Ventilation and Perfusion

Question 1

Define tidal volume

Answer 1

Amount of air flowing through airways during inspiration and expiration (can change decreasing at rest and increase during activity

Question 2

Define inspiratory reserve volume (IRV)

Answer 2

Maximum volume of air inhaled at inspiration

Question 3

Define expiratory reserve volume (ERV)

Answer 3

Maximum volume of air exhaled during expiration

Question 4

Define residual volume

Answer 4

The amount of air that remains in the airways after exhaling

Question 5

Define inspiratory capacity

Answer 5

The maximum amount of air that can be inhaled after reaching end of normal expiration

Question 6

Define vital capacity

Answer 6

The greatest volume of air that can be expelled from the lung after taking the deepest possible breath

Question 7

Define Functional residual capacity (FRC)

Answer 7

Volume of air present in the lungs at the end of passive expiration

Question 8

Define the total lung capacity (TLC)

Answer 8

Maximum volume of gas in the lungs after maximal inhalation

Question 9

Define respiritory rate (f)

Answer 9

Number of breaths taken per minute

Question 10

Define minute ventilation (VE) and outline its calculation

Answer 10

The volume of air inspired or expired per minute

Tidal volume x Frequency of breathing

Question 11

Define dead space (VD) and outline its calculation

Answer 11

Dead space represents the volume of ventilated air that does not participate in gas exchange.

The two types of dead space are anatomical dead space and physiologic dead space.

          Anatomical dead space is represented by the volume of air that fills the conducting zone of 
          respiration made up by the nose, trachea, and bronchi. 

          Alveolar dead space counts for the alveoli incapable of gas exchange (negligible in the healthy 
           animal)
          
          Physiologic or total dead space is equal to anatomic plus alveolar dead space 

Dead space volume x frequency of breathing

Question 12

Define alveolar ventilation (VA) and outline its calculation

Answer 12

The amount of fresh gas getting to the alveoli

(tidal volume - dead space) x Respiritory frequency

Question 13

Explain how ventilation is regulated

Answer 13

Lungs provide O2 and remove CO2

Respiratory centre in the brain stem, the medulla generates action potentials, modulated by feedback from

- Chemoreceptors (detection of arterial gas levels)
- Mechanoreceptors (e.g. stretch receptors)

Respiratory muscles contract, thoracic cavity expands

Question 14

Describe mechanisms that limit ventilation regionally

Answer 14

Lower portions of the lung are ventilated more than the upper zones

Intra-pleural pressure is higher (less negative) at the bottom (base) of the lung than at the top (apex) due to the weight of the fluid.

Lung easier to inflate at low volumes than at high volumes (becomes stiffer). Resting lung volume at base small so expands well on inspiration

Question 15

Describe mechanisms that limit ventilation globally

Answer 15

Resistance to flow in the airways

Lung compliance

Alveolar surface tension

Question 16

Explain what pulmonary perfusion is

Answer 16

Blood flow to the alveoli allowing uptake of oxygen and removal of CO2
Anything that affects blood flow to the lungs will affect pulmonary perfusion

Pulmonary Circulation
- Right Ventricle
- Deoxygenated blood via pulmonary artery
- Oxygenated blood via pulmonary vein

Systemic Circulation
- Left Ventricle
- Oxygenated blood to rest of body organs

Question 17

Outline how ventilation and perfusion are linked

Answer 17

Optimal gas exchange in the lungs requires appropriate ratio between ventilation and blood flow in each alveolus

So ratio (V/Q) should ideally be 1

Ventilation/perfusion mismatch – disturbance in O2 supply and blood supply to alveoli

Question 18

Explain how perfusion of the lung is affected by cardiac function

Answer 18

• Congenital heart defects
  
  • Hypovolemia
    
    • Pulmonary oedema

lead to poor blood flow to the lungs for oxygenation so will have a higher ratio of Q

Question 19

Explain how perfusion of the lung is affected by lung disease

Answer 19

• Asthma,
• Pneumonia
• Mountain Sickness/Brisket Disease
  Happen at altitude

lead to poorer ventilation of blood due to insufficient supply of oxygen lower ratio of VA

Question 20

Explain how perfusion of the lung is affected by posture

Answer 20

V/Q less at base of lung – more blood flow than ventilation

V/Q higher at apex – more ventilation than blood flow

With exercise – V/Q more even throughout lungs

Question 21

Describe the effects of ventilation perfusion mismatching in animals

Answer 21

Mountain sickness:
Animals kept at high altitude where reduced O2 avaible in atmosphere. Compensatory mechanism will happen all over the lungs . So arteriole constriction throughout lungs which can lead to pulmonary hypertension.

-lead to other issues such as with the heart

Question 22

Why might a ventilation/perfusion mismatch occur when you are carrying out abdominal surgery on an animal such as a horse?

Answer 22

Horse will be in dorsal recumbancy were the lungs are compressed by abdominal organs, making it more difficult for blood flow through the lungs