WO2009147597A1

WO2009147597A1 - Detection of impending syncope of a patient

Info

Publication number: WO2009147597A1
Application number: PCT/IB2009/052255
Authority: WO
Inventors: Geert G. G. Morren; Jens Muehlsteff
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2008-06-02
Filing date: 2009-05-28
Publication date: 2009-12-10

Abstract

The invention concerns a device for detection of impending syncope of a patient, comprising a photoplethysmogram sensor 1 for obtaining a photoplethysmographic signal on the patient's skin, wherein the photoplethysmogram sensor 1 is at least adapted for measuring a quasi-DC part of the photoplethysmographic signal, and a processor 7 which is at least adapted for processing the measured quasi-DC part of the photoplethysmographic signal and for outputting a processed signal which is at least based on the measured quasi-DC part of the photoplethysmographic signal, the processed signal indicating the risk of an impending syncope of the patient. In this way a possibility for detecting impending syncope of a patient is provided which is unobtrusive, efficient and reliable.

Description

DETECTION OF IMPENDING SYNCOPE OF A PATIENT

FIELD OF THE INVENTION

The invention relates to the field of detection of impending syncope of a patient and especially to a device for detection of impending syncope of a patient and an according method. BACKGROUND OF THE INVENTION

Syncope is a symptom, defined as a transient, self-limited loss of consciousness, the onset of which is relatively rapid, and the subsequent recovery is spontaneous, complete and usually prompt (< 1 minute). The underlying mechanism is a transient global cerebral hypoperfusion, which is accompanied by a rapid drop in blood pressure. As syncope is usually combined with falling, it often leads to injuries. The prevalence of syncope is estimated at 42% during the life of a person living 70 years. Due to age-related physiological changes, a higher prevalence of chronic illness, and concomitant (often multiple) medication, the incidence increases with age (23% prevalence during a 10-year period in the population older than 70). Furthermore, the consequences of syncope-related falls are usually more serious in elderly and can lead to hospitalization. The direct medical costs of syncope-related hospitalizations in the US were estimated in 2005 at 2.4 billion $ per year.

The cerebral hypoperfusion, which is common to all syncopes, can be caused by several mechanisms: neurally-mediated (reflex) syncope, orthostatic hypotension and cardiac arrhythmias. In some forms of syncope there may be a premonitory period in which various prodromal symptoms, e.g. light-headedness, nausea, sweating, weakness, visual disturbances, offer warning signs for an impending syncope. It has been shown that isometric counterpressure manoeuvres of the legs/arms are able to induce a significant blood pressure increase during the phase of impending vasovagal syncope, which allows the patient to avoid or delay losing consciousness in most cases. Therefore, it is important to detect the onset of syncope as early as possible, especially for persons with no or unclear prodromal symptoms.

Currently no unobtrusive monitoring devices are available to detect the onset of syncope. Ambulatory blood-pressure monitoring systems are not suited for this purpose, as they do not provide continuous blood pressure recordings. The intermittent, usually at most every 5 minutes, blood pressure measurements made by such devices are insufficient to capture the onset of syncope. Furthermore, such systems are very uncomfortable.

In US 2007/0070800 Al a device for detecting syncope of a patient is proposed which comprises a photoplethysmogram sensor and a processor for deriving an indicator for an autonomous nervous system (ANS) activity from the photoplethysmographic signal for estimating a probability of syncope as a function for the indicator. With respect to this, it is proposed that the indicator includes a measure of at least one of cardiac sympathetic activity and cardiac parasympathetic activity, preferably of the sympatho -vagal balance. Further it is described that analysis of ANS activity includes receiving at least two physiological signals that include at least one indicator of ANS activity. However, this device and related method seem to be complicated and might not be reliable in any cases of ANS states of the patient.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a possibility for detecting impending syncope of a patient which is unobtrusive, efficient and reliable. This object is achieved by a device for detection of impending syncope of a patient, comprising a photoplethysmogram sensor for obtaining a photoplethysmographic signal on the patient's skin, wherein the photoplethysmogram sensor is at least adapted for measuring a quasi-DC part of the photoplethysmographic signal, and a processor which is at least adapted for processing the measured quasi-

DC part of the photoplethysmographic signal and for outputting a processed signal which is at least based on the measured quasi-DC part of the photoplethysmographic signal, the processed signal indicating the risk of an impending syncope of the patient.

A photoplethysmogram (PPG) sensor generally comprises a light source, positioned at the skin on a preferably well perfused tissue site, and a light detector measuring the light that has been transmitted through and/or reflected from the tissue. The absorption of light in the near-infrared range (600-1000 nm) mainly depends on the hemoglobin in the blood. A PPG comprises a pulsatile component due to cardiac synchronous changes in blood volume with each heart beat, in the following called AC part. This AC part is superimposed on a slowly varying component, called quasi-DC part. The non-pulsatile absorption, i.e. the absorption of the quasi-DC part, is caused by non-pulsating blood, i.e. venous and arterial blood, and other non-pulsating tissue such as bone.

Accordingly, it is an essential idea of the invention to use the quasi-DC part of the photoplethysmographic signal in order to provide an indicator for the risk of an impending syncope of the patient. In this way, a non-invasive and unobtrusive monitoring of cardiac and/or vascular syncope-related physiological parameters is provided which is very reliable.

In general, it might be sufficient to use the quasi-DC part of the photoplethysmographic signal. However, according to a preferred embodiment of the invention, the photoplethysmogram sensor is further adapted for measuring an AC part of the photoplethysmographic signal. With respect to this it is further preferred that the processor is adapted for also processing the measured AC part of the photoplethysmographic signal and for outputting a processed signal which is further based on the measured AC part of the photoplethysmographic signal, the processed signal indicating the risk of an impending syncope of the patient. In this way, an even more reliable possibility of predicting the risk of syncope is achieved since more data is available for risk calculation.

Generally, the device does not require any further units or functions than described above. However, according to a preferred embodiment of the invention, the device further comprises an ECG sensor for measuring the electrical activity of the heart muscle as an ECG signal, and wherein the processor is further adapted for also processing the measured ECG signal and for outputting a processed signal which is further based on the measured ECG signal, the processed signal indicating the risk of an impending syncope of the patient. This provides for further measurement possibilities, i.e. the measurement of blood pressure. Furthermore, such data can also be used in order to improve the prediction of syncope.

Moreover, according to a preferred embodiment of the invention, the device further comprises a posture sensor for sensing the posture signal of the patient and/or a movement sensor for sensing a movement signal of the patient, wherein the processor is further adapted for also processing the sensed posture signal and/or the sensed movement signal for outputting a processed signal which is further based on the sensed posture signal and/or the sensed movement signal, the processed signal indicating the risk of an impending syncope of the patient. With respect to that it is especially preferred that the device comprises an accelerometer. The additional measurement of posture and/or activity, e.g. using an accelerometer, provides context information that helps to discriminate normal cardiovascular reactions due to posture changes, exercise, etc. from changes preceding syncope. Furthermore, according to a preferred embodiment of the invention, the device further comprises an event-marker unit for marking and storing at least one specific event. With respect to this it is preferred that the event-marker unit is controllable by the patient in order to mark an event. Additionally or alternatively it is preferred that the event-marker unit is adapted for automatically marking at least one predefined event.

According to another preferred embodiment of the invention, the device further comprises a feedback unit for providing feedback on the risk of an impending syncope of the patient, wherein the feedback unit is connected to the processor for receiving the processed signal. Preferably, the feedback is a warning signal, e.g. an auditory signal.

The processor can be provided in different ways. However, according to a preferred embodiment of the invention, the processor is provided in a hand-held processing unit which is provided with a data connection with the photoplethysmogram sensor. This data connection can be wired or wirelessly. The same applies for other sensors if they exist. Further, the hand-held processing unit is preferably battery powered.

Above mentioned object is further met by a method for detecting impending syncope of a patient, comprising the following steps obtaining a photoplethysmographic signal on the patient's skin by measuring at least a quasi-DC part of the photoplethysmographic signal, and processing the measured quasi-DC part of the photoplethysmographic signal and outputting a processed signal which is at least based on the measured quasi- DC part of the photoplethysmographic signal, the processed signal indicating the risk of an impending syncope of the patient.

Preferred embodiments of this method relate to the preferred embodiments of the device described above. Especially, according to a preferred embodiment of the invention, the method further comprises the steps of measuring an AC part of the photoplethysmographic signal, processing the measured AC part of the photoplethysmographic signal, and outputting a processed signal which is further based on the measured AC part of the photoplethysmographic signal, the processed signal indicating the risk of an impending syncope of the patient.

According to a preferred embodiment of the invention, the method further comprises the steps of measuring the electrical activity of the heart muscle as an ECG signal, processing the measured ECG signal, and outputting a processed signal which is further based on the measured ECG signal, the processed signal indicating the risk of an impending syncope of the patient.

Further, according to a preferred embodiment of the invention, the method comprises the steps of sensing a posture signal of the patient and/or sensing a movement signal of the patient, processing the sensed posture signal and/or the sensed movement signal, and outputting a processed signal which is further based on the sensed posture signal and/or the sensed movement signal, the processed signal indicating the risk of an impending syncope of the patient.

Moreover, according to a preferred embodiment of the invention, the method further comprises the step of automatically marking and storing at least one predefined event. It is also preferred that the method comprises the step of providing feedback on the risk of an impending syncope of a patient, preferably by a warning signal, especially by an auditory signal. BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the drawings:

Fig. 1 schematically depicts a device according to a preferred embodiment of the invention;

Fig. 2 schematically depicts the PPG sensor of the device according to a preferred embodiment of the invention;

Figs. 3 a, b, c show the change in pulse shape in the time preceding syncope; and

Fig. 4 shows the changes in PPG puls shape features in the last

10 minutes preceding syncope.

DETAILED DESCRIPTION OF EMBODIMENTS

According to a preferred embodiment of the invention, an ambulatory measurement device 10 is provided that records one or more syncope-related physiological parameters, processes the data and warns the patient when a certain risk of a syncope is detected. In addition, the data can be stored for diagnostic purposes. As depicted in Fig. 1, for that, the device according to the invention comprises a photoplethysmogram (PPG) sensor 1 , measuring the changes in blood volume, not only due to the arterial pulsations, given by the AC signal, but also slower changes, i.e. the quasi-DC signal. Either a reflective PPG-sensor that can be positioned at the forehead, neck or ear channel or a conventional transmission-PPG sensor, e.g. ear or finger clip, can be used.

Further, the device according to the preferred embodiment of the invention comprises an ECG sensor 2 for measuring the electrical activity of the heart muscle, either with conventional, typically adhesive electrodes or with electrodes integrated in textile. Furthermore, an accelerometer is provided as a posture/movement sensor 3.

For marking specific events such a syncopes, an event-marker unit 4 with an event-marker button 8 is provided, allowing the patient to mark specific events such as syncopes. Further an automated event-marker unit can be provided for automated detection of a fall using the accelerometer.

All these sensors can either be wired or connected wirelessly to a hand- held processing unit 6 in which a processor 7 is provided. This processor 7 is at least adapted for processing the measured quasi-DC part of the photoplethysmographic signal and for outputting a processed signal which is at least based on the measured quasi-DC part of the photoplethysmographic signal, the processed signal indicating the risk of an impending syncope of the patient. The hand-held processing unit 6 is small enough to be worn in a pocket. Alternatively, it might be a watch- like device and can be attached easily to the clothing of the patient, e.g. comparable to a mobile phone.

Futhermore, a feedback unit 5 is provided for providing feedback on the risk of an impending syncope of the patient. For that, the feedback unit 5 is connected to the processor 7 for receiving the processed signal. The feedback could be an auditory warning signal when an impeding syncope is detected. Further, the device is powered by batteries 9.

As already stated above, underlying mechanism of syncope, defined as a transient, self-limited loss of consciousness, is a transient global cerebral hypoperfusion, which is accompanied by a rapid drop in blood pressure. According to the preferred embodiment of the invention, an optical measurement of blood volume changes is used to detect the onset of syncope.

As can be seen from Fig. 2, the photoplethysmogram (PPG) sensor 1 according to the invention comprises a light source 11 , positioned at the skin on a preferably well perfused tissue site, and a light detector 12 measuring the light that has been transmitted through and/or reflected from the tissue. The absorption of light in the near-infrared range (600-1000 nm) mainly depends on the hemoglobin in the blood. As already stated further above, the PPG signal comprises a pulsatile component due to cardiac synchronous changes in blood volume with each heart beat, i.e. the AC part. This AC part is superimposed on a slowly varying component, i.e. the quasi-DC part. The non-pulsatile absorption, i.e. the absorption of the quasi-DC part, is caused by non- pulsating blood, i.e. venous and arterial blood, and other non-pulsating tissue such as bone. For almost all conventional PPG applications, such as pulse oximetry, the AC component is of primary interest. However, according to the preferred embodiment of the invention, the quasi-DC is used, too. The quasi-DC component, which reflects changes in blood volume not directly related to the arterial pulsations, enables the detection hypoperfusion of the tissue. As cerebral hypoperfusion causes syncope, monitoring the quasi-DC value of the PPG signal enables the detection of impending syncope. According to the invention, a reflective PPG sensor 1 with sufficiently large source-detector distance, is used to measure directly cerebral blood volume changes. On the other hand, the PPG sensor 1 can also be positioned at peripheral sites, i.e. a finger, as the peripheral perfusion will generally decrease before the cerebral due to the cerebral autoregulation mechanism.

Besides the quasi-DC value of the PPG signal, also the amplitude and the shape of the pulse wave, i.e. the AC part, changes in the minutes preceding the syncope, as shown in Figs. 3a, 3b, and 3c. In addition to the quasi-DC values, these changes can also be used for the detection of syncope. In Fig. 4, the time course of four such features in a period often minutes preceding syncope are shown. Clear changes in all these features can be observed at least one minute before the syncope, which occurs at minute 10. These features are defined as follows.

Amplitude: The amplitude of the AC component of the PPG signal, i.e. the difference of the maximum and minimum value during one heart cycle. Peak- Amplitude-Ratio (PAR): The ratio of the amplitude of the secondary peak in the PPG pulse waveform to the amplitude of the first peak. Peak-Peak-Time (PPT): The time interval between the secondary and first peaks. Pulse Arrival Time (PAT): The time interval between the R-peak in the ECG and the first peak in the PPG signal.

In order to determine the PAT, the ECG is recorded in addition to the PPG. Although this requires more hardware, it can also advantageously be used to make the feature extraction in the PPG signal more robust. This is due to prior knowledge about the peak times. In the period immediately preceding syncope, usually also the heart rate changes significantly. The heart rate can also be extracted from the PPG signal or ECG signal and be used for the detection the impending syncope.

The additional measurement of posture and activity using the accelerometer provides the context information to discriminate normal cardiovascular reactions due to posture changes, exercise, etc. from the changes preceding syncope. Accordingly, the system according to the preferred embodiment of the invention makes it possible to detect the onset of syncope ambulatory and unobtrusively.

When a patient wants to use the device 10 according to the preferred embodiment of the invention, he or a third person like a physician attaches the sensors 1, 2, 3 and hand-held processing unit 6, and starts the recording. Afterwards, the device 10 continuously measures and processes the incoming data. Optionally, the device 10 stores the data. When an impending syncope is detected, the patient is warned through an audible alarm. The monitoring can be stopped by the patient. The data can be transferred to a PC via a cable or wirelessly.

A preferred application is diagnosis and treatment of syncope. However, the invention can also be applied in any other condition where significant changes in cardiovascular parameters can cause hazardous situations.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

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.

Claims

CLAIMS:

1. A device for detection of impending syncope of a patient, comprising a photoplethysmogram sensor (1) for obtaining a photoplethysmographic signal on the patient's skin, wherein the photoplethysmogram sensor (1) is at least adapted for measuring a quasi-DC part of the photoplethysmographic signal, and a processor (7) which is at least adapted for processing the measured quasi-DC part of the photoplethysmographic signal and for outputting a processed signal which is at least based on the measured quasi-DC part of the photoplethysmographic signal, the processed signal indicating the risk of an impending syncope of the patient.

2. Device according to claim 1, wherein the the photoplethysmogram sensor (1) is further adapted for measuring an AC part of the photoplethysmographic signal, and wherein the processor (7) is further adapted for also processing the measured AC part of the photoplethysmographic signal and for outputting a processed signal which is further based on the measured AC part of the photoplethysmographic signal, the processed signal indicating the risk of an impending syncope of the patient.

3. Device according to claim 1 or 2, wherein the device further comprises an ECG sensor (3) for measuring the electrical activity of the heart muscle as an ECG signal, and wherein the processor (7) is further adapted for also processing the measured ECG signal and for outputting a processed signal which is further based on the measured ECG signal, the processed signal indicating the risk of an impending syncope of the patient.

4. Device according to any of claims 1 to 3, wherein the device further comprises a posture sensor (3) for sensing the posture signal of the patient and/or a movement sensor (3) for sensing a movement signal of the patient, wherein the processor (7) is further adapted for also processing the sensed posture signal and/or the sensed movement signal for outputting a processed signal which is further based on the sensed posture signal and/or the sensed movement signal, the processed signal indicating the risk of an impending syncope of the patient.

5. Device according to any of claims 1 to 4, wherein the device further comprises an event-marker unit (4) for marking and storing at least one specific event.

6. Device according to claim 5, wherein the event-marker unit (4) is controllable by the patient in order to mark an event.

7. Device according to claim 5 or 6, wherein the event-marker unit (4) is adapted for automatically marking at least one predefined event.

8. Device according to any of claims 1 to 7, wherein the device further comprises a feedback unit (5) for providing feedback on the risk of an impending syncope of the patient, wherein the feedback unit is connected to the processor for receiving the processed signal.

9. Device according to any of claims 1 to 8, wherein the processor (7) is provided in a hand-held processing unit (6) which is provided with a data connection with the photoplethysmogram sensor (1).

10. A method for detecting impending syncope of a patient, comprising the following steps obtaining a photoplethysmographic signal on the patient's skin by measuring at least a quasi-DC part of the photoplethysmographic signal, and processing the measured quasi-DC part of the photoplethysmographic signal and outputting a processed signal which is at least based on the measured quasi-DC part of the photoplethysmographic signal, the processed signal indicating the risk of an impending syncope of the patient.

11. Method according to claim 10, further comprising the steps of measuring an AC part of the photoplethysmographic signal, processing the measured AC part of the photoplethysmographic signal, and outputting a processed signal which is further based on the measured AC part of the photoplethysmographic signal, the processed signal indicating the risk of an impending syncope of the patient.

12. Method according to claim 10 or 11, further the steps of measuring the electrical activity of the heart muscle as an ECG signal, processing the measured ECG signal, and outputting a processed signal which is further based on the measured ECG signal, the processed signal indicating the risk of an impending syncope of the patient.

13. Method according to any of claims 10 to 12, further comprising the steps of sensing a posture signal of the patient and/or sensing a movement signal of the patient, processing the sensed posture signal and/or the sensed movement signal, and outputting a processed signal which is further based on the sensed posture signal and/or the sensed movement signal, the processed signal indicating the risk of an impending syncope of the patient.

14. Method according to any of claims 10 to 13, further comprising the step of automatically marking and storing at least one predefined event.

15. Method according to any of claims 10 to 14, further comprising the step of providing feedback on the risk of an impending syncope of a patient, preferably by an audible warning.