Prediction of Abnormal Functional Performance in Chronic Obstructive Pulmonary Disease Using Respiratory Models: A Pilot Study

Abstract

Introduction: The contribution of respiratory models to understanding and predicting functional capacity abnormalities in chronic obstructive pulmonary disease (COPD) has not yet been investigated.

Purpose: The aims of this study were: (1) To investigate the associations between the extended Resistance-Inertance-Compliance (eRIC) and the fractional-order (FrOr) models with changes in Glittre-ADL and handgrip tests and; (2) To evaluate the accuracy of these models in predicting abnormal functional capacity in COPD.

Patients and methods: The study was carried out in a group of 40 adults with COPD and a control group of 40 healthy individuals, both evaluated by respiratory oscillometry, spirometry, Glittre-ADL test and handgrip test. eRIC and fractional order models were also used to quantify biomechanical changes and obtain physiological information. The ability of model parameters to predict abnormal functional performance was evaluated by investigating the area under the receiver operating characteristic curve (AUC).

Results: Inverse relationships were observed between central airway resistance from the eRIC model and the handgrip test (p<0.005), while respiratory compliance (C) was directly related with handgrip strength test and inversely associated with the Glittre-ADL test time (p<0.05). The FrOr model showed direct associations among respiratory damping (G) and elastance with the Glittre-ADL test (p<0.02), while significant inverse relationships were observed with the handgrip test (p<0.05). Modeling parameters (peripheral resistance, total resistance and hysteresivity) achieved high prediction accuracy (AUC>0.90) in predicting non-normal functional capacity in COPD assessed by the Glittre-ADL test. Considering abnormal changes evaluated by the handgrip test as a reference, C (AUC=0.810) and G (AUC=0.786) obtained the highest predictive accuracies.

Conclusion: Parameters obtained from the eRIC and the fractional order models are associated with non-normal exercise performance in COPD and may help predict poor functional performance in these patients.

Keywords: COPD; Glittre-ADL; forced oscillation technique; handgrip test; respiratory oscillometry; respiratory system modeling.

Figure 1

Two-compartment integer-order model used to analyze respiratory. Impedance (A). The resistance (R), inductance (I) and capacitance (C) are the analogues of respiratory resistance, inertanceand compliance, respectively. Rprepresents the peripheral resistance. Two compartment fractional-order model evaluated in this study (B). It includes a constant phase inertance (CPL) and a constant phase compliance (CPC) composed by a frequency-dependent fractional inertia (FrL) and a frequency-dependent fractional compliance (FrC). The ability of the fractional terms to describe the resistive and reactive respiratory properties, depending of α and β values, is also described.

Figure 2

Predicted and measured values in tha basic COPD group for the Glittre test time (A) and handgrip analysis (B).

Figure 3

Parameters of the eRIC model classified according to the ADL-Glittre test.

Figure 4

Fractional order model parameters classified according to the ADL–Glittre test.

Figure 5

Parameters from the eRIC model according to the Handgrip.

Figure 6

Parameters from the fractional order model parameters according to the Handgrip.

Figure 7

Correlation plot in patients with COPD describing the association of integer and fractional-order model parameters with total Glittre-ADL test time and handgrip analysis. Abbreviation: Dominant hand (DH), non-dominant hand (NDH), percentual of the predicted values (p), central airway resistance (R), peripheral resistance (Rp), total resistance (Rt), pulmonary inertance (I), alveolar compliance (C), damping factor (G); respiratory elastance (H) and hysteresivity (n), * p<0.05, ** p<0.02 *** p<0.005.

Figure 8

Accuracy (point) and 95% confidence interval (bar) of respiratory model parameters in predicting abnormal functional capacity in COPD based on Glittre-ADL Test (A) and Handgrip analysis (B). Red dashed lines describe adequate (AUC>0.7) and highly accurate (AUC>0.9) limits. Central airway resistance (R), peripheral resistance (Rp), total resistance (Rt), pulmonary inertance (I), alveolar compliance (C), damping factor (G); respiratory elastance (H) and hysteresivity (η).