29
Pulmonary Function Testing (PFT): complete evaluation of the respiratory system including patient history, physical examinations, chest x-ray examinations, arterial blood gas analysis & tests of pulmonary function.
The primary purpose of PFT:
to identify any lung disease & the severity of pulmonary impairment
evaluates 1 or more major aspects of the respiratory system
lung volumes
airway function
gas exchange
PFT has diagnostic & therapeutic roles
helps clinicians in investigating patients with lung disease
PFT's are normally performed by a specialist technician.
Tests of lung functions include:
1. Spirometry
2. Measurements:
Maximal respiratory pressures
Diffusing capacity
Oxygen desaturation during exercise
Arterial blood gases, pulse oximetry
3. Helium dilution
4. Nitrogen washout
5. Plethysmography
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
Pulmonary function testing is a diagnostic & management tool used for a variety of reasons:
1. Paediatric neuromuscular disorders eg; Duchenne muscular dystrophy
helps to evaluate the respiratory status of patients at the time of diagnosis, monitor their progress and course, evaluate them for possible surgery, and gives an overall idea of the prognosis
2. Chronic dyspnea
3. Asthma diagnosis & management
4. Chronic obstructive pulmonary disease (COPD)
5. Restrictive lung disease (RLD)
6. Pre/postoperative testing
7. Impairment or disability
8. Accessing treatment
9. Health screening
DefactoHighlight
Spirometry - the most common of the PFT,
measuring lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled & exhaled.
it is an important tool used for generating pneumotachographs - helpful in assessing conditions eg; asthma, pulmonary fibrosis, cystic fibrosis, and COPD.
performed using a device - spirometer, which comes in several different varieties.
most spirometers display the following graphs, called spirograms: a volume-time curve, showing volume (liters) along the Y-axis and time (seconds)
along the X-axis
a flow-volume loop, which graphically depicts the rate of airflow on the Y-axis and the total volume inspired or expired on the X-axis
Flow-sensing spirometers directly measure flow by time k/a integration
this process requires a computer or microprocessor with appropriate software
the accuracy of the calculated volume measurement requires careful calibration & detection of low flow
Pneumotachograph (differential pressure device) is an airflow measuring device, consists of a tube with fixed resistance
the relationship among flow, pressure & resistance can be explained mathematically by formula:
Flow = Pressure / Resistance
Generally, the patient is asked to take the deepest breath they can, and then exhale into the sensor as hard as possible, for as long as possible, preferably at least 6 seconds.
it is sometimes directly followed by a rapid inhalation (inspiration), in particular when assessing possible upper airway obstruction.
sometimes, the test will be preceded by a period of quiet breathing in and out from the sensor (tidal volume), or the rapid breath in (forced inspiratory part) will come before the forced exhalation.
During the test, soft nose clips may be used to prevent air escaping through the nose. Filter mouthpieces may be used to prevent the spread of microorganisms.
The most common parameters measured in spirometry are;
tidal volume (TV), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), inspiratory capacity (IC), vital capacity (VC), forced vital capacity (FVC), however, it cannot measure residual volume (RV), functional residual capacity (FRC) & total lung
capacity (TLC) which can by plethysmograph or dilution test (helium)
forced expiratory volume (FEV)- at timed intervals of 0.5, 1.0 (FEV1), 2.0 & 3.0 seconds,
forced expiratory flow 2575% (FEF 2575)
maximal voluntary ventilation (MVV), also known as maximum breathing capacity
Results are usually given in both raw data (litres, litres per second) & percent predictedthe test result as a percent of the "predicted values" for the patients of similar characteristics (height, age, sex, sometimes race and weight).
The interpretation of the results can vary depending on the physician and the source of the predicted values.
generally speaking, results nearest to 100% predicted are the most normal, and results over 80% are often considered normal.
multiple publications of predicted values have been published and may be calculated online based on age, sex, weight and ethnicity.
however, review by a doctor is necessary for accurate diagnosis of any individual situation.
A FLOW-VOLUME LOOP GRAPH
GRAPH PATTERNS IN NORMAL &
DISEASES STATE
Forced vital capacity (FVC)
is the volume of air that can forcibly be blown out after full inspiration, measured in liters.
is the most basic maneuver in spirometry tests
Forced expiratory volume in 1 second (FEV1)
is the volume of air that can forcibly be blown out in one second, after full inspiration.
verage values for FEV1 in healthy people depend mainly on sex and age,
values of between 80% and 120% of the average value are considered normal.
predicted normal values for FEV1 can be calculated online and depend on age, sex, height, weight & ethnicity as well as the research study that they are based on.
FEV1/FVC ratio (FEV1%)
is the ratio of FEV1 to FVC.
in healthy adults - it should be approximately 7580%.
in obstructive diseases (asthma, COPD, chronic bronchitis, emphysema) FEV1 is diminished because of increased airway resistance to expiratory flow; the FVC may be decreased as well, due to the premature closure of airway in expiration, just not in the same proportion as FEV1 (for instance, both FEV1and FVC are reduced, but the former is more affected because of the increased airway resistance). This generates a reduced value (
Normal ratio (>80%)
Abnormal ratio (80%), but FVC
reduced
Average values for forced vital capacity
(FVC), forced expiratory volume in 1 second
(FEV1) and forced expiratory flow 2575%
(FEF2575%), according to a study in the
United States 2007 of 3,600 subjects aged 4
80 years.
Y-axis is expressed in litres for FVC and
FEV1, and in litres/second for FEF2575%.
Forced expiratory flow (FEF) - the
flow (or speed) of air coming out of the
lung during the middle portion of a
forced expiration
Peak expiratory flow (PEF) - the
maximal flow (or speed) achieved during
the maximally forced expiration initiated
at full inspiration, measured in liters per
minute.
OBSTRUCTIVE LD RESTRICTIVE LD
CHARACTERISTICS Limitation of airflow, due to
partial or complete
obstruction
Reduced expansion of lung
parenchyma accompanied
by reduced TLC
EXAMPLES emphysema, chronic
bronchitis, asthma,
bronchiectasis
Interstitial lung disease
lung fibrosis, pneumonia,
sarcoidoisis, tuberculosis,
chest neuromuscular dx
TOTAL LUNG
CAPACITY
normal reduced
FORCE VITAL
CAPACITY (FVC)
normal reduced
EXPIRATORY FLOW
RATE (FEV1)
decreased normal /reduced
FEV1/FVC RATIO (%) decreased (< 80%) normal
Step 1 - Look at the forced vital capacity (FVC) to see if it is within
normal limits.
Step 2 - Look at the forced expiratory volume in one second (FEV1)
and determine if it is within normal limits.
Step 3 - If both FVC and FEV1 are normal, then you do not have to
go any further - the patient has a normal PFT test.
Step 4 - If FVC and/or FEV1 are low, then the presence of disease is
highly likely.
Step 5 - If Step 4 indicates that there is disese then you need to go to
the %predicted for FEV1/FVC. If the %predicted for FEV1/FVC is 88%-90% or higher, then the patient
has a restricted lung disease.
If the %predicted for FEV1/FVC is 69% or lower, then the patient has an obstructed lung disease.
Predicted
Values
Measured
Values
%
Predicted
FVC 5.04 liters 5.98 liters 119 %
FEV1 4.11 liters 4.58 liters 111 %
FEV1/FVC 82 % 77 % 94 %
DefactoHighlight
Predicted
Values
Measured
Values
%
Predicted
FVC 6.00 liters 4.00 liters 67 %
FEV1 5.00 liters 2.00 liters 40 %
FEV1/FVC 38 % 50 % 60 %
DefactoHighlight
Predicted
Values
Measured
Values
%
Predicted
FVC 5.68 liters 4.43 liters 78 %
FEV1 4.90 liters 3.52 liters 72 %
FEV1/FVC 84 % 79 % 94 %
DefactoHighlight
Measurement of maximal inspiratory & expiratory pressures is indicated - whenever there is an unexplained decrease in vital capacity or respiratory muscle weakness is suspected clinically.
Maximal inspiratory pressure (MIP) - the maximal pressure that can be produced by the patient trying to inhale through a blocked mouthpiece.
Maximal expiratory pressure (MEP) - the maximal pressure measured during forced expiration (with cheeks bulging) through a blocked mouthpiece after a full inhalation.
Repeated measurements of MIP and MEP are useful in following the course of patients with neuromuscular disorders.
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
DefactoHighlight
Diffusing capacity (DL) - the series of tests that is done to determine the overall ability of the lung to transport gas into and out of the blood.
volume of gas transferred across alveolar/capillary membrane/per minute/mmHg of difference between the alveolar and capillary blood
Measurement of the single-breath diffusing capacity for carbon monoxide (DLCO) is a fast & safe tool in the evaluation of both restrictive and obstructive lung disease.
determined from CO uptake during 10 seconds of breath-holding rate of transfer of CO across respiratory membrane relates to hemoglobin affinity (240
fold higher than for O2)
CO transfer rate decreases in anemia & increases in polycythemia
DLCO is artificially low in smokers (have baseline CO in blood i.e. concentration gradient working against CO uptake)
High altitude increased transfer of CO
Schematic representation
of the rebreathing
system to measure
diffusing capacity during
rest ventilation. The
disappearance of carbon
monoxide (CO) from the
system and dilution of
helium (He) are
monitored continuously.
Arterial blood gases (ABGs) - blood test that is performed using blood from an artery.
involves puncturing an artery with a thin needle & syringe, and drawing a small volume of blood.
measures the arterial oxygen tension (PaO2),carbon dioxide tension (PaCO2), and acidity (pH).
in addition, arterial oxyhemoglobin saturation (SaO2) can be determined.
Such information is vital when caring for patients with critical illness or respiratory disease.
as a result, the ABG is one of the most common tests performed on patients in intensive care units (ICUs).
an elevated serum bicarbonate level, or chronic hypoxemia.
ABGs also provide a more detailed assessment of the severity of hypoxemia in patients who have low normal oxyhemoglobin saturation.
Parameters of ABG
Pulse oximetry - non-invasive method allowing the monitoring of the saturation of a patient's hemoglobin.
a sensor is placed on a thin part of the patient's body, usually a fingertip or earlobe, or in the case of an infant, across a foot.
light of two different wavelengths is passed through the patient to a photodetector.
the changing absorbance at each of the wavelengths is measured, allowing determination of the absorbances due to the pulsing arterial blood alone, excluding venous blood, skin, bone, muscle, fat, and (in most cases) nail polish.
it is possible to measure both oxygenated and deoxygenated hemoglobin on a peripheral scale (possible on both brain and muscle).
The helium dilution technique is the way of measuring the functional residual capacity of the lungs.
is a closed-circuit system where a spirometer is filled with a mixture of helium (He) and oxygen.
the amount of He in the spirometer is known at the beginning of the test (Concentration Volume = Amount).
the patient is then asked to breathe (normal breaths) in the mixture starting from FRC (Functional Residual Capacity), which is the gas volume in the lung after a normal breath. the spirometer measures helium concentration.
the helium spreads into the lungs of the patient,& settles at a new concentration (C2).
because there is no leak of substances in the system, the amount of helium remains constant during the test, and the FRC is calculated by using the following equation:
V2 = Total gas volume
( FRC + volume of spirometer).
V1 = Volume of gas in spirometer.
C1 = Initial (known) Helium concentration.
C2 = Final Helium concentration
(Measured by the spirometer)
Nitrogen washout (or Fowler's method) is a test for measuring dead space in the lung during a respiratory cycle, as well as some parameters related to the closure of airways.
The nitrogen washout technique uses a non-rebreathing open circuit.
the technique is based on the assumptions that the nitrogen concentration in the lungs is 78% and in equilibrium with the atmosphere, that the patient inhales 100% oxygen and that the oxygen replaces all of the nitrogen in the lungs
A nitrogen washout can be performed with a single nitrogen breath, or multiple ones.
both tests use similar tools, both can estimate functional residual capacity and the degree of non-uniformity of gas distribution in the lungs, but the multiple-breath test more accurately measures absolute lung volumes
A plethysmograph - 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).
Pulmonary plethysmographs give the most accurate measures on lung volumes & are commonly used to measure the functional residual capacity (FRC) and total lung capacity.
The plethysmography technique applies Boyle's law and uses measurements of volume and pressure changes to determine lung volume, assuming temperature is constant.
the law states that the absolute pressure and volume of a given mass of confined gas are inversely proportional, if the temperature remains unchanged within a closed system
1. Concise Human Physiology by M.Y. Sukkar, H.A.
El-Munshid, M.S.M. Ardawi.
2. Human Physiology: From Cells to Systems by
Lauralee Sherwood.
1. Ganong's Review of Medical Physiology, 24th
Edition by Kim E. Barrett, Susan M.
Barman, Scott Boitano, Heddwen Brooks.
