Surgery – Truss – Pad
Patent
1989-09-05
1991-09-10
Kamm, William E.
Surgery
Truss
Pad
A61B 5028
Patent
active
050465058
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a cardiac output measuring apparatus for use in a cardiac function inspection or the like.
BACKGROUND ART
Conventionally, the measurement of cardiac output by right heart catheterization, which is performed in a cardiac function inspection, employs the indicator dilution method. This indicator dilution method is classified into three categories: the thermal dilution method in which the cardiac output is obtained by utilizing thermal diffusion, the dye dilution method in which the cardiac output is obtained utilizing variations in the illuminance which are caused by the diffusion of a dye, and the electrolyte dilution method in which the cardiac output is obtained utilizing variations in the resistance caused by the diffusion of an electrolyte. The thermal dilution method will be described below in detail.
In right heart catheterization, a catheter 4 is introduced into the body from the cervical vein, the femoral vein, the basilic vein or the like. The forward end of the catheter passes through the superior vena cava or the inferior vena cava, the right atrium and then the right ventricle, and finally reaches the pulmonary artery, as shown in FIG. 16. The catheter 25 has a injection port 26 and a thermistor 1, which are respectively positioned in the right atrium and in the pulmonary artery when the forward end of the catheter 25 is located within the pulmonary artery. When a liquid having a temperature higher or lower than that of the blood is ejected into the right atrium from the injection port 26, it is diffused in the right atrium and the right ventricle and is diluted by the blood. The temperature of the liquid diluted is detected by the thermistor 27 located within the pulmonary artery to obtain a dilution curve of the temperature detected (which is a graph of the variations in the temperature with time), and the cardiac output is calculated from the area or the like of that dilution curve by the Stewart Hamilton Method using the following equation (1). ##EQU1## where CO is the cardiac output, Si is the specific gravity of the injectate, Ci is the specific heat of the injectate, Vi is the volume of injectate, Ti is the temperature of the injectate, Tb is the temperature of the blood, Sb is the specific gravity of the blood, Cb is the specific heat of the blood, and ##EQU2## is the area of the thermal dilution curve. Calculation of the cardiac output by the Stewart Hamilton Method is known as being relatively accurate. Cardiac output measuring apparatuses which perform measurement on the basis of this method have been available.
However, such a conventional cardiac output measuring apparatus requires a relatively high degree of skill and troublesome operation. Hence, there has been a demand for an apparatus which is simple and easy to use and which ensures accurate measurement. The inventors of this application have studied the measurement of the cardiac output by the dilution method, in particular, the measurement of the cardiac output by the thermal dilution method, and have found the following five problems with the conventional measuring apparatuses.
(i): As can be seen from the above equation, in the thermal dilution method, the volume of the injectate and the temperature thereof greatly affect the accuracy of the calculation. Normally, after the temperature Ti of the liquid has been accurately measured by a thermistor or the like, the catheter 26 is primed and the indicator is then injected into the blood vessel. However, the indicator may be cooled or heated by the body temperature before it enters the blood vessel, causing measurement errors. More specifically, when the indicator having a temperature set to the correct value is injected, the temperature of the liquid is raised or lowered by the body temperature from its initial value at the beginning of the injection, the liquid having substantially its original temperature being injected a certain period of time after the injection has started. This can be the cause of measurement errors, b
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Ikeda Makoto
Sekii Shigekazu
Tsuchida Kouji
Kamm William E.
Pontius Kevin
Terumo Kabushiki Kaisha
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