Final answer:
An increased respiratory rate is the characteristic contributed to sympathetic system changes during the first period of reactivity in a neonate, reflecting part of the 'fight-or-flight' response.
Step-by-step explanation:
The nurse will contribute increased respiratory rate, which is noted in the first period of reactivity to sympathetic system changes. This response is seen when the sympathetic nervous system is stimulated, often as part of the 'fight-or-flight' reaction. In neonates, during this phase, there is usually an increase in heart rate, increased minute respiration, and a widened eye pupil due to pupil dilation, which are signs of an active sympathetic system.
All the options provided (Decreased heart rate, Constricted pupils, Reduced startle reflex) are opposite of what's expected from sympathetic system activation. Instead, during the first period of reactivity, it's quite normal for a neonate to display increased heart rate, increased respiratory rate (B), pupils dilation, and a heightened startle reflex. These changes prepare the body to respond to new environmental stimuli immediately following birth.