A comparative study of bronchodilator response: utilizing pre-bronchodilator versus predicted normal values.

BACKGROUND: A positive bronchodilator response has been defined as a 12% increase in the forced expiratory volume in one second (FEV1) or forced vital capacity (FVC) from their respective pre-bronchodilator values, combined with at least a 0.2 L absolute change. Recent recommendations suggested the use of the percent change in FEV1 and FVC relative to their predicted normal values without having applied them in patients with airflow obstruction. The aim of the current study was to compare the two approaches over a wide range of pre-bronchodilator FEV1 and FVC values. METHODS: A retrospective review of consecutive patients undergoing spirometry and bronchodilator testing was completed. The change in FEV1 and FVC with a bronchodilator was expressed relative to the pre-bronchodilator and predicted normal FEV1 and FVC. RESULTS: In 1,040 patients with a non-paradoxical change in FEV1, 19.0% had a ≥ 12% change in FEV1 using their pre-bronchodilator value compared to 5.7% using their predicted normal value. For FVC, the respective values were 12.7% vs. 5.8%. The difference was retained in patients with a ≥ 0.2 L change in FEV1 or FVC. In unobstructed patients, the upper threshold (two standard deviations above the mean) of the bronchodilator response was 14% for FEV1 and 10% for FVC using predicted normal values. CONCLUSIONS: Expressing the percent change in FEV1 and FVC relative to predicted normal values reduces the over-estimation of the bronchodilator response, especially in patients with a very low pre-bronchodilator FEV1, including in those with a ≥ 0.2 L change in FEV1. Irrespective of pre-bronchodilator values, a ≥ 14% change in FEV1 and ≥ 10% change in FVC relative to the predicted normal values could be considered a positive bronchodilator response.

Quantifying ventilation by X-ray velocimetry in healthy adults.

RATIONALE: X-ray velocimetry (XV) has been utilized in preclinical models to assess lung motion and regional ventilation, though no studies have compared XV-derived physiologic parameters to measures derived through conventional means. OBJECTIVES: To assess agreement between XV-analysis of fluoroscopic lung images and pitot tube flowmeter measures of ventilation. METHODS: XV- and pitot tube-derived ventilatory parameters were compared during tidal breathing and with bilevel-assisted breathing. Levels of agreement were assessed using the Bland-Altman analysis. Mixed models were used to characterize the association between XV- and pitot tube-derived values and optimize XV-derived values for higher ventilatory volumes. MEASUREMENTS AND MAIN RESULTS: Twenty-four healthy volunteers were assessed during tidal breathing and 11 were reassessed with increased minute ventilation with bilevel-assisted breathing. No clinically significant differences were observed between the two methods for respiratory rate (average Δ: 0.58; 95% limits of agreement: -1.55, 2.71) or duty cycle (average Δ: 0.02; 95% limits of agreement: 0.01, 0.03). Tidal volumes and flow rates measured using XV were lower than those measured using the pitot tube flowmeter, particularly at the higher volume ranges with bilevel-assisted breathing. Under these conditions, a mixed-model based adjustment was applied to the XV-derived values of tidal volume and flow rate to obtain closer agreement with the pitot tube-derived values. CONCLUSION: Radiographically obtained measures of ventilation with XV demonstrate a high degree of correlation with parameters of ventilation. If the accuracy of XV were also confirmed for assessing the regional distribution of ventilation, it would provide information that goes beyond the scope of conventional pulmonary function tests or static radiographic assessments.