Graphic analysis of flow-volume curves: a pilot study

Degree of convexity calculated from expiratory flow-volume curves for identifying airway obstruction in nonsedated and nonparalyzed ventilated patients

The predictive performance of applying the degree of convexity in expiratory flow-volume (EFV) curves to detect airway obstruction in ventilated patients has yet to be investigated. We enrolled 33 nonsedated and nonparalyzed mechanically ventilated patients and found that the degree of convexity had a significant negative correlation with FEV₁% predicted. The mean degree of convexity in EFV curves in the chronic obstructive pulmonary disease (COPD) group (n = 18) was significantly higher than that in the non-COPD group (n = 15; 26.37 % ± 11.94 % vs. 17.24 % ± 10.98 %, p = 0.030) at a tidal volume of 12 mL/kg IBW. A degree of convexity in the EFV curve > 16.75 at a tidal volume of 12 mL/kg IBW effectively differentiated COPD from non-COPD (AUC = 0.700, sensitivity = 77.8 %, specificity = 53.3 %, p = 0.051). The degree of convexity calculated from EFV curves may help physicians to identify ventilated patients with airway obstruction.

Pulmonary function with expiratory resistive loading in healthy volunteers

Expiratory flow limitation is a key characteristic in obstructive pulmonary diseases. To study abnormal lung mechanics isolated from heterogeneities of obstructive disease, we measured pulmonary function in healthy adults with expiratory loading. Thirty-seven volunteers (25±5 yr) completed spirometry and body plethysmography under control and threshold expiratory loading of 7, 11 cmH2O, and a subset at 20 cmH2O (n = 11). We analyzed the shape of the flow-volume relationship with rectangular area ratio (RAR; Ma et al., Respir Med 2010). Airway resistance was increased (p<0.0001) with 7 and 11 cmH2O loading vs control (9.20±1.02 and 11.76±1.68 vs. 2.53± 0.80 cmH2O/L/s). RAR was reduced (p = 0.0319) in loading vs control (0.45±0.07 and 0.47±0.09L vs. 0.48±0.08). FEV1 was reduced (p<0.0001) in loading vs control (3.24±0.81 and 3.23±0.80 vs. 4.04±1.05 L). FVC was reduced (p<0.0001) in loading vs control (4.11±1.01 and 4.14±1.03 vs. 5.03±1.34 L). Peak expiratory flow (PEF) was reduced (p<0.0001) in loading vs control (6.03±1.67 and 6.02±1.84 vs. 8.50±2.81 L/s). FEV1/FVC (p<0.0068) was not clinically significant and FRC (p = 0.4) was not different in loading vs control. Supra-physiologic loading at 20 cmH2O did not result in further limitation. Expiratory loading reduced FEV1, FVC, PEF, but there were no clinically meaningful differences in FEV1/FVC, FRC, or RAR. Imposed expiratory loading likely leads to high airway pressures that resist dynamic airway compression. Thus, a concave expiratory flow-volume relationship was consistently absent-a key limitation for model comparison with pulmonary function in COPD. Threshold loading may be a useful strategy to increase work of breathing or induce dynamic hyperinflation.

Pulmonary function testing in COPD: looking beyond the curtain of FEV1

Chronic obstructive pulmonary disease (COPD) management remains challenging due to the high heterogeneity of clinical symptoms and the complex pathophysiological basis of the disease. Airflow limitation, diagnosed by spirometry, remains the cornerstone of the diagnosis. However, the calculation of the forced expiratory volume in the first second (FEV1) alone, has limitations in uncovering the underlying complexity of the disease. Incorporating additional pulmonary function tests (PFTs) in the everyday clinical evaluation of COPD patients, like resting volume, capacity and airway resistance measurements, diffusion capacity measurements, forced oscillation technique, field and cardiopulmonary exercise testing and muscle strength evaluation, may prove essential in tailoring medical management to meet the needs of such a heterogeneous patient population. We aimed to provide a comprehensive overview of the available PFTs, which can be incorporated into the primary care physician's practice to enhance the efficiency of COPD management.

Assessing small airway disease in GLI versus NHANES III based spirometry using area under the expiratory flow-volume curve

Background

Spirometry interpretation is influenced by the predictive equations defining lower limit of normal (LLN), while 'distal' expiratory flows such as forced expiratory flow at 50% FVC (FEF50) are important functional parameters for diagnosing small airway disease (SAD). Area under expiratory flow-volume curve (AEX) or its approximations have been proposed as supplemental spirometric assessment tools. We compare here the performance of AEX in differentiating between normal, obstruction, restriction, mixed defects and SAD, as defined by Global Lung Initiative (GLI) or National Health and Nutrition Examination Survey (NHANES) III reference values, and using various predictive equations for FEF50.

Methods

We analysed 15 308 spirometry-lung volume tests. Using GLI versus NHANES III LLNs, and diagnosing SAD by the eight most common equation sets for forced expiratory flow at 50% of vital capacity lower limits of normal (FEF50 LLN), we assessed the degree of diagnostic concordance and the ability of AEX to differentiate between various definition-dependent patterns.

Results

Concordance rates between NHANES III and GLI-based classifications were 93.7%, 78.6%, 86.8%, 88.0%, 93.8% and 98.8% in those without, with mild, moderate, moderately severe, severe and very severe obstruction, respectively (agreement coefficient 0.81 (0.80-0.82)). The prevalence of SAD was 0.6%-6.9% of the cohort, depending on the definition used. The AEX differentiated well between normal, obstruction, restriction, mixed pattern and SAD, as defined by most equations.

Conclusions

If the SAD diagnosis is established by using mean FEF50 LLN or a set number of predictive equations, AEX is able to differentiate well between various spirometric patterns. Using the most common predictive equations (NHANES III and GLI), the diagnostic concordance for functional type and obstruction severity is high.

Spirometric indices of early airflow impairment in individuals at risk of developing COPD: Spirometry beyond FEV1/FVC

Spirometry is the current gold standard for diagnosing and monitoring the progression of Chronic Obstructive Pulmonary Disease (COPD). However, many current and former smokers who do not meet established spirometric criteria for the diagnosis of this disease have symptoms and clinical courses similar to those with diagnosed COPD. Large longitudinal observational studies following individuals at risk of developing COPD offer us additional insight into spirometric patterns of disease development and progression. Analysis of forced expiratory maneuver changes over time may allow us to better understand early changes predictive of progressive disease. This review discusses the theoretical ability of spirometry to capture fine pathophysiologic changes in early airway disease, highlights the shortcomings of current diagnostic criteria, and reviews existing evidence for spirometric measures which may be used to better detect early airflow impairment.

Area under the forced expiratory flow-volume loop in spirometry indicates severe hyperinflation in COPD patients

BACKGROUND

Severe hyperinflation causes detrimental effects such as dyspnea and reduced exercise capacity and is an independent predictor of mortality in COPD patients. Static lung volumes are required to diagnose severe hyperinflation, which are not always accessible in primary care. Several studies have shown that the area under the forced expiratory flow-volume loop (AreaFE) is highly sensitive to bronchodilator response and is correlated with residual volume/total lung capacity (RV/TLC), a common index of air trapping. In this study, we investigate the role of AreaFE% (AreaFE expressed as a percentage of reference value) and conventional spirometry parameters in indicating severe hyperinflation.

MATERIALS AND METHODS

We used a cohort of 215 individuals with COPD. The presence of severe hyperinflation was defined as elevated air trapping (RV/TLC >60%) or reduced inspiratory fraction (inspiratory capacity [IC]/TLC <25%) measured using body plethysmography. AreaFE% was calculated by integrating the maximal expiratory flow-volume loop with the trapezoidal rule and expressing it as a percentage of the reference value estimated using predicted values of FVC, peak expiratory flow and forced expiratory flow at 25%, 50% and 75% of FVC. Receiver operating characteristics (ROC) curve analysis was used to identify cut-offs that were used to indicate severe hyperinflation, which were then validated in a separate group of 104 COPD subjects.

RESULTS

ROC analysis identified cut-offs of 15% and 20% for AreaFE% in indicating RV/TLC >60% and IC/TLC <25%, respectively (N=215). On validation (N=104), these cut-offs consistently registered the highest accuracy (80% each), sensitivity (68% and 75%) and specificity (83% and 80%) among conventional parameters in both criteria of severe hyperinflation.

CONCLUSION

AreaFE% consistently provides a superior estimation of severe hyperinflation using different indices, and may provide a convenient way to refer COPD patients for body plethysmography to address static lung volumes.

Effect of tiotropium on spontaneous expiratory flow-volume curves during exercise in GOLD 1-2 COPD

This substudy of a large, randomized, controlled trial (NCT01072396) examined tiotropium (18 μg qd) effects on dynamic hyperinflation during constant work rate treadmill exercise. Areas-under-the-spontaneous expiratory flow-volume (SEFV)-curves were compared in 20 COPD patients and 16 age-matched untreated controls, using rectangular area ratio (RAR) between peak intrabreath and end-expiratory flow. Seven patients exhibited SEFV curve concavity with RAR ≤ 0.5 (RAR_low) in ≥1 test without tiotropium; (mean ± SD FEV₁: 1.60 ± 0.59 L; 63.4 ± 14.0%predicted). In RAR_low patients, tiotropium increased end-exercise inspiratory capacity (IC, 2.10 ± 0.05 vs. 1.89 ± 0.05 L, tiotropium vs. placebo; p = 0.045) and RAR (0.57 ± 0.02 vs. 0.53 ± 0.02; p < 0.001). Patients without SEFV curve concavity with RAR > 0.5 (n = 13; RAR_high), had higher screening FEV₁ (2.15 ± 0.47 L; 79.6 ± 10.1%predicted) versus RAR_low patients and no difference in end-exercise IC and RAR between tiotropium and placebo (IC: 2.24 ± 0.03 vs. 2.17 ± 0.03 L; RAR: 0.63 ± 0.005 vs. 0.62 ± 0.005). RAR and%predicted IC at peak exercise were positively correlated in RAR_low patients (R² = 0.43, p = 0.0002). Tiotropium increased exercise RAR in GOLD 1-2 patients with SEFV curve concavity.

Expiratory Flow Limitation During Mechanical Ventilation

Expiratory flow limitation (EFL) is present when the flow cannot rise despite an increase in the expiratory driving pressure. The mechanisms of EFL are debated but are believed to be related to the collapsibility of small airways. In patients who are mechanically ventilated, EFL can exist during tidal ventilation, representing an extreme situation in which lung volume cannot decrease, regardless of the expiratory driving forces. It is a key factor for the generation of auto- or intrinsic positive end-expiratory pressure (PEEP) and requires specific management such as positioning and adjustment of external PEEP. EFL can be responsible for causing dyspnea and patient-ventilator dyssynchrony, and it is influenced by the fluid status of the patient. EFL frequently affects patients with COPD, obesity, and heart failure, as well as patients with ARDS, especially at low PEEP. EFL is, however, most often unrecognized in the clinical setting despite being associated with complications of mechanical ventilation and poor outcomes such as postoperative pulmonary complications, extubation failure, and possibly airway injury in ARDS. Therefore, prompt recognition might help the management of patients being mechanically ventilated who have EFL and could potentially influence outcome. EFL can be suspected by using different means, and this review summarizes the methods to specifically detect EFL during mechanical ventilation.

Feasibility of quantitative regional ventilation and perfusion mapping with phase-resolved functional lung (PREFUL) MRI in healthy volunteers and COPD, CTEPH, and CF patients

PURPOSE

In this feasibility study, a phase-resolved functional lung imaging postprocessing method for extraction of dynamic perfusion (Q) and ventilation (V) parameters using a conventional 1H lung MRI Fourier decomposition acquisition is introduced.

METHODS

Time series of coronal gradient-echo MR images with a temporal resolution of 288 to 324 ms of two healthy volunteers, one patient with chronic thromboembolic hypertension, one patient with cystic fibrosis, and one patient with chronic obstructive pulmonary disease were acquired at 1.5 T. Using a sine model to estimate cardiac and respiratory phases of each image, all images were sorted to reconstruct full cardiac and respiratory cycles. Time to peak (TTP), V/Q maps, and fractional ventilation flow-volume loops were calculated.

RESULTS

For the volunteers, homogenous ventilation and perfusion TTP maps (V-TTP, Q-TTP) were obtained. The chronic thromboembolic hypertension patient showed increased perfusion TTP in hypoperfused regions in visual agreement with dynamic contrast-enhanced MRI, which improved postpulmonary endaterectomy surgery. Cystic fibrosis and chronic obstructive pulmonary disease patients showed a pattern of increased V-TTP and Q-TTP in regions of hypoventilation and decreased perfusion. Fractional ventilation flow-volume loops of the chronic obstructive pulmonary disease patient were smaller in comparison with the healthy volunteer, and showed regional differences in visual agreement with functional small airways disease and emphysema on CT.

CONCLUSIONS

This study shows the feasibility of phase-resolved functional lung imaging to gain quantitative information regarding regional lung perfusion and ventilation without the need for ultrafast imaging, which will be advantageous for future clinical translation. Magn Reson Med 79:2306-2314, 2018. © 2017 International Society for Magnetic Resonance in Medicine.