ventilation and perfusion Flashcards
what is minute volume
the volume of air inspired or expired per minute
= tidal volume x frequency of breathing
what is dead space ventilation
the portion of the minute ventilation that is not availible for gas exchange
= dead space volume x frequency of breathing
how is ventilation regulated
- lungs provide O2 and remove CO2
- respiratory centre in the brain stem (medulla) coordinates coughing and swalling around breathing
- generates action potentials, modulated by feedback from chemoreceptors (detection of arterial gas levels) and mechanoreceptors (stretch receptors)
- respiratory muscles contract, thoracic cavity expands
what is the anatomical dead space, alveolar dead space and physiological dead space
anatomical dead space: the volume of the conducting airways not availible for gaseous exchange
alveolar dead space: alveoli incapable of gas exchange (negligible in health animals)
physiological dead space: sum of anatomical dead space and alveolar dead space
what is ventilation? describe the sequience of events
circulation of oxygen and co2 in the lungs
total ventilation = tidal volume x respiration frequency
- alveolar ventilation is of key importance and is the amount of fresh gas getting to the alveoli (todal volume - dead space) x resp frequency
what mechanisms limit ventilation regionally
- lower portions of the lung are ventilated more that upper zones
- intra-pleural pressure os higher (less negative) at the bottom of the lung than at the top 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
within respiration, dead space is defined as:
the parts of the lung that do not take place in gaseous exchange
what is pulmonary perfusion
blood flow to the alveoli allowing uptake of oxygen and removal of CO2
- anything that affects blood flow to the lungs affects pulmonary perfusion
how are ventilation and perfusion related
optimal gas exchange in the lungs requires appropriate ratio between ventilation and blood flow in each alveolus
- Va = alveolar ventilation, Q = perfusion, V/Q ratio should ideally be 1
- ventilation/perfusion mismatch = disturbance in O2 supply and blood supply to the alveoli
a P/Q ratio of less than 1 indicates
An issue with ventilation (O2 cant easily come into lungs) but good perfusion (less O2, more CO2)
what does a v/Q ratio of greater than 1 indicate
good ventilation, no perfusion. CO2 cant escape blood
give 3 examples of lung diseases that affect perfusion
- asthma
- pneumonia
- mountain sickness
give 3 examples of cardiac dysfunctions that affect perfusion
- congenital heart defects
- hypovolemia
- pulmonary oedema
describe the compensatory mechanisms of ventilation/perfusion mismatch
hypoxic vasoconstriction:
arterioles constrict due to decrease in O2 and increase in CO2 (poor ventilation = cant take CO2 away=CO2 builds up=more acidic environment =constriction of blood vessels around alveolus) and blood is diverted to areas that are well ventilated (= increased pressure being put on certain blood vessels)
why might a ventilation/perfusion mismatch occur when you are carrying out an abdominal surgery on an animal such as a horse
horse on back => organs of abdominal cavity put pressure on lungs
