Sternal acceleration ballistocardiograpby and arterial pressure wave analysis to determine stroke volume

Objective: To describe a cardiac output measurement using a new method to derive and analyze the long-axis ballistocardiogram that is less invasive than pulmonary artery thermodilution. Design: Prospective physiologic study. Setting: Intensive care unit of The Halifax Infirmary, a teaching hospital of Dalhousie University, Halifax, NS. Patients: Thirty-nine patients in sinus rhythm with pulmonary artery thermodilution catheters or radial artery catheters in place. The first 30 subjects were the 'learning set' and the next 9 were the 'test set.' Interventions: A small (54-g) accelerometer was taped on the patient's chest. Outcome measures: Measurements of time and amplitude coordinates of the acceleration and radial artery pressure wavepeaks, as well as anthropometric information. Results: A stroke volume prediction equation was generated (R² = 0.76) from the learning set. This equation was applied to the test set and correlated with the pulmonary artery thermodilution-derived stroke volumes (R = 0.79). Stroke volumes were compared using a previously decribed statistical method: a) bias (predicted > thermodilution) = 0.03 mL (95% confidence interval [CI] -4.2 to 4.8 mL); b) lower limit of agreement = -21 mL (95% CI -29 to -13 mL); c) upper limit of agreement = 22 mL (95% CI 14 to 29 mL). Of derived stroke volumes, 82% were within 15 mL of pulmonary artery thermodilution-derived values.