Transcript Cont… - SNS Courseware

BIO–MEDICAL INSTRUMENTATION
Name: Mr. T.balasubramanian
Designation: Assistant Professor
Department: Electrical and Electronics Engineering
Subject code: EI 65
Year: IV
Unit: III
Title: NON-ELECTRICAL PARAMETER MEASUREMENTS
NON-ELECTRICAL PARAMETER MEASUREMENTS
Measurement of blood pressure – Cardiac output – Heart
rate – Heart sound – Pulmonary function measurements
– spirometer – Photo Plethysmography, Body
Plethysmography – Blood Gas analysers : pH of blood –
measurement of blood pCO2, pO2, finger-tip oxymeter ESR, GSR measurements .
Measurement of blood pressure
Blood pressure (BP) is the pressure (force per unit area)
exerted by circulating blood on the walls of blood vessels, and
constitutes one of the principal Vital signs. The pressure of the
circulating blood decreases as it moves away from the heart
through arteries and capillaries, and toward the heart through
veins. When unqualified, the term blood pressure usually
refers to brachial arterial pressure: that is, in the major
blood vessel of the upper left or right arm that takes blood
away from the heart. Blood pressure may, however, sometimes
be measured at other sites in the body, for instance at the
ankle. The ratio of the blood pressure measured in the main
artery at the ankle to the brachial blood pressure gives the
Ankle Brachial Pressure Index (ABPI).
(Cont…)
Arterial pressure is most commonly measured via a
sphygmomanometer, which historically used the height of a
column of mercury to reflect the circulating pressure (see
Noninvasive measurement). Today blood pressure values are still
reported in millimetres of mercury (mmHg), though aneroid and
electronic devices do not use mercury.
(Cont…)
For each heartbeat, blood pressure varies between systolic and
diastolic pressures. Systolic pressure is peak pressure in the
arteries, which occurs near the end of the cardiac cycle when
the ventricles are contracting. Diastolic pressure is minimum
pressure in the arteries, which occurs near the beginning of the
cardiac cycle when the ventricles are filled with blood. An
example of normal measured values for a resting, healthy adult
human is 115 mmHg systolic and 75 mmHg diastolic (written
as 115/75 mmHg, and spoken (in the US) as "one fifteen over
seventy-five"). Pulse pressure is the difference between systolic
and diastolic pressures.
(Cont…)
Systolic and diastolic arterial blood pressures are not static but
undergo natural variations from one heartbeat to another and
throughout the day (in a circadian rhythm). They also change in
response to stress, nutritional factors, drugs, disease, exercise, and
momentarily from standing up. Sometimes the variations are
large. Hypertension refers to arterial pressure being abnormally
high, as opposed to hypotension, when it is abnormally low.
Along with body temperature, blood pressure measurements are
the most commonly measured physiological parameters.
(Cont…)
Arterial pressures can be measured invasively (by penetrating
the skin and measuring inside the blood vessels) or noninvasively. The former is usually restricted to a hospital setting.
The predominantly used unit for blood pressure measurement is
mmHg (millimeter of mercury). For example, normal pressure
can be stated as 120 over 80, where 120 is the systolic reading
and 80 is the diastolic.
Auscultatory method aneroid
sphygmomanometer with stethoscope
Mercury manometer
Digital BP measurement equipment
(Cont…)
The auscultatory method uses a stethoscope and a
sphygmomanometer. This comprises an inflatable (RivaRocci) cuff placed around the upper arm at roughly the
same vertical height as the heart, attached to a mercury or
aneroid manometer. The mercury manometer, considered to
be the gold standard for arterial pressure measurement
measures the height of a column of mercury, giving an
absolute result without need for calibration, and
consequently not subject to the errors and drift of
calibration which affect other methods. The use of mercury
manometers is often required in clinical trials and for the
clinical measurement of hypertension in high risk patients,
such as pregnant women
Classification of blood pressure for adults
Category
systolic, mmHg
diastolic,
mmHg
or < 60
Hypotension
< 90
Normal
90 – 119
and 60 – 79
Prehypertension
120 – 139
or 80 – 89
Stage 1 Hypertension
140 – 159
or 90 – 99
Stage 2 Hypertension
≥ 160
or ≥ 100
Placement of Blood Pressure Cuff
Cardiac output
Cardiac output (Q) is the volume of blood being pumped by
the heart, in particular by a ventricle in a minute. This is
measured in dm3 min-1 (1 dm3 equals 1000 cm3 or 1 litre). An
average cardiac output would be 5L.min-1 for a human male
and 4.5L.min-1 for a female Measuring Cardiac Output
Cardiac output
Q can be calculated from these measurements:
VO2 consumption per minute using a spirometer (with the
subject re-breathing air) and a CO2 absorber.
the oxygen content of blood taken from the pulmonary
artery (representing mixed venous blood) .
the oxygen content of blood from a cannula in a peripheral
artery (representing arterial blood).
From these values, we know that:
VO2 = (Q x CA) - (Q x CV)
where
CA = Oxygen content of arterial blood
CV = Oxygen content of venous blood.
This allows us to say
Q = (VO2/[CA - CV])*100
Cardiac rate
Heart rate (HR) is a measure of the number of heart beats
per minute (bpm). The average resting human heart rate is
about 70 bpm. Heart rate varies significantly between
individuals based on fitness, age and genetics. Endurance
athletes often have very low resting heart rates. Heart rate can
be measured by monitoring one's pulse. Pulse measurement
can be achieved using specialized medical devices, or by
merely pressing one's fingers against an artery (typically on
the wrist or the neck; note that this can be dangerous if done
incorrectly or for too long).
Heart sound
The heart sounds are the noises (sound) generated by the
beating heart and the resultant flow of blood through it,
specifically the turbulence created when the heart valves
snap shut. This is also called a heartbeat. In cardiac
auscultation, an examiner uses a stethoscope to listen for
these sounds, which provide important information about the
condition of the heart.
(Cont…)
In healthy adults, there are two normal heart sounds often
described as a lub and a dub (or dup), that occur in sequence
with each heart beat. These are the first heart sound (S1) and
second heart sound (S2), produced by the closing of the
tricuspid + mitral valves and aortic + pulmonic valves,
respectively. In addition to these normal sounds, a variety of
other sounds may be present including heart murmurs,
adventitious sounds, and gallop rhythms S3 and S4.
(Cont…)
Heart murmurs are generated by turbulent flow of blood,
which may occur inside or outside the heart. Murmurs may
be physiological (benign) or pathological (abnormal).
Abnormal murmurs can be caused by stenosis restricting the
opening of a heart valve, resulting in turbulence as blood
flows through it. Abnormal murmurs may also occur with
valvular insufficiency (or regurgitation), which allows
backflow of blood when the incompetent valve closes with
only partial effectiveness. Different murmurs are audible in
different parts of the cardiac cycle, depending on the cause of
the murmur
Respiratory rate
Respiratory rate (RR) (aka respiration rate, pulmonary
ventilation rate or ventilation rate) is the number of
breaths a living being, such as a human, takes within a
certain amount of time (frequently given in breaths per
minute).
(Cont…)
The human respiration rate is usually measured when a
person is at rest and simply involves counting the number of
breaths for one minute by counting how many times the chest
rises. Respiration rates may increase with fever, illness, OR
other medical conditions. When checking respiration, it is
important to also note whether a person has any difficulty
breathing.
General Control of Breathing
(Cont…)
Breathing is controlled by the medulla of the brainstem. It
repeatedly triggers contraction of the diaphragm initiating
inspiration. The rate of breathing changes with activity level
in response to carbon dioxide levels, and to a lesser extent,
oxygen levels, in the blood. Carbon dioxide lowers the pH
of the blood.
(Cont…)
Average respiratory rates, by age:
Newborns: Average 44 breaths per minute
Infants: 20–40 breaths per minute
Preschool children: 20–30 breaths per minute
Older children: 16–25 breaths per minute
Adults: 12–20 breaths per minute
Adults during strenuous exercise 35–45 breaths per minute
Athletes' peak 60–70 breaths per minute
Gas volume – Flow rate of Co2, o2 in
exhaust air
(Cont…)
Respiration refers to the mechanisms for obtaining oxygen
from the air and delivering it to the tissues, while eliminating
carbon dioxide from the body. It is related to cellular
respiration, the biochemical processes that consume this
oxygen and generate the carbon dioxide in the course of
making adenosine triphosphate (ATP). Respiration in the
former sense involves four processes: (1) breathing, or
ventilation of the lungs (2) gas exchange between air and blood
in the lungs (3) gas transport in the blood and (4) gas exchange
between the blood and target tissues.
(Cont…)
Gas Transport
Blood leaving the lungs is therefore relatively high in O2
(oxygen in its diatomic form) and low in CO2. It travels via the
pulmonary veins to the left side of the heart, which pumps it
out into the systemic circulation. This division of the
circulatory system delivers it to every organ of the body.
Systemic Gas Exchange
When the blood reaches the systemic blood capillaries, gases
undergo processes that are essentially the reverse of what
occurs in the pulmonary alveoli. The blood unloads O2, which
diffuses into the tissue fluid and thus reaches the cells around
the blood capillaries. At the same time, the CO2 generated by
the metabolism of those cells diffuses into the blood to be
carried away to the lungs for disposal.
(Cont…)
Blood typically contains 95 mmHg O2 upon arrival at the
systemic capillaries and 40 mmHg O2 upon leaving.
Conversely, the blood has 40 mmHg of CO2 on arrival at the
systemic capillaries and typically 46 mmHg CO2 when it
leaves. The blood does not, however, unload the same amount
of O2 to all tissues or pick up the same amount of CO2. The
more active a tissue is, the warmer it is, the lower its O2 level
is, and the lower its pH is (because it generates more CO2 and
CO2 reduces the pH of body fluids). Heat, low O2, low pH, and
other factors enhance O2 unloading and CO2 loading, so tissues
that need the most oxygen and waste removal get more than
less active tissues do. The biochemistry of hemoglobin is
mainly responsible for this elegant adjustment of gas exchange
to the individual needs of different tissues
PH of blood
(Cont…)
(Cont…)
(Cont…)
(Cont…)
(Cont…)
(Cont…)
(Cont…)
(Cont…)
(Cont…)
GSR measurements
Galvanic skin response (GSR), also known as electrodermal
response (EDR), psychogalvanic reflex (PGR), or skin
conductance response (SCR), is a method of measuring the
electrical resistance of the skin. There has been a long history
of electrodermal activity research, most of it dealing with
spontaneous fluctuations.
(Cont…)
(Cont…)
One branch of GSR explanation interprets GSR as an image
of activity in certain parts of the body. The mapping of skin
areas to internal organs is usually based on acupuncture
points
A Galvanic Skin Response 60 second sample signal. The
signal was acquired in the middle and ringer fingers. The
source file was processed with scipy and exported with
matplolib. The sampling rate was 256 Hz.
(Cont…)
The device measures electrical conductivity between 2
points, much like an ohmmeter. The two paths for current are
along the surface of the skin and through the body. Active
measuring involves sending a small amount of current
through the body. Due to the sensitivity of the human body to
electrical shock, sometimes more passive methods are used
to determine the conductivity of the skin. When correctly
calibrated, the GSR can measure these subtle differences.
Plethysmography
A plethysmograph is an instrument for measuring changes in
volume within an organ or whole body (usually resulting from
fluctuations in the amount of blood or air it contains).
In a traditional plethysmograph, the test subject is placed inside
a sealed chamber the size of a small telephone booth with a
single mouthpiece. At the end of normal expiration, the
mouthpiece is closed. The patient is then asked to make an
inspiratory effort. As the patient tries to inhale (a maneuver
which looks and feels like panting), the lungs expand,
decreasing pressure within the lungs and increasing lung
volume. This, in turn, increases the pressure within the box
since it is a closed system and the volume of the body
compartment has increased.
Plethysmography
(Cont…)
There are two types of plethysmographs: flow and pressure.
In flow plethysmography, airway resistance is measured by
two maneuvers. The patient first pants while the mouth
shutter is open to allow flow changes to be measured. Then,
the mouth shutter closes at the patient's end expiratory or
FRC level and the patient continues panting while
maintaining an open glottis. This provides a measure of the
driving pressure used to move air into the lungs.
(Cont…)
Pressure plethysmographs are usually measured at the endexpiratory level and are then equal to FRC. The patient sits in
the box, which has the pressure transducer in the wall of the
device, and breathes through a mouthpiece connected to a
device that contains an electronic shutter and a differential
pressure pneumotachometer. The mouth pressure and box
pressure changes that are measured during tidal breathing
and panting maneuvers which are performed during the test
by the patient at the end of expiration are sent to a
microprocessor unit that calculates thoracic gas volume.
THANK YOU