In upper airway obstruction, all of the following changes are seen except
**Core Concept**
Upper airway obstruction can lead to a range of physiological changes due to the increased resistance to airflow. The body's response to this obstruction involves the activation of various reflexes and physiological pathways to maintain adequate ventilation.
**Why the Correct Answer is Right**
In upper airway obstruction, the body attempts to compensate for the decreased airflow by increasing respiratory rate and depth. This results in an increase in negative intrathoracic pressure, which activates the Hering-Breuer inflation reflex. The Hering-Breuer inflation reflex inhibits further inspiration, leading to an increase in expiratory effort and a decrease in lung volumes. The increase in negative intrathoracic pressure also leads to an increase in venous return to the heart, causing a decrease in systemic vascular resistance and an increase in cardiac output.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a characteristic change seen in upper airway obstruction. In fact, the opposite is true: upper airway obstruction typically leads to a decrease in arterial oxygen saturation due to the increased dead space ventilation and decreased ventilation-perfusion ratio.
**Option B:** This option is incorrect because it is not a direct consequence of upper airway obstruction. While respiratory acidosis can occur in severe cases of upper airway obstruction, it is not a characteristic change seen in the early stages of obstruction.
**Option C:** This option is incorrect because it is not a typical response to upper airway obstruction. In fact, the body's response to upper airway obstruction is to increase respiratory rate and depth, not to decrease it.
**Clinical Pearl / High-Yield Fact**
A key clinical feature of upper airway obstruction is the presence of stridor, which is a high-pitched sound heard during inspiration. Stridor is caused by the turbulent airflow through the narrowed airway, and its presence can indicate a severe obstruction that requires immediate medical attention.
**Correct Answer: A. Decrease in arterial oxygen saturation. Decrease in arterial oxygen saturation.**