Measurement Of Coronary Blood Flow Velocity Research Articles

Noninvasive quantification of coronary blood flow reserve in humans using myocardial contrast echocardiography.

We hypothesized that coronary blood flow (CBF) reserve could be quantified noninvasively in humans using myocardial contrast echocardiography (MCE). Eleven patients with normal epicardial coronary arteries (group I) and 19 with single-vessel coronary stenosis (group II) underwent quantitative coronary angiography, MCE, and CBF velocity measurements at rest and during intravenous adenosine infusion. In group I patients, MCE-derived myocardial blood flow (MBF) velocity reserve (2.4+/-0.08) was similar to CBF velocity reserve using a Doppler flow wire (2.4+/-1.1). Patients with a single risk factor had a significantly higher MBF reserve (3.0+/-0.89) than those with >/=2 risk factors (1.7+/-0.22). In group II patients, significant differences were found in MBF velocity reserve in patients with mild (<50%), moderate (50% to 75%), or severe (>75%) stenoses (2.2+/-0.40, 1.6+/-0.65, and 0.55+/-0.19, respectively; P=0.005). A linear relation was found between flow velocity reserve determined using the 2 methods (r=0.76, P<0.001), and a curvilinear relation was noted between the percent coronary stenosis measured using quantitative coronary angiography and velocity reserve using both methods. CBF reserve can be measured in humans using MCE. This method may allow the noninvasive assessment of coronary stenosis severity and the detection of microvascular dysfunction.

Impact of Doppler guidewire size and flow rates on intravascular velocity profiles.

Coronary blood flow velocity measurements by conventional intravascular catheter-based Doppler devices are well known to be affected by catheter size. Moreover, it is of clinical importance that the assessment of maximum vasodilator capacity, i.e., the coronary reserve, might be considerably affected by a shape change of the velocity profile under hyperemia. Therefore, the present in vitro study aimed to assess the impact of a small-size Doppler guidewire on the velocity profiles interrogated in tubes with diameters corresponding to the epicardial coronary arteries at clinically relevant flow rates. A 0.014" guidewire was inserted into four serially connected silicone tubes of known diameter, which were perfused with discarded human whole blood by means of a roller pump. In order to determine the effect of the Doppler guidewire on the velocity profile antegrade and retrograde perfusion were carried out in each vessel segment. Vm, the true mean velocity, was calculated from the time collected flow divided by the corresponding vessel cross-sectional area. Average peak velocity (APV) measurements were obtained by pulling back the Doppler device across each of the four vessel segments with given flow rates ranging from 1.14-5.88 ml/s in antegrade and retrograde direction. The shape factor of the recorded velocity profile (fp) is defined as vm/APV and is generally assumed to be close to 0.5. Antegrade perfusion: APV = 1.63 vm + 5.35 (R2 = 0.98); fp = 0.001 vm + 0.51. Retrograde perfusion: APV = 1.71 vm + 3.33 (R2 = 0.98); fp = 0.001 vm + 0.52. Due to the constant relationship between APV and vm, velocity profiles within vessels of epicardial coronary artery size are not substantially disturbed by the presence of the Doppler guidewire. The slight, but significant increase of experimental fp with increasing flow is at variance with the theoretically expected fp values.

Protected Left Main Angioplasty: Alterations of Intracoronary Doppler Flow Velocity

Coronary blood flow velocity measurements during protected left main coronary angioplasty have not been previously reported. In a patient undergoing angioplasty of left main and circumflex vessels with prior coronary artery bypass grafting, distal coronary flow velocity was measured before, during, and after angioplasty, and again after stenting of the circumflex stenosis. The data demonstrated preserved coronary flow during left main occlusion in this individual and provided new observations that highlight the limitations of our understanding of myocardial blood flow in complex circumstances of high risk angioplasty and interventions following bypass graft surgery.

Measurement of coronary blood flow velocity in conscious rats

This study describes a technique for the continuous recording of coronary blood flow velocity (CBV) in conscious unrestrained rats. A pulsed Doppler flow probe consisting of a 1-mm2 crystal mounted in a 4-mm suction cup was positioned over the left coronary artery of pentobarbital sodium-anesthetized rats. The probe was held in place with mild suction and sutured to the surface of the myocardium. Probes were connected to a pulsed Doppler flowmeter, which measures Doppler shift and provides an index of blood flow velocity. While rats were still anesthetized, the measurement of CBV was validated by determining that CBV peaked during diastole and increased in parallel with arterial pressure. Phasic CBV signals obtained in conscious rats were similar to those observed in anesthetized animals. Intravenous infusion of dipyridamole (0.5-3 mg.kg-1 x mg-1) produced a dose-dependent increase in CBV and decrease in coronary vascular resistance in conscious unrestrained rats 7 days after placement of the probe. Light microscopic review of cardiac tissue from instrumented rats revealed minimal epicardial reaction (fibrin deposition) restricted to the immediate area of the probe without distortion of the coronary architecture, edema, inflammation, or necrosis compared with controls. Heart weight-to-body weight ratios of instrumented rats were also not different from those of control rats. This study describes the first technique by which CBV can be measured continuously in chronically instrumented rats.

Transluminal, subselective measurement of coronary artery blood flow velocity and vasodilator reserve in man.

Assessment of coronary blood flow and the vasodilator reserve capacity of individual coronary arteries in the catheterization laboratory has been hampered by methodologic limitations. We have developed and validated a small Doppler catheter that can subselectively measure phasic coronary blood flow velocity (CBFV). In seven anesthetized calves, CBFV was varied from 0.1 to 5.7 times control CBFV. Changes in mean CBFV measured intraluminally by catheter in the left anterior descending and left circumflex arteries were similar to those measured simultaneously with an epicardial Doppler probe on the surface of the same vessel (n = 85, r = .95, slope = 1.04) and to changes in coronary sinus flow (n = 69, r = .97, slope = 1.06) measured with timed venous collections. Identical maximal coronary reactive hyperemic responses with the catheter present and absent in the artery being studied demonstrated that coronary obstruction by the catheter was minimal. Safety studies in six additional calves demonstrated that the catheter caused small changes in coronary endothelial permeability. Histologic studies revealed no endothelial denudation or thrombus formation. Stable phasic recordings of coronary blood flow velocity have been obtained in 58 of 70 patients studied. One of the 70 patients studied had abrupt coronary occlusion probably related to catheter-induced vasospasm. In 10 normal patients, intracoronary meglumine diatrizoate increased CBFV to 3.5 times that at rest (range 2.8 to 5.0). CBFV rose 5.0-fold after an intravenous infusion of dipyridamole (range 3.8 to 7.0). In each patient, dipyridamole produced greater vasodilation than meglumine diatrizoate. The time- and dose-response characteristics to dipyridamole infusion were heterogeneous, underscoring the advantage of continuous on-line measurement of CBFV in the measurement of vasodilator reserve. This method of measuring CBFV and assessing vasodilator reserve in the catheterization laboratory should facilitate studies of the coronary circulation in man.