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Unit 1 > 9/25a Pulmonary Physiology II (Biomedical Sciences) > Flashcards

9/25a Pulmonary Physiology II (Biomedical Sciences) Flashcards

1
Q

What is partial pressure?

A
  • proportional to concentration in a gas mixture
  • the pressure a gas would exert if it occupied the entire volume of the mixture
  • the driving force for diffusion of gasses
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2
Q

Partial Pressure denominators

A

PA=alveolus
Pa=arterial blood
Pv=venous blood
Units = mmHg

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3
Q

Why is dry room air of PO2 160mmHg?

A 
Px = Pb x Fractional Concentration = 760 mmHg x0.21 = 160mmHg
Pb = barometric pressure = 760mmHg
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4
Q

Why does the PO2 drop to 150mmHg in the conducting zone?

A

Tracheal air drops to 150mmHg because when we are measuring partial pressure in humidified air (mucous traps particles and humidifies air) so we have to subtract the partial pressure due to water vapor from the barometric pressure and multiply by the fraction
– PO2 = (Pb-Pwater vapor) x 0.21

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5
Q

PAO2 = 100mmHg in the alveoli because?

A

It reflects the balance between O2 entry to and exit from alveoli

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6
Q

why is PACO2 40?

A

because CO2 diffuses into alveoli from venous blood

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7
Q

why does PAO2 = PaO2

A

arterial blood equilibrates with alveolar air under normal circumstances

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8
Q

what determines the rate of diffusion of gasses?

A

As PRESSURE GRADIENT increases, diffusion will increase
As SURFACE AREA increases, diffusion will increase
As MEMBRANE THICKNESS increases, diffusion will decrease

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9
Q

what is the total surface area of the alveoli?

A

about the size of a tennis court

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10
Q

How does blood equilibrate?

A
  • Normally, O2 equilibrates very quickly so PaO2=PAO2

- In fibrotic patients, thickening of blood-gas barrier slows O2 exchange so PaO2

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11
Q

what is exerting the partial pressure of oxygen in the blood?

A

oxygen that is dissolved in plasma

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12
Q

how do you calculate the concentration of Oxygen in the blood?

A

[O2]=PaO2 x Solubility of O2 in the blood
[O2]=100mmHg x 0.003 ml O2/100ml blood/mmHg
=0.3 ml O2/100 ml blood

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13
Q

If CO Is 5 L/min, how much O2 would be delivered to tissues each minute?

A

Delivery O2 = CO x [O2]a
=5l/min x 3 mlO2/l blood
=15 ml O2/min

We need 250 ml O2/min, SO it would take 4 seconds to become anoxic.

Thus, the oxygen dissolved in the plasma measured with PO2 is a really small part of the blood oxygen content

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14
Q

How do we get the blood O2 content

A
  1. Bound to hemoglobin: 98% of total O2 content is in bound form, 4 binding sites on each Hb, oxygen saturation measured by % binding sites occupied by oxygen (20 ml O2/ 100ml blood)
  2. Dissolved in plasma: 2% of the total O2 content, measured by PO2 (0.3 ml O2/ 100ml blood)

O2 content = (constant x [Hb] x %sat) + (solubility x PO2)
=20.3ml O2/ 100ml blood

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15
Q

PO2 tells us the amount of oxygen in the blood (T/F)

A

FALSE, it tells us about the gradient of oxygen

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16
Q

Oxy-Hb dissociation curve

A

relates SaO2 and PaO2

Flat at high PO2 and steep at low PO2

large change in PO2 at high PO2’s leads to really small changes in saturation, thus we can pick up a lot of oxygen even when we have significant changes in PO2

large changes in PO2 at low PO2’s leads to really large changes in saturation, b/c job of Hb at tissues is to get rid of oxygen to deliver to tissues. Thus Hb is very sensitive to PO2 at lower levels

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17
Q

at high PO2, what is the impact on the Hb saturation?

A

there is a high loading of PO2 on the lungs, so big changes in PO2 will NOT affect the Hemoglobin O2 saturation

18
Q

at low PO2, what is the impact on the Hb saturation?

A

there is a high unloading of PO2 on the tissues, so big changes in PO2 will affect the Hb O2 saturation

19
Q

What defines the affinity of Hb for O2?

A

P50 defines affinity of Hb for O2

-Normal P50 = 25mmHg and it’s the PO2 where 50% of binding sites are occupied when PaO2 = 25mmHg

20
Q

How does the affinity of Hb for O2 shift?

A
  • increasing the temperature and bohr effect (increase PCO2 and decrease pH) > decreases affinity of Hb for O2 > the curve shifts to the right
  • -P50 is now PaO2=37

When P50 increases, the affinity for Hb and O2 is LESS (Hb unloads oxygen more easily)

21
Q

when tissues are exercising what happens in the environment?

A
  • Increase in PCO2, because CO2 is a biproduct of metabolism
  • decrease pH because lactic acid is being produced
  • temperature is increasing
  • -When our muscles are most active, that is when they need the most oxygen, so rightward shift of P50, it helps hemoglobin release oxygen to the tissues
22
Q

what are the 3 modes of CO2 transport?

A 
-dissolved in plasma
– 5% of total
-bound to hemoglobin
– Binds at a different site than O2
– Accounts for 3%
-chemically modified form
– H+ and HCO3- (bicarbonate)
– 92% of all CO2 transport
23
Q

what is the process of CO2 transport?

A

RXN:
Tissue: Metabolism>CO2
Capillary:
1. CO2 diffuses down its concentration gradient into the blood, some is dissolved in the plasma and some is diffused into the RBC from the tissue and some in the RBC bind to Hb, and MOST interact with water
2. Carbonic anhydrase combines the CO2 and H2O into H2CO3 - Carbonic Acid
-SLOW REACTION
3. Carbonic Acid then dissociates into a proton (H+) and Bicarbonate (HCO3-)
-FAST REACTION

24
Q

what are the two ways the CO2 is transported?

A

Equilibrium reaction, so the rate and the direction at which the reaction goes depends on the concentration of the reactants and the products

  1. Where PCO2 is HIGH (in the tissues), RXN goes to the RIGHT and converts CO2 into biocarbonate and a proton (easier to carry bicarbonate in blood than CO2)
  2. Where PCO2 is LOW (in the lungs), RXN goes to the LEFT and converts bicarbonate to CO2 to release into the air
25
Q

when bicarbonate exits the cell what happens?

A
  • Proton can’t exit so there is an electrical gradient, in order to balance it a negative chloride ion enters
  • Proton is bound to a reduced Hb (Hb that is not carrying O2)
26
Q

Take home messages for oxygen dissolving in plasma and bound to Hb?

A
  • Dissolved O2 is refelcted in PaO2 which drives diffusion
  • Bound O2 to Hb is reflective of SaO2 (major store of O2)
  • Oxy-hb dissociation curve/P50
  • changes in affinity of Hb to oxygen can facilitate unloading onto tissues
27
Q

what is CO2 mainly carried in the form of?

A

BICARBONATE (HCO3-)

28
Q

Abnormalities on blood gas

A
  • Processed by respiratory centers in medulla and pons
  • Effect/end result is increased ventilatory drive
    1. Hypoxemia: PaO2 < 80 mm Hg
  • sensed by peripheral chemoreceptors in the carotid and aortic bodies
  • less sensitve than central chemoreceptors
    2. Hypercapnia: PaCO2 > 45 mm Hg
  • Sensed by chemoreceptors in the brain stem
  • VERY SENSITIVE to pCO2 and pH of CSF
  • MOST IMPORTANT REGULATOR OF VENTILATION
29
Q

what is the purpose of increased ventilatory drive?

A

reflex designed to maintain homeostasis of arterial blood gases in a normal range

  • exhalation of more CO2 > PaCO2 returns to normal
  • inhalation of more O2 > PaO2 returns to normal
30
Q

hypoxemia vs anemia

A
  1. Hypoxemia is a low partial pressure of Oxygen and the body works to increase oxygen content of the blood
  2. Anemia is low Hb levels
  • When the anemia levels drop, it has a way bigger impact on oxygen carrying capacity than hypoxemia!!!
  • Even when oxygen saturation is normal we still may have a patient who has deficits in oxygen carrying capacity because of the anemia
  • Major issue of Hypoxemia, is that the pressure gradient for diffusion decreases
31
Q

causes of hypoxemia

A
  1. diffusion limitation, can occur with fibrosis
  2. breathing in a low oxygen gas mixture (altitude, sucking in a helium balloon)
  3. Hypoventilation (decreased ventilatory drive from brain damage and drugs, paralysis/weakness of ventilatory muscles, damage to chest wall
  4. ventilation-perfusion matching, common in lung disease
32
Q

Ventilation-perfusion matching

A
  • ventilation is the amount of air coming into the lungs
  • perfusion is synonymous to blood flow/CO
  • ratio between the two is normally 0.8
  • in a normal well matched person, gravity causes gradients (regional):
  • —ventilation: base of lung > apex of lung
  • —perfusion: base of lung (below heart) > apex of lung (above heart)
33
Q

mismatch between perfusion and ventilation

A
  1. airway shunt: perfusion is normal, but ventilation is shut off (0). SO, ratio of ventilation to perfusion is 0. So alveolar PAO2 is 0, PaO2=PvO2 and PaCO2=PvCO2.
  2. Pulmonary Embolism (BF shunt): ventilation is normal, but BF is 0, so ratio of ventilation to perfusion is infinity. PAO2 is very high (air from trachea) and PACO2 is 0 because no CO2 from blood flow. PaO2 = PaCO2 = 0
34
Q

T/F capillaries are overperfused at apex and underperfused at base of lung

A

FALSE, capillaries are underperfused at the apex of the lungs while the capillaries are overperfused at the base of the lungs

35
Q

T/F: BF is affected by gravity and pressure in Pa, Pv, and PA and ventilation is not as strongly affected

A

TRUE

36
Q

V/Q relationships across the lung
V=ventilation
Q=Blood flow

A
  1. top of the lung, V is lower, Q is lowest, V/Q is highest (3), PaO2 is 130, PaCO2 is 28. Looks more like alveolar blood (overventilated)
  2. middle of the lung, V is mid, Q is mid, V/Q is mid (0.8), PaO2 is 100, PaCO2 is 40 (atm)
  3. bottom of the lung, V is higher, Q is highest, V/Q is lowest (0.6), PaO2 is 89, PaCO2 is 42. Looks more like venous blood (underventilated)
37
Q

when ventilation is greater than flow, what happens?

A

blood that comes out of lung looks more like atmospheric air

38
Q

when ventilation is less than flow, what happens?

A

blood that comes out of lungs looks more like venous blood

39
Q

ventilation during exercise?

A

must adapt to changing demands…response in vent drive that allows us to compensate for the increase in rate of O2 consumption and CO2 production in order to maintain homeostasis

40
Q

ventilation and moderate exercise

A
  1. Phase I: Fast! neural in origin because the response is immediate in increase in ventilation to exercise
  2. Phase II: Primary
  3. Phase III: Stead State.. Amount that ventilation goes up is well matched to the increase in O2 consumption and CO2 production (linear/proportional).
41
Q

why does the amount of PaO2 and PaCO2 stay the same during exercise?

A

Ventilation increases in proportion in response to the change in oxygen consumption and increase CO2 production

Well matched to the change in metabolic demand

PvCO2 increases, but PaCO2 stays the same, because we breath out CO2 because the amount of increase in our breathing is well matched to the increase in production of CO2

Unit 1 (28 decks)

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