Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2000-03-13
2001-11-27
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S538000, C600S561000
Reexamination Certificate
active
06322514
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for determining physiological characteristics produced by the functioning of the heart, such as stroke volume and cardiac output. The method of the present invention may provide absolute, as contrasted to relative, values of these characteristics.
In many instances, such as prior, during, or following major surgery, it is important to determine certain physical characteristics of a patient's heart. For example, it may be necessary or desirable to determine the volume of blood being discharged from the patient's heart. The volume may be expressed as the stroke volume (SV), which is the volume of blood discharged during each contraction or beat of the heart, or the cardiac output (CO), which is the volume of blood discharged over a given period of time, such as a minute. Or, it may be necessary or desirable to know atrial and/or ventricular ejection times in order to assess the contractility of the heart muscle.
The most direct way to measure these quantities is to use a pulmonary artery catheter. Such a catheter is surgically positioned inside the heart in a pulmonary artery catheterization procedure. However, such positioning is a highly invasive, labor intensive procedure which requires a high level of surgical skill and which places a patient at considerable risk. For these reasons, attempts have been made to develop less invasive, or non-invasive, methods for determining the amount of blood discharged from a patient's heart.
Approaches taken to this end include the following. Some methods use changes in the electrical impedance of the thorax, as measured by electrodes placed on the patient's skin to determine cardiac functioning. See U.S. Pat. Nos. 5,782,774; 5,685,316; 5,469,859; 4,870,578; 4,450,527; and 4,437,469. Other methods employ ultrasonic probes. For example, such probes may be placed in the suprastenal notch or in the esophagus to measure blood flow in the aorta. See U.S. Pat. Nos. 5,575,289; 5,085,220; 5,052,395; and WO 98/51212. Another approach is to apply various algorithms to the blood pressure waveform to determine cardiac output. See U.S. Pat. Nos. 5,876,347; 5,647,369; 5,584,298; 5,535,753; 5,390,679; 5,265,615; 5,241,966; 5,183,051; 5,101,828; 5,025,795; 4,676,253; 4,137,910 and WO 97/47236 and Japanese Patent Publication 10-094528. Dye dilution techniques have also been employed in which a dye is injected into the blood stream and a sensor detects the dye concentration in the blood after the dye has passed through the heart. See U.S. Pat. Nos. 5,494,031 and 5,458,128. In a technique, commonly called the Fick method, CO
2
is measured in the air expired by the patient and used to make a determination of the volume of blood discharged by the patient. See U.S. Pat. Nos. 5,836,300 and 5,043,576 and WO 98/26710 and WO 98/12963.
However, a problem with one or more of the foregoing methods is that they may produce inaccurate results due, for example, to the use of less than correct assumptions in deriving an algorithm for determining volumes from the shape of a blood pressure waveform. Further, the methods determine only a relative blood volume value. In order to produce an absolute blood output value, a calibration value obtained by a pulmonary artery catheter is required.
BRIEF SUMMARY OF THE INVENTION
It is, therefore, the object of the present invention to provide an improved method for determining functional characteristics of the heart, such as stroke volume and cardiac output, ejection times and the like.
The method of the present invention can be characterized as non-invasive when contrasted to invasive procedures that require surgical intervention into the heart or a blood vessel of the subject. The method of the present invention may provide absolute, as contrasted to relative, values for the blood volume characteristics.
A further feature of the present invention is that tonometric measurements of partial gas pressure in a hollow organ of the subject may be combined with the determination of cardiac characteristics.
The method of the present invention employs to unique advantage the phenomenon that volumetric changes in the thoracic cavity, such as those accompanying respiration or the beating of the heart, are reflected as pressure changes in other hollow organs of the body, such as the esophagus, stomach, or bladder. In the case of the lungs, volumetric changes occurring during the beating of the heart are reflected as pressure changes in the lungs.
To carry out the method of the present invention, a pressure transducer is placed in the hollow organ. During a sampling interval, the volume of breathing gases supplied to/removed from the lungs of the subject is measured to obtain the incremental quantity of breathing gas &Dgr;V
L
supplied or removed during the interval. The supply or removal of breathing gases alters the volume or size of the lungs in the thoracic cavity. During the same sampling interval, the pressure change in the hollow organ resulting from the change in lung volume &Dgr;VL is also measured, as pressure &Dgr;P
T
, using the pressure transducer. A relationship, or ratio, between volumetric changes in the thoracic cavity and pressure changes in the hollow organ is established as &Dgr;V
L
/&Dgr;P
T
.
The contraction of the heart when discharging blood also comprises a volumetric change in the thorax. In a second sampling interval, the reduction in hollow organ pressure resulting from the contraction of the heart when discharging blood is obtained as P
TH
. Knowing this pressure reduction P
TH
and the relationship between volumetric changes in the thoracic cavity and pressure changes in the hollow organ, as expressed by the relationship &Dgr;V
L
/&Dgr;P
T
, the volumetric reduction in the size of the heart during contraction, and hence its stroke volume, can be quantified as an absolute value by applying the latter to the former. The cardiac output (CO) of the heart can be ascertained by determining and summing the stroke volumes of the heart beats occurring in a given period of time, such as one minute. Ejection times can be measured by analyzing the temporal properties of the reduction in hollow organ pressure resulting from the contraction of the heart.
The pressure measurements in the hollow organs may be obtained with a catheter, filled with gas or liquid, and containing the pressure transducer. Such a catheter may also be used to carry out tonometric measurements in the hollow organ.
Various other features, objects, and advantages of the invention will be made apparent from the following detailed description and the drawing.
REFERENCES:
patent: 4137910 (1979-02-01), Murphy
patent: 4437469 (1984-03-01), Djordjevich et al.
patent: 4450527 (1984-05-01), Sramek
patent: 4643192 (1987-02-01), Fiddian-Green
patent: 4676253 (1987-06-01), Newman et al.
patent: 4870578 (1989-09-01), Vysin et al.
patent: 4893630 (1990-01-01), Bray, Jr.
patent: 5025795 (1991-06-01), Kunig
patent: 5043576 (1991-08-01), Broadhurst et al.
patent: 5052395 (1991-10-01), Burton et al.
patent: 5085220 (1992-02-01), Nudell et al.
patent: 5101828 (1992-04-01), Welkowitz et al.
patent: 5174290 (1992-12-01), Fiddian-Green
patent: 5183051 (1993-02-01), Kraidin et al.
patent: 5186172 (1993-02-01), Fiddian-Green
patent: 5241966 (1993-09-01), Finkelstein et al.
patent: 5265615 (1993-11-01), Frank et al.
patent: 5390679 (1995-02-01), Martin
patent: 5458128 (1995-10-01), Polanyi et al.
patent: 5469859 (1995-11-01), Tsoglin et al.
patent: 5494031 (1996-02-01), Hoeft
patent: 5535753 (1996-07-01), Petrucelli et al.
patent: 5575289 (1996-11-01), Skidmore
patent: 5584298 (1996-12-01), Kabal
patent: 5647369 (1997-07-01), Petrucelli et al.
patent: 5685316 (1997-11-01), Schookin et al.
patent: 5782774 (1998-07-01), Shmulewitz
patent: 5836300 (1998-11-01), Mault
patent: 5876347 (1999-03-01), Chesney et al.
patent: 10-94528 (1998-04-01), None
patent: 97/47236 (1997-12-01), None
patent: 98/12963 (1998-04-01), None
patent: 98/26710 (1998-06-01), None
patent: 98/51212 (1998-11-01), None
paten
Andrus Sceales Starke & Sawall LLP
Instrumentarium Corporation
Nasser Robert L.
Natnithithadha Navin
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