Heart rate and oxygen uptake kinetics obtained from continuous measurements with wearable devices during outdoor walks of patients with COPD: Validation study (Preprint)

BACKGROUND Continuous physiological measurements during a laboratory-based exercise test can provide physiological biomarkers, such as heart rate (HR) and oxygen uptake (V̇O2) kinetics, that carry clinically relevant information. In contrast, it is not yet clear how continuous data generated during daily life routines by wearable devices could provide meaningful biomarkers that, in turn, could improve telemonitoring applications. OBJECTIVE To determine whether valid HR and V̇O2 kinetics can be obtained from measurements with wearable devices during outdoor walks in patients with chronic obstructive pulmonary disease (COPD). As a secondary objective, we aimed to determine whether the amount of valid kinetics and kinetic model performance was comparable between outdoor walks and a conventional, laboratory-based exercise test. METHODS Eight patients with COPD measured HR (Polar Belt) and V̇O2 (METAMAX 3B) during three outdoor walks of different intensities and a six-minute walk test. For every patient and walk/test, HR and V̇O2 data were extracted after the following physical activity transitions: (i) starting a walk/test, (ii) finishing a walk/test and (iii) walking upstairs. An additional, averaged HR and V̇O2 response during outdoor walks was generated for each type of transition of every patient. Kinetic models were used to describe every separate and averaged HR and V̇O2 response when participants started a walk, finished a walk and walked upstairs. HR and V̇O2 kinetics were considered valid if the response magnitude and model fit were adequate, and model parameters were reliable. Kinetic model performance was assessed by model fit and standard errors of the parameter estimates. RESULTS Most HR kinetics were valid when starting (range 75% to 100% for separate walks; 100% for the averaged response) or finishing (range 63% to 88% for separate walks; 100% for the averaged response) an outdoor walk, but not when walking upstairs (≤29%). Many V̇O2 kinetics were valid when finishing (range 63% to 100% for separate walks; 100% for the averaged response), but not when starting an outdoor walk (range 38% to 50% for separate walks; 88% for the averaged response) or when walking upstairs (0%). The amount of valid kinetics, and kinetic model performance (P>.05), when starting/finishing an outdoor walk was comparable to starting (HR: 100%; V̇O2: 50%) or finishing (HR: 88%; V̇O2: 75%) a laboratory-based six-minute walk test. CONCLUSIONS Continuous measurements with wearable devices can provide valid HR kinetics when starting or finishing, and valid V̇O2 kinetics when finishing, an outdoor walk in patients with COPD. The amount of valid kinetics and kinetic model performance was comparable between outdoor walks and a conventional, laboratory-based exercise test. We envision that telemonitoring applications for patients with COPD could be improved by incorporating regular assessments of HR (and possibly V̇O2) kinetics, as obtained from continuous measurements with wearable devices during outdoor walks.