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Respiratory System > Ventilation and Compliance > Flashcards

Ventilation and Compliance Flashcards

1
Q

What is surfactant?

A

Produced by type II alveolar cells and reduces surface tension by disrupting cohesive forces between water molecules and therefore reducing tendency for alveoli to collapse

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2
Q

How is surface tension created?

A

By thin fluid between alveolar cells and air increasing stretch resistance, making breathing more difficult

Arises due to H bonds between water molecules

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3
Q

Explain the Law of LaPlace

A

The surface tension is directed toward the centre - law states that pressure inside a bubble is due to SURFACE TENSION (T) and RADIUS (r)

P = 2T/r

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4
Q

What is the relationship between the size of the bubble and surfactant effect?

A

IF two bubbles have different diameters but same surface tension:

The pressure inside the smaller one is GREATER and INCREASED resistance to stretch

If alveoli did not have surfactant and ST was equal in all alveoli - pressure would equalise by air flowing into the larger alveoli

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5
Q

What are the effects of surfactant?

A

Reduces surface tension and thus tendency for alveoli to collapse
Increases lung compliance
Reduces lung tendency to recoil
Makes work of breathing easier

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6
Q

What can premature babies suffer due to inadequate amount of surfactant?

A

Infant Respiratory Distress Syndome (IRDS)

Surfactant produced ~25weeks, so premature babies requires a lot of energy to breathe

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7
Q

What is the effect of saline in the lungs?

A

Less intrapleural pressure required to inflate lungs as it does not need to overcome surface tension as no air-water interface

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8
Q

What are the normal alveolar PO2 and PCO2 levels?

A

PO2 - 13.5kPa (100mmHg)

PCO2 - 5.3 kPa (40mmHg)

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9
Q

What happens in hyperventilation?

A

Increased alveolar ventilation causing ALKALOSIS

PO2 increase to 120mmHg
PCO2 falls to 20mmHg

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10
Q

What happens in hypoventilation?

A

Decreased alveolar ventilation causing ACIDOSIS

PO2 falls to 30mmHg
PCO2 increased to 100mmHg

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11
Q

Pulmonary vs alveolar ventilation

A

Pul - total air getting to lung
Alv - fresh air getting to alveoli and available for gas exchange

(L/min)

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12
Q

What is compliance?

A

Change in volume relative to the change in intrapleural/alveolar pressure

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13
Q

Why is greater change in pressure required during inspiration than expiration?

A

To overcome tissue inertia (initial ST) to allow compliance

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14
Q

Why does ventilation and compliance decrease from base to apex?

A

At rest, capillaries are closed at the apex due to low hydrostatic pressure, whereas they’re open at the base due to high hydro. pressure

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15
Q

What would happen to the FEV1/FVC ratio in obstructive disease?

A

Decrease - as airflow obstructed so cant expire as fast

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16
Q

What would happen to the FEV1/FVC ration in restrictive disease?

A

No change - as air flow not obstructed but cant take in as much air

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17
Q

What is Tidal Volume (TV) and its value?

A

Vol. of air breathed in and out at each breath

500mlmL

18
Q

What is Expiratory Reserve Volume (ERV) and its value?

A

Max. air that can be expelled at the end of normal expiration
1100mL

19
Q

What Is Inspiratory Reserve Volume (IRV) and its value?

A

Max. air that can be drawn into the lungs at the end of normal inspiration
3000mL

20
Q

What is the residual volume (RV) and its value?

A

Vol. of gas in lungs at end of maximal expiration

1200mL

21
Q

What is the vital capacity (VC) and its value?

A

Tidal volume + IRV + ERV

4600mL

22
Q

What is the Total Lung Capacity (TLC) and its value?

A

Vital capacity + residual volume

5800mL

23
Q

What is inspiratory capacity (IC) and its value?

A

TV + IRV

3500mL

24
Q

What is Functional Residual capacity and its value?

A

RV + ERV

2300mL

25
Q

What is FEV1:FVC?

A

Fraction of forced vital capacity expired in 1 sec

26
Q

How do you work out the total pulmonary ventilation from tidal volume and respiratory rate?

A

TV (mL) X RR = Total Pulmonary vent. (ml/min)

27
Q

What is partial pressure?

A

The pressure of a gas in a mixture

28
Q

How do you work out the partial pressure of a gas?

A

% of gas in mixture X pressure of entire gas mixture

29
Q

Why is surfactant more effective in smaller alveoli and why is this important?

A

Surfactant more concentrated in smaller alveoli, making their surface tension less than larger alveoli

Lower surface tension helps equalise the pressure among different sizes and makes it easier to inflate the smaller alveoli

30
Q

When does surfactant begin production in the foetus?

A

25 weeks gestation and complete by 36 weeks

31
Q

What causes infant respiratory distress syndrome (IRDS)?

A

Premature babies have inadequate surfactant conc. in alveoli which causing low-compliant (stiff) lungs and alveoli that collapse on expiration

32
Q

What does high compliance indicate?

A

Large increase in lung volume for small decrease in ip pressure

Beneficial only if you have high recoil as well

33
Q

What does low compliance indicate?

A

Small increase in lung volume for large decrease in ip pressure

34
Q

What is the effect of work of respiration in emphysema?

A

Loss of elastic and thus decreased recoil, so higher compliance (easy to fill lungs) but requires more work to expire

35
Q

What in the effect of fibrosis on work of respiration?

A

Inert fibrous tissue means effort of inspiration increases (less compliance)

36
Q

At any given transpulmonary pressure, which part of the lung produces a greater change in volume?

A

The base as it is more compliant than the apex

37
Q

Why does compliance decrease from the base to the apex?

A

Due to alveoli at the apex being more inflated at FRC
At the base, the alveoli are compressed between the weight of the lung above and the diaphragm below and hence more compliant on inspiration

38
Q

Why doe FEV1:FVC not decrease in restrictive diseases and give examples?

A

Loss of lung compliance due to lung stiffness and incomplete lung expansion

Fibrosis
IRDS
Oedema
Pneumothorax

39
Q

What is an investigation that can measure lung function?

A

Spirometry

40
Q

Can residual volume be measured with spirometry?

A

No

41
Q

What is the percentage of FEV1/FVC in someone with normal lung function?

A

80%

42
Q

Why is spirometry not always indicative of health?

A

As obstructive it will decrease, but can remain constant in restrictive diseases

Respiratory System (29 decks)

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