Blood Pressure - The force applied per unit area is called pressure. Similarly, blood pressure is defined as the force of blood on per unit area of blood vessel. Blood pressure is usually measured in the right arm in the brachial artery and is measured in millimeter of mercury. The variability in the blood pressure leads to two readings: the systolic BP and diastolic BP. Systolic pressure is the pressure exerted by blood on the blood vessel which occurs when the heart contracts or expands and is the peak pressure. Diastolic pressure is the pressure reading that occurs when the heart is relaxing and thus is a lower reading.
Blood pressure is measured by
invasive and non-invasive methods. The invasive method requires intra-arterial catheterization and is the most accurate method, but this method is not done routinely due to its invasive nature. Hence, the
standard practice of monitoring the blood pressure is non-invasive nature and all the blood pressure monitors discussed hereafter are non–invasive.
Blood Pressure Monitors: Till late 1990’s, mercury filled sphygmomanometer were maximally used for measuring the blood pressure even in intensive care settings. It is still the obvious choice for measuring BP in office practice. The older versions of mercury filled sphygmomanometer would with breakage lead to mercury spills that are toxic and can be hazardous. Thereafter, modern mercury filled sphygmomanometers have been introduced in market which do not spill mercury in case of breakage.
Further advancements have brought aneroid monitors and electronic monitors, which again are non-invasive. Finger monitors and wrist monitors are also new in the blood pressure monitors category, but all have their own pros and cons.
Mercury Sphygmomanometer – It has been one of the oldest blood pressure monitor, and includes a cuff that can be inflated or deflated. A mechanical bulb assists in inflating bulb while deflating is done through a valve. The reading is taken through mercury filled in glass tube.
Aneroid Blood Pressure Monitors – Aneroid blood pressure monitor includes a cuff, mechanical bulb, deflating valve and a round monitor. The basic difference in mercury sphygmomanometer and aneroid manometer is the round monitor that replaces the mercury column. This monitor has a round dial covered with glass and a metal spring that gives the reading.
Both aneroid and mercury BP apparatus require a stethoscope for reading the BP.
Digital Blood Pressure Monitors – This model again contains cuff but have semi automatic and fully automatic models. The semi automatic models has to be inflated manually and deflation is automatic while the fully automatic model has is inflated as well as deflated automatically Digital blood pressure monitors come with an inbuilt LCD screen to show the readings and hence a stethoscope is not required. The concern in this device is to hold the body at a specific position or irregular heart rate that can change the reading. These models are used in Neonatal Intensive Care Units and Pediatric Intensive Care Units.
Cuff requirements: Selection of right cuff size for measuring blood pressure e is always important. A smaller cuff size would lead to falsely elevated BP and a larger cuff would lead to falsely lower BP. The ideal cuff should cover 2/3 rd the length of the arm and should be 20% wider than the diameter of the limb. The cuff should encircle at least 75% of the arm and bladder should overlie the artery.
Wrist and Finger Blood pressure Monitors – Wrist blood pressure monitor can be used around the wrist and the button automatically inflates the cuff. The reading is than shown on the LCD panel.
Finger blood pressure monitor can be used by in inserting the index finger in the adjustable cuff. The automatic cuff fits to size and inflates and shows the reading LCD panel.
Wrist and Finger blood pressure monitor is its sensitiveness to body movement and temperature.
Choice of blood pressure monitor: The choice of Blood pressure Monitor often depends on the accuracy, ease of use, and the price, but it is necessary to have a proper understanding of any instrument that is used. Also it is important to understand the limitations of each device as well as having a proper training to use it.