Ambulatory Vascular Monitoring for Quantication of Lower Leg Hemodynamics and Severity of Venous Disease

Abstract

Persons with chronic venous disease experience progressive deterioration of their lower extremity hemodynamics. Different factors are thought to contribute to this hemodynamic decline, including incompetent venous valves, thrombotic blockage, and reduced efficiency of extremity muscle pumps. Left untreated, venous disease and resultant extremity hypertension can progress to the point of functional tissue changes, skin breakdown, and even amputation. Early clinical intervention directly increases positive outcomes; however, diagnostic efficiency in early or “mild” venous disease is low. This is due to a variety of reasons, one of which is the lack of a consensus “gold-standard” diagnostic method to quantify the global extent of extremity venous disease. The aims of this dissertation were to (1) design and validate tools for measurement of physiological and behavioral characteristics of persons with venous disease, (2) assess the utility of hemodynamic parameters derived from impedance plethysmography to quantify differences between diseased and healthy individuals, and (3) extend vascular monitoring beyond the clinic to assess how venous behavior changes over time during normal daily activity. A noninvasive behavioral datalogger was developed to utilize a variety of small noninvasive sensors to measure activity and behavioral characteristics of persons both in and out of the lab. This platform, named the ECHO system, is mounted at the ankle or on a prosthesis and can record continuous data from different sensors for up to 4 days before being recharged. Data from this system can be evaluated to gain insight into daily activities and behaviors to provide context and enhance analysis of physiological or clinical data. A portable multi-channel spectroscopic bioimpedance device was developed for the continuous measurement of lower extremity extracellular fluid volume changes. This device was shown to accurately quantify changes in blood volume in persons with and without vascular disease towards the aim of continuous noninvasive hemodynamic monitoring. Twenty healthy and vascular compromised individuals participated in a study protocol to measure their venous flow parameters using the impedance plethysmograph developed in Aim 1. Results showed differences in the amount of blood ejected during calf muscle pump activation and blood reflux during subsequent relaxation These hemodynamic differences suggest that individuals with a prior diagnosis of venous insufficiency may have lower calf muscle pump function and higher levels of retrograde flow. While this study reported physiological differences in venous flow parameters between groups, measurements were limited to a short temporal snapshot similar to current diagnostic techniques. Expanding from laboratory studies, extraclinical hemodynamic measurements were studied in a series of individuals with increasing level of previously diagnosed venous disease. All participants performed a structured series of activities including sitting, standing, walking, and ascending and descending stairs. This protocol was designed to emulate normal daily activities to evaluate their differing effects on hemodynamic parameters. Results showed increasing lower extremity blood retention correlating to greater severity of venous disease. Further evaluations showed an improvement in venous function when external compression stockings were worn across all subjects in the study. In a single participant comparison, old compression stockings were less effective at reducing venous blood pooling compared to a new pair.