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BRS > Ventilation and gas exchange > Flashcards

Ventilation and gas exchange Flashcards

1
Q

What is minute ventilation and how do you calculate it?

A 
Gas leaving and entering the lungs
Minute ventilation (L/min)= Tidal volume (L) x Breathing freq. (breaths/min)
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2
Q

What is alveolar ventilation and how do you calculate it?

A 
Gas entering and leaving the alveoli
Alveolar ventilation (L/min) = (Tidal volume (L) - Dead space (L)) x breathing freq. (breaths/min)
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3
Q

What factors affect lung volume and capacity?

A 
Body size (more height than weight)
Fitness
Age
Disease (pulmonary, neurological)
Sex
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4
Q

What is anatomical dead space?

A

Conducting zone of lungs with no gas exchange
Includes 16 generations of bronchiol bifurcations.
Typically 150ml in adults at FRC (functional residual capacity)

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5
Q

What is alveolar dead space?

A

Non-perfused parenchyma (part that carries out the function) with no gas exchange
Alveoli have no blood supply
Typically 0ml in adults

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6
Q

What is the respiratory zone?

A

Aka. alveolar ventilation
7 generations of bronchiol bifurcations
Typically 350ml in adults

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7
Q

What can increase dead space?

A

Anaesthesia circuit

Snorkelling

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8
Q

What decreases dead space?

A

Tracheostomy

Cricothyrotomy

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9
Q

What is the chest wall relationship?

A

Chest wall has tendency to spring outward and lung has tendency to recoil inwards
These forces are in equilibrium at end- tidal expiration (FRC) which is ‘neutral’ position of intact chest

Chest recoil = lung recoil
Inspiratory muscle effort + chest recoil >lung recoil
Expiratory muscle effort + lung recoil > chest recoil

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10
Q

What is the importance of pressure gradients?

A

Pressure gradients drive airflow

Normal breathing is called negative pressure breathing as Palv < Patm

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11
Q

What happens to air as it goes through our lungs?

A

As air enters our lungs its warmed, humidified and slowed down meaning pressure changes as you move from conducting zone to respiratory airways

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12
Q

What is transmural pressure?

A

Pinside - Poutside = transmural Pa

Same as transpulmonary pressure (Palv - Ppl)

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13
Q

What is transthroacic pressure?

A

PTT= Ppl- Patm

Difference between pressure in pleural cavity and atmosphere

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14
Q

What is trasresipratory pressure?

A

PRS= Palv - Patm

Difference between alveolar pressure and atmospheric pressure

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15
Q

What is transpulmonary pressure?

A

PTP = Palv- Ppl

Difference in pressure between alveoli and pleural cavity

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16
Q

What are the different gas laws?

A 
Dalton
Fick
Henry
Boyle
Charles
17
Q

What does Dalton’s gas law state?

A

Pressure of a mixture is equal to the sum of partial pressures in that mixture

18
Q

What does Fick’s gas law state?

A

Molecules diffuse from region of high conc. to low conc. at a rate proportional to the conc. gradient (P1-P2), the exchange SA (A) and the diffusion capacity (D) of the gas and inversely proportional to the thickness (T) of the exchange surface:

Vgas = (A/T) D [P1-P2]

19
Q

What does Henry’s gas law state?

A

At constant temp., amount of gas that dissolves in a given type and volume of liquid is directly proportional to PP. of that gas in equilibrium with that liquid
C = Agas Pgas
C= conc. of dissolved gas
Agas= henrys constant/ diffusion constant
Pgas= pressure of gas

20
Q

What does Boyle’s law state?

A

At constant temp. volume of gas is inversely proportional to pressure of that gas
Pgas ∝ 1/Vgas

21
Q

What does Charle’s law state?

A

At constant pressure, volume of gas is proportional to temp. of gas
Vgas ∝ Tgas

22
Q

How do we calculate oxygen solubility?

A 
Foe this we use henrys law C= KPgas
Where
C= solubility of gas
K= henry's constant
Pgas= Partial pressure of gas

For oxygen:
CO2 = 0.024 (constant) x 13.5
CO2= 0.32mLdL^-1
CO2= 0.32 x 10 (dL^-1 to L^-1) x 5L (L of blood) = 16mLmin^-1

23
Q

Is dissolved O2 enough?

A

Dissolved O2 is only 16mLmin^-1 and we require 250mLmin^-1 therefore dissolves O2 alone is not enough so we need haemoglobin

24
Q

How is haemoglobin structured?

A

Hb monomers consist of ferrous iron ion (Fe2+) at centre of a tetrapyrrole porphyrin ring connected to a protein chain- covalently bonded at proximal histamine reside

25
Q

How does binding of oxygen molecule to Hb affect it?

A

Hb has cooperativity mechanism of O2 binding- once the first O2 binds, its much easier for next O2 to bind

26
Q

What is left shift?

A 
Increased affinity - O2 binds at lower PP of O2
Occurs at:
Lower temp
Alkalosis
Hypocapnia (low Co2)
Lower 2,3 DPG
HbF
27
Q

What is right shift?

A 
Decreased affinity - O2 released more easily 
Occurs at:
Increased temp.
Acidosis
Hypercapnia
Higher 2,3 DPG
28
Q

What is upwards shift?

A

Increased O2 capacity carrying

Polycythaemia

29
Q

What is downwards shift?

A

Impaired O2 carrying capacity

Anaemia

30
Q

What is downwards left shift?

A

Decreases capacity, increased affinity

Increased HbCO

31
Q

What is foetal Hb?

A

Greater affinity than HbA to ‘extract O2’ from mothers blood in placenta- left shift

32
Q

What is myoglobin?

A

Much, much greater affinity to ‘extract O2’ from circulating blood and store it than HbA

33
Q

How is oxygen loaded at lungs?

A

When mixed venous blood reaches lungs it has a PvO2 (venous pressure) of 5.3KPa and sats of 75%
This creates an oxygen gradient with alveoli where PaO2 is higher than PvO2
O2 diffuses into blood and oxygenates Hb

34
Q

How is oxygen unloaded at tissues?

A

When oxygenated blood gets to the tissues where O2 is lower in cells, it moves down conc. gradient into cells.
Eventually mixed venous blood will be created again which will diffuse back into blood and go to lungs.

35
Q

How is carbon dioxide loaded at tissues?

A 
In cells where CO2 is high from respiration of glucose, CO2 moves from cells into blood down conc. gradient
In blood (not RBCs) CO2 binds with water to form carbonic acid (this is non-enzymatically so is slow). Carbonic acid dissociated into H+ and bicarbonate which dissolves in plasma

CO2 can also move into RBCs down conc. gradient
CO2 binds water and uses carbonic anhydrase to form carbonic acid. This dissociates into H+ and bicarbonate. Bicarbonate leaves RBC and is dissolved into plasma. Cl- moves into RBC via AE1 transporter to maintain resting membrane potential- this is chloride shift
C02 can also bind to n-terminal of Hb forming HbCO2- carbaminohaemoglobin
Also O2 is released from HbO2 to create HHb (deoxyhaemoglobin) and that O2 moves into tissues

36
Q

What is pulmonary transit time?

A

Time that blood supply is in contact with respiratory exchange surface (0.75S)

BRS (60 decks)

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