Determining the Respiratory State From a Seismocardiographic Signal--A Machine Learning Approach

Christian Ulrich1, Martin Jensen2, Rolf Hansen1, Kouhyar Tavakolian3, Farzad Khosrow-khavar4, Andrew Blaber5, Kasper Sørensen6, Samuel Emil Schmidt2
1Aalborg university, North Region Denmark, 2Aalborg University, 3Assistant Professor, 4PhD Student, 5Simon Fraser University, BC, Canada, Department of Biomedical Physiology and Kinesiology, 6University of Aalborg


Abstract

Seismocardiography (SCG) is the measurement of vi-brations on the chest wall originating from the heart. Thisnon-invasive method provides information about the me-chanical components of the heart. The morphology of theSCG-signal changes in relation to respiration, and under-standing these changes will improve the diagnostic valueof SCG. The aim of this study was to determine the am-plitude of a respiration signal measured through a nasalcatheter, using SCG features, for specific time points atmitral closure (MC) and aortic opening (AO) in a three-model comparison. The three proposed methods were mul-tiple regression analysis (MRA), support vector regression(SVR), and a neural network (NN). SCG, Electrocardio-graphy (ECG) and nasal-catheter flow signals were col-lected from 18 healthy subjects (age 29+/-6 years). Be-sides MC and AO were the isovolumic moment (IM), aorticclosure (AC) and mitral opening (MO) selected as fiducialpoints in the SCG-signal. These were found using an auto-matic algorithm followed by manual verification. Fiducialpoints amplitudes, frequency components, and timings be-tween these fiducial points formed 12 features. All modelswere trained on 80% of the data and underwent 10-foldcross validation. Testing was performed on the remain-ing 20% of the data. Predictions on test data for MC andAO time points, the Pearson correlations coefficient, andsum of squared errors of prediction were: (r_MC, r_AO,SSE_MC, SSE_AO) for the following models: NN (0.908,0.904, 11.71, 12.05), SVR (0.881, 0.833, 18.95, 19.76)and MRA (0.450, 0.437, 51.21, 51.48). These predictivemodels shows a measurable correlation between the SCG-signal and respiration, which enables modelling of the cor-relation.