Subcutaneous Accelerometer-Based Monitoring of Respiration : A Pre-Clinical Exploration

Subcutaneous accelerometers offer an alternative method to transthoracic impedance measurements for chronically monitoring respiration and detecting sleep apnea in cardiac implantable electronic devices. Two 3D accelerometer prototypes were implanted subcutaneously in one anesthetized pig. In the first prototype the accelerometer was on the tip of a cardiac pacing lead, and in the second prototype it was embedded inside an inactive pacemaker ‘can’. Respiratory signals were recorded from both prototypes across various different combinations of tidal volume and respiration rate, as imposed by an external ventilator, as well as during a simulated apnea episode. Mean peak-to-trough amplitudes of the recorded signals achieved excellent correlations to the imposed nominal ventilation tidal volumes (R2>0.98 in the lead and R2>0.94 in the can). Similarly, mean peak-peak intervals achieved low root-mean-square-deviation errors with respect to the imposed ventilation intervals (<4% in the lead and <11% in the can). Such methods make use of accelerometers similar to the current activity sensors already present in various devices, or to previously-reported subcutaneous cardiac hemodynamic sensors. Unlike transthoracic impedance measurements, subcutaneous accelerometers are less invasive as they do not require intracardiac leads, they allow for a more direct assessment of respiration, and they do not suppose an added energetic cost to the system.