Units of pressure and their conversion

•Respiratory system
•Biomechanics of breathing
•Negative intrapleural pressure and its importance
Lung volumes and capacities
•Spirometry
Dalton’s law
Molecular properties of gasses
states that the total pressure exerted by a gaseous
mixture is equal to the sum of the partial
pressures of each individual component in a gas
mixture
p =
p1 + p2
+ +
p n = p
V
i p
i
i = p
V
n
i=
1
partial pressure p i
of the i-th component we can determine from volume concentration
V i
/V and from total pressure of that mixture p

total atmospheric pressure P B
= 101,325 kPa (760 Torr)
Partial pressures and contents of dry air
Example 1. Calculate partial pressure N 2
and O 2
at P B
= 101,3 kPa; N 2
= 78,03 %, O 2
= 20,95 %:
pN 2
= 0,7803 . 101,3 kPa = 79,11 kPa;
pO 2
= 0,2095 . 101,3 kPa = 21,23 kPa.
Henry’s law
At a constant temperature, the amount of a given gas dissolved in a given type
and volume of liquid is directly proportional to the partial pressure of that gas.
V
p
αpiV
=
p
B
k
at P B
= 101,3 kPa a T = 37 °C je: α O2
= 0,024 ; α CO2
= 0,57
→ CO 2
solubility in water is 24-times higher than for O 2
In arterial blood pO 2
= 12,0 kPa, pCO 2
= 5,3 kPa;
How much of O 2
and CO 2
is dissolved in 1L of blood:
V p-O2
= 0,024 . 12000 / 101300 = 2,84 ml .l –1
V p-CO2
= 0,57 . 5300 / 101300 = 29,82 ml.l –1

Units of pressure and their conversion
•SI unit: [Pa] = N/m 2
•using height of liquid with the same pressure effect
p = h.ρ.g
h =height
ρ =density
g = gravitational acceleration
1m
1m
Torricelli pokus:
h
p
1 mm Hg = 1.36 cm H 2
O
Hg
ρ = 13 546 kg.m -3
h = 760 mm Hg = 760 torr …. 1 atm = 101 325 Pa
H 2
O
ρ = 1000 kg.m -3
h = 10.329 m H 2
O
…. 1 mm Hg (1 torr) = 133.322 Pa
…. 1atm = 101 325 Pa
…. 1 cm H 2
O = 98.1 Pa
http://brunelleschi.imss.fi.it
The Respiratory System
• Respiratory system
designed for gas
exchange
• Regulates acid-base
balance
• Regulates blood pressure
• Prevention of
thromboembolism
- upper respiratory tract is above vocal cords
- lower respiratory tract is below vocal cords

Human angiotensinogen
is 118 amino acids long
Pathway of RAAS
Trachea and Bronchial Tree

Terminal bronchiole Tree
300 million air sacs.
Large surface area (60 –
80 m2).
Cells Types of the Alveoli
• Type I alveolar cells
– simple squamous
cells where gas
exchange occurs
• Type II alveolar cells
(septal cells)
– free surface has
microvilli
– secrete alveolar
fluid containing
surfactant
• Alveolar dust cells
– wandering
macrophages
remove debris

Alveolar-Capillary Membrane
• Respiratory membrane = 1/2 µm
• Exchange of gas from alveoli to blood
4 Layers of membrane to cross
- alveolar epithelial wall of
type I cells
- alveolar epithelial basement
membrane
- capillary basement
membrane
- endothelial cells of capillary
Conductive and Respiratory Zones
• Conductive zone (Dead volume)
- Conducts air to respiratory zone
- Humidifies, warms, and filters air
Components:
– Trachea
– Bronchial tree
– Bronchioles
Respiratory zone
- Exchange of gases between air
and blood
Components:
– Terminal bronchioles
– Respiratory bronchioles
– Alveolar sacs

Breathing or Pulmonary Ventilation
Dimensions of the Chest Cavity
• Breathing in requires
muscular activity &
chest size changes
• Contraction of the
diaphragm flattens the
dome and increases the
vertical dimension of the
chest
Quiet Inspiration
• Diaphragm moves 1 cm & ribs lifted by external intercostal muscles
• Intrathoracic pressure falls and air is inhaled
Quiet Expiration
• Passive process with no muscle action
• Elastic recoil & surface tension in alveoli pulls inward
• Alveolar pressure increases & air is pushed out

Breathing or Pulmonary Ventilation
Air moves into lungs when pressure inside lungs is less than atmospheric
pressure
Air moves out of the lungs when pressure inside lungs is greater than
atmospheric pressure
Intra-pleural
Pressures
• Helps keep parietal &
visceral pleura stick
together and alveoli inflated
•Always subatmospheric
(756 mm Hg)
•As diaphragm contracts
intrapleural pressure
decreases even more (754
mm Hg)
Atmospheric
pressure = 1 atm
or 760mm Hg
Summary of Breathing

Compliance of the Lungs
•Compliance refers to the distensibility of the lung and is defined as the change in
lung volume produced by a change in pressure.
• Ease with which lungs & chest
wall expand depends upon
1. Elastic recoil of lungs &
2. surface tension
• Some diseases reduce
compliance
– tuberculosis forms scar tissue
– pulmonary edema => fluid in lungs
& reduced surfactant
Thin layer of fluid in alveoli
causes inwardly directed
force = surface tension, water
molecules strongly attracted to
each other causes alveoli to
remain as small as possible
Detergent-like substance called
surfactant produced by Type II
alveolar cells lowers alveolar
surface tension
If surface
tension is
high much
energy must
be used to
expand
alveoli
Laplace’s Law tells us that the
pressure within a spherical
structure with surface tension,
such as the alveolus, is inversely
proportional to the radius of the
sphere (P=2T/r). That is, at a
constant surface tension, small
alveoli will generate bigger
pressures within them than will
large alveoli.
Compliance of the Lungs
Emphysema is a disease characterized by dilation of the alveolar spaces and
destruction of the alveolar walls. With their loss, much of the elastic recoil of the lung
is also lost.
C = ∆V /∆P
Normal values are about 200 ml cmH 2 O -1
Airway’s resistance
this is a measure of the resistance to airflow in the airways expressed as the air
pressure divided by the flow. Normal adult values are about 2 cmH 2
Ol -1 s

Determination of Pulmonary Function
•To evaluate symptoms and signs of lung disease
•To assess the progression of lung disease
•To monitor the effectiveness of therapy
•To evaluate preoperative patients
•Screen people at risk of pulmonary disease
•To monitor for potentially toxic effects of certain
drugs/chemicals
Basic techniques:
peak air flow measurement
determination of lung volumes and capacities
forced expiratory volume measurement
flow/volume curve recording

Lung Volumes and Capacities
• Tidal volume TV = amount
air moved during quiet
breathing
• Minute ventilation MVR= is
amount of air moved in a
minute
• Maximum voluntary
ventilation MVV = volume of
air inspired per minute during
maximum voluntary hyper
ventilation. The patient is
asked to breathe at 50 min-1
as deeply as possible for 15 s.
The total volume of inspired
air is measured and multiplied
by four. Normal values for
men are about 150 l min-1,
• Reserve volumes = amount
you can breathe either in or
out above that amount of tidal
volume (IRV, ERV)
• Residual volume RV = 1200
mL permanently trapped air in
system (in the mouth, trachea
as well as the rest in the
lungs) This volume increases
with age and is slightly lower
in women.
• Vital capacity & total lung
capacity are sums of the
other volumes
Vital capacity (VC) is a change of
air volume in the lung which is
measured between the maximum
inspiration level and the maximum
expiration level. This
measurement which starts with
inspiration from the maximum
expiration level is called
inspiratory vital capacity (IVC).
The examination which starts with
expiration from the maximum
inspiration level is called
expiratory vital capacity (EVC).
VC = IRV + TV + ERV
The functional residual capacity
(FRC) is an amount of air which
remains in the lung after normal
expiration.
Lung Volumes and Capacities
FRC = ERV + RV
The total lung capacity (TLC) is the air volume in the lung at the end of maximum inspiration.
TLC = IRV + TV + ERV + RV

Forced Expiratory Volume Measurement
The forced expiration volume per second
(FEV1) is an air volume in liters which an
examined person expires in the first second
of forced expiration after maximum
inspiration.
This measured expiratory volume is often
expressed as a percentage of the forced
vital capacity, FEV1 /FVC and is called the
Tiffenea index [%].
FEV1 is called the second vital capacity or
distributed forced expiration per first second.
FEV1/FVC = 80%
Dynamic values of lung ventilation - flow/volume curve recording
Respiration frequency (df) [min-1] is a number of breaths in a given time
interval. It is usually given in units per minute. The normal respiration rate for a
baby is about 60 min -1 but, by the age of one year, this has fallen to 30-40 min -1
and, in an adult, 12-15 min -1 .
The respiration rate is not completely regular and changes with exercise, during talking and according to
the environment. The control centre for breathing is in the medulla of the brain and the major influence on
this is the CO 2
and O 2
level in the blood. The medulla, through its influence on the nerves supplying the
respiratory muscles and the diaphragm, can increase or decrease respiration rate and tidal volume.
Maximum expiratory flow values at 25% FVC –
(MEF25, also FEF25 ) [l.s -1 ], at 50% FVC (MEF50,
also FEF50), and at 75% FVC (MEF75, also FEF75).
They are usually given in liters per second and inform
us about expiratory flows of important segments of a
distributed forced expiration curve, respectively the
flow – volume curve.
The peak expiratory flow (PEF) [l.s -1 ], also called
the top expiratory velocity is the greatest flow
achieved during forced expiration from the
maximum inspiration.

FORCED EXPIRATION TEST
• Simplest test
• One of the most informative
• Requires minimal equipment
• Trivial calculations
• Majority of patients with lung disease: abnormal forced
expiration
Classification of ventilation defects
•obstructive
•restrictive
•combined
Obstructive ventilation defect
With purely obstructive ventilation defect, the expiratory flows are
significantly reduced, while the vital lung capacity is relatively well maintained.
The basic criterion for specifying the obstructive ventilation defect, that means a
reduced ability to ventilate lungs, is reduction of the FEV1 value.
A low degree of the obstructive ventilation defect is considered a reduction of
the FEV1 value from 60 % to the bottom limit of the standard, respectively to 80%
of the standard reference value.
A medium severe degree is considered a FEV1 reduction from 45 % to 59 % of
the reference value,
a severe degree is then a FEV1 reduction under 45 %.
These criteria are accurate enough only in the case that FEV1/VC index is lower
than the bottom limit of the standard (approximately 60 % and depends on age ).

Common Obstructive Lung Diseases
Asthma
COPD (chronic bronchitis, emphysema and the overlap between them)
Cystic fibrosis
-Airflow is reduced because the airways narrow and the FEV1 is reduced
-Spirogram may continue to rise for more than 6 seconds because lung take
longer to empty
-FVC may also be reduced because gas is trapped behind obstructed bronchi but
this reduction to a lesser extent than FEV1
Asthma is characterized by airway
hyperresponsiveness, which results in reversible
increases in bronchial smooth muscle tone, and
variable amounts of inflammation of the bronchial
mucosa.During an acute
asthma attack, the already
inflamed airways narrow
further due to bronchospasm,
which leads to increased
airway resistance
COPD
http://www.youtube.com/watch?v=aktIMBQSXMo

Large Airway Obstruction
1. Fixed obstruction
2. Variable extrathoracic obstruction
3. Variable intrathoracic obstruction
Fixed obstruction
1. Post intubation stenosis
2. Endotracheal neoplasms
3. Bronchial stenosis
Maximum airflow is limited to a similar extent in both inspiration and expiration
Variable extrathoracic Obstruction
1. Bilateral and unilateral vocal cord paralysis
2. Vocal cord constriction
3. Airway burns
The obstruction worsens in inspiration because the negative pressure narrows the
trachea and inspiratory flow is reduced to a greater extent than expiratory flow
Large Airway Obstruction
In variable intrathoracic obstruction
1. Tracheomalacia
2. Polychondritis
3. Tumors of the lower trachea or main bronchus.
The narrowing is maximal in expiration because of increased intrathoracic pressure
compressing the airway.
The flow volume loop shows a greater reduction in the expiratory phase

Restrictive ventilation defect
With a classic restrictive ventilation defect during forced expiration, the patient
expires a smaller air volume from lungs and this happens at normal or only slightly
lower speed.
The criterion for a restrictive ventilation defect for a tentative screening
examination of a lung function is a lower absolute value of the vital capacity VC with
normal values of FEV1/VC or FEV1/FVC indexes.
The vital capacity is considered lower if its value drops under 80 % of the reference
value.
When assessing seriousness, a low degree of RVD is considered a VC reduction
from 60 % to the bottom limit of the standard, respectively to 80 % of the reference
value.
A medium severe degree of RVP is considered a VC reduction from 45 % to x60
%,
a severe degree of RVP is considered a reduction under 45 %.
Restrictive Lung Diseases
A. Intrinsic Restrictive Lung Disorders
Sarcoidosis
Idiopathic pulmonary fibrosis
Interstitial pneumonitis
Tuberculosis
Pnuemonectomy (loss of lung)
Pneumonia
B. Extrinsic Restrictive Lung Disorders
Scoliosis, Kyphosis
Ankylosing Spondylitis
Pleural Effusion
Pregnancy
Gross Obesity
Tumors
Ascites
Pain on inspiration - pleurisy, rib fractures

Restrictive Lung Diseases
C. Neuromuscular Restrictive Lung Disorders
Generalized Weakness – malnutrition
Paralysis of the diaphragm
Myasthenia Gravis
Muscular Dystrophy
Poliomyelitis
Amyotrophic Lateral Sclerosis
Restrictive Lung Diseases
Restrictive lung disease :
Full lung expantion is prevented by fibrotic
tissue in the lung parenchyma and the FVC
is reduced .
Elastic recoil may increased by fibrotic
tissue lead to increase the airflow
Both FEV1 and FVC may be reduced
because the lungs are small and stiff ,but
the peak expiratory flow may be preserved
or even higher than predicted leads to
tall,narrow and steep flow volume loop in
expiratory phase.

A combined, restrictively – obstructive ventilation defect
reduced FVC and also FEV1 but the FEV1 is lowered disproportionately more
than the FVC and therefore the FEV1/FVC ratio is also lower.
Parameter
Obstruction
Restriction
Mixed
FEV1
Reduced
Reduced
Reduced
FVC
Normal
Reduced
Reduced
FEV1/FVC
Reduced
Normal
Reduced

Age :
FVC and flow rates decline with age. The value of FVC increases up to 24
years of age and remain stable to age 35.
-Elastic tissues deteriorate:
reducing lung compliance
lowering vital capacity
-Arthritic changes:
restrict chest movements
limit respiratory minute volume
-Emphysema:
affects individuals over age 50
depending on exposure to respiratory irritants (e.g., cigarette smoke)
Height :
All spirometric measurements increase with body weight. It is due to an
increase in number and/or size of alveoli relative to airways, the larger lungs
are likely to take longer than smaller one.
Sex :
Most pulmonary function values are lower in female than male.
Weight :
A spirometric results are positively correlated with weight to the extent that
increased weight means growth or muscle mass. Beyond this (in obesity)
spirometric values (and lung values specially ERV) decrease with greater
weight.
Instrumentation for measuring lung ventilation – volumes, airflows
- Bell spirometers – closed system
- Pneumotachographs with volume - flow integration – open system
- Whole-body plethysmograph
Pneumo comes from Greek and means lungs, so that the pneumograph is an instrument which gives a
graph of lung function; this is actually a graph of lung volume against lime. Tacho is also a Greek word and
means speed so that the pneumotachograph produces a graph of the speed of airflow into or out of the
lungs. Spiro is the Latin word meaning breath so that the spirometer is an instrument which measures
breath. The measurement is usually of volume. Pletho is another Greek word meaning fullness so that the
plethysmograph is an instrument which gives a graph of fullness. The body plethysmograph gives a
measurement of lung fullness.

Bell spirometers – closed system
http://ulb.upol.cz/videa/spirometry.mpg
An inverted cylindrical container floats in a liquid
and the volume of gas in the container can be
calculated from the vertical displacement of the
cylinder.
Actually a correction factor has to be applied to
allow for the fact that the air cools and thus
contracts when it passes from the patient into
the spirometer.
Pneumotachographs with volume - flow integration – open system
measures flow rate by means of a transducer through which the patient breathes.
The air passes through a fine mesh which offers a small resistance to flow, with the
result that there will be a pressure drop across the mesh in proportion to the flow
rate.
the instrument also calculates volume by integrating the flow signal

FORCED EXPIRATION TEST
http://www.nationalasthma.org.au/HTML/management/spiro_res/vid_spiro.asp
FORCED EXPIRATION TEST
http://www.nationalasthma.org.au/HTML/management/spiro_res/vid_spiro.asp

Whole-body plethysmograph
A body plethysmograph consists of a box in
which the patient sits and breathes through
a hole in the side. Each time the patient
inhales volume V, the total volume of their
body increases and so the pressure in the
box increases. If the initial pressure in the
box, Pb, and the air volume, Vb, are known,
then the reduction in volume, V, can be
calculated from the pressure rise, p, during
inspiration.
Boyle’s law (P · V = constant)
PbVb = (Pb+p)(Vb-V)
Residual Volume Measurement
• Helium dilution
• Spirometer of known volume and
helium concentration connected to the
patient
• Closed circuit
• Law of conservation of mass
At beginning
After several minutes
[He] initial · V s = [He] final · (V s + V L )
Unknown lung volume can be calculated
We solve for the volume after (the volume of the lung and spirometer), subtract out
the volume of the spirometer, and we get the volume of the lung.
Helium poorly soluble in water and thus diffuses very poorly across the alveolar wall.
Subjects breath a gas that cannot escape from the lungs

RESIDUAL VOLUME
RV = FRC - ERV
Peak-flow meter
Peak-flow meters are instruments used to measure peak expiratory flow rate
(PEFR).
The patient expires as forcefully as possible into the flowmeter which balances the
pressure exerted by the flow of air past a movable vane against a spiral spring.