Measuring blood pressure

1. A method for measuring non-invasively a blood pressure of a patient,

the method comprising the steps of:

determining a mechanical heart beat starting time point from an impedance cardiogram signal,

measuring the heart to peripheral site pulse beat transit time start point by measuring an ECG QRS-complex,

adding correction to the ORS-complex signal by averaging a QRS to impedance cardiogram (ICE) waveform timing point,

detecting a heart beat pulse arrival time at a peripheral site of the patient by using an optical plethysmographic sensor at the peripheral site,

calculating a pulse wave transit time from the heart to the peripheral site by utilizing said mechanical starting point of the heart beat and said heart beat pulse arrival time,

calculating an estimate of the blood pressure of the patient from said pulse wave transit time.

2. A method according to claim 1 , wherein the method comprises a step of

calibrating the blood pressure calculation by oscillometric cuff measurement of the blood pressure of the patient.

3. A method according to claim 2 , wherein the method comprises the step of

performing successively the step of calibrating the blood pressure calculation by oscillometric cuff measurement.

4. A method according to claim 3 , wherein said step of calibrating the blood pressure calculation is improved incrementally on each cuff inflation cycle.

5. A method according to claim 1 , wherein the method comprises a step of correcting a reflected wave component of a plethysmogram at the peripheral site in response to a change in the plethysmogram amplitude.

6. A system for measuring non-invasively the blood pressure of a patient wherein the system comprises:

an impedance cardiogram for determining the mechanical heart beat starting time point of a patient,

an optical plethysmographic sensor at a peripheral site for determining the heart beat pulse arrival time at the peripheral site of the patient,

a first calculator for calculating the pulse wave transit time from the heart to the peripheral site by utilizing said mechanical starting point of the heart beat and said heart beat pulse arrival time at the peripheral site of the patient,

a second calculator for calculating the blood pressure of the patient from said pulse wave transit times,

said system further arranged to measure the pulse wave transit time start point by measuring an electrocardiogram (ECG) OSR-complex; and

said system arranged to add correction to the QRS-complex signal by averaging QRS to impedance cardiogram (ICG) waveform timing point.

7. A system according to claim 6 for measuring non-invasively the blood pressure of a patient wherein said peripheral site plethysmogram is arranged to correct a reflected wave component of the plethysmogram at the peripheral site in response to a change in plethysmogram amplitude.

8. A system according to claim 6 for measuring non-invasively the blood pressure of a patient wherein the system comprises:

an oscillometric cuff for calibrating the blood pressure calculation by measuring the blood pressure of the patient.

9. A system according to claim 8 for measuring non-invasively the blood pressure of a patient wherein the oscillometric cuff is adapted to perform the calibration of the blood pressure calculation by successive oscillometric cuff measurements.

10. A system according to claim 9 for measuring non-invasively the blood pressure of a patient wherein the calibration of the blood pressure calculation is improved incrementally on each cuff inflation cycle.