Case R 3 Respiratory
A healthy college student went to Colorado at the end of the school year for a vacation. While there, he drove to the top of Pike's Peak. During his first hour on the peak, he walked about but had to sit down to rest three times. The last time was in the weather station. He glanced at the barometer and saw it read 450 mm Hg.
The barometric pressure at sea level is 760 mm Hg, and the pressure decreases with increasing altitude. Each gas in the atmosphere is present as the same fraction of the whole regardless of altitude. On Pike's Peak, each gas has a smaller partial pressure than at sea level. Because inspired PO2 is lower at altitudes higher than sea level, alveolar and arterial PO2 will also be lower.
Any change that reduces arterial PO2 (especially to values below about 60 mm Hg) stimulates the peripheral chemoreceptors (carotid and aortic bodies). The resulting reflex increases alveolar ventilation, oxygen delivery to the lungs, and the expiration of carbon dioxide. Other disturbances that lower arterial PO2 also stimulate ventilation via the peripheral chemoreceptors.
Predict that changes (increase, decrease, no change) that would have taken place in each of the listed parameters by the time the student entered the weather station compared with the values that he would have had at home (sea level).
Next, predict the effects (increase, decrease, no change) of the other listed conditions in an otherwise normal individual at sea level. Consider each listed condition independently of the others. Provide a summary (on the reverse) for each condition.
Condition | Alveolar PO2 | Arterial PO2 | Arterial Hb Saturation | Venous Hb Saturation | Tidal Volume | Arterial PCO2 | Arterial pH
---|---|---|---|---|---|---|---
On Pike's Peak | Decrease | Decrease | Decrease | Decrease | increase | decrease | increase
Moderate Exercise | No change | No change | No change | Decrease | increase | No Change | No change
Pneumonia | increase | decrease | decrease | decrease | increase | -/D/I | -/I/d
Partial tracheal obstruction | Decrease | Decrease | Decrease | Decrease | Decrease | increase | Decrease
CNS drug depression | Decrease | Decrease | Decrease | Decrease | Decrease | increase | decrease
Hb is hemoglobin
