Respiratory Physiology I

Question 1

What are the basic mechanics of breathing?

Answer 1

• Movement of air (in & out of the lungs) occurs due to pressure differences
• Pressure differences are created by changes in lung volume
• Air will flow from a region of high pressure to a region of low pressure

Question 2

How is the diaphragm?

Answer 2

Diaphragm contracts which leads to an increase in lung size and consequently air movement into the lungs
Diaphragm relaxes which leads to a decrease in lung size and consequently air movement out of the lungs

Question 3

How do we measure lung function?

Answer 3

Spirometry

Question 4

What is tidal volume?

Answer 4

Amount of air you move into and out of your lungs during rest

Question 5

What is forced vital capacity?

Answer 5

Maximum volume of air into and out of your lungs in a single respiratory cycle

Question 6

How do we measure lung function and assess whether a patient has reduced lung function?

Answer 6

o In order to understand differences in lung function capacity between healthy and asthma patients we need to revisit lung function

Question 7

What is inspiratory reserve volume?

Answer 7

Volume of air you can draw into your lungs

Question 8

What is the expiratory reserve?

Answer 8

Volume of air you can expel from your lungs

Question 9

What is residual volume?

Answer 9

Volume of air that remains in the lungs even after maximal exhalation

Question 10

What is the equation for forced vital capacity?

Answer 10

Forced vital capacity = inspiratory reserve capacity + tidal volume + expiratory reserve volume

Question 11

How is FEV1/FVC?

Answer 11

• FEVI/FVC is a ratio of Forced Expiratory Volume in 1 sec & Forced Vital Capacity
• Values above 70-80% = normal. Age/gender adjusted
• Airflow limitation (e.g. Asthma) : ↓FEV1/FVC

Question 12

How can we tell the difference between the spirometry of a healthy individual and individuals with asthma?

Answer 12

• In order to see differences between healthy individuals and individuals with asthma we must manipulate the previous basic spirometry diagram into Flow-volume loops. Where the y axis is …… and x-axis is…….
• After the starting point the curve rapidly mounts to a peak: Peak (Expiratory) Flow.
• After the PEF the curve descends (=the flow decreases) as more air is expired. A normal, non-pathological F/V loop will descend in a straight or a convex line from top (PEF) to bottom (FVC).

Question 13

How does asthma affect flow rate?

Answer 13

Asthma = reduced flow rate

Question 14

Which parts of the brainstem is involved in control of breathing?

Answer 14

Central chemoreceptors (TCO2) and respiratory centre in the medulla oblongata

Question 15

What happens during inspiration quiet/forced breathing?

Answer 15

• Inspiration: active part of passive breathing
  o Diaphragm & external intercostal muscles
• Inspiration: Diaphragm, external intercostal muscles & accessory muscles (E.g. Pectoralis major & minor, & Serratus anterior)

Question 16

How does the diaphragm cause inspiration?

Answer 16

-	Diaphragm 
o	Innervated by the phrenic nerves the diaphragm flattens, thus drawing air into the chest
o	Central tendon of the diaphragm 
	Rest = 1-2 cm
	Forced breathing < 10 cm

Question 17

How do the external intercostal muscles cause inspiration?

Answer 17

o Pump-handle movements; anterior end of each rib is elevated
o Bucket-handle movements: diameter of chest increases

Question 18

How does expiration occur in quiet/forced breathing?

Answer 18

Quiet Breathing
- Expiration: largely passive as a result of elastic recoil of the lungs
Forced Breathing
- Expiration: Active. Involves accessory respiratory muscles (E.g. Anterior abdominal muscles & quadratus lumborum).

Question 19

What is alveolar ventilation and why is it significant?

Answer 19

• Alveolar ventilation: portion of the total ventilation that reaches the alveoli and participates in gas exchange
• Hypoventilation or hyperventilation: Sign of lung diseases
• Gases move between air and blood by passive diffusion
• Movement of gases defined by partial pressure gradients

Question 20

How does airway ventilation and perfusion change as you descend the airways?

Answer 20

Both increase as you descend the airways

Question 21

What is anatomical dead space?

Answer 21

• Volume of air in the mouth, pharynx, trachea and bronchi up to the terminal bronchioles
• The anatomical dead space ≈ 150 ml

Question 22

What is alveolar dead space and what can cause it?

Answer 22

• Age or respiratory disease: Presence of alveolar dead space
• Alveolar dead space: alveoli that have insufficient blood supply to act as effective respiratory membranes

Question 23

What is alveolar ventilation and how can it be calculated?

Answer 23

Calculating Alveolar Ventilation
- Rate at which new air reaches the alveoli
- (Tidal volume –dead space) X respiratory rate
o Tidal volume=500 mL
o Anatomic dead space=150 mL
o Fresh air entering the lungs=350 mL
o Respiratory rate=12 breaths/min
o Alveolar ventilation (ml/min)
o 12X350=4200 mL/min (4.2L/min)
- This is the effective ventilation that brings about the exchange of O2 and CO2.

Question 24

Summarise respiratory physiology.

Answer 24

• A major function of the respiratory system is movement of air into and out of the Lungs
• Lung function can be assessed using Spirometry
• Lung function tests include Tidal volume, forced vital capacity (FVC) & forced expiratory volume in 1 sec (FEV1)
• Control of breathing: Role of Respiratory muscles & accessory muscles
• Alveolar ventilation: portion of the total ventilation that reaches the alveoli and participates in gas exchange