Which vital sign is measured by determining heart contractions?

The pulse is measured by determining heart contractions because it represents the rhythmic throbbing of the arteries as blood is pumped through them by the heart. Each contraction of the heart produces a wave of pressure that travels through the arterial system, which can be felt at various pulse points throughout the body, such as the wrist or neck. This measurement is crucial as it not only indicates the heart's rate but can also reflect the strength and rhythm of the heart contractions, providing valuable insight into a person's cardiovascular health.

In contrast, respiratory rate refers to the number of breaths taken in a minute, which is influenced by the respiratory system, not the heart. Body temperature measures the body’s thermal state, typically reflecting metabolic activity, and does not involve heart contractions at all. Blood pressure assesses the force of blood against the walls of the arteries during heartbeats and between beats, but it does not directly measure the contractions themselves; rather, it measures the resultant pressure from blood flow. Thus, the pulse is the vital sign that specifically captures the activity of heart contractions.