BACKGROUND

The present invention relates to a method and a device for assessing and monitoring cardiovascular health in humans. Cardiovascular impairments are the main cause of death in the western world. Cardiovascular problems are often related to or accompanied by stenosis in arteries, increase of arterial stiffness, hypertension, or other vascular changes, be it anatomical or physiological.

Assessment of the vascular system of humans has been subject of more than a century of research and development. Blood pressure measurements using the well-known sphygmomanometer, assessment using ultrasound (including Doppler), various ways of measurement of pressure waves, plethysmography and angiography have been used both clinically and in research.

However, there are one or more problems associated with all of the above known measurement methods. The known measurement methods may be expensive, such as ultrasound assessment and plethysmography, and/or invasive, such as angiography. Further, there may be a need to obtain more information than possible with the known measurement methods. For instance, the measurement methods may only obtain limited information on the vascular tree, such as when using a sphygmomanometer. Further, the known measurement methods may not give information about a part of the vascular system that actually matters.

It may often be important to obtain information about the central, abdominal or big arteries, such as aorta, carotid arteries, iliac arteries with branches, renal arteries, mesenteric arteries, and femoral arteries. Such information may provide an indication of a state of health/disease or may be used for assessment of medication induced changes to the vascular system. For instance, assessment or monitoring of the vascular system may be needed in relation to use of vasodilatory drugs, in assessing vascular disease, including coronary artery disease and diastolic dysfunction, in anesthesiology/intensive care for monitoring cardiac output, diabetes, kidney disease, rheumatoid arthritis, hypercholesterolemia, hyperlipidemia, or exercise monitoring.

The assessment and monitoring of the vascular system may present different problems depending on the particular use of the assessment and monitoring.

A specific area of interest is assessment and monitoring of cardiovascular changes in relation to pregnancies, births, and post-partum changes. There is a great interest in accomplishing early detection of any complications related to a pregnancy.

In particular, the vascularization of the uterus and the placenta of the pregnant woman may provide indications of the cardiovascular risk of the pregnant woman, and also whether the fetus is developing normally. It is possible to measure the blood flow of uterine and umbilical arteries of the pregnant woman using Doppler velocimetry. However, this requires the use of ultrasound scanning equipment, and the measurement needs to be performed by trained medical staff. Hence, the measurement of the blood flow may only be performed on occasion, requiring the pregnant woman to come to a clinic and involving medical staff for performing the measurement, and with the risk of undiscovered cardiovascular deterioration in the meantime.

Typically, monitoring of uterine and umbilical arterial blood flow is only started, when it is detected by other means that the fetus may not be developing normally or when the pregnant woman belongs to a high risk group. Monitoring may thus be used in cases such as: Intra Uterine Growth Restriction (IUGR), twin pregnancy, maternal hypertension, maternal pre-eclampsia, maternal diabetes, placental insufficiency leading to premature birth, miscarry or stillbirth, and women pregnant after In Vitro Fertilization (IVF).

When diagnosed as having a fetus not developing normally or belonging to a high risk group, the pregnant woman may become anxious and worry about the state of the fetus. The woman may therefore frequently ask for examinations to check the state of the fetus, whereby hospital resources are demanded each time an examination is made. Further, the nervous tension felt by the pregnant woman may also act to aggravate the condition, for instance when the pregnant woman suffers from pre-eclampsia or hypertensive disorder. Therefore, any method for allowing the pregnant woman to make an examination at home would be beneficial both in terms of medical resources required and in providing a possibility for the pregnant woman to check the condition of the fetus whenever worries arise.

Also, the sensitivity of uterine artery Doppler velocimetry using ultrasound increases proportionally with early onset of the clinical manifestations of IUGR and pre-eclampsia and with their severity, but the Doppler velocimetry has a low specificity which may lead to expected iatrogenic premature births and unnecessary interventions in the pregnancy contributing to maternal and neonatal morbidity and mortality.

Preeclampsia is one of the leading causes of pregnancy related maternal morbidity and mortality. In addition to the immediate risk, women who recover from preeclampsia are more likely to experience life-threatening cardiovascular disease later in life. The cardiovascular risk in preeclampsia is associated with increased central arterial stiffness and measures of arterial function as pulse wave analysis or pulse wave velocity (as increased carotid or femoral pulse wave velocity) is useful for clinical assessments.

As is evident from the above, it would be desirable to provide an improved method for continuously assessing the cardiovascular status of the pregnant woman and the development of a fetus. In particular, it would be desirable to provide a method that does not require medical staff to perform measurements and which may be performed by the pregnant woman in her home.

WO 2013/079073 discloses a system for monitoring a fetus in a pregnant woman. The system comprises a portable unit that can be worn by the pregnant woman so as to allow monitoring during daily life. The portable unit has a sound sensor to be positioned on the skin of the abdominal area of the pregnant woman so as to detect a vascular sound from the umbilical arteries of the fetus or from the uterine arteries of the pregnant woman. The sound sensor is functionally connected to a processing unit which executes a processing algorithm on the captured vascular sound and extracts a signal parameter accordingly.

The system allows a measurement of vascular sound to be made by means of a sound sensor that may be worn by the pregnant woman during daily life. Hence, the system may reduce the need for the pregnant woman to be examined at a medical clinic and may also reduce anxiety of the pregnant woman as the state of the fetus may be continuously monitored.

Although the technology disclosed in WO 2013/079073 may enable monitoring of a pregnant woman in her home, there is still room for improvement in the analysis of the vascular sound in order to determine a condition of the fetus.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

It is an object of the invention to provide an improved method for assessing and/or monitoring of cardiovascular health in humans. It is a further object of the invention to enable use of an improved analysis for detection of a vascular condition and to enable continuous monitoring of the condition.

These and other objects of the invention are at least partly met by the invention as defined in the independent claims. Preferred embodiments are set out in the dependent claims.

According to a first aspect of the invention, there is provided a method for assessment and/or monitoring of a person's cardiovascular state, the method comprising: using a sound and vibration transducer to acquire a vascular sound signal in order to detect a vascular sound from a cervical, thoracic, abdominal, pelvic or lower limb region of the person; filtering the vascular sound signal to isolate the vascular sound, said filtering using a filter which attenuates frequencies below a lower cut-off frequency in a range of 100-300 Hz; and analyzing the filtered sound signal in order to determine whether an indication of a dicrotic notch in the vascular sound exceeds a set threshold.

According to a second aspect of the invention, there is provided a device for assessment and/or monitoring of a person's cardiovascular state, the device comprising: a sound and vibration transducer, which is arranged to be positioned in relation to a cervical, thoracic, abdominal, pelvic, or lower limb region of the person so as to acquire a vascular sound signal in order to detect a vascular sound from the region of the person; and a processing unit, which is arranged to receive the vascular sound signal from the sound and vibration transducer and which is further configured to process the vascular sound signal by: filtering the vascular sound signal to isolate the vascular sound, said filtering using a filter which attenuates frequencies below a lower cut-off frequency in a range of 100-300 Hz; and analyzing the filtered sound signal in order to determine whether an indication of a dicrotic notch in the vascular sound exceeds a set threshold.

According to the invention, there is provided a method and device for acquiring vascular sounds originating from blood flow through arteries of a person. The vascular sounds may be obtained by means of a passive device that detects the sounds of blood flow and there is therefore no necessity to provide a signal into the person's body so as to detect a response to the signal. Further, there is no need for a clinician or other medically trained personnel to perform or trigger the acquiring of vascular sounds. Hence, the invention facilitates for continuous acquiring of vascular sounds such that it may provide continuous assessment or monitoring of the cardiovascular health of a person. The person may even wear or carry the device during daily life so that assessment or monitoring of the cardiovascular health may be provided at all times and an alert may be created when attention is needed to the condition of the person.

Although the invention may be especially suited for use in continuous monitoring of the cardiovascular health of a person, the invention may also be used in assessing the cardiovascular health of a person at a specific point of time, such as in an examination by a caregiver or during a surgery or other medical procedure.

According to the invention, a filter is used for attenuating frequencies below a lower cut-off frequency in a range of 100-300 Hz. This implies that sounds originating from a beating heart may be suppressed and that the filtered sound signal may relate to blood flow through arteries of the person. Hence, vascular sound signals may be acquired from a specific region of a person by means of placing a sound and vibration transducer in the specific region. Then, the acquired sound signals may relate to the blood flow in the specific region allowing analysis of the condition of the specific region.

According to the invention, a vascular sound signal is obtained, which is different from signals obtained by traditional, active methods wherein a signal is actively emitted into the person, such as in ultrasound examinations. Hence, analysis made on signals obtained through such traditional, active methods may not be directly transferred to the passive acquiring of vascular sound according to the invention.

The filtered vascular sound signal may comprise characteristics relating to a dicrotic notch. The dicrotic notch relates to a dip in aortic pressure that occurs in cardiac cycle after contraction of the ventricles and coincides with closure of the aortic valve, which prevents blood from flowing back into the ventricles. Blood vessels have elastic walls, which implies that blood flow distal to the aorta will be leveled out and be fairly constant. However, for people having relatively inelastic walls, the blood flow will not be leveled out as quickly distal to the aorta and the pulsatile characteristic of blood flow will be evident in distalarteries.

It is an insight of the invention that the filtered sound signal may be analyzed in order to determine characteristics of the dicrotic notch. Further, an indication of the dicrotic notch exceeding a set threshold may be related to a physical condition of the person, such as hypertension.

In the context of this application, vascular sound should be construed as any signal caused by blood flow through a blood vessel. Such signal will propagate through tissue of the person such that it may be detected by a sensor being positioned in relation to a region of interest of the person. The signal may be detected by means of a microphone arranged in close relationship to the person's skin, the microphone being able to convert air pressure variations to an electrical signal. However, the sound and vibration transducer may be arranged in a number of different manners for detecting the signal as air pressure variations or as vibrations on the skin surface. For instance, the sound and vibration transducer may be implemented as a microphone and air coupler, wherein the vibration on the surface of the skin is translated to a small air pressure inside the air coupler and the air pressure is recorded by the microphone. Alternatively, the sound and vibration transducer may be implemented as an accelerometer or a piezoelectric sensor attached to the surface of the skin.

According to a third aspect of the invention, there is provided a method for assessment and/or monitoring of a pregnant woman and/or a fetus in a pregnant woman, the method comprising: using a sound and vibration transducer to acquire a vascular sound signal in order to detect a vascular sound from an abdominal or pelvic region of the pregnant woman; filtering the vascular sound signal to isolate the vascular sound, said filtering using a filter which attenuates frequencies below a lower cut-off frequency in a range of 100-300 Hz; and analyzing the filtered sound signal in order to determine whether an indication of a dicrotic notch in the vascular sound exceeds a set threshold.

According to a fourth aspect of the invention, there is provided a device for assessment and/or monitoring of a pregnant woman and/or a fetus in a pregnant woman, the device comprising: a sound and vibration transducer, which is arranged to be positioned in relation to an abdominal or pelvic region of the pregnant woman so as to acquire a vascular sound signal in order to detect a vascular sound from the abdominal or pelvic region of the pregnant woman; and a processing unit, which is arranged to receive the vascular sound signal from the sound and vibration transducer and which is further configured to process the vascular sound signal by: filtering the vascular sound signal to isolate the vascular sound, said filtering using a filter which attenuates frequencies below a lower cut-off frequency in a range of 100-300 Hz; and analyzing the filtered sound signal in order to determine whether an indication of a dicrotic notch in the vascular sound exceeds a set threshold.

It is an object of the third and fourth aspect of the invention to provide an improved analysis of captured vascular sound and relating the vascular sound to a condition of a fetus or a pregnant woman.

The third and fourth aspect of the invention relates to a particular application, wherein vascular sound signals are acquired for analysis in relation to a pregnancy.

According to these aspects of the invention, there is provided a method and a device for monitoring a pregnant woman or a fetus in a pregnant woman using passive technology. There is no need of providing a signal or any kind of stimulation into the pregnant woman's body in order to listen to a response to the signal or stimulation, which is e.g. done in an ultrasound examination. Rather, sounds that are normally occurring in the pregnant woman are acquired and analyzed. This implies that there may be no need for an operator handling the equipment for performing the analysis and, in fact, the analysis may be performed continuously by the pregnant woman wearing a sound and vibration transducer during daily life.

The invention makes use of vascular sounds that stem from the blood supplying the fetus in the pregnant woman. It might not be possible to derive from exactly what artery the vascular sounds that are acquired originate. However, it may be assumed that the vascular sounds originate from a main artery in the abdominal or pelvic region of the pregnant woman, such as a uterine artery, an umbilical artery or an iliac artery. Regardless, according to the invention, it is possible to acquire vascular sound that may be analyzed by means of a sound and vibration transducer, which may be positioned in relation to the abdominal or pelvic region of the pregnant woman.

It is further an insight of the invention that the filtered vascular sound signal may be analyzed in order to relate an indication of a dicrotic notch in the vascular sound exceeding a set threshold to a condition of a fetus or a pregnant woman. For instance, in pregnant women, the blood flow increases to vascularize the uterus and placenta to satisfy the metabolic demands of the fetus and to meet the requirements of gas-exchanging to the fetal vascular system. The uterine arteries will go through structural enlargement during pregnancy, so that from gestational week24, the uterine arteries should be adapted to the increased blood flow. If the structural enlargement of the uterine arteries does not occur (or only partly occurs), the increased total blood volume is forced through the arteries by increased velocity and an indication of the dicrotic notch may persist from early pregnancy. The dicrotic notch may also occur when other pathology or external induced changes occur, such as endocrine changes, hypertension, diabetes, heavy smoking, etc. Therefore, it is a realization of the invention that if the indication of the dicrotic notch exceeds a set threshold, especially for a pregnant woman in mid- or late pregnancy, it may e.g. be an indication that vascularization of the uterus and the placenta is insufficient and that there is a risk of development of pre-eclampsia or IUGR in the pregnant woman. Thus, the threshold may be set such that the indication of a dicrotic notch exceeding the threshold may be related to development of pre-eclampsia or fetal IUGR.

According to an embodiment, the filtering uses a band-pass filter having a lower cut-off frequency in a range of 100-300 Hz and an upper cut-off frequency in a range of 300-20 000 Hz.

The analysis of the acquired vascular sound signal may comprise filtering the signal using a band-pass filter so as to isolate the frequencies that carry information of the vascular sound of interest. It is therefore desired to isolate frequencies for which the vascular sound is most prominent. This may typically be achieved by a band-pass filter having a bandwidth of 100-1000 Hz, or 200-800 Hz. However, it should be realized that the bandwidth of the band-pass filter may be varied by changing the lower cut-off frequency and/or the upper cut-off frequency, while the desired frequencies are being isolated. It is to be understood that the entire band-pass filtering effect or at least a part of it may be provided by the acoustical and/or mechanical design of the sound and vibration transducer. Thus, it may be preferred to use a specially designed sound and vibration transducer with frequency characteristics serving to suppress sound outside the most important frequency range, which may eliminate or at least supplement the need for a band-pass filter as part of the processing.

According to an embodiment, analyzing the filtered sound signal comprises: forming an envelope curve of the vascular sound signal; and determining a characteristic in the envelope so as to determine an indication of a dicrotic notch in the vascular sound.

The envelope curve provides a representation of the vascular sound signal which allows relevant characteristics to be extracted. Hence, the forming of an envelope curve facilitates making decisions based on the analysis of the filtered sound signal.

There are a number of different characteristics that may be extracted from the envelope curve. According to an embodiment, determining a characteristic comprises deciding whether a critical point is present between a global maximum in a single wave form of the envelope corresponding to a heartbeat and an end of the single wave form. This implies that it is determined whether a dicrotic notch affects the envelope curve such that a portion of the curve is at least flat.

According to another embodiment, determining a characteristic comprises differentiating the envelope of the vascular sound signal to calculate a derivative of the envelope; and determining a maximum of the derivative between a global maximum in a single wave form of the envelope corresponding to a heartbeat and an end of the single wave form as an indication of a dicrotic notch. Hence, the indication of the dicrotic notch may be related to the derivative of the envelope. According to one embodiment, the set threshold corresponds to the maximum of the derivative being zero. This implies that the determination of the derivative of the envelope curve may be used for determining if a critical point is present in the envelope curve.

According to another embodiment, determining a characteristic comprises determining a rise time in a single wave form of the envelope corresponding to a heartbeat as a time from a start of the single wave form to a global maximum in the single wave form; determining a decay time in the single wave form as a time from the global maximum in the single wave form to the end of the single wave form; and comparing the decay time to the rise time to form a relative decay time as an indication of a dicrotic notch. The decay time may be lengthened when the effect of the dicrotic notch is accentuated in the envelope curve. Hence, the comparison of the decay time to the rise time may provide a useful indication of the dicrotic notch. According to one embodiment, the relative decay time may be formed by dividing the decay time with the rise time. Further, the set threshold corresponds to the relative decay time and is set to be in the range of 1.0-5.0.

The analysis of the filtered sound signal may further comprise determining further characteristics in the envelope so as to form further measures of a dicrotic notch. Such further measures may be used for providing further information on the condition of the person. The further measures may optionally be correlated to corresponding thresholds in order to help in identifying a condition of the person that would need to cause an alert to be provided to the person or to a caregiver. Such a further measure may e.g. be the presence of high frequency murmurs in the sound signal, which may be an effect of turbulent bloodflow.

According to one embodiment, the analysis further comprises determining a local maximum and a local minimum between a global maximum in a single wave form of the envelope corresponding to a heartbeat and an end of the single wave form; and determining a dicrotic notch amplitude as the difference of the signal value between the local maximum and the local minimum, said amplitude forming a further measure of the dicrotic notch. The analysis may further comprise determining a heartbeat amplitude as a difference of the signal value between a global minimum and a global maximum in the single wave form, and comparing the dicrotic notch amplitude to the heartbeat amplitude to form a relative amplitude as a further measure of the dicrotic notch. Hence, the amplitude of the envelope curve may be analyzed for providing further information on the effect of the dicrotic notch on the envelope curve.

According to another embodiment, the analysis further comprises determining a local maximum between a global maximum in a single wave form of the envelope corresponding to a heartbeat and an end of the single wave form; and determining a peak delay time as a time between the global maximum and the local maximum, said peak delay time forming a further measure of the dicrotic notch. The analysis may further comprise determining a rise time in the single wave form as a time from a start of the single wave form to the global maximum in the single wave form; and comparing the peak delay time to the rise time to form a relative time of the dicrotic notch as a further measure of the dicrotic notch. Hence, the timing of features in the envelope curve may be analyzed for providing further information on the effect of the dicrotic notch on the envelope curve.

According to another embodiment, the analysis further comprises determining a local maximum and a local minimum between a global maximum in a single wave form of the envelope corresponding to a heartbeat and an end of the single wave form; determining a dicrotic notch area as an area defined between the envelope curve and a straight line at the signal value of the local minimum from the local minimum to a later point on the envelope curve crossing the signal value of the local minimum, said dicrotic notch area forming a further measure of the dicrotic notch. The analysis may further comprise determining a heartbeat area as an area under the envelope curve from the start to the end of the single wave form; and comparing the dicrotic notch area to the heartbeat area to form a relative area of the dicrotic notch as a further measure of the dicrotic notch. Hence, the size of an area in relation to the dicrotic notch may be analyzed for providing further information on the effect of the dicrotic notch on the envelope curve.

According to an embodiment, the analysis of the filtered sound signal may comprise identifying a sequence of wave forms, wherein each single wave form corresponds to a heartbeat and extends from a first local minimum to a second local minimum in the envelope. Then, the indication of the dicrotic notch may be determined based on a plurality of wave forms in order to provide better accuracy to the analysis.

According to one embodiment, determining a characteristic in the envelope comprises determining a characteristic of each single wave form in the sequence of wave forms. Hence, the characteristic for several wave forms may be compared to the set threshold, whereby a percentage of wave forms for which the indication of the dicrotic notch exceeding the threshold may be determined. This allows relating the condition of the person to the frequency with which an indication of the dicrotic notch occurs.

However, there is a realization of the invention that a single wave form may be too noisy and that characteristics determined based on a single wave form may therefore not be as reliable as desired. Therefore, it may be desired to obtain signals which provide stable and precise measurements for making a reliable determination whether an indication of a dicrotic notch in the vascular sound exceeds a set threshold.

According to another embodiment, the method further comprises normalizing each wave form in the sequence of wave forms to a common norm; and computing an average wave form based on the normalized wave forms; wherein determining a characteristic in the envelope comprises determining a characteristic of the average wave form. Hence, the indication of the dicrotic notch may be based on an average over a plurality of wave forms in order to not let analysis be based on a single wave form corresponding to a single heartbeat.

According to another embodiment, the method further comprises selecting wave forms in the sequence of wave forms, wherein the selected wave forms are validated as representing a typical wave form; aligning the selected wave forms, and forming an average wave form of the aligned wave forms.

Thus, the method provides that an average of the wave forms may be formed such that the characteristics of the vascular sound may be accentuated and reliably assessed. In particular, not all wave forms in a sequence of wave forms may be selected. Thus, wave forms that are highly divergent and which may make it difficult to analyze the vascular sound are not allowed to interfere with the analysis.

Further, the selected wave forms are aligned, which may imply that all the selected wave forms are e.g. fitted to a common time scale so that characteristics of the wave forms will be constructively strengthened when the selected wave forms are combined.

Then, an average may be formed from the aligned wave forms so as to smooth small irregularities of the respective selected wave forms and provide an average wave form which may allow for stable and precise analysis.

It should be realized that the average wave form may then be used in a similar manner as described for a single wave form above in order to extract characteristics from the envelope curve.

The method may further comprise comparing the determined characteristic to a historic characteristic previously determined for the person. Hence, the result of the analysis may be compared to historic results for the person so as to enable detection of a deteriorated condition of the person. For instance, an indication of the dicrotic notch exceeding a set threshold may be observed in one of the left and right uterine arteries for a pregnant woman, whereas the indication of the dicrotic notch does not exceed a set threshold for the other uterine artery. In such case, the vascular sound of the other uterine artery may be monitored. If an indication of the dicrotic notch exceeding the set threshold is observed, it may be concluded that the condition of the pregnant woman and/or the fetus has deteriorated.

The method may further comprise using a further sound and vibration transducer to acquire a heartbeat sound signal corresponding to sounds of the heartbeat of the person; cancelling influence of the heartbeat sound on the vascular sound by filtering the vascular sound signal using the heartbeat sound signal. This implies that sounds from the heartbeat of the person may be filtered out in order for the heartbeat not to disturb the measurement of the vascular sound.

The method may further comprise triggering an alert signal in response to the indication of a dicrotic notch in the vascular sound exceeding the set threshold. Hence, when the indication of the dicrotic notch exceeds the set threshold the person may be immediately informed. As an alternative, the alert signal may be transmitted directly to a hospital or clinic.

According to an embodiment, the sound and vibration transducer and the processing unit are arranged in a portable unit which is wearable by the person. This implies that the person may bring the portable unit with him or her at all times, such that the condition of the person may be continuously monitored during daily life.

According to another embodiment, the device may further comprise a communication unit for communicating a signal from the processing unit to a remote unit in dependence of whether the indication of the dicrotic notch exceeds the set threshold. This implies that the processing unit may send a signal to a remote unit when the indication of the dicrotic notch exceeds the threshold. For instance, the signal may be sent to a computer of a hospital or clinic in order to provide an alert that the condition of the person may need attention.

The device may further comprise an indicator, which is connected to the processing unit and which is selectively activated in dependence of whether the indication of the dicrotic notch exceeds the set threshold. This implies that the person may be alerted by means of the indicator when the indication of the dicrotic notch exceeds the set threshold.

According to an embodiment relating to the assessment and/or monitoring of a pregnant woman or a fetus in the pregnant woman, the method may further comprise using a plurality of sound and vibration transducers, which each detect a vascular sound signal, wherein the plurality of sound and vibration transducers are positioned differently in relation to the abdominal or pelvic region of the pregnant woman. It may be difficult to position a single sound and vibration transducer such that a signal of good quality may always be obtained. In particular, movements of the fetus may affect at which position in relation to the abdominal or pelvic region of the pregnant woman an optimal signal may be obtained. Hence, using a plurality of sound and vibration transducers increases the possibility of acquiring a signal that may be properly analyzed.

According to one embodiment, the method further comprises determining a quality of the vascular sound signal from each of the plurality of sound and vibration transducers, and selecting one of the plurality of sound and vibration transducers based on said quality for providing the vascular sound signal to be analyzed. This implies that the sound and vibration transducer that currently gives the best quality signal will be used.

According to another embodiment, the method further comprises forming an average vascular sound signal based on the signal from each of the plurality of sound and vibration transducers. This implies that a stable signal may be obtained regardless whether the quality of a single sound and vibration transducer deteriorates.

It may also be contemplated that a plurality of sound and vibration transducers are used and placed in anatomically different positions. This may allow measuring a pulse wave velocity. For example, the sound and vibration transducers may be positioned in relation to the carotid and the femoral arteries, respectively, or, for a pregnant woman, in relation to the carotid and uterine arteries, respectively.

