Lerios Theodore, Knopp Jennifer L, Zilianti Camilla, Pecchiari Matteo, Chase J Geoffrey
Department of Mechanical Engineering, Centre for Bio-Engineering, University of Canterbury, Christchurch, New Zealand.
Department of Mechanical Engineering, Centre for Bio-Engineering, University of Canterbury, Christchurch, New Zealand.
Comput Methods Programs Biomed. 2025 Mar;260:108520. doi: 10.1016/j.cmpb.2024.108520. Epub 2024 Nov 30.
Chronic obstructive pulmonary disease (COPD) is characterised by airway obstruction with an increase in airway resistance (R) to airflow in the lungs. An extreme case of expiratory airway resistance is expiratory flow limitation, a common feature of severe COPD. Current analyses quantify expiratory R with linear model-based methods, which do not capture non-linearity's noted in COPD literature. This analysis utilises a simple nonlinear model to describe patient-specific nonlinear expiratory resistance dynamics typical of COPD and assesses its ability to both fit measured data and also to discriminate between severity levels of COPD.
Plethysmographic data, including alveolar pressure and airway flow, was collected from n=100 subjects (40 healthy, 60 COPD) in a previous study. Healthy cohorts included Young (20-32 years) and Elderly (64-85 years) patients. COPD patients were divided into those with expiratory flow limitation (FL) and those without (NFL). Inspiratory R was treated as linear (R). Expiratory R was modelled with two separate models for a comparison: linear with constant resistance (R), and nonlinear time-varying resistance (R(t)) using b-splines.
Model fit to PQ loops show inspiration is typically linear. Linear R captured expiratory dynamics in healthy cohorts (RMSE 0.3 [0.2 - 0.4] cmHO), but did not capture nonlinearity in COPD patients. COPD cohorts showed PQ-loop ballooning during expiration, which was better captured by non-linear R(t) (RMSE 1.7[1.3-2.8] vs. 0.3[0.2-0.4] cmHO in FL patients). Airway resistance is higher in COPD than healthy cohorts (mean R(t) for Young (1.9 [1.6-2.8]), Elderly (2.4 [1.4-3.5]), NFL (4.9 [3.9-6.6]) and FL (13.5 [10.4-21.9]) cmHO/L/s, with p ≤ 0.0001 between aggregated measures for Young and Elderly healthy subjects and NFL and FL COPD subjects). FL patients showed non-linear R(t) dynamics during flow deceleration, differentiating them from NFL COPD patients.
Linear model metrics describe expiration dynamics well in healthy subjects, but fail to capture nonlinear dynamics in COPD patients. Overall, the model-based method presented shows promise in detecting expiratory flow limitation, as well as describing different dynamics in healthy, COPD, and FL COPD patients. This method may thus be clinically useful in the diagnosis or monitoring of COPD patients using Plethysmography data, without the need for additional expiratory flow limitation confirmation procedures.
慢性阻塞性肺疾病（COPD）的特征是气道阻塞，肺部气流的气道阻力（R）增加。呼气气道阻力的一种极端情况是呼气气流受限，这是重度COPD的常见特征。目前的分析采用基于线性模型的方法来量化呼气R，但这些方法未能捕捉到COPD文献中提到的非线性特征。本分析利用一个简单的非线性模型来描述COPD患者特有的非线性呼气阻力动态，并评估其拟合测量数据以及区分COPD严重程度的能力。
在之前的一项研究中，从n = 100名受试者（40名健康者，60名COPD患者）收集了包括肺泡压力和气道流量在内的体积描记数据。健康队列包括年轻（20 - 32岁）和老年（64 - 85岁）患者。COPD患者分为有呼气气流受限（FL）和无呼气气流受限（NFL）两组。吸气R被视为线性的（R）。呼气R用两个单独的模型进行建模以作比较：恒定阻力线性模型（R）和使用b样条的非线性时变阻力模型（R(t)）。
对PQ环的模型拟合显示吸气通常是线性的。线性R捕捉到了健康队列中的呼气动态（均方根误差[RMSE]为0.3[0.2 - 0.4] cmH₂O），但未捕捉到COPD患者的非线性特征。COPD队列在呼气时显示PQ环膨胀，非线性R(t)能更好地捕捉到这一特征（FL患者中RMSE为1.7[1.3 - 2.8] vs. 0.3[0.2 - 0.4] cmH₂O）。COPD患者的气道阻力高于健康队列（年轻组的平均R(t)为1.9[1.6 - 2.8]，老年组为2.4[1.4 - 3.5]，NFL组为4.9[3.9 - 6.6]，FL组为13.5[10.4 - 21.9] cmH₂O/L/s，年轻和老年健康受试者与NFL和FL COPD受试者的汇总测量值之间p≤0.0001）。FL患者在流量减速期间显示出非线性R(t)动态，这将他们与NFL COPD患者区分开来。
线性模型指标能很好地描述健康受试者的呼气动态，但无法捕捉COPD患者的非线性动态。总体而言，所提出的基于模型的方法在检测呼气气流受限以及描述健康、COPD和FL COPD患者的不同动态方面显示出前景。因此，该方法在使用体积描记数据诊断或监测COPD患者时可能具有临床实用性，而无需额外的呼气气流受限确认程序。
