A non-invasive method of measuring the real-time continuous pressure of fluid in elastic tube and the dynamic compliance of the elastic tube, wherein an elastic surrounding tissues are wrapped outside the elastic tube, a fluctuating fluid flows having a fluid pressure which can be divided into DC part of fluid pressure Pb and AC part of fluid pressure ΔPb in the elastic tube;
- and the measurement method is characterized as follows:
- Searching an initial critical depth λs:
- using Oscillometric Method, press a detection head by a DC-driven actuator on the surface of the surrounding tissues to locate the initial critical depth;
- Determining a decoupled ratio K:
- Hold at initial critical depth to determine the decoupled ratio K for partial or full tracking of the AC part of fluid pressure ΔPb;
- Updating a critical depth λs′:
- actuate DC-driven actuator to maintain a DC part of sensor's pressure Ps is equal to the DC part of fluid pressure Pb, where is the location of critical depth λs′;
- Estimating a reference pressure Δ{circumflex over (P)}b′(n):
- set AC-driven actuator in idling situation (Hold-stage) to obtain three previous reference pressures Δ{circumflex over (P)}b′(n−3) Δ{circumflex over (P)}b′(n−2) and Δ{circumflex over (P)}b′(n−1), and estimate the reference pressure Δ{circumflex over (P)}b′(n) at Step-stage;
- Measuring an impedance of elastic tube Zv2(n):
- use constant AC open loop gain and self-adaptive control rule to estimate the parallel impedance H1 and compute the impedance of elastic tube Zv2(n);
- Calculating an AC control gain Ga:
- use constant AC open loop gain Ka and parallel impedance H1 to calculate the AC control gain Ga for next Step-stage;
- Tracking the AC part of fluid pressure ΔPb to obtain an AC part of displacement Δλs′(n):
- send an AC control gain Ka from AC controller, and move the AC-driven actuator to track the AC part of fluid pressure ΔPb and earn the AC part of displacement Δλs′(n);
- Computing a real-time continuous fluid pressure Pb(n) in elastic tube:
- according to the impedance of elastic tube Zv2(n) and the AC part of displacement Δλs′(n) to compute the AC part of fluid pressure ΔPb′(n), then add the DC part of fluid pressure Pb′(n), which is equal to a DC part of sensor's pressure Ps, to have the real-time continuous fluid pressure Pb(n);
- Extracting a dynamic compliance of elastic tube Cv(n):
- a series of equivalent mechanical properties including mass Mv(n), damping Dv(n) and stiffness Kv(n) are extracted from dynamic impedance of elastic tube Zv2(n) by using parameter identification technique. In which the reciprocal of stiffness is the compliance of elastic tube Cv(n).