The validity of the flow-mediated dilation (FMD) test has been doubted due to the lack of normalization to the primary stimulus, shear stress. Shear stress can be calculated using a simplified mathematical model based...The validity of the flow-mediated dilation (FMD) test has been doubted due to the lack of normalization to the primary stimulus, shear stress. Shear stress can be calculated using a simplified mathematical model based on Poiseuille’s law. Poiseuille’s law assumes that the blood velocity profile is parabolic. The presence of turbulence will violate this assumption. The Reynolds number (RE) is used to define critical values for the transition from laminar to turbulent flow. Between RE values of 2000 and 4000, flow enters a transitional phase where turbulence is possible. Purpose: To determine whether brachial artery blood flow becomes turbulent during reactive hyperemia following forearm ischemia. Methods: Eleven healthy male subjects (25 ± 5 years) were tested. Brachial artery diameters and blood velocities were measured continuously following 2, 4, 6 and 10 minutes ischemia. The peak post-ischemic RE (REpeak) and RE integrated over 40 seconds (RE40) post-ischemia were calculated. Results: There was a significant change in REpeak (F4,7 = 98.573, p = ≤ 0.001) and RE40) (F4,7) = 50.613, p = ≤ 0.001) in response to ischemia. Within-subjects contrasts revealed a significant increase in REpeak and RE40 for each duration of ischemia versus baseline (p = ≤ 0.001). Following 4 minutes of ischemia there was approximately 12 seconds of potentially turbulent flow. Conclusion: Blood flow transitions between laminar and turbulent flow during ischemia-induced reactive hyperemia. This may limit the efficacy of estimating shear stress when using the standard FMD test protocol.展开更多
Introduction: In recent years, flow mediated dilatation (FMD) has become a popular technique in cardiovascular medicine. HOMA-IR was accepted to determine the insulin sensitivity as a valuable standard. In this study,...Introduction: In recent years, flow mediated dilatation (FMD) has become a popular technique in cardiovascular medicine. HOMA-IR was accepted to determine the insulin sensitivity as a valuable standard. In this study, we evaluated the association between HOMA-IR (homeostasis model assessment of insulin resistance) and vascular endothelial dysfunction, as assessed by endothelium- dependent flow-mediated dilatation (FMD) and nitroglycerin-mediated dilatation (NMD), in type 2 Diabetic (DM) patients. Material and Methods: Eighty four (84) consecutive out-patients were enrolled. HOMA-IR was calculated as fasting insulin (μU/ml) multiplied by fasting plasma glucose (FPG) (mg/dl) and divided by 405. The ultrasound method for measuring FMD and NMD has been used. Out of 84 patients, 42 patients were in control group and 42 patients were in diabetic group, which were further subdivided into two groups based on HOMA-IR > 3.0 and above was considered as Group I and HOMA IR < 3.0 and below was considered as Group II. Fasting Plasma Glucose (mmol/dl) (7.74 ± 2.56, 6.81 ± 1.9, p < 0.001) and Fasting Insulin (μU/dl) (13.26 ± 8.09, 6.65 ± 2.36, p < 0.001) were statistically significant in Group I. The baseline mean FMD in controls and cases (Group I and Group II) was 15.36 ± 9.56, 4.15 ± 2.29, 12.21 ± 6.24 (p < 0.001) respectively. By logistic regression analysis the factors which were effective on FMD percentage change (<5.5%) in Group I were BMI (p < 0.02), plasma Insulin (p < 0.04) and triglycerides (p < 0.02). There was a negative co-relation for FMD, NMD and HOMA-IR. Discussion: We conclude that increased HOMA-IR in hyperglycaemic patients is associated with severe endothelial dysfunction which is the marker of the atherosclerosis. Thus the measurement of endothelial vasomotor function which is a comprehensive analysis of atherosclerotic burden may provide a better predictive value of future cardiovascular events than the analysis of each of the traditional risk factors alone.展开更多
文摘The validity of the flow-mediated dilation (FMD) test has been doubted due to the lack of normalization to the primary stimulus, shear stress. Shear stress can be calculated using a simplified mathematical model based on Poiseuille’s law. Poiseuille’s law assumes that the blood velocity profile is parabolic. The presence of turbulence will violate this assumption. The Reynolds number (RE) is used to define critical values for the transition from laminar to turbulent flow. Between RE values of 2000 and 4000, flow enters a transitional phase where turbulence is possible. Purpose: To determine whether brachial artery blood flow becomes turbulent during reactive hyperemia following forearm ischemia. Methods: Eleven healthy male subjects (25 ± 5 years) were tested. Brachial artery diameters and blood velocities were measured continuously following 2, 4, 6 and 10 minutes ischemia. The peak post-ischemic RE (REpeak) and RE integrated over 40 seconds (RE40) post-ischemia were calculated. Results: There was a significant change in REpeak (F4,7 = 98.573, p = ≤ 0.001) and RE40) (F4,7) = 50.613, p = ≤ 0.001) in response to ischemia. Within-subjects contrasts revealed a significant increase in REpeak and RE40 for each duration of ischemia versus baseline (p = ≤ 0.001). Following 4 minutes of ischemia there was approximately 12 seconds of potentially turbulent flow. Conclusion: Blood flow transitions between laminar and turbulent flow during ischemia-induced reactive hyperemia. This may limit the efficacy of estimating shear stress when using the standard FMD test protocol.
文摘Introduction: In recent years, flow mediated dilatation (FMD) has become a popular technique in cardiovascular medicine. HOMA-IR was accepted to determine the insulin sensitivity as a valuable standard. In this study, we evaluated the association between HOMA-IR (homeostasis model assessment of insulin resistance) and vascular endothelial dysfunction, as assessed by endothelium- dependent flow-mediated dilatation (FMD) and nitroglycerin-mediated dilatation (NMD), in type 2 Diabetic (DM) patients. Material and Methods: Eighty four (84) consecutive out-patients were enrolled. HOMA-IR was calculated as fasting insulin (μU/ml) multiplied by fasting plasma glucose (FPG) (mg/dl) and divided by 405. The ultrasound method for measuring FMD and NMD has been used. Out of 84 patients, 42 patients were in control group and 42 patients were in diabetic group, which were further subdivided into two groups based on HOMA-IR > 3.0 and above was considered as Group I and HOMA IR < 3.0 and below was considered as Group II. Fasting Plasma Glucose (mmol/dl) (7.74 ± 2.56, 6.81 ± 1.9, p < 0.001) and Fasting Insulin (μU/dl) (13.26 ± 8.09, 6.65 ± 2.36, p < 0.001) were statistically significant in Group I. The baseline mean FMD in controls and cases (Group I and Group II) was 15.36 ± 9.56, 4.15 ± 2.29, 12.21 ± 6.24 (p < 0.001) respectively. By logistic regression analysis the factors which were effective on FMD percentage change (<5.5%) in Group I were BMI (p < 0.02), plasma Insulin (p < 0.04) and triglycerides (p < 0.02). There was a negative co-relation for FMD, NMD and HOMA-IR. Discussion: We conclude that increased HOMA-IR in hyperglycaemic patients is associated with severe endothelial dysfunction which is the marker of the atherosclerosis. Thus the measurement of endothelial vasomotor function which is a comprehensive analysis of atherosclerotic burden may provide a better predictive value of future cardiovascular events than the analysis of each of the traditional risk factors alone.
