Basic Respiratory Physiology

Question 1

What neural areas make us breathe?

Answer 1

In the brainstem the respiratory centre (pons and medulla) drives respiratory muscle activity dependent on the neural inputs they receive

Question 2

Why do we need to breathe?

Answer 2

Adequate ventilation must be maintained to keep neutral pH range to allow optimal cellular function

Question 3

What changes blood pH most from ventilation?

Answer 3

PaCO2 is the most important ABG affecting ventilation. Increased PaCO2 levels will drive ventilation (e.g. increasing tidal volume or increasing respiratory rate) which blows off the excess CO2 and returns PaCO2 (and therefore blood pH) back to baseline

Question 4

What are the stages of breathing?

Answer 4

1. At rest
2. During inspiration
3. End inspiration
4. During expiration

Question 5

Describe the “at rest” stage of breathing

Answer 5

The barometric pressure at the mouth is 0 (PB), the pressure in the lungs (alveolar pressure PA) is 0, and the intrapleural pressure (Ppl) is negative. Therefore, there is no airflow as PB = PA

Question 6

Describe the “during inspiration” stage of breathing

Answer 6

1. Inspiratory muscles contract
2. Thoracic cage expands
3. Lungs expand (increasing lung volume)
4. Intrapleural and intraalveolar pressure decreases
5. Air flows into the lungs because the pressure in the alveoli is less than the pressure at the mouth
   Therefore, there is airflow inwards as PA < PB

Question 7

Describe the “end inspiration” stage of breathing

Answer 7

When the intraalveolar pressure equals the mouth (barometric/atmospheric) pressure, airflow ceases (as PA = PB again)

Question 8

Describe the “during expiration” stage of breathing

Answer 8

1. Respiratory muscles relax
2. Lungs passively recoil (to FRC)
3. Alveolar pressure rises (becomes positive) compared to mouth pressure
4. Gas therefore moves towards the mouth
   Therefore, there is airflow outwards as PA > PB

Question 9

Total/minute ventilation equation

Answer 9

(VE) = Vt x RR (e.g. VE = 500ml x 12 breaths/min = 6000mL (or 6L/min). This shows the mass movement of gas in/out of lungs

Question 10

Define alveolar ventilation (VA)

Answer 10

VA is the amount of fresh gas getting to the alveoli

Question 11

Define the anatomic dead space (VD)

Answer 11

Gas in the conducting airwards (from nose to terminal bronchioles) is called anatomic dead space (VD) and is about 150mL (VA = (VT – VD) x RR) so normal alveolar ventilation is approx 4.2L/min. Low alveolar ventilation will result in increase PaCO2 and decreased PaO2

Question 12

What affects the distribution of ventilation?

Answer 12

1. Pressure gradients in the lungs (affecting lung compliance)
2. Lung volume at which you breathe in from (i.e. FRC)
3. Flow rate
4. Pattern of breathing

Question 13

Define lung compliance

Answer 13

The change in volume produced by a change in pressure (C = ΔV/ ΔP). Low lung compliance makes it harder to inflate (stiff), whereas high lung compliance makes it easier to inflate

Question 14

What structures make up the mucociliary clearance (MCC) apparatus?

Answer 14

MUCUS: provides mechanical, biological and chemical barrier to inhaled material. 100-250ml produced per day by bronchial submucosal glands (larger airways) and goblet cells (bronchial epithelium).
CILIA: moves particles caught in the mucus to pharynx for swallowing

Question 15

What increases MCC ability?

Answer 15

Exercise, the environment (less inhaled particles), and medications (ventolin)

Question 16

What decreases MCC ability?

Answer 16

Higher age, sleeping, respiratory disease, medications (anaesthesia, opiates) and smoking

Question 17

MCC dysfunction: Smoking

Answer 17

• Increases mucus production
• Increases viscosity of mucus
• Decreases ciliary movement/beat frequency
• Cilial destruction
• Alveolar macrophage dysfunction

Question 18

MCC dysfunction: Chronic bronchitis

Answer 18

• Increases size and number of secretory cells
• Increases volume of mucus

Question 19

What is the function of a cough?

Answer 19

To assist in the removal of material from the central airways (either inhaled or produced in the airways). It is used if the volume of mucus is too large for normal MCC or if the MCC is damaged

Question 20

What is alveolar clearance?

Answer 20

This deals with small particles (e.g. asbestos, tobacco smoke, virus) that reach the alveoli. As there are no cilia in the alveoli, alternative mechanisms are used. Deposit via sedimentation/diffusion, and these particles are engulfed by macrophages, which migrate to smaller airways to be removed by MCC/lymphatic system (taking 1-3 days)