Lecture 2: The respiratory cycle and mechanics of ventilation

Question 1

Define respiration:

Answer 1

1. To extract O2 from air and with CVS transport to respiring tissues
2. Remove CO2 from respiring tissues and exhaust into atmosphere

Question 2

What evolutionary factors have driven the formation of lungs in mammals?

Answer 2

• Increased size
• Increased diffusion distances
• Increased metabolic rate i.e cold vs warm blood
• Increased oxygen demand

Question 3

What sort of process is inspiration and what is the main driver?

Answer 3

Inspiration is an active process and the diaphragm is the main driver

Question 4

What are the muscles of inspiration and exhalation?

Answer 4

Inspriation: Diaphragm and external intercostals

Expiration: Internal intercostals and abdominal muscles

Question 5

Describe the chest movements of breathing:

Answer 5

Inspiration: Ribs move in and out, diaphragm flattens

Exhalation: Diaphragm moves up, ribs move in and down

Question 6

What sort of breathing occurs at rest and is it active?

Answer 6

At rest tidal volume ~0.5L; Inspiration is an active process whilst expiration is a passive process.

Question 7

What happens to the exhalation process during exercise?

Answer 7

Exhalation becomes active i.e internal intercostals and abdo muscles b/c you want to decrease insp and exp. time and inc RR

Question 8

What happens to pulmonary pressure during the respiratory cycle?

Answer 8

Inspiration: Pulm. pressure become negative as air is drawn in and returns to 0mmHg at the end of insp.

Expiration: Pulm. pressure becomes positive as air is forced out and returns to 0mmHg at end of exp.

Question 9

What happens to pleural pressure during the respiratory cycle?

Answer 9

Note pleural space is always negative relative to atmosphere; acts to adhere lungs to chest wall.

During inspiration pleural cavity space becomes MORE negative relative to atmosphere (as pleural volume increases) It is most negative at the end of inspiration.

During exhalation pleural cavity becomes less negative.

Question 10

What is an extrinsic problem that impacts the pleural space?

Answer 10

Pneumothorax;

• Thoracic puncture wound
• Collapsed lung
• Air rushes into chest
• Loss of negative pleural pressure

Question 11

What is an intrinsic problem that impacts the pleural space?

Answer 11

Atelectasis

• Insufficient air in the lung
• Obstruction in airway
• Surfactant deficiency (making the lung stiff)

Question 12

Why is a balloon in a conical flask a poor example of lung physiology?

Answer 12

The glass doesnt move i.e chest wall, so poorly models a negative pressure model

Question 13

What does a spirometer measure?

Answer 13

Lung volume

Question 14

How is minute ventilation calculated?

Answer 14

Vt (tidal volume) x Resp. Frequency

Question 15

What are some lung volumes measured in spirometry?

Answer 15

Tidal volume
Inspiratory reserve volume (IRV)

Inspiratory capacity = (IRV + TV)

Expiratory reserve volume
Residual volume

Functional residual capacity (ERV+RV)

Vital capacity = IRV+TV+ERV

TLC (IRV+TV+ERV+RV)

Question 16

Whats a method of measuring TLC?

Answer 16

C1 x V1 = C2 x V2

Using helium gas you can get the subject to breath in the helium from a known C1 and V1 until equilibrium is reached and then measure the new concentration (C2) and calculate the TLC of the lungs.

i.e Measuring the new concentration in the system and using C1, V1 and C2 to deduce V2.

Then you can subtract TLC (V2) with VC

Question 17

What happens to lung volumes with exercise?

Answer 17

Tidal volume increases reducing ERV and IRV

Question 18

What happens to oxygen consumption over time with exercise?

Answer 18

Tidal breathing has increased, over time in a constant cardio state the oxygen consumption falls to around 1.8L per unit time. I.e as the body switches energy metabolism and enters a steady state oxygen needs change…

Question 19

What is hyperventilation and hypoventilation?

Answer 19

Hyperventilation: >6L/min
Hypoventilation: <6L/min

Question 20

What is minute ventilation also equal to?

Answer 20

Ve = Va + Vd

Va (Alveolar ventilation)
Vd (Dead space ventilation) (~2.2mL/kg or 150mL)

Question 21

What is alveolar ventilation equal to?

Answer 21

Va = Vt - Vd (Dead space) x RR

Question 22

What is FEV1/FVC and what does it mean?

Answer 22

Tests lung health

FEV1 = Forced expiratory volume over 1s
FVC = Forced vital capacity (~5L), less during slow exh.

Healthy = ~80%

Question 23

What factors impact respiratory rate?

Answer 23

Size, age, exercise, body and environmental temperature, arousal state, pregnancy, degree of filling of digestive tract, lying or standing, health

Pregnancy and digestive tract filling influence diaphragm

Question 24

What is the resp-cardiac coupling?

Answer 24

Resp sinus arrhymia

Question 25

What other coupling is there of the resp. system?

Answer 25

Resp-locomotive coupling.