**Question:** In upper airway obstruction all of the following changes are seen except

A. Increased resting lung volume
B. Increased respiratory rate
C. Hypoxia
D. Hypercarbia

**Core Concept:**
Upper airway obstruction is a condition where the airway is obstructed at or above the level of the larynx, leading to alterations in respiratory mechanics and gas exchange. These changes manifest as altered respiratory parameters and systemic effects.

**Why the Correct Answer is Right:**
The correct answer is "Increased resting lung volume." In upper airway obstruction, the primary mechanism is the restriction of air flow. As a result, the respiratory system attempts to compensate by increasing tidal volume (VT) and decreasing respiratory rate (RR) to maintain oxygenation and carbon dioxide removal. However, increased resting lung volume is not a typical response and does not occur in upper airway obstruction.

**Why Each Wrong Option is Incorrect:**
A. **Increased respiratory rate (RR)**: In upper airway obstruction, the respiratory system tries to compensate for the reduced airflow by increasing tidal volume (VT) and decreasing respiratory rate (RR) to maintain oxygenation and carbon dioxide removal.

B. **Hypoxia**: Hypoxia usually occurs when oxygen supply to tissues is inadequate, and this is not the primary outcome of upper airway obstruction, which primarily affects airflow.

C. **Hypercarbia**: Hypercarbia results from impaired carbon dioxide removal due to decreased tidal volume (VT) and/or increased respiratory rate (RR). This is not the primary outcome of upper airway obstruction, which affects airflow.

D. **Decreased respiratory rate (RR)**: In upper airway obstruction, the respiratory system tries to compensate for the reduced airflow by increasing tidal volume (VT) and decreasing respiratory rate (RR) to maintain oxygenation and carbon dioxide removal.

**Clinical Pearl:**
In clinical practice, understanding the compensatory mechanisms of the respiratory system helps in recognizing and managing respiratory disorders effectively. Adequate assessment of respiratory rate, tidal volume, and other clinical signs can guide appropriate treatment strategies. Atypical findings like decreased respiratory rate should prompt a thorough evaluation of the respiratory system to identify the underlying cause.