In medical practice, blood pressure in humans is routinely measured using which of the following instruments?

Introduction:
Measuring blood pressure is a fundamental part of medical examination. It helps in diagnosing hypertension, hypotension and assessing cardiovascular risk. Each measuring device in science is designed for a specific type of physical quantity. This question tests whether you can identify the correct instrument used to measure arterial blood pressure in humans from among several commonly known instruments.

Given Data / Assumptions:
- The quantity to be measured is blood pressure in humans. - The instruments listed include a thermometer, barometer, sphygmomanometer and lactometer. - We assume a standard clinical setting such as a doctor's clinic or hospital. - The aim is to match each instrument with its typical use and pick the correct one for blood pressure.

Concept / Approach:
A sphygmomanometer is the instrument specifically designed to measure arterial blood pressure. It usually consists of an inflatable cuff, a measuring gauge and sometimes a stethoscope. The cuff is wrapped around the upper arm, inflated to temporarily stop blood flow, and then slowly deflated while listening to Korotkoff sounds to determine systolic and diastolic pressures. A thermometer measures temperature, a barometer measures atmospheric pressure and a lactometer measures the specific gravity of milk. Therefore, only the sphygmomanometer is relevant for measuring blood pressure.

Step-by-Step Solution:
Step 1: Recall that blood pressure readings such as 120/80 mm of mercury are taken using a cuff around the arm. Step 2: Remember the technical name of this device, which is sphygmomanometer. Step 3: Identify that a thermometer is used to measure body temperature in degrees Celsius or Fahrenheit, not pressure. Step 4: Recognise that a barometer is used in meteorology to measure atmospheric pressure, not blood pressure inside arteries. Step 5: Understand that a lactometer is used to check the purity or density of milk, not any cardiovascular parameter. Step 6: Conclude that sphygmomanometer is the only instrument among the options that measures blood pressure.

Verification / Alternative check:
Healthcare training materials and clinical procedure manuals clearly state that blood pressure is measured with a sphygmomanometer, whether it is a manual mercury device, an aneroid gauge or a digital automatic version. The word itself is derived from Greek roots meaning pulse pressure measuring device. In contrast, the other instruments have clearly defined roles in separate domains. This consistent usage across medical practice confirms the correct choice.

Why Other Options Are Wrong:
Thermometer: Measures temperature, used to detect fever or hypothermia, not blood pressure. Barometer: Measures atmospheric pressure in weather stations and physics experiments, not internal blood vessel pressure. Lactometer: Used in dairy industry to measure the specific gravity or density of milk and check for adulteration, not for health parameters.

Common Pitfalls:
Occasionally, students may mix up barometer and sphygmomanometer because both are associated with pressure. The key difference is that a barometer is for external atmospheric pressure while a sphygmomanometer is used on patients' arms in clinics. Remembering the typical doctor's office scene, where a cuff is wrapped around the arm and a gauge is monitored, helps fix the term sphygmomanometer in memory as the blood pressure instrument.

Final Answer:
Blood pressure in humans is measured with a Sphygmomanometer.