Final answer:
The heart rate of healthy children increases with inspiration and decreases with expiration, due to respiratory sinus arrhythmia. Children's respiratory rates decrease with age, starting from a high of 30-60 bpm in infancy to an adult-normal of 12-18 bpm by adolescence. Heart rates also vary with age, exercise, and fitness levels.
Step-by-step explanation:
In healthy children, the fluctuation of heart rate with the respiratory cycle is a phenomenon known as respiratory sinus arrhythmia. The heart rate increases with inspiration (breathing in) and decreases with expiration (breathing out). This variation is due to changes in the intrathoracic pressure and the influence of the vagus nerve on the heart during the respiratory cycle.
The normal respiratory rate of children varies with age. Infants typically have a higher respiratory rate, which decreases as they grow into adolescence. For instance, a child under 1 year of age may have a respiratory rate of 30 to 60 breaths per minute, which decreases to about 18 to 30 by the age of 10, and reaches an adult-normal range of 12 to 18 breaths per minute by adolescence.
Heart rates (HRs) also vary considerably with factors like exercise, fitness levels, and age. A newborn's resting heart rate may be around 120 bpm, which gradually decreases until young adulthood and then slightly increases with advancing age.