Automatic method for measuring and processing blood pressure

Abstract

The present invention concerns an automatic method, as well as the related system and the tools allowing the same to be executed, for measuring and processing blood pressure starting from a detected pressure signal, the method operating in the time domain for discriminating whether the detected signal is an adequate measurement or not and, where it is not, time domain analysis automatically selects a low-pass filter to, possibly iteratively, apply to the detected pressure signal for having correct values and wave form of the blood pressure.

1 - 13 . (canceled) 
     
     
         14 . Automatic method for measuring and processing blood pressure comprising the following steps:
 A. having a sampled detected pressure signal P(t) for one or more heart beats, each heart beat starting at an initial instant coinciding with the one of the initial diastolic pressure point and ending at a final instant coinciding with the one of the subsequent diastolic pressure point and comprising a dicrotic point, each beat having a systolic phase going from the initial diastolic point to the dicrotic point; and   B. automatically analysing and discriminating morphology of the pressure signal P(t) sampled for each heart beat, determining instant and pressure value of one or more characteristic points of the pressure signal P(t) selected from the group comprising
 an initial diastolic pressure point, 
 a systolic pressure point, 
 a dicrotic point, and 
 one or more resonance points, each one of which occurs in an instant wherein a second derivative d 2 P/dt 2  of the pressure signal P(t) has a local maximum, 
 at least one characteristic point of the pressure signal P(t) belonging to the systolic phase of the heart beat under consideration and being different from the initial diastolic pressure point; 
   C. for each heart beat, determining an energy efficiency RES through the following sub-steps:
 C.1 determining a direct dynamic impedance Z d     —     D (t) for each one of said one or more characteristic points belonging to the systolic phase of the heart beat under consideration and different from the initial diastolic pressure point, said direct dynamic impedance Z d     —     D (t) being equal to the ratio between a value of the pressure signal P(t) at the characteristic point and the distance of the respective time instant from the initial instant of the heart beat under consideration, and determining an impedance Z D  of a direct wave of pressure by summing with alternate signs the values of the direct dynamic impedances Z d     —     D (t) ordered according to a direct time order starting from the initial instant of the heart beat under consideration up to the dicrotic point instant, beginning to apply a positive sign to the direct dynamic impedance Z d     —     D (t) that is the first one in the direct time order; 
 C.2 determining a reflected dynamic impedance Z d     —     R (t) for each one of said one or more characteristic points, said reflected dynamic impedance Z d     —     R (t) being equal to the ratio between a value of the pressure signal P(t) at the characteristic point and the distance of the respective time instant from the final instant of the heart beat under consideration, and determining an impedance Z R  of reflected waves of pressure by summing with alternate signs the values of the reflected dynamic impedances Z d     —     R (t) ordered according to a reverse time order starting from the final instant down to the initial instant of the heart beat under consideration, beginning to apply a positive sign to the reflected dynamic impedance Z d     —     R (t) that is the first one in the reverse time order; 
 C.3 determining said energy efficiency RES as ratio between the impedance Z D  of the direct wave and the impedance Z R  of the reflected waves:
   RES= Z   D   /Z   R    
 
   D. for said energy efficiency RES determined in step C, checking whether a first derivative dP/dt of the pressure signal P(t) is lower than a first value T d  of maximum threshold in the whole heart beat under consideration and whether the second derivative d 2 P/dt 2  of the pressure signal P(t) is lower than a second value T d2  of maximum threshold in the whole heart beat under consideration, and in the case where the check has negative outcome making step E, otherwise, in the case where the check has positive outcome, making step F;   E. selecting a cutoff frequency of a low-pass filter on the basis of said energy efficiency RES determined in step C, of the first derivative dP/dt and of the second derivative d 2 P/dt 2  of the pressure signal P(t), and applying said low-pass filter to the pressure signal P(t), thus obtaining a new sampled pressure signal, and returning to execute the preceding steps starting from step B;   F. outputting the pressure signal P(t) on which step B has been made for the last time.   
     
     
         15 . Method according to  claim 14 , wherein said one or more resonance points are determined in step B through the following sub-steps:
 B.2 determining a total number N dP     —     max  of local maximum points of the first derivative dP/dt of the pressure signal P(t) in the heart beat under consideration;   B.3 determining local maximum points of the second derivative d 2 P/dt 2  of the pressure signal P(t) in the heart beat under consideration; and   B.4 selecting a number N dP     —     max  of local maximum points of the second derivative d 2 P/dt 2  having largest values, determining N dP     —     max  time instants t d2P     —     max (i) wherein said N dP     —     max  selected local maximum points of the second derivative d 2 P/dt 2 , occur, and assuming the points of the pressure signal P(t) in such N dP     —     max  instants t d2P     —     max (i) as resonance points.   
     
     
         16 . Method according to  claim 14 , wherein, in step B, the following characteristic points of the pressure signal P(t) are determined:
 the initial diastolic pressure point,   the systolic pressure point,   the dicrotic point, and   one or more resonance points.   
     
     
         17 . Method according to  claim 14 , wherein the first value T d  of maximum threshold and the second value T d2  of maximum threshold are functions of said energy efficiency RES determined in step C. 
     
     
         18 . Method according to  claim 14 , wherein, in step D, it is checked whether said energy efficiency RES determined in step C belongs to one of three or more adjacent ranges of variability. 
     
     
         19 . Method according to  claim 18 , wherein, in step E, said cutoff frequency is selected by
 discriminating the belonging of said energy efficiency RES determined in step C to one of three or more adjacent ranges of variability,
 for each one of said three or more adjacent ranges of variability of said energy efficiency RES determined in step C, discriminating the belonging of the first derivative dP/dt of the pressure signal P(t) in the whole heart beat under consideration to one of three or more adjacent ranges of variability, and
 for each one of said three or more adjacent ranges of variability of the first derivative dP/dt of the pressure signal P(t) in the whole heart beat under consideration, discriminating the belonging of the second derivative d 2 P/dt 2  of the pressure signal P(t) to one of three or more non overlapping ranges of variability, to which a respective value of said cutoff frequency corresponds. 
 
   
     
     
         20 . Method according to  claim 14 , wherein said cutoff frequency has a value decreasing upon increasing the first derivative dP/dt of the pressure signal P(t), under identical values of said energy efficiency RES and of the second derivative d 2 P/dt 2  of the pressure signal P(t). 
     
     
         21 . Method according to  claim 14 , wherein said cutoff frequency has a value decreasing upon increasing the second derivative d 2 P/dt 2  of the pressure signal P(t), under identical values of said energy efficiency RES and of the first derivative dP/dt of the pressure signal P(t). 
     
     
         22 . Method according to  claim 14 , wherein said cutoff frequency ranges from 0.5 Hz to 100 Hz. 
     
     
         23 . Method according to  claim 14 , wherein in step F the pressure signal P(t) is displayed on a display. 
     
     
         24 . Automatic apparatus for measuring and processing blood pressure comprising processing means capable to perform the steps of an automatic method for measuring and processing blood pressure comprising the following steps:
 A. having a sampled detected pressure signal P(t) for one or more heart beats, each heart beat starting at an initial instant coinciding with the one of the initial diastolic pressure point and ending at a final instant coinciding with the one of the subsequent diastolic pressure point and comprising a dicrotic point, each beat having a systolic phase going from the initial diastolic point to the dicrotic point; and   B. automatically analysing and discriminating morphology of the pressure signal P(t) sampled for each heart beat, determining instant and pressure value of one or more characteristic points of the pressure signal P(t) selected from the group comprising
 an initial diastolic pressure point, 
 a systolic pressure point, 
 a dicrotic point, and 
 one or more resonance points, each one of which occurs in an instant wherein a second derivative d 2 P/dt 2  of the pressure signal P(t) has a local maximum, 
 at least one characteristic point of the pressure signal P(t) belonging to the systolic phase of the heart beat under consideration and being different from the initial diastolic pressure point; 
   C. for each heart beat, determining an energy efficiency RES through the following sub-steps:
 C.1 determining a direct dynamic impedance Z d     —     D (t) for each one of said one or more characteristic points belonging to the systolic phase of the heart beat under consideration and different from the initial diastolic pressure point, said direct dynamic impedance Z d     —     D (t) being equal to the ratio between a value of the pressure signal P(t) at the characteristic point and the distance of the respective time instant from the initial instant of the heart beat under consideration, and determining an impedance Z D  of a direct wave of pressure by summing with alternate signs the values of the direct dynamic impedances Z d     —     D (t) ordered according to a direct time order starting from the initial instant of the heart beat under consideration up to the dicrotic point instant, beginning to apply a positive sign to the direct dynamic impedance Z d     —     D (t) that is the first one in the direct time order; 
 C.2 determining a reflected dynamic impedance Z d     —     R (t) for each one of said one or more characteristic points, said reflected dynamic impedance Z d     —     R (t) being equal to the ratio between a value of the pressure signal P(t) at the characteristic point and the distance of the respective time instant from the final instant of the heart beat under consideration, and determining an impedance Z R  of reflected waves of pressure by summing with alternate signs the values of the reflected dynamic impedances Z d     —     R (t) ordered according to a reverse time order starting from the final instant down to the initial instant of the heart beat under consideration, beginning to apply a positive sign to the reflected dynamic impedance Z d     —     R (t) that is the first one in the reverse time order; 
 C.3 determining said energy efficiency RES as ratio between the impedance Z D  of the direct wave and the impedance Z R  of the reflected waves:
   RES= Z   D   /Z   R    
 
   D. for said energy efficiency RES determined in step C, checking whether a first derivative dP/dt of the pressure signal P(t) is lower than a first value T d  of maximum threshold in the whole heart beat under consideration and whether the second derivative d 2 P/dt 2  of the pressure signal P(t) is lower than a second value T d2  of maximum threshold in the whole heart beat under consideration, and in the case where the check has negative outcome making step E, otherwise, in the case where the check has positive outcome, making step F;   E. selecting a cutoff frequency of a low-pass filter on the basis of said energy efficiency RES determined in step C, of the first derivative dP/dt and of the second derivative d 2 P/dt 2  of the pressure signal P(t), and applying said low-pass filter to the pressure signal P(t), thus obtaining a new sampled pressure signal, and returning to execute the preceding steps starting from step B;   F. outputting the pressure signal P(t) on which step B has been made for the last time.   
     
     
         25 . Computer-readable memory medium, having a program stored therein, wherein the program is adapted to perform, when operating on processing means of an apparatus, the following steps of an automatic method for measuring and processing blood pressure:
 the following steps:   A. having a sampled detected pressure signal P(t) for one or more heart beats, each heart beat starting at an initial instant coinciding with the one of the initial diastolic pressure point and ending at a final instant coinciding with the one of the subsequent diastolic pressure point and comprising a dicrotic point, each beat having a systolic phase going from the initial diastolic point to the dicrotic point; and   B. automatically analysing and discriminating morphology of the pressure signal P(t) sampled for each heart beat, determining instant and pressure value of one or more characteristic points of the pressure signal P(t) selected from the group comprising
 an initial diastolic pressure point, 
 a systolic pressure point, 
 a dicrotic point, and 
 one or more resonance points, each one of which occurs in an instant wherein a second derivative d 2 P/dt 2  of the pressure signal P(t) has a local maximum, 
 at least one characteristic point of the pressure signal P(t) belonging to the systolic phase of the heart beat under consideration and being different from the initial diastolic pressure point; 
   C. for each heart beat, determining an energy efficiency RES through the following sub-steps:
 C.1 determining a direct dynamic impedance Z d     —     D (t) for each one of said one or more characteristic points belonging to the systolic phase of the heart beat under consideration and different from the initial diastolic pressure point, said direct dynamic impedance Z d     —     D (t) being equal to the ratio between a value of the pressure signal P(t) at the characteristic point and the distance of the respective time instant from the initial instant of the heart beat under consideration, and determining an impedance Z D  of a direct wave of pressure by summing with alternate signs the values of the direct dynamic impedances Z d     —     D (t) ordered according to a direct time order starting from the initial instant of the heart beat under consideration up to the dicrotic point instant, beginning to apply a positive sign to the direct dynamic impedance Z d     —     D (t) that is the first one in the direct time order; 
 C.2 determining a reflected dynamic impedance Z d     —     R (t) for each one of said one or more characteristic points, said reflected dynamic impedance Z d     —     R (t) being equal to the ratio between a value of the pressure signal P(t) at the characteristic point and the distance of the respective time instant from the final instant of the heart beat under consideration, and determining an impedance Z R  of reflected waves of pressure by summing with alternate signs the values of the reflected dynamic impedances Z d     —     R (t) ordered according to a reverse time order starting from the final instant down to the initial instant of the heart beat under consideration, beginning to apply a positive sign to the reflected dynamic impedance Z d     —     R (t) that is the first one in the reverse time order; 
 C.3 determining said energy efficiency RES as ratio between the impedance Z D  of the direct wave and the impedance Z R  of the reflected waves:
   RES= Z   D   /Z   R    
 
   D. for said energy efficiency RES determined in step C, checking whether a first derivative dP/dt of the pressure signal P(t) is lower than a first value T d  of maximum threshold in the whole heart beat under consideration and whether the second derivative d 2 P/dt 2  of the pressure signal P(t) is lower than a second value T d2  of maximum threshold in the whole heart beat under consideration, and in the case where the check has negative outcome making step E, otherwise, in the case where the check has positive outcome, making step F;   E. selecting a cutoff frequency of a low-pass filter on the basis of said energy efficiency RES determined in step C, of the first derivative dP/dt and of the second derivative d 2 P/dt 2  of the pressure signal P(t), and applying said low-pass filter to the pressure signal P(t), thus obtaining a new sampled pressure signal, and returning to execute the preceding steps starting from step B;   F. outputting the pressure signal P(t) on which step B has been made for the last time.   
     
     
         26 . Method according to  claim 18 , wherein, in step D, the adjacent ranges of variability to which it is checked whether said energy efficiency RES determined in step C belongs are four adjacent ranges of variability. 
     
     
         27 . Method according to  claim 18 , wherein the first value T d  of maximum threshold and the second value T d2  of maximum threshold are functions of the range to which said energy efficiency RES determined in step C belongs. 
     
     
         28 . Method according to  claim 19 , wherein, in step E, the adjacent ranges of variability to which the belonging of said energy efficiency RES determined in step C is discriminated are four adjacent ranges of variability. 
     
     
         29 . Method according to  claim 19 , wherein, in step E, the adjacent ranges of variability to which the belonging of the first derivative dP/dt of the pressure signal P(t) in the whole heart beat under consideration is discriminated are six adjacent ranges of variability. 
     
     
         30 . Method according to  claim 19 , wherein, in step E, the non overlapping ranges of variability to which the belonging of the second derivative d 2 P/dt 2  of the pressure signal P(t) is discriminated are four non overlapping ranges of variability. 
     
     
         31 . Method according to  claim 22 , wherein said cutoff frequency ranges from 2 Hz to 80 Hz. 
     
     
         32 . Method according to  claim 31 , wherein said cutoff frequency ranges from 3 Hz to 60 Hz.