Final answer:
The nurse typically hears wheezing during the expiration phase of the respiratory cycle in a patient with asthma, as the airways are more likely to be narrowed and obstructed at this time.
Step-by-step explanation:
In a patient with asthma, the nurse often hears wheezing during the respiratory cycle. Wheezing is typically most prominent during expiration, at which point the airways are more likely to be narrowed and obstructed due to inflammation, increased mucus production, and bronchoconstriction associated with asthma. However, it is possible for wheezing to occur during both inhalation and exhalation when the condition is severe. The correct answer to the question 'In a patient with asthma, the nurse hears wheezing initially during which part of the respiration cycle?' is therefore expiration.
Pulmonary ventilation consists of the process of inspiration (or inhalation), where air enters the lungs, and expiration (or exhalation), where air leaves the lungs. During inspiration, the diaphragm and external intercostal muscles contract, leading to an expansion of the thoracic cavity and a decrease in intra-alveolar pressure, drawing air into the lungs. During expiration, the process reverses with relaxation of these muscles, leading to an increase in intra-alveolar pressure, pushing air out of the lungs.
Therefore, in the context of this question, wheezing is most often heard during expiration due to the increased difficulty for air to pass through constricted airways.