Measurement of left ventricular volume with admittance incorporated onto percutaneous ventricular assist device.

Percutaneous ventricular assist devices (pVADs) incorporated with admittance electrodes have been validated in animal studies for accurate instantaneous volumetric measurements. Since miniaturization of the pVAD profile is a priority to reduce vascular complications in patients, our study aimed to validate admittance measurements using three electrodes instead of the standard four. Complex admittance was measured between an electrode pair and a pVAD metallic blood-intake tip, both with finite element analysis and on the benchtop.

Modification of a Transvalvular Microaxial Flow Pump for Instantaneous Determination of Native Cardiac Output and Volume.

Background: The current Impella cardiopulmonary (CP) pump, used for mechanical circulatory support in patients with cardiogenic shock (CS), cannot assess native cardiac output (CO) and left ventricular (LV) volumes. These data are valuable in facilitating device management and weaning. Admittance technology allows for accurate assessment of cardiac chamber volumes.

Smart Drain for Post-Cardiac Surgery Left Ventricular Volumes Evaluated in Large Animal Models.

Background: Open heart surgeries for coronary arterial bypass graft and valve replacements are performed on 400,000 Americans each year. Unexplained hypotension during recovery causes morbidity and mortality through cerebral, kidney, and coronary hypoperfusion. An early detection method that distinguishes between hypovolemia and decreased myocardial function before onset of hypotension is desirable.

Data automated bag breathing unit for COVID-19 ventilator shortages.

Background: The COVID-19 pandemic has caused a global mechanical ventilator shortage for treatment of severe acute respiratory failure. Development of novel breathing devices has been proposed as a low cost, rapid solution when full-featured ventilators are unavailable. Here we report the design, bench testing and preclinical results for an 'Automated Bag Breathing Unit' (ABBU).

Admittance to detect alterations in left ventricular stroke volume.

Background: Implantable cardioverter-defibrillators monitor intracardiac electrograms (EGMs) to discriminate between ventricular and supraventricular tachycardias. The incidence of inappropriate shocks remains high because of misclassification of the tachycardia in an otherwise hemodynamically stable individual. Coupling EGMs with an assessment of left ventricular (LV) stroke volume (SV) could help in gauging hemodynamics during an arrhythmia and reducing inappropriate shocks.

Effect of formalin fixation on thermal conductivity of the biological tissue.

Effect of formalin fixation on thermal conductivity of the biological tissues is presented. A self-heated thermistor probe was used to measure the tissue thermal conductivity. The thermal conductivity of muscle and fatty tissue samples was measured before the formalin fixation and then 27 hours after formalin fixation.

Analysis of the spatial sensitivity of conductance/admittance catheter ventricular volume estimation.

Conductance catheters are known to have a nonuniform spatial sensitivity due to the distribution of the electric field. The Geselowitz relation is applied to murine and multisegment conductance catheters using finite element models to determine the spatial sensitivity in a uniform medium and simplified left ventricle models. A new formulation is proposed that allows determination of the spatial sensitivity to admittance.

A bio-telemetric device for measurement of left ventricular pressure-volume loops using the admittance technique in conscious, ambulatory rats.

This paper presents the design, construction and testing of a device to measure pressure-volume loops in the left ventricle of conscious, ambulatory rats. Pressure is measured with a standard sensor, but volume is derived from data collected from a tetrapolar electrode catheter using a novel admittance technique. There are two main advantages of the admittance technique to measure volume.

Left ventricular epicardial admittance measurement for detection of acute LV dilation.

There are two implanted heart failure warning systems incorporated into biventricular pacemakers/automatic implantable cardiac defibrillators and tested in clinical trials: right heart pressures, and lung conductance measurements. However, both warning systems postdate measures of the earliest indicator of impending heart failure: left ventricular (LV) volume. There are currently no proposed implanted technologies that can perform LV blood volume measurements in humans.

Accuracy considerations in catheter based estimation of left ventricular volume.

Cardiac volume estimation in the Left Ventricle from impedance or admittance measurement is subject to two major sources of error: parallel current pathways in surrounding tissues and a non uniform current density field. The accuracy of volume estimation can be enhanced by incorporating the complex electrical properties of myocardium to identify the muscle component in the measurement and by including the transient nature of the field non uniformity. Cardiac muscle is unique in that the permittivity is high enough at audio frequencies to make the muscle component of the signal identifiable in the imaginary part of an admittance measurement.

Dynamic correction for parallel conductance, GP, and gain factor, alpha, in invasive murine left ventricular volume measurements.

The conductance catheter technique could be improved by determining instantaneous parallel conductance (G(P)), which is known to be time varying, and by including a time-varying calibration factor in Baan's equation [alpha(t)]. We have recently proposed solutions to the problems of both time-varying G(P) and time-varying alpha, which we term "admittance" and "Wei's equation," respectively. We validate both our solutions in mice, compared with the currently accepted methods of hypertonic saline (HS) to determine G(P) and Baan's equation calibrated with both stroke volume (SV) and cuvette.

Effect of formalin fixation on thermal conductivity of the biological tissue.

Effect of formalin fixation on thermal conductivity of the biological tissues is presented. A self-heated thermistor probe was used to measure the tissue thermal conductivity. The thermal conductivity of porcine aorta, fat, heart, and liver was measured before the formalin fixation and then 1 day, 4 days, and 11 days after formalin fixation.

Electrical conductivity and permittivity of murine myocardium.

A classic problem in traditional conductance measurement of left ventricular (LV) volume is the separation of the contributions of myocardium from blood. Measurement of both the magnitude and the phase of admittance allow estimation of the time-varying myocardial contribution, which provides a substantial improvement by eliminating the need for hypertonic saline injection. We present in vivo epicardial surface probe measurements of electrical properties in murine myocardium using two different techniques (a digital and an analog approach).

Design of a wireless telemetric backpack device for real-time in vivo measurement of pressure-volume loops in conscious ambulatory rats.

Pressure - Volume (PV) analysis is the de facto standard for assessing myocardial function. Conductance based methods have been used for the past 27 years to generate instantaneous left ventricular (LV) volume signal. Our research group has developed the instrumentation and the algorithm for obtaining PV loops based on the measurement of real - time admittance magnitude and phase from the LV of anaesthetized mice and rats.

Real time pressure-volume loops in mice using complex admittance: measurement and implications.

Real time left ventricular (LV) pressure-volume (P-V) loops have provided a framework for understanding cardiac mechanics in experimental animals and humans. Conductance measurements have been used for the past 25 years to generate an instantaneous left ventricular (LV) volume signal. The standard conductance method yields a combination of blood and ventricular muscle conductance; however, only the blood signal is used to estimate LV volume.

Finite element analysis and experimental verification of multilayered tissue characterization using the thermal technique.

The objective of this research is to develop noninvasive techniques to determine thermal properties of layered biologic structures based on measurements from the surface. The self-heated thermistor technique is evaluated both numerically and experimentally. The finite element analyses, which confirm the experimental results, are used to study the temperature profiles occurring in the thermistor-tissue system.

Volume catheter parallel conductance varies between end-systole and end-diastole.

In order for the conductance catheter system to accurately measure instantaneous cardiac blood volume, it is necessary to determine and remove the contribution from parallel myocardial tissue. In previous studies, the myocardium has been treated as either purely resistive or purely capacitive when developing methods to estimate the myocardial contribution. We propose that both the capacitive and the resistive properties of the myocardium are substantial, and neither should be ignored.

Evidence of time-varying myocardial contribution by in vivo magnitude and phase measurement in mice.

Cardiac volume can be estimated by a conductance catheter system. Both blood and myocardium are conductive, but only the blood conductance is desired. Therefore, the parallel myocardium contribution should be removed from the total measured conductance.

Impact of physiological variables and genetic background on myocardial frequency-resistivity relations in the intact beating murine heart.

Conductance measurements for generation of an instantaneous left ventricular (LV) volume signal in the mouse are limited, because the volume signal is a combination of blood and LV muscle, and only the blood signal is desired. We have developed a conductance system that operates at two simultaneous frequencies to identify and remove the myocardial contribution to the instantaneous volume signal. This system is based on the observation that myocardial resistivity varies with frequency, whereas blood resistivity does not.

Effects of the time response of the temperature sensor on thermodilution measurements.

Thermodilution is widely used to measure cardiac output, ejection fraction and end diastolic volume. Even though the method is based on dynamic temperature measurements, little attention has been paid to the characterization of the dynamic behavior of the temperature sensor and to its influence on the accuracy of the method. This paper presents several theoretical and empirical results related to the thermodilution method.

Nonlinear conductance-volume relationship for murine conductance catheter measurement system.

The conductance catheter system is a tool to determine instantaneous left ventricular volume in vivo by converting measured conductance to volume. The currently adopted conductance-to-volume conversion equation was proposed by Baan, and the accuracy of this equation is limited by the assumption of a linear conductance-volume relationship. The electric field generated by a conductance catheter is nonuniform, which results in a nonlinear relationship between conductance and volume.

Design of instrumentation and data-acquisition system for complex admittance measurement.

Instantaneous left ventricular volume measurements have been made for many years using a tetrapolar conductance catheter. The main objective is to determine the efficiency of the beating heart, using a tetrapolar catheter inserted in the left ventricle of transgenic mice. The effect of the parallel myocardium contribution must be removed from the total measurement.

Analysis of a thermal method for assessing endothelial dysfunction.

The presence of atherosclerosis not only affects the normal functioning of the coronary blood vessels but also of the peripheral vasculature. Property measurements made in the peripheral vasculature hence do reflect the condition of the coronary blood vessels. The endothelial cells form the inner lining of the blood vessels, and are responsible for the release of nitric oxide (NO) in order to control the vascular tone.

In vivo measurements of heat transfer on the endocardial surface.

A catheter-based instrument was used to measure the heat transfer on the right atrial and ventricular endocardial surfaces of two pigs in vivo. The heat transfer parameters will assist in calculating the proper dose for radio-frequency ablation. The time constant of the device was 0.