Elliot V. Newman

Theoretical and Practical Requirements for the Valid Measurement by Indicator-Dilution of Regurgitant Flow Across Incompetent Valves

A theory is presented for the measurement of regurgitant flow across an incompetent valve by injection of indicator distal to the valve and recording of time concentration curves proximal and distal to the valve. The conditions which must be met for valid measurements are examined and demonstrated by a functioning mechanical model of the heart. The method is valid regardless of the size of the residual volumes or degree of mixing with these volumes if a representative sample of the concentration of indicator in the blood moving across the valve in both directions is obtained.

Effect of the Sampling System on the Shape of Indicator Dilution Curves

This paper describes the distorting effects produced by various sizes of polyethylene tubing and various flow rates on a square wave input of dye concentration. The importance of an accurate sampling system when recording dilution curves for analysis of their shape is emphasized and the distortion caused by inadequate sampling systems is demonstrated in vivo.

The Use of Indigo Carmine for Dye Dilution Curves

Investigation of the properties of indigo carmine reveals that it may be more suitable than the dye, T-1824, for circulatory studies that are now commonly carried out using the dye dilution principle of Stewart and Hamilton. Comparison is made of simultaneous dilution curves of indigo carmine and radioactive iodinated serum albumin. Apparently, indigo carmine is bound to protein firmly enough to remain the plasma in one passage through the heart and lungs, but not too firmly to be extracted rapidly from the plasma by excretory systems in the kidney and liver. This allows repeated injections without accumulation.

Indicator Dilution in an Atrioventricular System with Competent or Incompetent Valves

A mathematical analysis of the pumping action of a two-chambered system has been used to develop formulas describing the changes with time in the mass and concentration of an indicator in either chamber of such a system analogous to the atrium and ventricle with either competent or incompetent valves. Such formulas show how the parameters of a system control the shape of an indicator-dilution curve. From these formulas expressions were developed which permit the analysis of the system from an indicator-dilution curve. The theory was then used to analyze dilution curves produced by a model of known parameters.

Relative Effects of Heart Chambers, Lungs, and Mitral Insufficiency on the Shape of Indicator Dilution Curves

The shape of dilution curves obtained by sampling from different sites was studied in dogs following superior vena caval injections of dye. Synchronous sampling from paired sites enabled observations to be made on the separate effects of the right heart, left ventricle and aorta on the dye dilution curves, with and without mitral insufficiency. The results show that tile left ventricle and aorta have little effect on the final slope of a dilution curve across the lungs in dogs with normal hearts. In the presence of mitral incompetence the final slope across both lungs and heart was slower than in the normal, but these changes were related to cardiac output and increase in lung mixing volume rather than primarily to the incompetence of the valve.

An Improved Method for the Calibration of Continuously Recorded Dye Dilution Curves

A simplified method is described for the calibration of continuously recorded dye dilution curves. The accuracy of this method is demonstrated in vitro and in vivo.

Evaluation of cardiovascular complications.

In introducing my topic, I should like to point out tliat I am an internist and tliat, although the internist is interested in the results atid complications of anesthesia, he can assume no real continuous responsibility for it. The older patient has a narrower range o f possible adjustments to stress. Change in blood volume is always a complication o i surgery, aiid the evaluation of such change is of vital importance in the aged patient. The methods in common use for determining blood loss during an operation are subject to error. Certainly tlie surgeon’s usual estimate of hlood loss is not to be trusted completely. Weighing the sponges may be more accurate. However, there is no better method o f determining blood loss than the direct measureiiient of the quantity of blood reriiaiiiing iii the intielit. I t is particularly difficult to know if the blood volume is adequate in the early postoperative period when the wound is closed and there may be internal oozing. While I do not recommend using chemical determinations to the exclusion o i other clinical signs or o i good clinical judgment, I believe it is indispensahle in many cases to have an accurate measure of blood volume. Blood-volume determinations can now be carried out, without an uiireasonable expenditure of time and energy, by any physician f ainiliar with standard laboratory procedures. I t is possible to make accurate determinations o i blood volume within 10 minutes and to repeat the determination several times without harm to the patient. The necessary equipment for the method that I shall describe can be set up on a tray beside the anestliesiologist. The total initial cost of the equipment and of the materials is similar to tlie cost of the apparatus used for blood chemical determinations in hospital laboratories. The equipment consists of a well-type scintillation counter for radioactive iodine a i d a counting rate nieter. The nieter aiid the cuvette can be kept in the operating room and the electronic amplifier outside. A calibrated syringe is used to inject quantitatively a small amount of radioactive iodinated serum albumin into the patient’s circulation. In 5 to 10 minutes a blood sample is withdrawn froin the patient and placed iii the counter. The amount of blood necessary is 2 to 5 cc., although the determination can be done on less if necessary. In 2 minutes the answer (the patient’s blood volume) is read from a staiidard calibrated chart. The determination of hlood volume can be repeated easily at least 5 times without harmful radiation effects on the patient’s thyroid. The amount of radioactive inaterial einployed would have less effect than the usual dose of radioiodine used for a routine tracer study in the diagnosis of thyroid tlpsiunctioii. The radioactive iodinated sertiiii alliumin can be obtained in lots uf

Chronotropic Effects of Norepinephrine and Tyramine: A System Response Analysis

An analog simulation of the chronotropic effects of norepinephrine and tyramine in the canine heart-lung preparation is presented. The temporal aspects of those responses are described in quantitative terms. Reserpine produced deprivation suprasensitivity to norepinephrine may be considered as a corollary of the system response nonlinearity to that drug. Discrepancies between tyramine rate responses and the relatively small amounts of norepinephrine released are resolved by the assumption that the receptor space for norepinephrine has a capacitative function and is not in free dilutional equilibrium with the perfusing blood. This mechanism would allow for a unitary explanation of tyramine action based upon competition with norepinephrine for available storage sites.