Involvement of peripheral airways during methacholine-induced bronchoconstriction after lung transplantation

Longitudinal Assessment of Pulmonary Function and Bronchodilator Response in Pediatric Patients With Post-infectious Bronchiolitis Obliterans

Backgroud: Postinfectious bronchiolitis obliterans (PIBO) is a rare respiratory disease. In recent years, the disease has been recognized and diagnosed increasingly in children. Pulmonary function is important for diagnosis, identifying the severity of the PIBO and monitoring progression. But there have been only a few studies that followed the evolution of PIBO on the basis of pulmonary function tests (PFTs). Objective: The study targeted the evolution of pulmonary function and bronchodilator response in a case series of Chinese children with PIBO. Methods: Twelve children between the ages of 6-99 months with PIBO were studied retrospectively from 2009 to 2019. Forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), the FEV₁/FVC ratio, and maximal midexpiratory flow velocity 25-75% (MMEF_25-75%) were collected at each PFT, and bronchodilator responses were evaluated. Spirometric parameters were monitored over time, and generalized linear mixed models were used to analyze longitudinal panel data. Results: The median baseline PFT values for FVC, FEV₁, the FEV₁/FVC ratio, and MMEF_25-75% were 41.6, 39.75, 90.7, and 22.2%, respectively. At the initial PFTs, 10 (83.3%) patients demonstrated a significant bronchodilator response. FVC and FEV₁ increased by 8.212%/year and 5.007%/year, respectively, and the FEV₁/FVC ratio decreased by an average of 3.537%/year. MMEF_25-75% showed improvement at an average rate of 1.583% every year. Overall, FEV₁ and MMEF_25-75% showed different degrees of improvement after the use of inhaled bronchodilators at each PFT session for 10 patients, and FEV₁ measures demonstrated significant (>12%) β₂-bronchodilation in 56% of PFT sessions. Conclusions: Pediatric patients with PIBO showed an obstructive defect in pulmonary function. The FVC, FEV₁, and MMEF_25-75% improved as they grew older, while the FEV₁/FVC ratio decreased. This may be due to the development of lung parenchyma more than airway growth. Airway obstruction in some patients improved with the use of β₂ agonists.

Lung Clearance Index (LCI) in Patients with Bronchiolitis Obliterans: A Preliminary Report and Comparison to Cystic Fibrosis Patients

INTRODUCTION

Bronchiolitis obliterans (BO) is a chronic airway disease following an insult to the lower respiratory tract. Lung clearance index (LCI) measures ventilation inhomogeneity and has been studied in cystic fibrosis (CF). We aimed to evaluate LCI in BO and to compare it to LCI in CF patients.

METHODS

LCI was measured in BO patients, compared to CF patients, and correlated with spirometry and CT findings.

RESULTS

Twenty BO patients and 26 CF patients (with similar mean age and BMI) underwent evaluation. FEV1 % and FEF25-75 % predicted were significantly lower in the BO group (60.5 ± 17.8 vs. 72.7 ± 20.7, p = 0.041, and 42.8 ± 22.8 vs. 66.4 ± 37.4, p = 0.017, respectively). In both groups, LCI was inversely correlated with FVC %, FEV1 %, and FEF25-75 % predicted. LCI  % was slightly higher (190.4 ± 63.5 vs. 164.9 ± 39.4, p = 0.1) and FRC gas % (measured by multiple breath washout) was significantly higher in the BO group (92.5 ± 35.9 vs. 71.3 ± 18, p = 0.014). The strength of statistical association between the lower FEF25-75 % values and the higher LCI values was stronger in BO patients.

CONCLUSIONS

Similar to CF, LCI may provide estimation of ventilation inhomogeneity in BO. The results indicate greater small airway involvement and air trapping in BO. Further prospective longitudinal studies evaluating the correlation of LCI measurements with multiple clinical and physiological parameters should be performed to assess the clinical benefit of LCI measurement in BO.

Double tracer gas single-breath washout: reproducibility in healthy subjects and COPD

The applicability and interpretation of inert tracer gas washout tests is hampered by the lack of feasible protocols and reproducibility data. We assessed feasibility, variability and reproducibility of a new easy to perform double tracer gas (DTG) single-breath washout (SBW) test and compared this with conventional nitrogen washouts. In 40 healthy nonsmokers and 20 patients with stable chronic obstructive pulmonary disease (COPD), we performed three N2 vital capacity SBWs, three N2 multiple-breath washouts and three tidal DTG-SBW tests. Follow-up was after 1 week, 1 month and 6 months. Main outcomes were the lung clearance index (LCI) (N2 multiple-breath washout), slope of phase III (dN2) (N2 vital capacity SBW) and slope of phase III (SIIIDTG) (DTG-SBW). In healthy subjects, mean±sd LCI at baseline was 6.94±0.61, dN2 0.99±0.42% N2 per litre and SIIIDTG -0.206±0.108 g·mol(-1)·L(-1). In COPD, LCI and dN2 were significantly higher (LCI 12.23±2.67, dN2 7.43±5.38% N2 per litre; p<0.001) and SIIIDTG significantly steeper (-0.653±0.428 g·mol(-1)·L(-1), p<0.001). Reproducibility was high for main outcome parameters: the intraclass correlation coefficient over 6 months was 0.77 (0.86 in COPD) for LCI, 0.82 (0.89) for dN2 and 0.83 (0.93) for SIIIDTG. The tidal DTG-SBW is a reproducible test in healthy and COPD subjects that seems attractive for use in routine clinical settings.

Lung transplantation and lung volume reduction surgery

Since the publication of the last edition of the Handbook of Physiology, lung transplantation has become widely available, via specialized centers, for a variety of end-stage lung diseases. Lung volume reduction surgery, a procedure for emphysema first conceptualized in the 1950s, electrified the pulmonary medicine community when it was rediscovered in the 1990s. In parallel with their technical and clinical refinement, extensive investigation has explored the unique physiology of these procedures. In the case of lung transplantation, relevant issues include the discrepant mechanical function of the donor lungs and recipient thorax, the effects of surgical denervation, acute and chronic rejection, respiratory, chest wall, and limb muscle function, and response to exercise. For lung volume reduction surgery, there have been new insights into the counterintuitive observation that lung function in severe emphysema can be improved by resecting the most diseased portions of the lungs. For both procedures, insights from physiology have fed back to clinicians to refine patient selection and to scientists to design clinical trials. This section will first provide an overview of the clinical aspects of these procedures, including patient selection, surgical techniques, complications, and outcomes. It then reviews the extensive data on lung and muscle function following transplantation and its complications. Finally, it reviews the insights from the last 15 years on the mechanisms whereby removal of lung from an emphysema patient can improve the function of the lung left behind.

Monitoring the lung periphery of transplanted lungs

Lung transplantation is now accepted as a viable therapeutic option for patients with end-stage lung diseases, but long-term survival is threatened by bronchiolitis obliterans (BO), which is regarded as a manifestation of chronic allograft rejection. We have used studies of ventilation distribution for the early detection of this complication. In a prospective study of 57 bilateral-lung transplant recipients, we showed that the slope of phase III of the helium single-breath washout, which targets inhomogeneities of ventilation distribution in the terminal and respiratory bronchioles, was particularly sensitive to the development of BO. In a preliminary study using nitrogen multiple-breath washouts, we showed that S(acin) and S(cond), which reflect structural changes in the acinar and conductive lung zones, were both markedly increased in patients with BO. Taken together, these studies demonstrate that monitoring the function of the allograft by measuring the distribution of ventilation in the lung periphery may be a clinically valuable tool.

A Descriptive Study of Small Airway Reticular Basement Membrane Thickening in Clinically Stable Lung Transplant Recipients

BACKGROUND

Chronic rejection functionally manifested by fixed airflow limitation, bronchiolitis obliterans syndrome (BOS), is a major problem for all lung allograft programs. The inclusion of a pre-BOS category (BOS(0 approximately p)) in the newly revised guidelines, recognizes the potential importance of early changes. We tested the hypothesis that small airway reticular basement membrane thickening exists even in clinically stable lung transplant recipients with some evidence of inflammation but who are BOS-free.

METHODS

A bronchoscopic study was performed on 30 clinically stable lung allograft recipients at >/=3 months post-allograft, who were BOS-free but with some evidence of airway inflammation indicated by a pathologic diagnosis of lymphocytic bronchiolitis or raised exhaled nitric oxide (NO). After baseline physiologic assessment, small airway reticular basement membrane (Rbm) thickening was quantified in transbronchial biopsy (TBB) using image analysis, with inflammation assessed by bronchoalveolar lavage (BAL) differential cell counts.

RESULTS

Twenty-one patients had technically satisfactory measurements of Rbm thickness. We detected small airway Rbm thickening when compared with published data for control lung diseases. There was no correlation between Rbm thickening and lung function (forced expiratory volume in 1 second [FEV(1)] best post-operatively and Rbm r = -0.10, not significant).

CONCLUSIONS

Our data suggest that airway remodeling can occur early in lung allografts and before development of airflow limitation and BOS. Longitudinal pathophysiologic studies are needed to elucidate potential relationships between airway inflammation, Rbm thickening and allograft failure. Airway biopsies would be of value in such studies.

Feasibility of sputum induction in lung transplant recipients

Sputum induction (SI) is nowadays being applied as a non-invasive and safe method to investigate airway inflammation in pulmonary diseases. We investigated the feasibility of SI after lung transplantation (LTX), and compared sputum and bronchoalveolar lavage (BAL) cellular characteristics and interleukin-8 (IL-8) levels. Results were also compared with 11 healthy subjects. SI as performed between 26 and 1947 d after LTX in 19 recipients, was successful in 16 of 22 attempts (73%). Six patients failed to produce sputum after induction, mostly just post-LTX and with having a lower forced expiratory volume in 1 s (FEV1). The success rate in clinically stable patients after the first month post-LTX was 93%. Side-effects were absent. Sputum recovery, viability and squamous cell contamination were comparable between LTX patients and healthy subjects. In the LTX group, total cell counts, neutrophil percentages and IL-8 levels were much higher in SI than BAL (1.6 x 10(6)/mL, 65.5% and 54.2 ng/mL vs. 0.1 x 10(6)/mL, 3.0% and 0.01 ng/mL; p < 0.001). Although LTX-neutrophil percentages in SI and BAL correlated properly (rho=0.72, p=0.04), both techniques are not interchangeable. We conclude that sputum induction is feasible, well tolerated, and without major side-effects in stable patients after the first month post-LTX. Induced sputum may be a useful tool to study inflammatory changes of the airways after LTX, and because of the large quantity of neutrophils sampled, especially for further studies on the pathogenesis of bronchiolitis obliterans.

Peripheral airway function in childhood asthma, assessed by single-breath He and SF6 washout

To assess whether the peripheral airways are involved in pediatric asthma, 10 asthmatic children (aged 8-15 years), hyperresponsive to dry-air hyperventilation challenge (DACh), performed spirometry and a vital capacity He/SF(6) single-breath washout test at rest, after DACh, and after beta(2)-therapy. The normalized phase III slopes (Sn(III)) of the expired He and SF(6) concentrations served as measures of overall ventilation inhomogeneity, and the (SF(6) - He) Sn(III) difference served to indicate where along the peripheral airways obstruction occurs. While a greater increase in the He vs. SF(6) slope indicates that obstruction has occurred in the vicinity of the acinar entrance, the reverse suggests obstruction deeper in the intraacinar airways. The mean (SD) fall in FEV(1) after DACh was 35 (14)%. Both He and SF(6) Sn(III) increased significantly (P < 0.05) after the challenge, and were restituted after beta(2)-therapy (P < 0.05). After DACh, Sn(III) increased more for He than for SF(6), resulting in a negative (SF(6) - He) Sn(III) difference (P < 0.01), which was restituted after beta(2)-therapy (P < 0.05). Even though there was no correlation between baseline FEV(1) and the magnitude of the subsequent fall in this parameter after DACh (r(2) = 0.04; n.s.), a strong correlation was found between the (SF(6) - He) Sn(III) difference at rest and its change after DACh (r(2) = 0.81; P < 0.001). We conclude that airways close to the acinar entrance participate in the airway response to DACh in asthmatic children. The magnitude of this peripheral airway response is related to the severity of resting peripheral airway dysfunction.