Stanbrook M B, Chapman K R, Kesten S
Asthma Centre, Toronto Hospital, University of Toronto.
Chest. 1995 Apr;107(4):992-5. doi: 10.1378/chest.107.4.992.
Methacholine challenge studies are often conducted to diagnose asthma in patients with mild or intermittent respiratory symptoms when screening spirometry results are normal. We hypothesized that in patients with increased nonspecific bronchial hyperreactivity (NSB-HR), gas trapping might be present and that this information could be a factor in clinical decision making. To assess the relationship between gas trapping and NSBHR, we conducted a retrospective chart review of 500 patients who had undergone pulmonary function testing, including lung volume measurement and methacholine challenge. Measurements of airflow, lung volumes, and methacholine PC20 values were compiled and analyzed. FRC was determined by body plethysmography (FRCB) and by helium dilution (FRC-He). FRCB-FRC-He, RV (percent of predicted) RV/TLC, and RV/TLC (percent of predicted) were used as measures of gas trapping. RV% and RV/TLC% were the best predictors of a PC20 < or = 8 mg/mL. In the subset of 169 patients who had FEV1/FVC > or = 90% of pred, an RV/TLC% value of 125% of predicted or greater had a positive predictive value of 62.5% and a negative predictive value of 62.0%. RV/TLC% was the only measure of gas trapping that was associated with a PC20 < or = 8 mg/mL (p < 0.05). Linear regression revealed no correlation between any measure of gas trapping and quantified PC20 value (< or = 16 mg/mL). These results suggest that patients with a normal FEV1/FVC who show gas trapping have an increased likelihood of a positive methacholine challenge study. Furthermore, in these patients, RV/TLC (percent of predicted) is the best predictor of a positive methacholine challenge and this parameter may be useful in raising the clinical suspicion of asthma in the large population of patients presenting with respiratory symptoms and normal flow rates.
当筛查肺量计检查结果正常时，通常会进行乙酰甲胆碱激发试验来诊断有轻度或间歇性呼吸道症状的患者是否患有哮喘。我们推测，在非特异性支气管高反应性（NSB-HR）增加的患者中，可能存在气体潴留，并且这一信息可能是临床决策的一个因素。为了评估气体潴留与NSBHR之间的关系，我们对500例接受过肺功能测试（包括肺容积测量和乙酰甲胆碱激发试验）的患者进行了回顾性病历审查。收集并分析了气流、肺容积和乙酰甲胆碱PC20值的测量数据。功能残气量（FRC）通过体容积描记法（FRCB）和氦稀释法（FRC-He）测定。FRCB - FRC-He、残气量（RV，预测值百分比）、RV/TLC以及RV/TLC（预测值百分比）被用作气体潴留的测量指标。RV%和RV/TLC%是PC20≤8mg/mL的最佳预测指标。在169例第一秒用力呼气容积/用力肺活量（FEV1/FVC）≥预测值90%的患者亚组中，RV/TLC%值达到或高于预测值的125%时，其阳性预测值为62.5%，阴性预测值为62.0%。RV/TLC%是唯一与PC20≤8mg/mL相关的气体潴留测量指标（p<0.05）。线性回归显示，任何气体潴留测量指标与定量PC20值（≤16mg/mL）之间均无相关性。这些结果表明，FEV1/FVC正常但存在气体潴留的患者，乙酰甲胆碱激发试验呈阳性的可能性增加。此外，在这些患者中，RV/TLC（预测值百分比）是乙酰甲胆碱激发试验呈阳性的最佳预测指标，该参数可能有助于提高对大量有呼吸道症状且流速正常的患者患哮喘的临床怀疑度。
