Julio C. Davila

SOME PHYSICAL FACTORS AFFECTING THE ACCEPTANCE OF SYNTHETIC MATERIALS AS TISSUE IMPLANTS

The natural response of healing tissue to an implanted foreign body is to encapsulate it in scar. This represents a modification of the natural process of tissue repair only in that continuity of tissue is never fully restored as long as the implant remains to occupy space which would otherwise be filled by scar. All natural cavities, exposed surfaces or channels in the body are normally lined with highly specialized tissues adopted to certain roles, thus : epithelial, endothelial and mucosal surfaces. When the integument or the walls of hollow organs are injured, their repair consists of restoration of structural integrity by connective-tissue-scar formation. However, where scar bridges a gap at an exposed surface, simple connective tissue does not remain bare; it is always covered by new surface tissue which has the histologic characteristics of the adjacent normal epithelium, mucosa or endothelium. These specialized surface “finishes” are the protective coating which permits the underlying, supporting tissues to attain metabolic stability, free from the infection and irritation to which they are susceptible. Such surface tissues, the “finishing touch” of the healing process, halt fibrin deposition, proliferation of ‘granulation tissue and development of more

Venoarterial shunting from inferior vena cava to left atrium in atrial septal defects with normal right heart pressures: Report of two cases

Abstract Two unusual cases of atrial septal defect are presented with right to left shunting occurring from functional drainage of the inferior vena cava into the left atrium. The first had been unrecognized in a teenage boy who previously had undergone successful closed pulmonary valvotomy for congenital pulmonary valvular stenosis. The second occurred following a right pneumonectomy for bronchogenic carcinoma in a man with a previously undetected atrial septal defect. The respiratory embarrassment developing postoperatively was related to dislocation of the heart resulting in an anatomic shift of the atrial septum so that the inferior cava emptied directly into the septum secundum defect. Both patients had normal right heart pressures, and in each the diagnosis was established by selective dye-dilution curves and confirmed by selective cineangiography. Blood gas studies were instrumental in the second case in pointing toward a right to left shunt subsequently confirmed by dye-dilution studies. The importance of blood pH, pCO 2 , and pO 2 studies and selective indicator-dilution studies in the evaluation of patients with unexplained cyanosis or respiratory distress is emphasized.

Measurement of cardiac output by thermal dilution

Abstract The cardiac output was determined by the thermal dilution technique in dogs and calves, and the results were compared with the simultaneously determined electromagnetic flowmeter measurements of aortic flow. For these measurements the indicator, saline solution at room temperature, was injected into the superior vena cava, and the sensing thermistor catheter was placed in the main pulmonary artery. A simple analog computer solved a modified Stewart-Hamilton equation and displayed the calculated cardiac output on a digital readout meter. One hundred twenty simultaneous measurements were made in dogs and 76 determinations in calves. The standard error of estimate, when compared to electromagnetic flowmeter determinations, was approximately 10 percent of mean cardiac output (450 ml/min in dogs and 750 ml/min in calves). Since the measurement of aortic flow by the electromagnetic flowmeter does not include coronary flow, this discrepancy is to be expected. The reproducibility of the method was assessed by evaluating successive pairs of thermal curves recorded within 1 minute. The standard deviation of the difference between successive determinations was approximately 3.5 percent. Initial trials in 8 patients undergoing cardiac catheterization and in 14 patients in the operating room and intensive care unit have shown the method to be highly useful and practical.

Continuous measurement of left ventricular volume in the dog: II. Comparison of washout and radiographic technics with the external dimension method

Abstract Single plane angiocardiographic studies were performed using casts of the left ventricular cavity of the canine heart. Good agreement was found between true and calculated volume. End-diastolic volume estimated (EDV) from angiocardiographic measurements and that estimated with a method based on external cross-sectional areas and length (EAL), calibrated in each subject, correlate within 10 per cent. These data support the validity of either model. However, at end-systole, x-ray calculations always yielded an underestimation of the volume when compared with measurements by the EAL method. Immediate changes in ventricular dynamics were studied during and after the injection of 1.0 ml./kg. of Renografin. End-diastolic and stroke volumes were found to increase. Measurements by the EAL method were also compared with those from thermal washout recordings. A systematic overestimation of EDV and underestimation of SV/EDV was found. The difference was greater at faster heart rates. A linear relation between EDV, SV and ESV was found under conditions of volume overload.

Continuous measurement of left ventricular volume in the dog

Abstract Evidence is presented to show that a volume index derived from the ellipsoid model, and applied in open chest dogs by use of direct and continuously measured external dimensions, is compatible with left ventricular volume changes and can be calibrated in absolute terms in the dead heart of the same subject. The over-all accuracy of the method is better than ±2 ml. It is useful to study volume-dependent variables which characterize myocardial performance in the living animal. It can also be used as a standard in animals against which to compare left ventricular volume measurements made by angiocardiography or indicator washout.

A Nonthrombogenic, Nonanticoagulant-Dependent Mitral Valve Prosthesis

Thromboembolism stems from incompletely covered foreign body which is in physical continuity with tissue. Cardiac valve prostheses which remain partially exposed show, at the tissue-to-prosthesis junction, incomplete healing which is characterized by continuing granulation and proliferating immature unstable scar tissue, from which thrombosis originates and propagates.The principle of complete encapsulation with healthy granulation tissue, maturation into stable fibrous tissue without inflammation, covered by a normal antithrombogenic endothelial surface, is a more logical approach than [see Figure in the PDF file] methods which attempt to prevent thrombosis by altering the character of the surface of the exposed foreign body or the blood coagulation mechanism. A valve is described which functions eminently satisfactorily as a replacement for the calf mitral valve.