Medical Grand Rounds: The Pearls and Pitfalls of Pulmonary Function Tests
Georgia Kersche, MSc Candidate (TMED)
On Thursday, Translational Medicine graduate students had the privilege of hearing from Dr. Neder, an esteemed clinician-scientist of respirology. Using relevant clinical scenarios, Dr. Neder explained how pulmonary function tests (PFTs) help with clinical decision making, highlighting their value and the nuance of individual physiology.
PFTs are a valuable clinical tool that guide the diagnosis and care of patients with a possible respiratory pathology. They provide insight into the functioning of the large and small airways and the efficiency of gas exchange in the pulmonary capillary bed (1). Spirometry is the least invasive and most frequently used PFT (1). It involves plotting lung volume over time to show the total air expelled, called the forced vital capacity (FVC), and the forced expiratory volume in the first second (FEV1) (2). The ratio of FEV1/FVC helps identify obstructive or restrictive lung defects. A low FEV1 compared to FVC indicates obstruction, suggesting COPD or asthma, and a reduced FVC indicates restrictive disorders (1,2). In many patients, spirometry allows early detection of COPD so that interventional measures like smoking cessation can be started quickly (2). Another test involving the inhalation of 0.3% carbon monoxide analyzes the diffusing capacity of the lungs, called DLco (3). DLco helps identify emphysema and pulmonary emboli by evaluating the integrity and surface area of the alveolar membrane (3). By assessing how efficiently carbon monoxide can bond hemoglobin we determine if reduced blood flow in the lung parenchyma or thickening of alveolar membranes are contributing to limited respiratory functioning (3, 4). Other tests such as exercise studies assist in identifying and ruling out other conditions (1, 4).
Patient context is critical when interpreting PFT. Certain conditions can mask pulmonary pathologies or suggest illness when it is not there (4). For example, severely obese individuals may show a restrictive pattern on PFTs which would resolve with weight loss, but asthma in these individuals could be missed due to the pseudo-normalization of their scores to within normal limits as a result (5). A bronchodilator can help rule out false negatives of asthma in this cohort (5). Another confounding factor is a patient’s blood volume and hemoglobin content, as the Haldane effect can cause higher dissolved CO2 when oxygen saturation is higher which explains the problem of supplemental oxygen in COPD patients (6). But this should also be taken into account in patients with anemia, on hemodialysis, or in shock due to the lower hemoglobin and chloride present to buffer CO2 in the blood (6).
Dr. Neder and the class discussed translating these findings into a more comprehensive PFT requisition form to prevent misinterpretation of PFTs. This would give more context to the respirologists to determine gauge normal limits and would remind other physicians of the various factors that affect the performance and results shown on a PFT. We also proposed a more streamlined PFT report that includes only the most necessary information for a treating physician such as FEV1/FVC, adjusted DLCO, and abnormal findings. Finally, recent investigations into how artificial intelligence (AI) can assist in pulmonary dysfunction diagnostics have shown promising evidence for the role of algorithms in this field (7,8). Still, there is no replacing human intuition by specialists like the presenter, but any improvement in the efficiency of diagnosing patients with these minimally invasive techniques is worth further inquiry.
During our discussion Dr. Neder took the time to answer each of our questions thoroughly, explaining the science while sprinkling in some of his wisdom along the way. He encouraged the maintenance of a curious mind when conducting research. He also emphasized how vital the role of a clinician-scientist is, in that both the patient-facing role and the concurrent research is necessary to ask relevant questions about patient healthcare. Further, he mentioned the importance of having good mentors throughout our careers. This linked back to our first discussion after Grand Rounds where we heard from Dr. Trier about improving medical education using a coaching mentality. It seems that Dr. Neder embodies the passion and patience Dr. Trier is aiming to cultivate in established physicians, suggesting that he would be an excellent coach for learners.
As many of us TMED students have limited backgrounds in respirology, Dr. Neder did an excellent job at creating an in-depth, interesting presentation about respirology’s every-day role in the hospital. I look forward to hearing from my colleagues about their thoughts on the presentation and the potential for innovations around PFTs.
- Ranu, H., Wilde, M., & Madden, B. (2011). Pulmonary function tests. The Ulster medical journal, 80(2), 84–90.
- Pierce R. (2005). Spirometry: an essential clinical measurement. Australian family physician, 34(7), 535–539.
- Hughes, J., & Dinh-Xuan, A. (2017). The DL NO /DL CO ratio: Physiological significance and clinical implications. Respiratory Physiology & Neurobiology, 241, 17-22. doi: 10.1016/j.resp.2017.01.002
- Culver, B., Graham, B., Coates, A., Wanger, J., Berry, C., & Clarke, P. et al. (2017). Recommendations for a Standardized Pulmonary Function Report. An Official American Thoracic Society Technical Statement. American Journal Of Respiratory And Critical Care Medicine, 196(11), 1463-1472. doi: 10.1164/rccm.201710-1981st
- Pellegrino, R. (2005). Interpretative strategies for lung function tests. European Respiratory Journal, 26(5), 948-968. doi: 10.1183/09031936.05.00035205
- Petersson, J., & Glenny, R. (2014). Gas exchange and ventilation–perfusion relationships in the lung. European Respiratory Journal, 44(4), 1023-1041. doi: 10.1183/09031936.00037014
- Topalovic, M., Laval, S., Aerts, J., Troosters, T., Decramer, M., & Janssens, W. (2017). Automated Interpretation of Pulmonary Function Tests in Adults with Respiratory Complaints. Respiration, 93(3), 170-178. doi: 10.1159/000454956
- Topalovic, M., Das, N., Burgel, P., Daenen, M., Derom, E., & Haenebalcke, C. et al. (2019). Artificial intelligence outperforms pulmonologists in the interpretation of pulmonary function tests. European Respiratory Journal, 53(4), 1801660. doi: 10.1183/13993003.01660-2018