Study implicates diaphragm dysfunction as a potential cause for prolonged COVID-19 impairments

By using a neuromuscular ultrasound technique, US researchers reveal that patients who necessitate inpatient rehabilitation after acute hospitalization due to coronavirus disease (COVID-19) have a very high prevalence of diaphragm dysfunction, which is a major muscle of respiration. The study is currently available on medRxiv* preprint server.

Technique for neuromuscular ultrasound examination of hemi-diaphragm

Technique for neuromuscular ultrasound examination of hemi-diaphragm. Image Credit: medrxiv.org/content/10.1101/2020.12.10.20244509v1.full.pdf

The significant burden of chronic disability that ensues after a hospital stay as a result of COVID-19 is evident. Recent studies have shown that basically half of all the patients are not able to return to their working duties two months after hospital discharge.

Moreover, survivors of severe forms of COVID-19 frequently present with cough, shortness of breath, and fatigue following their hospitalization. And while these symptoms may be a result of the damaged lung parenchyma, there is a possibility of underlying neuromuscular respiratory weakness.

In support of the latter hypothesis, there is an increased awareness of neurological COVID-19 manifestations that target the neuromuscular system – stemming from a mild elevation of creatine kinase levels to tetraplegic conditions that end up with tracheostomy (i.e., a surgically created airway to allow for direct access to breathing tube).

In this new study, a research group led by Dr. Ellen Farr from the Northwestern University Feinberg School of Medicine and Shirley Ryan Ability Lab in Chicago, USA, unveils a surprisingly high prevalence of functional and structural alterations in the diaphragm muscle following hospitalization for COVID-19.

The use of portable ultrasound system

The researchers included 25 consecutive patients that have been admitted to the dedicated COVID-19 unit at a single Chicago-based rehabilitation hospital between July and September 2020, noting their comorbidities and many laboratory findings.

A portable ultrasound system was used to assess the diaphragm muscle; more specifically, individual characteristics were used to guide the selection of either a 6-14 MHz linear array or a 2-5 MHz curvilinear array in order to maximize the image clarity.

In any case, diaphragm thickness was assessed at the maximum inspiration and end of expiration, while the thickening ratio has been calculated as thickness at maximal inspiration divided by thickness at end-expiration.

Reduced contractility and atrophy of the diaphragm

From a study cohort (consisting of 76% male and 24% female individuals), there was at least one abnormality of diaphragm muscle function on structure visualized by ultrasound in 80% of cases. Of note, comorbidities such as hypertension, diabetes, and COPD/asthma were detected in 60%, 48%, and 12% of patients, respectively.

Furthermore, supplemental oxygen was provided to a total of 10 patients (40%) at the time of diaphragm ultrasound, and none of the individuals included in the study were dependent on mechanical or assisted ventilation.

In comparison to established normative data, 76% of the study cohort presented with reduced diaphragm thickening ratio (implying reduced contractility), and 20% of patients with diminished diaphragm muscle thickness (suggesting atrophic changes).

Implications for research and practice

"Our study provides new insight into neuromuscular respiratory weakness as an important contributor to prolonged functional impairments in survivors from COVID-19", study authors emphasize the importance of their findings.

Taking into account large numbers of COVID-19 survivors that have persistent dyspnea and fatigues months after disease onset definitely warrants the possibility that diaphragm muscle dysfunction may act as a key contributing factor.

Clinicians should consider a diaphragm ultrasound study if there is clinical concern for neuromuscular respiratory weakness in non-hospitalized patients with COVID-19"

And this is the population where neuromuscular rehabilitation protocols for respiratory muscles are of utmost importance. In the meantime, additional studies are needed to evaluate the exact correlates of diaphragm recovery after hospital discharge in relation to patients’ functional status and risk for further complications.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
  • Farr, E. et al. (2020). Short of Breath for the Long Haul: Diaphragm Muscle Dysfunction in Survivors of Severe COVID-19 as Determined by Neuromuscular Ultrasound. medRxiv. https://doi.org/10.1101/2020.12.10.20244509
Dr. Tomislav Meštrović

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Dr. Tomislav Meštrović

Dr. Tomislav Meštrović is a medical doctor (MD) with a Ph.D. in biomedical and health sciences, specialist in the field of clinical microbiology, and an Assistant Professor at Croatia's youngest university - University North. In addition to his interest in clinical, research and lecturing activities, his immense passion for medical writing and scientific communication goes back to his student days. He enjoys contributing back to the community. In his spare time, Tomislav is a movie buff and an avid traveler.

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