Respiratory physiology and lung mechanics 2

Question 1

Definition of FEV1

Answer 1

Forced expiratory volume in 1 sec

Question 2

Definition of forced vital capacity

Answer 2

The max volume of air that can be breathed out forcefully

Question 3

How would you measure lung compliance?
What equation do you need
How do you plot the results
What do the results tell you

Answer 3

Pl = Pa - Ppl

Pa = 0 when there’s no airflow
Ppl measured with esophageal balloon
Volume measured with spirometry

Breathe in from RV => TLC in steps
-At each step, measure volume and Ppl

Sigmoid curve of V against Pl

• Plateau at top and bottom => low compliance
• Steepest part => highest compliance, easiest to breathe at tidal volume

Question 4

How do these factors affect lung compliance
Obstructive lung disorders
-Emphesyma
-Neonatal Resp Distress Syndrome

Answer 4

Emphesyma
-Loss in alveolar SA => alveoli collapse, increased compliance

Neonatal Resp Distress Syndrome

• Normally, surfactant produced by T2 alveolar cells (mix of phospholipids) => at small r => low ST => low P
• Increased compliance and less likely to collapse, transudate

-Premature babies don’t produce enough, more work needed due to decreased compliance and alveolar collapse

Question 5

How do these factors affect lung compliance
Restrictive lung disorders
-Fibrosis

Answer 5

Fibrosis

-Loss of elastic tissue => loss of compliance

Question 6

What is the equation for compliance

What is the typical compliance of the lungs

Answer 6

Compliance = ∆V/∆Pl

1.5kPa

Question 7

What are the properties of obstructive lung disorders

• Asthma
• Bronchitis
• Emphysema

Answer 7

Decreased r => increased R => decreased F

Asthma

• bronchocontriction, mucosal edema
• alveoli ok

Bronchitis

• gland hypertrophy, mucus prod
• alveoli ok

Emphesyma

• loss of alveolar elastic tissue => increased compliance
• resp muscles ok

Question 8

What are the properties of restrictive lung disorders

• Fibrosis
• Resp muscle weakness

Answer 8

Low compliance, low lung volume

Fibrosis

• stiff lungs, harder to breathe
• alveoli ok
• resp muscles ok

Resp muscle weakness

• Resp muscles too weak to expand cage
• alveoli ok
• airways ok

Question 9

What are the 2 ways to measure lung function

When would you use either test

Answer 9

Spirometry
-establish if increased R is due to narrow airways

FEV1, FVC
-differentiate between obstructive and restrictive diseases

Question 10

Describe the 3 different outcomes in a FEV1, FVC test and why you’d get these results

• normal
• obstructive
• restrictive

Answer 10

Normal

• FEV1 normal
• FVC normal
• ratio >75%

Obstructive, can breathe in same volume as normal but takes longer due to increased R

• FEV1 low
• FVC low/normal
• ratio low

Restrictive, cannot breathe in same volume due to smaller lung capacity

• FEV1 low
• FVC low
• ratio >75%

Question 11

Describe the 3 max flow volume loops in

• normal
• obstructive
• restrictive

Answer 11

Normal
-has dynamic equilibrium in forced exhalation

Obstructive

• RV starts higher than normal as they were unable to remove it
• characteristic concave shape due to increased R => unable to remove all air

Restrictive
-same shape as normal but lower TLC

Question 12

What is FRC a measure of
How is it affected in
-lung fibrosis
-emphesyma
-resp muscle weakness

Answer 12

FRC a measure of the balance between lung recoil inwards and cage recoil outwards

Lung fibrosis

• lung recoil is greater than cage recoil
• FRC lower

Emphysema

• loss of alveolar elastic tissue => reduced lung recoil in
• greater cage recoil out => barrel chest
• FRC higher

Resp muscle weakness
-lung and cage recoil unaffected => FRC normal