CmHg, or centimeters of mercury, is a unit of pressure commonly used in medical and scientific contexts. It is based on the height of a column of mercury in a barometer, with one centimeter of mercury representing the pressure exerted by a column of mercury one centimeter in height.
CmHg is often used to measure blood pressure, with the systolic pressure (the pressure in the arteries during a heartbeat) and diastolic pressure (the pressure in the arteries between heartbeats) reported in units of mmHg (millimeters of mercury). For example, a blood pressure reading of 120/80 mmHg indicates a systolic pressure of 120 mmHg and a diastolic pressure of 80 mmHg.
CmHg is also commonly used in the field of respiratory medicine to measure lung function. In this context, it is used to measure the amount of pressure that a person can generate when exhaling forcefully, known as the forced expiratory volume in one second (FEV1). The FEV1 is typically reported in units of liters per second, but it can also be reported in units of cmHg, with one liter per second approximately equal to 10 cmHg.
CmHg is a useful and widely recognized unit of pressure, but it is important to note that mercury is a toxic substance and can be dangerous if it is not handled properly. In recent years, there has been a shift towards using alternative units of pressure that do not involve the use of mercury, such as kilopascals (kPa) or millimeters of water (mmH2O).