Purpose: The purpose of this research was to investigate changes in the morphology of seismocardiogram when the sensor is moved up the sternum or to the left of the chest. Method: Data was recorded from seven male subjects, in supine position, under an IRB approval from University of North Dakota. The accelerometers were placed in equal distance from each other starting from xiphoid process on the sternum and going up on the sternum and up to the suprasternal notch as shown in the figure below. The subjects were asked to perform a Valsalva maneuver and the signal was analyzed before and after this. Two independent annotators analyzed the morphology of the signal to detect the points corresponded to the opening and closure of aortic valve and also the closure of mitral valve, as conventionally defined on dorsoventral xiphoid process sesimocardiography. The annotations were performed for five cardiac cycles for every participant. The average of absolute percentage changes over the seven subjects was calculated. The correlation coefficients between all the signals were also calculated to quantify the linear relationships of the signals.
Results: Moving up to ¼ of the length of the sternum changes the mitral valve closure point an average of 3.2%, aortic valve opening annotation 2.6% and did not change at all. Going all the way up to the suprasternal notch significantly changed the annotation. The results were almost the same for cycles happening immediately after the Valsalva maneuver. The correlation coefficients are also reported on the right side of the Figure.
Conclusion: The signal morphology does depend on the placement of the sensor on the sternum, however, placement differences less than a quarter of the length of the sternum might not induce significant changes in the timing of the fiducial points of seismocardiogram.