Lung volumes, Dead space and pulmonary pressures

Question 1

What is Internal Respiration?

Answer 1

Exchange of gases between blood, interstitial fluid and cells.

Question 2

What is External Respiration?

Answer 2

Exchange of gases (O2&C02) between blood and external environment.

Question 3

What does External respiration involve?

Answer 3

Pulmonary ventilation, Gaseous diffusion, Transport of oxygen & Carbon dioxide.

Question 4

What are the major functions of the respiratory tract?

Answer 4

• Gas exchange
• Air filter
• Blood filter
• Reservoir of blood
• Metabolic functions, E.g. surfactant production; biological activation: angiotensin converting enzyme (these monitor and regulate NA and water in the kidneys to maintain blood PA (unneeded extra info)).
  Also, Inactivation e.g. arachidonic acid metabolites.

Question 5

This Q is about the organisation of the respiratory tract, Which area is classed as the: Upper respiratory tract??

Answer 5

The area above the vocal cords

Question 6

Which area is classed as the lower respiratory tract

Answer 6

Below the vocal chords.

Question 7

What is the role of the conducting zone, of the respiratory tract.

Answer 7

To bring air down in bulk flow

Question 8

The respiratory tract/ bronchiole tree is divided also by function. What are the 2 divisions in terms of function.

Answer 8

• Conducting zone

- Respiratory zone

Question 9

What is the role of the Respiratory zone of the respiratory tract.

Answer 9

Gas exchange, putting O2 into the blood and taking CO2 in the opposite direction.

Question 10

What is the pathway of gaseous exchange, including details of all the structures.

Answer 10

1. Begins with, deoxygenated blood coming from the venous circulation, up to the right side of the heart (Right atrium &ventricle)
2. Then through the pulmonary artery which divides into pulmonary arterioles, carrying deoxygenated blood, which arrives at the capillary network.
3. Then at the respiratory zone where the capillaries are in close association with the alveolus. Here they pick up O2 and put CO2 back into the alveolus.
4. Then these join to become pulmonary venules, which go back down to the left side of the heart via the Pulmonary vein.

Question 11

How many alveoli are present in a human lung. and what is their diameter?

Answer 11

• 500million.

- 1/3mm in diameter.

Question 12

What is pulmonary ventilation?

Answer 12

The physical movement of air into and out of the lungs.

The movement of air requires generation of a pressure gradient along the airways.

Question 13

In inspiration how do we generate a more (-) alveolar PA, to create a pressure gradient?

Answer 13

This is done by:
The Chest wall and lung are elastic structures. The chest wall naturally wants to spring outwards at end of expiration which is helpful, but the lungs want to spring inwards, not very helpful for inspiration. when these 2 forces are equal and opposite in magnitude that’s the resting volume of the lungs at end expiration. This creates a (-)interpleural PA, more (-) than atmospheric PA. This pulls the lung outwards preventing it from collapsing in on its self. Thus increasing the volume of the lung which decreases the Alveolar PA due to Boyles law (Pressure x Volume), This draws air in from the atmosphere into the lung.

Also this is an active process and requires the work of respiratory muscles mainly the diaphragm which is pulls down, pulling the chest wall outwards, with help from intercostal muscles, there are also others such as the sternocleidomastoid

Question 14

For expiration you need to generate a more +PA in the alveoli how is this achieved?

Answer 14

This is a passive process done by “switching off” your inspiratory muscles, as the natural springy recoil of the lungs is inwards, so once you stop pulling it outwards it will recoil inwards, reducing the volume thus, increasing the alveolar PA above atmospheric PA, and air moves passively out of the lungs.

Question 15

What are some of the mechanisms for Pulmonary ventilation?
sub headings;
-Functional anatomy
-pre-inspiration
-inspiration 
-expiration

Answer 15

Functional anatomy;
-Ribcage hinged to vertebral column which can be lowered, expanded (insp) & compressed (exp).
Pre-inspiration;
-The alveolar & atmospheric PA are =.
Inspiration;
active due to use of inspiratory muscles.
Expiration
-passive at rest.
-active via use of expiratory muscles when ventilatory demands increase.

Question 16

What are Obligate inspiratory muscles?

Answer 16

Inspiratory muscles that are always active even during quiet resting breathing.

Question 17

List all the Obligate inspiratory muscles and their functions.

Answer 17

• Diaphragm; responsible for 70% of minute ventilation at rest so is the main inspiratory muscle.
• External intercostal muscles (in the ribcage)
• Scalenes (deep neck muscles) they help lift the ribcage
• Parasternal intercostal muscles (prevent chest wall from collapsing inwards during inspiration)

Question 18

What are accessory inspiratory muscles and list some examples.

Answer 18

These are called upon when you need to increase ventilation above resting ventilation, e.g. COPD patients or anyone during exercise.
e.g. Neck muscles such as sternocleidomastoids.

Question 19

List all the Expiratory muscles.

Answer 19

• Internal intercostals
• Rectus abdominis (Abs)
• External oblique
• Internal oblique
• Transversus abdominis

(May also recruit chest wall and limb girdle muscles).

Used for forced expiration e.g. coughing, or exercise.

Question 20

Which pressure changes and muscles are involved in the respiratory process?

Answer 20

Intrapleural pressure (Ppl)
- (-)Ppl below PB (Barometric/ atmospheric PA) during inspiration, to oppose elastic recoil of the lung. (preventing lungs collapsing in on them selves)

Alveolar pressure (PA)
- Air flows into the lungs when PA becomes lower than PB.

Transpulmonary pressure (PL) 
- "Lung distending pressure" = the pressure difference between Ppl and PA, i.e. pressure across the lung wall. The work of breathing/ inspiratory difficulty increases when PL is high. (Patients will know this as they'll find that breathing is requiring more effort).

Inspiratory muscles
- Contraction increases the dimensions of the thoracic cavity, thus reducing Ppl & PA & increasing PL. Under autonomic (brainstem) and voluntary (cortical) control.

Question 21

Describe the steps of the expiratory process. (Include forced expiration as well)

Answer 21

• Passive at rest
• Inspiratory muscles relax
• Intrapleural pressure becomes less negative, so……
• …transpulmonary pressure (PL) decreases
• Stretched lung & its alveoli deflate (lung elastic recoil inwards)
• Alveolar pressure (PA) > mouth pressure (Pm)
• Air flows from lung to mouth until PA = PB
• During forced expiration, expiratory muscles are additionally activated
• Intrapleural pressure may be positive in these circumstances
• Lung elastic recoil acts in series with positive Ppl to further increase PA&raquo_space;> Pm

Question 22

What is Pneumothorax?

Answer 22

After e.g. chest wall puncture, the air is sucked in until Ppl is = PB which causes the lung to collapse as its elastic recoil inwards is no longer opposed.

In addition, the chest wall expands to its resting state as its outwardly directed recoil is also un opposed.

Question 23

Define the following terms:

• Respiratory cycle

- Tidal volume + what is the normal average VT?

Answer 23

Single cycle of inhalation and exhalation.

The amount of air moved in 1 cycle.
usually 500ml

Question 24

What are the 3 measurements that cannot be measured directly by spirometry? and what are they measurements of?

Answer 24

Total lung capacity/ TLC: is what it says on the tin.

Functional residual capacity (FRC) the volume of air left in your lungs after quiet/normal resting expiration.

Residual volume (RV): The amount of air left in the lungs after a forced expiration.

Question 25

What measurements can be recorded via spirometry and what are they measurements of?

Answer 25

Tidal Volume (VT): the amount of air moved in 1 cycle.

Vital Capacity (VC): The greatest volume of air that can be expelled from the lugs after taking the deepest possible breath.

Inspiratory reserve volume (IRV): The maximal amount of additional air that can be drawn into the lungs after normal inspiration.

Expiratory reserve volume (ERV): The maximal amount of additional air that can be drawn out of the lungs after normal expiration.

Inspiratory capacity (IC):
The maximum volume of air that can be inhaled by the patient without a forced exhalation beforehand

Question 26

Define dead space (VD).

Answer 26

Airway volume with no gas exchange

Question 27

Define anatomical dead space.

Answer 27

all dead space except alveoli & respiratory bronchioles, usually 150ml = volume of your conducting zone

Question 28

Define Physiological dead space.

Answer 28

Anatomical dead space + alveolar dead space (area where gas exchange dysfunctional)
So if you’re diseased and have more areas of dysfunctional gas exchange then your physiological dead space will increase.

Question 29

How do you calculate total minute volume?

Answer 29

VT (usually 500ml) x Respiratory rate (usually 15)

Question 30

How do you calculate alveolar ventilation?

Answer 30

VT- anatomic dead space x respiratory rate

Question 31

Just a little reminder

Answer 31

That the alveolar ventilation is roughly 5.2litres per min, with pulmonary blood flow around 5litres per min. these need to be similar as you may expect as that’s where gas exchange takes place.