Ventilation and Perfusion Flashcards
Define tidal volume
Amount of air flowing through airways during inspiration and expiration (can change decreasing at rest and increase during activity
Define inspiratory reserve volume (IRV)
Maximum volume of air inhaled at inspiration
Define expiratory reserve volume (ERV)
Maximum volume of air exhaled during expiration
Define residual volume
The amount of air that remains in the airways after exhaling
Define inspiratory capacity
The maximum amount of air that can be inhaled after reaching end of normal expiration
Define vital capacity
The greatest volume of air that can be expelled from the lung after taking the deepest possible breath
Define Functional residual capacity (FRC)
Volume of air present in the lungs at the end of passive expiration
Define the total lung capacity (TLC)
Maximum volume of gas in the lungs after maximal inhalation
Define respiritory rate (f)
Number of breaths taken per minute
Define minute ventilation (VE) and outline its calculation
The volume of air inspired or expired per minute
Tidal volume x Frequency of breathing
Define dead space (VD) and outline its calculation
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
Define alveolar ventilation (VA) and outline its calculation
The amount of fresh gas getting to the alveoli
(tidal volume - dead space) x Respiritory frequency
Explain how ventilation is regulated
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
Describe mechanisms that limit ventilation regionally
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
Describe mechanisms that limit ventilation globally
Resistance to flow in the airways
Lung compliance
Alveolar surface tension
Explain what pulmonary perfusion is
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
Outline how ventilation and perfusion are linked
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
Explain how perfusion of the lung is affected by cardiac function
- Congenital heart defects
- Hypovolemia
- Pulmonary oedema
- Hypovolemia
lead to poor blood flow to the lungs for oxygenation so will have a higher ratio of Q
Explain how perfusion of the lung is affected by lung disease
- 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
Explain how perfusion of the lung is affected by posture
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
Describe the effects of ventilation perfusion mismatching in animals
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
Why might a ventilation/perfusion mismatch occur when you are carrying out abdominal surgery on an animal such as a horse?
Horse will be in dorsal recumbancy were the lungs are compressed by abdominal organs, making it more difficult for blood flow through the lungs
