Novel Peripheral Perfusion Dynamics Indices for Detecting and Grading Arterial Stenosis.

PURPOSE: Peripheral artery disease causes severe morbidity, especially in diabetics and the elderly. There is a need for accurate noninvasive detection of peripheral arterial stenosis. The study has tested the hypothesis that arterial stenosis and the associated adaptation of the downstream circulation yield characteristic changes in the leg perfusion dynamics that enable early diagnosis, utilizing impedance plethysmography. METHODS: The arterial perfusion dynamic was derived from impedance plethysmography (IPG). Two degrees of arterial stenosis were emulated by inflating a blood-pressure cuff around the thigh to 45 and 90 mmHg, in healthy volunteers (n = 30). IPG signals were acquired continuously throughout the experiment. Ankle and brachial blood pressures were measured at the beginning of each experiment and at the end of each emulated stenosis phase. RESULTS: Thigh compressions did not affect the pulse-transit time, but prolonged the time to the peak perfusion wave. Segmentation of the perfusion upstroke into two phases, at the time point of maximum acceleration (MAT), revealed that arterial compression prolonged only the initial slow phase duration (SPd). The MAT and SPd were proportional to the emulated stenosis severity and detected the arterial stenosis with high sensitivity (> 93%) and specificity (100%). The SPd increased from 46.4 ± 21.2 ms at baseline to 75.4 ± 38.5 ms and 145 ± 39 ms under 45 mmHg and 90 mmHg compressions (p < 0.001), without affecting the pulse-transit time. CONCLUSIONS: The novel method and indices can identify and grade the emulated arterial stenosis with high accuracy and may assist in differentiating between focal arterial stenosis and widespread arterial hardening.

Extracorporeal acute cardiac pacing by high intensity focused ultrasound.

Ultrasound has been shown to produce Premature Ventricular Contractions (PVC's). Two clinical applications in which acute cardiac pacing by ultrasound may be valuable are: (1) preoperative patient screening in cardiac resynchronization therapy surgery; (2) Emergency life support, following an event of sudden death, caused by cardiac arrest. Yet, previously the demonstrated mean success rate of extra-systole induction by High Intensity Focused Ultrasound (HIFU) in rats is below 4.5% (Miller et al., 2011). This stands in contrast to previous work in rats using ultrasound (US) and ultrasound contrast agents (UCAs), where success rates of close to 100% were reported (Rota et al., 2006). Herein, bi-stage temporal sequences of accentuated negative pressure (rarefaction) and positive pressure HIFU transmission (insonation) patterns were applied to anaesthetized rats under real-time vital-signs monitoring and US imaging. This pattern of insonation first produces a gradual growth of dissolved gas cavities in tissue (cavitation) and then an ultrasonic impact. Results demonstrate sequences of successive successful HIFU pacing. Triggering insonation at different delays from the preceding ECG R-wave demonstrated successful HIFU pacing induction from mid ECG T-wave till the next ECG complex's PR interval. Spatially focusing the beam at different locations allows cumulative coverage of the whole left ventricle. Analysis of the acoustic wave patterns and temporal characteristics of paced PVCs is suggested to provide new insight into the mechanisms of HIFU cardiac pacing. Specifically, the observed HIFU pacing temporal success rate distribution suggests against sarcomere length modulation current being the dominant cellular level mechanism of HIFU cardiac pacing and may allow postulating that membrane deformation currents are dominant at the applied insonation conditions.