Robert P. Walton

Resistance Strain Gauge Arches for Direct Measurement of Heart Contractile Force in Animals.

Summary A strain gauge arch has been described which measures heart force changes in fully conscious, chronically operated dogs. Enclosure of the electrical component in a metal casing prevents insulation breakdown in body fluids.

Limitation of Myocardial Function by Reduced Coronary Blood Flow during Isoproterenol Action

The interpolated decrease in heart force or isometric systolic tension that occurs during isoproterenol stimulation has been examined in terms of changes in coronary flow and myocardial metabolism. In 67 open-chest dogs under pentobarbital anesthesia, determinations were made of lactate, pyruvate, Po2 and Pco2 in arterial and coronary sinus blood; coronary flow was measured with an electromagnetic flow transducer and ventricular force with a strain gauge arch. Although the characteristic, uncomplicated effect of isoproterenol is a marked increase in coronary flow and contractile force, this is briefly interrupted by a sharp decrease in these functions, and the decrease is associated with evidence of anaerobic metabolism. This decrease is concomitant with decreased coronary perfusion pressure and is intensified by sustained infusion of isoproterenol or by lowered oxygen concentrations in the inspired air. The stage of depressed function is counteracted by mechanical maintenance of high aortic pressure or by slow, controlled heart rate. When uncontrolled, tachycardia due to isoproterenol continues without phasic interruption. The intermediate period of depressed function is interpreted in terms of sharply decreased oxygen delivery when both cardiac rate and force are increased. The hemodynamic and metabolic values for these acutely occurring, reversible extremes have been specified.

Circulatory Effects of Salicylates

Sodium salicylate consistently produces a prompt increase in heart contractile force when injected in anesthetized dogs in doses of 100 mg./Kg. intravenously. The increase in force is about 30 per cent and declines to control levels in 15 to 20 min. This effect is not considered of important therapeutic significance. Total doses of about 400 mg./Kg. consistently produce marked hyperpyrexia which closely resembles that of dinitrophenol and applied external heat in its circulatory characteristics; conspicuous features are extreme tachycardia, depressed S-T segment, moderate increase in heart force, and aortic pulse contours which indicate reduced stroke volume and vasodilation.

Bleeding Volume Indices of Hydroxyethyl Starch, Dextran, Blood, and Glucose.∗

Summary Solutions of hydroxyethyl starch were approximately equivalent to dextran and autologous whole blood in restoring and maintaining near normal arterial pressures in bled dogs. Bleeding volume indices with hydroxyethyl starch solutions, dextran, or whole blood were not significantly different. With glucose solution, arterial pressures and bleeding volume indices were significantly lower. During the interval between bleedings, arterial hematocrit values were maintained at about 50% of prehemorrhage levels by hydroxyethyl starch and dextran, whereas with glucose solutions hematocrits progressively rose to levels in the range of prehemorrhage values.

Electrocardiographic and serum potassium changes in fatal hyperthermia

Abstract Although electrocardiographic records obtained during various types of febrile states have often been described, there have been very few studies concerned with the electrocardiographic changes occurring during fatal hyperthermia. In a recent investigation of the cardiovascular effects of hyperthermia produced by dinitrophenol, large doses of Dicumarol, and by externally applied heat, marked electrocardiographic changes were consistently observed. 1 In these preceding experiments, anestheti ed dogs in an advanced state of hyperthermia were observed through progressive changes to fatal termination. The characteristic electrocardiographic pattern associated with the hyperthermia consisted of extreme sinus tachycardia, heightened T waves, S-T depression, and, terminally, disappearance of the P wave, widening of the QRS complex, and ventricular fibrillation or cardiac arrest. As most of these changes resemble the effects produced by high serum potassium levels, the present study was primarily under-taken in order that serum potassium levels could be determined in similar hyperthermia experiments and correlated with the electrocardiographic changes. Additionally, the course of study was designed so that other blood chemical and cardiovascular changes produced by hyperthermia could be observed and their influence on the electrocardiogram similarly evaluated.

Effects of drugs on ballistocardiographic recordings: Correlation with other cardiovascular measurements in the dog and in man☆☆☆

I N DETERMINING the cardiovascular effects of drugs, the need for a convenient clinical method has led several investigators to the use of ballistocardiograph)I.‘-4 Most of these investigations have been concerned primarily with the drug-elicited changes in cardiac output as measured I))I the ballistocardiograph. However, Hamilton et al.” concluded that the amplitude of the ballistocardiogram was more closel!related to the velocityof ejection than to the quantity of blood ejected. Starr and others related the amplitude and contour of the ballistocardiographic complexes to the rate of application of simulated heart force in cadavers6-8 In addition, several investigators have shown that hallistocardiographic amplitude is greatly reduced but not completely eliminated by occluding the venous return to the heart or by preventing the ejection of blood by the heart. These investigators have concluded that the amplitude of the ballistocardiogram is largely determined I)v the forces involved in the movement of blood. !‘-11 Several methods have evolved for obtaining records of the l)ody movements occurring with each heart beat. NotalA)-, these arc the Starr table (a high-frequency system), the ultra-lowfrequency system, and the direct-hod>method. The physics of these systems and the artcfacts in their records have been descril,cd”-I4 and have been discussed also bv others in this Seminar. However, for the purpose of cI,aluating the acute influence of drugs on the human cardiovascular system some of the advanta,ges of the direct-bed\method might I)e pointed out here: (1) Directbody recordings are easily obtained without discomfort to the subject. (2) They may t)c ohtained from the patient confined to the hospital t)cd. (3) The low cost of installation of the equipment permits the use of direct-body units in the physician’s office. Based on the above considerations, studies were instituted in this laborator)to investigate the applicabilit\of t>allistocardiography as a clinical method of e\,aluating acute drug-produced changes in rn)-ocardial contractilit)-.i5-‘

Dibenamine Blockade as a Method of Distinguishing Between Inotropic Actions of Epinephrine and Digitalis.

’ The general plan of thcsc investigations has I)een

Sympathetic influences during hemorrhagic hypotension.

Summary and Conclusions In open-chest, vagotomized dogs, Dibenamine has been shown to be effective in producing a substantial blockade of the inotropic effects of epinephrine while leaving the inotropic effects of digitalis relatively unaffected. This inotropic blockade of epinephrine by Dibenamine is not the result of secondary cardiovascular changes.