Local PWV and other Hemodynamic Parameters Assessment

Validation of a New Optical Technique in an Healthy Population

T. Pereira

, I. Santos

, T. Oliveira

, P. Vaz

, T. Pereira

, H. Santos

, H. Pereira

1,3

, V. Almeida

J. Cardoso

and C. Correia

Instrumentation Center, Physics Department, University of Coimbra, Coimbra, Portugal

Coimbra College of Health Technology, Coimbra, Portugal

ISA- Intelligent Sensing Anywhere, Coimbra, Portugal

Keywords: Optical Probe, Waveform Distension, Hemodynamic Parameters, Pulse Wave Velocity, Pulse Waveform

Analysis.

Abstract: Presently the interest in non-invasive devices for monitoring the cardiovascular system has increased in

importance, especially in the diagnosis of some pathologies. The proposed optical device reveals an

attractive instrumental solution for local pulse wave velocity (PWV) assessment and other hemodynamic

parameters analysis, such as Augmentation Index (AIx), Subendocardial Viability Ratio (SEVR), Maximum

Rate of Pressure Change (dP/dt

max

) and Ejection Time Index (ETI). These parameters allow a better

knowledge on the cardiovascular condition and management of many disease states. Two studies were

performed in order to validate this technology. Firstly, a comparative test between the optical system and a

gold-standard in PWV assessment was carried out. Afterwards, a large study was performed in 131 young

subjects to establish carotid PWV reference values as well as other hemodynamic parameters and to find

correlations between these and the population characteristics. The results allowed the use of this new

technique as a reliable method to determine these parameters. For the total of subjects values for carotid

PWV vary between 3-7.69 m s

-1

a clear correlation with age and smoking status was found out. The Aix

varies between -6.15% and 11.46% and exhibit a negative correlation with heart, and dP/dt

max

parameter

shows a significant decrease with age.

1 INTRODUCTION

The interest in non-invasive assessment of

cardiovascular function has increased over the recent

times, particularly around solutions able to perform

multi parameter assessment for monitoring and early

diagnosis of cardiovascular pathologies (Willum-

Hansen et al., 2006); (Blacher et al., 1999); (Hayashi

et al., 2002); (Weber et al., 2004).

The pulse wave velocity and the parameters

extracted from pulse waveform analysis (PWA) are

widely used tools in the evaluation of the function of

large arteries and cardiac activity, which have been

shown to predict cardiovascular diseases

(Nürnberger et al., 2003); (Huck et al., 2007).

The assessment of the cardiovascular system

condition based on multi parameters allow a more

precise and accurate diagnosis of the heart and

arterial tree condition. Risk indicators that can be

assessed from the distension waveforms acquired

through the hereby presented system, can be

determined from the main parameters extracted from

the measured and analysed waveform, as well as its

time characteristics and the pulse wave velocity.

The PWV is defined as the speed at which the

pulse pressure propagates along the arterial tree. It is

known that PWV increases with age, blood pressure

(BP) and arterial stiffness (Vermeersch et al., 2010);

(Huck et al., 2007). The reference value for regional

PWV in healthy young population is 6.2 m s

-1

(range

of 4.7-7.6 m s

-1

) (Vermeersch et al., 2010) and is

usually measured from signals acquired in the

femoral and carotid arteries. The time delay, or pulse

transit time (PTT) between the two signals is

determined through different algorithms depending

on the commercial system used, while the distance

(D) between the two arteries is externally measured.

However, the large heterogeneity of the structure of

the arterial walls at different sites constitutes an

Pereira T., Santos I., Oliveira T., Vaz P., Pereira T., Santos H., Pereira H., Almeida V., Cardoso J. and Correia C..

Local PWV and Other Hemodynamic Parameters Assessment - Validation of a New Optical Technique in an Healthy Population.

DOI: 10.5220/0004237600610069

In Proceedings of the International Conference on Bio-inspired Systems and Signal Processing (BIOSIGNALS-2013), pages 61-69

ISBN: 978-989-8565-36-5

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

important limitation of PWV regional measurement

(Safar, 2007). In fact, the Expert Consensus

Document in Arterial Stiffness states that the PWV

increases from 4–5 m s

-1

in the ascending aorta to 5–

6 m s

-1

in the abdominal aorta and 8–9 m s

-1

in the

iliac and femoral arteries (Laurent et al., 2006). A

local PWV measurement technique is hence

preferred.

Some studies (Rabben et al., 2004) explored an

ultrasound method for local PWV assessment in the

carotid artery and obtained estimated PWV in the

range of 4-9 m s

-1

. In 2008 (Sørensen et al., 2008) an

experimental method for the local determination of

PWV in the carotid artery obtained values for PWV

of 3-4 m s

-1

The pulse wave analysis allows the non-invasive

determination of the main indices of cardiovascular

function: Augmentation Index (AIx), Subendocar-

dial Viability Ratio (SEVR), Maximum Rate of

Pressure Change (

dP/dt

max

)

and Ejection Time Index

(ETI). The most important points of the pulse

pressure waveform are presented in Figure 1. The

clinical definition for the referred parameters and the

mathematical expressions for their determination are

summarized in table 1.

Figure 1: Typical pressure waveform of a healthy subject

and its main features used to compute the indices of

cardiovascular function: pulse pressure (PP), systolic peak

(SP), reflection point (RP), dicrotic notch (DN), dicrotic

peak (DP), systolic duration (SD), total duration (TD) and

pressure in the reflection point (Pi).

If the backward wave arrives before the systolic

peak, the AIx parameter, by definition, has a positive

value due to the contribution of the increased

systolic pressure. If the backward wave arrives later,

it does not contribute to the increased pressure,

turning the AIx values negative.

Taking into account the existing commercial

devices, a new solution based on optical technology

was developed and demonstrably benefits by a non-

contact and more accurate measure and multi

parameter assessment ability (Pereira et al., 2011).

The PWV assessment from the commercial

system consists always on a regional measurement,

between two peripheral arteries as already described.

With this work a local measure of PWV is proposed,

where two measures are taken at the carotid artery,

simultaneously and separated by a 20 mm distance

(Pereira et al., 2011).

The carotid artery is the natural probing site for

pulse waveform measurement, due to the heart

proximity and because it is easily accessible due to

its proximity to the skin surface.

The objective of this study was to validate the

optical system for PWV and PWA measurements.

Firstly, it was intended to assess the values for local

PWV, to establish its reference values for the carotid

artery in a young and healthy population and

validate the technology for hemodynamic

parameters assessment from the pulse pressure

waveform. The study also aimed to find correlations

between hemodynamic parameters with the

population characteristics such as age, gender,

smoking, body mass index, blood pressure or heart

rate: main characteristics described in the literature

and have significant impact in the cardiovascular

system evaluation.

2 TECHNOLOGY

The pressure wave, generated by the contraction of

the left ventricle, originates a distension wave that

propagates through the aorta and other proximal

elastic arterial walls. The distensibility is determined

as the ratio between the variation of volume from

diastole to systole and the variation of pressure that

origins that distension in the arterial wall (Laurent et

al., 2006).

Previous studies on comparison between

pressure and distension waveforms have shown that

these waves can be used interchangeably for many

analysis due to their similar wave contour (Laurent

et al., 2006); (Boutouyrie et al., 2009); (Kips et al.,

2010); (Vermeersch et al., 2008).

The proposed probes were developed to measure

the arterial pulse wave profile at the carotid site and

are based on the reflectance fluctuations of the skin

surface during the underlying pulse wave

propagation. The propagation of the pulse pressure

waveform causes distension in the artery wall. This

distension, known as distension wave, changes the

optical reflectance angle of the wall which produces

a change in the reflection characteristics of skin,

causing an amplitude modulation of the light. This

BIOSIGNALS2013-InternationalConferenceonBio-inspiredSystemsandSignalProcessing

Table 1: Main parameters from pulse waveform analysis.

Parameter Definition Formula Reference Values

AIx

Describes the increase of systolic blood

ressure due to an early backward wave,

produced by the reflection of the forward

systolic wave on the peripheral arterial tree

structure.

100

- 22 to 40 (%)

(Siebenhofer et al. 1999)

SEVR

Parameter that estimates the myocardial

oxygen supply-demand relative to the cardiac

workload. It is an indicator of subendocardial

ischaemia.

100

)(





dttSystole

dttDiastole

119 to 254 (%)

(Siebenhofer et al. 1999)

dP/dt

max

The ventricular contractility can be evaluated

by the maximum rate of pressure change,

which gives information about the initial

velocity of the myocardial contraction, which

is also an index of myocardial performance.

772 ± 229 (mmHg/s)

(Payne et al. 2007)

ETI

Ventricular systolic ejection time between the

aortic valve opening and closing. It is an

important component on the evaluation of the

left ventricular performance.

30 to 42 (%)

(Istratoaie et al. 2010)

PWV

The velocity at which the

ulse wave

propagates along a length of artery.

PTT

6.2 (4.7 to 7.6) (m s

-1

)

(Sebastian J Vermeersch et al. 2010)

*PTT represents the delay between two acquired signals; D is the distance between two sensors that compose the optical probe.

effect can be used to generate an optical signal that

correlates with the passing pressure wave.

The illumination source is provided by local,

high brightness, 635 nm monochromatic light

emitting diodes (LEDs) and the light detection is

performed by two photodetectors, placed at a precise

distance of 20 mm apart. This guarantees the local

pulse wave profile assessment at two distinct spots,

providing the precise local determination of pulse

transit time (PTT) and thus of the local PWV. The

probe structure is enclosed in a plastic box with an

ergonomic configuration, comfortable to the patient

and simple to use by the operator (figure 2).

The plastic case contacts with the patient skin

although neither the LEDs nor the photodetectors

does. The electronic components remain at a fixed

distance, few millimetres from the skin ensuring a

totally non-contact and non-invasive local PWV

assessment.

Previous bench tests had shown that the optical

probe is capable of accurately measure PTT as short

as 1 ms with less than 1% of error, one can

guarantee the capability of the probes in truthfully

determine local PWV (Pereira et al., 2011).

The comparison tests to evaluate the capability

of the developed device in accurately detect the

pulse waveform were carried out using an ultrasound

imaging system, as source of reference data. When

compared with ultrasound system, the optical

sensors allow the reproduction of the arterial

waveform with a much higher time resolution,

adequate to feed feature extraction algorithms

(Pereira et al., 2011).

Figure 2: Structure of the optical probe with photodetector

and visible light sources (LEDs), inside an ergonomic

plastic box.

The signals from the photodetectors were

digitized with a 16-bit resolution data acquisition

system (National Instruments, USB6210

) with a

sampling rate of 20 kHz and stored for offline

analysis. All the algorithms were developed using

Matlab

7.8.0 (R2009a).

LocalPWVandOtherHemodynamicParametersAssessment-ValidationofaNewOpticalTechniqueinanHealthy

Population

3 PRELIMINARY VALIDATION

STUDY

In order to validate the data obtained by the

developed optical system, a number of volunteers

were previously submitted to a signal acquisition

procedure, using simultaneously the proposed

optical device and a gold-standard in the PWV

assessment, a Complior Analyse

device. This

preliminary study was undertaken in 14 healthy

subjects (9 females, average age 23.2±5.5 years).

Figure 3: Correlation between the two systems (Complior

and Optical probe) for PWV determination (top). Bland-

Altman plot (bottom) displaying the difference between

the two systems (Complior

and Optical probe) as a

function of the average of the determined PWV.

The results showed a great consistency between

the PWV obtained with the two devices. In spite of

this comparison, it is worth to note that the nature of

the PWV determination is different between the

optical system, that is based on local assessment

(carotid artery measure) and the Complior

system,

which is based on a regional assessment (carotid-

femoral measures).

Using a non-parametric correlation analysis

between the values obtained from the two systems,

the Pearson correlation value is 0.819, which is a

strong correlation and significant at the 0.01 level

(2-tailed).

The agreement between the PWV values

obtained by the Complior

and the optical probe is

shown in figure 3 (top). The values of PWV

obtained by the two systems are correlated (r

0.67). The average difference between the two

systems, Complior

and Optical probe, was -1.8557

m s

-1

with a SD of 0.5744 m s

-1

as shown in a Bland-

Altman plot in figure 2 (bottom). As one can

observe in figure 3 (top), there is a tendency to have

systematic lower values from the optical probe

device than Complior

. Again, it is important to bear

in mind that the values obtained using both devices

correspond to different PWV determination

processes (local vs. regional) and lower values are

expected for PWV in the carotid (local) than the

PWV in a carotid-femoral measurement (regional).

This issue could explain the associated deviate of

final values.

Taken together, these results allow the use of this

proposed optical system as a reliable method to

determine local carotid PWV.

4 STUDY PROTOCOL

The central purpose of these tests is to assess the

main hemodynamic parameters extractable from the

pressure waveform features and pulse wave velocity,

in a young and healthy population using the optical

system.

The complete study database contains 131

subjects constituting a representative cohort of 18–

35 year old subjects randomly sampled. The study

protocol was approved by the ethical committee of

the Centro Hospitalar e Universitário de Coimbra,

EPE Portugal. All the subjects were volunteers and

gave a written informed consent.

Measurements were performed after a rest period

in a temperature-controlled environment. Each exam

procedure consisted in the acquisition of a set of

cardiac cycles at the carotid artery during few

minutes, with the patient lying in supine position.

The assessment of the arterial blood pressure

(ABP) by conventional measurement using an

automated digital oscillometric sphygmomanometer

(Omron Matsusaka Co., Ltd., Japan) was performed

prior and after the exam for reference purposes. The

diastolic and systolic pressures of arm blood

pressure were used to calibrate the system.

2 3 4 5 6

PWV Optical Probe (m/s)

PWV Complior (m/s)

PWV complior = 1.4*PWV optical + 0.32

3 4 5 6 7

-3

-2.5

-2

-1.5

-1

-0.5

Difference in two systems (m/s)

Mean of two systems (m/s)

BIOSIGNALS2013-InternationalConferenceonBio-inspiredSystemsandSignalProcessing

5 SIGNAL PROCESSING

The stored signal data were processed offline in

order to parameterize the arterial pulse waveform

and to calculate the corresponding cardiovascular

performance indexes. A set of dedicated pre-

processing algorithms were developed to segment

the data stream in single cycles, generate an average

pulse and identify the corresponding remarkable

points in the waveform profile. Following this stage,

the signal streams underwent the full processing

sequence to determine all the significant APW

features and indexes along with the local PWV.

The pulse wave velocity was determined by a

cross-correlation method, based on the property of

the peak of the cross correlogram, from which time

delays can be calculated by subtracting the peak

time position from the pulse length.

The pulse wave analysis is based on differential

calculus, and uses zero-crossing of the three first

derivatives. The remarkable points were found by

means of an iterative third-order derivative method,

with which the consecutive zero-crossing of the first,

second and third derivatives are used to detect

inflection points that correspond to the clinically

interesting features of the waveform.

An assessment of ABP by conventional

measurement using a sphygmomanometer was

conducted prior and after the exam for calibration

purposes. Both brachial diastolic (DBP) and mean

arterial pressure (MAP) values were used to

calibrate the system. Studies have reported that

MAP is relatively constant along the arterial tree and

that DBP do not vary considerably between the

carotid and brachial arteries, whereas systolic blood

pressure (SBP) increases along the arterial tree

(Lamia et al., 2005); (Safar, 2007). Thus, we made

the assumption that brachial DBP and MAP are

approximately the same as carotid DBP and MAP.

These values were used to calibrate the carotid

pressure waveform as recommended and according

to the calibration method proposed by Kelly and

Fitchett (Kelly and Fitchett, 1992); (Laurent et al.,

2006); (Proudfoot, 2009).

6 RESULTS

The characteristics of the volunteers are presented in

Table 2. The group consisted of 131 subjects (62

men and 69 women), normotensive and with no

documented history of cardiovascular disorders or

diabetes, with mean (±SD) age of 22.6±5.3 years

old.

Table 2: Main characteristics of the volunteers.

Characteristics

n, Males/Females 131 (62/69)

Age, year 22.6±5.3

Height, cm 169.2±0.1

Weight, kg 64.5±13.2

BMI, kg/m

22.4±3.2

Brachial SBP

, mmHg 113.3±14.5

Brachial DBP

, mmHg

Brachial MAP

, mmHg

Estimated Carotid SBP

, mmHg

72.7±9.9

86.2±10.4

99.1±12.2

Heart Rate

, bpm 69.0±11.7

Values are numbers or means ±SD.

BMI indicates body mass index; SBP, systolic blood pressure; DBP,

diastolic blood pressure.

* Measure in brachial, with commercial sphygmomanometer

(blood pressure cuff).

** Determined using the calibration method

The results for the parameters that were assessed

by the optical probe are presented in the next

sections. Data are reported as mean values (± SD) or

95% confidence intervals, with P<0.05 considered

significant unless stated otherwise. The Shapiro-

Wilk test of normality was used to assess the

normality of the variables distribution. Mean

differences between variables were assessed using

ANOVA. The strength of the association between

two variables was assessed using Pearson

Correlation, for normal distributions, unless stated

otherwise.

All statistical analyses were performed with

Analytics Software Statistics 18.0.0 (SPSS, Inc,

Chicago, IL).

6.1 Carotid PWV Results

In a total of 131 subjects the mean value for PWV is

3.33±0.72 m s

-1

(range of 2.00-5.13 m s

-1

). The

results obtained for PWV approximated a normal

distribution. Statistically negligible differences

between genders were found. For females the mean

of PWV is 3.31±0.64 m s

-1

and for males is

3.35±0.81 m s

-1

It is well documented in other studies that PWV

tends to increase with age (Vermeersch et al. 2010).

Since the population under study is young we

categorized it in three groups: under 20 years (22

subjects), 21-29 years (93 subjects) and over 30

years old (16 subjects).

The correlation between PWV and age is weak

(0.244) but significant with a 2-tailed significance

value of 0.008 (p<0.01). The comparison of PWV

mean values among the different age categories

using ANOVA shown this statistically significant

difference, with a significance value = 0.024

LocalPWVandOtherHemodynamicParametersAssessment-ValidationofaNewOpticalTechniqueinanHealthy

Population

(p<0.05). The PWV mean value (±SD) for each age

category is 2.96±0.52 m/s for the less than 20 years

old group, 3.38±0.7 m/s for the 20-29 years group

and 3.58±0.7 m/s for subjects above 30 years old

(figure 4).

It was hypothesized whether there is a

statistically significant difference for PWV, between

smoker and non-smoker subjects. The data analysis

shows that smoking influences significantly the

PWV.

Figure 4: PWV by age category. The continuous line

connects mean values; error bars indicate the 95%

confidence interval of the sample mean.

Figure 5: Bar plot of PWV by smoking status. The error

bars indicate the 95% confidence interval of the sample

mean.

These results show a small but significant

correlation between PWV and smoking with a 2-

tailed significance value of 0.016 (p<0.05). Non-

smoker subjects presented a PWV mean value (±SD)

of 3.29±0.72 m s

-1

while smoker subjects showed a

mean PWV value of 3.81±0.6 m s

-1

, represented in

figure 5.

The comparison of PWV mean values among

these two groups using ANOVA confirms the

statistically significant difference between the

obtained PWV for smokers and non-smokers, with a

significance value = 0.021 (p<0.05).

The data suggests that, in spite of having a young

population, smoking would significantly influence

the arterial stiffness, thus leading to increased PWV.

Similar findings have been reported by N. Jatoi et al.

(Jatoi et al., 2007).

Contrary to expectations, no significant

correlation between blood pressure and PWV was

found. This contrasts with other studies where this

correlation is verified (Padilla et al., 2006);

(Vermeersch et al., 2010).

6.2 AIx Results

For the total of the subjects in study, the mean value

for AIx is -6.151±11.46% (range -44.31% to 24.26

%).

Small differences between genders were verified,

as the female mean of AIx is -5.59±1.36% and the

male is -6.93±1.59%. However, this difference did

not reach the statistical significance threshold

(P>0.05).

Also for this parameter, as well as for PWV,

statistically differences between smoker and non-

smoker subjects were found. AIx is higher for

smokers (-4.33±4.42%) than for non-smokers (-

6.35±1.04%), this shows that for smokers the

reflected wave arrives earlier in time, which is

consistent with a slight higher the arterial stiffness.

The negative correlation between the AIx and the

heart rate was described in other tests (Wilkinson et

al., 2000); (Weber et al., 2004b) and was confirmed

in this study (figure 6). The results of Person-

Correlation test were compatible with a significant

negative correlation, between heart rate (HR) and

AIx at a 0.05 level (2-tailed). Nevertheless, the

strength of the relationship found between these two

variables is medium, since the Pearson Correlation is

significant with a 2-tailed significance value of -

0.226 (p<0.05). The comparison of AIx mean values

among these three groups using ANOVA confirms a

statistically significant difference, with a

significance value = 0.024 (p<0.05).

The negative correlation between these two

parameters is explained due to the early return of the

reflected wave in systole when HR is lower, and the

long period of heart contraction.

BIOSIGNALS2013-InternationalConferenceonBio-inspiredSystemsandSignalProcessing

Figure 6: The continuous line connects plots of AIx mean

by heart rate category, with error bars representing the

95% confidence interval of the sample mean.

6.3 Other Hemodynamic Parameters

Results

The Ejection Time Index, Subendocardial Viability

Ratio and Maximum Rate of Pressure Change

are

other hemodynamic parameters assessed by the

optical system, and the results for the population in

study are shown in table 3.

It is remarkable that the mean values of SEVR

and ETI stay within the range presented by other

studies (table 1) even though it is clear that they

show a wide variation. For the SEVR parameter it

was also verified a decrease with the heart rate

(figure 7) with a significant variance (ANOVA,

P=0.01) and a significant Pearson correlation at 0.01

level (2-tailed).

Table 3: Hemodynamic Parameters obtained with the

Optical System.

Min. Max. Mean SD

SEVR (%) 86.41 412.25 176.86 53.44

dP/dt

max.

(mmHg/s)

212.59 953.33 443.92 151.68

ETI (%) 14.33 47.17 33.96 6.37

The derived values for dP/dt

max

differ

substantially from the ones presented by other

studies, a wider range than the expected and a

smaller mean value is evident probably originated by

the differences in the calibration method used.

However, a relation between dP/dt

max.

and gender,

was found, since the Pearson Correlation is -0.408.

The female subjects showed lower values for this

parameter, which are represented in figure 8.

The dP/dt

max

values decrease significantly with

subjects’ age, this allows the inferring that with the

increasing age the velocity of the myocardial

contraction is lower, meaning that there is a decrease

in the myocardial performance.

Figure 7: Box plot of data from the determined SEVR

versus heart rate categories.

Figure 8: Error plots of dP/dt

max

mean values according to

gender. The error bars represent the 95% confidence

interval of the sample mean.

For the ETI parameter there were verified slight

differences between gender, the mean vales for the

females is 36.80±0.72% and for males 33.60±0.85%.

This suggests that there is a shorter systole during

cardiac cycle in males than in females. Also for this

parameter, a significance correlation with heart rate

was found since the Pearson Correlation is -0.408.

7 CONCLUSIONS

These trial tests were carried out in a large group of

young and healthy subjects. This study has

attempted to validate the proposed optical system as

LocalPWVandOtherHemodynamicParametersAssessment-ValidationofaNewOpticalTechniqueinanHealthy

Population

a reliable method to assess non-invasively local

PWV in the carotid artery, to establish reference

values of the local PWV as well as other mentioned

parameters in this type of population.

Previously, this new system had also proved to

be reliable in reproducing the arterial waveform with

a higher resolution, adequate to feed feature

extraction algorithms, when compared to an

ultrasound image system that was used as a

reference for comparison.

Besides of the ability of the optical system in

acquiring non-invasively a carotid distension

waveform with high definition, the presented optical

system shows other advantages over the actual

commercial devices.

One advantage of this optical approach relies on

being a non-contact technique that avoids the

drawback of pressure application as happens with

piezoelectric transducers that could result in the

distortion of the signal of interest.

Another benefit is the possibility of local PWV

assessment, in a single arterial segment, avoiding

coarse approximations of the distance between test

points constituting an important advance in the PWV

assessment.

The validation test, in which the obtained values

using the optical probes were compared with those

obtained with a commercial device are supported by

all the previous bench test results and allowed to

consider this technique as a valid method to assess

PWV and analyse PWA parameters.

The range of the obtained values for local CA

PWV are in agreement with the values obtained by

other studies that also assessed the carotid local

PWV. The expected and obtained lower values of

the carotid PWV assessment when compared to

those obtained with Complior

device are due to the

different PWV determination processes (local vs.

regional). The lack of compatibility between

methods limits the inferences that can be made and

thus, more studies of repeatability, comparing the

local PWV obtained by the optical system with the

values estimated by ultrasound data, are necessary to

ensure accuracy of the proposed system.

The PWV measured by the optical probe

confirmed a significant increase of PWV with age.

Even though the sample consists of young subjects

with a relatively narrow age distribution, this result

generally agrees with those obtained in other studies.

The PWA parameters revealed the important

relations between some characteristics of the

population and the arterial system status. The

negative correlation between the AIx and the heart

rate were verified in this study, and differences

between gender and smokers/non-smokers were

found.

For the SEVR parameter was also verified a

decrease with the heart rate. The dP/dt

max.

analysis

showed a difference with gender, with lower values

for the female subjects, and this parameter decreased

significantly with age.

All the correlations obtained in this study

showed that the age contributes to the arterial

stiffness as reflected in the values found for the

various parameters. Smokers appear to have higher

arterial age, and therefore increased cardiovascular

risk.

The optical system under study proved to be a

good choice for the determinations of hemodynamic

parameters in a non-invasive and non-contact

assessment, which allows a better knowledge about

the cardiovascular condition and the management of

many disease states.

Although this method provides a set of

parameters strongly related to pulse waveform

morphology it needs a proper and extensive gold

standard comparison with an invasive system.

Finally, it is worth mentioning that, in spite of its

lack of maturity (meaning that many engineering

aspects of the probe can still be improved), the

proposed method exhibits a very high patient hit

success .In fact, for 119 out of 131 patients (90%) it

took around 1 to 2 mins to start acquiring reasonable

quality signals, each take lasting for 30 seconds.

Although some training is required, the method is

much less demanding on the operator skills as

compared to ultrasound, Complior

or tonometer.

ACKNOWLEDGEMENTS

The authors acknowledge the clinical collaboration

from Dr. Rui Providência and Coimbra College of

Health Technology, and acknowledge the support

from Fundação para a Ciência e Tecnologia (FCT)

for funding (PTDC/SAUBEB/ 100650/2008).

Project developed under the initiative of QREN,

funding by UE/FEDER, through COMPETE -

Programa Operacional Factores de Competitividade.

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LocalPWVandOtherHemodynamicParametersAssessment-ValidationofaNewOpticalTechniqueinanHealthy

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