key term - MmHg

Definition

mmHg, or millimeters of mercury, is a unit of pressure that measures the height of a column of mercury in millimeters under the influence of gravity. This measurement is commonly used in various fields, including meteorology and medicine, to express pressure values. Understanding mmHg is crucial for comparing different types of pressure, including gauge and absolute pressure, and is vital for accurate pressure measurement in scientific applications.

5 Must Know Facts For Your Next Test

1. 1 mmHg is defined as the pressure exerted at the base of a column of mercury that is 1 millimeter high under standard gravity.
2. Mercury is used for pressure measurements due to its high density, which allows for more compact and manageable column heights compared to other liquids.
3. Standard atmospheric pressure at sea level is defined as 760 mmHg, a value often used as a reference in various scientific calculations.
4. In clinical settings, mmHg is commonly used to measure blood pressure, where systolic and diastolic pressures are reported as two values (e.g., 120/80 mmHg).
5. Conversions can be made between mmHg and other pressure units; for example, 1 atm is equal to 760 mmHg, while 1 mmHg is approximately equal to 0.00131579 atm.

Review Questions

• Explain how mmHg relates to both gauge pressure and absolute pressure in practical applications.
  • mmHg serves as a common unit for measuring both gauge and absolute pressure. Gauge pressure is measured relative to atmospheric pressure and can be expressed in mmHg; for example, if a tire gauge shows 30 mmHg, it indicates the pressure above atmospheric levels. Absolute pressure adds atmospheric pressure to gauge measurements, meaning that if the gauge reads 30 mmHg, the absolute pressure would be the gauge reading plus 760 mmHg, equaling 790 mmHg in total.
• Discuss how the use of mmHg in blood pressure readings reflects its significance in medical diagnostics.
  • Blood pressure is typically reported using mmHg because it provides a clear and standardized way to communicate systolic and diastolic pressures. For instance, a reading of 120/80 mmHg indicates that the systolic pressure (when the heart beats) is 120 mmHg and the diastolic pressure (when the heart rests) is 80 mmHg. This unit allows healthcare professionals to quickly assess cardiovascular health and diagnose potential conditions such as hypertension or hypotension based on established thresholds.
• Analyze the implications of using different units of pressure like mmHg compared to pascal in scientific measurements and reporting.
  • Using different units such as mmHg versus pascal can have significant implications for clarity and standardization in scientific measurements. While mmHg is more intuitive in certain contexts like medicine and meteorology due to historical usage and direct visualization with devices like barometers and sphygmomanometers, pascal is favored in physics and engineering due to its foundation in SI units. When reporting data, scientists must ensure they convert values correctly between these units to maintain consistency and avoid confusion in interpretations across disciplines.

Related terms

Atmospheric Pressure:

The pressure exerted by the weight of the atmosphere at a given point, typically measured at sea level as approximately 760 mmHg.

Gauge Pressure:

The pressure measured relative to atmospheric pressure, which can be positive or negative depending on whether it is above or below atmospheric levels.

Pascal:

The SI unit of pressure, defined as one newton per square meter, where 1 mmHg is approximately equal to 133.322 pascals.