The Role of Pulmonary Function Testing in the Diagnosis and Management of COPD.

Pulmonary function testing (PFT) has a long and rich history in the definition, diagnosis, and management of COPD. For decades, spirometry has been regarded as the standard for diagnosing COPD; however, numerous studies have shown that COPD symptoms, pathology, and associated poor outcomes can occur, despite normal spirometry. Diffusing capacity and imaging studies have called into question the need for spirometry to put the "O" (obstruction) in COPD. The role of exercise testing and the ability of PFTs to phenotype COPD are reviewed. Although PFTs play an important role in diagnosis, treatment decisions are primarily determined by symptom intensity and exacerbation history. Although a seminal study positioned FEV1 as the primary predictor of survival, numerous studies have shown that tests other than spirometry are superior predictors of mortality. In years past, using spirometry to screen for COPD was promulgated; however, this only seems appropriate for individuals who are symptomatic and at risk for developing COPD.

Real-world diffusing capacity simulation data: how well do they fit current European Respiratory Society/American Thoracic Society acceptability criteria?

ERS/ATS D LCO standards recommend acceptability ranges for weekly D LCO simulation testing performed with a 3-L syringe. On some devices, the ERS/ATS limits may exceed or not fit a 3-sd range, in which case, simulation ranges based on 3 sd may be appropriate. https://bit.ly/3Z0YoZL.

Validation of the clinical utility of sGaw as a response variable in methacholine challenge testing.

BACKGROUND AND OBJECTIVE: Airway hyperresponsiveness (AHR) is commonly assessed by a methacholine challenge test (MCT), during which a provocative concentration causing a 20% reduction in forced expiratory volume in 1 second (FEV1 ) (PC20 ) < 8 mg/ml is considered a positive response. However, a fall in specific airway conductance (sGaw) may also have clinical significance. The purpose of this study was to assess whether AHR determined by a provocative concentration causing a 40% reduction in sGaw (PC40 ) < 8 mg/ml corresponds to a clinical diagnosis of asthma. METHODS: We analysed the changes in spirometry, lung volumes and sGaw during MCT in 211 randomly selected patients being evaluated for AHR to support a clinical diagnosis of asthma. RESULTS: The mean (SD) age of the group was 53 (15) years, with 141 women (67%). Overall lung function was normal, with FEV1  = 92 (15) % predicted, total lung capacity = 97 (13) % predicted and sGaw = 0.19 (0.15-0.23) L/s/cm H2 O/L, (median, 25-75 IQR). There were many more patients who responded by PC40 only (n = 120) than who responded by PC20 (n = 52). There was no significant difference in asthma diagnosis between the PC20 (98%) and PC40 (93%) groups, and we estimate 34% of patients with a diagnosis of asthma would have been classified as having no AHR if only the FEV1 criterion was used. CONCLUSION: Changes in sGaw during MCT indicate clinically significant AHR in support of a clinical diagnosis of asthma among patients being evaluated for asthma.

Verification of Assayed Blood Gas Quality Control Ranges.

BACKGROUND: Blood gas quality control (QC) is an essential and mandatory part of a laboratory's quality plan. The acceptable QC range should be 2 SD from the mean value. The use of assayed QC material does not negate the responsibility of the laboratory to calculate the mean and 2 SD ranges of QC measurements for verification. Verifying assayed QC ranges is a Clinical Laboratory Improvement Amendment (CLIA) requirement. This study shows the results of assayed QC mean and 2 SD range verification from a blood gas analyzer. METHODS: QC data from a blood gas analyzer were compared to manufacturer-provided mean and ranges. The percent difference between the measured mean and the manufacturer-provided mean was calculated to assess agreement. The measured SD was used to determine how many SD the manufacturer-provided ranges were from the measured mean. RESULTS: The largest difference in mean values was 2.27% > the manufacturer-provided mean. Forty-eight percent of all mean value comparisons showed a difference of 0%, and 71% were < 1%. The manufacturer-provided ranges were considerably wider than the measured 2 SD range, ranging from 2.4-75 SD. None of the manufacturer-provided ranges were deemed acceptable for clinical use. CONCLUSIONS: Our analysis validates the CLIA mandate and American Association for Respiratory Care Clinical Practice Guideline recommendation that laboratories must verify manufacturer-provided QC means and ranges and adjust QC means and ranges to match the performance of their blood gas analyzer.

Use of neurally adjusted ventilatory assist (NAVA) in a patient with severe SARS-CoV-2 pneumonia: A case report.

Introduction: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pneumonia may necessitate intubation and prolonged mechanical ventilation. Early in the course of mechanical ventilation neuromuscular blocking agents may be used to allow synchronous lung protective ventilation. However, patients with SARS-CoV-2 pneumonia tend to have an intense respiratory drive resulting in patient-ventilator asynchrony when neuromuscular blocking agents are discontinued. Case and Outcomes: A 75-year-old male was admitted to the hospital with SARS-CoV-2 pneumonia requiring invasive mechanical ventilation. By ventilator day 5 the neuromuscular blocking agent had been discontinued, and the patient was markedly asynchronous in the volume control mode despite receiving continuous intravenous sedatives. The ventilator mode was changed to the neurally adjusted ventilatory assist (NAVA) mode. Initially NAVA resulted in improved synchrony and reduced work of breathing. However, a few days later the patient's tidal volume had fallen to <300 mL on NAVA despite increases in the NAVA level. It appeared that the inspiratory phase was prematurely terminating, and the expiratory threshold in NAVA is not adjustable. The ventilator mode was changed to pressure support resulting in an increased tidal volume and reduced respiratory frequency. Conclusion: In patients with SARS-CoV-2 pneumonia and intense respiratory drive, the performance of NAVA may be variable. NAVA may result in hypopnea and tachypnea when compared with pressure support. An assessment of the impact of an adjustable expiratory threshold in NAVA is warranted.

Weight-based reference equations for the 6-min walk test can be misleading in obese patients.

Weight-based reference equations for the 6-min walk test can produce normal results despite poor performance. Using ideal body weight- or non-weight-based reference equations for the 6-min walk test may produce more clinically meaningful results. https://bit.ly/2wE9Sdn.

Pulmonary Function Reference Equations: A Brief History to Explain All the Confusion.

Predicted values for pulmonary function tests differ significantly from the reference values used for many other diagnostic tests. Historically, simple equations using age, height, and sex were used to "predict" normal lung function. However, these multiple factors interact in complex ways to determine what the expected lung function values are in healthy subjects. Healthy individuals exhibit a wide range of variability for most pulmonary function variables, and this variability is not consistent across all age ranges. Recent analysis of large groups of healthy subjects has allowed the development of sophisticated prediction models that take into account not only variability but also skew that occurs as the lungs develop and mature. These modern reference equations provide uninterrupted expected values from early childhood, through adolescence and adulthood, and extending into the ninth decade. Modern equations use upper and lower limits of normal to offer a statistically robust means of defining who is within normal limits. Despite these advances, interpretation of pulmonary function test results has not been highly standardized, largely because interpretation depends on the reference equations used and, more importantly, how they are applied. This review discusses the strengths and limitations of using reference equations to interpret pulmonary function data in the context of research and clinical practice.

Should spirometer quality control be treated like other laboratory devices?

The ATS/ERS spirometer calibration standards may not be adequate http://ow.ly/Pqdq30nwAmb.

The Impact of Using Non-Birth Sex on the Interpretation of Spirometry Data in Subjects With Air-Flow Obstruction.

BACKGROUND: Sex is an important determinant of lung capacity and function. This study examined the impact of using non-birth sex on the interpretation of spirometry data in transgender subjects with air-flow obstruction. METHODS: This study was a retrospective analysis of anonymous spirometry data. Eighty adult male and 80 adult female subjects were chosen from the database via random sampling. FVC, FEV1, and FEV1/FVC were collected and analyzed. Differences in percent of predicted, Z scores, classification of disease severity, and the incidence of a value migrating above or below the lower limit of normal between sex assignments were examined. RESULTS: For born male subjects, percent of predicted for FVC and FEV1 were significantly higher when the female sex was used: 100.5% versus 118.5% and 78% versus 91.5%, respectively (P < .001). FEV1/FVC Z score was -2.53 for male sex and -2.65 for female sex (P = .004). The presence of obstruction was not affected by sex assignment. Use of non-birth sex moved some FVC and FEV1 data above the lower limit of normal and improved severity classification in others. For born female subjects, percent of predicted for FVC and FEV1 were significantly lower when the male sex was used: 102% versus 87.5% and 81.5% versus 70.5%, respectively (P < .001). FEV1/FVC Z score was -2.17 for female sex and -2.12 for male sex (P < .001). Six born female subjects had their FEV1/FVC normalized when male sex was used. Use of non-birth sex moved some FVC and FEV1 data below the lower limit of normal and worsened severity classification in others. In total, using the non-birth sex affected spirometry interpretation in 45% of born male subjects and 70% of born female subjects. CONCLUSIONS: In transgender subjects with air-flow obstruction, using non-birth sex to calculate predicted spirometry values may have a significant impact on test interpretation and place these patients at risk for misdiagnosis and inappropriate treatment.

Basic spirometry testing and interpretation for the primary care provider.

Spirometry testing plays an important role in the diagnosis and management of COPD and asthma in the primary care setting. Verifying the accuracy of the spirometer, using accurate patient demographics and appropriate reference equations, and ensuring the competency of testing personnel are key components of spirometry test interpretation. Spirometry testing plays an important role in the diagnosis and management of lung disease in the primary care setting. Spirometry interpretation should include an assessment of test quality and be based on sound statistical principals.