Blood Pressure

System and method of determining whether to recalibrate a blood pressure monitor

Blood Pressure Abstract
A monitor for determining a patient's physiological parameter includes a calibration device configured to provide a calibration signal representative of the patient's physiological parameter. An exciter is positioned over a blood vessel of the patient for inducing a transmitted exciter waveform into the patient. A noninvasive sensor is positioned over the blood vessel, where the noninvasive sensor is configured to sense a hemoparameter and to generate a noninvasive sensor signal representative of the hemoparameter containing a component of a received exciter waveform. In this context, a hemoparameter is defined as any physiological parameter related to vessel blood such as pressure, flow, volume, velocity, blood vessel wall motion, blood vessel wall position and other related parameters. A processor is configured to determine a relationship between a property of the received exciter waveform and a property of the physiological parameter. The processor is connected to receive the calibration signal and the noninvasive sensor signal, and the processor is configured to process the calibration signal and the noninvasive sensor signal to determine the physiological parameter. In the preferred embodiment, the physiological parameter measured is blood pressure, however, the present invention can also be used to analyze and track other physiological parameters such as vascular wall compliance, strength of ventricular contractions, vascular resistance, fluid volume, cardiac output, myocardial contractility and other related parameters.

Blood Pressure Claims
What is claimed is:

1. A noninvasive blood pressure monitor, comprising:

an input calibration signal from a calibration device configured to provide an accurate representation of the blood pressure of a patient;

an input noninvasive sensor signal from a sensor configured to detect one or more attributes of a perturbation of an artery of the patient; and

a processor which determines when to employ the input calibration signal to recalibrate one or more of a plurality of parameters, wherein the processor uses the plurality of parameters and the input noninvasive sensor signal to continuously calculate the blood pressure of the patient,

wherein the one or more parameters comprise a combination of values of a pressure-volume relationship and a trigger parameter.

2. The noninvasive blood pressure monitor of claim 1, wherein the trigger parameter comprises a dispersion parameter.

3. The noninvasive blood pressure monitor of claim 1, wherein the trigger parameter comprises an attenuation parameter.

4. A monitor for determining a physiological parameter of a patient comprising:

a calibration device configured to provide a calibration signal representative of one of a patient's physiological parameters;

an exciter adapted to be positioned over a blood vessel of the patient and configured to induce a transmitted exciter waveform into the patient;

a noninvasive sensor adapted to be positioned over said blood vessel and configured to sense a hemoparameter and to generate a noninvasive sensor signal representative of said hemoparameter containing a component of a received exciter waveform;

a processor configured to determine a relationship between a property of said received exciter waveform and a property of said physiological parameter;

wherein said processor includes a filter configured to separate a signal exciter waveform component of said received exciter waveform from at least one other component of said received exciter waveform;

wherein said processor is connected to receive said calibration signal and said noninvasive sensor signal and is configured to determine said physiological parameter based at least in part on said calibration signal, said signal exciter waveform component, and said relationship;

wherein said processor is configured to determine the validity of said calibration signal and to initiate a calibration when said calibration signal is not valid;

wherein said processor employs an Internal Consistency Analysis (ICA) technique to determine when said calibration signal is not valid; and

wherein said ICA technique includes determining a plurality of parameters and comparing the parameters over time to a predetermined threshold to determine when said calibration signal is not valid.

5. A monitor for determining a physiological parameter of a patient comprising:

a calibration device configured to provide a calibration signal representative of one of a patient's physiological parameters;

an exciter adapted to be positioned over a blood vessel of the patient and configured to induce a vibrational transmitted exciter waveform into the patient;

a noninvasive sensor adapted to be positioned over said blood vessel and configured to sense a hemoparameter and to generate a noninvasive sensor signal representative of said hemoparameter containing a component of a received exciter waveform;

a processor configured to determine a relationship between a property of said received exciter waveform and a property of said physiological parameter;

wherein said processor includes a filter configured to separate a component of said noninvasive sensor signal having a phase that varies with blood pressure from at least one other component of said noninvasive sensor signal having a phase that does not so vary;

wherein said processor is connected to receive said calibration signal and said noninvasive sensor signal and is configured to determine said physiological parameter based at least in part on said calibration signal, said component having a phase that varies with blood pressure, and said relationship;

wherein said processor is configured to determine the validity of said calibration signal and to initiate a calibration when said calibration signal is not valid;

wherein said processor employs an Internal Consistency Analysis (ICA) technique to determine when said calibration signal is not valid; and

wherein said ICA technique includes determining a plurality of parameters and comparing the parameters over time to a predetermined threshold to determine when said calibration signal is not valid.

6. A monitor for determining a physiological parameter of a patient, comprising:

a calibration device configured to provide a calibration signal representative of one of a patient's physiological parameters;

at least one exciter adapted to be positioned over a blood vessel of the patient and configured to induce a plurality of different frequency transmitted exciter waveforms into the patient;

a noninvasive sensor adapted to be positioned over said blood vessel and configured to sense a hemoparameter and to generate a noninvasive sensor signal representative of said hemoparameter containing components of a plurality of different frequency received exciter waveforms;

a processor configured to determine a relationship between a property of one of said received exciter waveforms and a property of said physiological parameter;

wherein said processor is connected to receive said calibration signal and said noninvasive sensor signal and is configured to determine said physiological parameter based at least in part on said calibration signal, said noninvasive sensor signal and said relationship;

wherein said processor is configured to determine the validity of said calibration signal and to initiate a calibration when said calibration signal is not valid;

wherein said processor employs an Internal Consistency Analysis (ICA) technique to determine when said calibration signal is not valid; and

wherein said ICA technique includes determining a plurality of parameters and comparing the parameters over time to a predetermined threshold to determine when said calibration signal is not valid.

7. A method for determining a physiological parameter of a patient comprising:

providing a calibration signal representative of one of a patient's physiological parameters and storing the calibration signal;

inducing a transmitted exciter waveform into the patient;

noninvasively sensing a hemoparameter and generating a noninvasive sensor signal representative of said hemoparameter containing a component of a received exciter waveform; and

processing said noninvasive sensor signal including the steps of:

(a) determining a relationship between a property of said received exciter waveform and a property of said physiological parameter;

(b) separating a signal exciter waveform component of said received exciter waveform, from at least one other component of said received exciter waveform;

(c) determining said physiological parameter based at least in part on said calibration signal, said signal exciter waveform component, and said relationship;

wherein processing said noninvasive sensor signal also includes the step of determining the validity of said calibration signal and initiating said step of providing a calibration signal when said calibration signal is not valid;

wherein said processing includes employing an Internal Consistency Analysis (ICA) technique to determine when said calibration signal is not valid; and

wherein said ICA technique includes determining a plurality of parameters and comparing the parameters over time to a predetermined threshold to determine when said calibration signal is not valid.

8. A method for determining a physiological parameter of a patient comprising:

providing a calibration signal representative of one of a patient's physiological parameters and storing the calibration signal;

inducing a vibrational transmitted exciter waveform into the patient;

noninvasively sensing a hemoparameter and generating a noninvasive sensor signal representative of said hemoparameter containing a component of a received exciter waveform; and

processing said noninvasive sensor signal including the steps of:

(a) determining a relationship between a property of said received exciter waveform and a property of said physiological parameter;

(b) separating a signal exciter waveform component of said noninvasive sensor signal having a phase that varies with blood pressure, from at least one other component of said noninvasive sensor signal having a phase that does not so vary;

(c) determining said physiological parameter based at least in part on said calibration signal, said component having a phase that varies with blood pressure, and said relationship;

wherein processing said noninvasive sensor signal also includes the step of determining the validity of said calibration signal and initiating said step of providing a calibration signal when said calibration signal is not valid;

wherein said processing includes employing an Internal Consistency Analysis (ICA) technique to determine when said calibration signal is not valid; and

wherein said ICA technique includes determining a plurality of parameters and comparing the parameters over time to a predetermined threshold to determine when said calibration signal is not valid.

9. A method of determining a physiological parameter of a patient, comprising the steps of:

providing a calibration signal representative of one of a patient's physiological parameters and storing the calibration signal;

inducing a plurality of different frequency transmitted exciter waveforms into the patient;

noninvasively sensing a hemoparameter and generating a noninvasive sensor signal representative of said hemoparameter containing components of a plurality of different frequency received exciter waveforms;

processing said noninvasive sensor signal including the steps of:

(a) determining a relationship between a property of one of said received exciter waveforms and a property of said physiological parameter;

(b) determining said physiological parameter based at least in part on said calibration signal, said noninvasive sensor signal and said relationship;

wherein processing said noninvasive sensor signal also includes the step of determining the validity of said calibration signal and initiating said step of providing a calibration signal when said calibration signal is not valid;

wherein said processing includes employing an Internal Consistency Analysis (ICA) technique to determine when said calibration signal is not valid; and

wherein said ICA technique includes determining a plurality of parameters and comparing the parameters over time to a predetermined threshold to determine when said calibration signal is not valid.

Blood Pressure Description
FIELD

The present invention relates to an apparatus and method for noninvasively providing a determination of a patient's physiological parameter and other clinically important parameters.

BACKGROUND

Blood pressure is the force within the arterial system of an individual that ensures the flow of blood and delivery of oxygen and nutrients to the tissue. Prolonged reduction or loss of pressure severely limits the amount of tissue perfusion and could therefore result in damage to or even death of the tissue. Although some tissues can tolerate hypoperfusion for long periods of time, the brain, heart and kidneys are very sensitive to a reduction in blood flow. Thus, during and after surgery, blood pressure is a frequently monitored vital sign. Blood pressure is affected, during and after surgery, by the type of surgery and physiological factors such as the body's reaction to the surgery. Moreover, blood pressure is manipulated and controlled, during and after surgery, using various medications. Often, these physiological factors and the given medications can result in a situation of rapidly changing blood pressure requiring immediate blood pressure measurement, and corrective action.

Because of changes in the patient's blood pressure, constant monitoring is important. The traditional method of measuring blood pressure is with a stethoscope, occlusive cuff and pressure manometer. However, this technique is slow, subjective in nature, requires the intervention of a skilled clinician and does not provide timely readings frequently required in critical situations.

For these reasons, two methods of measuring blood pressure have been developed: noninvasive, intermittent methods that use an automated cuff device such as an oscillometric cuff; and invasive, continuous (beat-to-beat) measurements that use a catheter.

The oscillometric cuff method typically requires 15 to 45 seconds to obtain a measurement, and should allow sufficient time for venous recovery. Thus, at best there is typically 1/2 to 1 minute between updated pressure measurements. This is an inordinately long amount of time to wait for an updated pressure reading when fast acting medications are administered. Also, too frequent cuff inflations over extended periods may result in ecchymosis and/or nerve damage in the area underlying the cuff. The invasive method has inherent disadvantages including risk of embolization, infection, bleeding and vessel wall damage.

To address the need for continuous, noninvasive blood pressure measurement, several systems were developed. One approach relies on blood pressure values in a patient's finger as indicative of the patient's central blood pressure, as in the cases of Penaz, U.S. Pat. No. 4,869,261 and H. Shimazu, Vibration Techniques for Indirect Measurement of Diastolic Arterial Pressure in Human Fingers, Med. and Biol. Eng. and Comp., vol. 27, no. 2, p. 130