Respiratory Physiology IV Flashcards
How does the oxygen partial pressure change as you move from air entering the main bronchi to the partial pressure of oxygen in the blood at the tissues?
It decreases considerably.
What does Henry’s Law state?
The amount of a given gas dissolved in a given type and volume of liquid (e.g. blood) at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid.
What happens to the concentration of gas in the liquid phase if the partial pressure in the gas phase is increased?
It increases proportionally.
What does the partial pressure of a gas in solution mean?
The partial pressure of a gas in solution is its partial pressure in the gas mixture with which it is in equilibrium.
What does Henry’s Law mean for the amount of oxygen dissolved in the blood?
It is proportional to the partial pressure of oxygen.
Is the amount of oxygen dissolved in blood alone enough to meet the resting oxygen consumption of our body?
No, only 1.5% of the total blood oxygen concentration is dissolved in the blood.
What is the value for normal oxygen concentration in arterial blood and what is the normal haemoglobin (Hb) concentration?
200 ml/L oxygen concentration.
150 g/L haemoglobin (Hb) concentration.
How do the percentages of oxygen carried bound to haemoglobin and in the dissolved form compare?
Bound to haemoglobin - 98.5%.
Dissolved in blood - 1.5%.
How many haem groups are in each haemoglobin molecule and how many oxygen molecules can each group bind?
Four haem groups per molecule.
Each can bind one molecule of oxygen.
When is haemoglobin considered fully saturated?
When all four haem groups are bound to a molecule of oxygen.
What is the primary factor which determines the percentage saturation of haemoglobin?
The partial pressure of oxygen.
Describe the structure of haemoglobin.
Four sub-units (haem groups): two beta and two alpha chains.
Each haem group contains an iron ion which binds to an oxygen molecule.
Describe the shape of the oxygen-haemoglobin dissociation curve.
“Sigmoid curve.”
Initial increase in % saturation is slow but then this increase gets greater.
Slowly begins to tail off to a plateau.
How does oxygen concentration of the blood change as haemoglobin concentration is changed? Why is this?
An increase in haemoglobin concentration results in a large increase in blood oxygen concentration.
A decrease in haemoglobin concentration results in a large decrease in blood oxygen concentration.
This is due to the majority of oxygen in the blood being bound to haemoglobin (98.5%) so its concentration has a great influence on oxygen concentration.
What is the formula to calculate the oxygen delivery index, DO2I?
DO2I = CaO2 x CI.
where CaO2 = oxygen content of arterial blood (ml/L);
CI = cardiac index (L/min/m^2).
What does the cardiac index do?
Relates the cardiac output to the surface area of the body (i.e. size of the individual).
(Normal range = 2.4 - 4.2 L/min/m^2.)
What is the formula to calculate the oxygen content of arterial blood, CAO2?
CaO2 = 1.34 x [Hb] x SaO2.
where 1.34 is the amount of oxygen in ml one gram of haemoglobin can carry when fully saturated;
[Hb] = haemoglobin concentration in gram/L;
SaO2 = %Hb saturated with oxygen.
What three factors can impair oxygen delivery to the tissues?
- Respiratory disease.
- Heart failure.
- Anaemia.
What two factors does the partial pressure of inspired oxygen depend upon?
- Total pressure (i.e. atmospheric pressure).
2. Proportion of oxygen in the gas mixture (~21% in the atmosphere).
Why does decreased partial pressure of inspired oxygen/respiratory disease reduce oxygen delivery to the tissues?
These can both decrease arterial PO2 and hence decrease Hb saturation with oxygen as well as dissolved oxygen in the blood.
Why does anaemia reduce oxygen delivery to the tissues?
Anaemia decreases the Hb concentration of the blood and hence decreases the oxygen content of the blood.
Why does heart failure reduce oxygen delivery to the tissues?
Heart failure decreases cardiac output.
What occurs when one oxygen binds to a haem group of a haemoglobin molecule? What significance does this have for the oxygen-haemoglobin dissociation curve?
The haemoglobin’s affinity for further oxygen binding increases.
The curve is therefore sigmoid as initially binding of oxygen is slower but then the affinity increases with more oxygen binding.
It also flattens as the partial pressure of oxygen further increases as all sites are becoming occupied.
What is the physiological significance of the flat upper portion of the oxygen-haemoglobin dissociation curve?
This means that a moderate fall in alveolar partial pressure of oxygen will not greatly diminish oxygen loading of haemoglobin.
