Apparatus and method of assessing a narrowing in a fluid filled tube
View Patent ↗An apparatus and method of assessing a narrowing in a fluid filled tube having a fluid flow pressure wave having a backward-originating pressure component and a forward-originating pressure component without taking a flow velocity measurement, comprising: taking pressure measurements in the tube; separating the pressure components into the backward-originating pressure component and the forward-originating pressure component; identifying a time window when the differential of flow velocity (dU) is minimal or absent; and deriving the backward and forward pressure components for pressure measurements taken in at least the time window.
1. A method of assessing a narrowing in a blood vessel, the method comprising:
positioning at least one pressure-sensing probe within a blood vessel;
obtaining, with an intravascular processing system having a processor in communication with the at least one pressure-sensing probe, pressure measurements from within the blood vessel using the at least one pressure-sensing probe, the pressure measurements being obtained not during hyperaemia;
identifying, with the intravascular processing system, a wave free period corresponding to a time window when a differential of flow velocity is minimal or absent; and
calculating, with the intravascular processing system, a pressure ratio using the pressure measurements obtained during the wave free period to provide an assessment of a severity of the narrowing in the blood vessel.
2. The method of claim 1 , wherein the wave free period is identified heuristically.
3. The method of claim 1 , wherein the wave free period is identified based on a characteristic of a pressure waveform of the obtained pressure measurements.
4. The method of claim 1 , wherein the wave free period is identified as a certain time window before or after a characteristic of the pressure waveform.
5. The method of claim 1 , wherein the wave free period is identified by:
identifying a peak pressure time (t Pmax );
identifying an end of pressure waveform time (t Pend ); and
specifying the wave free period as a time window between t Pmax and t Pend .
6. The method of claim 5 , wherein the time window extends from t Pmax +150 ms to t Pend −50 ms.
7. The method of claim 5 , wherein the time window is a mid 3/5 window between t Pmax and t Pend .
8. The method of claim 1 , wherein the wave free period is identified by:
calculating a standard deviation of a pressure ratio of the obtained pressure measurements; and
specifying the wave free period as a time window after a peak pressure time point where the standard deviation is below a predetermined threshold.
9. The method of claim 8 , wherein the predetermined threshold is a bottom 10% or less of the calculated standard deviation.
10. The method of claim 8 , wherein the time window has a length of at least 100 ms.
11. A system of assessing a narrowing in a blood vessel, the system comprising:
at least one pressure-sensing probe sized and shaped for positioning within the blood vessel; and
a processor in communication, with the at least one pressure-sensing probe, the processor configured to:
receive pressure measurements obtained by the at least one pressure-sensing probe positioned within the blood vessel, the pressure measurements being obtained not during hyperaemia;
identify a wave free period corresponding to a time window when a differential of flow velocity is minimal or absent; and
calculate a pressure ratio using the pressure measurements obtained during the wave free period to provide an assessment of a severity of the narrowing in the blood vessel.
12. The system of claim 11 , wherein the processor is configured to identify the wave free period heuristically.
13. The system of claim 11 , wherein the processor is configured to identify the wave free period based on a characteristic of a pressure waveform of the obtained pressure measurements.
14. The system of claim 11 , wherein the processor is configured to identify the wave free period as a certain time window before or after a characteristic of the pressure waveform.
15. The system of claim 11 , wherein the processor is configured to identify the wave free period by:
identifying a peak pressure time (t Pmax );
identifying an end of pressure waveform time (t Pend ); and
specifying the wave free period as a time window between t Pmax and t Pend .
16. The system of claim 15 , wherein the time window extends from t Pmax +150 ms to t Pend −50 ms.
17. The system of claim 15 , wherein the time window is a mid 3/5 window between t Pmax and t Pend .
18. The system of claim 11 , wherein the processor is configured to identify the wave free period by:
calculating a standard deviation of a pressure ratio of the obtained pressure measurements; and
specifying the wave free period as a time window after a peak pressure time point where the standard deviation is below a predetermined threshold.
19. The system of claim 18 , wherein the predetermined threshold is a bottom 10% or less of the calculated standard deviation.
20. The system of claim 18 , wherein the time window has a length of at least 100 ms.