ventilation and perfusion Flashcards

1
Q

what is minute volume

A

the volume of air inspired or expired per minute
= tidal volume x frequency of breathing

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2
Q

what is dead space ventilation

A

the portion of the minute ventilation that is not availible for gas exchange
= dead space volume x frequency of breathing

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3
Q

how is ventilation regulated

A
  • 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
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4
Q

what is the anatomical dead space, alveolar dead space and physiological dead space

A

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

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5
Q

what is ventilation? describe the sequience of events

A

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

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6
Q

what mechanisms limit ventilation regionally

A
  • 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
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7
Q

within respiration, dead space is defined as:

A

the parts of the lung that do not take place in gaseous exchange

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8
Q

what is pulmonary perfusion

A

blood flow to the alveoli allowing uptake of oxygen and removal of CO2
- anything that affects blood flow to the lungs affects pulmonary perfusion

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9
Q

how are ventilation and perfusion related

A

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

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10
Q

a P/Q ratio of less than 1 indicates

A

An issue with ventilation (O2 cant easily come into lungs) but good perfusion (less O2, more CO2)

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11
Q

what does a v/Q ratio of greater than 1 indicate

A

good ventilation, no perfusion. CO2 cant escape blood

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12
Q

give 3 examples of lung diseases that affect perfusion

A
  • asthma
  • pneumonia
  • mountain sickness
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13
Q

give 3 examples of cardiac dysfunctions that affect perfusion

A
  • congenital heart defects
  • hypovolemia
  • pulmonary oedema
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14
Q

describe the compensatory mechanisms of ventilation/perfusion mismatch

A

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)

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15
Q

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

A

horse on back => organs of abdominal cavity put pressure on lungs

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