defect\isolating 怎么理解？

PFTs should be considered in patients with suspected tracheal stenosis who are clinically stable or to follow disease severity clinically once the diagnosis of tracheal stenosis has been made. Spirometric assessment with a flow-volume loop can show defects in the effort-dependent part of the curve in three classic patterns: (1) flattening of both expiratory and inspiratory limbs from fixed airway obstruction (tracheal stenosis, non-dynamic endotracheal tumors, bronchial obstructions), (2) flattening of the expiratory limb from variable intrathoracic obstruction (dynamic tumors of lower trachea, TBM, external compression of lower trachea), and (3) flattening of the inspiratory limb from variable extrathoracic obstruction (vocal cord paralysis, extrathoracic goiter, dynamic tumors of hypopharynx, laryngeal tumors). The advantages of PFTs are objective quantification of the airway disease, assessment of other comorbidities that may be present such as restrictive parenchymal disease, and assessment of pre- and post-procedural spirometric function.However, flow limitation may not be apparent in patients with an airway lumen greater than 8–10 mm [16]; hence, the spirometric diagnosis of tracheal stenosis has poor sensitivity. Moreover, spirometric abnormalities can be confounded by other obstructive lung diseases such as asthma, bronchiolitis, bronchiectasis, or chronic obstructive pulmonary disease (COPD). Thus, isolating the spirometric defect caused by tracheal stenosis can be very difficult. For these reasons, PFTs should not be used exclusively to rule out tracheal stenosis. Also, due to the possibility of inducing respiratory compromise with repeated forced expiratory maneuvers in patients with a tenuous respiratory status, PFTs should not be used in patients with ongoing respiratory distress or severe tracheal stenosis evidenced by imaging studies.

对于临床状况稳定的疑诊气管狭窄的患者，应考虑PFT，或在确诊支气管狭窄后，对疾病的严重程度进行随访。使用流速-容量环的肺量计评估可以以三种经典模式显示在用力呼吸时曲线的特征：(1)固定性气道梗阻（气管狭窄、非动力性气管内肿瘤、支气管阻塞）导致的呼气和吸气支变平、(2)可变性胸内梗阻（气管下段动力性肿瘤、TBM、气管下段外压迫）导致的呼气支变平、和(3)可变胸外梗阻（声带麻痹、胸外甲状腺肿、下咽动力性肿瘤、喉肿瘤）导致的吸气支变平。PFT的优势是客观量化气道疾病，评估可能的其他合并症（如限制性实质性疾病），并可评估术前和术后肺功能。然而，气道腔大于8-10mm的患者中，气流受限可能不明显[16]；因此，肺量测定诊断气管狭窄的敏感性较差。此外，肺量测定异常可能受到其他阻塞性肺病（如哮喘、毛细支气管炎、支气管扩张或COPD）的混淆。因此，鉴别由支气管狭窄引起的肺量计检测特征可能非常困难。因这些原因，PFT不应仅用于排除气管狭窄。此外，因呼吸状态脆弱的患者中反复用力呼气可能诱导呼吸功能受损，故PFT不应用于持续呼吸窘迫或影像学检查证实的重度气管狭窄的患者。

defect\isolating 怎么理解？这么理解可以吗？