Integrated flexible sensor for blood pressure measurements
Embodiments are directed to a blood pressure measurement device including a cuff that is operative to wrap around a limb of a user, a bladder coupled to the cuff and operative to compress the limb of the user when inflated, and a piezoelectric sensor coupled to the cuff and operative to detect blood flow through the limb of the user and output a signal indicative of the blood flow. The blood pressure measurement device can also include a processor coupled with the piezoelectric sensor that is operative to filter the signal to isolate sounds corresponding to changes in the blood flow through the limb due to inflation of the bladder, correlate the isolated sounds with a pressure inside the bladder, and determine a blood pressure of the user at least partially based on correlating the isolated sounds with the pressure.
1 . A blood pressure measurement device comprising:
a flexible cuff operative to wrap around a limb of a user;
a bladder coupled to the flexible cuff and configured to be secured to the limb of the user by the flexible cuff, the bladder operative to compress the limb of the user during inflation and decompress the limb during deflation;
a flexible piezoelectric sensor coupled to the flexible cuff and laterally positioned entirely between a lower edge of the bladder and a lower edge of the cuff, the flexible piezoelectric sensor defining an elongated strip that extends along the flexible cuff and is configured to conform to and at least partially encircle the limb of the user when the flexible cuff is wrapped around the limb of the user, the flexible piezoelectric sensor operative to:
detect blood flow through the limb of the user during the inflation, the deflation or both; and
output a signal indicative of the detected blood flow during the inflation, the deflation or both; and
a processor coupled with the piezoelectric sensor and operative to:
filter the signal to isolate sounds corresponding to changes in the blood flow through the limb due to the inflation of the bladder, the deflation of the bladder or both;
correlate the isolated sounds with a pressure inside the bladder; and
determine a blood pressure of the user at least partially based on correlating the isolated sounds with the pressure.
2 . The blood pressure measurement device of claim 1 , further comprising a pressure sensor, wherein:
the signal is a first signal;
the pressure sensor is operative to measure the pressure inside the bladder and output a second signal indicating the pressure to the processor;
the flexible cuff comprises an upper edge;
the bladder is positioned between the upper edge and the piezoelectric sensor;
the flexible piezoelectric sensor is positioned between the flexible cuff and the limb; and
filtering the first signal to isolate the sounds comprises identifying:
a first sound indicative of restriction of the blood flow due to partial collapse of a blood vessel within the limb; and
a second sound indicative of stoppage of the blood flow in the blood vessel.
3 . The blood pressure measurement device of claim 1 , wherein filtering the signal comprises:
applying a first band pass filter having a first frequency range to the signal;
applying a second band pass filter having a second frequency range to the signal; and
the first frequency range comprises higher frequency components of the signal than the second frequency range.
4 . The blood pressure measurement device of claim 3 , wherein:
the first frequency range comprises frequency components that correspond to the sounds resulting due to the changes in the blood flow.
5 . The blood pressure measurement device of claim 1 , further comprising a pump operative to inflate the bladder, wherein:
the flexible piezoelectric sensor is operative to detect changes in sounds corresponding to blood flow within a frequency range; and
the pump operates at a frequency that is greater than the frequency range.
6 . The blood pressure measurement device of claim 5 , wherein the pump is an ultrasonic pump.
7 . The blood pressure measurement device of claim 1 , wherein the flexible piezoelectric sensor is operative to wrap around an entirety of the limb.
8 . The blood pressure measurement device of claim 1 , wherein the flexible piezoelectric sensor is a differential piezoelectric sensor.
9 . The blood pressure measurement device of claim 1 , wherein the flexible piezoelectric sensor is positioned within an interior portion of the cuff.
10 . A blood pressure measurement device, comprising:
A flexible cuff operative to wrap around a limb of a user;
a bladder coupled to the flexible cuff and configured to be secured to the limb of the user by the flexible cuff, the bladder operative to compress the limb of the user during inflation and decompress the limb during deflation;
a flexible piezoelectric sensor coupled to the flexible cuff and laterally positioned entirely between a lower edge of the bladder and a lower edge of the cuff, the flexible piezoelectric sensor defining an elongated strip that extends along the flexible cuff, is positioned between the bladder and a lower edge of the flexible cuff and is configured to conform to and at least partially encircle the to the limb of the user when the flexible cuff is wrapped around the limb of the user, the elongated the flexible piezoelectric sensor operative to detect blood flow through the limb of a user; and
a processor operative to:
receive a signal from the flexible piezoelectric sensor that is indicative of the blood flow through the limb during the inflation, the deflation or both; and
filter the signal to:
identify a first sound that corresponds to a change in the blood flow due to a partial collapse of a blood vessel within the limb during the inflation, the deflation or both; and
identify a second sound that corresponds to a stoppage of the blood flow in the blood vessel within the limb during the inflation, the deflation or both; and
determine a blood pressure of the user at least partially based on the identified first and second sounds.
11 . The blood pressure measurement device of claim 10 , wherein the flexible piezoelectric sensor is contained within the flexible cuff.
12 . The blood pressure measurement device of claim 10 , wherein:
the bladder is contained within a proximal portion of the flexible cuff;
the flexible piezoelectric sensor is contained within a distal portion of the flexible cuff; and
the flexible piezoelectric sensor is separated from the bladder by a dampening material that is operative to isolate the piezoelectric sensor from pressure oscillations within the bladder.
13 . The blood pressure measurement device of claim 10 , wherein:
the signal is a first signal; and
the blood pressure measurement device, further comprises:
a pump coupled to the bladder and operative to inflate the bladder; and
a pressure sensor coupled to the bladder and operative to output a second signal indicative of a pressure within the bladder.
14 . The blood pressure measurement device of claim 13 , wherein the processor is operative to:
receive the second signal from the pressure sensor;
determine a first pressure within the flexible cuff that corresponds to identifying the first sound; and
determine a second pressure within the flexible cuff that corresponds to identifying the second sound.
15 . The blood pressure measurement device of claim 10 , wherein the processor is operative to determine the blood pressure of the user from signals corresponding to inflation of the bladder.
16 . A method for measuring blood pressure of a user, the method comprising:
inflating a bladder of a flexible cuff to increase a pressure within the bladder to compress a blood vessel of the user;
detecting, using a flexible piezoelectric sensor, changes in blood flow through the blood vessel during the inflating of the bladder, the changes corresponding to collapse of the blood vessel, the flexible piezoelectric sensor comprising an elongated strip extending along the flexible cuff, laterally positioned entirely between a lower edge of the bladder and a lower edge of the flexible cuff and configured to conform around the limb of the user when the cuff is wrapped around the limb of the user;
outputting a first signal indicative of the changes in the blood flow during the inflating of the bladder;
detecting, using a pressure sensors, the pressure within the bladder during the inflating of the bladder;
outputting a second signal indicative of the pressure during the inflating of the bladder; and
filtering the first signal to:
identify a first sound that corresponds to a change in blood flow through the blood vessel due to partial collapse of the blood vessel; and
identify a second sound that corresponds to a stoppage of blood flow in the blood vessel;
operating a processor to:
receive the first and second signals;
determine, using the first and second signals, a first pressure in the bladder corresponding to an occurrence of the first sound;
determine, using the first and second signals, a second pressure in the bladder corresponding to an occurrence of the second sound; and
estimate a blood pressure of the user using the first pressure and the second pressure.
17 . The method of claim 16 , wherein filtering the first signal comprises:
using a first band pass filter to isolate portions of the first signal falling within a first frequency band corresponding to changes in sound of the blood flow; and
using a second band pass filter to isolate portions of the first signal falling within a second frequency band corresponding to changes in the pressure within the bladder.
18 . The method of claim 17 , wherein:
the portions of the first signal falling within the first frequency band are used to determine systolic and diastolic blood pressure of the user; and
the portions of the first signal falling within the second frequency band are used to determine a mean blood pressure of the user.
19 . The method of claim 16 , wherein inflating the bladder comprises inflating the bladder until the second sound is identified.