Which of the following is a neurological test to assess inner ear functions?

The heel-to-toe test is a neurological assessment that evaluates balance and coordination, which are functions closely tied to the inner ear. The inner ear plays a crucial role in maintaining equilibrium through the vestibular system, which detects changes in head position and motion. By instructing an individual to walk in a straight line, placing one foot directly in front of the other, the evaluator can observe how well the person maintains balance and coordination. Difficulty in performing this test may indicate potential vestibular dysfunction, suggesting problems with the inner ear's ability to process spatial orientation and balance.

The other tests mentioned do not primarily assess inner ear functions. Chest expansion is typically a respiratory assessment, focusing on the lungs’ ability to expand and contract, while the breath-hold test evaluates a person's capacity to hold their breath. The airway reflex is related to respiratory responses and does not provide information specifically about balance or vestibular function. Thus, the heel-to-toe test is the most relevant for assessing inner ear functions among the options provided.