1. Spirometry
What is a spirometer?
Spirometer = an instrument for measuring air entering and leaving
the lungs, used to assess pulmonary function.

2. The spirometer
• It is simply a device used for quantifying lung volumes and
capacities.
•It measures volumes of air
•In pulmonary function testing, we use standardized protocols
A Collins Spirometer

3. How it works
Advantages of Volume spirometers
Cheap
Simple
Accurate
Reliable
Easy to maintain
Permanent record of test

4. Disadvantages of Volume
spirometers
Difficult to clean
Poor dynamic characteristics
Common patient related problems
with FVC measurements
1. Submaximal effort
2. Leaks between mouth and mouthpiece
3. Incomplete expiration
4. Hesitation of expiration
5. Cough
6. Obstruction of mouthpiece with tongue
7. Poor posture
8. Vocalization during the forced expiration

5. The mechanism of ventilation
Spirogram of lung volume changes
Values are for a young healthy male, values for females are somewhat lower

6. Lung volumes and capacities
• Tidal volume (TV):
•Inspiratory Reserve Volume (IRV):
• Inspiration capacity (IC):
•Expiratory Reserve volume (ERV):
•Residual Volume (RV):
Lung volumes and capacities
•Functional Residual Capacity (FRC):
•Vital Capacity (VC):
•Total lung Capacity (TLC):
•Peak Expiratory Flow (PEF):
•Dead space:

7. Forced volumes
• Forced vital capacity (FVC):
•Forced expiratory volume (FEV1):
•Forced expiratory Flow from 25-75% of exhalation (FEF25-75):
Factors affecting forced volumes
1. Gender: males have a larger FEV1, FVC, FEF25-75 and PEF but
lower FEV1/FVC%
2. Age: FEV1, FVC, FEF25-75 and PEF increase and FEV1/FVC%
decrease with age until about 20-25 years after this the gradually fall.
3. Height: All indices other than FEV1/FVC% increase with
standing height.

8. Typical lung volumes
IRV . 3.1 L men; 1.9 L women
TV . 0.5 L men; 0.5 L women
ERV . 1.2 L men; 0.9 L women
RV . 1.2 L men; 1.0 L women
TLC . 6.0 L men; 4.2 L women
Calculating FVC
FVC
Volume
Time (seconds)

9. Calculating FEV1.0
FVC
Volume
1 sec
Time (seconds)
Calculating FEF25-75
x0.25
FVC
Volume
x0.75
Time (seconds)

10. Components of IC, VC, FRC and
TLC
IC = IRV + TV . 3.6-3.8 L men; 2.4 L women
VC = IRV + TV + ERV .4.8 L men; 3.1 L women
FRC = ERV + RV .2.2 L men; 1.8 L women
TLC = VC + RV . 6 L men; 4.2 L women
Minute respiratory Volume
Minute respiratory volume(MRV)
MRV (ml/min) = TV (ml/breath) x f(breaths/min)
During quiet breathing: MRV = 6-8 L/min (12-16 breaths/min x
0.5L/breath)
During heavy breathing: MRV = 186-288 L/min (60 breaths/min x
3.1-4.8 L/breath

11. Ventilation rate
• Minute ventilation = tidal volume x breaths/min
• Minute ventilation = 0.5 L x 12 = 6.0 L
•Alveolar ventilation = (tidal volume – dead space) x breath/min
•Alveolar ventilation = (0.5 L – 0.05L) x 12 = 5.4 L/min
Lung volumes and capacities
during rest and exercise
Tidal volume increases during exercise

12. Factors that change airways
resistance
• Contraction or relaxation of bronchial smooth muscle (change in
radius of the airway).
a) Irritants, asthma, parasympathetic stimulation –
decrease the radius.
b) Sympathetic stimulation – increase the radius
•Lung volume
•Viscosity, or density, of inspired gas
•Sites of airways resistance –
Aging effects on healthy
pulmonary system
• Loss of the elastic recoil of the lungs
•Decreased surface area of the lungs
•Increased dead space ventilation
•Decreased rib cage compliance

13. The gas laws, and ATPS, BTPS
and STPD conditions
Review of the gas laws
- Boyle’s law
- Charles’s Law
- Gay-Lussac’s Law and Avogadro’s Law
- The ideal gas law
ATPS, BTPS and STPD conditions
Gas Standardization
Environmental conditions have a significant effect on pulmonary
gas volumes.
The volume is dependent on
• The temperature (T) and pressure (P)
•The volume occupied by water vapor (pH2O) depends on the
degree of saturation and temperature

14. The ideal gas laws
• Boyle’s Law: V % 1/P (constant T, n)
•Charles Law: V % T (constant P, n)
•Avogadro’s Law: V % n
If we combine these laws we get the Ideal Gas Law
where:
V % nT/P
V= volume T = temperature
P= pressure n= number of gas molecules
Correlation with gas laws
PV=nRT
• P,V,n & T all affect each other. That is if one of them varies, then
others will also.

15. STPD volume
Standard Temperature and Pressure dry
•Standard Temperature = 0°C
•Standard Pressure = 760 mmHg = 1 atm
•Dry = 0.0 mmHg H2O vapor pressure
•Units are commonly expressed in L/min.
ATPS volumes
Ambient Temperature, Pressure, and Saturation
•AT = Ambient Temperature in °C
•P = Ambient pressure
•S = Ambient PH2O (water vapor pressure)
•Units are commonly expressed in L/min

16. BTPS
Body Temperature, Pressure, and saturation
• BT = body temperature
• P = ambient pressure
• S = saturated with H2O
Converting From ATPS to BTPS
•The values from the spirometer are ATPS units
•In order for us to infer lung volumes from the data collected by
the spirometer we must convert them to BTPS.

17. BTPS correction factor
BTPSCF = TB(°C) + 273 PB – (PH2O)RT
x
TR(°C) + 273 PB – (PH2O)BT
Where:
TB = body temperature (37°C)
TR = Room Temperature in °C
273 = factor to convert from °C to Kelvin
PB = barometric pressure
PH2O = water vapor pressure at body temperature (BT) or room
temperature (RT)
BTPS correction factor
How to calculate BTPSCF
37 °C + 273 756-19.8*
x = 1.091
22°C + 273 756- 47.1**
*Water vapor pressure at 22 °C
** Water vapor pressure at 37°C
When TVATPS = 1.12 L
TVBTPS = 1.12 L x 1.091 = 1.22L
When VCATPS = 6.16 L
VCBTPS = 6.16 L x 1.091 = 6.72L

18. Measurement of residual volume
Residual volume (RV)
RV = VO2 x b
79.8 – b
Where VO2 the volume of oxygen in the bag
B= % nitrogen in the rebreathing bag
Fictional example:
5L x 21.72
RVATPS = = 1.87L
79.8-21.72
RVBTPS = 1.87L x 1.091 = 2.04L
Why spirometery
•Results from different forced spirometric test (FVC, FEV etc) help
to identify our state of pulmonary health.
•Because tests are valid and reliable we can compare results with
norms.