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Biomedical subjects

J Y Kresh

Publications and source records attributed to J Y Kresh.

27 records · Page 2Linked to original sources
PubMed1985

The intramyocardial pressure: a parameter of heart contractility.

A method of monitoring was developed to directly measure the intramyocardial pressure and to objectively assess the viability and contractility of a heart allograft before it is harvested, during its period of preservation and following its implantation. Intramyocardial pressure was measured in the subendocardial and subepicardial regions using implantable solid state sensors. The data demonstrated that a normally contracting in situ heart exhibits a transmural intramyocardial pressure gradient, the systolic subendocardial pressure being consistently greater than the left ventricle and subepicardial pressures. Subendocardial pressure markedly changes during inotropic stimulation or myocardial ischemia. In three canine allografts and in an isolated, perfused and vented beating heart similar responses were observed during pharmacologic and hemodynamic testing. The intramyocardial pressure measurement proved to be relatively insensitive to preload and afterload changes provided coronary perfusion remained unaltered. Ventricular fibrillation produced an elevated and oscillating intramyocardial pressure while cardioplegic arrest reduced it to near zero. Diastolic pressure measurements were most sensitive to detect myocardial contracture ("stone" heart) during which intramyocardial pressure increased significantly. The "stone" heart exhibited persistent mechanical activity despite no visible contraction. The edematous heart's response to inotropic stimulation was reduced. Ischemia induced by inadequate perfusion was detected by a rapid drop in systolic intramyocardial pressure, preferentially affecting the endocardial region. This study establishes that the change in diastolic intramyocardial pressures in response in inotropic stimulus is a reliable indicator of myocardial contractility and viability and could be used during the procurement and preservation of the heart for transplantation.

Animals↗
PubMed1984

An interactive microcomputer-based graphics system for analysis of cardiodynamic function.

An on-line interactive, modular, menu-driven microcomputer-based data acquisition and analysis system was designed and implemented. This system includes a low-cost commercial desk-top graphics computer with a modular construction. All these operations are performed using extended BASIC "CALL" statements. The system is designed to be used in a cardiovascular research and laboratory environment where the assessment of hemodynamic and cardiodynamic function includes routine measurements of pressure and flow. In addition, the measurement of regional and global left ventricular chamber dimensions have been implemented. The modular design of the software system is "human-engineered" to enable a simple, cost effective computer system to perform physiological measurement and control. Extended BASIC language instructions provide the casual computer user with a simple yet effective means of implementing on-line data acquisition, analysis and graphic production and display.

Cardiovascular Physiological Phenomena↗
PubMedDate not supplied

Wave transmission and input impedance of a model of skeletal muscle microvasculature.

We analyzed wave transmission properties and input impedance of a microvascular network model. The model, derived from rat spinotrapezius muscle and previously described and validated by other investigators for steady pressure-flow relations, was expanded to include pulsatile phenomena. Microvessels are considered purely elastic, with compliances a function of vessel type; viscous dissipation follows Poiseuille's law. Linear and nonlinear results are presented. In the nonlinear case, shear rate-dependent viscosity of blood and transmural pressure-dependent vascular diameters were calculated and small signal perturbations were imposed around several working points. We investigated effects on input impedance of physiological variability of network parameters and structure: distribution of capillary diameters, capillary segment length, and presence or absence of cross-connecting capillaries. Results show that although wave transmission properties are complex, input impedance is simple. Apparent wave speeds differ substantially from phase velocities and change markedly from branch to branch; pressure and flow waves appear to travel at different speeds. These features result from the mesh-like structure of the network and the prominence of reflection at branchpoints. Input impedance displays a similar form under all conditions: Magnitude is a monotonically decreasing function of frequency, and phase decreases from 0 to approximately -45 degrees. Consideration of the characteristic impedance of a microvessel leads to modification of the three-element Windkessel as a reduced model of the observed input impedance.

Animals↗
PubMedDate not supplied

Application of chaos theory to a model biological system: evidence of self-organization in the intrinsic cardiac nervous system.

The neutral organization that determines the specific beat-to-beat pattern of cardiac behavior is expected to be demonstrated in the independent regulation of the RR intervals (chronotropy) and the corresponding QT subintervals (inotropy), as the former defines the rate of contraction and the latter has a linear negative correlation with the peak pressure inside the contracting ventricular muscles. The neurons of the isolated cardiac nervous system, many of which are located in the fat-pads of the heart, exhibit the same types of mechanical and chemical receptors and the same types of cholinergic and noradrenergic effectors as those found in the neural superstructure. In the surgically isolated and perfused rabbit heart we studied the responses of the QT and RR intervals evoked by block of coronary blood flow. We found that if we separated each RR cycle into QT and RR-QT components, then the dynamics of variation for each subinterval series often had the same fractional number of degrees of freedom (i.e., chaotic dimensions), a finding which suggests they are both regulated by the same underlying system. The ischemia/anoxia evoked transient dimensional increases and separations between the two subinterval series that, after the temporary divergence, reconverged to having the same lower value. The dimensional fluctuations occurred repeatedly and preceded or coincided with alterations in the magnitude and sign of the slope of QT vs RR-QT. We interpret the dimensional fluctuations of the two subinterval series as correlates of adaptation-dependent self-organization and reorganization in the underlying intrinsic cardiac nervous system during accumulating ischemia/anoxia. Such attempts at functional reorganization in this simple neurocardiac system may explain the transient dimensional changes in the RR intervals that precedes by 24 hrs the occurrences of fatal ventricular fibrillation in high-risk cardiac patients.

Algorithms↗
PubMedDate not supplied

Vascular determinants of univentricular support.

The dynamic coupling between cardiac pump performance and vascular arterial-venous capacitive and resistive properties was examined analytically and experimentally to determine the feasibility of maintaining systemic and pulmonary circulation, devoid of the right heart. Analysis of the cardiovascular system (excluding neurohumoral factors), used a mathematical representation of the major determinants involved in cardiac output and demonstrated that change in pump flow output has reciprocal effects on the venous and arterial pressures. Independent of the pump's performance characteristics, cardiac output reserve was restricted, reaching a critical plateau (50% of normal) because of the rapidly depleting pulmonary venous pressure, concurrent with the translocation of the venous stressed volume to the arterial side of the circulation. Animal experiments aided by computer modeling confirmed that near normal flow can be sustained by actively mobilizing or augmenting blood volume, or by reducing selectively the unstressed volume and venous pooling. A single blood pump, in a form of a mechanical substitute, or the biologic left heart acting alone, can support the entire circulation. The right heart is not essential for normal pulmonary circulation, but serves to maintain low systemic venous pressure and a relatively high left heart flow reserve state. Peripheral vascular parameters, i.e., stressed volume and venous capacitance, serve a vital role in preserving the mechanical self regulation of cardiac output.

Animals↗