Week 7 - Respiration during exercise (p3) Flashcards
What is Dalton’s law?
total pressure of a gas mixture is equal to the sum of the pressure that each gas would exert independently
How is the partial pressure of a gas worked out?
fraction of gas within air x barometric pressure (x 750mmHg at sea level)
Oxygen 159 mmHg
Carbon dioxide 0.3 mmHg
Nitrogen 600.7 mmHg
(Inspired air)
Identify the difference between arterial partial pressure of oxygen and alveolar partial pressure of oxygen.
Arterial PO2 (100mmHg) is slightly less than alveolar PO2 (105mmHg) due to a very small gas exchange impairment.
Identify the difference between arterial PCO2 and alveolar PCO2.
both 40mm Hg
At rest, what is PO2 and PCO2 in deoxygenated blood?
PO2 40mmHg
PCO2 46mmHg
Venous PO2 is decreases whereas venous PCO2 is increases as tissues consume oxygen but produce CO2.
What happens to partial pressure of O2 and CO2 in the alveolar when inspired?
PO2 decreases to 105mmHg (from 159)
PCO2 increases to 40mmHg (from 0.3)
What are the four steps of pulmonary circulation?
- Pulmonary artery carries deoxygenated blood from
the right ventricle to the lungs - Gas exchange between the alveoli and pulmonary
capillaries occurs - Oxygenated blood is returned to the left atrium via
the pulmonary vein - Oxygenated blood is pumped around the systemic
circulation to systemic cells
What is the pressure and resistance of the pulmonary circuit like?
low pressure, low resistance
mean pulmonary artery pressure is 15mmHg
What is the mean pulmonary artery pressure compared to systemic arterial pressure?
15mmHg compared to 100mmHg
Why is the pulmonary circulation low resistance?
its thin walled and has little smooth muscle - this is it accepts the entire cardiac output so it doesn’t need to redistribute the blood.
During exercise, what happens to pulmonary vascular resistance?
decreases due to recruitment and distension (enlarge) of pulmonary capillaries which increases flow and decreases resistance
What does gas exchange require a matching of?
Ventilation to blood flow (V/Q)
- The ideal V/Q is 1
- V/Q > 1 = under perfused (apex of lung)
- V/Q < 1 = over perfused (base of lung)
Upon exercise, why does V/Q improve?
o Increased tidal volume
o Increased pulmonary artery pressures
In some cases, V/Q worsens, especially during heavy exercise
What are the two forms in which oxygen is carried in the blood?
- Dissolved into plasma (2%)
- Bind with haemoglobin (98%)
What is Henry’s law?
the amount of gas dissolved in blood is proportional to the partial pressure of that gas
o The amount of O2 dissolved is 0.003 mL O2/100 mL blood/mmHg.
o At an arterial PO2 of 100 mmHg, this results in 0.003*100=0.3 mL O2/100 mL blood.