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PHYSIO > Hypoxia > Flashcards

Hypoxia Flashcards

1
Q

Define these common terms:

A
a
v
P or p
C
F
A 
Alveolar
Arterial 
Venous
Partial pressures
Content
Fraction
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2
Q

What is barometric pressure (PB)?

A

The total pressure of all gases in the air (including inert)

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3
Q

Define partial pressure of a gas in a mixture

A

The pressure a gas would exert if it occupied that volume alone (Dalton’s Law)

OR the total pressure of a gas mix is the sum of each
gases partial pressure (P)

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4
Q

How do gases move in large airways (conducting zone)?

A

Gases move by convention

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5
Q

How do gases move in smaller airways?

A

By diffusion - from a high partial pressure to a low partial pressure

E.g. diffusion of o2 from alveoli to pulmonary capillaries is partly dependent on the partial pressure gradient

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6
Q

What is the uptake of o2 in pulmonary capillaries (and extraction of o2 at tissues) influenced by?

A

1) partial pressure gradient
2) transit time of blood through capillary e.g. too quick, equilibrium may fail

3) (and also the relationship between PO2 and Hb saturation)

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7
Q

What is the systemic o2 delivery equation?

A

DO2 = CO x CaO2

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8
Q

What is the aim of acclimatisation?

A

To maintain an adequate o2 delivery to the tissues, in the face of low inspired PO2

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9
Q

What kind of a response is acclimatisation?

A

An integrated and slowly developing response (hours-days-weeks), requiring adjustments to the following systems:

  • cardiac
  • respiratory
  • haematological
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10
Q

What are the three adjustments in response to hypoxia?

A
  • respiratory (hyperventilation and acid/base balance adjustments)
  • cardiovascular (HR)
  • haematological (erythropoiesis)
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11
Q

What is the equation for PB?

A

• PB = *PN2 + PO2 + PCO2 + PH20

*Includes inert gases

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12
Q

What are the pressure units?

A

Pressure units

1kPa = 7.5mmHg

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13
Q

What is dry PO2 in sea level?

A

PO2 = fractional concentration (FO2) x PB

  • FO2 = 0.209 (approx. 21%) in dry air
  • PB at sea level = 101kPa (760mmHg)

• So dry PO2 at sea level = 0.209 X 101 = 21kPa (159mmHg)

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14
Q

What happens when dry ambient air passes through airways?

A

Becomes quickly saturated with H20 vapour as it passes through airways

  • H20 exerts it’s own PP which needs to be taken into account
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15
Q

What does PH20 change with and what is its value at body temp?

A

Changes with body temp.

At body temp = 6.25kPa (47 mmHg)

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16
Q

What is the process of o2 uptake into the alv-cap membrane?

A

O2 into solution —> diffusion through membrane —> combination with Hb on RBC

17
Q

What is hypoxia?

A

Inadequate supply of o2 to the tissues

= cellular function may become compromised

18
Q

Why does PO2 decrease from air to alveoli?

A
  • addition of water vapour

- has exchange with co2

19
Q

Why is oxygen needed?

A

Acts as the final e- acceptor in the ETC

So, helps in the creation of the H+ gradient either side of the inner membrane, which drives oxidative phosphorylation (OXPHOS) and the production of ATP

20
Q

What decreases with increasing altitude?

A

PB decreases = PIO2 decreases too

This is because:
PIO2 = FO2 x (PB x H20)

= HALVES PAO2

21
Q

Why does FO2 stay the same with increasing altitude?

A

Proportion of gases stays the same, just fewer molecules overall

22
Q

Give an example of PB decreasing with altitude

A

(London) Sea level = 760 mmHg

Everest base camp = 403.5 mmHg

From participants breathing ambient air at various altitudes.
Grocott et al (2009) NEJM

23
Q

What is the first line of defence to hypoxia exposure?

A

Increasing CO - to maintain DO2 in the face of lower PIO2

1) HR increases immediately
- 4500m: HR 10-15% higher than sea level
- 7600m: HR ~100% higher than sea level

2) SV remains constant or decreases

24
Q

What is the second response to hypoxic exposure?

A

Restoration of CaO2.

Via 2 mechanisms:

1) ventilatory adjustments
2) haematological adjustments

Main ventilatory compensation mechanism = the hypoxic ventilatory response

25
Q

What is hyperventilation?

A

Where CO2 is eliminated in expired air at a faster rate than is produced (i.e. blow off CO2) - decrease in PaCO2

26
Q

Why does hyperventilation occur?

A

Due to hypoxic stimulation of arterial chemoreceptors

Most important feature of acclimatisation to high altitudes

27
Q

Why is hyperventilation beneficial?

A

As a person climbs to higher altitudes, the hypoxic ventilatory drive increases, and PCO2 decreases

  • above a certain altitude, the HV response aims to defend PO2 above a certain threshold (eg 35 mmHg) by extreme HV
  • this can reduce PCO2 to <10 mmHg!
  • keep going higher, eventually won’t be able to compensate
  • won’t be able to HV anymore + eventually become very hypoxic + pass out
28
Q

What is the equation for PAO2?

A

PAO2 = FIO2 x (PB x PH20) - (PaCO2/R)

29
Q

What is the equation for PIO2?

A

PIO2 = FIO2 x (PB - PH2O)

PHYSIO (12 decks)

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