It really is time for PT’s working with patients with COPD to consider their toolbox. If your toolbox does not include training the inspiratory muscles, please reconsider. The two systematic reviews that have really demonstrated a benefit are old enough that the understanding gleaned from them should be making it into practice (2007, 2011 - linked below); and I am hoping it is in all cardiopulmonary classes across the country now as a treatment for patients with COPD (or really with any condition that results in reversible weakness of the inspiratory muscles).

One thing you should keep in mind is that specific muscle training for the inspiratory muscles (IMT) is different than aerobic exercise. Most of the RCTs demonstrating an improvement in inspiratory muscle strength use a placebo (or sham) and aerobic exercise. So the benefits empirically observed in samples are not confounded by some sort of aerobic exercise improvement. And, your aerobic training program will not simply fix the specific impairment of weakness in the inspiratory muscles. If you have any background understanding of the Functional Movement Systems (FMS) approach, then you will understand that breathing is a fundamental movement. And like in FMS (the approach not necessarily the screen), general conditioning does not necessarily improve dysfunction in fundamental patterns. What typically happens is the individual adopts a compensated movement pattern that does not lead to improvement in the fundamental pattern. I have lived through this in a way. After tearing my quadricep and doing enough rehabilitation that I could walk with a limp, I knew that walking with a limp would not continue to strengthen my quadricep. I needed to continue to do specific quadricep training and slowly work on using the gained strength in a normal gait cycle (a skilled movement). My limp was a compensation - it’s purpose was to allow me to walk WITHOUT a quadricep that was strong enough to walk normally. Such  compensated pattern cannot train the quadricep to be strong enough to walk normally.

In order to include IMT in your toolbox for patients with COPD you will need to include testing the strength of the inspiratory muscles for both deciding that strengthening is needed, for the actual prescription, and for recording changes over time - if for nothing else to continue to update the prescription. The most common approach to testing the strength is to test “maximal inspiratory pressure” or “MIP.”

You should also consider the influence of dynamic hyperinflation (DHI) on your patient. That samples in the reviews below do not specifically address how DHI influenced their findings. From even a crude causal model of how COPD results in dyspnea on exertion (DOE) we can see that DHI is quite central (well, if you agree with the model I have made). If you disagree - please let me know, I would love to develop it further. In addition to the image below it is on DAGitty where you can modify it and make it your own -find it linked here.

dagitty-model-4

As you can see from the DAG DHI leads to a Low MIP and to a VQ Mismatch, both of which then can lead to DOE downstream. So to really understand whether your patients will benefit, and how much they will benefit from IMT you should consider how much DHI is playing a role in their initial problem. But again, this is only when there is a Low MIP in the first place. You should also not interpret a lack of hypoxia or lack of hypercarbia to mean they do not have DHI, as we are not sure whether the degree of DHI that leads to these downstream effects is proportional to the degree of DHI leading to changes in MIP.

If hyperinflation is so bad that the diaphragm cannot contribute to inspiration, such as someone with a positive Hoover’s sign (lower thoracic paradox) then expect less improvement in MIP with IMT, but we do not know how much (if any) improvement you should expect in DOE. We would reason either way, here rationalizations lead to contradiction, so we really do need some empirical work in this very select group of patients (i.e. impact of IMT on patients with positive Hoover’s sign).

Finally - I cannot at this time talk about IMT and HF as I am in the process of working with colleagues on a clinical practice guideline for PTs working with patients with HF and will be reviewing all of the evidence for a more systematic set of recommendations in that population. However, I would encourage those interested to look into the evidence, as well as the evidence for patients with other conditions. I will tell you, the evidence coheres nicely with our expectation based on knowledge. When those muscles are weak, improving their strength tends to bring some sort of benefit.

  1. Gosselink R, De Vos J, Van Den Heuvel SP, Segers J, Decramer M, Kwakkel G. Impact of inspiratory muscle training in patients with COPD: What is the evidence? Eur Respir J. 2011;37(2):416-425. doi:10.1183/09031936.00031810.

  2. 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;102(12):1715-1729. doi:10.1016/j.rmed.2008.07.005.