Medical Relevance of Oscillometric Blood Pressure Technology

Increased arterial blood pressures belong to the most relevant risk factors in the prosperous world. Long-term arterial hypertension leads inevitably to arteriosclerosis, which bears the risk of suffering from either a myocardial infarction or a brain stroke. These, so called "major vascular disease", are unfortunately very common in modern western world society.

In the United States each year 900.000 myocardial infarctions occur while in the UK 225.000 and in Germany 275000 patients suffer from this acute coronary disease. 40 % - 50 % of these patients do not survive the initial 4 weeks post - infarction period.

About 420.000 patients in the United States, about 100.000 patients in the United Kingdom and about 125.000 patients in Germany suffer from a brain stroke. 50 % of these patients are not anymore able to carry on with their professions due to this cerebral event.

Brain strokes and myocardial infarctions are responsible for 45 % of the western world's mortality rate.

Beside ensuring a normal cholesterol blood concentration and avoiding smoking, any long-term arterial hypertension must be avoided. Arterial hypertension however is very common.

The overall prevalence in prosperous countries is 20 %. That means, in the United States do suffer about 56 million patients from arterial hypertension. The correspondent figures are given with 13 million patients at the UK, and about 16 million patients at Germany.

Modern medicine fortunately offers a broad range of therapeutic measures, including diet, physical activity and pharmaceutical intervention. However, any kind of therapy needs in the first place a correct and fitting diagnosis of the arterial blood pressure.

The diagnosis may be done at the doctor's office. This however is in many cases not feasible. Firstly, the doctor's measurement is altered by the so called "white coat effect", which leads to an artificial increase in the blood pressure level of the patient. Secondly, patients on work do have certain limitations to attend frequently their doctors.

In order to assess the patient's blood pressure at a given daily schedule, patient's normally do have to perform these measurements by their own. Blood measurements can be taken at the patient's working places and / or at home. These measurements should be recorded and presented to the doctors in the course of the treatment.

Presently, there are only two technologies available in order to access the patient's arterial blood pressure. Patients may apply automatic devices, which are basing on the so called 'oscillometric' technology or chose devices, which derive from a so called 'auscultatoric' technology.

The auscultatoric technology, which is also referred as the 'Riva - Rocci' method, bases on the pick-up of arterial sound bursts, which do occur, when blood samples flow under a cuff, which is wrapped around the patients upper arm.

Most auscultatoric devices are manual devices. That means, patients try to detect the associated pulse sounds with a stethoscope and subsequently conclude on the systolic and diastolic blood pressures out of the sound pattern.

This method however does only work properly in educated and experienced patients, and if these patients additionally do still have no age - related hearing loss. Unfortunately many patients who suffer from arterial hypertension are elderly people. Since these patients often do suffer from a certain hearing loss, they may not properly apply manual auscultatoric devices.

Inexperienced patients, who are not used to the interpretation of an auscultatoric sound pattern, may also not apply these "Riva - Rocci" blood pressure monitors.

There are a few automatic auscultatoric blood pressure measurement devices on the market, which however prove to be critical towards artificial noise. They include a microphone, which basically also picks-up artefact sound signals.

Since about 10 years, the oscillometric technology has been introduced into the home blood pressure market. The technology also bases on cuff wrapped around a limb. Application sites for home use are either the upper arm or the wrist of a patient. Upper arm devices turn out to deliver more precise measurement results.

All cuffs cover a bladder, which detects pulse related pressure changes. They derive from blood samples which are streaming right under the cuff. These pressure changes are recorded in the course of a patient's measurement.

Two main advantages come with the oscillometric technology: First, patients do not need to be skilled in the interpretation of a pulse pattern. Secondly, patients do not need to detect pulses by their own.

Thus, the measurement may be applied also in elderly or disabled persons.

Basically only some specific conditions have to be met: The measurements have to be taken in rest condition, movements have to be avoided during the measurement process and the cuff position should be at heart level. There's no further skill necessary in order to perform these blood pressure measurements.

In present, at the beginning of the millennium, there's a broad range of oscillometric devices commercially offered to patients. The overall accuracy of these devices is sufficient, indeed.

However, there are device - specific accuracy differences, which derive from manufacturer specific design differences of these devices. This especially addresses:

- The suppression of motion artefacts.
- The ability to deal correctly with changes of the patient's heart rate
- The measurement in patients with low pulse volumes
- The measurement in patients with very low or very high blood pressure levels.

Most commonly patient's who are attempting to do a blood pressure measurement are not sufficiently in rest condition. Thus, sequential blood pressure results differ from each other. This limitation does not derive from a technological error, but from an imperfectly stable blood pressure itself.

Since any patient's arterial blood pressure may be changing dynamically, singular measurements should not be taken. It is advisable to do a series of repetition measurements, in order to define an actual blood pressure value.

It is very important that patients who are undergoing a blood pressure treatment supply their physicians with records of their blood pressure values. These recordings are greatly relevant towards further therapeutic decisions.

The oscillometric blood pressure measurement technology is sufficiently reliable to assess the blood pressure levels of patients who suffer from either hypotension or hypertension.

The medical benefit, which results from an application of this specific technology, is usually not significantly hampered by technological or physiological limitations of the method.

Klaus Forstner
Physician, M.D. cd

Forschungsinstitut für klinische Medizintechnik
Silberhälden 6
D - 71732 Tamm Germany

Tamm, May 16th, 2002