Ventilation

Question 1

Force expiratory volume (FEV1)

Answer 1

The volume of gas exhaled in 1 second by forced expiration from full inspiration

Question 2

Vital capacity

Answer 2

The total volume of gas that can be exhaled after a full inspiration

Question 3

Vital capacity measures with forced expiration vs. slower exhalation

Answer 3

Vital capacity measured with forced expiration may be less than that measured with a slower exhalation (so specify that it is forced vital capacity)

Question 4

Normal ratio of FEV1 to FVC

Answer 4

• approximately 80%

- but will decrease with age

Question 5

FEV1/FVC in obstructive disorders (i.e. COPD)

Answer 5

-the ratio is reduced

Question 6

FEV1/FVC in restrictive disorders (i.e. pulmonary fibrosis)

Answer 6

-ration unchanged/increased

Question 7

Use of FEV1/FVC tests

Answer 7

• valuable in assessing the efficacy of bronchodilator drugs (carry out before and after administration of drug)
• valuable in assessing the progress of disease

Question 8

FEV1/FVC in patient with bronchospasm

Answer 8

-both values are usually increased

Question 9

Forced expiratory flow

Answer 9

-the middle half (by volume) of a forced expiration is marked and its duration is measured
FEF 25-75% = volume (l)/ time (s)

Question 10

Correlation FEF25-75% and FEV1

Answer 10

Generally close in patients with obstructive pulmonary disease (although changes in FEF 25-75%) are often more striking

Question 11

What is vital capacity a measure of

Answer 11

Stroke volume

Question 12

Causes of stroke volume reduction

Answer 12

1) Diseases of the thoracic cage and acute injuries
2) Diseases affecting the nerve supply to the respiratory muscles or disease of the muscles themselves
3) Abnormalities of the pleural cavity
4) Disease of the lung itself
5) Increased pulmonary blood volume
6) Space occupying lesins (cysts)
7) Disease of airways that cause them to close prematurely during expiation (asthma, bronchitis)

Question 13

Diseases of the thoracic cage reducing stroke volume

Answer 13

1) Kyphoscoliosis

2) Ankylosing spondylitis

Question 14

Abnormalities of the pleural cavity causing reduction in stroke volume

Answer 14

1) Pneumothorax

2) pleural thickening

Question 15

Diseases of the lung reducing stroke volume

Answer 15

1) Pulmonary fibrosis (reduce distensibility)

Question 16

Cause of increased pulmonary blood flow causing reduction in stroke volume

Answer 16

-left heart failure

Question 17

What is the forced expiratory volume (and FEF 25-75%) affected by

Answer 17

• affected by airway resistance during forced expiration

- increase resistance will reduce these measures

Question 18

Causes of airway resistance

Answer 18

1) Bronchoconstriction
2) Structural changes in the airways
3) Obstructions within the airways
4) Destructive processes in the lung parenchyma (interfere with the radial traction that normally holds the airways open)

Question 19

Example causes of bronchoconstriction (2)

Answer 19

• asthma

- inhalation of irritants (cigarette smoke)

Question 20

Example structural changes in airways (1)

Answer 20

-chronic bronchitis

Question 21

Example obstruction within airways (2)

Answer 21

• foreign body

- excess bronchial secretions

Question 22

Simple model of factors that may reduce the ventilatory capacity

Answer 22

1) Those that reduce stroke volume

2) Those that increase airway resistance

Question 23

Expiratory flow-volume curves -how changes in obstructive and restrictive patterns

Answer 23

a) obstructive pattern
-decreased flow rate at larger lung volumes (maximal expiration begins and ends at abnormally high lung volumes)
b) restrictive pattern
-decreased flow rate at smaller volumes
(maximal expiration begins and ends at low lung volumes)

Question 24

Limit of expiratory flow-volume curve

Answer 24

• impossible to get values outside of the normal curve (no matter how change respiration) - -> flow rate will not increase beyond the envelope
• factor that is limiting the maximum flow rate = dynamic compression of the airways

Question 25

Consequences of dynamic compression of the airways

Answer 25

1) limits flow rate during a forced expiration 2) causes flow to be independent of effort 3) may limit flow during normal expiration in some patients with COPD 4) is a major factor limiting exercise in COPD

Question 26

Explanation of cause of dynamic compression

Answer 26

1. Initially (at rest) pressure in mouth, airways and alveoli = atm while pressure in intrapleural space is 5cm H2O below atm 2. Inspiration --> diaphragm lowers --> pressure in intrapleural space becomes more negative (at end of inspiration pressure is 8 cm H2O) --> this is the pressure expanding the airway (alveoli inflate and pressure moves from positive --> negative down into alveoli) 3. With forced expiration (diaphragm pushed back up) both the intrapleural pressure and alveolar pressure rise 4. But the pressure in the airways does not increase as much due to the pressure drop ecause of flow So get a pressure difference of 11 cm whcih tends to close the airways (i.e. intrapleural pressure pushing on airways) THEREFORE FLOW DETERMINED BY DIFFERENCE BETWEEN ALVEOLAR PRESSURE AND THE PRESSURE OUTSIDE THE AIRWAYS AT THE COLLAPSE POINT (aka staling resistor effect)

Question 27

Static recoil pressure

Answer 27

The pressure difference between alveolar pressure and the pressure outside the airways Depends only on lung volumes and compliance and is independent of expiratory effort

Question 28

Factors contributing to low flow rate in patients with obstructive long diseases

Answer 28

1) Thickening of walls of the airways and excessive secretions in the lumen due to bronchitis --> increasing flow resistance 2) Number of small airways reduced because of destruction lung tissue 3) Reduced static recoil pressure due to breakdown of elastic alveolar walls 4) Impaired traction from parenchyma due to loss alveolar walls --> collapse more easily than should

Question 29

Factors contributing to low flow rate in patients with restrictive lung diseases

Answer 29

- lung static recoil high | - reduced compliance of lung makes volumes of small so absolute flow rate is reduced

Question 30

What determines the flow rate when airways collapse during a forced expiration

Answer 30

Determined by the resistance of the airways up to the pint of collapse

Question 31

Where does airway collapse occur

Answer 31

-at the point where pressure inside the airways is equal to intrapleural pressure (equal pressure point)

Question 32

What happens to the equal pressure point as airway resistance increases

Answer 32

Pressure is lost more rapidly and the collapse point moves moves into more distal airways

Question 33

Normal equal pressure point

Answer 33

In the vicinity of the lobar bronchi early in a forced expiration???

Question 34

Peak expiratory flow rate

Answer 34

-maximum flow rate during a forced expiration starting from total lung capacity

Question 35

Measuring peak expiratory flow rate

Answer 35

-estimated with a portable peak flow meter

Question 36

Inspiratory flow-volume curve -what affects it

Answer 36

-useful in detecting upper airway obstruction --> will flaten the curve because maximum flow is limited

Question 37

Tests for uneven ventilation

Answer 37

1) Single breath nitrogen test | 2) multibreath nitrogen washout

Question 38

Single breath nitrogen test

Answer 38

-measuring nitrogen concentration at the mouth piece when patent takes a vital pacity inspiration of oxyen and then exhales slowly as far as he can to residual volume

Question 39

Four phases of single breath nitrogen test

Answer 39

1) Pure oxygen is exhaled from the upper airways, nitrogen concentration = 0 2) Nitrogen concentration rises rapidly as the anatomic dead space is washed out by alveolar gas 3) Third phase = alveolar gas - tracing only small upward slope (alveolar plateau) 4) Rise in nitrogen concentration