Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1993-04-19
2002-05-14
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S526000
Reexamination Certificate
active
06387052
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermodilution catheter, and more particularly, to a thermodilution catheter having a flexible heating filament disposed therein for applying heat to the patient's blood for purposes of measuring cardiac output, volumetric blood flow, blood pressure, blood volume, blood components and the like.
2. Description of the Prior Art
As is well known, catheters have been developed for purposes of applying physiologic preparations directly into the blood streams of animals or humans or for measuring cardiovascular parameters such as cardiac output, blood pressure, blood volume, blood components and the like. Conventional catheters are made from various materials including plastics and are typically inserted into various body compartments, cavities and vessels to either deliver therapeutic agents, diagnostic agents, or to measure directly various physiologic parameters.
Numerous techniques have been disclosed in the prior art for measuring blood flow using catheters. For example, in U.S. Pat. No. 4,507,974, Yelderman describes a technique for measuring blood flow by applying a stochastic excitation signal to a system inlet and measuring the output signal at a downstream system outlet. The blood flow rate is then extracted by cross-correlating the excitation signal and the measured output signal. The problem addressed by systems of this type is particularly difficult since the physiologic blood vessels are elastic, thereby making classic fluid measuring techniques unacceptably inaccurate. In fact, because the blood vessels are elastic, blood flow cannot be measured unless (1) the physical heart dimensions are measured simultaneously with the blood velocity, (2) a technique is used which is independent of the vessel geometry or (3) a blood velocity technique is used which is calibrated by some other technique. Examples of each of these techniques may be found in the prior art.
For example, a prior art approach for simultaneously measuring blood velocity and vessel geometry is described by Segal in U.S. Pat. Nos. 4,733,669 and 4,869,263 and in an article entitled “Instantaneous and Continuous Cardiac Output Obtained With a Doppler Pulmonary Artery Catheter”,
Journal of the American College of Cardiology
, Vol. 13, No. 6, May 1989, Pages 1382-1392. Segal therein discloses a Doppler pulmonary artery catheter system which provides instantaneous diameter measurements and mapping of instantaneous velocity profiles within the main pulmonary artery from which instantaneous cardiac output is calculated. A similar approach is taught by Nassi et al. in U.S. Pat. No. 4,947,852. A comparable ultrasound technique is disclosed by Abrams, et al. in U.S. Pat. Nos. 4,671,295 and 4,722,347 and in an article entitled “Transtracheal Doppler: A New Procedure for Continuous Cardiac Output Measurement”,
Anesthesiology
, Vol. 70, No. 1, January 1989, Pages 134-138. Abrams et al. therein describe a technique whereby a piezoelectric ultrasound transducer is placed in the trachea of a patient in proximity to the aorta or pulmonary artery so that ultrasound waves may be transmitted toward the path of flow of blood in the artery and reflected waves received. The cross-sectional size of the artery is measured based upon the Doppler frequency difference between the transmitted and received waves. Imaging techniques such as x-ray or radio isotope methods have also been used.
Previous techniques which are geometry independent include an indicator dilution or dye dilution technique of the type first disclosed by Stewart in an article entitled “The Output of the Heart in Dogs”,
American Journal of Physiology
, Vol. 57, 1921, Pages 27-50. Other such geometry independent techniques include a thermodilution technique as first described by Fegler in an article entitled “Measurement of Cardiac Output in Anesthetized Animals by a Thermo-Dilution Method”,
Quarterly Journal of Experimental Physiology
, Vol. 39, 1954, Pages 153-164 and an ionic dilution technique as described by Geddes et al. in U.S. Pat. No. 4,572,206.
On the other hand, prior art techniques for measuring blood velocity which require a secondary calibration technique include a pulse contour technique of the type described by Schreuder, et al. in an article entitled “Continuous Cardiac Output Monitoring During Cardiac Surgery”,
Update In Intensive Care And Emergency Medicine
, Berlin: Springer-Verlag, 1990, Pages 413-416. Another so-called “hot wire” anemometer or heated thermistor technique has been described, for example, by Tanabe, et al. in U.S. Pat. No. 4,841,981 and EP 235811 and by Sekii, et al. in U.S. Pat. No. 4,685,470 and WO 8806426.
The present invention relates to a geometry independent technique, namely, indicator dilution. In conventional indicator dilution techniques, different methods of indicator delivery may be used. For example, Khalil in U.S. Pat. No. 3,359,974 introduces indicator as a step increase and measures the resultant distal temperature change. Newbower, et al., on the other hand, discloses in U.S. Pat. No. 4,236,527 the technique of introducing the indicator as a sinusoid and measuring the distal wave attenuation. In addition, the indicator may be applied as an impulse so that the area under the resultant response may be measured as described by Normann in U.S. Pat. No. 4,576,182. Eggers, et al. in U.S. Pat. No. 4,785,823 similarly provide an impulse, but Eggers, et al. use high frequency energy to provide large heat fluxes to the blood without increasing the filament temperature. In addition, Petre describes in U.S. Pat. No. 4,951,682 an intra-cardiac impedance catheter which measures cardiac output based on changes in the electrical impedance of the blood in the right ventricle. By contrast, as described by Yelderman in the afore-mentioned U.S. Pat. No. 4,507,974, the indicator may be supplied according to a pseudo-random binary sequence and the distal response measured. Cross-correlation can then be performed between the input sequence and the output sequence, and flow is computed based upon the area under the cross-correlation curve. Each of these techniques may provide either an intermittent or a continuous measurement.
Although each of the above-mentioned techniques may use a variety of indicators, heat is the preferred indicator to be used in the clinical environment, for unlike other indicators, heat is conserved in the immediate vascular system but is largely dissipated in the periphery in one circulation time so as to eliminate recirculation and accumulation problems. On the other hand, if cold (negative heat) indicators are used, large amounts of cold may be used, for cold has relatively no deleterious effects on blood and surrounding tissues. However, when cold is used, it must be supplied in a fluid carrier such as saline since cold producing transducers are not readily economical or technically available at present. For example, such a technique is described by Webler in U.S. Pat. No. 4,819,655 and by Williams in U.S. Pat. No. 4,941,475, but the cold-based technique of Webler or Williams has significant clinical limitations in that the circulating fluid must be cooled to near ice temperature prior to input into the catheter and temperature equilibrium established, which takes a significant amount of time. In addition, the enlarged catheter segment containing the cooling elements may restrict blood flow. By contrast, if heat is used, a maximum heat infusion limitation is quickly reached since small increases in heat transducer temperature can have a deleterious effect on blood and local tissue. In fact, it can be inferred from the teachings of Ham et al. in “Studies in Destruction of Red Blood Cells, Chapter IV. Thermal Injury”,
Blood
, Vol. 3, pp. 373-403 (1948), by Ponder in “Shape and Transformations of Heated Human Red Cells”,
J. Exp. Biol.
, Vol. 26, pp. 35-45 (1950) and by Williamson et al. in “The Influence of Temperature on Red Cell Deformability”,
Blood
, Vol. 46, pp. 611-624 (1975), that a maximum safe filament
Quinn Michael D.
Yelderman Mark L.
Edwards Lifesciences Corporation
Nasser Robert L.
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