During exercise, both QO2 and QCO2 increases as well as cardiac output, Qa. Supp
ID: 3515311 • Letter: D
Question
During exercise, both QO2 and QCO2 increases as well as cardiac output, Qa. Suppose that during exercise QO2 increases to 2000 mL/min and the respiratory quotient remains at 0.8, and that Qa increases to 18 L/min. Assume that PaO2 remains at 95 mmHg, that O2 saturation is at 98% and PaO2 is 40 mmHg and that blood [Hb] = 15 g %. A. What is the total arterial content of O2? B. What is the venous content of O2? C. What is the QCO2? D. Determine the new alveolar ventilation from the alveolar ventilation equation.
Explanation / Answer
ANSWER:
QO2 during exercise is 20L/min
RESPIRATORY QUOTIENT IS 0.8
CARDIAC OUTPUT Qa is 18L/min
PaO2 is 95 mmHg
O2 SATURATION IS 98%
PaO2 OF BLOOD IS 40 mmHg
HAEMOGLOBIN IS 15g %
Then the total arterial content of O2 is
The number of ml of oxygen carried in each 100 ml of blood in combination with Hb depends on the Hb concentration.Each Hb can combine with 1.34 ml of O2.
So the arterial content of O2 is = 1.34 ml(15 g%)
A. Arterial content of O2 is = 20.1ml of oxygen / 100 ml of blood
that is equal to 20.1 volume %
The Hb in systemic arterial blood is about 98% saturated with oxygen which is equal to 20.1% of volume carried by Hb.
When the blood passes through the systemic capillaries , it is the dissolved oxygen that diffuses to the tissues.
If dissolved oxygen decreases PO2 also decreases and there is less force to keep oxygen attached to Hb.
Oxygen comes off Hb and dissolves in the plasma to maintain the flow of oxygen to the tissues.
C.QCO2
Carbondioxide is 24 times more soluble in blood than oxygen.
The blood PCO2 is between 40mmHg and 47 mmHg .
About 5% of the total CO2 is carried as carbamino compounds.
Qa is 18L/min
QCO2 is 5% of it is = 90L/min
D. ALVEOLAR VENTILATION: The alveolar ventilation is driven mainly from the input of specific chemoreceptors to the central nervous system.
The stronger the stimulation of these receptors ,the greater the level of alveolar ventilation.
Chemoreceptors monitor the chemical composition of the body fluids.
There are receptors that respong to pH, PCO2 and PO2
The receptors are of two types
1.CENTRAL CHEMORECEPTORS
2.PERIPHERAL CHEMORECEPTORS
In a healthy quier breathing the man inspires and expires about 500ml of air.
150ml of air merely fills the conducting air passages between mouth and nose and the respiratory bronchioles.
The remainder effectively ventilates the alveoli thereby lowering the pCO2 and the rising pO2 of the alveoli in the air.
The alveoli still contain some 2-2.5 litres of air after a quiet expiration.
The overall rise of PO2 is 350 ml.
The alveolar ventilated air contains 6% of CO2 and 14% of O2.
Hence the effective alveolar PO2 = inspired O2 X%X N2 EXPIRED AIR/%N2INSPIRED AIR
-ARTERIAL PCO2/EXPIRED RQ
20.1X90-90/0.8
=1809/112.5
The new alveolar ventilation is =16.8 L/min.
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