physiology Flashcards
how is your pattern of breathing determined?
want to minimise your total work of breathing for a given minute ventilation
total WOB = elastic + resistive WOB
if you have elastic forces to overcome -work decreases with increased frequency of breathing
- faster, shallow breaths
if you have resistive forces to overcome (airflow obstruction) - work decreases with decreased frequency of breathing
- slower, deeper breaths
what is the main stimulus for ventilation?
what else stimulates
main - CO2 - strong stimulant (small change co2 - rapid change ventilation)
other: oxygen - but large fall is needed
how much do you have to drop pO2 to to see any change in ventilation?
<60mmHg (normal 80-100)
What happens to minute ventilation as metabolic activity changes
what happens to paO2, paCO2, pH
as metabolic activity changes, minute ventilation rises linearly - is matched to O2 consumption and CO2 prodution
paO2, paCO2 and pH remain constant - because ventilation is matched
What happens to minute ventilation in metabolic acidosis
what happens to paO2, paCO2, pH
minute ventilation»_space; O2 consumption and CO2 production (because we want to correct the acidosis)
paO2 rises
paCO2 falls
so that pH returns to just below normal
What happens to minute ventilation with exercise
what happens to paO2, paCO2, pH
minute ventilation is matched to O2 consumption, CO2 and H+ production
ventilation increases with work to keep paO2 and paCO2 steady
after the anaerobic threshold - start producing lactic acid -> extra H+
so there is a relative increase in minute ventilation (steeper curve)
paO2 will remain constant, as do paCO2 and pH initially
after threshold, have decrease in paCO2 and pH
What happens to minute ventilation as with anxiety
what happens to paO2, paCO2, pH
minute ventilation is excessive for O2 consumption/CO2 production
-> get a respiratory alkalosis
pao2 increases, paco2 decreases, ph increases
