Surgery – Diagnostic testing
Reexamination Certificate
2002-05-09
2004-06-15
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
C600S485000, C600S504000, C600S507000, C600S508000
Reexamination Certificate
active
06749567
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of noninvasive measurement of physiologic parameters in a subject. In particular the present invention relates to a method of noninvasive and non-pulsatile measurement of physiologic fluid parameters as well as a combination of nonpulsatile and pulsatile physiologic parameters for a subject, or patient, which may include any animal with body fluid compartments.
2. Discussion of the Related Art
Known art noninvasive methods have been disclosed for determining physiologic parameters such as arterial blood pressure (U.S. Pat. No. 4,178,918), pulse oximetry (U.S. Pat. No. 3,998,550), and vascular compliance (Shankar, U.S. Pat. Nos. 5,241,963 and 5,724,981) using pulsatile signals acquired from the subject. However, these methods are dependent upon and limited by naturally occurring pulsations in the arteries of the subject.
Other known art noninvasive methods have been disclosed for determination of vascular behaviors by rheoplethysmography (Piquard, U.S. Pat. No. 4,169,463) and determination of blood pressure in the veins and arteries (Blazek et al., U.S. Pat. No. 5,447,161) by observing non-pulsating signals acquired from the subject by a technique known as “venous occlusion plethysmography.” This method relies upon a time-based accumulation of blood in the veins of the subject in order to make the physiologic measurements. However, these methods require that the occlusive device be proximal or downstream from the measuring device along the body region of the subject. Also, these methods further lack the ability to calibrate directly to the subject and rely upon coefficients of standardization, which are characteristic of the healthy vascular operation of a normal limb of the same type as the limb under study. In some instances, these methods are limited to application on fingers and toes.
Cardiovascular System Background
Referencing Table 1 and
FIGS. 1-2
, the functional parts of the cardiovascular system include the heart, the lungs, the arteries, the capillary beds, the veins, and the blood. The cardiovascular system is comprised of two independent vascular circuits, the pulmonary circuit and the systemic circuit. Each vascular circuit has a system of arteries and a system of veins separated by a capillary bed. Blood is primarily a composite of plasma and red blood cells. The human heart is a four-chamber pump organized as a right half and a left half with two sequential pumping chambers in each half. The upper pumping chamber of the heart is called the atria and the lower pumping chamber of the heart is called the ventricle. The atria serve as filling chambers for the ventricles and contract prior to the time of contraction of the ventricle. This difference in time of contraction allows the atria to pre-load the ventricles prior to the ventricular contraction. The ventricles are the primary pumping chamber for each circuit. The right ventricle pumps blood into the pulmonary circuit and the left ventricle pumps blood into the systemic circuit.
Thus, the right half of the heart supplies blood flow to the pulmonary circuit and the left half of the heart supplies blood flow to the systemic circuit. Each circuit returns blood to the other side of the heart through its associated venous system. The pulmonary circuit is composed of the pulmonary arteries, the lungs, and the pulmonary veins. The pulmonary circuit oxygenates the blood in the lungs and returns the oxygenated blood to the left heart to be pumped into the systemic circuit. The systemic circuit, composed of the systemic arteries, the systemic capillary beds, and the systemic veins, supplies oxygenated blood to all areas of the body. The systemic blood flow is then returned to the right heart by the systemic veins.
The Origin of Arterial Pulsations
The heart produces pulsatile blood flow in the arteries by forcing a volume of blood into the aorta during each contraction of the heart. This volume of blood, known as the “stroke volume”, causes an arterial pressure wave to propagate throughout the systemic arteries up to the arterioles (FIG.
1
). The arterioles, which are the smallest arteries in the systemic circuit, have the ability to dynamically vary the resistance to blood flow (Table 1) in response to demands from the end cells of the body. This resistance to blood flow is known as the “peripheral vascular resistance”. The peripheral vascular resistance causes a reduction in arterial blood pressure as the blood flows through the arterioles into the capillary bed as shown in FIG.
2
.
In particular, the arterial blood pressure before the arterioles is highly pulsatile and time variant, while after the arterioles, the arterial blood pressure is primarily steady state, lacking any significant pulsation. Generally, known noninvasive methods of measuring arterial blood pressure, pulse oximetry, and vascular compliance, rely upon the pulsation of arterial blood pressure. As shown in
FIG. 2
, the blood pressures that exist in the capillary beds and veins after the arterioles, is substantially non-pulsatile and therefore does not lend itself for measurement by known noninvasive pulsatile plethysmographic methods. Furthermore, other physiologic attributes such as oxygen saturation of the blood and compliance of the vessel wall in the non-pulsatile vessels cannot be determined by methods that are reliant on arterial pulsations.
Vascular Compliance and Vessel Wall Tension
Blood vessels have elastic walls that stretch in response to the volume of blood contained within them. The degree of elasticity or tension of the vessel wall determines how much pressure is produced within a vessel for a specific amount of blood volume or change in blood volume. The blood vessel wall is an active organ with the ability to vary its compliance, or its inverse, wall tension, as discussed below, dependent on sympathetic nervous stimulation to the vessel.
In arteries of the subject, there is both a steady state and a pulsatile time variant volume of blood in the vessel. This is due to the stroke volume of blood forced into the arteries by each contraction of the heart. The increased stroke volume of blood in the arteries caused by the heartbeat creates pulsatile pressure waves that propagate to a point of extinction within the arterial bed. The actual point of extinction of the pulsatile pressure wave can be dependent upon the physiologic state of the arteries of the subject but is generally thought to be in the small arteries and before the arterioles. The amount of arterial pulse pressure change that occurs during each cardiac cycle is dependent on: the elasticity of the arterial wall, the stroke volume produced by the heartbeat, and the peripheral vascular resistance of the systemic circuit.
The elasticity of the vessel is commonly referred to as the “vascular compliance”. Vascular compliance is defined as the rate of change of volume in the vessel versus the rate of change of pressure within the vessel. The inverse of compliance is called the vessel wall tension. Compliance and tension are in effect a measure of the level of elasticity or stiffness of the vessel wall. The loss of elasticity of the blood vessel wall contributes to the disease state known as hypertension or elevated blood pressure. It has been extensively reported in medical literature that both a thickening of the blood vessel wall (Atherosclerosis) as well as a plaquing of the interior lining of the blood vessel (Arteriosclerosis) contributes to a reduction in blood vessel elasticity and a general increase in arterial blood pressure. Furthermore, pathologies of the sympathetic nervous system and the adrenal medullae have been shown to dramatically affect the tension or compliance of the blood vessel wall.
The compliance of a vein is generally six to eight times greater than the compliance of an artery. Therefore, veins can accept and hold much larger volumes of blood at lower pressures than arteries. The tension of the vein wall and the volume of blood that it is containing regula
Davis Charles L.
Harrison Patrick D.
Hemonix, Inc.
Mallari Patricia C.
Nasser Robert L.
Pauley Petersen & Erickson
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