TABLE 1

Predictive factors for 6-min walk test (6MWT) outcomes in patients with interstitial lung disease (ILD) in real-world studies

Patient populationFactors found to be predictive for 6MWT outcomes in multivariate analyses
Patients with IPF evaluated for lung transplantation (n=124) [27]6MWD: mPAP, Caucasian race (univariate only: DLCO, PaO2, mRAP, sPAP, PVR, PAOP)
Not predictive: age, BMI, FVC, FEV1, TLC, residual volume, cardiac index, pulse pressure, SV, pulmonary capacitance
Patients with IPF (n=40) or SSc-ILD (n=31) [28]6MWD: DLCO, sex (for IPF), minimum SpO2, pre-walk Borg rating (SSc-ILD)
Patients with ILD (n=46) [29]6MWD: DLCO, FVC (univariate only: PaO2, PVR)
Not predictive: age, BMI, PaCO2, mean AP, RAP, mPAP, PCWP, cardiac output, cardiac index
Oxygen desaturation: DLCO, PVR (univariate only: PaO2, mPAP)
Not predictive: age, BMI, FVC, PaCO2, mean AP, RAP, PCWP, cardiac output, cardiac index
Dyspnoea (Borg scale) at end of test: DLCO (univariate only: PaO2, mPAP)
Not predictive: age, BMI, FVC, PaCO2, mean AP, RAP, PCWP, cardiac output, cardiac index, PVR
Patients with ILD (n=62) [30]6MWD: VO2peak, RVSP, chronotropic response (peak heart rate minus resting heart rate), age
Not predictive: resting heart rate, Borg rating at end of test
Patients with DPLD evaluated for PH (n=48) [31]6MWD: mPAP, RVSP
Not predictive: FEV1, FVC, TLC, DLCO, FVC/DLCO ratio, RV dysfunction
Patients diagnosed with IPF (n=34) [32]6MWD: FEV1, PA–aO2 (univariate only: FVC, FEF25–75%)
Not predictive: MRC score, PaO2, PaCO2, IC, CPI score, residual volume, TLC, HRCT score
Patients with IPF (n=76) [33]Abnormal HRR1#: DLCO, RVSP, change in heart rate from baseline to
6 min (bivariate only: FVC, 6MWD, using supplemental oxygen, nadir SpO2, baseline heart rate)
Not predictive: age, sex, maximum heart rate

IPF: idiopathic pulmonary fibrosis; SSc: systemic sclerosis; DPLD: diffuse parenchymal lung disease; PH: pulmonary hypertension; 6MWD: 6-min walk distance; mPAP: mean pulmonary arterial pressure; DLCO: diffusing capacity of the lung for carbon monoxide; PaO2: partial pressure of oxygen; mRAP: mean right atrial pressure; sPAP: pulmonary arterial systolic pressure; PVR: pulmonary vascular resistance; PAOP: pulmonary artery occlusion pressure; BMI: body mass index; FVC: forced vital capacity; FEV1: forced expiratory volume in 1 s; TLC: total lung capacity; SV: stroke volume; SpO2: peripheral oxygen saturation; PaCO2: partial pressure of carbon dioxide; AP: arterial pressure; RAP: right atrial pressure; PCWP: pulmonary capillary wedge pressure; VO2peak: peak oxygen uptake; RVSP: right ventricular systolic pressure; RV: right ventricle; PA–aO2: alveolar–arterial oxygen gradient; FEF25–75%: forced expiratory flow between 25% and 75% of FVC; MRC score: Medical Research Council dyspnoea score; IC: inspiratory capacity; CPI: Composite Physiologic Index; HRCT: high-resolution computed tomography; HRR1: heart rate recovery at 1 min. #: heart rate at the end of the 6MWT minus heart rate at 1 min after completion of the 6MWT; defined as abnormal if ≤13 beats.