## **Core Concept**
Obstructive sleep apnea (OSA) is a sleep disorder characterized by repeated episodes of partial or complete upper airway obstruction during sleep, leading to reduced airflow (hypopnea) or complete airflow cessation (apnea). The apnea-hypopnea index (AHI) is a critical measure used to quantify the severity of OSA, calculated as the total number of apneas and hypopneas per hour of sleep.

## **Why the Correct Answer is Right**
The severity of obstructive sleep apnea is categorized based on the apnea-hypopnea index (AHI) as follows: mild OSA (AHI 5-14), moderate OSA (AHI 15-29), and severe OSA (AHI ≥ 30). Therefore, an AHI of greater than 29 indicates severe obstructive sleep apnea. This classification is crucial for determining the appropriate treatment and management plan for patients.

## **Why Each Wrong Option is Incorrect**
- **Option A:** An AHI of 5-14 indicates mild OSA, not severe.
- **Option B:** An AHI of 15-29 indicates moderate OSA, not severe.
- **Option D:** While an AHI of 30 or greater does indicate severe OSA, the question asks which option correctly represents an AHI greater than a certain value for severe OSA, making this option less directly responsive to the question's phrasing compared to option C.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that patients with severe OSA (AHI ≥ 30) are at a higher risk for complications such as cardiovascular disease, stroke, and nocturnal hypoxemia. These patients often require more aggressive treatment, including continuous positive airway pressure (CPAP) therapy, and lifestyle modifications.

## **Correct Answer:** C. 30.