Shortness of breath, sometimes also called air hunger, is a frequent symptom of Long COVID syndrome and may last for months after acute SARS-CoV-2 infection. One of the reasons for persistent shortness of breath is dysfunctional breathing, which is a respiratory condition described as abnormal breathing patterns at rest or exercise. The best-known form of dysfunctional breathing is hyperventilation syndrome. Healthy people can experience short-term dysfunctional breathing after heavy exercise or due to stress. Chronic changes in breathing patterns can be caused by infection, including with SARS-CoV-2, which can result in persistent shortness of breath. Because we still know little about dysfunctional breathing associated with Long COVID, a recent Swiss study investigated a group of Long COVID patients with long-term shortness of breath.
Long COVID patients from two Swiss clinics
This retrospective study included 51 adult patients experiencing shortness of breath more than six weeks after confirmed SARS-CoV-2 infection who were referred to Long COVID outpatient clinics of the Hôpital du Valais and Hôpital Riviera Chablais in Switzerland. The median age of patients was 64 years and two-thirds were men. All patients underwent cardiopulmonary exercise testing (CPET) on a cycle ergometer, which measures the performance of the lungs and heart at rest and during exercise. Patients also filled in standard questionnaires to assess anxiety and depression, as well as their quality of life.
Dysfunctional breathing was observed more than 200 days after SARS-CoV-2 infection.
Dysfunctional breathing is common among patients with Long COVID
Results of CPET showed that approximately 30% of patients (n=15) were diagnosed with dysfunctional breathing. These patients had different both breathing frequency and the amount of inhaled or exhaled air (i.e., tidal volume) during exercise compared with healthy individuals but most of them did not hyperventilate. This can be seen in the Figure below, presenting breathing frequency (violet dots) and tidal volume (yellow dots) in patients with dysfunctional breathing and healthy people. Many patients also experienced air hunger and sighing at rest, and deep sighing with yawning during exercise. Despite this important respiratory discomfort, patients had normal exercise capacity.
Of other patients included in the study, 28 had a respiratory limitation, which means that only a smaller amount of air can be breathed in or out because of disruption of the oxygen and carbon dioxide exchange in the lung. A small group of 8 patients had normal CPET results but they had low oxygen content in the blood (hypoxia) due to gas exchange abnormalities.
Patients with dysfunctional breathing
BF, breathing frequency; VE, minute ventilation, VT, tidal volume (amount of air that moves into or out of the lungs during a breath)
What does this study add to existing knowledge?
These data are important because this is the first study to report dysfunctional breathing without hyperventilation in patients with long-lasting shortness of breath after SARS-CoV-2 infection. However, the Swiss researchers noted that these findings need to be further explored in larger studies.
Another important observation of this study is that patients with dysfunctional breathing had no signs of lung disease that could cause shortness of breath. One of the explanations is that SARS-CoV-2 infection might spread to the respiratory center in the brain and disturb breathing control. The authors underlined that the association between dysfunctional breathing and the involvement respiratory center in COVID-19 patients is only a hypothesis and should be verified with further studies.
Almost 40% of patients had an anxiety score >7, indicating a possible or certain anxiety.
The impact on clinical practice
This study contributes to a better understanding of dyspnea in patients with Long COVID. Although patients experiencing dysfunctional breathing had normal oxygen consumption, they reported reduced quality of life because of the harmful effect of the disease. As the authors highlighted, these data suggest that improvement in exercise capacity may not relieve the feeling of shortness of breath in this patient group. In practice, rehabilitation programs should therefore include specific physiotherapeutic interventions that target control of breathing.