Year of Publication

2012

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department

Biomedical Engineering

First Advisor

Dr. Abhijit R. Patwardhan

Abstract

Noninvasive assessment of diabetic cardiovascular autonomic neuropathy (AN): Cardiac and vascular dysfunctions resulting from AN are complications of diabetes, often undiagnosed. Our objectives were to: 1) determine sympathetic and parasympathetic components of compromised blood pressure regulation in patients with polyneuropathy, and 2) rank noninvasive indexes for their sensitivity in diagnosing AN. Continuous 12-lead electrocardiography (ECG), blood pressure (BP), respiration, regional blood flow and bio-impedance were recorded from 12 able-bodied subjects (AB), 7 diabetics without (D0), 7 with possible (D1) and 8 with definite polyneuropathy (D2), during 10 minutes supine control, 30 minutes 70-degree head-up tilt and 5 minutes supine recovery. During the first 3 minutes of tilt, systolic BP decreased in D2 while increased in AB. Parasympathetic control of heart rate, baroreflex sensitivity, and baroreflex effectiveness and sympathetic control of heart rate and vasomotion were reduced in D2, compared with AB. Baroreflex effectiveness index was identified as the most sensitive index to discriminate diabetic AN.

Four-dimensional multiscale modeling of ECG indexes of diabetic autonomic neuropathy: QT interval prolongation which predicts long-term mortality in diabetics with AN, is well known. The mechanism of QT interval prolongation is still unknown, but correlation of regional sympathetic denervation of the heart (revealed by cardiac imaging) with QT interval in 12-lead ECG has been proposed. The goal of this study is to 1) reproduce QT interval prolongation seen in diabetics, and 2) develop a computer model to link QT interval prolongation to regional cardiac sympathetic denervation at the cellular level. From the 12-lead ECG acquired in the study above, heart rate-corrected QT interval (QTc) was computed and a reduced ionic whole heart mathematical model was constructed. Twelve-lead ECG was produced as a forward solution from an equivalent cardiac source. Different patterns of regional denervation in cardiac images of diabetic patients guided the simulation of pathological changes. Minimum QTc interval of lateral leads tended to be longer in D2 than in AB. Prolonging action potential duration in the basal septal region in the model produced ECG and QT interval similar to that of D2 subjects, suggesting sympathetic denervation in this region in patients with definite neuropathy.

Heart Model and ECG.wmv (19500 kB)
Four dimensional model of ventricles: Normal electrical activities, cardiac source (dipoles) and lead I ECG in one heart cycle