National Registry of Certified Medical Examiners (NRCME) DOT Practice Exam

The correct answer is based on the importance of arterial blood oxygen levels in determining a driver's fitness for duty, especially in the context of chronic respiratory disorders exacerbated by smoking. A PaO2 (partial pressure of oxygen in arterial blood) of less than 70 mm Hg indicates significant hypoxemia, which can impair a person's ability to function properly while driving. Therefore, maintaining a PaO2 above this threshold is critical for ensuring that the driver has adequate oxygenation, which is essential for safe operation of a commercial vehicle. In contrast, a PaO2 of less than 60 mm Hg, indicative of more severe respiratory compromise, poses a greater risk and would not meet the standards for certification. Evidence of smoking cessation is definitely important for long-term health and management of respiratory conditions, but it is not the singular critical factor for immediate certification. Improvement in symptoms would also be relevant, but the immediate focus is on ensuring stable and adequate oxygen levels that demonstrate safety for driving responsibilities. Thus, the emphasis on the specific PaO2 threshold aligns with the medical standards for commercial driver certification concerning respiratory disorders.