Electroventilation

Christine Elizabeth Riscili, Purdue University

Abstract

Electroventilation is a new term used to describe the production of artificial respiration by electrical stimulation of the inspiratory nerves and muscles using transthoracic electrodes. Electroventilation causes artificial respiration by negative pressure, and therefore, may not have the deleterious effects on blood pressure that occurs when using positive pressure ventilators. Experiments were performed on dogs, baboons, and man, to determine the efficacy of electroventilation. The optimal location for electrode placement was determined, and found to be similar in each of the species. Two stimulation sites were located; one in the anterior axillary region and the other just lateral to the xiphoid process. These sites remained relatively constant among animals. The relationship between stimulating current and inspired volume was also determined. In all cases, an increase in stimulating current resulted in an increased inspired volume. Passing current across the thorax raises the question of the safety of electroventilation. It is important to note that we are able to monitor blood pressure and the ECG continuously, and no cardiac arrhythmias have ever been detected during electroventilation. The safety factor (i.e., the ratio of the current required to produce an ectopic beat to the current required to produce an inspired volume of 225 ml which is approximately twice tidal volume) was determined in 12 dogs using transthoracic electrodes positioned at the optimal electroventilation site. The relationship between inspired volume and stimulus intensity was determined using a 0.8 second burst of stimuli (60/sec) with a pulse duration of 0.1 msec. Using the same electrodes, the threshold current for producing ectopic beats was determined for single pulses ranging from 0.1-10 msec duration. In all dogs, the current required to produce an ectopic beat increased greatly as the pulse duration decreased. At 0.1 msec, the safety factor for electroventilation was calculated to be 25.8. The chronaxie value, which describes the excitability characteristic of a tissue was determined for motor-nerve in the baboon and the dog, and also for ventricular myocardium in the dog. The chronaxie for motor-nerve in the dog was calculated to 0.17 msec, and 0.18 msec in the baboon. The chronaxie for myocardium was calculated to be 1.82 msec. These results indicate that to optimize stimulation of the inspiratory motor nerves, and to minimize the risk of myocardial stimulation, a very short-duration stimulating pulse should be used.

Degree

Ph.D.

Advisors

Geddes, Purdue University.

Subject Area

Anatomy & physiology|Animals|Veterinary services

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