RESP Introduction to Respiratory Function & Failure

Question 1

How does oxygen get from the atmosphere to tissues?

Answer 1

1. O2 inhaled from atmosphere into alveoli within lungs
   2.O2 diffuses from
   alveoli into blood within
   pulmonary capillaries.
   3.O2 transported in
   blood (>98% bound to
   haemoglobin)
   4.O2 diffuses into
   cells/tissues for use in
   aerobic respiration.
   5.CO2 diffuses from
   respiring tissues to blood
2. CO2 diffuses from
   capillaries to alveoli,
   then expired into
   atmosphere.

Question 2

What is partial pressure?

Answer 2

the level of a
specific, individual gas in a specific location

Question 3

What is alveolar parital pressure?

Answer 3

the level of a specific gas present in the alveoli

Question 4

How do changes in respiratory function enable blood gas homeostasis?

Answer 4

1. The rate at which gases diffuse between alveoli
   and blood is proportional to the difference in
   partial pressure between the two areas
   (i.e. ↑ difference = ↑ rate of diffusion)
2. So, if the level of O2 or CO2 in the alveoli (or
   blood) changes, the rate at which O2 enters the
   blood, or CO2 leaves, will change accordingly.
3. The body modulates alveolar PO2 and PCO2 by
   altering the rate of ventilation.
   Generally; ↑ventilation = ↑PAO2 and ↓PACO2
4. So, by changing the rate of ventilation, the body
   modulates the rate of gas exchange and the level
   of O2 and CO2 in the blood.

Question 5

What are the key functional requirements for efficient supply of oxygen from
atmosphere to tissues?

Answer 5

• An adequate rate of ventilation - sufficient O2 is provided to achieve an effective rate
  of gas exchange and full oxygenation of Hb)
• An appropriate level of cardiac output – blood is being pumped between the lungs
  and tissues
• Efficient coupling of ventilation and perfusion within individual alveolar units

Question 6

What is O2 saturation and how is it measured?

Answer 6

-The proportion of available haemoglobin molecules that are currently oxygenated
-Normal range greater than or equal to 95%
-Measured by pulse oximetry

Question 7

What is PaO2, normal range and how it is measured?

Answer 7

-The partial pressure (i.e. level)
of O2 in arterial blood
-10.3 – 13.3 kPa
-Measured by an ABG

Question 8

What is PaCO2, normal range and how its measured?

Answer 8

-The partial pressure (i.e. level) of CO2 in arterial blood
-4.9 – 6.0 kPa
-Measured by an ABG

Question 9

What is respiratory failure?

Answer 9

Respiratory failure is a serious condition where inadequate oxygenation of blood is
being facilitated by the lungs relative to the metabolic demands of the body (technical
clinical definition ≈ ≤ 8kPa

Question 10

What does inadequate oxygen lead to?

Answer 10

Inadequate oxygen supply leads to organ dysfunction and injury.

Question 11

What does insufficient removal of CO2 lead to?

Answer 11

Insufficient removal of
CO2 leads to acidosis as it reacts with H2O to form carbonic acid.

Question 12

What is the cause of Type 1 respiratory failure?

Answer 12

↓ oxygenation
(↓ diffusion of O2 from alveoli to blood)

Question 13

What happens to the levels of PaO2 and PaCO2 in type 1 respiratory failure?

Answer 13

-PaO2 decreases(Hypoxaemia)
-PaCO2 remains normal

Question 14

What are examples of type 1 respiratory failyre?

Answer 14

Pneumonia, ARDS, pulmonary
embolism

Question 15

What is the cause of type 2 respiratory failure?

Answer 15

↓ ventilation
(↓ movement of air between
atmosphere & alveoli)

Question 16

What happens to the levels of PaO2 and PaCO2 in type 2 respiratory failure?

Answer 16

-PaO2 decreases(Hypoxaemia)
-PaCO2 increases(hypercapnia)

Question 17

What are clinical examples of type 2 respiratory failures?

Answer 17

Asthma, COPD, cystic fibrosis

Question 18

what happens in an asthma attack?

Answer 18

1. Reduced rate of ventilation
   due to constricted airways
   2.If ventilation is
   inadequate, alveolar CO2
   will increase, O2 will
   decrease, which then
   impacts on pressure
   gradients between alveoli
   and blood.
   3.Reduced gas exchange
   between alveoli & blood.

Question 19

What is the equation for alveolar ventilation(Valv)?

Answer 19

VAlv (Alveolar ventilation) = (VTidal – VDeadspace) x breathing frequency

Question 20

What is ventilation in type 1 respiratory failure effective against but also less effective against?

Answer 20

the compensatory increase in ventilation is typically effective at
eliminating excess CO2, it is much less effective at increasing blood oxygenation (i.e.
resolving hypoxaemia)

Question 21

What happens in atelectasis with increased ventilation

Answer 21

1.Increased ventilation of
functional lung supplies
additional O2 to alveoli and
removes additional CO2
2.Additional ventilation has
little/no impact on blood
perfusing dysfunctional lung
3.By the time blood perfusing different lungs mixes
together again, hypoxaemia remains.

Question 22

Why does the hypoxaemia remain in type 1 respiratory failure?

Answer 22

-Transport of O2 relies on Hb, of which there is a finite amount
-Transport of CO2 relies less on Hb and is determined by partial pressure gradient, hence why CO2 level is impacted by changes in ventilation