Pressure-flow characteristics in the right and left ventricular perfusion territories of the right coronary artery in swine

Regional pressure-flow relationships within the right coronary artery (RCA) circulation of swine were determined. Enflurane-anaesthetized swine (n=7) were studied during step-wise reductions of RCA perfusion pressure using an extracorporeal circuit. Regional blood flow was measured using microspheres and contractile function of the right ventricle was measured using sonomicrometry. The RCA perfusion territory was divided into its anatomic components: right ventricular free wall (RV), interventricular septum (with further division in transmural thirds; SEP-LV, SEP-MID and SEP-RV) and right atrium (RA). Pressure-flow relations were constructed for each region and autoregulatory capacity assessed through calculation of an autoregulatory index (AI, closed-loop gain). The pressure-flow relationship for the entire RCA exhibited autoregulation down to a pressure of 40 mmHg. The SEP-LV exhibited a similar relationship with loss of autoregulation at approximately 40 mmHg. The pressure-flow relationship of the RV, however, showed autoregulation to a pressure of 30 mmHg with a decrease of blood flow only at a pressure of 20 mmHg. Little autoregulation was observed in the RA. Autoregulatory gain assessed by AI was similar in RV, SEP-LV and SEP-RV as pressure was reduced from 90 to 55 mmHg (RV=0.54±0.41; SEP-LV=0.58±0.36; SEP-RV=0.83±0.36). With further reductions of pressure, AI was highest in the RV, followed by the SEP-RV and then SEP-LV. AI of the SEP-LV and SEP-RV was negative when pressure was reduced from 30 to 20 mmHg. AI of the RA was negative at the high and low pressure ranges and demonstrated little autoregulatory gain otherwise. Regional contractile function of the RV was maintained to a pressure of 30 mmHg and appeared to be closely related to regional blood flow. Thus, the RCA perfusion bed is characterized by a markedly heterogeneous autoregulatory capacity based on its anatomical makeup.     

The influence of coronary pressure and coronary flow on intracoronary blood volume and geometry of the left ventricle

Summary Intracoronary blood volume in relation to coronary perfusion pressure was estimated in dog hearts in situ with cannulated left coronary arteries. Electromagnetically measured inflow into coronary arteries times mean transit time, obtained by a dye dilution technique determined the intracoronary blood volume. Within the range from 70 and 170 mm Hg coronary perfusion pressure the mean value of intracoronary blood volume increases from 11.0 to 17.8 ml per 100 g wet weight; an increase of about 62%. The mycocardial wall at 70 mm Hg consists of 10.4% intracoronary blood and at 170 mm Hg of 15.1%. A significant increase in intracoronary blood volume is seen with increasing coronary perfusion pressure at constant coronary flow.With increasing coronary perfusion pressure the outer volume of the heart and the volume of the myocardial wall increases while the inner volume of the left ventricle decreases in blood perfused dog hearts in situ and in isolated cat hearts. The mean radius of the left ventricle is not changed by the coronary perfusion pressure. This change in the geometry of the left ventricle influences the pressurevolume relation of the heart and can explain the effect of coronary perfusion pressure on the performance of the heart.     

Die extravasale Komponente des Coronarwiderstandes mit steigendem linksventrikulären Druck

Summary In experiments on anaesthetized dogs the arterial blood pressure and the left ventricular pressure were enhanced by intraarterial blood transfusion. The circumflex branch of the left coronary artery was perfused by constant blood pressure at 65, 100 or 200 mm Hg. After elimination of the sinus node the heart rate was kept constant at 150 beats per minute by electrical stimulation of the right auricle. The metabolically regulated component of coronary resistance of the circumflex branch was kept constant by a maximal pharmacological dilatation. On this condition the coronary blood flow decreases with increasing left intraventricular systolic pressure. The coronary resistance increases. The increasing coronary resistance with increasing intraventricular blood pressure is caused by an enhancement of the extravascular component because the perfusion pressure and hematocrit were constant, and the coronary vessel maximal dilated. The rise of coronary resistance with increasing intraventricular blood pressure depends on the height of perfusion pressure. Low perfusion pressure is combined with a marked increase, while the increase is small in the experiments with high perfusion pressure. The pathophysiological significance of the results has been discussed.

     

Superdominant right coronary artery with absent left circumflex artery

Noninvasive imaging of coronary artery disease is rapidly replacing angiography as the first line of investigation. Multislice CT is the non-invasive modality of choice for imaging coronary artery disease and provides high speed with good spatial resolution. CT coronary angiography in addition to detecting and characterising atherosclerotic coronary artery disease is also a good imaging tool for evaluating anomalies of coronary arteries. Superdominant right coronary artery with absent left circumflex artery is one such rare coronary artery anomaly which is well evaluated with multislice CT angiography. The authors report one such case of superdominant right coronary artery with absent left circumflex artery imaged with 64-slice MDCT.     

The relative anatomy of the coronary arterial and venous systems

An anatomical understanding of human coronary arterial and venous systems is necessary for device development and therapy applications that utilize these vessels. We investigated the unique use of contrast‐CT scans from perfusion‐fixed human hearts for three‐dimensional visualization and analysis of anatomical features of the coronary systems. The coronary arterial and venous systems of eleven perfusion‐fixed human hearts were modeled using contrast‐CT and Mimics software. The coronary arteries that coursed near the major coronary veins, how close coronary arteries were to coronary veins, and the size of adjacent coronary arteries were recorded and analyzed. The majority of coronary veins were within 5 mm of a coronary artery somewhere along its length. Interventricular veins elicited the largest occurrence of overlaps. There was significant variability in the percentage of each vein that coursed within 0.5, 1, 2, and 5 mm of a nearby artery. The left marginal veins and anterior interventricular vein had the largest portion of the vein that coursed near a coronary artery. The right coronary artery most often coursed near the middle cardiac vein. The inferior veins of the left ventricle elicited the most variation in adjacent arteries. The left circumflex artery and/or branches of the circumflex artery coursed near the left marginal vein in all cases where there was an artery near the marginal vein. The wide variation of measurements reinforces the importance of a precise understanding of individualized cardiac anatomy in order to provide the highest quality care to cardiac patients. Clin. Anat. 27:1023–1029, 2014. © 2014 Wiley Periodicals, Inc.     

Anatomical study of a left single coronary artery with special reference to the various distribution patterns of bilateral coronary arteries

A left single coronary artery of heart was observed during anatomy practice at Kumamoto University School of Medicine in a 73-year-old female cadaver who died from a thalamic hemorrhage. The left single coronary artery, having a single orifice in the left aortic sinus, bifurcated into the anterior interventricular (IVa) and circumflex (CIR) arteries. No orifice of the right coronary artery was found on the aortic wall. Giving off a branch which traversed the upper part of the infundibulum to supply the anterior upper region of the right ventricle, the IVa descended in the anterior interventricular sulcus to supply the apex of the heart. The CIR curved leftwards in the atrioventricular sulcus to reach the posterior surface, after which it continued to emerge again into the anterior surface. The atrial arteries showed no anomalous distribution pattern and histological observation revealed no pathological abnormality other than a slightly thickened tunica intima. Furthermore, we observed the distribution patterns of bilateral coronary arteries in 377 hearts dissected during anatomical practice over 13 years at Kanazawa University (1980–1986) and Kumamoto University (1993–1998). Although the reason why only the right coronary artery was absent is left unexplained, it was concluded that the left single coronary artery in this study, having the developed left conal and circumflex branches, was an extreme case of the left dominant series of coronary arteries. The formation of single coronary arteries can be explained embryologically by the change of flow in the capillary plexus established on the ventricle wall.     

Influence of transmural pressure on myogenic responses of isolated cerebral arteries of the rat

We examined the diameter responses of isolated and pressurized posterior cerebral artery branches to various static and dynamic pressure alterations. These vessels, dissected from an anatomically identifiable location in the rat brain, developed tone when placed in a normal calcium physiological salt solution (1.6 mM Ca-PSS). Following a series of transmural pressure steps (Δp) of 25 or 50 mm Hg completed in 1–2 s and made every 5 min, they attained additional tone resulting in a mean luminal diameter of 139 μm at 100 mm Hg which was 35% less than their relaxed size measured in 1 mM EGTA-PSS. Continuous measurements of wall thickness and lumen diameter were obtained using a video electronic system in 1–2 mm long arterial segments, and autoregulatory gain factors calculated. Myogenic responses were obtained from each of 6 vessels taken from 6 WKY rats. Diameters following the step pressure changes were usually stable within 2–4 min. The data defined a myogenic regulatory pressure range from 49–145 mm Hg. Gain values averaged about 17% of that necessary for these arteries to maintain perfect flow autoregulation. Our results for myogenicity are comparable with the pressure range for blood flow autoregulation reported by others for the rat. We conclude that myogenic mechanisms, at least in this size artery, are partly responsible for flow autoregulation, and that they are supplemented by metabolic mechanisms operative in the intact rat brain. Research supported by grant HL 17335 from the NHLBI.     

Surgical management of tetralogy of Fallot with anomalous coronary artery.

Fifteen patients of tetralogy of Fallot with an anomalous left anterior descending coronary artery arising from the right coronary artery were operated during a period of 1982 and 1988. One patient died in the early post-operative period (6.6%). Two patients had a hemodynamically insignificant residual ventricular septal defect. Post-operative peak systolic pressure gradient between the right ventricle and pulmonary artery ranged from 10 mm Hg to 40 mm Hg (mean 24 mm Hg) in 4 patients. There was no incidence of inadvertent coronary artery division.     

Changes in the cardiac output and general peripheral resistance after obstruction of a coronary artery

Summary The left subclavicular, both carotid and femoral arteries were shunted; then the brachiocephalic artery and aorta were obstructed, distal to the origin of the left subclavicular artery. The output of the left ventricle, excluding that portion of it which flows into the coronary arteries, entered the rotameter through theleft subclavicular artery and flowed into the distal sections of carotid arteries and the proximal sections of the femoral artery. The average blood pressure in the system was measured by an electric manometer. From these data, general peripheral resistance could be estimated according to the data obtained. An average blood pressure of 80–100 mm Hg is the best at which to study the changes of hemodynamic indices occurring after obstruction of the coronary artery.(Presented by V.V. Parin, Active Member of the AMN SSSR) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 50, No. 7, pp. 27–33, July, 1960     

Regional,segmental, and temporal heterogeneity of cerebral vascular autoregulation

Autoregulation of cerebral blood flow is heterogeneous in several ways: regional, segmental, and temporal. We have found regional heterogeneity of the autoregulatory response during both acute reductions and increases in systemic arterial presure. Changes in blood flow are less in brain stem than in cerebrum during decreases and increases in cerebral perfusion pressure. Segmental heterogeneity of autoregulation has been demonstrated in two ways. Direct determination of segmental cerebral vascular resistance indicates that, while small cerebral vessels (<200 μm in diameter) make a major contribution to autoregulation during acute increases in pressure between 80 and 100 mm Hg, the role of large cerebral arteries (>200 μm) becomes increasingly important to the autoregulatory response at pressures above 100 mm Hg. Measurement of changes in diameter of pial vessels has shown that, during acute hypotension, autoregulation occurs predominantly in small resistance vessels (<100 μm). Finally, there is temporal heterogeneity of autoregulation. Sudden increases in arterial pressure produce transient increases in blood flow, which are not observed under steady-state conditions. In addition, the blood-brain barrier is more susceptible to hypertensive disruption after rapid, compared to step-wise, increases in arterial pressure. Thus, when investigating cerebral vascular autoregulation, regional, segmental, and temporal differences in the autoregulatory response must be taken into consideration.     

Reactive hyperaemic flow characteristics of the right coronary artery compared to the left anterior descending coronary artery in the open-chest dog

Reactive hyperaemia, the cardiovascular response to transient occlusion of a vessel, was examined and compared in the right coronary artery (RCA) and the left anterior descending coronary artery (LAD) in the same heart of an open-chest dog. First, to study the relationship between reactive hyperaemia and occlusion time in the RCA and LAD, respective flows were measured and reactive hyperaemia was induced with different occlusion times. Occlusion time required for half the maximum peak percentage reactive hyperaemic flow (%PRH), t _1/2, for the RCA was approximately twice that of the LAD: 11.4±2.3 s versus 5.9±1.4 s. Maximum %PRH of the RCA was significantly greater than that of the LAD while the percentage repayment of the RCA was lower than that of the LAD. Augmentation of right ventricular oxygen consumption shortened t _1/2 and increased percentage repayment significantly. Second, to determine critical pressure, which was defined as the perfusion pressure below which reactive hyperaemia was abolished completely, the RCA and LAD were perfused through a shunt from the carotid artery, perfusion pressure was varied in the range of 100 to 20 mmHg and reactive hyperaemia was induced. Critical pressure in the RCA was significantly lower than in the LAD: 32.2±5.7 mmHg versus 41.5±5.0 mmHg. These results suggest that the RCA has a greater flow reserve than the LAD. These results were consistent with the difference of oxygen metabolism between the right and left ventricles. The difference of oxygen metabolism between the two ventricles would, at least partly, account for these results.     

Observations on coronary collateral communications and the control of flow in the coronary circulation of the dog

1. Pressure was measured in the small arterial anastomosing branches of the coronary vascular network. The mean value was 30 mm Hg not significantly different from the mean value of 33 mm Hg for peripheral coronary pressure measured distal to a ligature on the anterior descending branch of the left coronary artery. Evidence was adduced to show that either the anterior descending or the circumflex artery had the capacity to maintain network pressure at levels adequate for tissue perfusion.2. The network has both capacity and compliance. Filling of the network compliance during systole probably accounts for the systolic phase of coronary flow. Flow through the microcirculation is probably entirely diastolic, the combined compliance of the aorta and large vessels together with the network provides the necessary reservoir, the potential energy indicated by diastolic pressure provides the perfusion pressure head.3. Resistance of vessels between the aorta and network cannula (pre-net) was approximately double that of the microcirculation (post-net). The smaller pre-network vessels are of the order 70 mum in diameter. Both pre- and post-network vessels are vaso-active and respond similarly to adrenaline and haemorrhage.     

Decreased regional contractility in nonischemic myocardium during acute coronary artery occlusion in conscious pigs

The purpose of this study was to use the relationship between end-systolic left ventricular pressure and segment length to assess the inotropic state of nonischemic myocardium during acute coronary artery occlusion in the conscious pig. Eight pigs were chronically instrumented with sonomicrometers to measure midwall segmental shortening and a micromanometer to measure left ventricular pressure. Occlusion of the inferior vena cava with a pneumatic occlusive cuff caused transient decreases in left ventricular pressure so that the relationship of left ventricular pressure and segment length at end systole could be determined over a range of pressures. In preliminary studies using open-chest pigs, this relation was shown to be highly linear and best quantified using a calculated segment length at a left ventricular pressure of 100 mm Hg (ESL100). During acute, 1-min occlusion of the left anterior descending coronary artery, the ESL100 of the nonischemic lateral and posterior walls was significantly increased from 8.75 +/- .18 mm to 9.64 +/- .21 mm (mean +/- SD, p less than .01), indicating a decreased inotropic state. Similarly, during occlusion of the left circumflex coronary artery, the ESL100 of the nonischemic anterior wall increased from 8.44 +/- 2.53 mm to 9.26 +/- 3.12 mm (p less than .05). This was not associated with a change in the amount of shortening during systole. Pharmacological autonomic blockade using atropine and propranolol failed to alter the response of nonischemic zones to acute coronary artery occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Anatomical study of the internal thoracic arteries; implications for use in coronary artery bypass graft surgery

Purpose

The feasibility of coronary artery bypass grafting using an internal thoracic artery (ITA) depends on the length of the graft with respect to the optimal route to reach the coronary target. The goal of this study was to assess the gain in length afforded by skeletonization and to evaluate the lengths of different pathways of the ITAs to the left coronary arteries.

Methods

The left and right ITAs were dissected out from 20 specimens and measured before and after skeletonization. Distance between the origin of the right ITA and the base of the left atrial appendage, corresponding to the proximal circumflex artery, was measured for both the transverse pericardial sinus and preaortic routes.

Results

Skeletonization gave a significant gain of length for both ITAs. Analysis showed no significant correlation between the ITA length and the height, weight, and BMI of specimens. We found no association between the length of the sternum and the length of skeletonized RITA or LITA. The anterior route of the skeletonized right ITA was shorter than the transverse pericardial sinus route in 18 cases. The average length to the circumflex artery territory was 132.8 ± 23.5 mm in front of the aorta and 150.5 ± 18.8 through the transverse pericardial sinus with a gain of length of 17.7 mm (p < 0.0001).

Conclusion

Skeletonization gave significant gains in length of both ITAs. The preaortic route for the skeletonized right ITA toward the circumflex territory was shorter than the transverse pericardial sinus route in 90 % of cases.

     

Threshold pressure for the pressure-dependent renin release in the autoregulating kidney of conscious dogs

1. The effect of varying renal artery pressure between 160 and 40 mm Hg on renal blood flow and renin release was studied in seven conscious foxhounds under β-adrenergic blockade receiving a normal sodium diet (4.1 mmol/kg/day). Pressure was either increased by bilateral common carotid occlusion or reduced in steps and maintained constant by a control-system using an inflatable renal artery cuff. Carotid occlusion itself had no influence on renal blood flow and renin release when renal artery pressure was kept constant and the β-receptors in the kidney were blocked.
2. Between 160 mm Hg and resting pressure there was no change in renal blood flow; between resting blood pressure and the lower limit of autoregulation (average 63.9 mm Hg) renal blood flow increased slightly (average 7%) indicating a high efficiency of renal blood flow autoregulation.
3. The relationship between renal artery pressure and renin release could be approximated by two linear sections:a low sensitivity to a pressure change (average slope: ?0.69 ±0.26ng AI/min/mm Hg) was found above a threshold pressure (average: 89.8±3.3 mm Hg) and a high sensitivity to a pressure change (average slope: ?64.4±20.8 ng AI/ min/mm Hg) was observed between threshold pressure and 60 mm Hg. There was no further increase of renin release between 60 and 40 mm Hg.
4. It is concluded that within the autoregulatory plateau the kidney of a conscious β-blocked dog receiving a normal sodium diet releases only negligible amounts of renin until renal artery pressure falls below a threshold pressure of 90 mm Hg which is close to the animals resting systemic pressure. Since beyond that a decrease of systemic pressure by as little as 1.3 mm Hg below threshold can raise resting renin release (84.8±29.8 ng/min) by 100%, it is suggested that systemic blood pressure tends to stabilize at a level at which renin release is minimal.

     

Terminal branching pattern of the right coronary artery in left-dominant hearts: a cadaveric study

BackgroundLeft coronary dominance has been reported to be associated with increased mortality and severity in case of myocardial ischemia involving left coronary artery. The present cadaveric study was proposed to objectively study and document the termination and branching pattern of the right coronary artery in left-coronary-dominant hearts in relation to the blood supply to the posterior surface of the right ventricle.MethodsSeventy-five cadaveric hearts were studied. The coronary vessels were injected with colored cellulose acetate butyrate and dissected. The coronary dominance was determined. In left-dominant hearts, branches and termination of the right coronary artery were studied.ResultsLeft coronary dominance was found in 13% of the specimens. The number of ventricular branches was found to be present as 0, 1, 2, and 4 in two, four, two, and two of the cases, respectively. The average length of the ventricular branch was 12.7 mm with a range of 5–35 mm. The atrial branch was found in 50% of hearts, varying from 2 to 3 mm in length. In three hearts, the acute marginal artery did not give any posterior ventricular branch, while two, three, and five posterior ventricular branches were seen in four, two, and one heart(s), respectively. The length of the posterior ventricular arteries was between 5 and 15 mm.ConclusionThe RCA is an inconstant and unreliable source of posterior right ventricular perfusion in a significant percentage of population with left-coronary-dominant hearts. This might be the reason for the increased morbidity and mortality seen in the event of left coronary ischemia.     

Blood transfusion requirements in coronary artery surgery with and without the activated clotting time (ACT) technique

Summary Control of anticoagulation during cardiopulmonary bypass (CPB) with the automated activated whole blood clotting time (ACT) and reversal of heparin after CPB using a computerized ACT dose-response curve method resulted in significant reductions of blood transfusion requirements, surgical time, and protamine doses in 150 patients undergoing coronary artery bypass grafting procedures (ACT group) as compared to 200 patients for whom a standard fixed dose protocol for heparin and protamine was used (control patients). Mean transfusion requirements were 1,938±60 SEM ml whole blood and 853±48.3 SEM ml red blood cells for control patients and 1,397±59 SEM ml whole blood (P<0.001) and 695±34 SEM ml red blood cells (P<0.01) in the ACT group. ACT group patients also required less protamine with 26.2±0.60 SEM ml Protamine 1,000 (Roche) as compared to 33.9±0.49 SEM ml for control patients (P<0.001) but more heparin with 31,440±783 SEM I.U. versus 26,760±263 SEM I.U. (P<0.001). Surgical time decreased from 321±5.5 SEM min for control patients to 289±5.4 SEM min for ACT group patients (P<0.001).Abbreviations AB autologous blood - ACD right coronary artery - ACT activated clotting time - ACT_o ACT — before heparin administration - ACT₃₆₀ ACT — 5 min. after 360 I.U. heparin/kg body wt. - CPB cardiopulmonary bypass - Cx circumflex branch of the left coronary artery - DIAG diagonal branch of the left coronary artery - ECC extracorporeal circulation - FB fresh blood - FFP fresh frozen plasma - POD postoperative day - RBC red blood cells - RIA descending branch of the left coronary artery - RIP posterior descending branch of the right coronary artery - WB whole blood     

Hydrostatic pressures within the vascular structures of the rat kidney

Summary The pressure conditions at the distal end of the interlobular arteries and in the interlobular veins were investigated from the pressures obtained in superficial small arteries and veins, accidentally found on the kidney surface, during the subsequent blockade of the blood stream in the down-stream and up-stream direction, respectively.The results suggested a hydrostatic pressure in the distal end of the interlobular arteries of about 85 mm Hg under normotensive conditions-a pressure which remained fairly constant when the perfusion pressure in the renal artery was decreased within the autoregulation range. The results indicate a considerable pressure drop of about 40 mm Hg along the interlobular arteries. During hypotension this pressure drop decreased, implying a decreased resistance in the interlobular arteries, i.e.a typical autoregulative response.The pressure in the interlobular veins amounted to about 5 mm Hg, which is a few mm Hg higher than that in the renal vein and about 7 mm lower than that in the peritubular capillary network. The results suggest a flow resistance located somewhere between the peritubular capillaries and the intrarenal veins. This resistance is not influenced by vasoactive substances but it is decreased when the systemic venous pressure is raised above 10 mm Hg. The resistance seems to act in the direction of protecting the peritubular capillaries from minor changes in the central venous pressure.     

Single coronary artery arising from the right sinus of Valsalva (case report)

A single coronary artery is a rare congenital anomaly of the coronary arteries where only one coronary artery arises from the aortic trunk by a single coronary ostium, supplying the entire heart. We report a case of a 70 years-old man with mitral valvular insufficiency and atherosclerotic right and left circumflex coronary arteries, in whom coronary angiography showed a single coronary artery arising from a single ostium in the right sinus of Valsalva (R-II-B subtype) and transverse trunk coursed between aorta and pulmonary artery. The clinical significance and subtype of the single coronary artery are discussed.     

A coronary active perfusion system for off-pump coronary artery bypass: advantage over passive perfusion regarding the physiology of the coronary artery

To avoid myocardial ischemia during off-pump coronary artery bypass, we developed a coronary active perfusion system (CAPS) that perfuses arterial blood to the coronary artery at the diastolic phase of the cardiac cycle by a syringe pump system. We report herein the details and compare CAPS with a passive shunt circuit from the femoral artery (FA shunt), regarding the physiology of the coronary artery. Six pigs were used for this study. After CAPS or FA shunt perfusion was established, coronary flow and coronary pressure were measured. The coronary flows in the native coronary artery, FA shunt perfusion, and CAPS perfusion with syringe pump stroke volume settings ranging from 0.1 to 0.4 ml were 27.2+/-3.0, 4.1+/-1.5, 12.7+/-1.2, 24.8+/-1.9, 33.3+/-1.6, and 42.2+/-1.9 ml/min, respectively. Mean coronary pressures under FA shunt perfusion and CAPS perfusion with stroke settings from 0.1 to 0.4 ml were 23.7+/-4.6, 48.8+/-5.0, 61.3+/-7.5, 70.8+/-5.4, and 82.3+/-5.2 mm Hg, respectively. CAPS had an advantage over the FA shunt regarding coronary flow with safe coronary pressure. Using CAPS, an off-pump coronary artery bypass can be performed safely without myocardial ischemia.