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Pulmonary function
63
PULMONARY FUNCTION
INTRODUCTION
The respiratory system of the body includes the lungs, the airways and the
respiratory muscles and is involved in the exchange of O2 and CO2 between the
blood (brought to the alveoli in the lungs) and the inspired air (filling the alveoli
in the lungs).
Respiration is composed of four steps: ventilation (i.e. breathing), gas exchange
in the lungs, circulation of blood between the lungs and tissues and gas exchange
at between the blood and tissues.
Lung volumes during ventilation are assessed using a method called spirometry.
BREATHING (VENTILATION)
During inspiration, air is forced into the lungs due to expansion of the thoracic
cavity (contraction of the diaphragm at the bottom of the rib cage and the
contraction of the external intercostal muscles, causing the ribs to move upwards
and outwards). The expansion of the thoracic cavity increases thoracic volume
and decreases thoracic pressure so that the net flow of air is down its pressure
gradient and into the lungs.
During resting respiration, only a small portion of the lung capacity is used. This
allows plenty of reserve capacity for those occasions (such as exercise) when the
body requires much greater flow of oxygen. During exercise, the body's need for
oxygen increases dramatically and ventilation rate and depth is increased.
SPIROMETRY
SPIROMETER
The volume of air that moves in and out of the lungs during breathing is
measured with a spirometer. When a spirometer is used a spirogram can be
recorded.
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Physiology laboratory exercises
A wet spirometer measures lung volumes based on the simple mechanical
principle that air, exhaled from the lungs, will cause displacement of a closed
chamber that is partially submerged in water. The spirometer consists of two
chambers: a larger chamber, which is filled with water, and a smaller chamber
which is inverted inside the first and "suspended" in water, this also has a
breathing hose attached to it. A counterweight and indicator (frequently a simple
or thermal pen) are attached to the inverted chamber by means of pulleys. Air
blown into the inverted chamber causes the volume of air under it to increase
and the chamber to rise; this in turn will move (lower) the indicator along a scale.
Inhaling air from the chamber causes the inversed chamber to lower thus raising
the indicator (Figure no. 9). The scale is calibrated in liters (to give lung volume
measurements) and is fixed on a revolving drum that rotates with constant
speed. The various lung volumes are presented in Figure no. 10 and defined
below (Table no. 2).
All volumes measured are dependent on gender, age, height and weight and also
on pressure, temperature and water saturation of air.
Figure no. 9.
measurements.
Spirometer;
the
method
of
spirometric
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Table no. 2. Lung volumes
Parameter
(abbreviation)
Definition
Normal
(average)
values
Tidal
Volume The amount of air that moves in and out 500 ml
of the lungs during a normal respiratory
(VT)
cycle.
Minute
The amount of tidal air that passes in and VT x RF
Respiratory
out of the lungs in one minute.
Volume (MRV)
Expiratory
The amount of air that can be expired 1000-1200 ml
Reserve Volume beyond the tidal volume
(ERV)
Inspiratory
The amount of air that can be drawn into 2500-3500 ml
Reserve Volume the lung by maximal inspiration after VT
(IRV)
Vital
Capacity Is determined by directing an individual 5000 ml
(VC)
to take as deep a breath as possible and
exhale all the air possible (calculate by
VT+ERV+IRV)
Residual Volume The volume of air in the lungs that 1200 ml
(RV)
cannot be forcedly expelled
Total Lung
The volume of air contained in the lung 6000 ml
Capacity (TLC)
at the end of maximal inspiration
(calculate by RV+VC)
Inspiratory
The maximal volume that can be inhaled 3000-4000 ml
Capacity (IC)
following a normal expiration (calculate
by VT+IRV)
Functional
The amount of air left in the lungs after a 2200 ml
Residual Capacity tidal breath out (calculate by ERV+RV)
(FRC)
Forced Expiratory The maximum volume of air (measured -Volume in 1
in liters) that can forcibly blow out in the
Second (FEV1)
first second during the forced expiration
maneuver.
Percentage of VC that is expelled during at least 80%
Tiffeneau Index
the first second of expiration.
(FEV1/VC (%))
Maximal
The amount of air that passes in and out 60-90 l/min
Voluntary
of the lungs in one minute during (females)
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Physiology laboratory exercises
Ventilation
(MVV)
Peak Expiratory
Flow (PEF)
maximal ventilation (hyperventilation).
Usually approximated by FEV1 x 30
The maximal flow (or speed) achieved
during maximal forced expiration
initiated at full inspiration, measured in
liters per minute
110-140 l/min
(males)
depending on
gender,
age,
height
Figure no. 10. Lung volumes.
PROCEDURE
Figure no. 11. Spirogram recorded with VitaloGraph Eutest.
The objective is to measure the lung volumes of each member of the group using
a spirometer (VitaloGraph Eutest). Attach a disposable mouthpiece to the tubing.
Clamp the subject's nostrils closed and have the subject breathe normally. DO
NOT INHALE from the spirometer - ONLY EXHALE into the spirometer.
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Breathe in as deeply as possible, and then exhale into the mouthpiece as fully
(forcefully) as possible. The recording should look like the one in Figure no. 11.
Read the FEV1 and VC values from the recording. Use these values to calculate
the rest of the parameters (see below).
1. First you must adjust the recorded VC volume according to BTPS (correction to
adjust the gas volume as if it were saturated with water vapor at body
temperature (37°C) and at the ambient barometric pressure; Table no. 3).
VC c  VC  f BTPS
Table no. 3. BTPS correction factors.
Temperature
20
21
22
23
24
25
26
27
28
29
fBTPS
1.102
1.096
1.091
1.085
1.080
1.075
1.068
1.063
1.057
1.051
2. Then you must calculate the predicted values for your age, gender and height.
Use 0.8 only in case of females.
VC pr  H 3  coeff age (0.8)
Table no. 4. Age related correction factors.
Age
18-19
20-29
30-34
35-39
40-44
45-49
50-54
coeffage
0.990
1.025
1.020
1.010
1.000
0.990
0.970
K
24.6
24.0
23.4
23.0
22.7
22.3
22.0
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Physiology laboratory exercises
3. Then you can determine the percentage of your actual volume compared to the
normal predicted value.
VC c
 100
VC pr
4. Calculate Tiffeneau index:
FEV1% 
FEV1
 100
VC
5. Calculate MVV and then the BTPS (Table no. 3) corrected value:
MVV  FEV1  30
MVVc  MVV  f BTPS
6. Calculate the predicted value using age related correction factor "K" (Table no.
4):
MVV pr  VC pr  K
7. Then you can determine the percentage of your actual MVV compared to the
normal predicted value.
MVVc
 100
MVV pr
CLINICAL SIGNIFICANCE
Measurement of lung volumes and forced expiratory flow rates are useful in the
clinical setting. Two types of lung disorders can be identified by spirometric
measurements:
► Obstructive lung disorders (e.g. asthma): there is an obstructive
process in the airways (the bronchi) of the lung and this is detected by a
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decreased ability to empty the lungs quickly during a forced expiration.
The decrease of FEV1 also alters the FEV1/VC ratio.
► Restrictive lung disorders (e.g. pneumonia): it is characterized by
reduced lung volume, either because of an alteration in lung parenchyma
or because of a disease of the pleura, chest wall, or neuromuscular
apparatus. In physiological terms, restrictive lung diseases are
characterized by reduced vital capacity. Usually the airflow is preserved
and the airway resistance is normal.
Lung diseases frequently are not of just one specific type, but rather result from a
combination of the above two disorders or in combination with a variety of
factors
that
lead
to
compromised
respiratory
functions.