Biomagnetic Validation to Skin Level for Blood Pressure Curves and Venous

doi:10.4236/ojapps.2012.23018

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Open Journal of Applied Sciences, 2012, 2, 128-134

doi:10.4236/ojapps.2012.23018 Published Online September 2012 (http :/ /www.SciRP.org/journal/ojapps)

Biomagnetic Validation to Skin Level for Blood Pressure

Curves and Venous

T. Cordova-Fraga1*, Francisco Gómez-Aguilar1, T. Bravo-Arellano1, M. A. Hernández-Gonzalez2,

S. Solorio-Meza2, H. A. Perez-Olivas1, M. Sosa-Aquino1, J. J. Bernal-Alvarado1,

C. R. Contreras-Gaytan3

1Departamento de Ingeniería Física—DCI, Universidad de Guanajuato Campus León Loma del Bosque, León, México

2Unidad de Investigaciones Médicas, Los Paraísos, León, México

3Facultad de Ingeniería en Computación y Electrónica, Universidad De La Salle Bajío Campus Campestre,

Lomas del Campestre, León, México

Email: *[email protected], theoco rdo [email protected]

Received May 31, 2012; revised June 28, 2012; accepted July 12, 2012

ABSTRACT

An analysis of the reproducibility from signal record bioelectric heart activity is presented. The measurements were

carried out with a recently patented medical device, which one is able to record the curves of pressure arterial and ve-

nous as those obtain ed using th e gold standard tech nique in these evalu ation s, the card iac catheterization techn ique. The

measurements were carried out 15 health subjects and patients; each one was measured 5 times in order to have

auto-correlations and correlations of these records. Analysis indicates correlations from 0.9 to 1 as long as p values

were below 0.05. It is indicated an excellent reproducibility of ev aluated patients.

Keywords: Bioelectric Heart Activity; Curves of Pressure Arterial and Venous; Correlation Coefficient; Statistical

Analysis

1. Introduction

The arterial and venous pressures are values attributed to

blood flow through human body [1,2]. As far as it is

known, the first record about blood circulation existence

was performed in China by Nei Ching, 2600 years a. C.

[3] Although Miguel Servet made the first description of

pulmonary circulatory system [4]. Later, William Harvey

raised the pri nciple of hem ody nam ics to veri fy that the heart

muscle had phases of movement and rest [5]. Poiseuille

used a pr essure gauge in an imals to eva luate the pre ssure

in units of mmHg [6], Faivre used the Poiseuille he-

modinamometer on a human being to measure intra-

arterial pressure [7].

Some non-invasive studies have shown that hemo-

dynamic forces have a relationship with the pulse pres-

sure [8]. It has also been noted that with age, it is

increased cardiovascular risk, and it is directly related to

aortic pressure increase [8-12]. Currently there are two

methods of clinical routine use for measurement of blood

pressure and only one to record venous pressure: cardiac

catheterization and sphygmomanometer to arteries. The

second one is widely used, however provides a register

subjective due to its nature. As long as, the technique of

cardiac catheterization is able to record venous pressure

in their inside, it is considered the gold standard in these

assessments, despite it is widely invasive and it demands

high trained personnel and special patients areas for

implementation [9 ]. Nevertheless, it pr esen ts an obj ectiv e

record.

In this paper, it is presented the validation of records

on blood pressure in healthy subjects and patients. It has

been used a device recently patented, the pulse pressure

cardiac gauge (PPC). This diagnostic and monitoring

device is able to have a distinction of recording of the

curves shape of pressure of arterial and venous as those

recorded by catheterization, it offer an express evaluation

with the advantage of carrying out the valuation on skin

level; the ionizing radiation is avoided and does not

require a sterile room for evaluation.

2. Methodology

Each one of the patients enrolled in this study gave a

written consent previous to carrying out measurements,

which were performed according to the treaty of Helsinki

for studies in humans. These assessments did not present

any risk or exposed the patient to any ionizing radiation.

To each volunteer was asked to be placed in semi-fowler

position with the head turned to the right, then the artery

*Corresponding a uthor.

T. CORDOVA-FRAGA ET AL. 129

or vein was identified by palpation and auscultation, this

is, the location of the internal jugular vein and common

carotid artery as shown in Figure 1; when the right

location under skin of artery or vein is done, on skin is

placed a magnetic marker (a magnet of 3 × 4 mm, diameter

and height, respectively), then, it is fixed the sensor base

of the PPC in contact with the skin. Without exerting

more pressure that the base and the magnetic sensor

weight on the neck of the person, the magnetometer is

always separated a distance of 2.5 cm from magnetic

marker on patient skin. This magnetic marker is light

enough not to crush the vessel but has the intensity of the

magnetic moment sufficiently intense, µ = 0.13 Am2.

Magnetic signal is registered with an excellent signal/

noise rate, such it is not required filtering digital addi-

tional so that the detected signal is read.

Mechanical action by the flow of blood in the v essel is

transmitted to magnetic marker. So, it generates a variable

magnetic field which increases as it approaches the sen-

sor having variability in time and decreases away from

this one.

In this validation study were measured 10 healthy sub-

jects, all with no history of heart disease and 5 patients

who underwent cardiac catheterization for suspected

coronary artery disease, while they were registered with

the cardiac catheter. So, after placing the magnetic

marker, it was measured pressure curves repetitively

every 30 seconds according to following order: 5 records

for aspiratory inhalation and 5 records for aspiratory ex-

halation. It was asked an apnea around of 30 s. These

measurements were performed on the left side of the

neck and suprasternal area, some of them also included

alternate position: semi-fowler and supine.

Validation of the obtained signals is carried out esti-

mating the correlation coefficient of the reproducibility

of the signal (cross-correlation of a signal with itself)

using mathematical procedures for processing biological

signals, first among the same individual (auto-correlation)

and then correlate measurements between healthy sub-

jects and patients.

3. Results

The first part of the measurements performed with the

PPC device shows an excellent behavior of the pulse

waves from arterial and venous, see Figures 2 and 3; it is

a stage of apnea where it is shown the wave morphology

of the artery and vein of the pulses according to the

physiological theory of the cardiac cycle, this was done

in healthy subjects.

A typical blood pressure waves recorded with the PPC

in an apnea segment is shown in Figure 4.

The positive waves of pulse venous coincide with a

delay or with the reverse of the flow, while each de-

pression indicates an acceleration of venous return.

When contracting the right atrium (RA), the blood cannot

enter the right ventricle (RV) flows back to the vena cava,

resulting in venous pulse wave. The wave “a” is pro-

duced by the contraction of the RA in a presystolic

period; the wave “c” occurs immediately after the wave

“a” and at the beginning of “x”, is produced by inter-

ference in the carotid arterial pulse, see Figure 5.

Figure 1. Schematization of magnetic marker position on

subject skin, it is right over jugular artery.

Figure 2. Arterial pressures register on suprasternal region

for a healthy subject and stage of apnea in the supine position.

Figure 3. Pressure waveform in internal jugular artery, it

was recorded with two stages: breathing and apnea. Similar

pattern is repeated for a blood pressure pulse, at the stage

of apnea the signal present pattern de fined according to the

morphology searched.

T. CORDOVA-FRAGA ET AL.

130

Figure 4. Typical pressure wave recorded, using the PPC

device, on zone suprasternal in supine position with brea-

thing noise. In the curve is reached to clearly distinguish

three points of interest, dicróticas waves due to backflow of

blood as well as maximal and minimal corresponding to the

systolic pressure (SP) and diastolic pressure (DP) as the

cardiac cycle.

Figure 5. Waveform pressure recorded from the internal

jugular vein, taken on the left side of the neck, in a healthy

subject in inspiratory apnea phase and semi-fowler position.

Note the characteristic morphology “a”, “c”, “v”, and de-

clines calle d “x” and “y”.

The sine “x” is one of the predominant decreases, oc-

curs during diastole atrial due to pressure drop in the

atria, then follows the wave “v”, due to increased atrial

filling pressure right under the return of blood through

the vena cava and finally the depression “y” is produced

because the pressure in the RA descends to the open

tricuspid valve in the relaxation phase in the filling

period RV.

When the registration is made by reversing the polarity

of the magnet there is an inversion of the curves and

venous blood pressure in the temporary space, the Figure

6 shows the case of arterial register, there are the same

waveforms with an inverted orientation only.

For the standardization ph ase, waveforms are obtained

for healthy subjects, see Figures 7 and 8. The records

have the following identification: ica (internal carotid in

apnea aspiratory), ici (internal carotid in apnea inspiratory),

ija (internal jugular in apnea aspiratory) and iji (internal

jugular in apnea inspiratory). Measurements in the

suprasternal area with two variants are: saa (suprasternal

in apnea aspiratory) and sai (suprasternal in apnea inspi-

ratory).

Figure 6. Waveform pressure from suprasternal area, in a

healthy subject, at the stage of apnea aspiratory and supine

position. It shows the morphology characteristic of the

curve of blood pressure.

Figure 7. Pressure waves ica, ija and saa, superimposed on

the phase of respiration in apnea aspiratory for the same

subject. The pressure in ica and ija are in semi-fowler

position, while the saa is supine. Note the difference in

amplitude, and morphological consistency that emerges as

the cardiac cycle, regardless of the different areas where

each record was taken, this is mentioned for blood pressure

supine and semi-fowler.

T. CORDOVA-FRAGA ET AL. 131

3.1. Statistical Analysis

A statistical analysis was performed in order to deter-

mine correlation between the pressure differences (Pd)

measures in mmHg obtained with the digital sphygmoma-

nometer standardization in healthy subjects and voltage

differences (Vd) for the PPC, Figure 9. At the same time

is the correlation for values of PPC and cardiac catheteri-

zation, see Figure 10. Using the correlation coefficient

model of Pearson, Spearman, and Kendall. Also per-

forms a linear fit for both cases, which is shown in Ta-

bles 1 and 2.

3.2. Repeatability and Reproducibility Test

For repeatability tests between measurements, there is a

phase shift in the signals, so that, to establish their corre-

lation between them, the area under the curve of each

signal was estimated and establishing an area correlation

see Figure 11. Subtracting point to point from the curves

Figure 8. Pressure waves ici, iji and sai, superimposed on

the phase of respiration in apnea aspiratory for the same

subject. The pressure in ici and iji are in semi-fowler position

while the sai is supine. Note the difference in amplitude.

Figure 9. Adjustment of correlation PPC vs. sphygmoma-

nometer in the suprasternal zone in supin e in h ealthy sub jects.

Figure 10. Adjustment of correlation PPC vs. catheteriza-

tion in the suprasternal zone in supine in healthy subjec t s.

Table 1. Summary of correlation results PPC vs. blood pres-

sure and linear regression.

Fitting curve: y = ax + b dV[V] = 0.98x + 9.4

Pearson Spearman Kendall

Corr. Coefficient r = 0.91 p = 0.92 τ = 0.82

Table 2. Summary of correlation results PPC vs. catheteri-

zation and linear regression.

Fitting curve: y = ax + b dV[V] = 0.9x + 12.8

Pearson Spearman Kendall

Corr. Coefficient

r = 0.95 p = 0.91 τ = 0.79

Figure 11. Area under the curve for the set sai.

integrated, there are correlations over 0.9 and p values

well below 0.05. Obtaining an excellent correlation and

thus validating the measurements using this device.

T. CORDOVA-FRAGA ET AL.

132

3.3. Hemodynamic Study and Calibration

In the cardiac catheterize lab of highly specialized medi-

cal unit (HSMU) No.1 at the Mexican Social Security

Institute (IMSS), printed data were obtained from the

pressure curves recorded by catheterization in 7 patients.

The Figure 12 shows one of the curves obtained simul-

taneously with the PPC and the polygraph in a cardiac

catheter intervention, consi dering the gold st andard.

4. Discussion

PPC is a device which measures variations in the in-

tensity of a magnetic field generated by a magnetic

marker at a fixed distance from a transducer that converts

mechanical movement to analog signals and a source to

amplify the signals recorded, filter, and stored in a com-

puter as digital signal, becoming text file for further

study and manipulation. Each of the elements constituting

the complete device are easy to transport and install in

any area where it is required to measure, only consists of

a horseshoe that supports the sensor connected to a

flexible tube attached to a microphone stand for easy

positioning at the time of measurement and a computer

with the software needed to acquire the data.

Because of the magnetic field measurements provide

a good approximation to see the angular dependence

exists around a coaxial cable or a cylindrical permanent

magnet, it is the possibility to register the oscillations of

a source for a determined distance. This measurement

modalities relates the blood pressure carried by the

conduits different called vessels and they are divided

according to their morphology and function in arteries,

veins and capillaries, wh ich not being rigid conduits tend

to contract and expand due to the strength that is against

the walls to resist the flow of blood pumped by the heart,

and this motion due to it is soft waves can be recorded by

the PPC successfully locating the vessel to be measured.

Figure 12. Superposition of signals obtained with the PPC

and polygraph and made the switch from units of volts to

The PPC device provides informatio

millimeters of mercury in the PPC signal.

n (voltage-time)

s of

pr robic/

nd to

forms o btained w ith the PPC are very sensitiv e

e protocol to PPC shows that

ents to the same test subject was

out the compliance of the arteries or veins. The maxi-

mum value of each wave equals the pressure systolic and

the minimums is equal to pressure diastolic, while the

decrease or dicrotic wave is related to the backflow of

blood, thus has a new way of measuring the patient’s

health status, graduating flexibility and arterial diameter

with the pressure non-invasively and continuously.

The PPC has a good correlation “0.9r” value

essure vs. sphygmomanometer (anaedigital), but

unlike the sphygmomanometer no have operation on the

whole sample. Excluded are subjects mainly in the

suprasternal space not have a reflection of the rebound of

the arteries confined and also in subjects in which their

side zones to the neck is not palpable the location of the

carotid arteries and the internal jugular vein, this group

includes those individuals who have a body mass index

(BMI) greater than 25 kg/m2 and elderly patients.

The waveforms obtained with the PPC correspo

e cardiac cycle and are similar to the curves obtained

by cardiac catheterization. The PPC can help determine

one of the many parameters of the catheterization, since

it is easy to use and does not require specialized personnel

for its use.

The wav e

any movement of the test subject among which are:

respiration, the fluid passes through the esophagus or

involuntary displacement.

When is standardized th

r venous pressure and arterial pressure the waveforms

were very similar in terms of amplitude, frequency and

period, being that biologically come to have a value

deferred of at least 60 mmHG between blood pressure

and venous, since the venous for transport higher amounts

of blood is not pulsatile compared with the pressure in

arteries reaching values of 120 mmHg, while the vein is

5 mm Hg, this is an important consideration when

calibrating the PPC in the modalities of arterial and

venous pressure.

During the measurem

served that had a change in amplitude in curves when

the variants were apnea in inspiration or aspiration, as,

when there deep breath, the chest cavity and the lungs

expand, the chest wall expands and diaphragm low. This

causes the pressure intrapulmonary becomes more nega-

tive, which causes the lungs, heart and the and the thoracic

vein cava is expand decreasing the pressure inside them.

As the right atrial pressure decreases during inspiration,

the pressure gradient between the inferior vein cava and

right atrium increases, which impulse blood into the r ight

atrium (there is an effect of “suction”), thereby increasing

the volume of right ventricular ejection, to the pulmonary

circulation. On the other hand, although the atrium and

left ventricle also increases volume during inspiration,

T. CORDOVA-FRAGA ET AL. 133

the lungs in expanding work as a reservoir (increase the

volume of pulmonary blood), so that, left ventricular filling

does not increase during inspiration. During aspiration,

however, is produced the opposite effect: the thoracic

cavity volume decreases, because the chest wall is re-

tracts and the diaphragm up. This produces a pressure

increase intrapulmonary, causing a decrease in lung

volume, the heart and the thoracic vena cava. Therefore,

the accumulated blood in the pulmonary reservoir during

the inspiration is forced to pass into the atrium and left

ventricle, which increases left ventricular filling and

stroke volume of ejection into the aorta artery, in other

words, when inhaled, there is an increase in venous

pressure and when exhaling, there is a decrease in this,

these small variations are also detected by the PPC.

Gravity, temperature and metal objects also affect the

se that suggest the possibility that

5. Conclusions

s shown an excellent signal, w

th BMI indicating a

ore measurements com-

6. Acknowledgements

artial support to the DAIP

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