Gerhard A. Brecher

The Relief of Acute Right Ventricular Strain by the Production of an Interatrial Septal Defect

Since sudden resistance increase in the pulmonary circulation leads to right ventricular overdistension and subsequent failure, the question was studied whether or not the existence of an experimentally produced interatrial septal defect could prevent an overstretching of the right myocardium in acute pulmonary stenosis. It was found that myocardial overdistention could be prevented by a small interatrial septal perforation without essentially changing normal interatrial pressure relations. A large defect, which also protected the right heart muscle from overstretching, changed atrial pressure relations and cardiac dynamics entirely.

A modified bristle flowmeter for measuring phasic blood flow.

Summary A new type of electrically recording bristle flowmeter is described, which permits measurement of volume flow of blood and its phasic changes. By recording superior vena cava flow, direct evidence is presented that the greatest acceleration of blood and a marked volume inflow into the right atrium occurs during ventricular systole, when the tricuspid valves are closed. This demonstrates the active influence of ventricular contractions on venous return.

A new method for direct recording of cardiac output.

Summary A modification of a bristle flowmeter is described which permits direct recording of cardiac output and its fluctuations from one heartbeat to another. The device is inserted into the trunk of the pulmonary artery of anesthetized, heparinized dogs without blood loss and without interrupting blood flow. Zero flow can be established by mechanical means without occluding the vessel. Phasic changes during the cardiac cycle consist of a marked forward flow during cardiac ejection and a brief period of backflow following ejection. Mean cardiac output can be directly recorded by electrically averaging the phasic flows.

Regulation of Blood Flow in Gross-Circulation for Intracardiac Surgery.

Summary In acute experiments on dogs 2 types of flowmeters were compared for regulating the 2-way flow of blood in donor cross-circulation during intracardiac surgery. (1) By arranging 2 flow rate recorders (5734 bristle flowmeters) to act as a flow-difference-meter, differences in the volume flow of blood from donor to recipient and vice versa could be recorded. This method appears, however, rather complicated for use in the operating room. (2) A cumulative flow recording method was found to be simple and reliable. For this purpose, the donor rested on zero reading scales which acted as a cumulative flowmeter indicating blood inflow and outflow from the donor. With the aid of the scales, blood loss from the donor could be accurately measured and replaced by intravenous infusion. For practical purposes it is felt that continuous weighing of the donor provides the best method for insuring equal bidirectional flow in cross-circulation under operating room conditions.

Amplifier for 5734‐Tube Bristle Flowmeter

An amplifier and power supply for a stable, high‐frequency, electronic, bristle flowmeter is described. The transducer element is the RCA 5734 tube. The difficulty in applying this tube to blood flow measurements is overcome by use of a 500 000 ohm load resistor instead of the 75 000 ohm value recommended by the manufacturer. The advantages of this device are commercial availability of flow‐sensing element, high signal‐to‐noise ratio, good maintenance of the zero flow base line, response to backflow as well as forward flow, and provision for the recording of either phasic or mean flow.

An Optically Recording Tambour Flowmeter and a Compensator for Large Volume Blood Flow

An optically recording flowmeter for measuring rate and volume of blood flow in experimental animals by the phlebotomy method is described. The advantages of the flowmeter are its great accuracy, sensitivity, linear calibration, minimal time lag, and above all its simplicity when used with optically recording manometers. In conjunction with a simple ``compensating switch for the outflowing blood, it permits measurement of very large volume flows without reduction of the arterial blood pressure.