Small Airways: Not Just Air Ducts - Pathophysiological Aspects and Clinical Implications

The airways smaller than 2 mm diameter are named small airways. They are essential for the transport and exchange of oxygen and carbon dioxide and at the same time play a relevant role in pulmonary mechanics, contributing to the subdivision of lung volumes. Measurement of small airway function is, therefore, crucial in patients with respiratory disease. This overview focuses on the physiological aspects of the small airways, considered as air ducts as well as determinants of pulmonary mechanics, the most common tools for evaluating their function and treatment implications.

Reduction of Lung Hyperinflation Improves Cardiac Preload, Contractility, and Output in Emphysema: A Prospective Cardiac Magnetic Resonance Study in Patients Who Received Endobronchial Valves

RATIONALE

Pulmonary hyperinflation in patients with Chronic Obstructive Pulmonary Disease (COPD) has been related to smaller cardiac chamber sizes and impaired cardiac function. Nowadays, bronchoscopic lung volume reduction (BLVR) with endobronchial valves is a treatment option to reduce pulmonary hyperinflation in patients with severe emphysema.

OBJECTIVES

We hypothesized that reduction of hyperinflation would improve cardiac preload in this patient group. In addition, we investigated whether the treatment would result in elevated pulmonary artery pressures due to pulmonary vascular bed reduction.

METHODS

We included patients with emphysema and severe hyperinflation (defined by a baseline residual volume >175% of predicted) who were eligible for BLVR with endobronchial valves. Cardiac magnetic resonance imaging was obtained one day prior to treatment and at eight week follow-up. Primary endpoint was cardiac preload, as measured by the right ventricle end-diastolic volume index (RVEDVI). As secondary endpoints, we measured indexed end-diastolic and end-systolic volumes of the right ventricle, left atrium, and left ventricle, pulmonary artery pressures, cardiac output, ejection fraction, and strain.

MEASUREMENTS AND MAIN RESULTS

Twenty-four patients were included. At eight week follow-up, RVEDVI was significantly improved (+7.9 ml/m2, SD 10.0, p=0.001). In addition to increased stroke volumes, we found significantly higher ejection fractions and strain measurements. Although cardiac output was significantly increased (+0.9L/min, SD 1.5, p=0.007), there were no changes in pulmonary artery pressures.

CONCLUSIONS

We found that reduction of hyperinflation using BLVR with endobronchial valves significantly improved cardiac preload, myocardial contractility, and cardiac output, without changes in pulmonary artery pressures. Clinical trial registered with ClinicalTrials.gov (NCT03474471).

Microdeletion in Xq28 with a polymorphic inversion in a patient with FLNA-associated progressive lung disease

Lung phenotype was reported as a novel phenotype in patients with mutations in the filamin A gene (FLNA) in 2011. FLNA mutations can result in pulmonary hyperinflation during the neonatal period or early infancy with progressive respiratory failure, culminating in a diagnosis of FLNA-associated progressive lung disease, particularly if the patient has periventricular nodular heterotopia and cardiac complications, such as patent ductus arteriosus, atrial septal defect, and pulmonary hypertension. We report the first Japanese case of FLNA-associated progressive lung disease caused by a microdeletion in Xq28 encompassing the FLNA gene with a polymorphic inversion.

Comparative efficacy and tolerability of beclomethasone/formoterol and fluticasone/salmeterol fixed combination in Taiwanese asthmatic patients

BACKGROUND

The study was designed to compare the efficacy and tolerability of a fixed combination of extra-fine beclomethasone and formoterol, with the fixed combination fluticasone and salmeterol in Taiwanese asthmatic patients.

METHODS

This was a phase III, multicentre, randomized, two-arm parallel groups, controlled study. Patients with moderate to severe asthma were randomized to a 12-week treatment with either beclomethasone 100 mcg plus formoterol 6 mcg (BDP/F) or fluticasone 125 mcg plus salmeterol 25 mcg (FP/S), both delivered 2 inhalations twice daily. The efficacy and tolerability of these two combinations were compared.

RESULTS

Among the 253 randomized subjects, 244 patients were evaluable (119 in the BDP/F group and 125 in the FP/S group). A significant improvement from baseline to the end of treatment period was observed in both BDP/F and FP/S groups in forced expiratory volume in the first second (FEV₁), forced vital capacity (FVC), morning and evening peak expiratory flow (PEF), Asthma Control Test (ACT) score and the use of rescue medication. FVC increase from pre-dose was significant after 5 min post inhalation in the BDP/F group only, while statistically significant within group improvement was not achieved until 30 min post inhalation in the FP/S group.

CONCLUSION

The BDP/F combination is comparable in efficacy and tolerability to FP/S combination in Taiwanese asthmatic patients, with the advantage of rapid onset of improvement of FVC, consistent with the faster improvement of pulmonary hyperinflation with BDP/F.

Effect of pulmonary hyperinflation on central blood volume: An MRI study

Pulmonary hyperinflation attained by glossopharyngeal insufflation (GPI) challenges the circulation by compressing the heart and pulmonary vasculature. Our aim was to determine the amount of blood translocated from the central blood volume during GPI. Cardiac output and cardiac chamber volumes were assessed by magnetic resonance imaging in twelve breath-hold divers at rest and during apnea with GPI. Pulmonary blood volume was determined from pulmonary blood flow and transit times for gadolinium during first-pass perfusion after intravenous injection. During GPI, the lung volume increased by 0.8±0.6L (11±7%) above the total lung capacity. All cardiac chambers decreased in volume and despite a heart rate increase of 24±29 bpm (39±50%), pulmonary blood flow decreased by 2783±1820mL (43±20%). The pulmonary transit time remained unchanged at 7.5±2.2s and pulmonary blood volume decreased by 354±176mL (47±15%). In total, central blood volume decreased by 532±248mL (46±14%). Voluntary pulmonary hyperinflation leads to ∼50% decrease in pulmonary and central blood volume.

Blood pooling in extrathoracic veins after glossopharyngeal insufflation

PURPOSE

Trained breath-hold divers hyperinflate their lungs by glossopharyngeal insufflation (GPI) to prolong submersion time and withstand lung collapse at depths. Pulmonary hyperinflation leads to profound hemodynamic changes.

METHODS

Thirteen divers performed preparatory breath-holds followed by apnea with GPI. Filling of extrathoracic veins was determined by ultrasound and magnetic resonance imaging and peripheral extravasation of fluid was assessed by electrical impedance. Femoral vein diameter was measured by ultrasound throughout the easy-going and struggle phase of apnea with GPI in eight divers in a sub-study.

RESULTS

After GPI, pulmonary volume increased by 0.8 ± 0.6 L above total lung capacity. The diameter of the superior caval (by 36 ± 17%) and intrathoracic part of the inferior caval vein decreased (by 21 ± 16%), while the diameters of the internal jugular (by 53 ± 34%), hepatic (by 28 ± 40%), abdominal part of the inferior caval (by 28 ± 28%), and femoral veins (by 65 ± 50%) all increased (P < 0.05). Blood volume of the internal jugular, the hepatic, the abdominal part of the inferior caval vein, and the combined common iliac and femoral veins increased by 145 ± 115, 80 ± 88, 61 ± 60, and 183 ± 197%, respectively. In the sub-study, femoral vein diameter increased by 44 ± 33% in the easy-going phase of apnea with GPI, subsequently decreasing by 20 ± 16% during the struggle phase. Electrical impedance remained unchanged over the thigh and forearm, thus excluding peripheral fluid extravasation.

CONCLUSIONS

GPI leads to heart and pulmonary vessel compression, resulting in redistribution of blood to extrathoracic capacitance veins proximal to venous valves. This is partially reversed by the onset of involuntary breathing movements.

Comparison of airway dimensions with once daily tiotropium plus indacaterol versus twice daily Advair(®) in chronic obstructive pulmonary disease

BACKGROUND

Current guidelines recommend combining long-acting bronchodilators with different modes of action in patients with moderate-to-severe chronic obstructive pulmonary disease (COPD). We evaluated the effects of airway dimensions and pulmonary function with tiotropium plus indacaterol versus Advair(®).

METHODS

Subjects (n = 46) were randomized to receive tiotropium (18 μg once daily) plus indacaterol (150 μg once daily) or Advair(®) (50/250 μg twice daily) for 16 weeks. Airway geometry was determined by quantitative computed tomography (luminal area, Ai; total area of the airway, Ao; wall area, WA; and percentage wall area, WA/Ao and wall thickness, T). Spirometry (forced expiratory volume in 1 s, FEV1; forced vital capacity, FVC and inspiratory capacity, IC) and St. George's Respiratory Questionnaire (SGRQ) were evaluated.

RESULTS

Tiotropium plus indacaterol significantly increased CT-indices including Ai corrected for body surface area (Ai/BSA), and decreased WA/BSA, WA/Ao and T/√BSA compared with Advair(®) (p < 0.05, respectively). In physiological parameters, mean difference in IC was significantly higher under treatment with tiotropium plus indacaterol than Advair(®) (p < 0.05). The changes in Ai/BSA, WA/BSA, WA/Ao and T/√BSA were significantly correlated with changes in IC (r = 0.535, p = 0.011; r = -0.688, p < 0.001; r = -0.555, p = 0.002 and r = -0.542, p = 0.007; respectively). There were more significant improvements in SGRQ scores after treatment with tiotropium plus indacaterol than Advair(®).

CONCLUSIONS

These findings suggest that dual bronchodilation with tiotropium plus indacaterol is superior in airway geometry and lung function compared with Advair(®) in COPD.

Dynamic pulmonary hyperinflation occurs without expiratory flow limitation in chronic heart failure during exercise

To assess the occurrence of tidal expiratory flow limitation (EFL) and/or dynamic pulmonary hyperinflation (DH) in chronic heart failure (CHF) during exercise 15 patients with stable systolic CHF, aged 69 ± 6yr, underwent pulmonary function testing and incremental cardio-pulmonary exercise testing. They subsequently performed constant load exercise testing at 30, 60 and 90% of respective maximum workload. At each step the presence of EFL, by negative expiratory pressure technique, and changes in inspiratory capacity (IC) were assessed. Ejection fraction amounted to 36 ± 6% and VO₂, peak (77 ± 19% pred.) was reduced. EFL was absent at any step during constant load exercise. In 6 patients IC decreased more than 10% pred. at highest step. Only in these patients TLC, FRC, RV FEF(25-75%) and DL(CO) were decreased at rest. VO₂, peak correlated with DL(CO), TLC and IC at rest and with IC (r(2)=0.59; p<0.001) and decrease in IC (r(2)=0.44; p<0.001) at 90% of maximum workload. During exercise CHF patients do not exhibit EFL, but some of them develop DH that is associated with lower VO₂, peak.