measurements of ventilation
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define tidal volume
volume of gas moved into or out of the lungs during a normal breath
What is the VT of a healthy adult?
500ms (7ml/kg)
Define respiratory rate?
number of breaths taken per minute
What is the normal adult respiratory rate?
-between 12-20 breaths per minuete
What factors affect respiratory rate?
-excersise -emotion -injury
What clinical factos increase RR?
-fever -dehydration -anxiety -respiratory disease -heart disease
What clinical factors decrease RR?
-head injury -narcotic overdose -sleep apnoea
What is minute ventilation?
the total volume of air which the lung exchanges with the outside
What are the units of minute ventilation?
ml/min
What is the equation for minute ventilation?
tidal volume x respiratory rate
What is normal minute ventilation?
5-9 litres/min
What is dead space ventilation?
due to the lungs structure some air inspired in each breath remains in the conducting airway and never reaches the gas exchange areas
Define alveolar ventilation
the volume of air/min which reaches the gas exchange regions
What is the relationship between minute ventilation, dead space ventilation and alveolar ventialtion?
minute ventilation = dead space ventilation + alveolar ventilation
Describe dead space in the lungs
-divided into anatomic deadspace (air in conducting airways) -alveolar deadspace- air within alveoli that are poorly perfused physiological dead space-total dead space
What is the relationship between physiological dead space, anatomic deadspace and alveolar deadspace?
physiological dead space= anatomic deadspace+ alveolar dead space
What is the alveolar ventialtion equation?
VA= (VT-VD) x RRml/min
what does alveolar ventialtion help determine?
the alveolar partial pressure of carbon dioxide PACO2 and oxygen PAO2
What is PAO2?
partial pressusre of xygen in alveoli
What is PaO2?
parital pressure of oxygen in arterial blood
What is PvO2?
partial pressure of oxygen in venous blood
What is PACO2, PaCO2 and PCO2
PACO2-partial pressure of co2 in alveoli -PaCO2-partial pressure of co2 in arterial blood -PCO2-partial pressure of carbon dioxide
What is the actual equation for alveolar ventilation?
VA= VCO2/PaCO2 ml/min
describe what happnes during hypoventilation
-a reduction in ventilation causes an increase in pp of CO2 in arterial blood -reduction in ventilation -hypercapnia -acidosis would occur due to carbonic acid formation