Generating pressure gradients - Respiratory Cycle

Question 1

What is the relationship between pressure, flow and resistance?

Answer 1

Flow = pressure / resistance

Flow requires a pressure gradient large enough to overcome any resistance that slows the flow down

Question 2

At rest what is the relationship between PA (alveola pressure)and PB (Barometric pressure)?

Answer 2

PA = PB so no air flow

Question 3

During Inspiration what is the relationship between PA and PB?

Answer 3

PA < PB so air flows in

Question 4

During Expiration what is the relationship between PA and PB?

Answer 4

PA > PB so air flows out

Question 5

What is FRC?

Answer 5

Functional Residual capacity - the air volume within the lungs before inspiration (2.5L)

Question 6

At what point do we have the fastest flow during inspiration / expiration?

Answer 6

The point at which we are halfway through inspiration/ expiration we have the greatest pressure gradient and thus the air flow is fastest at this point.

Question 7

During resting breathing, which muscles are working the breathing mechanism?

Answer 7

Only the diaphragm will be involved during quiet breathing where the muscle moves approximately 1cm.

Question 8

What are the muscles used for inspiration?

Answer 8

External intercostal muscles - move ribcage up and out

Scalene - lifts the top few ribs up

Sternocleidomastoid

Question 9

What muscles are used in expiration?

Answer 9

Internal intercostal muscles - pull the ribcage down and in

Abdominal muscles - push against the diaphragm to reduce the size of the thoracic cavity

Question 10

How is resting expiration passive?

Answer 10

The muscles used in inspiration simply recoil without recruiting the expiration muscles

Question 11

How is the FRC produced/maintained

Answer 11

Lungs will collapse to small equilibrium volume and the chest wall will expand to a large equilibrium volume. Therefore when the volumes are equal and opposite, recoil sets the FRC

Question 12

What is the equilibrium volume?

Answer 12

Volume of the structure with no external influences.

Question 13

What is the Visceral pleura?

Answer 13

Membrane around the outside of the lungs

Question 14

What is the parietal Pleura?

Answer 14

Membrane that is lining the chest wall.

Question 15

What is the Pleural Fluid?

Answer 15

a small volume of blood filtrate that lies between the 2 pleural membranes

Question 16

What are the functions of the pleural membranes and fluid?

Answer 16

create a low friction environment meaning that less energy is required for breathing to occur.

Question 17

What is the main role of the Pleural Fluid?

Answer 17

Keeps the lungs and chest wall close together (coupled). also provides a low friction environment for easy breathing.

Question 18

How does the Pleural fluid couple the lungs and the chest wall together?

Answer 18

Lungs equilibrium volume is small
at FRC lungs are stretched away from the equilibrium volume (outwards)
this generates an inward elastic recoil pressure

Chest wall equilibrium volume is large
at FRC the chest wall compressed away from the equilibrium volume (inwards)
this generates an outward elastic recoil pressure

Question 19

How is the intrapleural pressure generated?

Answer 19

By increasing the volume of the intrapleural space and the fluid causes the pressure to fail due to the lung and chest wall elastic recoil.

The intrapleural pressure is more negative than the recoil pressures of the lungs and chest wall (sub atmospheric) meaning that the two structures are pulled together.

Question 20

What are the absolute pressures for the barometric and intrapleural pressure?

Answer 20

PB = 100kPa
Pl = 99.5kPa

Intrapleural pressure is 0.5 kPa lower than the barometric pressure.

Question 21

How do we calculate the distending pressure?

Answer 21

P(dist) = P(aleveolar) - P(intrapleural)

Question 22

How do we inflate the lungs?

Answer 22

Inflation requires a positive distending pressure where the Pressure in the lungs is greater than the pressure out

Question 23

What is the distending pressure at FRC?

Answer 23

P(dist) = 0 - -o.5

therefore there is a positive distending pressure of 0.5kPa at FRC so they are slightly inflated at FRC.

Question 24

Explain how we carry out inspiration

Answer 24

1. inspiratory muscles contract increasing thoracic cavity volume
2. intrapleural pressure becomes more negative
3. Lung distending pressure increases
   Pdist = 0 – -1 = +1kPa
4. lungs inflate
5. increase in lung volume causes PA to fall below PB
6. air flows into the lungs until PA = PB at end inspiration

(in quiet breathing then expiration is simply the reverse of this)

Question 25

What is the conducting zone and what does it do?

Answer 25

Respiratory passages that carry air to the site of gas exchange.
Filters, humidifies and warms air.

Question 26

What is the respiratory zone and what is it composed of?

Answer 26

Site of gas exchange
Composed of:
Respiratory bronchioles
alveolar ducts
alveolar sacs

Question 27

What is minute ventilation?

Answer 27

Total air that flows in and out of respiratory system in a minute.

Question 28

How can minute ventilation be calculated?

Answer 28

Tidal volume x respiration rate

Question 29

What is alveolar ventilation?

Answer 29

a measure of the volume of fresh air that reaches the alveoli each minute

Question 30

How can the alveolar ventilation be calculated?

Answer 30

Minute volume - the anatomical dead space (the combined volume of the non-exchanging airways)