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The longer-term effects of COVID-19 on lung physiology remain poorly understood. Here, a new technique, computed cardiopulmonography (CCP), was used to study two COVID-19 cohorts (MCOVID and C-MORE-LP) at both ∼6 and ∼12 mo after infection. CCP is comprised of two components. The first is collection of highly precise, highly time-resolved measurements of gas exchange with a purpose-built molecular flow sensor based around laser absorption spectroscopy. The second component is estimation of physiological parameters by fitting a cardiopulmonary model to the data set. The measurement protocol involved 7 min of breathing air followed by 5 min of breathing pure O2. One hundred seventy-eight participants were studied, with 97 returning for a repeat assessment. One hundred twenty-six arterial blood gas samples were drawn from MCOVID participants. For participants who had required intensive care and/or invasive mechanical ventilation, there was a significant increase in anatomical dead space of ∼30 mL and a significant increase in alveolar-to-arterial Po2 gradient of ∼0.9 kPa relative to control participants. Those who had been hospitalized had reductions in functional residual capacity of ∼15%. Irrespectively of COVID-19 severity, participants who had had COVID-19 demonstrated a modest increase in ventilation inhomogeneity, broadly equivalent to that associated with 15 yr of aging. This study illustrates the capability of CCP to study aspects of lung function not so easily addressed through standard clinical lung function tests. However, without measurements before infection, it is not possible to conclude whether the findings relate to the effects of COVID-19 or whether they constitute risk factors for more serious disease. NEW & NOTEWORTHY This study used a novel technique, computed cardiopulmonography, to study the lungs of patients who have had COVID-19. Depending on severity of infection, there were increases in anatomical dead space, reductions in absolute lung volumes, and increases in ventilation inhomogeneity broadly equivalent to those associated with 15 yr of aging. However, without measurements taken before infection, it is unclear whether the changes result from COVID-19 infection or are risk factors for more severe disease.

BackgroundPost-COVID-19 syndrome presents a challenge when determining the occupational grading of symptomatic military personnel, and their ability to deploy. In particular, the accurate assessment of patients with post COVID-19 syndrome is complicated by health anxiety and coincident symptomatic autonomic dysfunction. We therefore sought to determine whether either symptoms or objective cardiopulmonary exercise testing could predict clinically significant findings in the UK Armed Forces.Methods113 consecutive patients were assessed in a post COVID-19 military clinical assessment pathway. This included symptom reporting, history, examination, spirometry, echocardiography and cardiopulmonary exercise testing (CPET) in all, with chest CT, dual-energy CTPA and cardiac MRI where indicated. Symptoms, CPET findings and presence/absence of significant pathology were reviewed. Data were analysed to identify diagnostic strategies that may be used to exclude significant disease.Results7/113 (6%) patients had clinically significant disease adjudicated by cardiothoracic multi-disciplinary team. These patients had reduced fitness (&Vdot;O2 26.7(±5·1) vs. 34.6(±7·0) ml/kg/min; p = 0·002) and functional capacity (peak power 200 (±36) vs. 247 (±55) Watts; p = 0·026) compared to those without significant disease. Simple CPET criteria (&Vdot;O2 30.0 or VE/&Vdot;CO2 slope >35.0 in isolation) excluded significant disease with sensitivity and specificity of 86% and 83% respectively (AUC 0.89). The addition of capillary blood gases to estimate A-a gradient improved diagnostic performance to 100% sensitivity and 78% specificity (AUC 0.92). Symptoms and spirometry did not discriminate significant disease.ConclusionUK Armed Forces personnel with persistent symptoms post SARS-CoV-2 infection demonstrate reassuringly little organ pathology. CPET and functional capacity testing, but not reported symptoms, allow the exclusion of clinically significant disease.