V/Q relationships

Question 1

What do the terms V and Q represent?

Answer 1

v= ventilation - the amount of air that reaches the alveoli

p= perfusion = the amount of air that is actually exchanged

Question 2

are pulmonary ventilation/alveolar ventiation the same?

Answer 2

no, pulmonary ventialtion = tidal volume and respiratory rate

alveolar ventilation = volume of air exchanged between the atmosphere and the alveoli per minute - more important than the amount of air breathed in and out, but less than pulmonary ventilation b/c of anatomic dead space

Question 3

how do we calculate alveolar ventilation?

Answer 3

(tidal volume - dead space)x respiratory rate

Question 4

what are the functions of the pulmonary circulation?

Answer 4

reoxygenate blood and dispose of CO2

Question 5

how does gas exchange occur?

Answer 5

down partial pressure gradients

Question 6

why is the alveolar oxygen partial pressure less than atmospheric?

Answer 6

• Due to dilution
  
  • H20 Vapour present
  • deadspace/old air present
• remains constant
  
  • O2 arriving in alveoli exactly replaces the O2 diffusing out of the alveoli to the pulmonary capillaries (does not accumulate)
    *

Question 7

what is Fick’s Law of diffusion?

Answer 7

the greater the surface area and the shorter the distance, the greater rate of diffusion

Question 8

how do improve gas exchange?

Answer 8

increase the area and reduce the distance

ex) during exercise the area available for exchange can be physiologically increased by opening capillaries , stretching aleolar membranes (decerease thickness of membrane) , and taking deeper breaths = larger tidal volumes

Question 9

what is the implication of emphysema?

Answer 9

reduces the pulmonary surface area by loss of alveolar walls, thus decreasing gas exchange

Question 10

what is the effect of pulmonary oedema on pulmonary gas exchange?

Answer 10

excess accumulation of interstitial fluid increases the alveolar wall thickness - therefore it decreases gas exchange

Question 11

How does lung fibrosis effect gas exchange?

Answer 11

replaces lung tissue with thick fibrotic tissue - increases surface thickness = decreases gas exchange

Question 12

how does pneumonia effect gas exchange?

Answer 12

fluid inside and around the alveoli due to infection increases the wall thickness in alveoli and decreases gas exchange

Question 13

mismatch of ventilation and pulmononary blood flow leads to what?

Answer 13

leads to impaired O2 and CO2 transfer

Question 14

does a normal V/Q ratio indicate a normal ventilation/perfusion?

Answer 14

no

in lobar pneumonia, ventilation is decreased due to liquid in the alveolar and fluid builds up around the alveola decreasing perfusion -

therefore the V/Q ratio is normal, but only b/c both are effected

Question 15

how does the V/Q differ in regions of the lung?

Answer 15

at apex - ventilation is greater than perfusion

at base- perfusion is greater than ventilation

Question 16

Define the following terms

• arterial hypoxemia
• hypoxia
• hypercapnia
• hypocapnia

Answer 16

hypoxemia = partial pressure of oxygen is less than necessary in an adult due to airway obstruction, high altitude, cirrhosis - leads to shunting of the deoxygenated blood past the lungs (low V/Q)

hypoxia = insufficient O2 to carry out metabolic functions- low perfusion but under ventilated

hypercapnia = increase in partial pressure of CO2 above range due to hypoventilation - associated with lung disease

hypocapnia = low partial pressure of CO2 in artery due to hyperventilation - triggered by anxiety or fever -and can cause respiratory alkalosis

Question 17

is the V/Q increased or decreased in respiratory disease?

Answer 17

Either

increased when overventilation but underperfusion = alveolar deasd space and wasted ventilation due to emoblis for example

decreased when underventilated but overperfused= shunting is occuring - due to asthma, bronchitis or obstruction

Question 18

What is hypoxic pulmonary vasoconstriction?

Answer 18

obstruction in the airway leads to relaxation of the airway smooth muscle but contraction of the pulmonary arterioles -

diverts blood waya from poorly ventilated alveoli

if this occurs over a long period of time it can cause pulmonary hypertension

Question 19

Explain how airway obstruction could cause hypoxaemia?

Answer 19

1)Low ventilation = shunting = hypoxaemia

Question 20

what is pulmonary vasodilation?

Answer 20

when a blockage is pressent in the capillaries, relaxes capillaries and contracts alveoli?

Question 21

what is hyperpnea?

Answer 21

increased ventilation that matches increased metabolic demand - during exercise

Question 22

what is shunting?

Answer 22

1)Shunting = deoxygenated blood reaches alveoli – then deoxygenated blood is sent into circulation

Question 23

describe the pulmonary circulation network

Answer 23

• Begins at right atrium – deoxygenated blood enters right ventricle and then onto the lungs via pulmonary arteries.
• Blood passes through a progressively smaller series of branching vessels (arteries>arterioles>capillaries) before ending in a complex mesh-like network of capillaries.
• Oxygenated blood leaves via series of veniolesthat coalesce to form pulmonary veins to return blood to the left artrium