Adrenergic coronary vasoconstriction helps maintain uniform transmural blood flow distribution during exercise.

Huang, Alice H.; Feigl, Eric O.

doi:10.1161/01.res.62.2.286

Cited by 101 publications

(62 citation statements)

References 46 publications

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“…Thus important issues pertaining to the cardiac circulation have been impossible to study. Recently, transthoracic duplex ultrasound (TTD) has been introduced as a promising tool for the assessment of coronary circulatory parameters (5)(6)(7)(8)(9)(10)(11)(12). This technique allows investigators to measure real-time changes in CBV in a segment of the left anterior descending artery (LAD) that is in close proximity to the chest wall.…”

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Transthoracic Doppler echocardiography to noninvasively assess coronary vasoconstrictor and dilator responses in humans

Momen

Kozak

Leuenberger

et al. 2010

American Journal of Physiology-Heart and Circulatory Physiology

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Momen A, Kozak M, Leuenberger UA, Ettinger S, Blaha C, Mascarenhas V, Lendel V, Herr MD, Sinoway LI. Transthoracic Doppler echocardiography to noninvasively assess coronary vasoconstrictor and dilator responses in humans. Am J Physiol Heart Circ Physiol 298: H524 -H529, 2010. First published November 25, 2009 doi:10.1152/ajpheart.00486.2009.-Human studies of coronary circulation are limited because of methodological issues. Recently, a noninvasive transthoracic duplex ultrasound (TTD) technique has emerged as an important tool to measure coronary blood flow velocity (CBV) in conscious humans. We employed two protocols to determine whether noninvasive "native" coronary artery velocity responses to constrictor or dilator stimuli assessed by TTD provide reliable data. In the first protocol, coronary vascular resistance (CVR ϭ diastolic blood pressure/CBV) responses to static handgrip were examined in the left internal mammary artery (LIMA) and native left anterior descending artery (LAD) into which the graft was inserted (patient age 63 Ϯ 3 years). Our prior report documented increased CVR in the LIMA graft during static handgrip (Momen et al., J Appl Physiol 102: 735-739, 2007). We hypothesized that the magnitude of increases in CVR during handgrip would be similar in the LIMA graft and LAD in the same individual. Percent increases in CVR were similar in the LIMA and distal native LAD (27 Ϯ 4% vs. 28 Ϯ 6%). In the second protocol, we studied six patients (age 61 Ϯ 3 years) who underwent cardiac catheterization of the LAD. We compared coronary vasodilator responses to intravenous adenosine infusion (0.14 mg⅐kg Ϫ1 ⅐min Ϫ1) obtained by intracoronary Doppler guidewire technique and TTD on separate studies. The relative increases in CBV with adenosine obtained by intracoronary Doppler guidewire and TTD were similar (62 Ϯ 10% vs. 65 Ϯ 12%). Noninvasive TTD provides reliable human coronary circulatory constrictor and dilator data. coronary flow velocity; duplex ultrasound; handgrip FROM A PHYSIOLOGICAL STANDPOINT there are relatively few human studies of coronary circulatory function. This has largely been due to methodological issues. Specifically, until recently, invasive measurements of coronary blood flow velocity (CBV) were needed to determine an index of coronary flow velocity. Although these invasive approaches are certainly possible, studies in large groups of patients and in those not already undergoing cardiac catheterization are not feasible. Thus important issues pertaining to the cardiac circulation have been impossible to study. Recently, transthoracic duplex ultrasound (TTD) has been introduced as a promising tool for the assessment of coronary circulatory parameters (5-12). This technique allows investigators to measure real-time changes in CBV in a segment of the left anterior descending artery (LAD) that is in close proximity to the chest wall. TTD has the potential to measure rapid and sequential changes in CBV during a variety of stressful maneuvers in a safe and noninvasive way.We have recently ...

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Transthoracic Doppler echocardiography to noninvasively assess coronary vasoconstrictor and dilator responses in humans

Momen

Kozak

Leuenberger

et al. 2010

American Journal of Physiology-Heart and Circulatory Physiology

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“…18 In their experiments, during dynamic exercise in dogs, the ratio of subendocardial to subepicardial blood flow in an unblocked anterior control region was better than in a posterior region of the left ventricle that was a-adrenergically blocked with phenoxybenzamine. 17 However, no separate data for subendocardial and subepicardial blood flow in the a-adrenergically blocked and in the intact region were presented, and an increase in inner to outer flow ratio does not necessarily imply an increase in subendocardial blood flow. '156'9 It is also unclear whether phenoxybenzamine, which predominantly blocks a,-adrenoceptors20 in the present study and in the study by Giudicelli et al, 16 completely blocked a2-adrenoceptors.…”

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Impact of alpha-adrenergic coronary vasoconstriction on the transmural myocardial blood flow distribution during humoral and neuronal adrenergic activation.

Baumgart¹,

Ehring²,

Kowallik³

et al. 1993

Circulation Research

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Increased heart rate and left ventricular pressure during humoral and neuronal adrenergic activation act to restrict blood flow preferentially in the subendocardium. The hypothesis was advanced that a-adrenergic coronary vasoconstriction preferentially in the subepicardium may counterbalance the enhanced extravascular compression in the subendocardium and serve to maintain blood flow transmurally uniform. In 40 anesthetized dogs, regional myocardial blood flow was determined with colored microspheres; wall function, with sonomicrometry. Humoral adrenergic activation (HAA) was induced by a combination of intravenous atropine, intravenous norepinephrine, and atrial pacing during baseline coronary vasomotor tone (group 1, n=6) and in the presence of maximal coronary vasodilation with intravenous dipyridamole (group 2, n=6). In an additional group, HAA was induced by intravenous norepinephrine in the presence of dipyridamole but without atropine and atrial pacing in order to increase end-diastolic left ventricular pressure (group 3, n=6). Measurements were performed at rest, during HAA, and during ongoing HAA with the intracoronary infusion of the a-antagonist phentolamine (Phen). At unchanged mean aortic pressure, Phen improved blood flow particularly to the inner layers as follows: from 1.42±0.40 (mean+SD) to 1.90±0.40 mL/(min g) (group 1, P<.05), from 4.99+2.31 to 5.53±2.56 mL/(min g) (group 2, P<.05), and from 6.01±1.41 to 6.29±1.27 mL/(min -g) (group 3, P<.05), associated with a decrease in outer layer blood flow in groups 2 and 3. In 16 additional dogs, 13-adrenoceptors were blocked by propranolol and muscarinic receptors by atropine. Neuronal adrenergic activation (NAA) was induced by cardiac sympathetic nerve stimulation (CSNS) during baseline coronary vasomotor tone (group 4, n=8) and in the presence of maximal vasodilation (group 5, n=8). Measurements were performed at rest, during a first CSNS, and 20 minutes later during a second CSNS+Phen. The reproducibility of two consecutive episodes of CSNS 20 minutes apart was demonstrated in a separate set of experiments (n=6). At matched mean aortic pressures, Phen improved blood flow to all myocardial layers in group 4, whereas in group 5, Phen induced a redistribution of myocardial blood flow toward subepicardial layers [from 4.44±0.96 to 4.81±0.83 mL/(min * g), P<.051 at the expense of inner layers.With the addition of Phen, there was no change in regional wall function in any group of dogs studied. Thus, during HAA, ar-adrenergic coronary vasoconstriction does not exert a beneficial effect on transmural blood flow distribution. During NAA, a beneficial effect of a-adrenergic coronary vasoconstriction becomes apparent only under conditions of maximal coronary vasodilation. (Circ Res. 1993;73:869-886

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“…a-receptors appear to be more abundant in the epicardial vessels, resulting in a relatively higher vascular resistance in these vessels with exercise. The net effect appears to be preservation of blood flow to the subendocardial region during a period of high oxygen demand by these tissues (24).…”

Section: Resultsmentioning

confidence: 99%

The Effects of Hypoxemia on Myocardial Blood Flow during Exercise

Paridon¹,

Bricker²,

Dreyer³

et al. 1989

Pediatr Res

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ABSTRACT. We evaluated the adequacy of regional and transmural blood flow during exercise and rapid pacing after 1 wk of hypoxemia. Seven mature mongrel dogs were made hypoxemic (mean Oz saturation = 72.4%) by anastomosis of left pulmonary artery to left atrial appendage. Catheters were placed in the left atrium, right atrium, pulmonary artery, and aorta. Atrial and ventricular pacing wires were placed. An aortic flow probe was placed to measure cardiac output. Ten nonshunted dogs, similarly instrumented, served as controls. Recovery time was approximately 1 wk. Cardiac output, mean aortic pressure, and oxygen saturation were measured at rest, with ventricular pacing, atrial pacing, and with treadmill exercise. Ventricular and atrial pace and exercise were at a heart rate of 200. Right ventricular free wall, left ventricular free wall, and septa1 blood flow were measured with radionuclide-labeled microspheres. Cardiac output, left atrial blood pressure, and aortic blood pressure were similar between the two groups of dogs in all testing states. Myocardial blood flow was significantly higher in the right and left ventricular free wall in the hypoxemic animals during resting and exercise testing states. Myocardial oxygen delivery was similar between the two groups of animals. Pacing resulted in an increase in myocardial blood flow in the control animals but not the hypoxemic animals. Myocardial blood flow increased significantly over resting flow with exercise in both groups of animals. Endocardia1 to epicardial flow ratio were above one and similar both within and between groups of animals for all testing states. We conclude that myocardial blood flow in hypoxemic dogs increases to supply similar oxygen delivery as the control dogs. The endocardia1 to epicardial ratio would indicate no exhaustion of subendocardial coronary vascular reserve with hypoxemia in any testing state. (Pediatr Res 25:280-284,1989) Children with cyanotic congenital heart disease have a limited exercise capacity. What role the adequacy of myocardial blood flow plays in the exercise limitation of these children is not known. Hypoxemia, polycythemia, and myocardial hypertrophy all have the potential to increase the demands made on myocardial blood flow during exercise. Little is known about their effects on the global and regional myocardial blood flow during exercise.The purpose of this study was to isolate one of these factors 28by evaluating the effects of hypoxemia on global and regional myocardial blood flow during exercise. In experiments with dogs, we created a left pulmonary artery to left atrial appendage anastomosis that resulted in a level of hypoxemia frequently found in cyanotic congenital heart disease in children. Using isotope-labeled microspheres, we measured transmural and regional blood flow at rest, during atrial and ventricular pacing, and during steady state exercise. We hypothesized that the combined effects of hypoxemia and exercise might result in inadequate myocardial blood flow, especially in vulnerable areas su...

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Adrenergic coronary vasoconstriction helps maintain uniform transmural blood flow distribution during exercise.

Cited by 101 publications

References 46 publications

Transthoracic Doppler echocardiography to noninvasively assess coronary vasoconstrictor and dilator responses in humans

Transthoracic Doppler echocardiography to noninvasively assess coronary vasoconstrictor and dilator responses in humans

Impact of alpha-adrenergic coronary vasoconstriction on the transmural myocardial blood flow distribution during humoral and neuronal adrenergic activation.

The Effects of Hypoxemia on Myocardial Blood Flow during Exercise

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