Pulmonary Function Tests
PFT
• Simple, non-invasive and inexpensive
• To assess the type and degree of functional
impairment- diagnosis and prognosis of lung disease
Classification of PFTs
1.Tests that assess ventilation
a. Lung volumes
i) Tidal volume
ii) Inspiratory reserve volume
iii) Expiratory reserve volume
iv) Residual volume
b. Lung capacities
i) Vital capacity
ii) Inspiratory capacity
iii) Functional residual capacity
iv) Total lung capacity
c. Mechanics of breathing
i) Timed vital capacity
ii) Maximum mid-expiratory flow rate
iii) Maximum voluntary ventilation
iv) Peak expiratory flow rate
v) Flow-volume curve
vi) Closing volume
vii) Maximal expiratory pressure
viii) Maximal inspiratory pressure.
Others
2. Tests that assess gas exchange in lungs
a. Assessment of ventilation-perfusion matching- nitrogen washout
method
b. Assessment of diffusing capacity
c. Determination of arterial blood gasses
3. Assessment of pulmonary blood flow and pressure
Uses of PFTs
PFTs help in:
• Diagnosis of respiratory dysfunctions.
• Monitoring the progress of the disease.
• Evaluating the efficiency of treatment.
• Assessing the health status of the person prior to recruitment to military or
police services.
• Determining the efficacy of physical training.
• Studying the prevalence of respiratory diseases in the community or respiratory
industrial hazards.
• Assessing the respiratory fitness of the patients for general anesthesia prior to
surgery.
• Finalizing medico-legal cases to decide fitness or degree of compensation.
Lung Volumes and Capacities
Lung Volumes
• TIDAL VOLUME: Tidal volume (TV) is the volume of gas inspired or expired
during quiet breathing. 500 ml .
• INSPIRATORY RESERVE VOLUME: The volume of air inspired with a
maximal inspiratory effort in excess of the tidal volume is the inspiratory
reserve volume (IRV). The normal value -3000 ml
• EXPIRATORY RESERVE VOLUME: The volume of air that can be expired
with a maximum expiratory effort after passive expiration is the expiratory
reserve volume (ERV). The normal value of ERV is 1100 ml
• RESIDUAL VOLUME: The volume of air remaining in the lungs at the end of
maximum expiratory effort is the residual volume (RV). 1200 ml
Lung Capacities
• VITAL CAPACITY: The maximum volume of air that can be expired after a
maximal inspiratory effort is called the vital capacity (VC). 4600 ml
• Forced Vital Capacity (FVC):The total volume expired with greatest force
and speed after a maximal inspiration is the FVC. FVC differs very little from
VC more reduced when there is airway obstruction.
• INSPIRATORY CAPACITY: This is the volume of gas that can be inspired
from the resting expiratory level. This is the IRV+TV.
• FUNCTIONAL RESIDUAL CAPACITY: This is the volume of air
remaining in lungs at the end of resting expiratory level. ERV+RV
• TOTAL LUNG CAPACITY: The volume of air present in the lungs at the
end of maximal inspiration is the total lung capacity (TLC). The normal value
MECHANICS OF BREATHING
TIMED VITAL CAPACITY (FEV1):
• This is also called forced expiratory volume in 1 second
(FEV1). This is defined as the percentage of air expired in
the specified time, e.g. FEV1 (FEV in first second).
• This is an index of air-flow rate. In normal conditions, 80
to 85% of the forced vital capacity is expired in the first
second, 95% in two seconds and 97% in three seconds.
• It is one of the most useful tests to detect generalized
airway obstruction.
• MAXIMUM MID-EXPIRATORY FLOW RATE (MMFR): the
maximum flow achieved during the middle third of the total expired volume.
flow at 25% to 75% of the lung volume (FEF25-75%). indicates the patency of
small airways. 300 L/min, 0.5 sec – inc in obstructive lung disease
• MAXIMUM VOLUNTARY VENTILATION (MVV): This is also called
as maximum breathing capacity (MBC). MVV indicates the maximum
volume of gas that can be breathed per minute by maximal voluntary effort.
The normal value of MVV in adult male is 80-170 liters per minute
• PEAK EXPIRATORY FLOW RATE (PEFR): It is the maximum velocity
in liters per minute with which air is forced out of the lungs. PEFR can be
read directly from the dial of the peak-flow meter. The normal value of
PEFR is 400 to 600 L/min
Pulmanory reserve or breathing reserve
• Maximum amount of air above the pulmonary ventilation that can be
inspired or expired in one minute
PR = MVV-PV/min
% PR= DI
DI = MVV-PV × 100
MVV
Normal- 60-90%
Measurement of Ventilatory Functions
• Most of the pulmonary functions are measured by
spirometry.
• The spirometer records the volume and capacities of the
lung.
• computerized spirometer.
• RV, FRC and TLC can’t be measured by spirometry as
they include volume of gases present in the lungs even after
maximal expiration. They are measured by helium dilution
technique and total body plethysmography.
Normal Values of PFTs
Normal values of various parameters of PFTs in adult male subjects:
TV : 500 ml
IRV : 3000 ml
ERV : 1100 ml
FVC : 4600 ml
FEV1 : > 80% of FVC
FEV1/FVC : 0.75 – 0.80
PEFR : 400 to 600 L/min
RMV : 6000 ml
MVV : 125 to 170 L/min
Breathing reserve (MVV – RMV): 115 to 160 L/min
Dyspneic index : > 90% (< 60% indicates dyspnea at rest).
Abnormalities of Ventilation
Restrictive And Obstructive Patterns.
Obstructive diseases Restrictive diseases
i) Pulmonary fibrosis
ii) Pneumoconiosis
• Asthma iii) Radiation-induced interstitial lung disease
• iv) Neuromuscular diseases
• Myasthenia gravis
COPD(chronicbronchiti • Paralysis of diaphragm
s, emphysema) • Muscular dystrophy
v) Chest wall diseases
• Bronchiectasis • Kyphoscoliosis
• Bronchiololitis • Obesity
• Ankylosing spondylitis
• Cystic fibrosis
Features of Obstructive Diseases
• TLC is normal or increased.
• RV is elevated due to trapping of air during expiration.
• Ratio of RV/TLC is increased.
• VC is frequently decreased (not due to decreased lung
volumes but due to increased RV).
• FEV1 is less than 80% of TLC
• FEV1/FVC decreases.
• MMFR decreases.
Features of Restrictive Diseases
• Decreased TLC
• Decreased VC
• Decreased RV
• Preservation of forced expiratory flow rates, especially
FEV1 expressed, as percentage of FVC is normal or
supernormal
