2. What is pulmonary function
(tests?(PFTs
Pulmonary function tests are a group of test that
measure how well the lungs take in and release
air and how well they move oxygen into the
(blood.(it is a non invasive
3. Pulmonary Function Tests are used for
the following reasons :
• Screening for the presence of obstructive and
restrictive diseases
4. • Evaluating the patient prior to surgery – for
patients who :
a. are older than 60-65 years of age
b. are known to have pulmonary disease
c. are obese (as in pathologically obesity)
d. have a history of smoking, cough or wheezing
e. will be under anesthesia for a lengthy period
of time
f. are undergoing an abdominal or a thoracic
operation.
5. • Evaluating the patient's condition
for weaning from a ventilator.
• Documenting the effectiveness of
therapeutic intervention
7. ?What is Spirometry
• a simple and safe test
• that measures lung volumes
• with a graphical display
• gives an estimation of lung function
• Allows for diagnosis of airflow obstruction
• Permits good follow-up for asthma and
COPD
9. …SPIROMETRY
In a spirometry test, you breathe into a
mouthpiece that is connected to an
instrument called a spirometer. The
spirometer records the amount and the
rate of air that you breathe in and out
.over a period of time
15. • Lung volume measurement can be performed
in two ways:
• The most accurate way is for a person to sit in a
body plethysmograph, a sealed, transparent box
that resembles a telephone booth, while breathing
in and out against into a mouthpiece. Changes in
pressure inside the box allow determination of the
lung volume.
• Lung volume can also be measured when a person
breathes nitrogen or helium gas through a tube for
a specified period of time. The concentration of the
gas in a chamber attached to the tube is measured,
allowing estimation of the lung volume.
16.
17.
18. Table 22–1. Lung Volumes and Capacities.
Measurement Definition Average Adult
Values (mL)
Tidal volume (VT) Each normal breath 500
Inspiratory reserve volume Maximal additional volume 3000
(IRV) that can be inspired above
V T
Expiratory reserve volume Maximal volume that can be 1100
(ERV) expired below VT
Residual volume (RV) Volume remaining after 1200
maximal exhalation
Total lung capacity (TLC) RV + ERV + VT + IRV 5800
Functional residual capacity RV + ERV 2300
(FRC)
19. Two important parameters
• FVC - Forced Vital Capacity. This is
the total amount of air that you blow out
in one breath.
• FEV1 - Forced Expiratory Volume
in one Second. This is the amount of
air you can blow out within one second.
With normal lungs and airways you can
normally blow out most of the air from
your lungs within one second.
20. • Normal FEV1/FVC ~ 80%
Restrictive (fibrosis) ratio normal or increased
Obstructive (asthma, COAD) usually low
• Normal values vary, depending on gender, race,
age and height.
21. Spirometry: Normal and COPD
0
FEV1 FVC FEV1/ FVC
Normal 4.150 5.200 80 %
1 COPD 2.350 3.900 60 %
2
FEV1
Liter
3
COPD
4 FVC
FEV1
5 Normal
FVC
1 2 3 4 5 6 Seconds
22. Flow-Volume Loops
Flow volume loops
provide a graphical
illustration of a patient's
spirometric efforts. Flow
is plotted against volume
to display a continuous
loop from inspiration to
expiration. The overall
shape of the flow volume
loop is important in
interpreting spirometric
results
23. ?How is a flow-volume loop helpful
• Helpful in evaluation of air flow limitation on
inspiration and expiration
• In addition to obstructive and restrictive patterns,
flow-volume loops can show provide information on
upper airway obstruction:
• Fixed obstruction: constant airflow limitation on inspiration and
expiration—such as in tumor, tracheal stenosis
• Variable extrathoracic obstruction: limitation of inspiratory flow,
flattened inspiratory loop—such as in vocal cord dysfunction
• Variable intrathoracic obstruction: flattening of expiratory limb; as in
malignancy or tracheomalacia
24. • Spirometry measures volume differences between
identifiable lung capacities (TLC, FRC, RV), but
cannot measure the absolute volume of these key
volumes.
• Lung volumes measure FRC and use spirometry to
calculate TLC and RV.
• FRC can be measured by following techniques:
• Closed circuit helium dilution
• Open circuit nitrogen washout
• Plethysmography or body box
25. Dilution Techniques
• Closed circuit helium dilution – starting at FRC, patient
breathes helium for 7 minutes (until equilibrium) from known
volume system with known He concentration; measure helium
concentration after maneuver
• Open nitrogen washout – starting at FRC, begin inspiring
100% O2 and collect/measure all nitrogen exhaled from the
lungs for 7 minutes (N2 essentially washed out). Given known
initial concentration of nitrogen in the lungs (81%), use the
measured concentration and volume of nitrogen in collected
air to calculate the starting lung volume (FRC) at end of
maneuver
• Both techniques underestimate actual FRC if
ventilation isn’t homogeneous (i.e. obstructive lung disease)
27. Plethysmography
• Measures thoracic gas –performed at FRC
• Underlying principle: Boyle’s Law
• Patient sits in sealed box, patient pants against shutter
that is closed at FRC
• Alveolar pressure changes measured at mouth
(presumes open glottis/equal pressures);
• Box pressure changes measured with respiratory efforts
– proportional to lung volume increases/decreases due
to respiratory efforts
Mouth Pressue (Pm)
(Pm,V)
r
PV = (P + ∆P)(V + ∆V)
(Pm +∆Pm, V +∆V)
V = FRC
Volume (V)
(monitored by box pressu
re)
28. Diffusing capacity (Transfer
(factor
The volume of a substance (CO) transferred across
the alveoli per minute per unit alveolar partial
pressure. CO is rapidly taken up by haemoglobin; its
transfer is therefore limited mainly by diffusion. A
single breath of 0.3% CO and 10% helium is held for
20 seconds. Expired partial pressure of CO is
measured. Normal value 17-25 ml/min/mmHg.
Value is reduced with increased alveolar membrane
thickness (e.g. pulmonary fibrosis). May also be
reduced with pneumonectomy (results in reduced
alveolar membrane).
