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F J Klocke

Publications and source records attributed to F J Klocke.

At least 19 recordsLinked to original sources
PubMed1993

Tone-dependent coronary arterial-venous pressure differences at the cessation of venous outflow during long diastoles.

BACKGROUND: The origin and magnitude of the back pressure opposing diastolic coronary inflow remain controversial. The arterial pressure at which coronary inflow stops during a prolonged diastole, ie, "zero-flow pressure," is higher than coronary venous pressure. However, because of capacitive discharge as distending pressure falls, flow at the microcirculatory level exceeds inflow, and coronary outflow ceases later than inflow. If coronary arterial pressure continues to exceed venous pressure at the point of venous flow cessation, zero-flow pressure cannot be an artifact of capacitive discharge. METHODS AND RESULTS: Coronary inflow and outflow, arterial pressure, and right atrial pressure have been measured during long diastoles in closed-chest dogs chronically instrumented with volumetric flow probes on the great cardiac vein or coronary sinus as well as the circumflex artery. Although venous outflow continued for 1 to 4 seconds after arterial inflow ceased, coronary artery pressure at the point of venous flow cessation (Pfv = 0) always exceeded right atrial pressure (13 +/- 1.3 mm Hg [SEM] vs 6 +/- 0.7 mm Hg, P < .001). When vasomotor tone was augmented using vasopressin, the diastolic pressure-flow relation shifted to the right, with Pfv = 0 increasing to 21 +/- 2.4 mm Hg despite an unchanged right atrial pressure (6 +/- 0.5 mm Hg). CONCLUSIONS: Transcoronary pressure differences persist when venous outflow stops and are larger when vasomotor tone is augmented. Measurements of zero-flow pressure that exceed venous pressure cannot be considered an artifact of continuing capacitive discharge after the cessation of arterial inflow. Diastolic coronary back pressure exceeds right atrial pressure and is tone dependent.

Animals↗
PubMed1991

Dissociation of diastolic pressure-segment length and pressure-wall thickness relations during vasodilation in the conscious dog.

The effects of pharmacologic vasodilation and reductions in circumflex coronary artery pressure on the ventricular diastolic pressure-segment length and pressure-wall thickness relations were studied in nine conscious dogs equipped with an inflatable cuff on the proximal circumflex artery, a micromanometer in the left ventricle and four sets of piezoelectric crystals to measure wall thickness and endocardial segment length in the left circumflex and left anterior descending artery territories. Adenosine infusion into the circumflex coronary artery increased endocardial and transmural blood flow to that territory (measured by microspheres) by 436% and 487%, respectively (both p less than 0.05), and shifted the left circumflex artery territory pressure-wall thickness curve upward (p less than 0.05) without affecting the circumflex pressure-segment length, the left anterior descending artery territory pressure-segment length or pressure-wall thickness curves significantly; papaverine also shifted the circumflex region pressure-wall thickness curve upward (p less than 0.05). Both with and without vasodilation, moderate reductions in circumflex artery perfusion pressure did not affect the position of the ventricular pressure-wall thickness or the pressure-segment length curve (although during adenosine infusion endocardial blood flow decreased from 436% to approximately 100% of control values). More severe reductions in perfusion pressure (less than 45 mm Hg under control conditions and less than 30 mm Hg during adenosine infusion) decreased coronary blood flow below control values and caused a marked downward shift of the circumflex region pressure-segment length curve without affecting the position of the pressure-wall thickness curve.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1991

First-pass entry of nonionic contrast agent into the myocardial extravascular space. Effects on radiographic estimates of transit time and blood volume.

BACKGROUND: Almost all x-ray-based techniques intended to assess regional myocardial perfusion from myocardial concentration-time curves following the administration of soluble contrast agents assume that these agents behave as intravascular indicators and can therefore provide measurements of intravascular transit time and intramyocardial blood volume. METHODS AND RESULTS: We tested this assumption by comparing a conventional nonionic contrast agent (ioversol) to a particulate emulsion (ethiodol) that remained in the vascular space in closed-chest dogs during pharmacological vasodilation. Using fast computed tomography (CT), pairs of myocardial CT intensity-time curves were obtained following sequential bolus aortic administration of the two contrast agents. The emulsion (particle size less than 3 microns) was almost completely washed out of the myocardial region of interest within a few seconds, as would be anticipated for a vascular indicator. At the onset of recirculation, CT intensity for ethiodol fell to 5 +/- 1% (SEM) of peak values in normally perfused areas and to 10 +/- 4% of peak values in an area in which flow had been reduced by 50% by a chronically implanted coronary artery occluder (p = NS). In comparison, the diffusible nonionic contrast agent ioversol showed substantial intramyocardial retention at the onset of recirculation. At the time of recirculation, CT intensities for ioversol averaged 36 +/- 2% of peak values in normally perfused nonstenotic areas and 54 +/- 4% of peak values in stenotic areas (p less than 0.01). Using residue function analysis for a diffusible indicator, first-pass extractions of the conventional nonionic agent averaged 33 +/- 2% in normally perfused areas and 50 +/- 3% in stenotic areas (p less than 0.01). Because of the significant first-pass myocardial retention of ioversol, both mean myocardial appearance time and intramyocardial blood volume were consistently overestimated. CONCLUSIONS: Soluble radiographic contrast agents, like other small molecules, enter the interstitial space to a degree, which is important because it affects estimates of myocardial perfusion based on transit time and intramyocardial blood volume. Indicator dilution models intended to quantify myocardial perfusion with conventional radiographic contrast agents need to account for this extravascular exchange.

Animals↗
PubMed1991

ACC/AHA guidelines for cardiac catheterization and cardiac catheterization laboratories. American College of Cardiology/American Heart Association Ad Hoc Task Force on Cardiac Catheterization.

It is evident that the practice of cardiac catheterization has undergone, and continues to undergo, marked change. Most prominent are the recent very rapid proliferation of catheterization laboratories in general and the development of newer types of catheterization laboratory. No uniform definitions exist for these newer laboratories, so meaningful communication is difficult. The new settings are of particular concern because their location, mobility, organization, and ownership raise questions about the quality of patient care. Most difficult to address are the questions about patient safety and physician conflict of interest. There are no objective data in peer-reviewed literature to support the reported safety and cost savings of these newer settings. Through deliberations, surveys, interviews, and correspondence with the cardiology community embraced by the ACC and the AHA, the task force generally found that in freestanding catheterization laboratories, access to emergency hospitalization may be delayed, and appropriate oversight may be lacking. Additionally, opportunities for self-referral may be fostered and the perception of commercialism and entrepreneurial excess in practice created. All of these problems must be avoided. The growth and development of some freestanding facilities, particularly the mobile laboratories, do not seem to have been driven by an increased need in remote communities or for temporary support but rather almost exclusively by a desire to capture market share. Accordingly, a series of definitions, guidelines, and recommendations for the laboratories as well as for patient selection has been developed. The consensus was that a very restrictive and cautious attitude to the newer settings is appropriate at this time. The justification for development or expansion of cardiac catheterization services must be patient need. Documentation of this need must be based on objective estimates of the number of patients with known or suspected cardiac disease who meet generally accepted indications for laboratory study. Concerns about the lack of data from prospective clinical trials of patient safety in such a group necessitate a very cautious attitude toward any new catheterization services, in particular those without in-house cardiac surgical support. In view of the lack of appropriately controlled safety and need data for hospital-based, mobile, or freestanding laboratories operating without on-site (accessible by gurney) cardiac surgery facilities, the task force reaffirms the position that further development of these services cannot be endorsed at this time. In addition, there is reason for major concern that such proliferation in catheterization services may contribute to increasing costs and troubling ethical questions.

American Heart Association↗
PubMed1991

Tone-dependent waterfall behavior during venous pressure elevation in isolated canine hearts.

We examined the "vascular waterfall" hypothesis, which proposes that coronary flow is unaffected by elevations in outflow pressure until the latter reaches a critical threshold level, in 29 isolated canine hearts. In fibrillating hearts vasodilated with adenosine or carbocromen, coronary flow and the coronary pressure-flow relation were not affected by changes in great cardiac vein pressure (PGCV) below a threshold value of 11 +/- 0.9 (mean +/- SEM) mm Hg. Further elevations of PGCV reduced flow and shifted the pressure-flow relation to the right, increasing its pressure-axis intercept (Pf=0). When vasomotor tone was augmented with vasopressin, threshold PGCV increased to 25 +/- 2.7 mm Hg (p less than 0.001). Once again, the pressure-flow relation was unaffected by changes in PGCV below the threshold value and shifted to the right when this value was exceeded. The amount by which spontaneous values of Pf=0 exceeded threshold values of PGCV was greater when vasomotor tone was augmented than during vasodilation. Pf=0 continued to exceed PGCV when the latter was raised above the threshold level. Both Pf=0 and threshold values of PGCV were less during a long diastole than during ventricular fibrillation. We reached the following conclusions. 1) During changes in PGCV below a threshold value, the coronary circulation exhibits traditional waterfall behavior. 2) The threshold pressure for altering waterfall behavior is affected by vascular tone and mechanical activity. 3) Pf=0 remains above PGCV when the latter is increased above the threshold value needed to alter flow.

Animals↗
PubMed1989

Effects of graded reductions in coronary perfusion pressure on the diastolic pressure-segment length relation and the rate of isovolumic relaxation in the resting conscious dog.

To assess the relations between coronary perfusion pressure, blood flow, and the diastolic pressure-segment length relation in the conscious animal, circumflex pressure was incrementally decreased in 10 resting, chronically instrumented dogs by a hydraulic occluding cuff while monitoring left ventricular pressure and regional segment length (with piezoelectric crystals) in the circumflex and left anterior descending territories. In five dogs, regional blood flow was measured by microsphere injections at selected circumflex pressures. The diastolic portion of the pressure-segment length curve was unchanged when decrements in circumflex pressure were within the autoregulatory range, that is, unassociated with changes in blood flow or systolic function. Further decrements in circumflex pressure, which decreased blood flow and regional segment shortening (both p less than 0.05), caused a progressive downward and rightward shift of the pressure-segment length curve (p less than 0.05). The rate of relaxation, as measured by tau (the time constant of pressure decay during isovolumic relaxation, which is calculated assuming either a fixed or a variable asymptote) and peak negative dP/dt, decreased slightly during reductions in circumflex pressure within the autoregulatory range and greatly at lower pressure (all p less than 0.05). Thus, in the conscious animal, reductions in coronary perfusion pressure within the autoregulatory range do not affect the diastolic pressure-segment length curve but cause modest decreases in the rate of isovolumic relaxation. Further reductions in coronary perfusion pressure, below the limits of blood flow autoregulation, cause an increased extent of relaxation with a marked downward shift of the diastolic pressure-segment length curve as well as a large decrease in the rate of relaxation.

Animals↗