According to a team of German researchers, chronic breathlessness (dyspnea) is common after COVID-19, even with normal heart and lung function. In a recent study, they investigated the diaphragm muscle’s role in the experience of long-term breathing problems after COVID-related hospitalization and recovery. Their findings could have clinical significance for helping long-haulers recover breathing function.*

What is the role of the diaphragm?

The diaphragm is a thin, dome-shaped skeletal muscle just beneath the lungs and heart, dividing the abdomen and chest. It’s the principal muscle used in respiration or breathing, and it contracts and expands every time we inhale and exhale. When we breathe in, the diaphragm contracts and flattens, producing a vacuum that draws air into the lungs; when we exhale, the diaphragm relaxes and air is moved out of the lungs.

What the researchers did

A team of researchers from Germany’s University Hospital RWTH Aachen investigated the strength of the diaphragm muscle in COVID-19 survivors who continued experiencing breathlessness upon exertion. As described in the American Journal of Respiratory and Critical Care Medicine, the study followed 50 patients who had been hospitalized with COVID-19.

• The average age was 58 years.
• Fourteen patients were women.
• Half the patients received mechanical ventilation, the other half non-intensive care.
• Patients were evaluated using a variety of measures, including:
  • Pulmonary function tests
  • 6-minute walk test
  • Echocardiography
  • Diaphragm ultrasound
  • Phrenic nerve stimulation in the neck, to determine diaphragmatic strength

Diaphragmatic strength was then compared to that of healthy controls.

What they found

Compared to controls, patients’ diaphragmatic strength was significantly impacted at 15 months post-hospitalization, regardless of whether or not patients had received mechanical ventilation. The researchers found that:

• Ultrasound detected diaphragmatic dysfunction in about 80% of patients.
• About two-thirds of patients had mild or severe breathlessness upon exertion. 
• In the remaining one-third, there was mild-to-no breathlessness upon exertion.

Finally, diaphragmatic weakness after phrenic nerve stimulation was associated with some breathlessness upon exertion.

No significant heart or lung function abnormalities were found.

What it means

The authors concluded that the study result “identifies diaphragm muscle weakness as a correlate for persistent dyspnea in patients after COVID-19 in whom lung and cardiac function are normal.”

Study co-author Jens Spiesshoefer, M.D. says that finding a potential explanation for exertional breathlessness in Long COVID can be reassuring for patients. It also means that respiratory muscle training, shown to be effective for diaphragmatic weakness, could have therapeutic benefits.

The authors note their study is limited in important ways. For example, diaphragmatic weakness could be due to more general post-infection muscle weakness and not COVID-19 specifically. Other factors leading to a weak diaphragm could be phrenic nerve dysfunction or ICU bedding, for instance. Studies with control subjects who’ve survived non-COVID pneumonia are needed to better understand diaphragmatic weakness after lung infection, they say.

Still, regardless of COVID specificity, “the extent of diaphragm muscle weakness and its clear association with otherwise unexplained persistent dyspnea is a significant finding,” especially given the global healthcare impact from the large number of post-COVID patients, they say.

*Short, E. (2023, January 6). Weakened Diaphragm May Contribute to Long COVID Dyspnea. MedPage Today. https://www.medpagetoday.com/infectiousdisease/longcovid/102547