CO2 & control of respiration Flashcards
(Pa)CO2
partial pressure of arterial carbon dioxide
(PA)CO2
partial pressure of alveolar carbon dioxide
is PAO2 < or > PaO2?
why?
>
to maintain driving force for O2 uptake
compare PaCO2 to PACO2
why?
they are approximate
as some build of of CO2 in the blood is necessary for regulation of pH
how is CO2 carried in the blood?
as H+ in plasma (10%) - produced by the reaction of CO2 with water
reacts with water to form HCO3- (80%)
reacts with globin to form carbamino haemoglobin (10%)
what is the primary drive in control of breathing
PaCO2
why is hypoxic drive not relied on in the control of breathing?
can be problematic and cause symptoms of hypoxia
mild symptoms of hypoxia
poor judgement
decline in cognition
uncoordinated movement
symptoms of severe hypoxia
complete unawareness and unresponsiveness
pupils do not react to light
respiratory failure
how does breath holding affect PaCO2?
it will increase
what is CO used to measure in lung experiments?
measure the transfer factor
what is He used to measure in lung experiments?
residual volume
what effect does pulmonary fibrosis have on PaO2 and PaCO2?
why?
results in decreased PaO2 (hypoxia) and increased PaCO2 (hypercapnia)
walls of the alveoli are thickened .˙. less O2 diffuses into the capillaries and less CO2 diffuses out
what effect does emphysema have on PaO2 and PaCO2?
why?
decreased PaO2 (hypoxia) and increased PaCO2 (hypercapnia) as less surface area available for sufficient diffusion of gases
what is the hypercapnic drive?
respiration rates driven by PaCO2 levels
why can O2 therapy be potentially dangerous?
can cause increased PaCO2 and subsequently acidoses (which disturbs normal function of systems in the body including neurological and cardiovascular)
what three mechanisms can increase PaCO2?
1- Ventilation/perfusion mis-matching
2- Loss of respiratory homeostasis
3- The Haldane effect
explain ventilation perfusion mismatching
supplemental O2 abolishes vasoconstriction of blood supply to under ventilated alveoi, leading to poor ventilation/perfusion matching reducing the amount of CO2 eliminated from the system
explain the Haldane effect
CO2 competes with O2 for carriage on deoxyhaemoglobin. Increasing the amount of O2 in the blood by administering supplemental O2 reduces the amount of deoxyhaemoglobin, and thus reduces the capacity of blood to carry CO2 resulting in more CO2 being carried in the plasma
explain the danger of loss of respiratory homeostasis
in healthy individuals, the hypercapnic drive causes an increase in the drive to breathe. However, in some patients with COPD, this response has been blunted, leaving hypoxic drive as the main stimulus for respiration. Giving supplemental O2 reduces the hypoxic drive, respiration rate may slow (hypoventilation), allowing CO2 to accumulate in the body
