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Supply & Demand > Respiratory physiology > Flashcards

Respiratory physiology Flashcards

1
Q

What are the two subsystems of the mammalian respiratory system?

A

External respiratory system: lungs and the pulmonary circulation
internal respiratory system consisting of the tissue cells

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2
Q

What is really important for effective gas exchange?

A

Ventilation and perfusion must be matched

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3
Q

In terms of ventilation what is highly variable and what remains fairly constant?

A

rate of ventilation and tidal volume are highly variable between healthy individuals

  • Adult males: 10-18 breaths per min and tidal volumes of 350-900 ml
  • Adult females: 10-18 breaths per min and tidal volumes of 200-650 ml

Rate of oxygen uptake at rest is relatively constant
Adult males: 240ml/min
Adult females: 200ml/min

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4
Q

What does it mean by anatomical dead space?

A

Not all of the air inspired during relaxed ventilation reaches the respiring airways - remainder says in the mouth, pharynx and large conducting airways

Dead space ventilation = dead space volume X ventilation frequency - therefore dead space ventilation increases as breathing gets faster

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5
Q

What is the physiological importance of dead-space?

A

sum of the anatomical dead space and the alveolar dead space

alveolar dead space= unperfused alveoli and a proportion that are only partially perfused

defined as “part of tidal volume that does not participate in gaseous exchange”

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6
Q

What are the functions of the blood-gas barrier?

A

Prevents air bubbles forming in the blood and the blood leaking into the alveoli

Permeable to oxygen, carbon dioxide and other gases

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7
Q

What does the blood-gas barrier comprise of?

A

type 1 pneumocytes,

the endothelial cells and the basement membrane of the two cells

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8
Q

What is the ventilation perfusion rate and how is it calculated?

A

V/Q = 0.8
Every minute, an average of 4L of air enters the alveoli and round 5L of blood passes through the pulmonary capillaries in healthy adults

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9
Q

Why is the ventilation/perfusion ratio in the lungs not evenly distributed?

A

Wide range of ratios from one extreme to another

  • no blood perfuses a well-ventilated alveolus: V/Q = >1
  • no air ventilated a well-perfused alveolus: V/Q = 0

Due to gravity perfusion is greater at the base of the lungs and ventilation is greatest at the apex of the lungs

It is often compromised in respiratory disease

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10
Q

How is optimal gas exchange achieved by the pulmonary circulation?

A

Effective ventilation matched to effective perfusion

A balance between oxygen uptake and CO2 excretion and work of breathing

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11
Q

What is Henry’s law?

A

the degree to which a gas dissolves in a liquid (blood) is directly proportional to the partial pressure of the gas above (alveolus)

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12
Q

What is Fick’s law?

A

the rate of diffusion is proportional to the diffusion constant, surface area and pressure gradient and inversely proportional to the tissue thickness.

= dV/dt = D x (P1-P2)

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13
Q

What are the two forms of Hb?

A

taut (tense) form and relaxed form

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14
Q

What factors favour taut form?

A

low pH
higher CO2
higher temperature

it causes Hb to have a lower affinity for oxygen causing it to release oxygen

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15
Q

What factors favour the relaxed form of Hb?

A

higher pH
lower CO2
lower temp

binds oxygen more strongly in the alveolar capillaries

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16
Q

Where is 2,3-BPG present and what does it do?

A

present in human erythrocytes
binds with greater affinity to deoxyghaemoglobin decreasing its affinity for oxygen

therefore promotes the release of remaining oxygen molecules

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17
Q

Which way does the Bohr shift go in terms of the oxygen dissociation curve and what promotes it?

A

Shifts the sigmoidal curve to the right

  • increased temperature
  • increased 2,3-BPG
  • decreased pH
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18
Q

Which way does the Haldane shift go in terms of the oxygen dissociation curve and what promotes it?

A

Shifts the sigmoidal curve to the left

  • decreased temperature
  • decreased 2,3-BPG
  • increased pH
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19
Q

What is aerobic respiration?

A

Chemical process by which organisms extract energy from food
= oxidation reaction that produces chemical energy from glucose and oxygen
C6H1206 + 602 goes to 6H20 + 6CO2 + ENERGY

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20
Q

How is CO2 transported in the blood?

A

dissolved in the plasma (5%)
bound to Hb and plasma proteins (about 10%)
majority is transported as bicarbonate ions (HCO3-)

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21
Q

What is the equation for the formation of bicarbonate ions?

A

CO2 + H20 catalysed by carbonic anhydrase to H2CO3 which goes to HCO3- and H+

22
Q

What are the two main buffer systems and what do they do?

A

The lungs removal CO2 produced by metabolism

The kidneys deal with ingested dietary acids

Buffer systems help the kidney and lungs maintain pH within narrow limits

23
Q

What is the principle buffer system?

A

Bicarbonate buffer, though phosphate and proteins are also involved

24
Q

What is the Henderson-Haslebalch equation?

A

Modified version to relate to the pH of blood

pH = pKa(H2CO3) + log([HCO3-]/[H2CO3])

pKa(H2CO3)= -ve log of the acid dissociation constant of carbonic acid = 6.4

25
Q

What are the different respiratory gas analysis approaches?

A

may analyse blood gases, exhaled gases or non-invasive methods via the skin surface

26
Q

What are the invasive methods of respiratory gas analysis?

A

Arterial blood gas sampling (ABG)

Capillary Blood Gas sampling (CBG)

27
Q

What are the non-invasive methods of respiratory gas analysis?

A

Pulse Oximetry

Transcutaneous monitoring

28
Q

Describe the ABG

A

Gold standard method
Direct from the artery (usually radial artery)
No potential for contamination with the air
Can make duplicate measurements from one sample or serial measurements with an arterial line
Can be very painful

29
Q

Describe the CBG

A

Useful and under-used alternative to ABGs
Sampled from the earlobe so its not as painful and invasive

Site is prepared with vasodilator cream (deep heat) to arterialise the blood
Blood must free-flow into the tube and not be forced
Although outcome measures are not exactly the same studies have shown no significant difference

30
Q

What are the outcome measures and their normal values for ABG/CBG?

A 
PaO2: 10-13.5kPa
PaCO2: 4.8-6 kPa
pH: 7.35-7.45
HCO3-: 23-27mmol/L
Base excess (surplus alkali): -3 to 3 mmol/L
Oxygen saturation: 96-99%
31
Q

What is the alveolar gas equation?

A

allows the calculation of the alveolar partial pressure of oxygen from data the is practically measurable:

= FiO2 (Patm -PH2O) - PaCO2/RER
……..

= 0.21(101-6.25)-PaCO2/0.8

32
Q

What is the alveolar-arterial difference?

A

A-a gradient is a measure of the difference between alveolar and arterial oxygen
Normally 0.5-1.5kPa

33
Q

What does it mean if the A-A gradient increases, >1.5kPa?

A

means a low PaCO2, low PaO2 or both
e.g. patient breathing hard to try and achieve normal oxygenation, a patient breathing normally and attaining low oxygenation

34
Q

What is a pulse oximetry?

A

small, portable device capable of measuring oxygen saturation and heart rate
Not as accurate as full blood gas analysis but..
Simple, useful and non-invasive
Used during spot-checks (within community) or continual monitoring (overnight sleep studies)

35
Q

What is transcutaneous monitoring?

A

Monitor partial pressures of oxygen (TcO2) and carbon dioxide (TcCO2)

Measured via a sensor attached to the skin (upper forearm or below collar bone)

Useful for monitoring patients with more sever respiratory compromise (where CO2 may be raised)

36
Q

What happens in respiratory failure?

A

impaired pulmonary ventilation and/or perfusion effects gas exchange and can lead to altered respiratory blood gas composition
= breathlessness, decreased exercise tolerance, impaired cognition and even loss of consciousness

37
Q

What are the different types of respiratory failure?

A

Type I
Acute type II
Chronic type II
Metabolic acidosis/alkalosis

38
Q

What is type I respiratory failure?

A

PaO2 < 8kPa (Severe hypoxia)
Mild hypoxia may not be pathologically significant
More severe hypoxia is a major cause of organ dysfunction and patient death
Long term oxygen therapy can be indicated

39
Q

What is nocturnal hypoxia?

A

Established mild hypoxia worsens during sleep due to suppression of respiratory system
Nocturnal oxygen often prescribed

40
Q

When can intermittent hypoxia occur?

A

can result from sleep-related breathing disorders - e.g. obstructive sleep apnoea

41
Q

What is acute type II respiratory failure?

A

Hypoxia in conjunction with hypercapnia
- increased CO2 leads to increased H+ = decreased pH
Kidneys have not yet compensated (base excess will be normal)
Often occurs during an exacerbation of respiratory disease (e.g. chest infection in COPD)

42
Q

What is chronic type II RF?

A

Abnormal pH
If increased CO2 persists the kidneys produce more alkali to compensate which returns the pH to normal (3-5 days)

Common in people with severe respiratory disorders (COPD, khphoscoliosis) and long-term ventilatory support may be required

43
Q

What is the spirometry lung function test?

A 
Spiro=breath
metry=measurement 
Assess pulmonary ventilation 
Simple and most common 
Versatile and informative that often correlated well to disease severity
44
Q

What measures do you gain from a spirometry test?

A 
Vital capacity
Forced vital capacity (FVC)
Forced expired volume in 1 second (FEV1)
FEV1/FVC ratio %
Peak expiratory flow (L/s)
45
Q

What is the spirometry procedure?

A

Full inspiration then immediate full expiration at relaxed speed (VC) or at max speed (FVC)

Inspiration at relaxed speed (IVC) OR at max speed (FIVC) is optional

46
Q

What is the most useful aspect of determining lung volumes?

A

it provides information on the functional status of the lungs - not hugely information
-useful with severe airflow obstructions

47
Q

What is FRC, ERV, RV, EVC & IVC, and TLC?

A 
FRC: functional residual capacity (L)
ERV: expiratory reserve volume (L)
RV: residual volume (L)
EVC: expiratory vital capacity 
IVC: inspiratory vital capacity 
TLC: total lung capacity (L)
48
Q

What tests can be used to measure lung volume?

A

Gas dilution techniques
- helium wash in
- nitrogen wash out
Body plethysmography

49
Q

What is the helium dilution test?

A

Known vol and conc of helium breathed tidally
diluted in lungs until equilibrium is met
degree to which the gas is diluted will be proportional to the FRC

50
Q

What is the nitrogen wash out test?

A

Nitrogen = 78% gas in lungs.
FRC can be determined by calculating the total volume of nitrogen in the lungs
Breath in 100% O2 to gradually wash out nitrogen
Expired gas collected in spirometer and nitrogen conc is recorded breath by breath

51
Q

What is the single breath gas transfer test?

A

Most common test
Quantifies oxygen uptake by respiratory system
Using CO as it binds in the same manner as O2 to Hb but at a much greater affinity (210x)

52
Q

What is the TLco, VAeff and Kco?

A

TLco: transfer factor of the lungs for CO
- estimate of overall efficiency of oxygen uptake
(also dependent on Hb)
VAeff: effective alveolar volume
- Surface area over which gas transfer occurs
Kco: transfer coefficient (TL/VA)
- estimate of efficiency of O2 uptake at alveolar level

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