Question

Ms. Y has suddenly experienced a substantial loss of endurance capacity. Six months ago, she was a good runner and swimmer, capable of exercising for hours, yet now she can only exercise for a few minutes before tiring.

As the local physiology expert, you are called in to help the M.D. diagnose the problem.

Her red blood cell count and hemoglobin levels are normal. What problems do these results eliminate? 1 pt

Heart rate is normal at rest, but goes to a very high level (near 200 beats per min) even with mild exercise.

First, you must determine whether the primary problem is with the respiratory system or the cardiovascular system.

You measure arterial P_O2, arterial hemoglobin per cent saturation, and arterial P_CO2.

If the problem is with the respiratory system, what should the numbers be for these parameters? (2 pts)

Arterial P_O2

Hemoglobin percent saturation:

arterial P_CO2:

Explain why. 1 pt.

If the problem is with the cardiovascular system (such as anemia or a weak left ventricle), what should the numbers be for these parameters? Explain why (2 pts)

Arterial P_O2:

arterial hemoglobin percent saturation:

arterial P_CO2:

Explain why.

Suppose you determine that the problem is with the respiratory system.

Your next goal is to determine whether the problem is with alveolar ventilation (getting fresh air to the alveoli, as can occur with asthma) or diffusion (getting oxygen from alveoli to blood, as can occur with pulmonary edema). Assume you can measure oxygen (P_O2) in the exhaled air, the alveoli, and the arterial blood.

How should these P_O2 values compare to normal if the problem is inadequate alveolar ventilation? (3 pts)

exhaled P_O2?

alveolar P_O2?

arterial P_O2?

Explain why .

How should these P_O2 values compare to normal if the problem is a poor alveolar diffusing capacity? (2 pts)

exhaled P_O2?

alveolar P_O2?

arterial P_O2?

Explain why.

Answer 1

Since her red blood cells and hemoglobin count is normal , she is not anemic.

If the problem is with the respiratory system, arterial O2 and hemoglobin saturation will be less and CO2 will be more. Since the victim is not able to exercise after a few minutes, less O2 or arterial Hb saturation may be the cause where due to insufficient supply of O2 or Hb ,the energy available for exercise is less.

PO2 = < 75 torr.

PCO2= > 45 torr

Hb saturation < 94%

If the problem is with weak left ventricle or anemia, the values of PO2 and Hb % age will be low. PO2 will be less than 72 torr and Hb % will be <85%.

Reason: If the left ventricle is weak then the arterial blood from the left ventricle due to lack of sufficient pressure or force wont reach all the tissues where O2 is needed. In that case fatigue will result instantly. More over, an anemic person due to lesser RBCs or Less Hb will lack O2 carrying capacity,

For inadequate alveolar ventilation

exhaled PO2 will be slightly less, arterial PO2 and alveolar PO2 will decrease significantly.

Inadequate ventilation refers to airway obstruction or inadequate effort. In both these cases insufficient oxygen will reach and thus diffusion will be less.

Alveolar diffusing capacity:

In case the person is assumed to have asthma, diffusion capacity values do not undergo significant changes.If the victim has emphysema, diffusion capacity will decrease. It is due to the available surface area which gets decreased when emphysema is the cause . a reduction in the surface area reduces the rate of diffusion.