PFTs measure lung function through tests of ventilation, gas exchange, ventilation control, and exercise response. Key measurements include FEV1, FVC, FEV1/FVC ratio, DLCO, and arterial blood gases. PFT results are interpreted to identify obstructive, restrictive, or combined patterns and determine the severity of lung abnormalities.

1. Interpretation of PFTs

2. PFTs
 Tests of ventilation
• Ventilatory capacity (FE spirogram, flow volume loop)
• Lung volume and capacity
• Respiratory mechanics (airways resistance)
 Tests of gas exchange
• Diffusion tests (DLCO)
• Blood gas studies (ABG)
• Measuring physiological dead space
 Tests of ventilation control
 Tests of response to exercise

3.  PFTs measure disturbances in….
• Ventilatory function
• Pulmonary circulation
• Gas exchange

4. Tidal Volume (TV): Volm. of air entering the nose or mouth per breath
(500 ml).
Residual Volume (RV): Volm. of air left in the lungs after a maximal
forced expiration (1.5L).
Expiratory Reserve Volume (ERV): Volm. of air expelled from the lung
during a maximal forced expiration that starts at the end of normal tidal
expiration (1.5L).
Inspiratory Reserve Volume (IRV): Volm. of air inhaled into the lung
during a maximal forced inspiration starting at the end of a normal tidal
inspiration (2.5L).

5. Functional Residual Capacity (FRC): Volm. of air remaining in the lungs
at the end of a normal tidal expiration (3 L).
Inspiratory Capacity (IC): Volm. of air inhaled into the lungs during a
maximal forced inspiration effort that begins at the end of a normal tidal
expiration (VT+IRV=3L).
Vital Capacity (VC): Volm. of air expelled from the lungs during a
maximal forced expiration effort starting after a maximal forced
inspiration (4.5L).
Forced vital capacity (FVC): Volm. of air exhaled forcefully and quickly
after inhaling as much as possible.

6. Total Lung Capacity (TLC):
 Volm. of air inhaled into the lungs after a maximal inspiration effort
(5-6 L);
 TLC = RV + VC
 ↑ed: obstructive defects (e.g., emphysema);
 ↓ed: restrictive abnormalities, chest wall abnormalities and
kyphoscoliosis.
Residual Volume (RV):
 Volm. of air left in the lungs after a maximal forced expiration (1.5L);
 ↑ed: in obstructive lung diseases (incomplete emptying of lungs and
air trapping);

7. Forced Expiratory Time (FET):
 Bedside test; in screening of OAD;
 Time taken to forcefully exhale through an open mouth from
Total Lung Capacity until airflow is no longer audible.
 Normal : ≤ 4 secs.; > 6 secs. (implies airway obstruction)
Forced expiratory volume (FEV): Volm. of air exhaled during
the 1st, 2nd, and 3rd seconds of the FVC test.
Forced expiratory flow (FEF): The average flow rate during
the middle half of the FVC test.

8. Peak Expiratory Flow Rate (PEFR):
 Done using the peak flow meter;
 It is the largest expiratory flow achieved w/ a
maximally forced expiratory effort from a position of
maximal inspiration.
 Best of three successive readings are noted.
 Males (450 – 550 L/min.); Females (350 – 450 L/min.);
 PEFR (L/min.) = [Height (in cms.) – 80] x 5

10.  Useful in…
• diagnosis of asthma, exercise-induced asthma;
occupational asthma;
• recognizing the severity of asthma;
 Peak flow meters are cheap; compact; portable; simple
to use.
 Diurnal variability =
PEFR evening – PEFR morning
x 100
½ (PEFR evening + PEFR morning)

11.  Diurnal variability of PEFR > 20% for at least three
days in a week for 2 weeks is typical of asthma.
 Disadvantages:
• Any condition which reduces the Vital Capacity also
reduces the PEFR.
• It cannot distinguish between obstruction and restriction.
• The calculation is time-consuming when in clinical
practice.

12. Forced Expiratory Spirogram
 Is a simple yet highly informative test of lung function;
 The recording is obtained as Volume-time tracing.
 The patient breathes in maximally and then exhales as
fast and as much as possible.
 The forced expiratory spirogram enables the following
to be calculated:
• Forced Vital Capacity (FVC)
• Forced Expiratory Volume (FEV, FEV1)
• Forced Expiratory Flow rates (FEF)at various % of FVC
(e.g., FEF 25-75%);

13. FVC: max. amount of air exhaled after a maximal inhalation;
 If normal:
o Normal lung tissue (fairly normal elasticity)
o Normal thoracic cage (configuration of thoracic spine/ribs).
o Respiratory muscles are not too weak.
 If low: one or more of the above is an issue (Restrictive disorder)
FEV1: amount of air exhaled in the first second as forcefully as
possible from a full lung;
 Measuring the speed of the air being exhaled can provide info.
about the airways;
 Unit is litres/second;
 ↓ed speed indicates ‘obstructed’ or narrowed airways;

14. PFT INTERPRETATION
FEV1/FVC ratio
 < 70% (or < LLN): Obstructive pattern (COPD, asthma)
 ≥ 70%: Normal or Restrictive disease
Severity of obstruction (GOLD Criteria for COPD)
FEV1 COPD STAGE
80 - 100% predicted Mild (Stage I)
50 - < 80% predicted Moderate (Stage II)
30 - < 50% predicted Severe (Stage III)
< 30% predicted Very severe (Stage IV)
< 50% with Rt. side heart failure Very severe (Stage IV)

15. Classification of airflow limitation severity in COPD (based
on post-bronchodilator FEV1):
FEV1 Airflow
obstruction
CATEGORY
≥ 80% predicted MILD GOLD-1
50 to < 80%
predicted
MODERATE GOLD-2
50 - 60% predicted MODERATELY
SEVERE
30 to < 50%
predicted
SEVERE GOLD-3
< 30% predicted VERY SEVERE GOLD-4
In patients with FEV1/FVC < 0.70

16. Bronchodilator response:
 ≥ 12% ↑ and an absolute improvement of at least 200 ml after
inhaling a beta agonist (usually neb. Salbutamol)
 FEV1 or FVC is considered a significant response.
Total Lung Capacity (TLC)
 Normal range: 80 - 120% of predicted
 > 120% = Hyperinflation
 < 80% = Restrictive disease
 Use the ATS criteria for severity.
RV/TLC ratio
 Normal range: < 35% or < predicted
 > 35% or > predicted indicates Air trapping

17. Flow Volume Loop
 It is a graphical analysis of the flow generated during
the FEV manoeuvre (plotted against the volume
change) followed by a FIV manoeuvre (plotted against
the volume change).
 Volume (X-axis); Flow rates (Y-axis)
 Gives additional info. about airflow at various lung
volumes from RV (reserve volume) to TLC.
 Ascending part of expiratory component is patient-
effort dependent.
 Descending part of expiratory component is mostly
effort independent; represents the elasticity and recoil
of the alveoli and smaller airways;
 The peaks represent PEFR and PIFR.
 Observing the loop indicates either ‘Obstruction’ or
‘Restriction’.

20. Spirometry Patterns:
 These depend on how much air is breathed out and
what proportion is exhaled in the first second.
 Usually shows one of three main patterns: Normal;
Obstructive; Restrictive patterns
Normal pattern:

21. Obstructive pattern:
 When lung conditions (COPD and asthma) narrow the
airways.
 Inference: Air flows out of the lungs more slowly than
it should (low FEV1) < 70% of the total amount in the
first second.

22. Restrictive Pattern:
 The total amount of air breathed in is reduced but the
speed to breathe out is preserved.
 Both FEV1 and FVC will be lower than predicted.
 Causes:
• by various conditions that affect the lung tissues or the
capacity of the lungs to expand and hold a normal
amount of air, (pulmonary fibrosis, sarcoidosis,
pneumoconiosis, pleural effusion, pneumothorax,
pleural thickening).
• also seen in people who are significantly overweight,
have an abnormal curvature of the spine or weak
respiratory muscles.

23. RESTRICTIVE PATTERN (CONTD’.)

24. Combined patterns:
 Sometimes these two processes combine (obstruction
and restriction).
 Both the total amount of air (inspired and expired), and
how fast a patient can blow out are reduced. This
happens in severe emphysema, cystic fibrosis, in
obesity.

25. Common Spirometry Patterns
Normal:
 Normal spirometry (normal FVC, FEV1/FVC ratio)
Obstruction to airflow:
 Normal FVC + ↓ FEV1 + low FEV1/FVC%; must assess BD
response
Restrictive changes:
 ↓ FVC + ↓ FEV1 + ‘normal’ FEV1/FVC%; must assess lung
volumes and DLCO
Combined obstructive and restrictive:
 ↓ FVC + ↓ FEV1 + ↓ FEV1/FVC%; must assess lung volumes
and DLCO

26. Reversibility testing:
 Helps to assess if inhaled medication can open up the
airways.
 Reversibility testing helps to grade the severity of the
conditions according to the FEV1 measurement after
taking the bronchodilator (usually by using Neb.
Salbutamol).
 If there is obstructive abnormality, then bronchodilators
are given to assess the degree of reversibility. Post-
obstruction bronchodilator study is done, and the
graphs (FE Spirogram and Flow volume) are assessed
to determine if reversal had occurred, and to what
extent.

27. RV/TLC Ratio:
 Ratio of residual volume to the total lung capacity.
 Indicates the extent of air trapping in the lungs after
complete expiration.
 Normal values upto 35%
 Can be ↑ed in bullous disease, emphysema, AEBA
DLCO:
 Measures the diffusing capacity of the lungs for carbon
monoxide.
 The measure of the amount of gas transferred across
the interstitium per unit time as a function of the mean
pressure gradient of the gas across the interstitium.
 Units: ml/min./mm of Hg
 Is a diagnostic indicator of Interstitial lung disease.
 Values < 80% of predicted are abnormal.

28. DLCO is ↑ed in….
• Alveolar haemorrhage
• Polycythemia
• L to R cardiac shunt
• Exercise
• Supine position
• Pregnancy
DLCO is ↓ed in….
• ILD
• Emphysema
• Anaemia
• Pneumonectomy

29. Pre and Post Arterial Blood Gas Analysis:
 Helps to determine the blood gas status pre and post exercise and
post-administration of 100% O2;
 Provides important information on gas exchange and oxygen
delivery to the tissues;
 Post-exercise: ↑ of upto 10 mm Hg in PaO2;
PaCO2 should be normal or lower;
 Abnormality can be inferred if post-exercise…
• PaO2 does not rise or is ↓ed;
• ↑ed PaCO2
 Post 100% O2: There should be a normal rise of upto atleast 5x in
PaO2 levels. If this rise in PaO2 levels is lower, it is indicative of an
abnormality.

30. ABG test (contd’.)
Type-1 Respiratory Failure
 PaO2 < 8 kPa with normal PaCO2;
 Causes: Pneumonia and Pulmonary embolism;
Type-2 Respiratory Failure
 When hypoxia is accompanied by hypercapnia (PaCO2 > 6.5 kPa);
 Seen in ventilatory failure;
 Causes: Respiratory muscle weakness and COPD;
 Type-2 respiratory failure may also occur in patients with advanced
type-1 respiratory failure as they tire and develop ventilatory failure.

31. ABG test (contd’.)
 Acidemia: Arterial pH < nml (< 7.35)
 Alkalemia: Arterial pH > nml (>7.45)
 Metabolic acidosis: Process that ↓es serum HCO3 → ↓ pH
(bicarbonate consumption could resolve this);
 Respiratory acidosis: Process that ↑es serum pCO2 → ↓ pH
(hypoventilation)
 Metabolic alkalosis: Process that ↑es serum HCO3 → ↑ pH
(excess bicarbonate is observed)
 Respiratory alkalosis: Process that ↓es serum pCO2 → ↑ pH
(hyperventilation)

32. Bronchoprovocation testing:
 To determine the Provocative dose or PD20%
 PD20% is the max. exposure to bronchoprovocative substances
(histamine and methacholine) that can cause a 20% drop in
FEV1.
 To determine extent of airway reactivity; assess airway
response to inhaled antigens (as in occupational asthma);

33. Cardiopulmonary Exercise Testing:
 Multi stage study involving the monitoring of various
parameters for evaluation of unexplained dyspnoea or
for disability evaluation due to cardio-pulmonary
disease.
 Allows the tester to judge the response of the
cardiopulmonary system to ‘graded exercise’ and
measures gas exchange in the form of O2 consumption,
CO2 production, and minute ventilation.

34. Pointers to Remember
TLC
 ↑ed: COPD; Acromegaly; Athletes (swimmers);
 ↓ed: Restrictive ILD; Chest wall; NMD (neuro muscular
disease);
Severity of restriction
 Mild (60-80%)
 Moderate (50-60%)
 Severe (<50%)
 Hyperinflation (> 120%)

35. Residual Volume (RV)
 ↑ed: Air trapping (Obstructive disorders such as COPD and
asthma);
 ↓ed: Parenchymal restriction;
Functional Residual Capacity (FRC)
 The volume of air left in the lungs after a normal, passive
exhalation;
 Is used to evaluate the lung function;
 ↑ed: Age; Emphysema; Loss of elastic recoil
 ↓ed: Lung fibrosis; Obesity;

36. THE END

37. For your Info. …

38. Patient-effort
dependent

39. Parameters Obstructive Restrictive Combined
FVC NML or ↓ ↓ ↓
(L)
FEV1 (L) ↓ ↓ ↓↓
FEV1/FVC(%) ↓ NML or ↑ed ↓

41. Source: NICE clinical guideline CG101: Chronic obstructive pulmonary disease
in over 16s. June 2010,
GRADE OF AIRFLOW
OBSTRUCTION
FEV1
MILD ≥ 80% of the predicted value.
MODERATE 50-79% of the predicted value after medication
SEVERE 30-49% of the predicted value after medication
VERY SEVERE < 30% of the predicted value after medication