What factor can affect the reliability of a cardiac examination in newborns?

The reliability of a cardiac examination in newborns can indeed be significantly influenced by whether the infant is awake or asleep during the examination. When a newborn is awake, they may display more active physiological responses, such as variations in heart rate and respiratory rate. These responses can provide important insights into the cardiovascular status of the infant. Conversely, if the newborn is asleep, especially in deep sleep, there may be reduced heart rate variability, and subtle cardiac anomalies may not be as easily detected. Hence, the state of consciousness during the examination can impact the clinician's ability to accurately assess cardiac function and structure.

Other factors presented, such as the time of day the examination is performed, previous medical history, and family history of heart disease, may influence the context or understanding of the examination but do not have the same direct and immediate impact on the physical examination findings at that moment. For example, variations in physiological parameters might not differ significantly based solely on the time of day. Meanwhile, understanding previous medical and family histories provides vital background information but does not directly alter the assessment occurring during the cardiac examination itself.