The single breath nitrogen test and mortality – A 38 years follow up

Using the phase III slope of exhaled methane during a single breath DLCO test to assess ventilation heterogeneity

BACKGROUND

The Phase III slope from a single breath nitrogen washout test provides information about ventilation heterogeneity (VH) in the lungs.

PURPOSE

To determine if the Phase III slope from the exhaled tracer gas concentration during a standard, single breath DLCO test using rapid gas analysis provides similar information about VH.

BASIC PROCEDURES

Retrospective analysis of clinical pulmonary function laboratory data including spirometry, lung volumes, and DLCO. The normalized Phase III slope from the exhaled CH4 concentration (SnCH4) was compared among different patterns of physiologic abnormality and with VA/TLC as an indicator of VH.

MAIN FINDINGS

SnCH4 was the steepest in the group with "Obstruction and Low DLCO", with significant differences between this group and the "Normal", "Obstruction with Normal DLCO", "Mixed Obstruction and Restriction" and "Isolated Low DLCO" groups. SnCH4 was steeper in current and former smokers compared to non-smokers. Among the entire study sample, SnCH4 correlated with VA/TLC (Spearman rho = -0.56, p < 0.01) and remained a significant determinant of VA/TLC by regression modeling.

PRINCIPAL CONCLUSIONS

The SnCH4 derived from a standard, single breath DLCO test using rapid gas analysis varied among distinct patterns of physiologic abnormalities and was associated with VA/TLC as a measure of VH.

Single breath nitrogen test as predictor of lung function decline and COPD over an 8-year follow-up

BACKGROUND

The single breath nitrogen (SBN2) test was proposed for early detection of "small airways disease" in the seventies. Few longitudinal studies have subsequently evaluated the relationships between SBN2 test measurements and lung function decline or COPD incidence.

AIM

This study evaluates whether SBN2 test abnormalities may be significant predictors of lung function decline and COPD incidence over an 8-year follow-up.

STUDY DESIGN AND METHODS

In this longitudinal study, 907 adults (20+ years old; 56% males) from the prospective Po River Delta epidemiological study underwent SBN2 test at baseline and spirometry testing at both baseline and follow-up 8-year apart. Multinomial and multiple regression models were used to assess associations of SBN2 indexes and rates of FEV1 decline or risk of COPD incidence over time, after adjusting for sex, height and baseline age, FEV1 and smoking status. COPD was defined according to either GOLD or ATS-ERS criteria.

RESULTS

Among SBN2 indexes, only the slope of alveolar plateau (N2-slope) was significantly associated with rates of FEV1 decline (7.93 mL/year for a one-unit change in N2-slope, p<0.0001), and with an increased risk of developing COPD as defined by GOLD (RR 1.81, 95%CI 1.29-2.52, mild; RR 2.78, 95%CI 1.70-4.53, moderate or severe obstruction) and ATS-ERS criteria (RR 1.62, 95%CI 1.14-2.29, mild; RR 3.40, 95%CI 1.72-6.73, moderate or severe obstruction).

CONCLUSION

In this population-based study, N2-slope from SBN2 test is a significant predictor of lung function decline and COPD incidence over an 8-year follow-up, confirming the role of the "small airways disease" in the natural history of COPD.

Prediction of COPD and Related Events Improves by Combining Spirometry and the Single Breath Nitrogen Test

Chronic obstructive pulmonary disease (COPD) develops in small airways. Severity of small airway pathology relates to progression and mortality. The present study evaluated the prediction of COPD of a validated test for small airway disease, i.e. a slope of the alveolar plateau of the single breath nitrogen test (N₂-slope). The N₂-slope, spirometry, age, smoking habits, and anthropometric variables at baseline were obtained in a population-based sample (n = 592). The cohort was followed for first COPD events (first hospital admission of COPD or related conditions or death from COPD) during 38 years. During follow-up, 52 subjects (8.8%) had a first COPD event, of which 18 (3.0%) died with a first COPD diagnosis. In the proportional hazard regression analysis adjusted for age and smoking habits, the cumulative COPD event incidence increased from 5% among those with high forced expired volume in one second (FEV₁) to 25% among those with low FEV₁, while increasing from 4% among those with the lowest N₂-slope to 26% among those with the highest. However, combining the N₂-slope and FEV₁ resulted in considerable synergy in the prediction of first COPD event and even more so when taking account of smoking habits. The cumulative COPD event incidence rate was 75% among heavy smokers with the highest N₂-slope and lowest FEV₁, and less than 1% among never smokers with the lowest N₂-slope and highest FEV₁. Thus, combining the results of the single breath N₂-slope and FEV₁ considerably improved the prediction of COPD events as compared to either test alone.

Utility of single versus multiple breath washout in adult asthma

Nitrogen multiple breath washout (N2 MBW) is a sensitive method to identify peripheral airway involvement in asthma, but is a time-consuming test. The N2 vital capacity single breath (VC SBW) test offers greater time efficiency, but concordance with N2 MBW is poorly understood. The prevalence of peripheral airway abnormality was determined by N2 MBW and N2 SBW tests in 194 asthmatic subjects aged 18-1 years. N2 MBW data were related to findings in 400 healthy controls, aged 17-71 years, while N2 SBW data were compared to findings in 224 healthy controls, aged 15-65 years, to derive equipment-specific reference values. Amongst asthmatic subjects, relationships between N2 SBW and N2 MBW outcomes were studied. N2 SBW relationship with clinical history, spirometry, blood eosinophils and fraction exhaled nitric oxide (FENO) data was also explored. The prevalence of peripheral airway involvement (i.e. abnormal ventilation distribution) determined by N2 SBW-derived phase III slope (N2 SIII ) was 24·7%, compared to 44% determined by N2 MBW-derived lung clearance index (LCI) (P<0·001). Predictors of abnormal N2 SIII were older age, smoking history and lower FEV1. N2 SBW offers lower sensitivity than N2 MBW to detect small airway dysfunction in adult asthma, but may be a marker of more severe disease.