Dynamic cardiovascular monitor

Details Dynamic cardiovascular monitor Dynamic cardiovascular monitor

2000-04-14

2003-11-11

Layno, Carl (Department: 3762)

Surgery

Diagnostic testing

Cardiovascular

C600S485000

Reexamination Certificate

active

06647287

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to medical diagnostic and monitoring systems. More specifically, this invention is directed to a system and method for reconstructing an aortic blood pressure waveform using a model that is adapted to a specific subject.
2. Description of Related Art
Arterial blood pressure and heart rate are the principal variables used by medical personnel to assess and monitor cardiovascular function and identify adverse cardiovascular events. Such events include tachycardia, bradycardia, arrhythmias, hemorrhage and myocardial ischemia, among others. Ideally, medical personnel would continuously monitor the blood pressure at the root of the aorta, which is the primary driving source for blood flow throughout the body. As illustrated in
FIG. 1
, blood pressure is produced by the contraction of the heart
1
, which ejects a volume of blood into the ascending aorta
2
. The aorta
2
distributes the blood to the large arteries of the body, which in turn continually branch into smaller arteries to deliver the blood to the capillaries where oxygen and nutrients are delivered to the tissue. One of these branches is the left subclavian artery
3
, which carries blood to the brachial artery
4
in the upper arm. The brachial artery divides into the radial artery
5
and the ulnar artery
6
, which then rejoin in the hand from which the five digital arteries
7
emanate to supply the small arteries and capillaries
8
of the fingers.
Except in very special cases when insertion of a catheter into the aorta
2
is warranted for diagnostic purposes, blood pressure measurements are conducted in arteries located some distance from the heart. The most common blood pressure monitoring sites are the brachial artery, radial artery, and finger as illustrated in FIG.
1
.
A wide range of patient monitoring devices has been developed for monitoring the blood pressure of patients. Patient monitors usually operate by methods and include devices that measure, analyze and display the electrocardiogram (ECG), intermittent non-invasive blood pressure (NIBP) measurement using a cuff, transcutaneous blood oxygen saturation (SpO2) measurement, continuous direct blood pressure (A-line) measurement, and, in some monitors, non-invasive continuous blood pressure measurement using tonometers.
NIBP monitors take blood pressure measurements periodically and provide numerical values for systolic blood pressure (SBP), mean aortic blood pressure (MBP), and diastolic blood pressure (DBP). When continuous blood pressure measurement is needed, it is continuously monitored with fluid-filled catheters connected to external pressure transducers. The catheter is normally placed in a peripheral vessel such as the radial artery. Continuous blood pressure monitoring can also be performed with tonometers that non-invasively monitor the pressure in a peripheral artery, e.g., the radial artery. (see, Kenmotsu, O., M. Ueda, H. Otsuka, T. Yamamura, D. C. Winter, and J. T. Eckerle, “Arterial Tonometry for Noninvasive, Continuous Blood Pressure Monitoring During Anesthesia,” Anesthesiology, 1991, Vol. 75, pp 333-340, incorporated herein by reference in its entirety). Other methods have been reported in the literature that are able to provide continuous measurements and recording of the blood pressure in peripheral vessels in the arms and legs. (see, Meyer-Sabellek, W., Schulte, K. L., and Gotzen, R., “Non-invasive Ambulatory Blood Pressure Monitoring: Technical Possibilities and Problems,” Journal of Hypertension, 1990, Vol. 8 (Suppl. 6), pp S3-S10, and Nielson, P. E., and Rasmussen, S. M., “Indirect Measurement of Systolic Blood Pressure by Strain Gage Technique at Finger, Ankle, and Toe in Diabetic Patients without Symptoms of Occlusive Arterial Disease,” Diabetologia, 1973, Vol. 9, pp 25-29, incorporated herein by reference in their entireties).
However, it is well known that the actual blood pressure in peripheral arteries is different than that at the root of the aorta. (see, MacDonald, D. A., “Blood Flow in Arteries,” London, Edward Arnold, 1960, and O'Rourke, Michael F., Raymond P. Kelly, and Alberto P. Avolio,
The Arterial Pulse,
Philadelphia & London, Lea & Febiger, 1992, both incorporated herein by reference in their entireties).
The MBP decreases slightly as the blood passes from the aorta through the large arteries to the smaller diameter, aortic and radial branches of the arterial tree. As shown in
FIG. 1
, the pulse pressure increases in amplitude as it passes through the aortic to radial arterial branches after which it begins to decrease in amplitude. (see, Fung, Y. C.,
Biodynamics: Circulation,
Spinger-Verlag, New York, Berlin, Heidelberg, Tokyo, 1984, p.134, incorporated by reference in its entirety). The increase in pulse pressure, or amplification, usually exceeds the small drop in mean blood pressure resulting in an increase in the systolic (maximum) pressure and a smaller magnitude decrease in the diastolic (minimum) pressure. In addition, the shape of the arterial pulse waveform is altered as it passes from the aorta to the periphery. As a result, the pressures measured at peripheral sites may not accurately represent the pressure at the root of the aorta. These amplifications and alterations of the waveform shape have been widely studied and reported by a number of investigators. These changes are caused by the compliant nature of the blood vessels, the terminal impedance of each arterial branch, and wave reflections produced at bifuircations. (see, Taylor, M. G. “Wave Travel in Arteries and the Design of the Cardiovascular System.” In Pulsatile Blood Flow, ed. Attinger, E. O., McGraw Hill, N.Y., 1964, pp 343-367, incorporated by reference in its entirety).
Modeling studies have taken three approaches to identifying change in an arterial pulse as the pulse propagates.
A first conventional approach has been to develop mathematical descriptions of the physical structure of the vascular system. These models have taken the form of collections of tubes of varying complexity, (see, Taylor, M. G. “The Input Impedance of an Assembly of Randomly Branching Elastic Tubes,” Biophysical Journal, Vol. 6, 1966, pp 29-51 and Avolio, A. P. “Multi-branched Model of the Human Arterial System,” Medical & Biological Engineering & Computing, Vol. 18, November 1980, pp 709-718, incorporated by reference in their entireties) and lumped parameter models. (see, Taylor, M. G. “An Experimental Determination of the Propagation of Fluid Oscillations in a Tube with a Visco-elastic Wall; Together with an Analysis of the Characteristics Required in an Electrical Analogue,” Physics in Medicine and Biology, Vol. 4, 1959, pp 62-82, and Ocasio, Wendell C., David R. Rigney, Kevin P. Clark, and Roger G. Mark, “bpshape_wk4: A Computer Program that Implements a Physiological Model for Analyzing the Shape of Blood Pressure Waveforms,” Computer Methods and Programs in Biomedicine, Vol. 39 (1993) pp. 169-194, both incorporated by reference in their entireties). Measurements of the cardiovascular system (e.g., vessel dimensions, tissue elasticities, etc.) are then used to develop the coefficients of the model equations. Using the model equations, the approach is able to determine characteristics of the cardiovascular system by modeling the aortic pulse at the aorta root using the characteristics of the aorta pulse at the peripherial artery.
However, this approach is severely limited because of the complexity of the vascular system and the number of parameters that must be known. Most importantly, the cardiovascular system is non-linear and its physical properties vary depending upon the patient's physiological state at the time of measurement.
A second conventional approach uses lumped parameter elements that represent the major resistive and reactive elements of the vascular system. (see, Strano, Joseph J., Walter Welkowitz, and Sylvan Fich, “Measurement and Utilization of In Vivo Blood-Pressure Transfer Functions of Dog and Chicken Aortas,” IEEE Transactions on Biomedical Engi

Affiliated with

Also associated with

Rating

Dynamic cardiovascular monitor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Dynamic cardiovascular monitor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dynamic cardiovascular monitor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3183249