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GSSE pshysiology > Respiartory physiology > Flashcards

Respiartory physiology Flashcards

1
Q

What are the normal spirometry values expected for a 70 kg adult male?

A

(a) Inspiratory reserve volume (IRV)
(b) Expiratory reserve volume (ERV)
(c) Tidal volume (TV)
IRV 3500 mL
ERV 1000 mL
TV 500 mL

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2
Q

What is the functional residual capacity (FRC) of the lung?

A

FRC is the volume left in the lung at the end of quiet expiration. It is equal to the
expiratory reserve volume plus the residual volume. It represents the volume at which
the want of the chest wall to spring out matches the want of the lung to recoil inwards.

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3
Q

What is anatomical dead space? How can it be measured?

A

Volume of gas in the conducting airways that does not take part in gas
exchange; ~150 mL. Measured using Fowler’s method.

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4
Q

What is physiological dead space? How can it be measured?

A

This is the volume of lung that is not cleared of CO2. Made up of the anatomical
dead space plus the poorly perfused alveoli where there is ventilation without gas
exchange (alveolar dead space). Measured using Bohr’s method.
In health there is little difference between the anatomical dead space and the
physiological dead space. However, in disease states the physiological dead
space may be considerably larger than anatomical dead space.

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5
Q

Functional residual capacity (FRC) can be altered by different disease states;

A

name three conditions where FRC is increased?
FRC is the lung volume at the end of quiet expiration (end of tidal volume). This
can be increased by emphysema, positive pressure ventilation as well as going
from supine position to standing.

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6
Q

A patient’s PACO2 rises from 40 mmHg to 80 mmHg. What has happened to their
alveolar ventilation?

A

It has halved. This is because alveolar ventilation and PACO2 are inversely
proportional.

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7
Q

What three lung volume values can not be measured with spirometry?

A

Residual volume, functional residual capacity and total lung capacity.
The residual volume can not be measured with spirometry. This means that both the functional
residual capacity and the total lung capacity can not be measured with spirometry
as these capacities contain the residual volume in their measurement.

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8
Q

Why does CO2 diffuse more quickly than O2?

A

This is because CO2 is 20 times more soluble than O2, and therefore has a higher
diffusion constant. Diffusion constant ∝ solubility/square root of molecular weight.

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9
Q

A patient is admitted with shortness of breath due to severe pulmonary fibrosis.
In pulmonary fibrosis, which component of Fick’s law is altered?

A

The blood-gas thickness is increased in pulmonary fibrosis. As diffusion is
inversely proportional to thickness, diffusion is slower

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10
Q

Give an example of a gas that is diffusion limited?

A

Carbon Monoxide. As CO rapidly binds with haemoglobin, the partial pressure
of CO in the blood is close to zero, therefore the rate of transfer of CO from the
alveolar space into the blood is determined by the partial pressure of alveolar CO
and the diffusion capacity of the lung for CO (which is ~80% to that of O2 and
~4% to that of CO2). Therefore the rate of the transfer of CO from the alveoli into
the blood, for a given lung, is principally determined by the alveolar partial pressure of CO and hence the transfer is diffusion limited.

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11
Q

Give an example of a gas that is perfusion limited?

A

Nitrous oxide. Nitrous oxide rapidly diffuses and is NOT bound by any proteins,
resulting in a quick rise in the partial pressure. Therefore equilibrium between
the alveoli and capillary is quickly reached, preventing further diffusion, before
blood reaches the end of the capillary.

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12
Q

Under normal conditions, how long does it take for equilibrium to be established
between partial pressure of oxygen in the alveoli and the capillaries?

A

0.25 s. This is a third of the normal transit time of blood in the capillaries.

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13
Q

what is ficks law ?

A

states that diffusion is proportional to tissue surface area and the difference in partial pressure, and inversely
proportional to tissue thickness
• It also takes into account the ‘diffusion constant’ which is proportional to gas
solubility, and inversely proportional to the square of the gas molecular
weight (MW)

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14
Q

what does carbon monoxide rapidly bind to in the blood?

A

Hb

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15
Q

what does nitric oxide bind to in the bloodstream ?

A

nothing

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16
Q

What are the two mechanisms whereby pulmonary vascular resistance can be
deceased?

A

Recruitment and distension of capillaries

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17
Q

Describe the changes in lung resistance at different lung volumes?

A

At low lung volumes there is high resistance because of loss of radial traction of
the extra-alveolar vessels.
At high lung volumes there is an increase in resistance, as the alveolar pressure
exceeds the capillary pressure and therefore squeezes the capillaries shut preventing
blood flow.
At lung volumes close to FRC, the vascular resistance is near its lowest
with neither of the aforementioned mechanisms having significant effect

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18
Q

Why is pulmonary vascular resistance increased when there is hypoxia?

A

This is due to hypoxic pulmonary vasoconstriction. This mechanism tries to
divert blood from the poorly ventilated areas to areas of the lung with better
ventilation. The underlying mechanism is unknown, but it is thought to be
involved with nitric oxide (NO).

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19
Q

in Wests Zone of of the lung 1 is arterial or alveolar pressure higher?

A

pulmonary arterial pressure falls below alveolar pressure
• This squashes the capillaries and no blood flow occurs
• Does not occur normally, but may with haemorrhage or hypotension.
• This adds to alveolar dead space as ventilated but not perfused.

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20
Q

in Wests mid zone 2 in the lung what determines blood flow to this area?

A

Blood flow is determined by arterial-alveolar difference

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21
Q

which is higher in zone 3 of the lung?

A

the vascular pressure outweighs the alveolar pressure

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22
Q

. Except for gas exchange, what are some other functions of the lung?

A

(a) Metabolism
(b) Blood filter
(c) Reservoir for blood
(d) Vocalisation
(e) Conversion of angiotensin I to angiotensin II

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23
Q

what result does hypoxia have on the lungs resistance?

A

Hypoxia causes increased vascular resistance, due to the reflex to shunt blood
away from hypoxic alveoli, (mainly if the partial pressure of oxygen is less than
70 mmHg), thus increasing the resistance in the blood vessels leading to the
hypoxic area

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24
Q

low blood pH will cause what to the vessels of the lungs?

A

vasoconstriction

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25
Q

What are the different percentages of nitrogen, oxygen and carbon dioxide in the
atmosphere?

A

Nitrogen = 78%
Oxygen = 21%
Carbon dioxide = 0.04%

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26
Q

Name five causes of hypoxia.

A

(a) Decreased FiO2
(b) Hypoventilation
(c) Diffusion abnormality
(d) Shunt
(e) Ventilation-perfusion ( V Q / ) mismatch

27
Q

If a patient hypoventilates, what direction will their CO2 move?

A

It will increase. Ventilation is inversely proportional to the amount of CO2 in the
blood. If ventilation halves, then the CO2 will double.

28
Q

Define a shunt.

A

This is blood that exits the right ventricle then exits the left ventricle without
undergoing gas exchange.

29
Q

Is a shunt always pathological?

A

No. This is because in health, there is a small shunt from the bronchial circulation that does not pass through the ventilated lung tissue. Furthermore, the thebesian veins that drain directly into the left side of the heart contribute to the
physiological shunt.

30
Q

Which of the five causes of hypoxia can not be corrected by oxygen therapy?

A

Shunt.

31
Q

Is the PAO2 higher at the top or bottom of the lung?

A

The Top. This is because there is proportionally higher ventilation but poorer
perfusion, meaning less oxygen diffuses from the alveoli into the blood stream,
resulting in a higher PAO2.

32
Q

what is the pA02 of alveolar gas?

A

(PAO2) is about 100 mmHg

33
Q

the ventilation perfusion ratio is what at the top and bottom of the lung?

A

ventilation/perfusion ratio is high at the top and low at the bottom
Ventilation is still less at the top, but perfusion is even less

34
Q

What are the two ways that oxygen can be carried in blood?

A

Dissolved and bound to haemoglobin.

35
Q

What globin chains make up adult haemoglobin?

A

Two alpha and two beta. Known as haemoglobin A.

36
Q

What form of iron is found in haemoglobin?

A

It’s ferrous form, Fe2+. If it is Fe3+ then it is called methaemoglobinaemia.

37
Q

In venous blood what proportion of carbon dioxide is found,

  1. Dissolved
  2. Bound to Hb as carbaminoHb and
  3. Bicarbonate?
A
  1. Dissolved
  2. Bound to Hb as carbaminoHb and
  3. Bicarbonate?

(1) 10%, (2) 30%, (3) 60%

38
Q

In arterial blood what proportion of carbon dioxide is found (1) Dissolved (2)
Bound to Hb as carbaminoHb and (3) Bicarbonate?

A

(1) 5%, (2) 5%, (3) 90%.

39
Q

Explain the Haldane effect.

A

This explains the effect of oxygen on carbon dioxide carriage in the blood. In the
peripheries the deoxygenated haemoglobin is able to carry more carbon dioxide.
Conversely in the lungs, the loading of oxygen on haemoglobin assists the
unloading of carbon dioxide.

40
Q

Does the lung or the kidney have a greater ability to excrete acid?

A

The lung. 100 times greater, this is done by altering the ventilation and therefore
altering the PaCO2.

41
Q

What is the main muscle of respiration? What direction does it move in inspiration?

A

Diaphragm; downwards- 1 cm in quiet respiration but up to 10 cm in deep inspiration.

42
Q

Name the accessory muscles of inspiration?

A

Scalenes and sternocleidomastoid muscles.

43
Q

What are the muscles of expiration?

A

Expiration is largely a passive phenomenon due to the elastic recoil of the lungs.
However the abdominal wall muscles and internal intercostal muscles can aid
active expiration.

44
Q

What effect does age have on airway closure volumes?

A

As age increases, the volume at which the airways closes increases (e.g. gets
closer to FRC).

45
Q

Define compliance of the lung.

A

This is the volume change per unit pressure change; equates to the slope of the
pressure volume curve

46
Q

Name two conditions that decrease lung compliance?

A

(a) Pulmonary surfactant deficiency/dysfunction
(b) Pulmonary fibrosis
(c) Alveolar oedema
(d) Atelectasis
(e) Increased venous pressure

47
Q

Name two conditions that increase the lung compliance?

A

(a) Emphysema

(b) Age

48
Q

Describe the mechanism by which a pulmonary embolism decreases the surfactant production.

A

Surfactant is produced by type 2 pneumocytes in the lungs. It is a mixture of ~95%
phospholipid and 5% protein. DPPC (dipalmitoylphosphatidylcholine) is the most
abundant phospholipid. This is produced from fatty acids, which are extracted
from the lungs blood circulation. The turnover of surfactant is rapid, hence will be
quickly depleted in the setting of decreased blood supply (e.g. a PE).

49
Q

What role does surfactant play?

A

(a) Decreases the surface tension in the alveoli hence decreases the work of
breathing
(b) Increases the stability of the alveoli
(c) Prevents transudation of fluid

50
Q

How does surfactant work?

A

Surfactant phospholipids have hydrophobic tails and hydrophilic heads. This
makes them energetically favour the surface environment in polar solvents (e.g.
water). As the intermolecular attraction of phospholipids is much lower than
that of water, by displacing water at the surface, the surface tension is lowered
~1/5 that of plasma.

51
Q

In an asthmatic, bronchoconstriction halves the radius of the bronchioles. If the
flow is laminar, how much is the resistance to flow increased by?

A

16 times. Resistance is inversely proportional to r4

.

52
Q

What two factors are proportional to resistance to laminar flow?

A

Viscosity of the fluid and length of the tube.

53
Q

In turbulent flow, is it viscosity or density that is more important to the resistance of flow?

A

Density.

54
Q

. What equation can be used to predict if flow is going to be turbulent or
laminar?

A

Reynolds number.
Reynolds number is low in the terminal bronchioles but higher in the trachea,
especially during exercise.

55
Q

apart from the diaphragm which muscles aim in inspiration?

A

External intercostal muscles play a much smaller role in changing the anteriorposterior diameter

56
Q

Surface tension plays an important role in lung compliance, does it increase or decrease lung compliance?

A

(reduces compliance as it hold surfaces together).
– Surfactant significantly lowers the surface tension and stabilises the alveoli
(especially at small volumes) and keeps them dry
– Produced by type 2 pneumocytes

57
Q

the intrapleural pressure is more or less negative at the base and apex of the lung

A

apex intrapleural pressure is lowest (most negative) - 4.0

base less nagative or positive -2.5 to +3.5

58
Q

Which sensors are the most important for minute to minute control of ventilation?

A

The chemoreceptors near the ventral surface of the medulla in the vicinity of the
9th and 10th cranial nerve site of exit.

59
Q

where are the 1: peripheral and 2. central chemoreceptors located?

A

Peripheral chemoreceptors are located in both the carotid body and the aortic body.
Central chemoreceptors are located in the medulla oblongata of the brainstem.

60
Q

what do the periheral and central chemoreceptor respectively detect?

A

Peripheral chemoreceptors : They detect large changes in the partial pressure of oxygen (pO2) as the arterial blood supply leaves the heart.
Central chemoreceptors : They detect changes in the arterial partial pressure of carbon dioxide (pCO2).

61
Q

when the peripaheral chemoreceptors detect low levels of oxygen what is the response?

A

The respiratory rate and tidal volume are increased to allow more oxygen to enter the lungs and subsequently diffuse into the blood
Blood flow is directed towards the kidneys and the brain (as these organs are the most sensitive to hypoxia)
Cardiac Output is increased to maintain blood flow, and therefore oxygen supply to the body’s tissues

62
Q

biggest drive for ventilation in COPD patietns with co2 retention?

A

arterial hypoxaemia

63
Q

what receptors are located in the airway smooth muscle?

A

pulmonary stretch receptors

64
Q

irritant receptors in the brinchi lie between the epithelial cells and impulses travel via the vagus nerve , what response is happens when triggered?

A

bronchoconstriction adn hyperpnea

GSSE pshysiology (5 decks)

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