Physiology

Question 1

What is Boyle’s law?

Answer 1

At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas i.e. as the volume of the gas increases the pressure exerted decreases

Question 2

two forces that hold the thoracic wall and lungs in close opposition

Answer 2

intrapleural fluid cohesiveness (water molecules attracted to each other so pleural membranes stick together) and the negative intrapleural pressure (it is sub-atmospheric so transmural pressure gradient created across the lung wall and the thoracic wall, so the lungs are forced to expand as the chest is forced to squeeze inwards)

Question 3

How is volume of thorax expanded?

Answer 3

Contraction of diaphragm which flattens it, by phrenic nerve from C3, 4, 5

Question 4

What happens in inspiration?

Answer 4

Active process of contraction of inspiratory muscles, chest wall and lungs stretch. Lungs increase in size so intra alveolar pressure falls (Boyle’s law) so air enters down the pressure gradient until alveolar pressure equals atmospheric.

Question 5

What happens in expiration? What causes the lungs to recoil?

Answer 5

Passive process of relaxation of inspiratory muscles, chest wall, and stretched lungs recoil so intra alveolar pressure rises and air leaves down pressure gradient
Lungs recoil due to elastic connective tissue and alveolar surface tension (attraction between water molecules at liquid air interface, force produced that resists stretching of the lungs, if they were lined wth just water surface tension would be too string and the alveoli would collapse)

Question 6

Define pneumothorax

Answer 6

air in the pleural space, which abolishes the transmural pressure gradient.

Question 7

What is a tension pneumothorax?

Answer 7

Could be a puncture in the chest wall eg stabbed. Air is drawn into pleural space during inspiration and has no where to go in expiration. the mediasteinum is pushed over to the other side which compresses veins.
To treat give 100% oxygen, insert a large bore cannular with syringe into 2nd intercostal space, midclavicular line - do this before CXR and then insert a chest drain

Question 8

What is a spontaneous pneumothorax?

Answer 8

Hole in the lung

Question 9

Signs/symptoms of a pneumothorax?

Answer 9

Reduced expansion, hyper-resonance, sudden onset dyspnoea, pleuritic chest pain, diminished breath sounds on side affected, hypotension

Question 10

What is LaPlace law?

Answer 10

Smaller alveoli have a higher tendency to collapse

Question 11

What is pulmonary surfactant?

Answer 11

A mix of lipids, proteins, which are secreted by type 2 alveoli.
Developing foetal lungs cant synthesise it so premature babies can have resp distress
it lowers the alveoli surface tension, it lowers it more in smaller alveoli
P = 2T/r (inward directed collapsing pressure = 2 x surface tension/radius

Question 12

What is alveolar interdependence?

Answer 12

collapsing alveoli pulled open by surrounding alveoli

Question 13

Muscles of active expiration

Answer 13

interbal intercostal, abdominal

Question 14

Accessory muscles of inspiration

Answer 14

Sternocleidomastoid, scalenus

Question 15

Major muscles of inspiration

Answer 15

Sternum, ribs, external intercostal, diaphragm

Question 16

normal FEV1/FVC ratio

Answer 16

more than 75%, asthmatic will be less than this

Question 17

Will FEV1/FVC ratio reduce in restrictive disease?

Answer 17

No, problem with lung parenchyma not airway so can’t actually hold as much air so lower FVC as well as FEV1

Question 18

Equation to measure airway resistance?

What determines airway resistance?

Answer 18

flow = pressure/resistance (F=Delta P/R)

Resistance is usually low so air moves will small pressure gradient, radius of airway determines airway resistance

Question 19

What is pulmonary compliance?

Answer 19

measure of effort that has to go into stretching the lungs, the less compliant the more work is required.
It is decreased by pulmonary oedema, fibrosis, lung collapse, pneumonia, absence of surfactant
can cause restrictive pattern, SOB.
It is increased by emphysema where patients need to work harder to get the air out - hyperinflation of lungs. Compliance also increases with age

Question 20

Equation to work out pulmonary ventilation and define it

Answer 20

vol of air breathed in and out in one min

tidal volume x resp rate

Question 21

Equation to work out alveolar ventilation and define it

Answer 21

vol of air exchanged between alveolar and atoosphere per minute
(tidal vol-dead space) x resp rate
lower than pulm ventilation due to presence of dead space
eg 500ml enter alveoli, but 150 of this is dead space

Question 22

Match between air in alveoli and blood in pulm capillaries is not always perfect, what do we call alveoli which are not adequately perfused
what local controls are there to fix this

Answer 22

alveolar dead space
physiological dead space = anatomical dead space + alveolar dead space
Changes to smooth muscle of airways and arterioles match airflow to blood flow, eg too much CO2 in alveoli decreases airway resistance as airways dilate so there is increased airflow (due to increased perfusion).
Increase in O2 causes pulmonary vasodilation increasing the blood flow. (due to increased ventilation) and systemic arteries constrict

Question 23

What is the partial pressure of a gas?

Answer 23

Pressure that one gas would exert of it were the only gas in at a given temp