Respiratory - from West's 9th ed Chapter 7 - Mechanics of Breathing (1) Flashcards
Concerning contraction of the diaphram:
a) The nerves that are responsible emerge from the spinal cord at the level of the lower thorax
b) It tends to flatten the diaphram
c) It reduces the lateral distance between the lower rib margins
d) It causes the anterior abdominal wall to move in.
e) It raises intrapleural pressure
B
Concerning the pressure-volume behaviour of the lung:
a) Compliance decreases with age
b) Filling an animal lung with saline decreases compliance
c) Removing a lobe reduces total pulmonary compliance
d) Absence of surfactant increases compliance
e) In the upright lung at FRC, for a given change in intrapleural pressure, the alveoli near the base of the lung expand less than those near the apex
C is correct. If there is less lung, the total change in volume per unit change in pressure will be reduced. E is incorrect because it describes what would happen at RV, not at FRC.
Two bubbles have the same surface tension, but bubble X has 3 times the diameter of bubble Y. The ratio of the pressure in bubble X to that in bubble Y is:
a) 0.3 : 1
b) 0.9 : 1
c) 1 : 1
d) 3 : 1
e) 9 : 1
A (one third)
Pulmonary surfactant is produced by:
a) Alveolar macrophages
b) Goblet cells
c) Leukocytes
d) Type I alveolar cells
e) Type II alveolar cells
E
The basal regions of the upright human lung are normally better ventilated than the upper regions because:
a) Airway resistance of the upper regions is higher than of the lower regions
b) There is less surfactant in the upper regions
c) The blood flow to the lower regions is higher
d) The lower regions have a small resting volume and a relatively large increase in volume
e) The PCO2 of the lower regions is relatively high
D
Pulmonary surfactant
a) Increases the surface tension of the alveolar lining liquid
b) Is secreted by type I alveolar epithelial cells
c) Is a protein
d) Increases the work required to expand the lung
e) Helps to prevent transudation of fluid from the capillaries into the alveolar spaces
E
Concerning normal expiration during resting conditions
a) Expiration is generated by the expiratory muscles
b) Alveolar pressure is less than atmospheric pressure
c) Intrapleural pressure gradually falls (becomes more negative) during the expiration.
d) Flow velocity of the gas (in cm/sec) in the large airways exceeds that in the terminal bronchioles.
e) Diaphragm moves down as expiration proceeds.
D
An anaesthetised patient with paralyzed respiratory muscles and normal lungs is ventilated by positive pressure. If the anaesthetist increases the lung volume 2 litres above FRC and holds the lung at that volume for 5 seconds, the most likely combination of pressures (in cm H2O) is likely to be:
a) Mouth 0, Alveolar 0, Intrapleural -5
b) Mouth 0, Alveolar +10, Intrapleural -5
c) Mouth +10, Alveolar +10, Intrapleural -10
d) Mouth +20, Alveolar +20, Intrapleural +5
e) Mouth +10, Alveolar 0, Intrapleural -10
D
When a normal subject develops a spontaneous pneumothorax of his right lung, you would expect the following to occur:
a) Right lung contracts
b) Chest wall on the right contracts
c) Diaphragm on the right moves up
d) Mediastinum moves to the right
e) Blood flow to the right lung increases
A
According to Poiseuille’s law, reducing the radius of an airway to one-third will increase its resistance how many fold?
a) 1/3
b) 3
c) 9
d) 27
e) 81
E is correct. Poiseuille’s law states that during laminar flow, airway resistance is inversely proportional to the 4th power of the radius, other things being equal. Therefore, reduction of the radius by a factor of 3 increases the resistance by 3^4, that is, 81.
Concerning airflow in the lung
a) Flow is more likely to be turbulent in small airways than in the trachea
b) The lower the viscosity, the less likely is turbulence to occur
c) In pure laminar flow, halving the radius of the airway increases its resistance eightfold
d) For inspiration to occur, mouth pressure must be less than alveolar pressure
e) Airway resistance increases during scuba diving
E
The most important factor limiting flow rate during most of a forced expiration from total lung capacity is:
a) Rate of contraction of expiratory muscles
b) Action of diaphragm
c) Constriction of bronchial smooth muscle
d) Elasticity of chest wall
e) Compression of airways
E
Which of the following factors increases the resistance of the airways?
a) Increasing lung volume above FRC
b) Increased sympathetic stimulation of airway smooth muscle
c) Going to high altitude
d) Inhaling cigarette smoke
e) Breathing a mixture of 21% O2 and 79% helium (molecular weight 4)
D is correct. Inhalation of cigarette smoke causes reflex constriction of airway smooth muscle as a result of stimulation of irritant receptors in the airway wall.
A normal subject makes an inspiratory effort against a closed airway. You would expect the following to occur:
a) Tension in the diaphragm decreases
b) The internal intercostal muscles become active
c) Intrapleural pressure increases (becomes less negative)
d) Alveolar pressure falls more than intrapleural pressure
e) Pressure inside the pulmonary capillaries falls
E is correct. When an inspiratory effort is made against a closed airway, all the pressures inside the thorax fall including the pulmonary vascular pressures.
