Lung Physiology 2

Question 1

Forced expiration

Question 2

PEF- Peak Expiratory Flow

Answer 2

Single measure of highest flow during expiration
Peak flow meter, spirometer

Gives reading in litres/minute (L/min)
Very effort dependent
May be measured over time, by giving a patient a PEF meter and chart

Question 3

Lung volume

Answer 3

Expiratory procedures only measure Vital Capacity, not Residual Volume
Various other ways to measure RV and TLC are needed

These include;
Gas dilution
Body box (total body plethysmography; shown in picture)

Question 4

Lung volumes- Gas dilation

Answer 4

Measurement of all air in the lungs that communicates with the airways

Does not measure air in non-communicating bullae

Gas dilution techniques use either closed-circuit helium dilution or open-circuit nitrogen washout

Question 5

Lung volumes-Total body plethysmography

Answer 5

Alterative method of measuring lung volume, (Boyle’s law), including gas trapped in bullae.

From the FRC, patient “pants” with an open glottis against a closed shutter to produce changes in the box pressure proportionate to the volume of air in the chest

The volume measured (TGV) represents the lung volume at which the shutter was closed

FRC, inspiratory capacity, expiratory reserve volume, vital capacity all measured

From these volumes and capacities, the residual volume and total lung capacity can be calculated

TLC = VC+RV

Question 6

Transfer estimates

Answer 6

Carbon monoxide used to estimate TLCO, as has high affinity for haemoglobin

TLCO is an overall measure of the interaction of;
-alveolar surface area
-alveolar capillary perfusion
-physical properties of the alveolar capillary interface
-capillary volume
-haemoglobin concentration, and the reaction rate of carbon monoxide and hemoglobin.

Single 10 second breath-holding technique
-10% helium, 0.3% carbon monoxide, 21% oxygen, remainder nitrogen.

Alveolar sample obtained;
-DLCO is calculated from the total volume of the lung, breath-hold time, and the initial and final alveolar concentrations of carbon monoxide.

Question 7

Measured values- normal ranges

Answer 7

Each measured value has its own normal range
Derived normally from regression equations based on normal populations
Wide range of values hence normal
Lowest 5% arbitrarily defined as abnormal (and upper 5%)

Question 8

Abnormal values- FEV1- Forced expiratory volume in one second in litres

Answer 8

Compare with predicted value
80% or greater “normal”
Above the lower limit of normal for that patient (LLN)
Above mean minus 1.645 SD

Question 9

Abnormal values- Forced Vital Capacity- FVC

Answer 9

Compare with predicted value
80% or greater “normal”
Above the lower limit of normal for that patient (LLN)
Above mean minus 1.645 SD

Low value indicates likely Airways Restriction (less than 80% predicted )

Question 10

Abnormal values

FEV1/FVC ratio

Answer 10

There is a predicted ratio for each individual, but..

Abnormal ratio < 0.70 = airways obstruction

[Can also use the LLN* for each individual patient]
*Lower limit of normal

Question 11

Airways obstruction-

Answer 11

FEV1 / FVC ratio < 0.70

FEV1 / FVC ratio < 0.70 = airways obstruction