In cases of coronavirus disease 2019 (COVID-19), patients with poor baseline health have an elevated risk of severe respiratory complications and worse outcomes following hospital admission and mechanical ventilation. In addition, these patients are generally more likely to demonstrate impaired respiratory muscle performance.1

In a recent review published  in the American Journal of Medicine, Rich Severin PT, DPT, PhD(c), CCS, a PhD candidate in the department of physical therapy at the University of Illinois-Chicago, and colleagues “hypothesize that impaired respiratory muscle performance is an underappreciated factor contributing to poor outcomes unfolding during the coronavirus pandemic.” As such, they advocate for routine screening and intervention to address these impairments as indicated “with the goal of unburdening healthcare systems during future pandemic crises.”1

Assessment of maximal static inspiratory pressure (MIP) using noninvasive handheld manometers has been shown to quantify respiratory muscle strength across heterogeneous populations. Standardized protocols for the use of these devices have been published by the American Thoracic Society and the European Respiratory Society.2,3 While the devices are easily accessible and affordable, MIP reflects only one measure of respiratory muscle weakness, and patients with the same MIP may demonstrate substantial intersubject differences in other measures of respiratory muscle performance.3

Alternately, the Test of Incremental Respiratory Endurance (TIRE) captures MIP along with other relevant measures, and the “combination of these values provide a more comprehensive assessment which may identify characteristics of respiratory muscle weakness or fatiguability that may be missed when only measuring” MIP, Dr Severin and colleagues noted.4,1


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Although researchers have not yet explored the effects of respiratory muscle training on the risk for virus-associated respiratory failure, a range of findings support its potential value in this setting. Across various studies, training prior to surgery was linked to reductions in postoperative pulmonary complications — up to 50% in patients undergoing cardiothoracic or abdominal surgery — and reduced length of hospitalization.1,5

In other studies, patients with chronic obstructive pulmonary disease who participated in home-based training experienced reductions in mortality and the risk of intubation, and in those who required mechanical ventilation,  improved weaning outcomes and reduced lengths of hospital stay.6-8

The authors hypothesized “that screening for respiratory muscle impairment in patients with dyspnea or characteristics associated increased risk of severe respiratory complication due to viral infection may be advantageous.”1 They suggested a model in which high-risk patients would be screened at routine annual visits or during seasonal vaccinations, and those with impaired performance would be instructed to implement a home-based respiratory muscle training program, with a follow-up assessment to occur after 4 weeks.

“This model could potentially result in substantial downstream benefits by reducing the number of infectious cases requiring intensive care unit and mechanical ventilation during a pandemic,” which would also help to preserve the availability of these resources for other treatment needs unrelated to pandemic care.1

We further discussed this concept in a recent interview with Dr Severin.

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How does impaired respiratory muscle performance contribute to poorer outcomes after ICU admission and mechanical ventilation?

This answer has 2 components to it: If you have weaker respiratory muscles, they operate at lower efficiency and with a smaller reserve. This can potentially create an imbalance between the demands of breathing and the ability to generate force, which can lead to shortness of breath. The use of mechanical ventilation can induce profound and rapid atrophy and weakness of the respiratory muscles, especially in the context of someone with a critical illness. Therefore, if someone with respiratory muscle weakness at baseline receives mechanical ventilation, they may have a difficult time weaning from it. Prolonged weaning time may lead to additional complications and poorer outcomes. 

What is the potential role of respiratory muscle performance screening in reducing the burden of future pandemics?

The current evidence demonstrates that individuals who are at the greatest risk for COVID-19 infection and significant manifestations (such as ARDS [acute respiratory distress syndrome) are individuals with poor baseline health and obesity.1 Interestingly, respiratory muscle weakness and increased demands of breathing are often observed in these populations. As I mentioned, when a patient has weaker respiratory muscles or higher demands of breathing, the muscles operate close to their margins and have a limited reserve. When these patients sustain a lung infection, the demands increase further, and they have problems due to the lack of adequate reserve. 

Unfortunately, respiratory muscle performance testing has not frequently been performed in clinical practice — even prior to this pandemic — and it is not included in the guidelines for patients with dyspnea or anesthesia screening.1 Therefore, we proposed screening respiratory muscle performance in these high-risk patients. Following testing, if patients are identified as having weaker respiratory muscles, they can undergo a prophylactic respiratory muscle training program. The evidence suggests that improvements in respiratory muscle strength can occur after very short durations —as short as 5 days.1 Thus, training could either be done long-term or even at the outbreak of a viral pandemic.  

When and how should these services be implemented?

We proposed several different clinical touchpoints in the paper. An interesting model would be that when high-risk patients receive their routine annual vaccinations, they could easily receive the screening. The tests are noninvasive, inexpensive, low-risk, reliable, short in duration, and easy to conduct. Patients could be prescribed a training device for home use, many of which have testing features as well. With the use of an app or telehealth platform, patients could conduct both training and monitoring remotely.

What should be the focus of further investigation regarding this topic?

There is a need for research to better characterize respiratory muscle performance using measures beyond the MIP. Most of the literature investigating respiratory muscle performance uses MIP as the primary outcome. While MIP is reliable, valid, and well-established, its ability to assess the muscles is limited. Peak static pressures are essentially the one-rep max of the respiratory muscles. [Editor’s note: The one-repetition maximum is a term used in weight training to indicate the maximum amount of weight that an individual can lift for one repetition of an exercise.]

However, we typically do not breathe at our one-rep max. This measure also only provides a single snapshot or a “low-resolution” assessment of respiratory muscle performance. We proposed the use of the TIRE, which provides peak static pressure as well as a fatigability measurement by measuring how long the patient can sustain a maximal effort. We feel that this may be a more robust assessment. This test has been validated in several clinical populations but needs to be investigated in other populations. 

The other important area would be to conduct a research study to investigate whether our hypothesis is valid. There has been no evidence to date to indicate whether respiratory muscle performance influences outcomes following a viral infection of any kind. However, there is some preliminary work that does suggest this is a plausible hypothesis, and we are currently working on developing studies to test this hypothesis at our institution.

References

1. Severin R, Arena R, Lavie CJ, Bond S, Phillips SA. Respiratory muscle performance screening for infectious disease management following COVID-19: a highly pressurized situation [published online April 25, 2020]. Am J Med. doi:10.1016/j.amjmed.2020.04.003

2. Laveneziana P, Albuquerque A, Aliverti A, et al. ERS statement on respiratory muscle testing at rest and during exercise. Eur Respir J. 2019;53(6).

3. American Thoracic Society/European Respiratory Society. ATS/ERS Statement on respiratory muscle testing. Am J Respir Crit Care Med. 2002;166(4):518‐624.

4. Formiga MF, Roach KE, Vital I, et al. Reliability and validity of the test of incremental respiratory endurance measures of inspiratory muscle performance in COPD. Int J Chron Obstruct Pulmon Dis. 2018;13:1569‐1576.

5. Martin AD, Smith BK, Davenport PD, et al. Inspiratory muscle strength training improves weaning outcome in failure to wean patients: A randomized trial. Crit Care. 2011;15(2):R84.

6. Nikoletou D, Man WDC, Mustfa N, et al. Evaluation of the effectiveness of a home-based inspiratory muscle training programme in patients with chronic obstructive pulmonary disease using multiple inspiratory muscle tests. Disabil Rehabil. 2016;38(3):250-259.

7. Langer D, Charususin N, Jácome C, et al. Efficacy of a novel method for inspiratory muscle training in people with chronic obstructive pulmonary disease. Phys Ther. 2015;95(9):1264-1273.

8. Sørensen D, Svenningsen H. Adherence to home-based inspiratory muscle training in individuals with chronic obstructive pulmonary disease. Appl Nurs Res. 2018;43:75-79.