Long COVID Patients Have Impaired Gas Transfer In Lungs Which Cannot Be Detected By Normal CT Scans

A new study led by researchers from University of Oxford-UK and Oxford University Hospitals NHS Trust-UK that was also supported by experts from the University of Birmingham-UK, University of Sheffield-UK and GE Healthcare-Germany has found that many non-hospitalized breathless Long COVID patients have impaired gas transfer in lungs which alarmingly cannot be detected by normal CT scans.

The study findings were published on a preprint server and are currently being peer reviewed. 

https://www.medrxiv.org/content/10.1101/2022.02.01.22269999v1

On 11th March 2020, COVID-19 was declared a global pandemic by the World Health Organisation (WHO). Beyond the acute respiratory manifestations of COVID-19 infection, which can result in severe illness, hospitalisation and death, the medium and long-term problems experienced by people following COVID-19 can be considerable(1).

Large cohort studies have revealed that symptoms can persist months after initial infection in both patients hospitalised with COVID-19 pneumonia and those managed in the community.

The presence of ongoing symptoms related to prior COVID-19 infection is colloquially known as Long-COVID. Although over 200 symptoms have been reported, the most common problems are that of breathlessness, fatigue and brain fog.

Long-COVID presents a global health burden, with many people unable to return to normal activities or employment months after becoming unwell.

The Chest X-ray (CXR) is the commonest imaging modality used in the diagnostic work-up of acute COVID-19 pneumonia and this is often repeated three months after the acute infection in patients requiring hospital admission. Computed Tomography (CT) may be performed to investigate persistent breathlessness if the CXR is normal or there are other concerns regarding COVID-19-related lung damage.

In a small proportion of patients, interstitial lung abnormalities persist and evidence of post-COVID fibrosis is demonstrated(2). These abnormalities may account for dyspnoea, but in the majority of individuals with Long-COVID, CT scans are normal or near normal. Similarly, lung function tests are usually within the normal range.

A recent study looking at a small cohort of post-hospitalised COVID-19 patients at 3 months, reported that hyperpolarised Xenon MRI (Hp-XeMRI), was able to detect abnormalities of alveolar gas transfer even when the CT scans and lung function tests were normal or near normal(3).

HP-XeMRI enables the assessment of ventilation and gas transfer across the alveolar epithelium into red blood cells. It provides regional information of pulmonary vasculature integrity and may be able to identify lung abnormalities not apparent on CT(4).

In Long-COVID, breathing pattern disorder is commonly identified and contributes to breathlessness in a significant proportion of patients(5), but whether there are additional reasons for their breathlessness, such as longer term pulmonary damage is currently unclear.

Specifically, whether the lung abnormalities on Hp-XeMRI in post-hospitalised COVID-19 patients are present in non-hospitalised patients with Long-COVID has not been previously evaluated and is the aim of this study.