Physiology II
Cardiovascular Case
Respiratory Case D

The Patient: a 21-year-old man

Principal Complaint: none

History: This individual was encountered while he was participating as a subject in a scientific investigation of respiratory function during exercise in high-altitude natives. He has no history of respiratory disease or dyspnea, and has been healthy for as long as he can remember. He works 50-60 hours/week at a physically demanding job and enjoys playing soccer on his days off. He lives in Morococha, Peru, at an elevation of 4,540 m (14,900 ft), where average barometric pressure is 446 mm Hg and the PO2 of inspired air is 84 mm Hg.

Clinical Examination: The patient was a muscular young man in apparent good health with a resting heart rate of 72 beats/min and a blood pressure of 94/64 mm Hg. Respirations were regular at a rate of 17 breaths/min. Analysis of an arterial blood sample yielded the following values: PaO2, 48 mm Hg; PaCO2, 27 mm Hg; bicarbonate, 16.3 mmol/l; hematocrit, 59.5%; hemoglobin, 20.1 gm/dl; arterial percent saturation, 80%. Venous PO2 and percent saturation were 35 mm Hg and 55%, respectively. His P50 was 33 mm Hg. The results of all pulmonary function tests met or exceeded the predicted values for a person of his age, sex, and body size. Measurements of diffusion capacity for carbon monoxide and total pulmonary compliance yielded results within the high normal range.

FIO2

PAO2

PaO2

PaCO2

A-a O2
difference

FIO2
helpful?
84 mmHg
@ pressure 446 mmHg 		50 48 27 2 Yes

STUDY QUESTIONS:

1. Is the patient’s arterial hydrogen ion concentration normal or abnormal? Why or why not? Support your answer with calculations based on data from the REFERENCE CASE.  Normal.  The PCO2 is normal.

2. What sort of compensatory responses are indicated by this patient’s hematocrit and hemoglobin values?  He has a very high Hb and Hct.  This helps move the oxygen dissociation curve up to a larger max.

3. Would an arterial percent saturation of 80% support adequate tissue oxygenation in this individual? What would arterial oxygen content be under these circumstances?  Yes.  A normal oxygen content would be around (16* 1.36 * 0.95)=20.  Notice that in his case it is (Hb * 1.36 * 0.8) = (20.1 * 1.36 * 0.8) = 21.9.  Even at a low PO2, he is able to carry enough O2.

4. What sort of an adaptive response is suggested by this patient’s thoracic structural changes and elevated resting minute ventilation?  He must have a larger lung with more effective breathing muscles.

5. How are the adaptive changes observed in this healthy high-altitude native similar to those seen in a patient with chronic obstructive pulmonary disease?  Increased Hb, Hct and 2,3 DPG.

6. What is this patient’s calculated alveolar PO2 while breathing the rarified air in his home town up in the Andes?  50.  See table above.

Last Updated 04/10/00 12:27:11 PM
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