Introduction to the Respiratory System & Lung Mechanics

Question 1

What is the difference between internal and external respiration?

Answer 1

Internal respiration = gas exchange between blood and cells/interstitial fluids

External respiration = exchange of gases between blood and the external environment

Question 2

What X3 things are involved in external respiration?

I.e. what X3 things need to happen before we can get to the internal respiration stage?

Answer 2

1) pulmonary ventilation (breathing)
2) gaseous diffusion
3) transport of O2 and CO2

Question 3

What formulae (no name needed but provide letters for each component) links air flow, pressure gradient and resistance?

What does this formula imply for the relationship between:

1) flow and pressure?
2) flow and resistance?

Answer 3

Flow (Q) = pressure gradient (p1-p2) / resistance (R)

1) flow ∝ pressure
2) flow ∝ 1/resistance

Question 4

How would you exploit the flow, pressure, resistance formula to increase flow?

Answer 4

Either:

a) increase the pressure gradient
b) decrease the resistance

Question 5

What is the shorthand notation for atmospheric pressure?

Answer 5

PB

Question 6

What is the shorthand notation for pressure of air from the mouth/nose?

Answer 6

PM

Question 7

What is the shorthand notation for alveolar pressure?

What does that make the shorthand notation for arterial pressure?

Answer 7

Alveolar = PA

Arterial = Pa

NB: as the alveoli come BEFORE the arterial blood in the chain of gas exchange in breathing.

Question 8

What relationship needs to exist between PM and PB in order for inspiration to take place?

Answer 8

PM > PA

Question 9

What relationship needs to exist between Pm and Pb in order for expiration to take place?

Answer 9

PA > PM

Question 10

Explain Boyle’s law.

Answer 10

For a fixed number of gas molecules.

At a contestant temperature.

The pressure it exerts and the volume of the container it is occupying are inversely proportional.

P1V1 = P2V2.

Therefore P x V is always constant, and if one increases the other decreases.

Question 11

Why is boyle’s law relevant for breathing?

Answer 11

Breathing involves increasing the volume (thoracic cavity) which in turn decreases the alveolar pressure causing air to be entrained.

Question 12

Explain the types of recoil that exist in the chest at resting end expiration and the types of movement they are ‘wanting to do’.

Answer 12

Outward recoil exists = the chest wall wanting to ‘move outwards’

Inward recoil exists = the lungs wanting to ‘move in’

Question 13

What is the effect of the opposing recoils between the chest wall and lungs at resting end expiration?

Give values.

Answer 13

It creates a negative intra-pleural pressure (PPL) between the parietal and visceral pleura which at resting end expiration = -5cmH2O.

Question 14

What does -5cmH2O actually mean?

Answer 14

It means the pressure is -5cmH2O BELOW atmospheric pressure as respiratory pressures are expressed RELATIVE to PB.

Question 15

Name X4 obligate (always used) inspiratory muscles.

Answer 15

1) diaphragm
2) external intercostals
3) scalenes
4) parasternal intercostals

Question 16

Are there any obligate expiration muscles and why?

Answer 16

No, expiration (AT REST) is passive.

Question 17

How long is a normal respiratory cycle?

What is the breakdown of this in terms of time spent inhaling and exhaling; which is longer?

Answer 17

5 seconds.

3 spent inhaling (longer).

Question 18

What happens to pleural pressure (PPL) during X1 respiratory cycle?

Answer 18

It begins at a resting end expiration pressure of -5cmH2O.

It then decreases over the 3 seconds of inhalation to around -8cmH2O.

It then returns on exhalation to the resting end expiratory pressure of -5cmH2O.

Question 19

What is alveolar pressure at resting end expiration?

Answer 19

0cmH2O, the same as PB. That is why there is no air movement!

Question 20

What happens to alveolar pressure during X1 respiratory cycle?

Answer 20

It begins at 0cmH2O.

During inspiration it decreases to around -1cmH2O below the atmospheric pressure which allows air to flow in.

It then returns back to 0cmH2O as inspiration comes to an end.

During expiration, as the chest wall relaxes, it increases to around +1cmH2O which causes air to leave. It gradually returns back to 0cmH2O as expiration comes to an end.

Question 21

What is positive and negative flow (graphically) in terms of inhalation and expiration?

Answer 21

Positive deflections on flow graphs = flow outwards

Negative deflections on flow graphs = flow inwards

Question 22

What happens to air flow during X1 respiratory cycle?

Answer 22

Air flow starts at 0L/sec.

It increases (negative flow = inhalation) to -5L/sec and then back to zero over the course of inspiration.

It then does the same in reverse to +5L/sec and then back to zero over the course of expiration.

Question 23

What is the name of the volume of air in the lungs after passive expiration?

Answer 23

Functional residual capacity.

Question 24

What is the name of the group of pressure used to predict the movement of the lungs and is measured across different compartments of the chest?

Answer 24

Transmural pressures.

Question 25

What is the key rule in remembering how to calculate the transmural pressures?

Answer 25

It is ALWAYS the inside compartment minus the outside compartment.

Question 26

Which X3 pressures make up the transmural pressures? What are their shorthand notations? What are their formulas?

Answer 26

Trans chest wall (PW) = across the chest wall (between the pleural cavity and the atmosphere) = PPL (pleural) - PB Transpumonary (PL) = across the lungs (between alveoli and pleural cavity) = PA - PPL Trans total system (PRS) = across the whole system (between alveoli and atmosphere) = PA - PB

Question 27

Is the transpulmonary pressure (PL) always positive or negative?

Answer 27

Positive.

Question 28

What is transpulmonary pressure (PL) also known as? What happens when PL increases?

Answer 28

It is known as the ‘distending pressure’. As it increases it inflates the lungs.

Question 29

What is the relationship between PL and elastic lung recoil?

Answer 29

They are equal and opposite in value.

Question 30

What is a normal FRC volume?

Answer 30

3500ml

Question 31

What is a normal TLC volume?

Answer 31

7300ml

Question 32

What does IRV stand for, what does it mean and what is a normal volume?

Answer 32

Inspiratory reserve volume = the volume that can be inspired beyond a normal inhalation (tidal volume). Normal = 3300ml

Question 33

What does IC stand for, what does it mean and what is a normal volume?

Answer 33

Inspiratory capacity = the maximal amount that can be inspired including today volume. Therefore it is tidal volume (500) + IRV (3300) = 3800ml.

Question 34

What does ERV stand for, what does it mean and what is a normal volume?

Answer 34

Expiratory reserve volume = the volume that can be expired beyond a normal expiration. Normal = 1700ml.

Question 35

What does RV stand for, what does it mean and what is a normal volume?

Answer 35

Residual volume = the volume of air remaining in the lungs after maximal expiration. Normal = 1800ml.

Question 36

What is dead space? What is its shorthand notation?

Answer 36

The volume of conducting airway not involved in gas exchange. Dead space = Vd

Question 37

What are the X2 types of dead space and what do they include? What is a normal value for the first kind of dead space?

Answer 37

Anatomic = all of the airway except alveoli and respiratory bronchioles. = usually around 150ml. Physiologic = anatomical dead space + areas where gas exchange should take place but is dysfunctional.

Question 38

What is the normal ratio of anatomic Vd to physiological Vd?

Answer 38

Normally equal in health.

Question 39

What is minute ventilation and how is it calculated?

Answer 39

Minute ventilation = volume of air moved into OR out of the lungs in a minute. Tidal volume = 500ml RR = 15/min 500 x 15 = 7500ml/min

Question 40

How can we calculate alveolar ventilation?

Answer 40

Alveolar ventilation = minute ventilation - dead space ventilation. Minute ventilation = 7500 Anatomic dead space = 150ml RR = 15/min 150 x 15 = 2250ml/min 7500 - 2250 = 5250ml/min = alveolar ventilation.

Question 41

What can we note about normal alveolar ventilation and pulmonary perfusion?

Answer 41

Alveolar ventilation (V) = 5250ml/min Pulmonary blood flow (perfusion) (Q) = SV x HR SV = 70ml HR = 70bpm 70 x 70 = 4900ml/min Therefore V and Q are matched in health! The V/Q ratio = 1!

Question 42

Which X2 resistances must we overcome in order to inhale? NB: these are both areas which will change in disease states so think about it in that respect.

Answer 42

1) the elastic resistance of the lung | 2) the airway resistance to airflow (usually in expiration)

Question 43

What is the technical term for lung elastic resistance/stiffness?

Answer 43

Compliance.

Question 44

What formula denotes lung compliance?

Answer 44

Compliance = change in lung volume (V) / change in transpulmonary pressure (PL) Therefore high compliance means large changes in lung volume for small changes in transpulmonary pressure.

Question 45

Which pressure increases and turns positive in forced expiration?

Answer 45

Pleural pressure (PPL)

Question 46

What class of drugs cause bronchoconstriction and what receptors do they act on?

Answer 46

Cholinergic agonists acting on M3 receptors.

Question 47

Explain how dynamic compression of the airways works?

Answer 47

During forced expiration, the intrapleural (PPL) pressure is made positive and rises above the pressure in the airways. This forces them shut and blocks air exiting.