Respiration Module

Lung function testing
tests need to assess
the mechanical condition of the lungs
resistance of the airways
diffusion across alveolar membrane
Kufa’s university

Pulmonary Function Test
Spirometry
Lung volumes
Diffusions capacity
Oxygen saturation and ABG(arterial blood gases) analysis.

PFT’S

Non invasive testing
lung function may be inferred from measurement of
volumes
pressures/flows composition
at the mouth
Kufa’s university

Volume
remember the spirometer
vital capacity
maximum inspiration to maximum expiration
Vital
Capacity

What limits vital capacity?
maximum inspiration
compliance of the lungs
force of inspiratory muscles
maximum expiration
increasing airway resistance
as the lungs are compressed

If vital capacity is less than normal
tables predict what vital capacity should be
if less maybe because
cannot breathe in maximally
cannot breathe out maximally
how to tell the difference?

Vital-ograph trace
plot of volume expired vs time
initial rapid rise tails to a plateau
Time
Volume expired
FEV1.0
FVC

Restrictive deficit
if lungs are difficult to fill
stiff
weak muscles
problem with chest wall
they will start less full
so FVC will be reduced
but air will come out normally
so FEV1.0 will be >70% FVC
Time
Volume expired
Restrictive deficit
Normal

Obstructive deficit
if airways are narrowed
lungs will still be easy to fill
but resistance will increase in expiration
so air will come out more slowly
and FEV1.0 will be reduced
but FVC be relatively normal
Time
Volume expired
Normal
Obstructive deficit

Flow volume curves
plot of volume expired
against flow rate
derived from vitalograph trace
A
B
C
D
Time
Volume expired

Flow volume curves
Volume expired
A
Flow
B
C
D
A
B
C
D
Time
Volume expired

Flow volume curves
when lungs are full
little air expired
airways stretched
so resistance at minimum
flow rate will be maximal
Peak Expiratory Flow Rate (PEFR)
Flow
B
C
D
PEFR
Volume expired

Flow volume curves
as lungs are compressed
more air expired
airways begin to narrow
resistance increases
flow rate falls
the narrower the airways to start with the more rapidly it falls
Flow
B
C
D
Obstruction
Volume expired

Flow volume curves
a much more sensitive indicator of airway narrowing
can also discriminate large & small airway narrowing
This is Flow-Volume loop

Peak Expiratory Flow Rate
can be measured with a simple, cheap device
so often used as a screening test for airway narrowing
but very insensitive

Measurement of Residual volume
cannot be measured by spirometer
use Helium dilution
Nitrogen Washout
Body Plethysmography

Nitrogen washout
subject takes one normal breath of pure oxygen
breathes out via meter measuring % nitrogen
initially only oxygen expired from airways
Nitrogen washout. Until recently, this was the most commonly used method of lung volume determination. In this technique, 100% oxygen in inhaled briefly and nitrogen in the exhaled gas is measured - this allows calculation of the total amount of gas in the lung originally.

Helium dilution
helium not normally present in air
and insoluble in blood
breathe in known concentration
starting at FRC
and see how much concentration reduced by mixing with air already in lungs

Measuring diffusion conductance
measure how easily carbon monoxide crosses from alveolar air to blood
use CO because binding to Hb means no partial pressure in mixed venous blood

The lung function report
Vital Capacity
FEV1.0 (before after bronchodilators)
ratio FEV1.0 /FVC
Peak Expiratory Flow

The lung function report
FRC
RV
TLC total lung capacity
RV/TLC

The lung function report
transfer factor
carbon monoxide conductance

The lung function report
learn how to interpret them!