Chronic Performance of a Subcutaneous Hemodynamic Sensor
ABSTRACT A subcutaneous photoplethysmography (PPG) sensor uses light to detect changes in vascular volume from a location outside the bloodstream. Incorporation into a chronically implanted device, such as a pacemaker or an implantable cardioverter defibrillator, may facilitate therapy optimization and disease monitoring by providing continuous assessment of hemodynamic function and arterial oxygen saturation. However, performance of a chronically placed subcutaneous sensor has not been established.
Six dogs were implanted with 2-4 PPG sensors subcutaneously in the neck or posterior thorax. Half of the sensors were directed toward deep tissue and half toward overlying cutaneous tissue. Each sensor contained a red and an infrared light emitting diode, a photodetector, and supporting electronics, which were encapsulated in epoxy and attached to a transcutaneous connector. Data were collected at implant and every 3 ± 1 days for 4-9 months starting 3 weeks postimplant. At explant, the fibrous encapsulation was histologically analyzed.
A minimally to moderately neovascularized encapsulation formed over all sensors, consisting of fibrous and granulation tissue. Higher cardiac pulse amplitudes and direct current (DC) components were recorded in sensors oriented toward deep tissue, but no significant difference between orientations was found in respiratory wave amplitude. Cardiac pulse amplitude, respiratory wave amplitude, and DC component amplitude, as recorded by the sensor, did not significantly change over time.
Despite fibrous encapsulation of PPG sensors, cardiac pulses and respiratory waves could easily be measured throughout the study and remained constant over time. These results suggest suitability of subcutaneous PPG technology for chronic applications.
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ABSTRACT: Background Our objective was to evaluate the systolic index (SI), the ratio between rate-corrected left ventricular ejection time (LVETc), and a preejection period surrogate (PEPsu), to assess cardiac function in patients with DDD and cardiac resynchronization therapy (CRT) pacemakers. MethodsLVETc and PEPsu were automatically measured from electrocardiogram and finger photoplethismography. Atrioventricular (AV) and mode switch (CRT to DDD) were used as hemodynamic challenges. Performance of SI, beat-by-beat systolic blood pressure (SBP), and Doppler aortic velocity/time integral (AoVTI) were compared in 36 patients, and SI's detection of CRT to DDD mode switch in nine patients, responders to CRT. AVs were changed from 30 ms to 250 ms (20 ms steps) at constant paced heart rate, alternating with a reference AV (RefAV), to reduce hemodynamic drift. The coefficient of variation (standard deviation/mean) of SI, SBP, and AoVTI during all RefAVs were used as error marker. The percentage detection of hemodynamic changes during AV transitions was a marker of sensitivity. ResultsFifty-five patients (males 62%, age 69.6 17) were studied. SI detected 441 of 544 transitions (81%) versus 361 (66%) of SBP (P = 0.005). Error during RefAVs was smaller for SI (3.4%) as compared to AoVTI (7.8%, P = 0.015) and to SBP (5.7%, P = 0.005). SIs correlated with AoVTI (R from 0.71 to 0.98, all P < 0.001). SI detected all CRT to DDD changes (P < 0.001). Conclusion The noninvasive SI obtained with a simple, observer-independent hemodynamic assessment procedure has higher accuracy than SBP and AoVTI and better sensitivity than SBP. It detects mechanical resynchronization in CRT and allows programming a suitable AV delay.Pacing and Clinical Electrophysiology 06/2013; 36(10). DOI:10.1111/pace.12200 · 1.25 Impact Factor