The childhood years before the age of 18 are a period of continuous growth and development. Because children's organs and body systems mature with each passing day, at different ages their anatomy, heart rate, blood pressure, and respiratory rate are different (the heart and respiratory rates slow down with age, whereas the blood pressure rises).
18 歲以下的兒童及青少年，屬於不斷成長發育的階段，隨著年齡增長，各器官、系統的發育日趨成熟，因此不同年齡的身體結構、心跳、血壓呼吸頻率都不相同（心跳、呼吸頻率會隨年齡增加而趨緩；血壓則隨年齡增加而升高）。