NONINVASIVE MEASUREMENT OF BLOOD ACID-BASE (pH)

USING CONCENTRATIONS OF EXHALED GASES

A. S. Altaan

, O. Abdallah

, Mohammad T. Othman

, Nasser Musaab

and A. Bolz

Biomedical Engineering Institute, Karlsruhe Institute for Technology, Karlsruhe, Germany

Department of Physical Education, College of Basic Education, Mosul University, Mosul, Iraq

Department of Internal Medicine and Cardiovascular, Ibn Sina Teaching Hospital, Mosul, Iraq

Keywords: Exhaled Breath, Partial Pressure of Oxygen, Concentration of Carbon Dioxide, Non-invasive Blood Acid-

base (pH).

Abstract: An important property of blood is its degree of acidity and alkalinity which is referred to as acid-base

balance. The acidity or alkalinity of the blood is indicated on the pH scale. The blood pH has a serious

effect on all of the body’s systems and the body uses different mechanisms to control the blood’s acid-base

balance. Acid-base imbalances result primarily from metabolic or respiratory failures, both imbalances

cause changing in the normal range of CO2 in the blood. The concentrations of oxygen and carbon dioxide

from the exhaled breath were used to evaluate the pH of the blood. The results show the relation between

concentration of the exhaled CO2 and the blood acid-base pH; decreasing CO2 causes the blood to be

alkaline, while increasing CO2 leads the blood to become acidic.

1 INTRODUCTION

During exercise the muscles are working harder than

normal and, as a result, they require more energy

than normal. Since the ATP energy used by the

muscles is generated with the aid of oxygen, it

follows that an increase in exercise intensity will

result in an increase in muscular oxygen demands.

Therefore, increased exercise intensity ultimately

corresponds to an increased in the volume of the

consumed oxygen. As the muscles working harder

they release more CO2 this will affect the balance of

O2 and CO2 in the blood, this is the reason that

breathing gets progressively faster and deeper as

exercise intensity increases, the body is trying to

provide more oxygen to the working muscles and

release the resulting carbon dioxide so that they can

generate enough ATP energy to keep the athlete

moving. Homeostasis is the overall process of

maintaining stability of the body’s internal physical

and chemical systems. These processes involve rapid

correction of disturbances that may arise, as well as

instance by instance adjustments to prevent gross

disturbance from arising. A simple example is that if

the heart rate and the respiratory rate did not

increase during physical exertion, body chemistry

would be significantly altered by the resulting deficit

in oxygen and accumulation of carbon dioxide. The

amount of carbon dioxide in the blood has an

immediate and direct effect on the body’s acid-base

balance, a key aspect of the internal chemical state.

1.1 Effect of the O2 and CO2 on the pH

Hydrogen ion activity can significantly affect the

metabolic function of the cells. Bicarbonate ion

(HCO

) is the most important form of CO2, both

HCO

and H

are carriage by blood. CO2 combines

with water to form carbonic acid, and this

dissociates to HCO

and H

. The conversion of CO2

to H

and HCO

ions has tremendous implications

for acid–base physiology. Every day, resting

metabolism produces more than 15,000 mmol of

CO2, or 15,000 mmol/L of carbonic acid, and this

acid leaves the body through the lungs. By

comparison, the kidneys typically excrete only 100

mmol/L of acid per day. The ability to change blood

pCO2 levels rapidly by changing ventilation has a

powerful effect on blood pH, so acid–base balance

depends on the integrated function of respiratory and

renal systems. Regulation of hydrogen ion (H

)

balance is similar in some ways to the regulation of

other ions in the body. For instance, to achieve

264

S. Altaan A., Abdallah O., T. Othman M., Musaab N. and Bolz A..

NONINVASIVE MEASUREMENT OF BLOOD ACID-BASE (pH) USING CONCENTRATIONS OF EXHALED GASES.

DOI: 10.5220/0003789502640269

In Proceedings of the International Conference on Bio-inspired Systems and Signal Processing (BIOSIGNALS-2012), pages 264-269

ISBN: 978-989-8425-89-8

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

homeostasis, there must be a balance between the

intake or production of H+ and the net removal of

H+ from the body.

1.2 Chemical Relations of CO2 in the

Blood

Hydration (combination with water) of dissolved

carbon dioxide sets up an equilibrium with carbonic

acid, which plays a key role in acid-base balance:

O+CO

In turn, dissociation of this weak acid yields

hydrogen ion and the conjugate base, bicarbonate

ion:

+ HCO

Therefore carbonic acid can be viewed as a

traditional stage between the hydration of dissolved

carbon dioxide on one side, and the dissociation into

hydrogen and bicarbonate ions on the other side:

O+CO

+ HCO

Increasing one of the chemical species in a system

pushes the equilibrium toward the opposite side.

Thus a rise in carbon dioxide levels in the blood

causes an increase in the hydrogen ion

concentration. Blood acid-base (pH) varies inversely

with hydrogen ion concentration according to the

relation below:

pH = log



(1)

Table 1: pH values with H

ion concentration.

pH Ion Concentration (gram

equivalent per liter)

Type of Solution

0 1.0

Acid Solution

- Hydrogen ions -

1 0.1

2 0.01

3 0.001

4 0.0001

5 0.00001

6 0.000001

7 0.0000001 Neutral Solution

8 0.000001

Basic (alkaline) Solution

- Hydroxide ions -

9 0.00001

10 0.0001

11 0.001

12 0.01

13 0.1

1.0

The pure water have pH of 7 which considered

neutral, acid solutions have pH less than 7 like the

orange juice (3-4) while the basic solutions have pH

more than 7 like soapy water (12). Table 1 showed

the pH values with the corresponding hydrogen ion

concentration and the type of solution.

2 METHODS

Because of the direct relation between the carbon

dioxide in the blood and the pH, determining the

level of carbon dioxide in the blood is very

important. The air we inhale is roughly 78% by

volume nitrogen, 21% oxygen, 0.96% argon and the

rest 0.04% contain carbon dioxide, helium, water,

and other gases. The permanent gases in the breath

we exhale are roughly 4% to 5% more carbon

dioxide and 4% to 5% less oxygen than was inhaled.

There are different methods to determine the

level in the blood, one of the important one

which is invasive is the Arterial Blood Gas Analysis

method which gives the partial pressure of the O2

and CO2, but what was accomplished in this

research is non-invasive method of determining

pCO

and pO

in the arterial blood. Measurements

using the Vista-MX device from (Vacu•Med) were

taken from 60 person (45 male, 15 female) in the

rest and for 5 Athletes during exercise. These

measurements give many parameters of the exhaled

breath, we use some of these parameters which are

, VCO

, O

% and CO

%. The meaning of each

of these parameters is:

: Oxygen consumption in liter per minute.

VCO

: CO

output in liter per minute.

% and CO

%: the concentrations of oxygen and

carbon dioxide in the exhaled breath.

According to the ideal gas law VO

and VCO

were

converted to pressure which is then multiplied by the

concentration of the related gas to give the partial

pressure of the oxygen and carbon dioxide in the

exhaled breath (pO

and pCO

n. T.

(2)

n: number of moles, T: temperature, K: Boltzmann

constant and V: volume. Table 2 shows some gases

constants used to calculate the number of moles for

the above equation.

Table 2: O

and CO

constants.

molecular weight 31.9989 44.01

Density(kg/m

) at 25

C 1.308 1.799

After obtaining the partial pressure of oxygen

NONINVASIVE MEASUREMENT OF BLOOD ACID-BASE (pH) USING CONCENTRATIONS OF EXHALED

GASES

265

and carbon dioxide (pO2, pCO2)

in the exhaled

breath, paO2 and paCO2 have to be calculated in the

arterial, this can be done by using the ventilatory

exchange ratio (R), which can be calculated from the

ratio between the carbon dioxide output and the

oxygen uptake:

VCO2

VO2

(3)

Figure 1 shows ventilatory exchange ratio (R=0.8)

plotted in the pO

- pCO

plane. The figure shows

four important points for the values of pO2 and

pCO2 (E: Exhaled, A:Alveoli i:ideal and a:arterial).

These four points play the main idea in the

calculations of the partial pressure of oxygen and

carbon dioxide in the arterial blood.

A method is developed in this research to

estimate the actual values of pAO2 and pACO2 in

the Alveoli according to the ventilatory exchange

ratio (R). The ideal values for the pO2 and pCO2 in

the arterial blood are 100 and 40 respectively. But

the actual values may be different from these values.

Most of the references state that the partial pressure

of the carbon dioxide is the same in the alveoli and

the alveoli arteries. The arterial partial pressure of

oxygen was calculated from alveoli pAO2 using the

equation below which gives the normal gradient

between the partial pressure of oxygen in the alveoli

and the arterial:

Normal A-a gradient = (Age+10) / 4 (4)

After getting the arterial partial pressure of the

oxygen and carbon dioxide, a neural network was

built to determine the level of blood acid-base (pH).

The neural network based on the arterial pO2 and

pCO2 which are directly related to the pH of the

blood.

Figure 1: Ventilatory exchange ratio (R).

3 RESULTS

The theoretical chemical reaction states that increase

the carbon dioxide in the blood causes increasing

hydrogen ion in the blood which results in lower pH

(the logarithmic relation), that means the blood

becomes acidic. Also vice versa is correct, when the

carbon dioxide decreases in the blood causes

decreasing the hydrogen ion which results in higher

pH and the blood becomes alkaline.

At the beginning the developed algorithm was

applied to the data obtained from the athletes. As

stated in the introduction section about the

consumed oxygen which is increased during the

exercise that results the concentration of the exhaled

oxygen to be decreased. Figure 2 (Up) clarifies the

decrease in oxygen concentrations with the

respiratory rate in the exhaled breath during

exercise. While the opposite happened with the

carbon dioxide concentration which is increased

with increasing the respiratory rate as shown in

figure 2 (Down).

Figure 2: Up: change of the O2 concentration with the

respiratory rate. Down: change of the CO2 concentration

with the respiratory rate.

When the muscles are working harder they

BIOSIGNALS 2012 - International Conference on Bio-inspired Systems and Signal Processing

266

release more carbon dioxide, this will causes the

partial pressure of carbon dioxide in the blood to be

raised, and as a result the concentration of the CO2

in the exhaled breath will be increased. The body

respond to this change in gases concentrations by

raises the respiratory rate to throw out more CO2

from the body. Figure 3 shows the change of the

CO2 concentration in the exhaled breath with the

partial pressure of CO2 in the Blood. Figure 4 shows

the increase of the partial pressure of the carbon

dioxide with the respiratory rate.

Figure 3: Change of the pCO2 in the arterial with the CO2

concentration in the exhaled breath.

Figure 4: Change of the pCO2 in the arterial with the

respiratory rate.

After the practical proof of the direct relation

between the concentration of the exhaled gases with

the partial pressure of these gases in the blood, a

neural network has been designed to determine the

blood acid-base level depending on the partial

pressure of the gases. A neural network was built,

two types of the neural networks achieved the goals,

the characteristics of the two neural networks chosen

are listed in the table 3.

The network was trained by data sets (from rats)

have been taken from Bioinformatics Program of

Human & Molecular Genetics Center-Medical

College of Wisconsin, USA. Two data groups were

used the first one contain 673 data sets and the

second contain 860 data sets. During the network

training many of learning functions were used and

many performances of the network were obtained.

One of the best performances of the neural network

is shown in the figure 5.

Table 3: Neural network characteristics.

Network type Layer

Recurrent

Elman bachprop

Training function Traingdm Traingdm

Adaption learning

function

Learngdm Learngdm

No. Of Layers 2 2

No. Of neurons 10 10

Transfer function Purelin Purelin, Tansig

Figure 5: Neural network performance.

The results given by the neural network are clear.

They give that the change of the blood acid-base

level is directly related to the change of the partial

pressure of the CO2 in the blood. Figure 6 shows the

clear inversely change of the pH with the partial

pressure of the carbon dioxide in the blood.

Figure 6: Change of the pH with the pCO2.

NONINVASIVE MEASUREMENT OF BLOOD ACID-BASE (pH) USING CONCENTRATIONS OF EXHALED

GASES

267

Then it will be obvious that the pH will be

changed with the concentration of the CO2 in the

exhaled breath because of the change of pCO2 with

CO2 concentration, figure 7 shows this change.

Figure 7: Change of the pH with the concentration of CO2

in the exhaled breath.

As stated in the beginning of the result section all

of the above results were for the athletes during

exercise. Also the same algorithms were applied to

individuals at the rest. The obtained results show the

inverse changes of the pH level with the

increase/decrease of CO2 in the blood. Figure 8

shows the results of inversely change of pH with the

partial pressure of CO2 in the arterial blood for

individuals.

Figure 8: Change of the pH with the pCO2 for persons at

the rest.

4 CONCLUSIONS

Blood pH is tightly regulated by a system of buffers

that continuously maintain it in a normal range of

7.35 to 7.45 (slightly alkaline). Carbon dioxide is

one of the central roles in this blood pH abnormality.

Resting metabolism produces more than 15,000

mmol of CO2, or 15,000 mmol/L of carbonic acid,

and this acid leaves the body through the lungs.

More CO2 in the blood causes more hydrogen ion

which is the major factor specifies the blood acid-

base level pH. This means that the respiratory

system is playing an important role in the regulation

of blood acid-base level pH. This fact lead us to

develop a noninvasive method for finding pH

depending on exhaled gases.

A direct method to noninvasively determine the

blood acid-base level pH was developed. The

developed method depends on the concentration of

the carbon dioxide that the person exhaled. The CO2

concentration is associated with the level of the

partial pressure of CO2 in the blood which we used

to determine the pH level. The increase of CO2

causes the blood to be acidic while decrease CO2

makes the blood more alkaline. Increasing the CO2

in the blood causes increasing the respiratory rate to

exhaled more CO2 which results the pH to be

returned to its normal level.

ACKNOWLEDGEMENTS

We thank the staff and the students in the

Department of Physical Education-College of

Basic Education-Mosul University in Iraq, who

help us to get the data of more than 80 people.

REFERENCES

T. Tiger, J. K. Kirk, R. J. Solomon, 1999. Mathematical

Concepts in Clinical Science, Prentice Hall.

Instruction Manual, Manual No. X17001-5, TurboFit_

Software for Windows Version 5.11, Last Update 17

February 2010.

Poul-Erik Paulev, M. D., D.Sci, 1999 – 2000. Medical

Physiology And Pathophysiology Essentials and

clinical problems, Copenhagen Medical Publishers.

J. S. Gravenstein, Michael B. Jaffe, David A. Paulus,

2004. Capnography: clinical aspects, Cambridge

University Press, United Kingdom.

Rob Law, H. Bukwirwa, 1999. The Physiology of Oxygen

Delivery.

http://www.shapesense.com/fitnessexercise/articles/vo2-an

d-vo2max.aspx#whatareVO2andVO2max

Terry Des Jardins, MEd, RRT, 2002. Cardiopulmonary

Anatomy & Physiology Essentials for Respiratory

Care, Delmar, a division of Thomson Learning, Inc.

Thomson Learning Fourth Edition.

Michael Krause, Andrea Doescher, Beate Zimmermann,

BIOSIGNALS 2012 - International Conference on Bio-inspired Systems and Signal Processing

268

and Thomas H. Müller, 2010, Noninvasive pH

measurement to monitor changes during suboptimal

storage of platelet concentrates, Transfusion

2010;50:2185-2192.

Bhavani-Shankar K, Moseley H, Kumar A Y et al. 1992

Capnometry and Anaesthesia. Can J Anaesth; 39:

617–32.

Lawrence Martin, M. D., 1999, All You Really Need to

Know to Interpret Arterial Blood Gases , 2

edition.

Babs R. Soller, PhD, Ronald H. Micheels, PhD, John

Coen, B. S., Bhairavi Parikh, M. S., Ling Chu, PhD,

and Charles Hsi, MiD, 1996, Feasibility of Non-

invasive Measurement of Tissue Ph using Near-

infrared Reflectance Spectroscopy, Journal of Clinical

Monitoring 12: 387-395.

Arthur C. Guyton, M. D., 2006, John E. Hall, Ph.D.,

Textbook of Medical Physiology, Elsevier Inc.

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GASES

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