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Biomedical subjects

W Heimisch

Publications and source records attributed to W Heimisch.

48 records · Page 3Linked to original sources
PubMed1976

[Hemodynamic studies after the implantation of Hancock-heart valves (author's transl)].

Velocity profile, pressure gradient across the valve and blood flow have been measured in 10 patients after the implantation of bioprostheses of the sizes 27 and 29 millimeters in aortic position. According to these hemodynamic measurements the use of bioprostheses for the aortic valve replacement is recommendable. The low flow velocities in the area of the muscle containing valve cusp did not effect a detectable stenosis intraoperatively under the conditions of rest. The hemodynamic data showed no differences between the Hancock-Zuhdi and the Edwards-Carpentier bioprostheses. Despite of good hemodynamic conditions and a low risk of thromboembolic complications after the aortic valve replacement with bioprostheses reservation is recommended to its clinical use until the long term mechanical stability (more than 6 years) of the biological heart valve prosthesis has been secured.

Adolescent↗
PubMed1976

[Direct measurement of papillary muscle dynamics in the intact canine left ventricle during acute coronary occlusion (author's transl)].

UNLABELLED: The functions of the normal and ischemic papillary muscle in the intact canine heart were studied using an ultrasonic transit time method. Miniaturized piezoelectric crystals (1.5-2 mm 0) were implanted during extracorporeal circulation into the root and tip of the anterior and posterior papillary muscle of the left ventricle. RESULTS: 1. Phasic changes of left ventricular geometry during the heart cycle determine the dynamic pattern of papillary muscle movements. 2. The amplitude and velocity of papillary muscle length is directly related to those of myocardial wall segments. 3. Experimental ischemia induces total dysfunction of the papillary muscle within seconds. 4. Despite total muscle dysfunction no mitral insufficiency occured.

Animals↗
PubMed1975

[Instantaneous blood flow velocity profiles before and after aortic valve replacement (author's transl)].

In 17 patients the instantaneous velocity profile was recorded before and after aortic valve replacement (Starr-Edwards, Björk-Shiley, Lillehei-Kaster). A single gated pulsed Doppler Ultrasonic flownmeter was used for analysis. Distal of these valves a flat flow profile was recorded showing high velocity gradients near the walls. As a main cause of this, numerous eddies and turbulent flow have been suggested. Downstream of a Starr valve a flat profile appears with a slowing down of forward flow just behind the ball. The disk valves Lillehei-Kaster and Björk-Shiley demonstrated a higher flow velocity in direction to the larger opening. The "in vivo" studies have been supported by "in vitro" measurements. The highest flow velocities were above 100 cm/sec and thus, according to Reynolds definition, in the turbulent range. The turbulent flow produces a washing effect, which is emphasized during the cardiac cycle. The importance of these data can be discussed by clinical results only.

Aorta↗
PubMed1975

[Ultrasound transit-time method for evaluation of regional myocardial function (author's transl)].

The validity of an ultrasound transit-time method for defining local function was evaluated under experimental conditions in the anaesthetized open chest dog. Miniaturized piezoelectric crystals (1,5-2 mm phi) functioning as emitters and receivers were inserted into different depths of the myocardium to study the contraction patterns of defined muscle segments in different muscle layers and the dynamic changes of left ventricular wall thickness during the heart cycle. Changes in myocardial function were induced by coronary stenosis or occlusion and by the application of drugs. This method was shown to be a sensible and reliable tool for the evaluation of local myocardial function.

Animals↗
PubMedDate not supplied

Effect of urapidil on the performance of ischemic myocardium in anesthetized dogs.

Urapidil (URA) is used to treat acute hypertension in patients with coronary artery disease, but the effect of URA on the performance of ischemic myocardium has not yet been investigated. The present study was intended to assess the function of ischemic myocardium following URA administration. In eight anesthetized (piritramide) open-chest dogs systolic contraction (dL) and end-diastolic length (edL) of myocardium supplied by the left descending (LAD) and circumflex (LCA) coronary arteries were measured by sonomicrometry simultaneously with aortic pressure (AoP), left ventricular end-diastolic pressure (LVedP), heart rate (HR), stroke volume (SV), and LAD-flow (QLAD). QLAD was reduced by LAD stenosis to about 50% of control, decreasing dLLAD by 55%. Concomitantly, edLLAD increased by about 9% and LVedP by 22%, whereas AoP decreased by 5%. Then, URA was given i.v. (0.25 + 0.25 + 0.50 + 1.0 mg/kg) in 15-min intervals. Following URA, the performance of the non-ischemic area was not systematically affected, but dLLAD increased by about 50%. This could neither be related to the significant reduction in afterload (AoP: -8%), nor to an increase in preload (LVedP and edLLAD did not change significantly), nor to an improved oxygen supply via the LAD (QLAD even decreased), although an increased collateral flow the LCA could not be excluded. The increase in systolic shortening correlated very closely to a decrease in heart rate (r = -0.92). It is concluded that the improved function of ischemic myocardium following urapidil resulted from a reduced oxygen demand in consequence to the decrease in heart rate.

Animals↗
PubMedDate not supplied

The effect of hemodilution on regional myocardial function in the presence of coronary stenosis.

Hemodilution decreases blood viscosity and circulatory input impedance and thus reduces afterload. Its use in treatment of LV power failure has been advocated, but the safe limits of isovolemic hemodilution are not known. Compensation of the reduced O2-capacity of the blood was therefore studied with normal and impaired coronary reserve. In 20 dogs the LAD was stenosed to a degree just not affecting the supplied region and central and coronary hemodynamics were studied. Regional myocardial function was assessed by ultrasound transit time between transducers implanted in the LV wall. Lowering the hematocrit to 15% by isovolumic exchange of blood for Dextran 60 increased CVP (18%), PAP (47%), LAP (64%), LVedP (46%), CO (67%), and flow to the intact area (LCA: 211%). Flow in the stenosed LAD increased slightly. Enddiastolic length (EDL) of LAD dependent muscle segments rose to 120% and their contraction amplitude deltaL was decreased by 46%. Whereas non-ischemic segments showed compensatory rise in deltaL (38%) at almost constant EDL (+9%). After release of the LAD stenosis EDL and deltaL returned to normal. During progressive anemia myocardial O2-demand is not adequately met if coronary reserve capacity is depleted. Reversion of hypokinesia after removal of the stenosis shows unimpaired myocardial function at a hematocrit as low as 15% provided the coronary circulation is intact.

Animals↗
PubMedDate not supplied

Effect on coronary artery flow reserve and resistance in the remote area after acute coronary artery occlusion in the pig model.

BACKGROUND: It has been reported that vasodilator function in remote myocardial regions supplied by "angiographically normal" coronary arteries is impaired in patients after acute myocardial infarction (MI). The aim of this study was to determine whether coronary artery flow reserve and coronary artery resistance in remote, nonischemic areas are also altered in experimental MI. METHODS: Experiments were performed in anesthetized pigs. In group 1 infarction was induced by ligation of the left-anterior descending artery (LAD); group 2 consisted of sham-operated animals. Hemodynamic parameters, coronary artery resistance, and myocardial blood flow (MBF) were measured before and 4 hours after MI under rest and during infusion of adenosine. RESULTS: Coronary artery dilation by adenosine caused a similar increase in MBF before and 4 hours after coronary artery occlusion. Resting MBF after acute MI was not altered, although a significant reduction (15%; P < .04) in mean aortic pressure was observed compared with baseline. Coronary artery resistance was significantly reduced by adenosine (P < .04) before MI, as well as at 4 hours after MI (P < .03). Coronary artery flow reserve was not adversely affected. The sham-operated animals showed similar results without any significant differences between the two study groups. CONCLUSION: This study indicates that an acute MI in pigs did not increase coronary artery resistance in the remote area after MI and therefore did not adversely affect coronary artery flow reserve in the nonischemic vascular bed. Further studies are necessary to fully understand the exact mechanism of the alterations in remote flow reserve of patients after MI.

Adenosine↗
PubMedDate not supplied

[Clenbuterol and fenoterol--animal experiment comparison of 2 tocolytic agents (with special reference to cardiovascular side effects)].

During animal experiments two substances, which are used for tocolysis (Fenoterol and Clenbuterol) have been compared regarding their tocolytic efficiency (determinations of myometrial cyclic AMP after long term treatment of the pregnant rat), their effects upon myocardial high energy phosphates (determinations of maternal myocardial high energy phosphates as well as of maternal and fetal myocardial cyclic AMP after long term treatment of the pregnant rat) and upon the hemodynamic situation (acute experiments with thoracotomized dogs). While significant hemodynamic derangements could be stated when using Fenoterol, no significant evidence for such alterations could be found during Clenbuterol administration during acute experiments. Determinations of myocardial high energy phosphates however reflected an augmented myocardial workload, both after Fenoterol and Clenbuterol administration. As by means of myometrial cyclic AMP determinations Clenbuterol proved to be at least as efficient as Fenoterol, concerning the tocolytic effect, Clenbuterol can be recommended as an oral tocolytic because of its pharmaco-cinetic advantages and the encouraging results from our hemodynamic investigations. According to results from chronical experiments an additional cardioprotection by means of magnesium substitution and eventually beta 1-blockade is still recommended.

Animals↗