Pulse transmit time measurement device and method

Abstract

Proposed is a Pulse Transit Time, PTT, measurement concept wherein a forced oscillation technique, FOT, is used to determine a pulse arrival time at alveoli of the lungs of a patient.

Claims

1. A method comprising the steps of: determining a pulse start time; using a forced oscillation technique to determine a pulse arrival time at alveoli of lungs of a patient, the determination of the pulse arrival time based on determining a change in impedance at the alveoli, the change in impedance based on a blood pressure wave arriving at the alveoli; determining a pulse transit time based on the pulse start time and the pulse arrival time; and transmitting the pulse transit time to an output interface for monitoring of a cardiovascular function for the patient.

2. The method of claim 1, wherein the step of determining a pulse start time comprises: using a phonocardiograph to determine a point in time when a heart pulmonary valve of the patient opens.

3. The method of claim 1, wherein the step of determining a pulse start time comprises: using an electrocardiogram to determine a point in time when a right ventricle of a heart of the patient contracts.

4. The method of claim 1, wherein using a forced oscillation technique comprises: applying pressure oscillations into airways of the patient at a higher frequency than a natural breathing frequency of the patient.

5. The method of claim 1, further comprising measuring blood pressure based on the pulse transit time.

6. A pulse transit time measurement device, comprising: a pulse detection unit adapted to determine a pulse start time; a forced oscillation technique unit adapted to perform a forced oscillation technique to determine a pulse arrival time at alveoli of the lungs of a patient, the determination of the pulse arrival time based on determining a change in impedance at the alveoli, the change in impedance based on a blood pressure wave arriving at the alveoli; and a processing unit adapted to determine the pulse transit time based on the pulse start time and the pulse arrival time and transmit the pulse transit time to an output interface for monitoring of a cardiovascular function for the patient.

7. The pulse transit time measurement device of claim 6, wherein the pulse detection unit comprises: a phonocardiograph apparatus adapted to determine a point in time when a heart pulmonary valve of the patient opens.

8. The pulse transit time measurement device of claim 6, wherein the pulse detection unit comprises: an electrocardiogram apparatus adapted to determine a point in time when a right ventricle of a heart of the patient contracts.

9. The pulse transit time measurement device of claim 6, wherein the forced oscillation technique unit comprises an apparatus adapted to apply pressure oscillations into airways of the patient at a higher frequency than a natural breathing frequency of the patient.

10. A system, comprising: a pulse detection unit adapted to determine a pulse start time; a forced oscillation technique unit adapted to perform a forced oscillation technique to determine a pulse arrival time at alveoli of the lungs of a patient, the determination of the pulse arrival time based on determining a change in impedance at the alveoli, the change in impedance based on a blood pressure wave arriving at the alveoli; and a processing unit adapted to determine the pulse transit time based on the pulse start time and the pulse arrival time and transmit the pulse transit time to an output interface for monitoring of a cardiovascular function for the patient.

11. The system of claim 10, wherein the pulse detection unit comprises: a phonocardiograph apparatus adapted to determine a point in time when a heart pulmonary valve of the patient opens.

12. The system of claim 10, wherein the pulse detection unit comprises: an electrocardiogram apparatus adapted to determine a point in time when a right ventricle of a heart of the patient contracts.

13. The system of claim 10, wherein the forced oscillation technique-unit comprises an apparatus adapted to apply pressure oscillations into airways of the patient at a higher frequency than a natural breathing frequency of the patient.

14. The system of claim 10, wherein the system comprises a blood pressure measurement device comprising the pulse detection unit, the forced oscillation technique unit, and the processing unit.

15. The system of claim 10, wherein the system comprises a cardiac monitoring system comprising the pulse detection unit, the forced oscillation technique unit, and the processing unit.

16. The system of claim 10, wherein the system comprises a spirometer comprising the pulse detection unit, the forced oscillation technique unit, and the processing unit.

17. The method of claim 1, wherein transmitting comprises transmitting the pulse transit time on a beat-by-beat basis.

18. The pulse transit time measurement device of claim 6, wherein the pulse transit time is transmitted to the output interface on a beat-by-beat basis.

19. The system of claim 10, wherein the pulse transit time is transmitted to the output interface on a beat-by-beat basis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

(2) FIG. 1 depicts a flow diagram of a PPT measurement method according to an embodiment; and

(3) FIG. 2 depicts a schematic block diagram of a measurement device according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(4) Embodiments employ the concept of using an acoustical diagnostic system/method to identify a pulse pressure wave arrival time in the alveoli of a patient. The invention may therefore provide for the measurement of PTT using a FOT. Such use of a FOT may therefore enable a non-invasive, unobtrusive acoustical way of measuring the PTT of a pulse pressure wave in the pulmonary arteries. Embodiments may therefore be useful for the field of monitoring BP.

(5) The diagrams are purely schematic and it should therefore be understood that the dimensions of features are not drawn to scale. Accordingly, the illustrated thickness of any of the layers should not be taken as limiting. For example, a first layer drawn as being thicker than a second layer may, in practice, be thinner than the second layer.

(6) Referring to FIG. 1, there is depicted a flow diagram of a PTT measurement method 100 according to an embodiment.

(7) The method begins with step 110 wherein a pulse start time T1 is determined. The pulse start time T1 may be considered as being indicating the time of a heartbeat and may be identified, for example, as the time at which the pulmonary heart valve opens and the blood pressure wave runs into the pulmonary artery filling up the pulmonary arteries. The pulse start time T1 may be identified by using a phonocardiograph to determine a point in time when the pulmonary valve of the heart opens.

(8) A phonocardiograph is a widely known system in the field of cardiology and is typically used to monitor and diagnose (in real time) the contraction of heart chambers and the opening of the cardiac valves. Thus, a phonocardiograph system can be used to identify a time at which the pulmonary heart valve opens and the blood pressure wave runs into the pulmonary artery filling up the pulmonary arteries.

(9) Phonocardiography is a well-known diagnostic technique that creates a graphic record (or phonocardiogram) of the sounds and murmurs produced by the contracting heart, including its valves and associated great vessels. The phonocardiogram is obtained either with a chest microphone or with a miniature sensor in the tip of a small tubular instrument that is introduced via the blood vessels into one of the heart chambers. The phonocardiogram usually supplements information obtained by listening to body sounds with a stethoscope (auscultation). It may therefore be of special diagnostic value when performed simultaneously with measurement of the electrical properties of the heart (electrocardiography) and pulse rate.

(10) In step 120, a pulse arrival time T2 at the alveoli of the lungs of a patient is determined. In this embodiment, the pulse arrival time T2 is the time at which the blood pressure wave arrives at the alveoli of a patient and is determined using a FOT. FOT is known in pulmonology to measure the respiratory resistance of lung and upper airway. FOT was introduced by DuBois et al. in 1956 and is an acoustical measurement system/method that has been used for the evaluation of respiratory characteristics in a variety of clinical applications.

(11) The basic principle of FOT is the application of pressure oscillations of small amplitude into the airways of a patient at a higher frequency than the natural breathing frequency. Classically, a loudspeaker generates the pressure oscillations, whereas flow (V) and pressure (P) signals are recorded close to the airway opening by means of a pneumotachograph and a pressure transducer, respectively. The complex relationship between applied pressure and resulting flow, called impedance (Zrs), is determined by the mechanical properties of the airways, the lung tissue and the chest wall. Zrs, in general, is dependent on the frequency of oscillation. In a simplistic model, the in-phase relationship between pressure and flow, the resistance or real part of impedance (Rrs), is determined by the resistive properties of the respiratory system. The 90-degree out-of-phase relationship, reactance or imaginary part of impedance (Xrs), is determined by the elastic properties of the respiratory system at low frequency and by the inertive elements at high frequency. There are two different ways of applying FOT. To study the frequency-dependent behaviour of Zrs, multiple frequencies can be applied simultaneously after which a Fast Fourier transform identifies the different frequencies applied. Alternatively, a monosinusoidal pressure oscillation can be applied which enables a cycle-per-cycle analysis of the pressure and flow signals (one cycle=1/(frequency of oscillation)) so that the time-dependent changes of Zrs can be monitored optimally. The latter methodology results in a high time resolution of information and allows tracking of changes of Zrs along the breathing cycle and changes of Zrs along the cardiac cycle, in particular the change of Zrs at the arrival of the pulmonary blood pulse wave.

(12) Next in step 130, the PTT (T.sub.PTT) for same cardiac cycle is calculated based on the pulse start time determined in step 110 and the pulse arrival time determined in step 120. Thus, for the same cardiac cycle (e.g. for a single pulse or heartbeat), the PTT is calculated based on the time taken for a pulse pressure wave to travel between two (pulmonary) arterial sites, wherein the first arterial site is the pulmonary heart valve or artery and the second arterial site is alveoli of the lungs. More specifically, in step 130 of this embodiment, the PTT (T.sub.PTT) is calculated based on the time difference between the pulse start time T1 and the pulse arrival time T2. An equation for this calculation may therefore be (Equation 2):
T.sub.PTT=T2T1(Eq. 2),
wherein: T.sub.PTT is the PTT for a cardiac cycle of interest; T1 is the pulse start time for the cardiac cycle of interest; and T2 pulse arrival time at the alveoli of the lungs.

(13) Finally, in step 140, the calculated value of PTT (T.sub.PTT) is output (for example, to a BP monitoring device).

(14) The method may then return to step 110 for the purpose of calculating/measuring the PTT of a subsequent cardiac cycle. It will therefore be appreciated that the proposed method may be executed repeatedly on a beat-by-beat basis so as to enable continuous measurement and monitoring of PTT for a patient.

(15) Referring now to FIG. 2, there is depicted a PTT measurement device 200 according to an embodiment.

(16) The PTT measurement device 200 comprises: a pulse detection unit 210 adapted to determine a pulse start time; a FOT unit 220 adapted to perform a FOT to determine a pulse arrival time; a processing unit 230; and an output interface 240.

(17) Here, the pulse detection unit 210 comprises: phonocardiograph apparatus 250 adapted to determine a point in time T1 when the pulmonary valve of the patient's heart opens; and electrocardiogram apparatus 260 adapted to determine a point in time T1 when the right ventricle of the patient's heart contracts. The determined values of T1 and T1 may be different, due to differences in the measurement techniques and/or accuracies for example. Both such values of T1 and T1 may therefore be used to determine a pulse start time T1, for example by using T1 as an error checking vale for T1 (or vice versa) and/or by extrapolating between the value of T1 and T1.

(18) The FOT unit 220 comprises FOT acoustical measurement apparatus adapted to determine a pulse arrival time T2 at the alveoli of the lungs of the patient.

(19) The values of T1 and T1 obtained by the pulse detection unit 210, and the value of T2 obtained by the FOT unit 220, are provided to the processing unit 230.

(20) The processing unit 230 is adapted to calculate a PTT based on the values of T1, T1 and T2 it receives (from the pulse detection unit 210 and the FOT unit 220) for the same cardiac cycle. More specifically, the processing unit 230 calculates the PTT (T.sub.PTT) based on the time difference between the pulse start time T1 and the pulse arrival time T2, wherein the pulse start time T1 is determined from the values of T1 and T1. The processing unit 230 then provides the calculated value of PTT (T.sub.PTT) to the output interface 240.

(21) In this embodiment, the output interface 240 comprises a communication interface which is adapted to communicate calculated values of PTT (T.sub.PTT) to another apparatus (such as a BP calculation or monitoring device) for further processing and/or use.

(22) It will be understood, however, that processing unit 230 may be further adapted to calculate a PWV value and/or a BP value based on a calculated value of PTT (T.sub.PTT). This may be done, for example, by determining a value of PWV from the calculated value of PTT and then calculating a corresponding BP value from the PWV value (using a relationship such as the Moens-Korteweg-relation for example). Such a value of PWV and/or BP may therefore be provided by the processing unit 230 to the output interface 240.

(23) Accordingly, in a slightly modified embodiment, the output interface may comprise a display device adapted to display a BP value that has been calculated by the processing unit. By arranging the device to obtain a PTT measurement for each heartbeat, the processing unit may therefore be adapted to determine a corresponding BP value for each heart beat and output such BP values, thereby enabling continuous monitoring of the patient's BP.

(24) Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.