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.
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.
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.