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Biomedical subjects

U Mittmann

Publications and source records attributed to U Mittmann.

53 records · Page 3Linked to original sources
PubMed1975

[Effect of coronary bypass surgery on myocardial pressure and ventricular function in the dog].

In 7 dogs a severe stenosis of the left circumflex coronary artery (CCA) is produced in the course of 18 days. The influence of myocardial revascularization on left ventricular function and on intramyocardial pressures in the areas supplied by the CCA and by the left anterior descending coronary artery is studied. Neither under control conditions nor during acute left ventricular pressure load does opening a bypass graft between the carotid artery and CCA induce a significant change in total ventricular function (dp/dtmax, Vmax, left ventricular enddiastolic pressure). However, immediately after opening the graft intramyocardial pressure rises in the CCA area indicating a regional improvement of myocardial function.

Animals↗
PubMedDate not supplied

[Intramyocardial pressure at various depths, during aortic constriction and myocardial ischemia in the dog (author's transl)].

Systolic intramyocardial pressure (IMP) is measured with a modification of the "closed perfusion technic" in 3 different layers of the myocardium in 8 anesthetized mongrel dogs. In the subendocardium IMP exceed left ventricular pressure (LVP) by about 30% whereas it is 30% lower than LVP in the subepicardium. Under resting conditions the level of isobaric balance of IMP and LVP is at a distance of 57% from the epicardium. During thoracic aortic constriction the ratio of IMP/LVP increases in the subepicardium but decreases in the subendocardium. Occlusion of the left circumflex coronary artery for 30 seconds results in a decrease of IMP and IMP/LVP in the ischemic region. In 25% of all cases, however, an increase of these parameters is found.

Animals↗
PubMedDate not supplied

[Effects of coronary stenosis and mean aortic pressure on coronary blood flow, poststenotic coronary pressure, and reactive hyperemia].

Six dogs were subjected to an acute stenosis of the left anterior descending coronary artery. The mean aortic pressure was fixed with a windkessel and an occluder on four different levels. A significant decrease of coronary blood flow and poststenotic coronary pressure was closely related to the level of mean aortic pressure. With lower aortic pressure the decrease occurred earlier than with higher aortic pressure. A 50% stenosis did not significantly influence coronary flow and poststenotic coronary pressure. A 90% stenosis resulted in decrease below 10% of control. In a range of aortic pressure between 60 and 140 mm Hg reactive hyperemia was significantly diminished at a 60% stenosis. Reactive hyperemia was completely abolished when coronary stenosis was 90%.

Animals↗
PubMedDate not supplied

Hemorrhagic shock with fixed hypotension and with spontaneous recovery of blood pressure. A comparison of two shock models.

In 26 dogs anesthetized with a barbiturate peripheral blood flow, O2 consumption and acid-base balance have been studied in two kinds of hemorrhagic shock: 1. Hemorrhagic shock with fixed hypotension (hypotensive shock, n = 12) 2. Hemorrhagic shock with spontaneously recovering arterial blood pressure (normotensive shock, n = 14). In both groups the same amount of blood is withdrawn and stored in a reservoir (31-32 ml/kg) to reduce arterial pressure to 40 mm Hg. In hypotensive shock there is a continuous outflow of blood into the reservoir in order to maintain an arterial pressure of 40 mm Hg. After 1 1/2 hours this shift of blood reverses itself spontaneously. In normotensive shock the arterial pressure is allowed to increase after the initial withdrawal of blood. 1 1/2 hours later it reaches a peak of 93 mm Hg after which it starts declining again. The duration of oligemia which the animals control themselves is nearly identical in both groups (4 hours). Both kinds of hemorrhagic shock have a mortality rate of 80%. The survival time is shorter (p less than 0.01) in hypotensive (3 hours) than in normotensive shock (7 1/2 hours). In both kinds of shock heart rate increases to more than 200 beats/min. However, in hypotensive shock it decreases in the late stage of hypovolemia, whereas the increase is continuous in normotensive shock. Cardiac output is significantly higher in the normotensive animals nearly throughout the entire hypovolemic phase although the initial decrease is the same in both groups (71%). Also a greater increase in total peripheral resistance occurs in these animals. The increased cardiac output and total peripheral resistance. A "centralization" of the circulation is also observed in this kind of shock as is made evident by the changes in the relationship between cardiac output and carotid blood flow. Hyperventilation occurs in both kinds of shock. In hypotensive shock respiratory rate decreases at the end of the oligemic phase possibly due to a smaller cerebral blood flow.

Acidosis↗
PubMedDate not supplied

[Injection methods for the demonstration of the coronary arterial vasculature (author's transl)].

Four different methods for the demonstration of the coronary arterial vasculature are examined. Among the techniques studied corrosion casts (epoxid- and acrylic resin) permit the best qualitative and quantitative evaluation of superficial and deep arteries and arterioles. Down to the smallest infusible vessels of 15-25 mum there is practically no shrinkage. X-ray arteriography with an aqueous solution of barium sulphate is less suitable because X-rays allow no satisfactory stereoscopic view. The demonstration of arterioles and collaterals is limited to vessels larger than 50 mum because of the low resolution of the X-ray tube. Silicone rubber does not only fill the arteries, but also the capillary bed and the venous system. Therefore deeper parts of the vasculature can only be studied after slicing the heart. The substantial shrinkage of the material makes quantitative measurements difficult.

Animals↗
PubMedDate not supplied

Effects of moderate coronary stenosis on myocardial flow reserve in man and in the dog.

The influence of coronary stenosis on resting blood flow (201Tl-uptake) and myocardial flow reserve (bicycle ergometry) is studied in 18 patients with coronary disease. Severe coronary stenosis of 75--90% caused a reduced 201Tl-uptake both at rest and peak exercise. In contrast to this group patients with a 50--60% stenosis have a normal scintigram at rest but focal defects of 201Tl-uptake at peak exercise. Results are compared with experimental data obtained after acute coronary constriction and simultaneous coronary dilatation (myocardial flow reserve, MFR) in 12 dogs. 60% coronary constriction causes a 37% decrease of poststenotic MFR measured with tracer microspheres. Changes of transmural flow distribution (endo/epi ratio) are minor in the left ventricular free wall but significant in the poststenotic septum (endo/epi = .84). It is concluded that even a moderate coronary stenosis of 60% not affecting resting blood flow becomes "critical" under conditions of high flow velocities.

Adult↗
PubMedDate not supplied

Effects of acute vagally-mediated bradycardia on systemic hemodynamics and coronary blood flow before and after coronary stenosis.

The effects of short episodes (1 min) of vagally-mediated bradycardia were studied in 9 anesthetized dogs utilizing vagal stimulation and slow atrial pacing (120 and 80 beats/min) before and after graded coronary constriction of the left anterior descending (LAD) and the left circumflex (CCA). In the presence of 90% LAD stenosis, bradycardia tended to restore both the elevated total LAD coronary vascular resistance (CVR-LAD) and the reduced, total CVR-CCA towards control levels obtained at corresponding slow rates in the absence of coronary stenosis; as a result, LAD coronary flow (F-LAD) was relatively less reduced and the accessory rise of F-CCA disappeared. In the presence of combination of 90% LAD plus 70% CCA stenosis, the effects of bradycardia on total CVR-LAD and F-LAD were similar to those obtained with single 90% LAD stenosis, but the accessory flow through the CCA was abolished resulting in no significant difference of the rate-dependent alterations of total CVR-CCA and F-CCA as compared with those observed in the absence of coronary stenosis. In the presence of single or combined coronary stenosis, bradycardia restored the depressed aortic pressure and cardiac output towards control values obtained at comparable slow rates before coronary stenosis. The results support the concept that in the presence of 90% LAD stenosis vagally-mediated bradycardia 1) decreases the tension-time index (myocardial nutritional demand) shifting cardiac performance to less expensive "flow work" and 2) facilitates antegrade flow through the highly stenotic LAD thereby inhibiting accessory flow through the nonstenotic CCA.

Animals↗
PubMedDate not supplied

Effect of brief periods of paced ventricular tachycardia on coronary blood flow in dogs before and after graded coronary stenosis.

The effect of short bouts (1 min) of electrically induced ventricular tachycardias (VT) of increasing rates (160-240/min) was studied in 8 anesthetized dogs before and after graded constrictions of the left anterior descending (LAD) and the circumflex (CCA) coronary arteries. In the absence of coronary stenosis, paroxysmal VT caused a significant decrease in tension-time index (TTI), coronary blood flow (CBF) and coronary vascular resistance (CVR). Single and combined coronary stenosis caused relatively small alterations of the VT-induced depression of the systemic hemodynamics but reversed the effect of paroxysmal VT on the CVR. In the presence of single 90% LAD stenosis, VT resulted in an increase in CVR-LAD and a decrease in F-LAD associated with a fall in CVR-CCA and a rise in F-CCA. Combination of 90% LAD plus 70% CCA stenosis abolished the compensatory fall of CVR-CCA resulting in a pronounced reduction of F-CCA during VT. The results support the concept that in the presence of severe coronary stenosis brief paroxysmal ventricular tachycardias do increase myocardial nutritional demand but rather decrease nutritional supply.

Animals↗
PubMedDate not supplied

Myocardial flow reserve in experimental cardiac hypertrophy.

The distribution of myocardial blood flow (MBF) was evaluated in pressure-induced LV hypertrophy of foxhounds. At the early stage of developing hypertrophy, i.e., 3 months after aortic banding (+ 53% LV weight) resting MBF and flow reserve were not significantly different from control hearts. One year after banding (+94% LV weight) myocardial flow reserve had clearly decreased. Acute coronary stenosis of 60 and 70% cross-sectional area resulted in a moderate fall of flow reserve in controls and hearts with early hypertrophy. In hearts with extensive hypertrophy the drop of poststenotic MBF was considerably greater affecting preferentially the subendocardium. The data suggest that myocardial blood flow was impaired before any signs of heart failure were observed. Furthermore a decrease of MBF may not be confined to forms of hypertrophy induced by renal and idiopathic hypertension.

Animals↗
PubMedDate not supplied

The influence of the size of acute ischaemic myocardial lesions on coronary reserve and left ventricular function in the dog.

Acute ischaemic lesions of 5 and 15% of the left ventricular mass were produced in 10 dogs by ligations of branches of the left anterior descending coronary artery. Under maximal coronary dilatation by Dipyridamole and at constant aortic pressure, an ischaemic lesion of 15% caused reductions of blood flow in the left anterior descending coronary artery of 50% (p less than 0.05), , the R. circumflexus of 36% and of total myocardial blood flow (Argon method) by 44% (p less than 0.02). Parameters of left ventricular function, dp/dtmax and Vmax fell by 26 and 27% respectively (p less than 0.02). Ischaemic lesions of 5% LV mass were detected by 133 Xenon clearance estimations, but had no effect on any of the other variables measured. There was good agreement between estimations of total myocardial blood flow (Argon) and direct measurement of coronary flow with electromagnetic flowmeters (r = 0.957).

Acute Disease↗