MODULE III

• The human nervous system. Neuron, action potential of

brain, brain waves, types of electrodes, placement of
electrodes, evoked potential, EEG recording, analysis of
EEG.
• Electrical activity of muscles- EMG. Signal Acquisition and
analysis. Applications of EMG - myoelectric control
system. Electrical stimulation of the muscle and nerve,
Functional Electrical Stimulation- Principle and
applications.
• Physiology of respiratory system (overview), Respiratory
parameters, spirometer, body plethysmographs, gas
exchange and distribution.
Nervous systems

3
 Nervous systems
• The nervous system is the control and communication network of
the body which coordinates the functions of the various organs.
• It is the most complex system in the human body.
• It acts as a highway for information to travel.
• It controls the movement in the body and converts the information
for the body to read and process.
• It composed of Brain, Sensors, high speed communication links
,spinal cord.
• It is classified into two,
1) Central Nervous System (CNS)
2) Peripheral Nervous System (PNS)
• CNS is enclosed in skull and vertebral column and PNS in nervous
tissue outside the skull and vertebral column.

4
Central Nervous System (CNS)

• The main part of CNS is brain and spinal cord.

• The brain is the large soft mass of nerve tissue contained in the skull.
• Brain is the control center of the body.
• Brain is covered by protective layer called meninges.
• It has three layers : outer layer, middle layer, inner layer
• Brain is divided into three main sections: cerebrum, cerebellum, brain
stem.
 Cerebrum
• Cerebrum or cortex is the largest part of the brain.
• It controls thought and actions like reasoning, planning, speech,
movement, visual processing and memory.

Cerebellum
• It is the second largest part of the brain.
• It is located just above the brain stem and back of the brain.
• The outer part of it is made up of gray matter and inner part of white
matter.
• It provide smooth body muscle movement, balance and equilibrium.

Brain stem
• It consists of medulla oblongata, pons , midbrain and diencephalon.
• It extends to spinal cord.
• It controls breathing, heart rate and blood pressure.
Peripheral nervous System

• It contains nerve cells outside the brain and spinal cord.

• The main function is to connect central nervous system to limbs and
organs.
• PNS is not protected by bone of spine and skull.
• It is divided into
1) Somatic Nervous System
2) Autonomic Nervous System
• Somatic Nervous System is responsible for coordinating the body
movements and receiving external stimuli.
• Autonomic Nervous System is responsible for coordinating
involuntary actions like heart beat, respiration etc.
 Nervous System-Neuron

• Basic unit of nervous system is the neuron.

• Neurons are the basic building blocks of the nervous system.
• Neuron is a single cell with a cell body. It is sometimes called soma.
• Neuron cells are the information-processing units of the brain responsible
for receiving and transmitting information.
• One or more input fiber branches are called dendrites
• Long transmitting fiber is called axon
• Each part of the neuron plays a role in the communication of information
throughout the body.
Types:
Sensory Neurons (Afferent Neurons):
• Transmit sensory information from the sensory organs (such as eyes, ears,
skin) to the central nervous system (CNS).
• Have long dendrites and a short axon.
Motor Neurons (Efferent Neurons):
• Transmit motor signals from the central nervous system to muscles and
glands, controlling movements and secretions.
• Have long axons and relatively short dendrites.
 Interneurons (Association Neurons):

• Act as intermediaries between sensory and motor neurons, facilitating

communication between them.
• Primarily located in the central nervous system (CNS), forming complex
neural circuits.
Anatomy of the Nervous systems
• Neurons
Composed of:
a. Cell Body
Part that contains the nucleus
b. Dendrite(s)
Carries a nerve impulse towards the
cell body
c. Axon(s)
Carries a nerve impulse away from the cell body (and towards the dendrite
of the next neuron)
• Axons are also called nerve fibers.
11
Neuron
Main functions of the nervous system are:
1. Reception of general sensory information (touch, pressure, temperature,
pain, vibration)
2. Receiving and perceiving special sensations (taste, smell, vision, sounds)
3. Integration of sensory information from different parts of the body and
processing them
4. Response generation
Action Potential of Brain (Neuron)
Propagation of Action Potential
 EEG ELECTRODES

1. Scalp: silver pads, discs, or cups; stainless steel rods; and

chlorided silver wires.
2. Sphenoidal: Alternating insulated silver and bare wire and
chlorided tip inserted through muscle tissue by a needle.
3. Nasopharyngeal: silver rod with silver ball at the tip
inserted through the nostrils.
4. Electrocorticographic: cotton wicks soaked in saline
solution that rests on the brain surface (removes artifacts
generated in the cerebrum by each heartbeat).
5. Intracerebral: sheaves of Teflon-coated gold or platinum
wires cut at various distances from the sheaf tip and used to
electrically stimulate the brain
 Types of Electrodes used in EEG Measurement
Reusable disks
• These electrodes can be placed close to the scalp, even in
a region with hair because they are small.
• A small amount of conducting gel needs to be used under
each disk.
• The electrodes are held in place by a washable elastic
head band.
• Disks made of tin, silver, and gold are available. They can
be cleaned with soap and water.
EEG Caps with disks
• Different styles of caps are available with different
numbers and types of electrodes.
• Some caps are available for use with replaceable disks
and leads. Gel is injected under each disk through a hole
in the back of the disk.
REUSABLE ELECTRODES
• Since the disks on a region of the scalp covered with hair
cannot be placed as close to the scalp as individual disc
electrodes, a greater amount of conducting gel needs to
be injected under each.
• After its use, more time is required to clean the cap and
its electrodes, as well as the hair of the subject.

Adhesive Gel Electrodes

• These are the same disposable silver/silver chloride
electrodes used to record ECGs and EMGs, and they can
be used with the same snap leads used for recording those
signals.
• These electrodes are an inexpensive solution for
recording from regions of the scalp without hair
• They cannot be placed close to the scalp in regions with
hair, since the adhesive pad around the electrode would
attach to hair and not the scalp.

Subdermal Needles
• These are sterilized, single-use needles that are placed
under the skin.
• Needles are available with permanently attached wire
leads, where the whole assembly is discarded
 Placement of Electrodes
10- 20 electrode placement system

• An internationally recognized method that allows EEG

electrode placement to be standardized.
• Ensures inter-electrode spacing is equal
• Electrode placements proportional to skull size & shape
• Covers all brain regions
F = Frontal P = Parietal
T = Temporal O= Occipital
• Numbering system
Odd=Left Side Even=Right Side Z=Midline
10- 20 electrode placement system
Four Skull Landmarks

•Nasion
•Inion
•Left Pre-auricular point
•Right Pre-auricular point

• Lead FP1 for example, is in the frontal area and lies on a

circle with other leads.
• Nineteen electrodes, plus one for grounding the subject,
are used.
• Electrodes are placed (using a flexible tape measure) by
measuring the nasion-inion distance and marking points
on the (shaved) head 10%, 20%, 20%, 20%. and 10% of this
length.
• The vertex. Cz electrode is the midpoint.
• Electrode arrangements may be either unipolar or bipolar.
• A unipolar arrangement is composed of a number of scalp
leads connected to a common indifference point such as
an earlobe.
• Hence, one electrode is common to all channels.
• A bipolar arrangement is achieved by the interconnection
of scalp electrodes.
• Montages are patterns of connections between electrodes
and recording channels
 Evoked Potential

• An evoked potential or evoked response is an electrical

potential in a specific pattern recorded from a specific part
of the nervous system following presentation of a stimulus
such as a light flash or a pure tone.

• A special form of electroencephalography is the recording

of evoked potentials from various parts of the nervous
system.

• In this technique the EEG response to some form of

sensory stimulus, such as a flash of a light is measured.
• Figure given below shows a raw EEG record containing an
evoked response from a single presentation of the stimulus
and the effect of averaging 8 and 64 presentations,
respectively.
• These electrical signals are used in diagnosis and
monitoring of diseases and drug-related sensory
dysfunction.
• The process can be applied to intraoperative monitoring of
sensory pathways to ensure they maintain their integrity.
• Visual evoked potential (VEP) is an evoked potential
elicited by presenting light flash or pattern stimulus
which can be used to confirm damage to visual
pathway including retina, optic nerve and visual cortex.
Block Diagram of EEG Machine
1) Montage selector:

• Montages are patterns of connections between the electrodes

and the recording channels.
• The montage selection switch is used for selecting a particular
channel. Different channels convey different information.
• Montages are always symmetrical and hence in the 10-20
electrode placement system the electrodes are also placed
symmetrically.
• The EEG signals are transmitted from the electrodes to the
montage selector panel.
• The montage selector of an EEG machine is a large frame which
consists of different switches so as to allow the user to select the
desired electrode pair.
2) Amplifier

• The function of amplifiers in the EEG measuring system is clear

from the name itself.
• As the EEG signals are having amplitude levels in microvolt range it
is compulsory that they are to be amplified before further
processing.
• It is to ensure that the information from the EEG electrodes is not
affected by any external noise.
• We normally use high gain, high CMRR operational amplifiers

3) Filters
• The muscle artifacts (noise) are a major problem regarding the
EEG waveform. These noises can make the representation
dishonest. So we have to filter out these noise contents.
4) Analog to Digital Converters (ADC)

• For the detailed analysis of the EEG waveform, we use computers and
oscilloscopes.
• As the computers only accept digital data we have to convert the
analog EEG information in to digital form.
• The function of ADC is to convert the analog EEG signal to digital
form.
• Thus the computer can store the EEG waveform for future reference.

5) Writing recorder and paper drive

• The writing part of an EEG machine is usually consists of an ink type

direct writing recorder.
• The recorder will be a chart paper which is driven by a synchronous
motor.
• For the clear representation of the EEG waveform an accurate and
stable paper drive mechanism is provided by the synchronous
motor. Also there are provisions to control the paper speed.
 Applications of EEG

1. Diagnose epilepsy and types of seizures.

2. Check if a person is brain dead.
3. Study sleep disorders.
4. Monitor brain activity during surgery.
5. Differentiate a physical problem with mental health problem.
6. Diagnose brain dysfunction.
 Analysis of EEG

• The analysis of EEG (electroencephalogram) data typically

involves several steps to extract information about the electrical
activity of the brain.

1. Preprocessing: The raw EEG data is first preprocessed to

remove noise and artifacts that can obscure the underlying signals.
This may involve filtering the data to remove high-frequency noise,
removing slow drifts, and removing specific artifacts such as eye
movements or muscle activity.

2. Event Detection: Once the data is preprocessed, specific

events of interest can be detected. These could include visual or
auditory stimuli, movements, or specific phases of the sleep cycle.
Event detection allows for the extraction of specific segments of the
EEG data that are relevant to the analysis.
3. Feature Extraction: Various features can be extracted from the
EEG data, such as spectral power, coherence, or event-related
potentials. These features can provide insights into the brain
activity during specific events or phases of the sleep cycle.

4.Statistical Analysis: Statistical techniques can be used to

compare the EEG data between different conditions or groups of
participants. This can help identify differences in brain activity
related to cognitive processes, neurological disorders, or
experimental manipulations.

5.Source Localization: Source localization techniques can be

used to identify the specific regions of the brain that are generating
the EEG signals. This can help to understand the underlying neural
mechanisms that are producing the observed EEG activity.

.
Electromyogram
• Electromyography is the technique for calculating and recording the
action potential of muscles.
• EMG is taken using a device called electromyograph and the record
obtained is known as electromyogram.
• The electrical activity of muscle cells when they are active and at
rest can be analyzed using an EMG.
• The measured EMG potentials range from 50 µ Volt to 30 millivolts.
• Mainly there are two kinds of EMG measurements.
• The first method is using surface electrodes and the second one is
using needle electrodes.
• The Surface EMG electrodes are used to monitor the electrical
activity of muscles generally whereas the needle electrodes are
used to observe the electrical activity of only few fiber
Mainly there are two kinds of EMG measurements.

• The first method is using surface electrodes and the second one is
using needle electrodes.
• The Surface EMG electrodes are used to monitor the electrical
activity of muscles generally whereas the needle electrodes are
used to observe the electrical activity of only few fibers.

• A trained expert can observe the electrical activity of muscles

when the needle is inserted.
• There is a normal electrical activity for the muscle fibers at rest.
• The physician or concerned expert examines the normal activity
of muscles when the needle is inserted.
• The abnormal spontaneous activity indicates that some nerve or
muscle cells are damaged.
• At a time potentials from different electrodes are taken.
• So the needle electrodes have to be placed at different locations to
obtain an accurate EMG.
• So the intramuscular EMG is considered to be too invasive.

• So in order to obtain the general activity of the muscle cells we use

surface electrodes which need to be placed only on the concerned
area.
• So no insertion is required.
• This technique is commonly used in many applications such as in a
physiotherapy clinic where the muscle activity is monitored by the
surface EMG electrodes and the patients can have visual stimulus
when they activating the muscles.
• So when the motor neuron or muscle fiber is stimulated, the action
potential is transmitted across the muscle it is passed to the
connected nerve fibers.
• Actually during EMG we are evaluating this bioelectric potential
from different cells.
• This potential is collectively called motor unit action potential
(MUAP). EMG signals are made up of superimposed MUAPs.

• Hence the shape of the electromyogram is affected by factors such

as number of muscle fibers under consideration, the metabolic type
of muscle fibers etc.
 EMG Block Diagram

1. EMG electrode:
• Electrode used for EMG recording can be of surface type or needle
type depending on the area from which the EMG is to be obtained
and the type of measurement.
• If we need to have EMGs from many individual muscle cells rather
than from the surface as a group, needle electrodes are the best
choice.
• But if the general activity of a muscle is to be analyzed the surface
electrodes can give the accurate values.
2. Bioelectric amplifier:
• As the name implies, the bioelectric amplifiers are used to amplify
the bioelectric signals obtained from EMG electrodes
3. AF amplifier:
• Abnormal and spontaneous activity may be distinguished by the
sudden change in sound and this can be analyzed by the physician.
• The abnormal activity usually indicates muscle damage and they
can easily find out the nerve or muscle damage.
• So physicians normally use AF amplifiers during EMG
measurement so as to distinguish there sounds clearly.
4. Oscilloscope:
• The measured EMG can be connected to the oscilloscope to
visualize the EMG.
• The abnormalities in the working of nerves and muscle cells can
be identified by a physician by analyzing the EMG waveform.
• The EMG can also be stored using special oscilloscopes such as
DSO (Digital Storage Oscilloscope) for future analysis.
5. EMG recorder:
• Unlike ECG, EMG cannot be recorded in a low speed chart paper
recorders because of its extreme low frequencies.
• So it will be less useful.
• Normally we use the photographic recording of EMG.
• For this a light sensitive paper is used.
 Applications of EMG
1. Diagnosis and monitoring of neuromuscular disorders:
EMG is commonly used to diagnose and monitor conditions that
affect the function of muscles and nerves.

2. Rehabilitation and physical therapy: EMG can be used to

evaluate muscle function and to guide rehabilitation and
physical therapy after injury or surgery. It can also be used to
monitor the progress of treatment and to assess the
effectiveness of interventions.

3. Prosthetics and orthotics: EMG can be used to control

prosthetic devices or orthotic braces by detecting and
interpreting the electrical signals generated by muscles.
4. Sports science: EMG can be used to study muscle activation
patterns and to measure muscle strength and endurance in
athletes. This information can be used to optimize training
programs and to prevent injuries.

5. Human-machine interfaces: EMG can be used to develop

interfaces between humans and machines, such as robots or
computers, by detecting and interpreting muscle signals.
RESPIRATORY SYSTEM
71
 Respiratory systems
▪ Respiration is the process of supplying oxygen to the tissues and removing
carbon dioxide from the tissues.
▪ These gases are carried through the blood
- oxygen from lungs to tissues
- carbon dioxide from tissues to lungs
External respiration: The gas exchanges in the lungs
Internal Respiration: The gas exchanges in the tissues
▪ Respiratory system is a pneumatic system.
▪ A system that work with air pressure.
▪ An air pump(diaphragm) which alternatively create negative and positive
pressures in a sealed chamber(Thoracic cavity).
▪ Thoracic cavity sucked air in to and forced out to lungs, which is a pair of
elastic bag.

74
 Respiratory systems
▪ The lungs are connected to the external environment through a pass way
(nasal cavities, pharynx, larynx, trachea, bronchi and bronchioles)
▪At one point , this passage is common with the tube that carries liquid and
solids to stomach.
▪A special valving arrangement interrupts the respiratory system whenever
solid or liquid passes through the common region.
▪The passage divides to carry air in to each bag.
▪In each bag , it is sub divided many times to carry air in to and out of each of
many tiny air spaces (pulmonary alveoli).
▪ Through alveolar membrane gas diffusion is taking place.
▪In case of nasal blockage , air input can be taken from mouth.
▪Oxygen is taken from the air and transferred in to blood.
▪Carbon dioxide is transferred from blood to air.
▪The system has a number of fixed volumes and capacities.

75
RESPIRATORY PARAMETERS
Tidal volume
▪The volume inspired and expired during each normal breath
Inspiratory reserve volume
▪Additional volume that can be inspired after a normal inspiration.
Expiratory reserve volume
Additional volume that can be expired after a normal expiration.
Residual volume
▪Amount of air remaining in the lungs after all possible air has been forced
out.
Vital capacity
▪Tidal volume+ Inspiratory reserve volume+ Expiratory reserve volume

76
Functions of Respiratory System
1. Inhalation and Exhalation

2. Exchange of Gasses between Lungs and Blood

3. Exchange of Gasses between Bloodstream and Body Tissues

4. Air Vibrating the Vocal Cords Creates Sound

5. Olfaction or Smelling
 Spirometer

• Spirometer is the most widely used instrument for the

measurement of various lung capacities and respiratory
volume.
• A spirometer is a medical device used to measure the volume of air
inspired and expired by the lungs.
• It's commonly used in respiratory assessments to evaluate lung function,
diagnose respiratory conditions, and monitor the progression of diseases
such as asthma, chronic obstructive pulmonary disease (COPD), and cystic
fibrosis.
Working

• The standard water seal spirometer consists of a movable bell

inverted over a chamber of water.
• To balance the bell jar we use a weight to maintain the gas
inside the atmospheric pressure.
• The height of the bell jar above the water will be
proportional to the amount of gas inside it.
• A breathing tube is connected to the mouth of the patient
with the gas under the bell.
• When no one is breathing into the mouth piece, the bell will
be at rest with a fixed volume above the water level.
• When the patient expires the pressure inside the bell
increases above the atmospheric pressure causing the bell to
rise.
• Similarly when the patient inspires, the pressure inside the
bell decrease below the atmospheric pressure and the bell
drops down.
• As the change in bell pressure changes the volume inside
the bell, the position of the bell jar is varied with respect to
the inspiration and expiration.
• As the bell position varies, the position of the weight which
balances the bell jar also varies.
• A pen is attached to the weight in order to record the
volume changes in a piece of graph paper.
• The chart recorder is called spirograph or kymograph and it
is a rotary drum.
• The graph obtained corresponding to breathing is called
spirogram.
• Some spirometers also have the provision to offer an electrical
output that is analog equivalent of the spirogram.
• Here we connect the pen and weight assembly to a linear
potentiometer.
• If we connect certain positive and negative potentials to the
end of the potentiometer, then the resulting electrical output
can provide the same data as the pen.
• When the patient is not breathing the output will be zero.
• When the patient inspires the output will have one polarity
and it will be of opposite polarity during expiration
Testing Procedure:

• Inhalation: The patient inhales deeply and then exhales forcefully

into the mouthpiece or mask connected to the spirometer.
• This exhalation can be performed either as a rapid forced exhalation
or as a slow, steady exhalation, depending on the specific test being
conducted.

• Measurement: As the patient exhales, the spirometer measures

various parameters including:

• Forced Expiratory Volume (FEV): The volume of air exhaled in the first
second of forced expiration (FEV1) and the total volume exhaled
(FEV1/FVC ratio, where FVC stands for Forced Vital Capacity).
• Forced Vital Capacity (FVC): The total volume of air exhaled forcefully
and completely after maximal inhalation.
• Peak Expiratory Flow (PEF): The maximum speed at which the patient
can exhale air during forced expiration.
• Tidal Volume (TV): The volume of air inspired and expired during
normal breathing.
• Residual Volume (RV): The volume of air remaining in the lungs
after maximal expiration.
• Total Lung Capacity (TLC): The total volume of air in the lungs at
maximal inflation.

Data Analysis: The spirometer records and displays the measured

parameters in real-time, allowing healthcare professionals to analyze
the patient's lung function.
Applications
• Spirometers is the primary equipment used for PFT meaning
Pulmonary Function Tests.
• It is a useful test for assessing the health conditions of the
patient’s lungs.
• In addition, it is often used for finding the cause for shortness
of breath, analyzing lung functions, effect of medication, and
progress for disease treatment.
Body Plethysmography
• The volume-constant whole-body plethysmograph is a
chamber resembling a glass-walled telephone box in
shape and volume (about 700–1000 L).
• During measurement the box is closed with an airtight
seal, except for a small controlled leak that is used to
stabilize the internal pressure by allowing for equilibration
of slow pressure changes.
• One pressure transducer serves to measure the pressure
inside the box relative to ambient pressure, another one is
placed close to the mouth for recording mouth pressure
• The shutter mechanism can be used to deliberately block
the airflow by transient occlusion.
• Moreover, respiratory flow rate is recorded by
conventional equipment, such as pneumotachograph,
anemometer, or ultrasound measurement, all of which is
calibrated via syringes delivering a defined volume.

Principle of measurement

• The principle of measurement of the commonly used

plethysmographs relies on detecting changes in box
pressure in combination with either changes of mouth
pressure or with flow rate under defined breathing
conditions.
• These signals are evaluated in order to determine static lung
volumes and airflow resistance.
• The basic physical principle exploited by body
plethysmography is the law of Boyle- Mariotte.
• Assumes temperature remains constant
• When subject breathes in and out against a shutter, changes
in pressure and volume occur.
• When a fixed amount of gas in a closed compartment the
relative changes in the compartment’s volume are always
equal in magnitude but opposite in sign to the relative
changes in pressure
WORKING
• The term plethysmograph is derived from the Greek Word
“plethysmos “ meaning enlargement and “graphien “ for to write.
• Through this procedure total volume in lungs is determined
including the volume that can’t be exhaled.
• The idea behind body plethysmography is to measure lung
volume non- invasively and outside the thorax.
• For this thoracic movements during breathing is recorded as the
pressure changes in the surrounding air, which are converted
subsequently into changes in the lung volume.
• This type of measurement work only in a closed set-up.
• Accordingly, patients sit in an air-tight cabin, breathing air in and
out from outside the cabin via a mouthpiece.
• Inside the cabin there is a pressure sensor that registers the
pressure change within the cabin.
• A second pressure sensor is in the mouthpiece that can
simultaneously measure the pressure in the mouth and airflow.
• Since the cabin is closed and it doesn’t change its shape, the
volume and pressure in the cabin always changes simultaneously
and in opposite directions.
• This means if one value increases, the other value decreases
automatically and conversely.
• The product of pressure and volume inside the cabin is constant.
• This relationship is also known as Boyle's Law.
• During the inspiration, volume of lungs and therefor the thorax
increases. The body occupies more space in the cabin, as a result
the volume of the surrounding air in the chamber decreases by the
same amount through which the volume of thorax increases.
• The surrounding air is compressed and cabin pressure is increased.
• During the expiration the lungs and therefore, thorax constrict
again. The space available to the surrounding air enlarges.
• If the displaced volume required for inspiration is 1% of the total
volume.
• By measuring cabin pressure, we can calculate how large the
displaced volume is in milliliters.
• From this we can calculate the total lung volume (100%)
 Gas Exchange and Distribution

• Once air is in the lungs, oxygen and carbon dioxide must be

exchanged between the air and the blood in the lungs and
between the blood and the cells in the body tissues.
• In addition, the gases must be transported between the
lungs and the tissue by the blood.
• A number of tests are thre to determine the effectiveness
with which these processes are carried out

Measurements of Gaseous Exchange and Diffusion

• The mixing of gases within the lungs, the ventilation of the

alveoli, and the exchange of oxygen and carbon dioxide
between the air and blood in the lungs all take place
through a process called diffusion.
• Diffusion is the movement of gas molecules from a point of
higher pressure to a point of lower pressure to equalize the
pressure difference.
• This process can occur when the gas is unequally distributed in
a chamber or wherever a pressure difference exists in the gas
on two sides of a membrane permeable to that gas.
• Measurements required for determining the amount of
diffusion involve the partial pressures of oxygen and carbon
dioxide, Po2 and Pc02 respectively.
• There are many methods by which these measurements can
be obtained, including some chemical analysis methods and
measurements of diffusing capacity
 GAS EXCHANGE

• All of our cells need energy, they get it by breaking down glucose,
a simple sugar we get from food.
• This process called cellular respiration.
• It uses oxygen and produces carbon dioxide as waste.
• The main function of the respiratory system is to provide the
oxygen out of the air and remove the carbon dioxide into the air.
This takes place in the lungs.
• With the gases carried to and from the cells by the bloodstream,
the exchange of gases between the blood and the air occurs in the
alveoli, microscopic air sacs in the lungs that are surrounded by
tiny blood vessels.
• When we inhale all 300 million alveoli expand and fill with air.
• Oxygen diffuses from the alveoli into the blood and carbon dioxide
diffuses from the blood into the alveoli.
• Diffusion is the natural movement of gas or liquid particles from an
area of higher concentration to an area of lower concentration.
• Diffusion can even take place through a membrane if the particles
are small enough to get through it .
• for example a helium balloon that's been left for a couple of days
gets smaller and softer because the helium has slowly diffused
through the skin of the balloon into the surrounding air .
• The walls of the alveoli are membranes.
• Oxygen and carbon dioxide can diffuse through it, because
breathing keeps bringing fresh air into the lungs.
• The circulatory system keeps bringing blood that is low in oxygen
and high in carbon dioxide diffusion always acts to bring oxygen
into the body and take carbon dioxide out
1. Chemical analysis methods.
• In the original gas analyzers devices, a gas sample of
approximately 0.5 ml is introduced into a reaction chamber
by use of a transfer pipet at the upper end of the reaction
chamber capillary.
• An indicator droplet in this capillary allows the sample to be
balanced against a trapped volume of air in the
thermobarometer.
• Absorbing fluids for C02 and 02 can be transferred in from
side arms without causing any change in the total volume of
the system.
• The micrometer is adjusted so as to put mercury into the
system in place of the gases being absorbed.
• The volume of the absorbed gases is read from the
micrometer barrel calibration.
2. Diffusing capacity using CO infrared analyzer.

• To determine the efficiency of perfusion of the lungs by

blood and the diffusion of gases, the most important tests
are those that measure 02, C02, pH, and bicarbonate in
arterial blood.
• In trying to measure the diffusion rate of oxygen from the
alveoli into the blood, it is usually assumed that all alveoli
have an equal concentration of oxygen.
• Actually, this condition does not exist because of the
unequal distribution of ventilation in the lung; hence, the
terms diffusing capacity or transfer factor (rather than
diffusion) are used to describe the transfer of oxygen from
the alveoli into the pulmonary capillary blood.
Gas chromatograph.

• The quantities of various gases in the expired air can also be

determined by means of a gas chromatograph, an
instrument in which the gases are separated as the air
passes through a column containing various substances that
interact with the gases.
• The reactions cause different gases to pass through the
column at different rates so that they leave the column at
different times.
• The quantity of each gas is measured as it emerges.
• To identify the gases in the expired air other than oxygen,
nitrogen, or COj, a mass spectrometer is used in
conjunction with the gas chromatograph.
• The mass spectrometer identifies the ions according to their
mass/charge ratio.
Measurements of Gas Distribution

• The distribution of oxygen from the lungs to the tissues

and carbon dioxide from the tissues to the lungs takes
place in the blood.
• The process, by which each gas is transported, however, is
quite different. As mentioned earlier, oxygen is carried by
the hemoglobin of the red blood cells.
• On the other hand, carbon dioxide is carried through
chemical processes in which C02 and water combine to
produce carbonic acid, which is dissolved in the blood.
• The amount of carbonic acid in the blood, in turn, affects
the pH of the blood.
• In assessing the performance of the blood in its ability to
transport respiratory gases, then, measurements of the
partial pressures of oxygen (Pq}) and carbon dioxide (Pco2)
]n the blood, the percent of oxygenation of the hemoglobin,
and the pH of the blood are most useful.