in patients with asthma. Can Respir J 2002;9:307-12.
  7. Weiner P, Berar-Yanay N, Davidovich A, Magadle R, Weiner M. Inspiratory muscle training in patients with mild asthma with high consumption of inhaled b(2)-agonists. Chest 2000;117:722-7.
  8. Weiner P, Azgad Y, Ganam R, Weiner M. Inspiratory muscle training in patients with bronchial asthma. Chest 1992;102:1357-61.
  9. Romer LM, McConnell AK, Jones DA. Effects of inspiratory muscle ­training on time-trial performance in trained cyclists. J Sports Sci 2002;20:547-62.

Resources
POWERbreathe
W:www.powerbreathe.com
Respironics
W:www.respironics.com

Further reading
Dyspnoea in health and obstructive pulmonary disease: the role of respiratory muscle function and training McConnell AK, Romer LM. Sports Med 2004;34:117-32
Respiratory muscle training in health humans: ­resolving the controversy McConnell AK, Romer LM. Int J Sports Med 2004;25:284-93
Dyspnoea in COPD: can ­inspiratory muscle training help? Hill K, Jenkins SC, Hillman DR, Eastwood PR. Aust J Physiother 2004;50:169-80
The effect of specific ­inspiratory muscle training on the sensation of ­dyspnoea and exercise ­tolerance in patients with congestive heart failure. Weiner P, Waizman J, Magadle R, Berar-Yanay N, Pelled B. Clin Cardiol 1999;22:727-32.