Non-invasive blood pressure measurement techniques based on wave shape change during an external pressure cycle

A method for determining a blood pressure parameter of a user, the method comprising:

• causing a restriction device to apply an external pressure cycle to a blood vessel of the user;
• receiving a pressure signal corresponding to a set of measured pulse pressure waves occurring within the blood vessel during the external pressure cycle;
• determining a first set of pressure values from the pressure signal, each pressure value in the first set of pressure values corresponding to a minimum pressure for a respective pulse pressure wave in the set of measured pulse pressure waves;
• generating a first fit parameter defining a first fit line that represents changes in pulse pressure waves of the first set of pressure values over the external pressure cycle;
• determining a second set of pressure values, each second pressure value in the second set of pressure values corresponding to a pressure upstroke that occurs during a descending pressure phase of the respective pulse pressure wave in the set of measured pulse pressure waves;
• generating a second fit parameter defining a second fit line that represents changes in pulse pressure waves of the second set of pressure values over the external pressure cycle;
• determining an intersection point of the first fit line and the second fit line;
• using the intersection point to identify a corresponding pressure wave in the set of measured pulse pressure waves;
• and
• determining the blood pressure parameter of the user using the corresponding pressure wave.

A blood pressure measurement device comprising:

• a restriction device configured to wrap around a limb of a user and apply an external pressure cycle to a blood vessel of the user;
• a pressure sensing device coupled to the restriction device and configured to:
• detect pressures within the blood vessel during the external pressure cycle;
• and
• output a signal indicative of the detected pressures;
• and
• a processing device configured to:
• receive the signal from the pressure sensing device;
• analyze the signal to determine, for each pulse pressure wave occurring in the blood vessel during the external pressure cycle:
• a local minimum pressure value that occurs between subsequent pulse pressure waves;
• and
• a descending pressure value that occurs during a descending phase of each pulse pressure wave;
• and
• determine a blood pressure parameter of the user based on the local minimum pressure value and the descending pressure value for each pulse pressure wave.