Method of Approximating a Patient's Pulse Wave Based on Non-Invasive Blood Pressure Measurement, A Logic Unit Therefore and a System Therefore
The present invention refers to a method of approximating a patient's pulse wave based on non-invasive blood pressure measurement, comprising the following steps: (a) non-invasively measuring a sequence n−1 . . . N of pulse signals pulse n — measured (t) of a patient, thereby applying a clamp pressure clamp n (t), (b) weighting the measured pulse signals pulse n measured (t) using a weighting function to obtain weighted pulse signals pulse n weighted (t), and (c) adding up the weighted pulse signals pulse n weighted (t) to obtain an approximation of the patient's pulse wave pulse approx (t). The invention also refers to a logic unit and a system for approximating a patient's pulse wave based on non-invasive blood pressure measurement.
1 . Method of approximating a patient's pulse wave based on non-invasive blood pressure measurement, comprising the following steps:
(a) non-invasively measuring a sequence n=1 . . . N of pulse signals pulse n — measured (t) of a patient, thereby applying a clamp pressure clamp n (t);
(b) weighting the measured pulse signals pulse n — measured (t) using a weighting function to obtain weighted pulse signals pulse n — weighted (t);
(c) adding up the weighted pulse signals pulse n — weighted (t) to obtain an approximation of the patient's pulse wave pulse approx (t).
2 . Method according to claim 1 , wherein the clamp pressure clamp n (t) is an input parameter of the weighting function, and wherein the weighting function is preferably a differential pressure function.
3 . Method according to claim 1 , wherein method steps (b) and (c) are iteratively repeated at least one more time.
4 . Method according to claim 3 , wherein the weighting function applied in the second and/or higher iteration loop differs from the weighting function applied in the first iteration loop.
5 . Method according to claim 4 , wherein the weighting function applied in the second and/or higher iteration loop is a differential pressure function having the clamp pressure clamp n (t) as an input parameter and having the approximated pulse wave pulse approx (t) obtained in the previous iteration loop as another input parameter.
6 . Method according to claim 3 , wherein the weighting function applied in the second and/or higher iteration loop is a triangular function, preferably having its maximum when the clamp pressure clamp n (t) equals a predetermined difference, preferably zero, to the approximated pulse wave pulse approx (t) obtained in a previous iteration loop.
7 . Method according to claim 3 , wherein the weighting function applied in the second and/or higher iteration loop is a bell-shaped function, preferably having its maximum when the clamp pressure clamp n (t) equals a predetermined difference, preferably zero, to the approximated pulse wave pulse approx (t) obtained in a previous iteration loop.
8 . Method according to claim 4 , wherein the weighting function of the first iteration loop is determined as follows:
weight1 n =1 if DAP<clamp(t)<SAP,
weight1 n =0 otherwise.
9 . Method according to claim 3 , wherein method step (c) of the second and/or higher iteration loop further comprises: scaling the approximated pulse wave pulse approx (t) to the difference between the diastolic blood pressure value DAP and the systolic blood pressure value SAP of the patient.
10 . Method according to claim 1 , wherein, in method step (a), the clamp pressure clamp n (t) is increased or decreased continuously, preferably at a substantially constant rate.
11 . Method according to claim 1 , wherein method step (a) further comprises: scaling the measured pulse signals pulse n — measured (t) to the difference between the diastolic blood pressure value DAP and the systolic blood pressure value SAP of the patient.
12 . Method according to claim 11 , wherein, scaling of the measured pulse signals pulse n — measured (t) in method step (a) is performed by applying the following formula:
pulse n — measured — scaled ( t )=offset n +scale n ×pulse n — measured ( t ),
wherein the parameter offset n is preferably calculated as follows:
offset n =DAP−min(pulse n — measured ( t )), and
wherein the parameter scale n is preferably calculated as follows:
scale
n
=
SAP
-
DAP
max
(
pulse
n
_
measured
(
t
)
)
-
min
(
pulse
n
_
measured
(
t
)
)
.
13 . Logic unit for approximating a patient's pulse wave based on a non-invasive blood pressure measurement, configured to carry out the following steps:
weighting previously measured pulse signals pulse n — measured (t) using a weighting function to obtain weighted pulse signals pulse n — weighted (t);
adding up the weighted pulse signals pulse n — weighted (t) to obtain an approximation of the patient's pulse wave pulse approx (t),
wherein these steps are preferably iteratively repeated at least one more time.
14 . System for approximating a patient's pulse wave based on a non-invasive blood pressure measurement, comprising the logic unit according to claim 13 and a blood pressure measurement device, the blood pressure measurement device being configured for non-invasively measuring a sequence n=1 . . . N of pulse signals of a patient to obtain the measured pulse signals pulse n — measured (t), wherein the system is configured for providing the measured pulse signals pulse n — measured (t) as input values to the logic unit.
15 . System according to claim 14 , wherein the blood pressure measurement device comprises a pressure cuff, the pressure cuff being preferably configured for being disposed around a patient's arm so as to measure the patient's arterial blood pressure in a non-invasive way.
16 . System according to claim 15 , further comprising a second blood pressure measurement device being adapted for non-invasively measuring peripheral blood pressure waveform data of the patient in a continuous way, wherein the system is adapted to apply a transfer function to reconstruct central blood pressure waveforms from the measured peripheral blood pressure waveform data based on the approximated pulse wave pulse approx (t).
17 . System according to claim 16 , wherein the approximated pulse wave pulse approx (t) of the patient is determined at substantially regular intervals, and wherein the transfer function is regularly recalibrated based on the regularly determined approximated pulse wave pulse approx (t) of the patient.