As the cases of COVID-19 continue to increase, the long term effects are still emerging. One interesting aspect of this will be what impact it has on the long term effects of the lungs. Treating these patients will continue to be a journey of learning.
The lungs tend to be the most affected organ by COVID-19. And one of the first things you find with patients who have been diagnosed with COVID-19 is the ongoing impairment of the lungs. Some of these patients report continual shortness of breath, fatigue, and palpitations. With the disease, the alveolar epithelial cells and the endothelial cells often receive extensive damage, which could lead to pulmonary fibrosis and pulmonary hypertension.
Patients need to follow up post infection to further follow the disease process. Two of the tests ordered would be CT scans and Pulmonary Function Tests (PFT). It is recommended that patients follow up with full PFTs at 12 weeks post severe infection. Patients with a mild to moderate infection are recommended to perform PFTs if there is an abnormal chest x-ray.
Of all the tests performed during the PFT, the diffusion capacity (DLCO) seems to be the one where there is the most abnormality post COVID-19, with a decrease in values. This decrease in the DLCO appears to be associated with disease severity also. This is what we will look further into.
In the systematic review by Torres-Castro et al, they reviewed data from seven studies (six from China, one from France). In these studies, 380 patients were reviewed. The review looked at restriction, obstruction, and altered diffusion. It reported finding 15% of patients with a restriction, 7% of patients with an obstruction, and 39% of patients with an altered diffusion.
While three of the seven studies did not report DLCO, all of the others found the greatest effect of COVID-19 in follow-up to be the decrease in DLCO. Where the difference in these studies appears is when the patients had their tests performed. Three of the studies performed testing within 30 days of discharge, seeing the greatest decrease in DLCO, between 44-53% of patients. The one study that was performed 3 months after discharge only reported 16.4% of patients with an altered diffusion. This would seem to imply that the long term effects of DLCO may not be as significant with time.
In the report by Qin et al in the European Respiratory Journal, 81 patients performed full PFTs at the 3 month follow up. This study broke the patients into two groups, non-severe (41 patients) and severe (40 patients). This study found that 68% of the severe patients had altered diffusion (<80% of predicted) and 42% of non-severe patients. Patients with ARDS, putting them in the severe category, were more likely to have an impaired diffusion possibly causing pulmonary interstitial damage. This study also showed only 10% of patients with a reduction in TLC and 6% of patients had a FEV1/FVC less than 70%.
In a study by Mendez et al found similar results to the one reported by Torres-Castro. In their study, they found only 24% out of 215 patients had altered diffusion at the three month follow up. This data would almost make you think that the diffusion improves with time, as was seen in similar infections, including SARS and MERS.
Patients with moderate to severe COVID-19 will need to be followed for longer periods to fully understand the impact of COVID-19. As more studies become available, it will be interesting to see if the DLCO will improve in these patients. One option for the patients who continue to suffer from symptoms is enrollment in a Pulmonary Rehabilitation program to improve their quality of life.
- Decrease in DLCO can be seen in patients following COVID-19, with varying results based on severity of disease and time performed
- A decrease in DLCO can be found in Pulmonary Hypertension and Pulmonary Fibrosis, which may possibly be caused by COVID-19 infections
- Pulmonary Rehab programs may be vital to improve the quality of life in patients who have had COVID-19.
- Méndez, R., Latorre, A., González-Jiménez, P., Feced, L., Bouzas, L., Yépez, K., Ferrando, A., Zaldívar-Olmeda, E., Reyes, S., & Menéndez, R. (2021). Reduced Diffusion Capacity in COVID-19 Survivors. Annals of the American Thoracic Society, 10.1513/AnnalsATS.202011-1452RL. Advance online publication. https://doi.org/10.1513/AnnalsATS.202011-1452RL
- Torres-Castro, R., Vasconcello-Castillo, L., Alsina-Restoy, X., Solis-Navarro, L., Burgos, F., Puppo, H., & Vilaró, J. (2020). Respiratory function in patients post-infection by COVID-19: a systematic review and meta-analysis. Pulmonology, S2531-0437(20)30245-2. Advance online publication. https://doi.org/10.1016/j.pulmoe.2020.10.013
- Qin W, Chen S, Zhang Y, et al. Diffusion Capacity Abnormalities for Carbon Monoxide in Patients with COVID-19 At Three-Month Follow-up. Eur Respir J 2021; in press. https://doi.org/10.1183/13993003.03677-2020