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Part 1 Viva > Respiratory > Flashcards

Respiratory Flashcards

1
Q

Non-Respiratory Functions of the lung

A 
Blood reservoir function
Blood filtration
Metabolic function
- Surfactant Production
- removal of proteases
- protein synthesis
- carbohydrate metabolism
- hormonal activation
Immunological function
Heat regulation
Airway flow for speech
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2
Q

What is surfactant

A

surfactant is a mixture of phospholipids, lipids and proteins (plasma and surfactant) that is produced by type 2 alveolar cells. It is an amphipathic substance.
It’s main function is to reduce the surface tension of alveoli therefore decreasing work of breathing.

Other functions include

  • keeping alveoli dry
  • stabilise alveoli

Main phospholipid: Dipalmitoyl phosphatidyl choline (DPPC)

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3
Q

How is carbon dioxide carried within the blood?

A

Carried as 3 forms.
Dissolved: 5% arterial, 10% venous
Bicarbonate: 90% arterial, 60% venous
Carbamino compounds: 5% arterial, 30% venous

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4
Q

What is the oxygen cascade?

A

The stepwise decrease in partial pressure of oxygen from the atmosphere to the tissues allowing the passive diffusion/movement of oxygen to the tissues.

Atmosphere: 159mmhg
Mouth: 149mmhg
Lungs: 100mmhg
Arterial blood: 95-98mmhg
Venous blood: 40mmhg
Tissues: 2-20mmhg
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5
Q

What is closing capacity?

A

Volume of the lungs at which the small airways begin to close.
CC = CV + RV

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6
Q

Where is O2 stored in the body?

A 
4 main stores:
Within the lungs ~ 290mls
Bound to Hb ~ 1000ml
Bound to myoglobin ~ 200mls
Dissolved ~ 200mls
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7
Q

What is normal resting O2 consumption?

A

250mls or 3.5mls/kg

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8
Q

What is FRC?

A

FRC is the volume of air remaining in the lungs at the end of normal tidal expiration.
It is comprised of RV + ERV.
Normal value is 30mls/kg

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9
Q

What are the functions of FRC

A
  1. O2 store
  2. O2 buffer to allow continual diffusion of oxygen during expiration
  3. Prevents atelectasis
  4. Reduces WOB
  5. Decreases PVR
  6. Decreases V/Q mismatch
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10
Q

What factors affect FRC?

A

Factors that increase FRC:

  1. changing from supine to erect position
  2. increasing height
  3. disease states with increased compliance/reduced lung elastic recoil

Decrease FRC:

  1. obesity
  2. pregnancy
  3. lying supine
  4. General anaesthesia
  5. increase lung elastic recoil
  6. muscle paralysis
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11
Q

What is hypoxia?

A

Hypoxia is inefficient supply of oxygen to the tissues for normal cellular function
Hypoxaemia is decreased partial pressure of oxygen within the blood. PaO2 < 60mmhg

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12
Q

Can you classify hypoxia?``

A
  1. Hypoxic hypoxia - PaO2
  2. Anaemic hypoxia - lack of Hb for carriage
  3. Ischaemic hypoxia - lack of blood getting to the tissues
  4. Histotoxic hypoxia - tissues unable to utilize the oxygen.
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13
Q

What is perfusion limitation?

A

This occurs when gas concentrations on either side of a membrane equalise rapidly and therefore the only way to increase diffusion is to increase pulmonary blood flow.
N2O or O2 under normal circumstances

(rate of gas uptake in capillary is determined by the capillary blood flow)

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14
Q

What is diffusion limitation? Can you give examples?

A

Rate of gas uptake is dependent on the rate of diffusion across a membrane. There is a concentration gradient for diffusion along the whole length of the capillary
CO is an example.

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15
Q

What is the alveolar gas equation?

A

PAO2 = PiO2 - PaCO2/R

PiO2 = FiO2 (Patm - PH2O)

R = respiratory quotient.
= CO2 produced/O2 consumed.

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16
Q

What is shunt?

A

Shunt is blood that enters the arterial system without having passed through ventilated lung. ie it is lung that is perfused but not ventilated.

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17
Q

What is venous admixture?

A

Venous admixture is a theoretical volume. It is the volume of mixed venous blood that would have to be added to end pulmonary capillary blood to account for the drop in O2 partial pressure in arterial blood.

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18
Q

What is the shunt equation?

A

QS/QT = CcO2 - CaO2/CcO2-CvO2.
Normal = 5%
Normal A-a gradient <10mmhg

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19
Q

What is physiological shunt?

A

Bronchial venous blood and thebesian veins

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20
Q

Functional Shunt?

A

V/Q scatter

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21
Q

What is deadspace?

A

Deadspace is the fraction of the tidal volume that does not partake in gas exchange. IE it is lung that is ventilated but not perfused.

22
Q

Can you classify deadspace?

A

Deadspace can be classified into Physiological and Apparatus deadspace.
Physiological can be classified into Anatomical and Alveolar.

Anatomical deadspace is the conducting airways and is usually around 150mls or 2.2mls/kg

23
Q

How do we measure deadspace?

A

It can either be measured using Fowlers method - nitrogen wash-out to measure anatomical deadspace.
Or via the Bohr equation to calculate physiological deadspace.

24
Q

Can you tell me the Bohr Equation?

A

We mostly use the Enghoff modification which is:
Vd/Vt = PaCO2 - PeCO2/PaCO2
normal is 0.2-0.35

The Enghoff Modification substitutes PaCO2 for PACO2.

25
Q

What is compliance?

A

Compliance is the change in volume for a given change in pressure

26
Q

What is total lung compliance or Respiratory Compliance?

A

Total lung compliance is made up of lung compliance and chest wall compliance.
It has a value of 100mls.cmh20

27
Q

What is the typical value for lung compliance?

A

200mls/cmH20

28
Q

How can compliance be classified?

A

Lung classified can either be defined as static or dynamic or specific.

Static Compliance: compliance in the absence of airflow
Dynamic Compliance: compliance in the presence of airflow and is therefore always lower than static compliance as it factors in airflow resistance.
Specific compliance is static compliance/FRC - compliance normalised by lung volume.

29
Q

How can FRC be measured?

A

2 methods

  1. Body Plesmythography in which the subject breathes in and out from a box via closed circuit and Boyles law is applied to calculate FRC from the changes in pressure and volume of the box when the patient inhales and exhales.
    Accounts for air trapped behind closed airways.
  2. Helium/Gas dilutional method.
    Patient breathes in and out of a box containing a known volume and concentration of helium. After a few breaths and equilibrium has occurred the new concentration is measured and FRC calculated from those values.
    This method only accounts for air that is communication with the atmosphere
30
Q

How can compliance be measured?

A

Static compliance:
1. patient inhales in incremental volumes and then stops and the pressure and volume of the lungs is measured at the mouth by an oesophageal balloon and it is plotted on a compliance curve.

  1. or pressure and volume can be measured at the beginning and end of expiration and inhalation and the values plotted - accounts for airway compliance.
31
Q

What factors affect compliance?

A 
Lung volume - compliance highest at FRC
Surfactant - decreases surface tension
Posture
Pulmonary blood flow
Age - increased age - increased compliance - loss of lung conncetive tissue. 
Airway resistance
air flow
lung elastic recoil.
32
Q

Tell me the structure of HbA

A

HbA is comprised of 4 globin chains - 2 alpha + 2 beta , each containing an iron atom in its ferrous form to which oxygen binds.

33
Q

How does the structure of Hb aid it’s function?

A

As there are 4 chains each Hb molecule can bind 4 oxygen molecules - increased carriage capacity.
It also displays co–operative binding. De-oxygenated = tense form - decreased O2 affinity. 1 O2 binds, conformational change to relaxed form - increased O2 affinity + therefore binding.
ie there is a rapid increase in saturation for a small change in PaO2.

34
Q

How does the structure of HbF differ and why is this important?

A

HbF is comprised of 4 globin chains 2 alpha and 2 gamma. The gamma chains do not have the binding site for 2,3 DPG and therefore have an increased affinity of oxygen meaning there is a higher saturation for a lower PaO2.

35
Q

What is the Bohr Effect?

A

The Bohr effect is where Hb has a decreased affinity for O2 in the presence of high CO2. This causes a right shift in the Hb dissociation curve.

36
Q

What is the Haldane effect?

A

The Haldane effect is where de-oxygenated Hb has an increased capacity for CO2 than oxygenated Hb.

37
Q

What is the oxygen flux equation?

A

O2 flux is the amount of oxygen that is delivered to the tissues per unit time - usually mls.min
O2 flux = CO * (Hb (g/dl) * SpO2 * 1.34) + (PaO2 * 0.003)

1.34 = Huffners constant.

38
Q

What are the 3 gas laws?

A

Boyles law:
At a constant temperature the volume of a gas is inversely proportional to the pressure.

Charles law:
At a constant pressure the volume of a gas is proportional to the temperature

Guy-Lussacs law:
At a constant volume the pressure of a gas is proportional to the temperature.

39
Q

What is a perfect gas?

A

One that obeys all 3 laws.

40
Q

What is Henry’s law?

A

That the amount of gas dissolved in solution is proportional to the partial pressure of that gas within the solution.

41
Q

What is ficks law of diffusion?

A

Amount of substance that diffuses across a semipermeable membrane is:

  1. proportional to the area
  2. inversely proportional to the thickness
  3. proportional to the pressure difference across the membrane
  4. dependent on the diffusion constant = solubility/square root of the molecular weight.
42
Q

What is myoglobin?

A

Myoglobin is globular protein that binds and delivers O2 that is found within muscle cells - being on O2 store for muscular contraction.

43
Q

How does myoglobin differ from Hb

A
  1. single globular chain - only binds 1 oxygen molecule.
  2. hyperbolic dissociative curve.
  3. much lower P50 - 2.75mmHg rather than 26.6mmHg.
    requires this for its function - to take oxygen from the blood and release it in the muscle cell which has a much lower partial pressure than blood.
44
Q

What is flow?

A

Flow is the change in pressure over resistance.

45
Q

What are the different types of flow?

A

There are 2 main types of flow - laminar and turbulent. There is also transitional flow which occurs between laminar and turbulent.

46
Q

Can you describe these 2 types of flow?

A

Laminar flow is streamlined flow of concentric rings where flow in the centre is much faster.
This can be calculated using the Hagan-Pouiselle law:
flow = Ppir (to the power 4)/8viscositylenght

Turbulent flow is chaotic where all air/liquid is moving forward as a front.
here flow is proportional to the square root of the pressure change.

47
Q

How do we determine the likelihood of turbulent or laminar flow?

A 
This is determined by reynolds number. 
Re = 2rvd/viscosity
radius
velocity
density
viscosity.

a number <2000 = laminar flow
2000-4000 = transitional flow
>4000 = turbulent flow.

48
Q

What is viscosity?

A

It is the measure of a liquids internal resistance to flow.

49
Q

What is density?

A

Density relates the mass of a substance to it’s volume. kg/m3

50
Q

Can you list some of the differences between the apex and the base of the lung?

A

PO2 - higher at the apex ~ 132mmg. base ~ 89mmHg
PCO2 - lower at the apes ~ 28mmHg. base ~ 42mmhg
pH - apex - more alkaline pH 7.51. base pH 7.39
V/Q ratio - apex 3.3 - closer to deadspace. base 0.6 - closer to shunt.
Alveolar size - apex large + well distended/ base small, mid collapse.
Perfusion - better at base - due to gravitational forces.
Ventilation - better at base - but not as steeply improved
Compliance - better at base - dependednt lung - deflated alveoli at optimum point on curve.
Pleural pressure. apex = -7cmh20. base -3cmh20
PVR - high at apex. low at base

51
Q

What is the cough reflex?

A

It is protective airway reflex. It is an afferent, efferent and integrator system

Receptor: pulmonary irritant receptors
Afferent pathway: internal laryngeal nerve (from vagus) to the medulla
Central integrator: medulla + cerebellar cortex
Efferent pathway: vagus and superior laryngeal nerve.
Effectors: glottis, external intercostals, diaphragm.

Mechanism:
1. deep breath - diaphragm, external intercostals contract
2. glottis + vocal cords close
3. diaphragm relaxes + abdominal muscles contract simulatneously with other expiratory muscles - increasing pressure within lungs.
4. glottis and vocal cords suddenly open - expulsion of high velocity turbulent air.
the bronchi and non-cartilaginous portions of the trachea become a slit through which air is forced - clearing irritants attached to the lining of the airway.

Part 1 Viva (14 decks)

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