Question

Suzy is a 14 year old with pulmonary fibrosis. This disease causes progressive scarring of the lungs and therefore, reduced inspiratory volumes and chronic hypoxemia. Suzy is very inquisitive. Due to her disease, she knows that when she breathes in, her lungs help to bring oxygen into her blood, and when she breathes out, she gets rid of carbon dioxide from her blood. At her appointment today, you note that she has cyanosis (blue coloration) and clubbing in her fingers and toes – symptoms of hypoxemia. When Suzy asks why her fingers and toes look the way they do, you tell her that she is not getting enough oxygen to them. This answer does not satisfy Suzy! She then asks:

1. “How EXACTLY does oxygen get into my blood and carbon dioxide get out of my blood when I breathe?” (How do I oxygenate my blood?)

2. “And how does the oxygen get from my blood into my toes and fingers so they won’t turn blue?” (How do I oxygenate my tissues?)

Be thorough (or Suzy will just keep asking “how…why?” She is annoying like that!)

For both 1 and 2: Be sure you describe the events in the correct sequence. Your answer should include the how each gas’s partial pressure affects its diffusion, and the chemical reactions that occur within the blood during gas exchange.

3. Concerned, the doctor asks you to determine Suzy’s inspiratory reserve volume (IRV). Using a spirometer, you measure her tidal volume (TV) at 100 mL, expiatory reserve volume (ERV) at 800 mL, and her vital capacity (VC) at 1100 mL. What is her inspiratory reserve volume?

4. Finally, you treat Suzy by giving oxygen via a mask. Explain why this would be helpful in oxygenating her blood even though her inspiratory volumes are reduced.

Answer 1

1. Inhalation is the process of taking oxygen from atmospheric air. When the diaphragm contracts it pulls the ribs upward which increases the thoracic volume and the pressure decreases.  let the air rushes into the lungs to the areaof decreased pressure. During expiration, relaxation of diaphragm decreases the volume of thoracic cavity and the pressure within increases pushes the air out of lungs. Inhaled oxygen passess across the thing lining of tiny air sacs called alveoli into the blood via passive diffusion.These diffused oxygen molecules are carried in blood via a special protein called hemoglobin and supplied to every cell and removes carbondi oxide from blood.

2. The arteries branches off into minor capillaries through which the blood along with oxygen and other nutrients are supplied. The hemoglobin's affinity for oxygen is better explained by oxygen-dissociation curve. When the  partial pressure of oxygen decreases, dissociation of oxygen occur as the affinity decreases at the tissue level. Therefore, highly active muscle tissues lowers the  partial pressure of oxygen to about 20 mm Hg which enable rapid dissociation of oxygen at specific tissues which are further utilized to produce ATP.

3. Tidal volume (TV) = 100 mL

Expiratory reserve volume (ERV) =  800 mL

Vital capacity (VC) =  1100 mL.

IRV= VC - Vt - ERV.

IRV = 1100 -100-800 = 200mL

Suzy’s inspiratory reserve volume (IRV) is 200mL.

4. Inspiratory reserve volume is the the maximal additional volume that can be inhaled from after the inspiration of a normal tidal volume. Lower IRV impair the efficient supply of oxygen which can be externaly suppliemented in a portable tank to cope up witht he oxygen demand. It assist the total ventilatory requirement unaffected by the pattern of ventilation. Oxygen mask helps to transfer breathing oxygen gas from a storage tank to the lungs.