Determination of the noise source in the electrocardiogram during cardiopulmonary resuscitation.

During cardiopulmonary resuscitation (CPR), the electrocardiogram (ECG) is often obscured by noise. This noise is in the form of baseline variations in the ECG, which often necessitate stopping chest compressions to adequately assess the ECG. Because survival from cardiac arrest has been shown to be related to blood flow generated during CPR, and because interruption of chest compressions will reduce blood flow, survival may be compromised by these interruptions.

Implementing the FDA performance standard on electrode lead wires and patient cables in hospitals.

The U.S. Food and Drug Administration (FDA) Performance Standard on Electrode Lead Wires and Patient Cables became mandatory for all relevant devices on May 9, 2000.

Canine sternal force-displacement relationship during cardiopulmonary resuscitation.

A viscoelastic model developed to model human sternal response to the cyclic loading of manual cardiopulmonary resuscitation (CPR) [8] was used to evaluate the properties of canine chests during CPR. Sternal compressions with ventilations after every fifth compression were applied to supine canines (n = 7) with a mechanical resuscitation device. The compressions were applied at a nominal rate of 90/min with a peak force near 400 N.

Hemodynamic effects of direct biventricular compression studied in isovolumic and ejecting isolated canine hearts.

Background: Biventricular direct cardiac compression (DCC) can potentially support the failing heart without the complications associated with a blood/device interface. The effect of uniform DCC on left and right ventricular performance was evaluated in 7 isolated canine heart preparations.

Methods And Results: A computer-controlled afterload system either constrained the isolated heart to contract isovolumically or simulated hemodynamic properties of physiological ejection.

Imaging asynchronous mechanical activation of the paced heart with tagged MRI.

A method for imaging the rapid temporal-spatial evolution of myocardial deformations in the paced heart is proposed. High time resolution-tagged MR images were obtained after stimulation of the myocardium with an MR-compatible pacing system. The images were analyzed to reconstruct dynamic models of local 3D strains over the entire left ventricle during systole.

Reverse remodeling from cardiomyoplasty in human heart failure. External constraint versus active assist.

Background: Cardiomyoplasty (CM) is a novel surgical therapy for dilated cardiomyopathy. In this procedure, the latissimus dorsi muscle is wrapped around the heart and chronically paced synchronously with ventricular systole. While studies have found symptomatic improvement from this therapy, the mechanisms by which CM confers benefit remain uncertain.

Observations of ventilation during resuscitation in a canine model.

Background: Fear of infection limits the willingness of laymen to do cardiopulmonary resuscitation (CPR). This study assessed the time course of change in arterial blood gases during resuscitation with only chest compression (no ventilation) in an effort to identify the time for which ventilation could be deferred.

Methods And Results: Aortic pressures and arterial blood gases were monitored in seven 20- to 30-kg dogs in ventricular fibrillation (VF) at 2-minute intervals during chest compression alone (no ventilation) at 80 to 100 compressions per minute.

New method for mechanistic studies of cardiomyoplasty: three-dimensional MRI reconstructions.

The imaging modalities used to study the mechanism of cardiomyoplasty, such as echocardiography and radionuclide scintigraphy, are seriously limited by their two-dimensional format. Radiofrequency-pulse-tagged magnetic resonance imaging was used to generate three-dimensional reconstructions of the left ventricle throughout the cardiac cycle after cardiomyoplasty. In 2 dogs that had undergone conditioned, right anterior cardiomyoplasty, wrap stimulation with alternating heartbeats was found to produce marked translation of the left ventricle in the short-axis plane, rotation around the long axis, and displacement along the long axis with net long-axis compression; there was no augmentation of radial squeeze.

A preliminary study of cardiopulmonary resuscitation by circumferential compression of the chest with use of a pneumatic vest.

Background: More than 300,000 people die each year of cardiac arrest. Studies have shown that raising vascular pressures during cardiopulmonary resuscitation (CPR) can improve survival and that vascular pressures can be raised by increasing intrathoracic pressure.

Methods: To produce periodic increases in intrathoracic pressure, we developed a pneumatically cycled circumferential thoracic vest system and compared the results of the use of this system in CPR (vest CPR) with those of manual CPR.

Pressure-volume analysis of changes in cardiac function in chronic cardiomyoplasty.

Reports of clinical improvement in human studies of dynamic cardiomyoplasty lack support by consistent objective hemodynamic evidence. Animal studies have also yielded conflicting results, likely due to nonuniform models, particularly the use of unconditioned wraps, and to limitations in commonly used study modalities caused by exaggerated heart motion during wrap stimulation. Our purpose was to assess the primary functional properties of the heart wrapped by conditioned muscle using pressure-volume relation analysis based on conductance catheter volume data.

Sternal force-displacement relationship during cardiopulmonary resuscitation.

A viscoelastic model is presented to describe the dynamic response of the human chest to cyclic loading during manual cardiopulmonary resuscitation (CPR). Sternal force and displacement were measured during 16 clinical resuscitation attempts and during compressions on five CPR training manikins. The model was developed to describe the clinical data and consists of the parallel combination of a spring and dashpot.

Estimation of myocardial mechanical properties with dynamic transverse stiffness.

There are currently no validated methods for accurately estimating regional ventricular mechanical properties. We recently developed a dynamic indentation system that can determine dynamic transverse stiffness (the slope of the relation between the indentation stress and indentation strain during high frequency indentations) in as little as 10 msec. The apparatus consists of an indentation probe coupled to a linear-motor and a computerized control system.

Brain bioenergetics during cardiopulmonary resuscitation in dogs.

Cardiac arrest causes a rapid loss of cerebral adenosine triphosphate [corrected] (ATP) and a decrease in cerebral intracellular pH (pHi). Depending on the efficacy of cardiopulmonary resuscitation (CPR), cerebral blood flow levels (CBF) ranging from near zero to near normal have been reported experimentally. Using 31P magnetic resonance spectroscopy, the authors tested whether experimental CPR with normal levels of cerebral blood flow can rapidly restore cerebral ATP and pHi despite the progressive systemic acidemia associated with CPR.

Modeling the circulation with three-terminal electrical networks containing special nonlinear capacitors.

Development, first of analog and later of digital computers, as well as algorithms for analysis of electrical circuits, stimulated the use of electrical circuits for modeling the circulation. The networks used as building blocks for electrical models can provide accurate representation of the hydrodynamic equations relating the inflow and outflow of individual segments of the circulation. These networks, however, can contain connections in which voltages and currents have no analogues in the circulation.

Vital organ perfusion during assisted circulation by manipulation of intrathoracic pressure.

Background: We have previously shown, in dogs with severe cardiac depression, that modest cyclic increases in intrathoracic pressure, starting synchronously with left ventricular isovolumic contraction, significantly increase aortic flow and pressure. However, little is known of changes in vital organ perfusion during this technique of assisted circulation.

Methods And Results: We studied regional organ flow using radioactive labeled microspheres in 13 20-25-kg mongrel dogs.

Servo-controlled indenter for determining the transverse stiffness of ventricular muscle.

Regional ventricular wall stress is a critical determinant of cardiac function. There are, however, no validated methods for accurately estimating this stress. We have shown in the isolated ventricular septum that, during steady-state indentations, the transverse stiffness (the ratio of indentation stress [pressure acting on indenter face] to indentation strain [amount of indentation/nonindented thickness]) can be used as an estimate of the in-plane wall stress.

Optimization of the timing of skeletal to cardiac muscle contraction during dynamic cardiomyoplasty: analysis using a mathematical model.

Cardiomyoplasty, or the use of skeletal muscle to assist the failing heart, has been studied for many years but has enjoyed only minimal success. It has been suggested that a delay in the start of skeletal muscle contraction relative to the QRS complex would enhance aortic flow. To study the effects of simulated changes in the relative timing of skeletal muscle contraction, heart rate and skeletal muscle contraction duration, a mathematical model was used to predict the vascular pressures and flows during cardiomyoplasty.

Observations of hemodynamics during human cardiopulmonary resuscitation.

To evaluate hemodynamics during human CPR, 32 patients with witnessed cardiac arrest were studied during manual and mechanical conventional CPR. In eight patients during manual conventional CPR, peak systolic radial artery, right atrial (RAP), and pulmonary artery pressures were found to be similar (59.8 +/- 4.

Identification of dynamic mechanical parameters of the human chest during manual cardiopulmonary resuscitation.

Survival from cardiac arrest is dependent on timely cardiopulmonary resuscitation (CPR). Since CPR is often unsuccessful, the outcome may be improved by a better understanding of the relationship between force applied to the sternum and the resulting hemodynamic effects. The first step in this complex chain of interactions is the mechanical response of the chest wall to cyclical compression.