Blood pressure monitoring method and apparatus

• US 4,802,488 A
• Filed: 01/27/1987
• Issued: 02/07/1989
• Est. Priority Date: 11/06/1986
• Status: Expired due to Term

• Current Assignee: SRI International, Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Eckerle, Joseph S.
• Primary Examiner(s): Jaworski, Francis
• Assistant Examiner(s): MANUEL, GEORGE C
• Application Number:
  US07/007,038
• Time in Patent Office: 742 Days
• Field of Search: 178/672, 178/677-683, 178/687-690
• US Class Current: 600/485
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers

Abstract

Intraarterial blood pressure is measured noninvasively by an electromechanical transducer (22) that includes an array of transducer elements (22-1 through 22-19). The transducer extends across an artery (24) with transducer elements at the ends of the array extending beyond opposite edges of the artery. A set of diastolic and/or systolic pressure and pulse amplitude values is obtained from the outputs from the transducer elements, which values are stored in computer (62). Information concerning the subject related to the diameter of the underlying artery including, for example, the subject'"'"'s age, weight, arm and wrist diameter also is entered into computer (62) through keyboard (64), from which information an estimation of the diameter of the underlying artery is obtained. Using the set of pulse amplitude values, a transducer element at the center of a search area located substantially at the center of the artery is identified. A center of gravity, a two humps and/or a curve fitting method may be used to identify the transducer element at the center of the search area. A group of transducer elements that overlies the artery of estimated diameter then is identified. Using outputs from only said group of transducer elements, one transducer element having a local minimum of one of the diastolic and systolic pressures, relative to the transducer at the center of the search area, is identified, which transducer element is selected for monitoring blood pressure.

Claims

1. A system for the continuous external measurement of blood pressure in an underlying artery of a subject including an array of individual pressure sensitive elements, the length of which array exceeds the diameter of the underlying artery,

means employing outputs from all elements of the array for identifying one element at a center of a region to be searched,

user information input means for entering information concerning the subject related to the diameter of the underlying artery into the system,

means employing said information concerning the subject related to the diameter of the underlying artery for estimating an extent of said region to be searched, and

means responsive to outputs from only those elements within said region for selecting one element having a local minimum of at least one of the diastolic and systolic pressures on a plot of diastolic or systolic pressure versus transducer element number.

2. A system as defined in claim 1 wherein said selecting means comprises means for selecting the one element having a local minimum of diastolic pressure.

3. A system as defined in claim 1 wherein said selecting means comprises means for selecting the one element having a local minimum of systolic pressure.

4. A system as defined in claim 1 wherein said selecting means includes means for selecting the one element that has both a local minimum of diastolic pressure and a local minimum of systolic pressure.

5. A system for continuous external measurement of blood pressure in an underlying artery of a subject including an array of individual pressure sensitive elements, the length of which array exceeds the diameter of the underlying artery,

means employing outputs from all elements of the array for identifying one element at the center of a region to be searched, said means including means for finding the center of gravity of the pulse amplitude values for the transducer elements in the array,

means employing information concerning the subject related to the diameter of the underlying artery for estimating the extent of said region to be searched, and

means responsive to outputs from only those elements within said region for selecting the one element having a local minimum of at least one of the diastolic and systolic pressures on a plot of diastolic or systolic pressure versus transducer element number.

6. A system for continuous external measurement of blood pressure in an underlying artery of a subject including an array of individual pressure sensitive elements, the length of which array exceeds the diameter of the underlying artery,

means employing outputs from all elements of the array for identifying one element at the center of a region to be searched, said means including means for identifying two local maxima of the pulse amplitude values and for identifying the element substantially midway between the two local maxima as the element at the center of the region,

means employing information concerning the subject related to the diameter of the underlying artery for estimating the extent of said region to be searched, and

means responsive to outputs from only those elements within said region for selecting the one element having a local minimum of at least one of the diastolic and systolic pressures on a plot of diastolic or systolic pressure versus transducer element number.

7. A system for continuous external measurement of blood pressure in an underlying artery of a subject including an array of individual pressure sensitive elements, the length of which array exceeds the diameter of the underlying artery,

means employing outputs from all elements of the array for identifying one element at the center of a region to be searched, said means including means for fitting a polynomial of at least second order to the pulse amplitude versus transducer element values and for identifying the point on the graph of the polynomial at which it is maximum as the location of the element at the center of the search region,

means employing information concerning the subject related to the diameter of the underlying artery for estimating the extent of said region to be searched, and

means responsive to outputs from only those elements within said region for selecting the one element having a local minimum of at least one of the diastolic and systolic pressures on a plot of diastolic or systolic pressure versus transducer element number.

8. A system for continuous external measurement of blood pressure is an underlying artery of a subject including an array of individual pressure sensitive elements, the length of which array exceeds the diameter of the underlying artery,

means employing outputs from all elements of the array for identifying one element at the center of a region to be searched,

means employing information concerning the subject related to the diameter of the underlying artery for estimating the extent of said region to be searched, which information includes at least one of the subject'"'"'s sex, age, height, weight, arm diameter and wrist diameter, and

means responsive to outputs from only those elements within said region for selecting the one element having a local minimum of at least one of the diastolic and systolic pressures on a plot of diastolic or systolic pressure versus transducer element number.

9. A system for the continuous external measurement of blood pressure in an underlying artery of a subject comprising,

a pressure sensitive transducer that includes an array of pressure sensitive elements, a group of which elements overlie the artery and with elements extending beyond both edges of the artery, elements of the array producing continuous waveforms which are a function of blood pressure in the underlying artery,

means responsive to outputs from the array for obtaining a set of pulse amplitude values for elements of the array, and

means for selecting one element which is substantially located adjacent the center of the underlying artery, said selecting means including means for finding the center of gravity of the set of pulse amplitude values.

10. A system for continuous external measurement of blood pressure in an underlying artery of a subject comprising,

a pressure sensitive transducer that includes an array of pressure sensitive elements, a group of which elements overlie the artery and with elements extending beyond edges of the artery, elements of the array producing continuous waveforms which are a function of blood pressure in the underlying artery,

means responsive to outputs from the array for obtaining a set of pulse amplitude values for elements of the array, and

means for selecting one element which is substantially located adjacent the center of the underlying artery, said selecting means including means for identifying the two largest local maxima of the set of pulse amplitude values and for identifying the element substantially midway between the two local maxima as the element which is substantially located adjacent the center of the underlying artery.

11. A system for the continuous external measurement of blood pressure in an underlying artery of a subject comprising,

a pressure sensitive transducer that includes an array of pressure sensitive elements, of group of which elements overlie the artery and with elements extending beyond both edges of the artery, elements of the array producing continuous waveforms which are a function of blood pressure in the underlying artery,

means responsive to outputs from the array for obtaining a set of pulse amplitude values for elements of the array, and

means for selecting one element which is substantially located adjacent the center of the underlying artery, said selecting means including means for fitting a polynomial of at least second order to the set of pulse amplitude values, and means for selecting the point on the graph of the polynomial at which it is maximum as the location of the element which is substantially located adjacent the center of the underlying artery.

12. A method for continuous external measurement of blood pressure in an artery of a subject comprising,

positioning a transducer array that includes a plurality of pressure sensitive elements over an underlying artery such that some elements extend beyond both edges of the artery,

employing output from all of the elements, identifying one element at substantially the center of the artery,

based upon information which includes at least one of the subject'"'"'s sex, age, height, weight, arm diameter and wrist diameter, estimating the diameter of the underlying artery and the number of elements in a group thereof which substantially overlie the artery, and

employing outputs from only those elements in said group thereof, selecting for monitoring the one element having a local minimum of at least one of the diastolic and systolic pressures, where "local minimum" refers to a local minimum on the plot of diastolic or systolic pressure versus transducer element number.

13. A method for the continuous external measurement of blood pressure in an artery of a subject comprising,

positioning a transducer array that includes a plurality of pressure sensitive elements over an underlying artery with some elements extending beyond both edges of the artery,

for each element of the array obtaining a pulse amplitude value in response to the output from the element to obtain a set of pulse amplitude values, and

using the center of gravity of the set of pulse amplitude values for identifying one element which is located substantially at the center of the underlying artery.

14. A method for the continuous external measurement of blood pressure in an artery of a subject comprising,

positioning a transducer array that includes a plurality of pressure sensitive elements over an underlying artery with some elements extending beyond both edges of the artery,

for each element of the array obtaining a pulse amplitude value in response to the output from that element to obtain a set of pulse amplitude values,

identifying the two largest local maxima in the set of pulse amplitude values, and

identifying the element substantially midway between these two local maxim as the element located substantially at the center of the underlying artery.

15. A method for the continuous external measurement of blood pressure in an artery of a subject comprising,

positioning a transducer array that includes a plurality of pressures sensitive elements over an underlying artery with some elements extending beyond both edges of the artery,

for each element of the array obtaining a pulse amplitude value in response to the output from that element to obtain a set of pulse amplitude values,

fitting a polynomial of at least second order to the set of pulse amplitude values,

identifying the point on the graph of the polynomial at which pulse amplitude is maximum,

identifying the element nearest the point on the graph of the polynomial at which the polynomial is maximum as being the element which is substantially located adjacent the center of the underlying artery.