| Outcome Measures: |
Primary: Change in Insulin Sensitivity, Hypothesis 1: Metformin will improve insulin function in Type 1 Diabetes. Insulin function will be measured using a euglycemic-hyperinsulinemic clamp procedure at both baseline and after 3 months of treatment. A clamp measures insulin sensitivity. A higher number indicates a better outcome; a lower number indicates a worse outcome., Baseline, Month 3 | Secondary: Change in ADP Time Constant, Hypothesis 1b: Metformin will improve mitochondrial function in Type 1 Diabetes. 31Phosphorus magnetic resonance spectroscopy (MRS) was used before, during, and after 90 seconds of near-maximal isometric exercise of the calf muscle for post-exercise muscle mitochondrial function. ADP time constant is the time for conversion of ADP → ATP and is a measure of muscle mitochondrial health (energy metabolism). A faster recovery is a better outcome; a slower recovery is a worse outcome., Baseline, Month 3|Change in Pulse Wave Velocity (PWV), Hypothesis 2a: Metformin will improve central vascular function in Type 1 Diabetes via pulse wave velocity (PWV) by MRI. PWV is a measure of central arterial stiffness. A lower value indicates a better outcome., Baseline, Month 3|Change in Central Arterial Intimal Medial Thickness (cIMT), Hypothesis 2a: Metformin will improve central vascular function in Type 1 Diabetes via central arterial intimal medial (cIMT) thickness by carotid ultrasound. cIMT is a measure used to diagnose the extent of carotid atherosclerotic vascular disease. The test measures the thickness of the inner two layers of the carotid artery-the intima and media. A lower result is a better outcome., Baseline, Month 3|Change in Mitral Valve E/A Ratio by Echocardiogram, Hypothesis 2b: Metformin will improve cardiac function in Type 1 Diabetes by echocardiogram. Mitral Valve E/A ratio is the ratio of early (E) to late (A) ventricular filling velocities. Ideal myocardial tissue relaxation is indicated by a ratio of \>0.8 and \<2.0., Baseline, Month 3|Change in Aortic Wall Sheer Stress (WSS), Hypothesis 2a: Metformin will improve central vascular function in Type 1 Diabetes via Aortic Wall Sheer Stress (WSS) by MRI. WSS is a measure of central arterial stiffness. A lower value indicates a better outcome., Baseline, Month 3 | Other: Change in Brachial Artery Distensibility, Hypothesis 2a: Metformin will improve peripheral arterial stiffness in Type 1 Diabetes via Dynapulse. Peripheral arterial stiffness is measured by the distensibility of the arterial wall. Increased arterial stiffness results from reduced elasticity of the arterial wall. A higher result is a better outcome., Baseline, Month 3
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