A rate-responsive pacemaker controlled by right ventricular blood temperature.

To demonstrate the capabilities of a rate-responsive pacemaker controlled by right ventricular blood temperature, a prototype pacemaker was developed and tested in dogs with complete atrioventricular (AV) block. Using a previously obtained data base of right ventricular blood temperature recorded both during rest and during treadmill exercise from dogs with either induced AV block or normal AV conduction, a control algorithm which identified periods of exercise was developed. This algorithm was implemented in a microprocessor-based, rate-responsive pacemaker which generates two pacing rates: a basal rate (86 bpm) during rest and a higher rate (113 bpm) during moderate exercise.

Cardiac, thoracic, and abdominal pump mechanisms in cardiopulmonary resuscitation: studies in an electrical model of the circulation.

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.

Safety factor for precordial pacing: minimum current thresholds for pacing and for ventricular fibrillation by vulnerable-period stimulation.

Temporary cardiac pacing by means of rapidly applied, precordial electrodes can be of great value in selected patients suffering cardiac arrest or profound bradycardia, post-defibrillation atrioventricular block, or digitalis intoxication. This study provides data pertaining to the safety of precordial pacing measured as the ratio of the minimum current required to induce ventricular fibrillation (VF) to the minimum current required to pace the ventricular myocardium. Single rectangular pulse stimuli having durations of 1-50 ms were evaluated.

Electrical stimulation on skin wound healing in the horse: preliminary studies.

The effect of low-level direct-current stimulation on skin wound healing in the horse was assessed. Self-sustaining electrical circuits with electrodes were implanted subcutaneously in or near the wound. Stimulation by direct current (10 or 20 microA) was used to determine the effect on equine skin healing.

The relationship between arterial pulse-wave velocity and pulse frequency at different pressures.

Pulse-wave velocity was measured in isolated canine common carotid arteries using sinusoidal frequency pulses of 1, 2, 5, 10, 15 and 20 Hz at 50, 100 and 150 mmHg. It was found that the pulse-wave velocity was independent of frequency and dependent on pressure. Using the Moens-Korteweg equation, the predicted pulse-wave velocity (y) was compared with measured pulse-wave velocity (x).

Industry-university cooperative research.

Industry-university cooperative research ventures offer significant benefits to sponsoring firms and university scientists alike. Society also benefits, since such ventures can accelerate the emergence of new technologies and the practical application of these technologies to important new products and services. Potential issues of concern to industrial sponsors and university researchers, such as the timing of publication of research results, can be resolved through well-designed research contracts responsive to the needs and expectations of both parties.

Right-side cardiac output determined with a newly developed catheter-tip resistivity probe using saline indicator.

Right-heart cardiac output was determined in 10 dogs using a newly developed, highly accurate catheter-tip resistivity probe. A saline indicator was injected into the right atrium and the blood resistivity was monitored at the catheter tip in the pulmonary artery. The resulting dilution curves were calibrated electrically according to the manner in which blood resistivity changes with saline concentration and cardiac output values were calculated.

Relationship of blood pressure and flow during CPR to chest compression amplitude: evidence for an effective compression threshold.

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 (xo) between 1.

Skin burns from electrosurgical current.

At 34 skin sites on anesthetized pigs, graded levels of average electrosurgical current density, J (A/cm2), at 500 kHz were delivered for specified times (t sec) to cause thermal injury. The severity of cutaneous response was determined by gross and microscopic study 56 hours later. The product J2t has been defined as the relative energy density factor, and is proportional to the delivered energy that determines skin heating.

Thermographic evaluation of horses with podotrochlosis.

The distal forelimbs of 10 clinically normal horses with hair clipped on 1 limb were thermographically scanned before and after exercise. The thermal patterns, temperature distribution, and temperature changes after exercise were determined and compared with those of 8 horses with podotrochlosis. Clipping the hair did not cause changes in the thermal patterns, but the clipped limbs were warmer than the unclipped limbs.

Alterations induced by a single defibrillating shock applied through a chronically implanted catheter electrode.

In ten beagles ranging in weight from 7.4 to 13.0 kg, a defibrillating shock of 10 A (three dogs), 20 A (four dogs), or 30 A (three dogs) intensity was applied through a chronically implanted right ventricular catheter electrode.

Efficacy and safety of defibrillation with rectangular waves of 2- to 20-milliseconds duration.

The effect of suprathreshold defibrillator shocks on cardiac function was compared in 8 isolated, perfused, contracting canine hearts using 4 durations of rectangular electrical waveforms. Defibrillation threshold was first determined for each duration; then overdose shocks of 3, 4.5, 6, and 9 times threshold current density were delivered.

Myocardial stimulation with ultrashort duration current pulses.

In order to identify a practical short-duration limit for stimulating myocardium, theoretical and experimental studies were carried out using dog and turtle hearts. The strength-duration curves for current, charge and energy were derived from the standard excitable membrane model which employs a parallel resistance and capacitance. From these derivations, the predicted duration for minimum energy was identified.