Albert Andrew Yen

Digital thermal monitoring (DTM) of vascular reactivity closely correlates with doppler flow velocity

The noninvasive measurement of peripheral vascular reactivity, as an indicator of vascular function, provides a valuable tool for cardiovascular screening of at-risk populations. Practical and economical considerations demand that such a test be low-cost and simple to use. To this end, it is advantageous to substitute digital thermal monitoring (DTM) for the more costly and complex Doppler system commonly used for this measurement. A signal processing model was developed to establish the basis for the relationship between finger temperature reactivity and blood flow reactivity following a transient brachial artery occlusion and reperfusion protocol (reactive hyperemia). Flow velocity signals were acquired from the radial artery of human subjects via an 8 MHz Doppler probe while simultaneous DTM signals were acquired from a distal fingertip via DTM sensors. The model transforms the DTM temperature signals into normalized flow signals via a deconvolution method which employs an exponential impulse function. The DTM normalized flow signals were compared to simultaneous, low-frequency, normalized flow signals computed from Doppler sensors. The normalized flow signals, derived from DTM and Doppler sensors, were found to yield similar reactivity responses during reperfusion. The reactivity areas derived from DTM and Doppler sensors, indicative of hyperemic volumes, were found to be within ± 15%. In conclusion, this signal processing model provides a means to measure vascular reactivity using DTM sensors, that is equivalent to that obtained by more complex Doppler systems.

New Indices of Endothelial Function Measured by Digital Thermal Monitoring of Vascular Reactivity: Data from 6084 Patients Registry

Background. Endothelial function is viewed as a barometer of cardiovascular health and plays a central role in vascular reactivity. Several studies showed digital thermal monitoring (DTM) as a simple noninvasive method to measure vascular reactivity that is correlated with atherosclerosis risk factors and coronary artery disease. Objectives. To further evaluate the relations between patient characteristics and DTM indices in a large patient registry. Methods. DTM measures were correlated with age, sex, heart rate, and systolic and diastolic blood pressure in 6084 patients from 18 clinics. Results. DTM vascular reactivity index (VRI) was normally distributed and inversely correlated with age (r = −0.21, p < 0.0001). Thirteen percent of VRI tests were categorized as poor vascular reactivity (VRI < 1.0), 70 percent as intermediate (1.0 ≤ VRI < 2.0), and 17 percent as good (VRI ≥ 2.0). Poor VRI (<1.0) was noted in 6% of <50 y, 10% of 50–70 y, and 18% of ≥70 y. In multiple linear regression analyses, age, sex, and diastolic blood pressure were significant but weak predictors of VRI. Conclusions. As the largest database of finger-based vascular reactivity measurement, this report adds to prior findings that VRI is a meaningful physiological marker and reflects a high level of residual risk found in patients currently under care.

Digital (Fingertip) Thermal Monitoring of Vascular Function: A Novel, Noninvasive, Nonimaging Test to Improve Traditional Cardiovascular Risk Assessment and Monitoring of Response to Treatments

Digital thermal monitoring (DTM) is a noninvasive, inexpensive, easily performed, operator-independent vascular function test designed to complement the existing, risk-factor based assessment of vascular health and to monitor the vascular response to therapies. It is similar to a blood pressure device, with the addition of adhesive temperature probes on the right and left index fingertips that measure fingertip temperature fall and rebound during a brief (2–5 min), arm-cuff occlusion, and release procedure (reactive hyperemia). The higher the temperature rebound, the better the vascular reactivity. In our studies, we have found that DTM indices of vascular reactivity correlate strongly with the number of cardiovascular risk factors, measured by the Framingham Risk Score (FRS), and with the burden of asymptomatic (subclinical) coronary atherosclerosis, measured by coronary calcium score and CT angiography, as well as with myocardial perfusion defects on nuclear stress testing in symptomatic subjects. Moreover, our studies have shown that DTM provides incremental predictive value over risk factor assessment for the identification of high-risk patients with both subclinical atherosclerosis (Coronary Artery Calcium Score ≥100) and coronary artery stenosis (CT angiography showing ≥ 50% stenosis). Finally, DTM indices of vascular function have shown reproducibility comparable to blood pressure measurements. These very promising findings will require corroboration, particularly in long-term, prospective studies and clinical trials. It is important to emphasize that DTM is not intended to replace measurement of risk factors or advanced imaging tests. Rather, its purpose is to complement them by providing a powerful, noninvasive vascular function assessment of coronary health.