Measuring blood pressure correctly is anything but trivial. Hypertension specialists at the Medica have tips for both patients and doctors. Specialists complain that measuring blood pressure correctly is anything but trivial because a great many errors are made.
Elderly patient at the doctor having his blood pressure checked. The cuff is correctly positioned at the same level as the heart. Photo: Lisa F. Young©www.fotolia.de
By Thomas Meißner
In Germany there are at least 20 million people with hypertension (more than 140 over 90 mm Hg). Over many years hypertension can lead to strokes, heart attacks and renal failure. Only one in three of those affected is aware of their own high blood pressure. Only just under 16 percent of Germany's hypertension patients are keeping the disease under control by means of medication and other general measures.
Classical blood pressure measurement
Indirect measurement of the blood pressure using an inflatable cuff on the upper arm and a sphygmomanometer was developed by the Italian doctor Scipione Riva-Rocci (1863-1937). When the cuff is inflated it compresses the brachial artery. Then the air is gradually released until a pulse can be felt again in the patient's wrist (radial artery), which means that the arterial pressure just overcomes the pressure in the cuff. This air pressure in the cuff corresponds to the systolic blood pressure. Later the method was combined with listening to the artery using a stethoscope placed on the inside of the elbow. This allows you to hear the sounds produced by the flow of the blood in time with the pulse (Korotkoff sounds, named after Nikolai S. Korotkoff, 1874-1920). The pressure in the cuff matches the systolic pressure when the first Korotkoff sound is heard, and the pressure when the Korotkoff sounds disappear completely (in adults) matches the diastolic blood pressure. Traditionally blood pressure is still given in millimetres of mercury (mm Hg), although use of measuring devices actually containing mercury has been forbidden for a long time now.
Automatic blood pressure measurement
Automatic devices measure blood pressure by oscillometry. This means that as the cuff gradually deflates the machine records not acoustic signals but oscillations of the cuff pressure caused by the re-appearance of the arterial pulse in the patient's arm. Initially these oscillations become stronger, and then they gradually die away until they cease altogether. The machine actually measures the mean blood pressure (time of the largest oscillation). Systolic and diastolic values are calculated by applying mathematical algorithms. As the blood pressure has a diurnal rhythm, blood pressure measurement over 24 hours using automatic machines has proved its value in diagnostic workup for hypertension. This also applies to treatment monitoring, because it is often not possible to predict whether an antihypertensive medicine taken in the morning will still have the desired effect late in the evening.
Direct blood pressure measurement
This can be done using a sensor located in the arterial bloodstream which registers the pressure wave emanating from the heart. This method is used, when necessary, in intensive care departments or during major operations. Its advantage is the continuous registration of the blood pressure and greater precision in comparison to indirect measurement.
14.30 bis 17.30 Uhr, CCD-Süd, Raum 01
Leitung: Prof. Bernd Krönig, Trier und Prof. Manfred Anlauf, Bremerhaven