Biomedical Engineering and Bioengineering Commons^™

Cardiac, Thoracic, And Abdominal Pump Mechanisms In Cardiopulmonary Resuscitation: Studies In An Electrical Model Of The Circulation, Charles F. Babbs, Christopher Weaver, Sandra H. Ralston, Leslie A. Geddes

Weldon School of Biomedical Engineering Faculty Publications

To investigate alternative mechanisms generating artificial circulation during cardiopulmonary resuscitation (CPR), an electrical model of the circulation was developed. Heart and blood vessels were modeled as resistive-capacitive networks; pressures in the chest, abdomen, and vascular compartments as voltages; blood flow as electric current; blood inertia as inductance; and the cardiac and venous valves as diodes. External pressurization of thoracic and abdominal vessels, as would occur in CPR, was simulated by application of half-sinusoidal voltage pulses. Three modes of creating artificial circulation were studied: cardiac pump (CP), in which the atria and ventricles of the model were pressurized simultaneously; thoracic pump …

Intrapulmonary Epinephrine During Prolonged Cardipulmonary Resuscitation: Improved Regional Blood Flow And Resuscitation In Dogs, Sandra H. Ralston, William D. Voorhees, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Publications

Blood flow to vital organs was measured at five-minute intervals during 20 minutes of cardiopulmonary resuscitation (CPR) and ventricular fibrillation in two groups of anesthetized dogs (n = 15 per group). The relationship between organ blood flow and restoration of circulation after 20 minutes was assessed with no additional treatment in Group I and with intrapulmonary epinephrine in Group II. Cardiac output and organ blood flow did not vary significantly in Group I. In Group II, intrapulmonary epinephrine significantly improved blood flow to the myocardium, the brain, and the adrenal glands. A mean myocardial blood flow of less than 0.13 …

Theoretical Advantages Of Abdominal Counterpulsation In Cpr As Demonstrated In A Simple Electrical Model Of The Circulation, Charles F. Babbs, Sandra H. Ralston, Leslie A. Geddes

Weldon School of Biomedical Engineering Faculty Publications

Animal studies and preliminary clinical observations suggest that the addition of interposed abdominal compressions (IAC) to ventilation and chest compression of standard cardiopulmonary resuscitation (CPR) augments blood flow, blood pressures, and immediate survival. To investigate the physical basis for enhanced circulation during IAC-CPR, we developed an electrical model of the circulation. Heart and blood vessels were modeled as resistive-capacitive networks, pressures as voltages, blood flow as electric current, blood inertia as inductance, and the cardiac and venous valves as diodes. External pressurization of the heart and great vessels, as would occur in CPR, was simulated by application by half-sinusoidal voltage …

Efficacy And Safety Of The Reciprocal Pulse Defibrillator Current Waveform, M J. Niebauer, Charles F. Babbs, L A. Geddes, J D. Bourland

Weldon School of Biomedical Engineering Faculty Publications

The efficacy and safety of a new defibrillating current waveform, consisting of a low-tilt 5 ms trapezoidal pulse followed closely by a second identical pulse of opposite polarity, was tested m seven isolated, perfused, working canine hearts suspended in an isoresistive, isosmotic shock bath at 37 oC. The efficacy and safety of the reciprocal pulse was compared with a single 5 ms pulse, a single 10 ms pulse, and a dual (unidirectional) 5 ms pulse waveform. The mean threshold average current densities for the 5 ms single pulse, 10 ms single pulse, dual 5 ms pulse, and reciprocal pulse (absolute …

Effects Of Myocardial Infarction On Catheter Defibrillation Threshold, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Publications

Because the automatic implantable defibrillator may be used in patients having ischemic heart disease, it is important to know whether myocardial ischemia changes the threshold for ventricular defibrillation under experimental conditions simulating automatic internal defibrillation. We determined changes in ventricular defibrillation threshold following coronary occlusion, using an electrode catheter designed for use with an automatic implantable defibrillator. Acute myocardial ischemia was produced without thoracotomy in 10 dogs (experimental group) by embolization with a plastic bead injected via a catheter into the left coronary artery. A control group of 4 dogs had only saline injected into the artery. Defibrillation threshold was …

Simple Methods For Determining The Accuracy Of Tumor Blood Flow Measurements Using Radioactive Microspheres In Rats, Rosanna C. Chan, Charles F. Babbs, Richard J. Vetter

Weldon School of Biomedical Engineering Faculty Publications

Two simple methods are presented that allow positive identification of the accuracy and precision of the microsphere technique and a quick verification of sphere entrapment in tumor vessels. A known flow of Ringer's solution from a motor-driven syringe is perfused through the rat's isolated systemic circulation from left ventricle to right atrium and collected in a funnel. Using this preparation, total blood flow in rats measured with radioactive microspheres injected into the left ventricle was 97% of actual flow. The coefficient of variation (standard deviation/mean) of the microsphere measurements was 0.22. In the same preparation, non-entrapment of microspheres in subcutaneous …

Improved Oxygen Delivery During Cardiopulmonary Resuscitation With Interposed Abdominal Compressions, William D. Voorhees, Mark J. Niebauer, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Publications

The ability of a new modification of cardiopulmonary resuscitation (CPR) to deliver oxygen to tissues was evaluated. The method utilizes standard CPR techniques with the addition of manual abdominal compressions (100 mm Hg) interposed between chest compressions, and is termed interposed abdominal compression-CPR (IAC-CPR). Oxygen delivery was measured by a spirometer in a closed circuit designed to permit positive-pressure ventilation synchronized with mechanical chest compression. Ventricular fibrillation was induced electrically in 10 anesthetized dogs. In each dog, trials of IAC-CPR and standard CPR were alternated every five minutes during a 30-minute period. Arterial and central venous blood pressures, oxygen consumption, …

Relationship Of Blood Pressure And Flow During Cpr To Chest Compression Amplitude: Evidence For An Effective Compression Threshold, Charles F. Babbs, W D. Voorhees, K R. Fitzgerald, H R. Holmes, L A. Geddes

Weldon School of Biomedical Engineering Faculty Publications

This study was conducted to investigate the importance of the depth of chest compression in producing effective cardiopulmonary resuscitation (CPR) in animals, as indicated by cardiac output and mean arterial blood pressure. Cardiac output was measured by a modified indicator dilution technique in 8 anesthetized dogs, 6 to 12 kg body weight, during repeated 2-minute episodes of electrically induced ventricular fibrillation and CPR provided by a mechanical chest compressor and ventilator (Thumper^®). Chest compression exceeding a threshold value (x₀) between 1.5 and 3.0 cm was required in each animal to produce measurable cardiac output. In particular, …

Equipment For Local Hyperthermia Therapy Of Cancer, Charles F. Babbs, James R. Oleson, John A. Pearce

Weldon School of Biomedical Engineering Faculty Publications

Rapid improvements in hyperthermia apparatus are being achieved by industrial and university-based research groups that have already led to the marketing of a variety of commercial systems for heat therapy of malignancy. These tissue heating systems employ microwaves, capacitively or inductively coupled radiofrequency current, or high intensity ultrasound to produce controlled local heating of tumor tissues. No single system is superior to others in all applications; each has its limitations.

Characterization Of The Oscillometric Method For Measuring Indirect Blood Pressure, L A. Geddes, M Voelz, C Combs, D Reiner, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Publications

In this study, human subjects and dogs were used to determine the ability of the oscillometric method to indicate systolic and diastolic pressure. In the human studies, the auscultatory method was used as the reference. In the animal studies, directly recorded blood pressure was used as the reference. The ability of the sudden increase in cuff pressure oscillations during cuff deflation to indicate systolic pressure was examined and found to overestimate systolic pressure slightly in man, but more in animals. Systolic pressure was encountered when the cuff pressure oscillations were about one half of their maximum amplitude. However, in both …

Biology Of Local Heat Therapy For Cancer, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Publications

Successful cancer therapy must selectively destroy tumor tissue while sparing the host's normal tissues. Local heat treatment can have such a selective effect because abnormalities in tumor blood vessels supply less oxygen to heat-stressed tumor cells and are less efficient in cooling tumor tissue by blood perfusion.

Hydralazine-Enhanced Selective Heating Of Transmissible Venereal Tumor Implants In Dogs, William D. Voorhees Iii, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Publications

This study was designed to test the hypothesis that vasodilator drugs can enhance selective heating of solid tumors by producing a favorable redistribution of blood flow between tumor and normal tissues. Subcutaneous transmissible venereal tumor implants were heated by inductive diathermy using Helmholtz coils in 8 dogs. The temperature rise in tumor and adjacent muscle was measured before and after giving hydralazine (0.5 mg/kg i.v.). Blood flow to the tumors and underlying muscle was measured with radioactive tracer microspheres. Before hydralazine treatment mean muscle blood flow was about one-third tumor blood flow (0.11  0.02 vs. 0.28  0.09 ml/min/g), …

Theoretical Feasibility Of Vasodilator-Enhanced Local Tumor Heating, Charles F. Babbs, David P. Dewitt, William D. Voorhees, Janet S. Mccaw, Rosanna C. Chan

Weldon School of Biomedical Engineering Faculty Publications

Normal arterioles, in contrast to the abnormal microvasculature of many solid tumors, provide a target for selective drug action that can enhance local heat treatment of the tumors. Measurements of tissue blood flow with radioactive microspheres and estimates of changes in blood flow with thermal clearance methods revealed that vasodilator drugs either decreased or did not alter blood flow in hamster melanoma, rat hepatoma, and canine transmissible venereal tumor, while increasing perfusion in adjacent normal tissues 2 to 4-fold. Solutions of the bio-heat transfer equation, which take into account such selective effects of vasodilators on blood flow in normal tissues, …

Cardiopulmonary Resuscitation With Interposed Abdominal Compression In Dogs, Sandra H. Ralston, Charles F. Babbs, Mark J. Niebauer

Weldon School of Biomedical Engineering Faculty Publications

This study was conducted to evaluate the hemodynamic effectiveness of a new modification of cardiopulmonary resuscitation (CPR), termed interposed abdominal compression- CPR (IAC-CPR). IAC-CPR utilizes all the steps of standard CPR with the addition of abdominal compressions interposed during the release phase of chest compression. Ventricular fibrillation was induced electrically in 10 anesthetized dogs, and either IAC-CPR or standard CPR was initiated while arterial and venous blood pressures and cardiac output were monitored. The two CPR methods were alternated every three minutes over a period of thirty minutes. The addition of interposed abdominal compressions to standard CPR improved arterial pressures …

Physical Principles Of Local Heat Therapy For Cancer, Charles F. Babbs, David P. Dewitt

Weldon School of Biomedical Engineering Faculty Publications

Local hyperthermia therapy for cancer can produce selective heating of solid tumors on the basis of known physical laws. If energy is deposited in the general region of the tumor, temperature tends to develop in the tumor higher than that in surrounding normal tissues. The goal of therapy is to achieve cytotoxic temperature elevations in the tumor for an adequate period of time, without damaging nearby normal tissues. Several modalities exist for local heat treatment, of which radiofrequency and ultrasound offer the most promise for controlled, localized heating at depth. A paucity of blood flow in the tumor compared to …

Alteration Of Defibrillation Threshold By Antiarrhythmic Drugs: A Theoretical Framework, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Publications

No abstract provided.

Cardiac Output During Cpr: A Comparison Of Two Methods, D L. Silver, R J. Murphy, Charles F. Babbs, L A. Geddes

Weldon School of Biomedical Engineering Faculty Publications

Simultaneous Fick and saline dilution methods were compared for measuring cardiac output during experimental cardiac arrest and resuscitation in anesthetized dogs. During cardiopulmonary resuscitation (CPR) cardiac output averaged 53 ± 30 ml/min-kg (42% of pre-arrest values). Values obtained using the Fick vs. saline methods were highly correlated (r = 0.96), and were not statistically different (t = 1.47, df = 16).

Transchest Defibrillation Under Conditions Of Hypothermia, W A. Tacker, Charles F. Babbs, D R. Abendschein, L A. Geddes

Weldon School of Biomedical Engineering Faculty Publications

This study was conducted to determine whether or not hypothermia changes ventricular defibrillation threshold. Ventricular fibrillation was induced by electrical stimulation of the endocardium in pentobarbital anesthetized dogs, both during normothermia and hypothermia produced by circulating 8 °C water through a rubber bladder implanted in the peritoneal cavity. Defibrillation threshold was determined as the shock strength needed to defibrillate the ventricles and differing no more than 10 percent from a shock strength that failed to defibrillate. Defibrillation threshold current was stable for body temperatures ranging from 37 oC to 22 oC. Threshold energy increased linearly with decreasing temperature in keeping …

Effect Of Thoracic Venting On Arterial Pressure, And Flow During External Cardiopulmonary Resuscitation In Animals, Charles F. Babbs, Nicholas Bircher, Dennis E. Burkett, Henry A. Frissora, Brian C. Hodgkin, Peter Safar

Weldon School of Biomedical Engineering Faculty Publications

To test the hypothesis that fluctuations in global intrathoracic pressure are the dominant cause of blood flow during external cardiopulmonary resuscitation (CPR) the authors studied the effects of open pneumothorax on experimental CPR in 7 domestic pigs and 12 mongrel dogs. Similar studies were conducted independently at three laboratories and are reported jointly. All studies were conducted during electrically induced ventricular fibrillation and with standard CPR technique, including ventral-dorsal chest compression at 60/min, 0.5 sec compression duration, 1:5ventilation:compression ratio. During alternate periods of CPR, intrathoracic pressure was vented through bilateral chest tubes, placed to create open pneumothorax and partial collapse …

Cardiac Output During Cardiopulmonary Resuscitation At Various Compression Rates And Durations, Kevin R. Fitzgerald, Charles F. Babbs, Henry A. Frissora, Robert W. Davis, Douglas I. Silver

Weldon School of Biomedical Engineering Faculty Publications

Cardiac output during cardiopulmonary resuscitation (CPR) was measured by a modified indicator-dilution technique in 20 anesthetized dogs (6-12 kg) during repeated 1- to 2-min episodes of electrically induced ventricular fibrillation and CPR, produced by a mechanical chest compressor and ventilator. With compression rates from 20 to 140/min and compression durations (duty cycles) from 10 to 90% of cycle time, cardiac output (CO) was predicted by the equation:

,

where CR is compression rate, DC is duty cycle, SV_max (19 ml) is the effective capacity of the pumping chamber, and k_l (0.00207 min) and k₂ (0.00707 min) are …

Influence Of Interposed Ventilation Pressure Upon Artificial Cardiac Output During Cardiopulmonary Resuscitation In Dogs, Charles F. Babbs, W D. Voorhees, K R. Fitzgerald, H R. Holmes, L A. Geddes

Weldon School of Biomedical Engineering Faculty Publications

This study was conducted to determine the effects of high pressure interposed ventilations during cardiopulmonary resuscitation (CPR). Cardiac output was measured by a modified indicator dilution technique in eight anesthetized, intubated mongrel dogs. Positive pressure ventilations (12/min, 80% O2) were interposed after every five chest compressions (performed at 62/min) by a mechanical chest compressor (Thumper®). On repeated trials in the same animal, ventilation pressures from 10-50 cm of H2O were tested in randomized sequence, while the technique of chest compression was held constant. Arterial blood gases immediately after resuscitation were monitored. Increasing ventilation pressure had surprisingly little effect on cardiac …

Evaluation Of The Operating Internal Resistance And Capacitance Of Intact Trapezoidal Waveform Defibrillators, Charles F. Babbs, Sj Whistler, La Geddes

Weldon School of Biomedical Engineering Faculty Publications

No abstract provided.

Regional Blood Flow During Cardiopulmonary Resuscitation In Dogs, W D. Voorhees, Charles F. Babbs, W A. Tacker

Weldon School of Biomedical Engineering Faculty Publications

To determine differences in regional blood flow during cardiopulmonary resuscitation (CPR) versus normal cardiac function, we measured regional blood flow to sev~ral organs in 19 pentobarbital-anesthetized dogs (6-12 kg). Regional blood flow was measured during sinus rhythm in 5 dogs and during electrically induced ventricular fibrillation with CPR in the other 14 dogs. Regional blood flow and cardiac output were measured using radioactively labelled polystyrene microspheres of 15 ±3P diameter, injected into the left ventricle. Adequacy of microsphere mixing at low cardiac outputs was verified by comparing flow rates to paired organs. Cardiac output was 175 ml/kg/min during sinus rhythm …

Therapeutic Indices For Transchest Defibrillator Shocks: Effective, Damaging, And Lethal Electrical Doses, Charles F. Babbs, Willis A. Tacker, John F. Vanvleet, Joe D. Bourland, Leslie A. Geddes

Weldon School of Biomedical Engineering Faculty Publications

Although prospective studies of defibrillator shock overdose cannot be performed in man, the therapeutic indices of various defibrillating current waveforms can be measured in animals. We determined the ratios TD50/ED50 and LD50/ ED50 (where TD50 = median "toxic" or damageinducing dose, ED50 = median effective or defibrillating dose, and LD50 = median lethal dose) as measures of the therapeutic index for damped sine wave defibrillator shocks in dogs. Death of an animal and/or any degree of cardiac damage found by gross or microscopic examination were defined as harmful effects of shock, analogous to drug toxicity. In terms of peak current, …

An Animal Model For Testing Automatic Defibrillators, J D. Bourland, Charles F. Babbs, W A. Tacker, L A. Geddes

Weldon School of Biomedical Engineering Faculty Publications

A promising therapy for ventricular fibrillation--a life-threatening cardiac arrhythmia--is the implantation of an automatic defibrillator. A critical component of such a device is the system that detects the presence of ventricular fibrillation. Automatic systems for detecting ventricular fibrillation have been tested with arrhythmias produced by electric shocks in normal canine hearts, but have not been tested with spontaneous arrhythmias in hyperirritable hearts. We have developed an animal model to create arrhythmias without electrical stimulation and have used it to test our automatic defibrillator. This model permits evaluation of both reliability to diagnose ventricular fibrillation and reliability to reject other tachyarrhythmias.

A New Technique For Repeated Measurement Of Cardiac Output During Cardiopulmonary Resuscitation, L A. Geddes, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Publications

We have developed a method for measurement of cardiac output during CPR with ventricular fibrillation. The method avoids the problems encountered when conventional techniques are used under the conditions of very low cardiac output. The method consists of injecting 5% saline as the indicator into the left ventricle and detecting its appearance in the descending aorta by withdrawing blood through an electrically calibrated conductivity cell. The adequacy of indicator mixing has been verified by obtaining dilutions curves simultaneously from the brachial and femoral arteries. Cardiac output can be determined even when output is as low as 7 ml/min/kg during CPR …

Influence Of Adrenergic Drugs Upon Vital Organ Perfusion During Cpr, H R. Holmes, Charles F. Babbs, W D. Voorhees, W A. Tacker, B De Garavilla

Weldon School of Biomedical Engineering Faculty Publications

To determine whether adrenergic drugs administered during cardiopulmonary resuscitation (CPR) alter the distribution of artificial card:l.ac output, we measu"red regional blood flow and cardiac output using radioactive microspheres in 12 dogs. Ventricular fibrillation was induced electrically and CPR was immediately begun with a mechanical chest compressor and ventilator (Thurn per ( R) ) at 60 compressions/min, with a ventilation:compression ratio of 1:5, a compression duration of 0.5 sec, and a ventilation pressure of 20 em H 2 o. Compression force was sufficient to develop 40-50 mmHg peak intraesophageal pressure. After 30 sec of CPR, either 0.9% saline vehicle or 50 …

Dependence Of Defibrillation Threshold Upon Extracellular/Intracellular K+ Concentrations, Charles F. Babbs, S J. Whistler, G Yim, L A. Geddes

Weldon School of Biomedical Engineering Faculty Publications

The effect of increasing extracellular potassium concentration (K_o) upon electrical ventricular defibrillation threshold was investigated in pentobarbital anesthetized dogs treated with intravenous potassium chloride. Defibrillation threshold fell during potassium intoxication. The percent decrease in defibrillation threshold was linearly related to the logarithm of K_o and to the potassium equilibrium potential, E_K, calculated from measured extracellular and intracellular potassium concentrations of ventricular muscle. In dogs supported by left ventricular bypass in order to maintain the circulation during potassium intoxication, the values of K_o and E_K required for spontaneous, K⁺ induced defibrillation (electrical defibrillation …

Dynamic Intraesophageal Imagining Of The Heart With Ultrasound, N E. Fearnot, Charles F. Babbs, J D. Bourland, L A. Geddes

Weldon School of Biomedical Engineering Faculty Publications

Real-time images of the heart from within the esophagus are produced by a new intraesophageal ultrasonic sector scanner. Sixty images per second are displayed on a gray scale CRT in real-time and recorded on standard videotape for review. By interactive positioning of the esophageal probe, heart ventricles, atria, and valves can be visualized and their dynamics can be studied. The esophageal probe comprises four 5 MHz PZT-5 piezoelements of 6.35 mm diameter, mounted on a shaft that rotates at 900 rpm. The piezoelements are pulsed at a 5 kHz rate and the echoes are processed electronically.

New Versus Old Theories Of Blood Flow During Cpr, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Publications

Today, the physiology of blood flow during external chest compression appears more complicated than had previously been imagined. New evidence requires that at least two possible mechanisms be considered for generating artificial circulation by external chest compression. The first is the classical mechanism in which the heart propels blood because it is squeezed between the sternum and the spine. The second is a more recently appreciated mechanism in which the entire thorax acts as a pump because of global intrathoracic pressure changes. The first might be called the cardiac pump mechanism and the second might be called the thoracic pump …