The quantitative determination of coronary flow with a positron (rubidium-84)

Racial differences in the responses to shear stress in human umbilical vein endothelial cells

Background:

African American ethnicity is an independent risk factor for exaggerated oxidative stress, which is related to inflammation, hypertension, and cardiovascular disease. Recently, we reported that in vitro oxidative stress and inflammation levels differ between African American and Caucasian human umbilical vein endothelial cells (HUVECs), African American HUVECs having higher levels of both. However, it remains to be shown whether the cells would respond differently to external stimuli.

Methods:

We used a cone and plate viscometer to apply laminar shear stress (LSS) as an aerobic exercise mimetic to compare the responses by race. HUVECs were exposed to static conditions (no LSS), low LSS (5 dyne/cm²), and moderate LSS (20 dyne/cm²).

Results:

It was found that African American HUVECs had higher levels of oxidative stress under static conditions, and when LSS was applied protein expression levels (NADPH oxidase NOX2, NOX4 and p47phox subunits, eNOS, SOD2, and catalase) and biomarkers (NO, SOD, and total antioxidant capacity) were modulated to similar levels between race.

Conclusion:

African American HUVECs may be more responsive to LSS stimulus indicating that aerobic exercise prescriptions may be valuable for this population since the potential exists for large in vivo improvements in oxidative stress levels along the endothelial layer in response to increased shear flow.

[Value and limitations of coronary blood flow measurement in man (author's transl)]

Attempts to measure coronary blood flow in man have made considerable progress during the last 25 years. The major techniques are based on the direct or indirect Fick principle; coronary flow is calculated from the arterio-coronary venous difference of inert gases or from the precordial recorded disappearance curve of radioactive gases or substances. The accuracy of the techniques depends upon the properties or the indicators used and the precision of their determination. All techniques applied hitherto are intricate and unsuitable for general use. -A lot of information is obtained about coronary circulation in health and disease by coronary flow measurements in man. Further studies in this field may influence pathophysiological and clinical concepts especially concerning coronary heart disease.

Total and effective coronary blood flow in coronary and noncoronary heart disease

There are no data available concerning total coronary blood flow to the whole heart (CBF) in man. "Effective" or "nutrient" coronary blood flow to the whole heart (MBF), supposedly a measure of flow through exchanging channels of the coronary circulation, has been measured but its validity has not been established. Accordingly, CBF and MBF were measured in 9 normal subjects, 26 patients with coronary heart disease (CHD), and 19 with noncoronary, mostly valvular heart disease (NCHD), by coincidence counting 84Rb technique. Two methods were used: single bolus (24 cases) and continuous infusion (30 cases). Various other parameters including myocardial oxygen utilization (MVO2) and lactate extraction ratio were determined. In the normal subjects CBF (386 +/- 77 ml/min) was significantly higher (P < 0.05) than in CHD (288 +/- 124 ml/min) and NCHD (292 +/- 111 ml/min). Likewise the normal MBF (380 +/- 81 ml/min) was significantly higher (P < 0.01) than in CHD (251 +/- 105 ml/min) as well as NCHD (258 +/- 104 ml/min). The myocardial Rb extraction ratio epsilon Rb) was significantly lower in normal subjects (39 +/- 9%) than in CHD (50 +/- 7%) and NCHD (52 +/- 11%) and this supports the view that epsilon Rb is flow-dependent. In both CHD and NCHD there was significant diminution of MVO2 as well as CBF. In CHD this was accompanied by a significant anaerobic trend but in NCHD it was not. It might therefore appear that in CHD, MVO2 is determined by perfusion whereas in NCHD, perfusion is determined by MVO2. In comparing CBF with MBF by paired observation testing, there was no significant difference in the normals (P > 0.3), whereas the differences were significant in CHD (P < 0.01) and NCHD (P < 0.02). This was merely a reflection of a reduced ratio of myocardial to total body epsilon Rb in CHD and NCHD, and available evidence indicates that this may be an expression of depressed transport of Rb+ rather than true shunting.

Direct and reflex effects of nitroglycerin on coronary and left ventricular dynamics in conscious dogs

The effects of intravenous and sublingual glyceryl trinitrate (nitroglycerin), 40 mug/kg, were studied on coronary blood flow and resistance, left ventricular (LV) pressures (P) and diameters (D), rate of change of pressure (dP/dt), (dP/dt)/P, and on the velocity (V) of myocardial fiber shortening in conscious dogs. Nitroglycerin i.v. caused substantial coronary vasodilatation prior to any changes in systemic hemodynamics. Mean coronary flow increased by a maximum of 47 ml/min and coronary sinus P(o2) rose from 16 to 26 mm Hg while pressure and diameter began to fall, and heart rate began to rise. After the maximal fall in mean arterial pressure (-26 mm Hg), a secondary peak in coronary flow occurred which was associated with increases in heart rate (100 beats/min), (dP/dt)/P (22%), and isolength V (12%). Beta blockade prevented the reflex increases in contractility but only a part of the reflex tachycardia; the remainder was prevented by cholinergic blockade. Maintaining heart rate constant minimized the decreases in LV D and increases in contractility. When the reflex inotropic and chronotropic effects were prevented by a combination of atrial pacing and beta blockade the early coronary vasodilatation was unaltered, but the later coronary vasodilatation was minimized. Thus i.v. nitroglycerin in the conscious dog exerts a potent direct coronary vasodilating action and also a secondary coronary vasodilation caused by reflex increases in contractility and heart rate. The decreases in diameter are largely the result of tachycardia. Sublingual nitroglycerin produced directionally similar, but quantitatively lesser effects on coronary flow and resistance, LV D, LV P, and contractility.