Anatomy and Physiology

Question 1

List some anatomical factors that can make intubation difficult.

Answer 1

Small mouth
Receding chin
High arched palate
Large tongue
Acquires injuries (e.g. burns, tumours)
Poor dentition (e.g. loose teeth)
TMJ disease limiting mouth opening
Adenotonsillar hypertrophy

Question 2

What type of epithelium is the nasal epithelium?

Answer 2

PseudostratifieWd ciliated columnar epithelium containing numerous mucous and serous glands

Question 3

What is the normal vital capacity per kilogram?

Answer 3

60 mL/kg

Question 4

List some techniques for measuring lung volumes.

Answer 4

Water-sealed spirometer
Dry spirometer
Body plethysmograph
Helium dilution 
Nitrogen washout

Question 5

Describe the helium dilution method for measuring lung volumes.

Answer 5

Helium has a low solubility so is hardly absorbed into the blood
Subject breathes in a known concentration of helium in a closed system with a spirometer and wait for it to equilibrate
Then measure the expired concentration of helium to determine the total lung volume

Question 6

What is the normal FRC in most normal subjects?

Answer 6

2500 mL

Question 7

How long does the oxygen reservoir last when breathing oxygen vs being preoxygenated?

Answer 7

Oxygen Consumption: 250 mL/min

Breathing Air: 375 mL of oxygen = 1.5 mins
Breathing Oxygen: 2250 mL of oxygen = 9 mins

Question 8

Describe the relationship between FRC and pulmonary vascular resistance.

Answer 8

PVR is lowest at FRC
At low lung volumes, walls of the large pulmonary vessels are less supported by traction from the tissues + hypoxic vasoconstriction

At high lung volumes, capillaries become squished by hyperexpanded alveoli

Question 9

Define dead space.

Answer 9

Volume of inspired air that does not take part in gas exchange

Question 10

What are alveolar time constants?

Answer 10

The time it takes for an alveolus to fill or empty with gas 

It is determined by the resistance to airflow in the airways and the compliance of the alveoli 

Question 11

Describe the graph produced by Fowler’s method.

Answer 11

1: anatomical dead space
2: mixed alveolar and dead space gas
3: alveolar air
4: closing capacity

Question 12

Describe Fowler’s method.

Answer 12

The subject breathes normally and then takes a vital capacity inspiratory breath of 100% oxygen from the end of normal expiration 
Exhaled nitrogen is then measured through slow maximal expiration to residual volume 

Question 13

Explain the slight rise in exhaled nitrogen at the end of expiration during Fowler’s method.

Answer 13

During normal tidal breathing, the upper alveoli are better ventilated
During the forced vital breath, more oxygen enters the lower airways

At closing capacity, the lower airways collapse and the exhaled gas will mainly be coming from the upper alveoli which has a higher nitrogen concentration – thereby causing this slight increase in the expired nitrogen 

Question 14

Derive the Bohr equation for calculating physiological dead space.

Answer 14

FACO2 x VA = FECO2 x VT
VA = VT – VD 
FACO2(VT – VD) = FECO2 x VT 
(FACO2 x VT) – (FACO2 x VD) = FECO2 x VT
FACO2 x VT – FECO2 x VT = FACO2 x VD
VT(FACO2 – FECO2) = FACO2 x VD
FACO2 – FECO2/FACO2 = VD/VT

The partial pressures are used instead and arteries pCO2 is used as a surrogate for alveolar pCO2

Question 15

What is the normal lung compliance roughly?

Answer 15

200 mL/cm H2O

Question 16

What does hysteresis mean with regards to a pressure-volume graph for the lung?

Answer 16

The expiratory limb does not follow the same path as the inspiratory limb

Question 17

State the equation that describes the law of Laplace.

Answer 17

For SPHERICAL bubble:
P = 4T/r

For one surface:
P = 2T/r

Question 18

Describe the differences in the relative effects of viscosity and density on laminar and turbulent flow.

Answer 18

Laminar: viscosity has a greater effect than density

Turbulent: density has a greater effect than viscosity

Question 19

Define dynamic airway compression.

Answer 19

Compression of the airways by intrathoracic pressure (occurs on forced expiration)

Question 20

Where are the central chemoreceptors found?

Answer 20

Ventral surface of the medulla
Where glossopharyngeal and vagus nerve originate

Question 21

Describe the structure and function of the dorsal respiratory group.

Answer 21

At floor of 4th ventricle where sensory afferents for glossopharyngeal and vagus terminate

Predominantly inspiratory neurones (phrenic and intercostal)
Involved in timing of respiratory cycle

Question 22

What four nuclei make up the ventral respiratory group?

Answer 22

Botzinger Complex (expiratory)
Nucleus Para-ambigualis (inspiratory)
Nucleus Ambiguus (dilator function of larynx/pharynx/tongue)
Nucleus Retro-Ambigualis (expiratory)

Question 23

What is the function of the pneumotaxic centre?

Answer 23

Off-switch for inspiration
Stimulation causes earlier termination of inspiration (leads to higher RR and lower VT)

NOTE: part of pontine respiratory group which is involved in fine control of respiratory rhythm

Question 24

What is the function of the apneustic centre?

Answer 24

Prolongs inspiration

NOTE: part of pontine respiratory group which is involved in fine control of respiratory rhythm

Question 25

What do central chemoreceptors respond to?

Answer 25

Arterial pCO2 This occurs via changes in the hydrogen ion concentration in the CSF

Question 26

What do peripheral chemoreceptors respond to?

Answer 26

CAROTID: pO2, pCO2, pH AORTIC: pO2, pCO2

Question 27

Describe how central chemoreceptors work.

Answer 27

The BBB is permeable to CO2 but impermeable to H+ and bicarbonate This means that CO2 diffuses into the CSF where it hydrates and generates H+ and HCO3-  This is then thought to be detected by pH sensitive enzymes 

Question 28

What type types of cell make up the carotid body?

Answer 28

Type 1 (Chief) Cells - chemoreceptive cells in contact with afferent nerve endings of sinus nerve (branch of glossopharyngeal) Type 2 (Sheath) Cells - supporting cells

Question 29

How does blood flow affect the functioning of the carotid body and aortic arch chemoreceptors?

Answer 29

Aortic Arch: lower blood flow meaning higher arterio-venous oxygen difference, responds to both oxygen content (e.g. haemoglobin) and arterial oxygen tension Carotid Bodies: higher blood flow meaning it primarily responds to dissolved oxygen (pO2) and is more sensitive to changes in ventilation

Question 30

What is the Hering-Breuer reflex?

Answer 30

Inhibition of inspiration in response to distension of the large airways Afferent information sent via vagus nerve