Spirometry

Question 1

Spirometry

Answer 1

Quantitative diagnostic test to analyse the lung volume changes over time
Normal values predictable
Static- volume only
Dynamic- time to exhale a volume
Lung volumes can be measured either directly or indirectly

Question 2

Direct measurements

Answer 2

Piston spirometer
Water cell spirometer
Needs to be:
-as frictionless as possible (light piston)
-sealed mouthpiece and nose clips

Question 3

Indirect measurement

Answer 3

Peak flow meter- peak expiration flow PEFR, pushes piston on a spring, used to monitor lung function over time can be given to patients
PEFR- inspire to TLC then forcible exhale to RV, best of 3 recorded, used in asthma monitoring. Dependent upon tissue recoil as well as airway diameter

Pneumotachograph:
Analogous to Ohms law change in P proportional to flow
Measure flow directly or volume by integrating the flow signal
Measures difference in partial pressures and flow directly used to see how flow rates change over time

Sources of potential bias:
- larger airway damage will effect results more than smaller airways
-dependent on effort= need consistent and maximal effort for results to be useful

Question 4

Helium dilution method for measuring residual volume

Answer 4

Spirometry cant be used because RV never leaves lungs
Initial helium - final helium
Amount in spirometer= amount in spirometer and lung
Due to the low solubility of helium it wont dissolve in blood
Used to measure full volume of lungs
V2= V1(C1/C2-1)

Question 5

Lung disease and pulmonary function test

Answer 5

Restrictive: reduced lung volume, reduced effective surface area for gas exchange changes in compliance and elasticity eg fibrosis. FEV1/FVC>0.8 smaller VC
Obstructive: increased airway resistance, reduced airways diameter, R propositional to 1/r^4, bronchitis/asthma. FEV1/FVC<0.8 FEV1 decreased in obstructive disease

Question 6

PEFR with restrictive and obstructive disease

Answer 6

Obstructive: reduced peak flow and scooped out descending limb , area under curve is normal due to VC still normal but obstruction means takes longer to reach
Restrictive: reduced peak flow and steeper descending limb , area under curve is reduced due to VC reduced changed elastic recoil different pressure gradient smaller vital capacity

Question 7

Emphysema (COPD)

Answer 7

Can no unnoticed for a while as lungs have lots of reserve capacity, resistance mainly in larger airways, quite disease progress few symptoms, silent zone later diagnosis
Early: loss of alveolar elastic structure- loss of diffusive surface area- Restrictive
Later: inflammation of small airways- increased resistance- obstructive
Loss of alveolar elastic structure/support- collapse on expiration- obstructive

Question 8

Flow volume loops

Answer 8

Demonstrates spirometric efforts
Restrictive:
-maximal flow reduced, reduced total volume expired, increased flow in latter expiration phase due to increased recoil
Obstructive: flow rate is low, scooped out appearance