Vital sign monitor for cufflessly measuring blood pressure using a pulse transit time corrected for vascular index

Abstract

A method and apparatus for measuring a patient's blood pressure featuring the following steps: 1) measuring a time-dependent optical waveform with an optical sensor; 2) measuring a time-dependent electrical signal with an electrical sensor; 3) estimating the patient's arterial properties using the optical waveform; 4) determining a pulse transit time (PTT) from the time-dependent electrical signal and the time-dependent optical waveform; and 5) calculating a blood pressure value using a mathematical model that includes the PTT and the patient's arterial properties.

1 - 20 . (canceled) 
     
     
         21 . A method for measuring a patient's blood pressure with a blood pressure monitor, the method, comprising:
 determining a vascular index (VI) according to the equation VI=(A1+[(b-c-d-e)/a])/A2, where A1 is 1.515, A2 is 0.023, and a, b, c, d, and e are fiduciary features obtained from a time-dependent plethysmography signal measured using an optical sensor disposed on the patient's finger;   determining a first systolic blood pressure using a pulse transit time (PTT) obtained from the first time-dependent plethysmography signal and a time dependent electrical waveform measured using an ECG sensor disposed on the patient's chest;   determining a second systolic blood pressure using the PTT, the VI, and the patient's age.   
     
     
         22 . The method of  claim 21 , wherein a, b, c, d, and e are obtained from the time-dependent plethysmography signal by calculating a second derivative of the time-dependent plethysmography signal and identifying a, b, c, d, and e in the second derivative waveform. 
     
     
         23 . The method of  claim 21 , further comprising determining arterial stiffness for the patient. 
     
     
         24 . The method of  claim 21 , wherein the PTT is obtained by analyzing a first time-dependent feature from the time dependent electrical waveform or a derivative thereof, and a second time-dependent feature from the time-dependent plethysmography signal or a derivative thereof. 
     
     
         25 . The method of  claim 21 , wherein the first time-dependent feature comprises a peak corresponding to a QRS complex. 
     
     
         26 . The method of  claim 25 , wherein the second time-dependent feature comprises a foot in the time-dependent plethysmography signal or a derivative thereof.