The tonometer shows the letter e. View Full Version

Why does the tonometer show different pressure? This is often asked by users when buying a new electronic device. And it also happens that it shows different blood pressure (BP), if you measure it several times in a row. It turns out that there are many reasons for this.

Why does the tonometer show the pressure incorrectly

Tonometers are special medical devices that measure blood or eye pressure. In the latter case, the device is called a pneumotonometer. Such devices are an indispensable attribute of doctors. However, today many people, especially those suffering from hypertension and heart disease, successfully use devices for measuring blood pressure at home. A tonometer is even recommended for them, because patients should always keep their pressure under control in order to avoid complications caused by an increase in blood pressure.
The tonometer readings are recorded as two measurements, for example, 120/80 mm Hg. Art. What do these numbers mean? This is a different pressure created in each of the two phases of the heart. The first reading is the highest blood pressure pumped by the heart. In our example, this is 120 - it is called systolic. The second reading is the minimum. It is observed in diastole, when the heart relaxes, fills with blood, then to push it out. This “lower” pressure is referred to as diastolic.

The device does not show pressure

Why does the tonometer not show pressure? Unfortunately, this happens very often. Most likely, this is the reason for the inability to use the device. You should carefully study the instructions for use or consult a doctor.
Tonometers for home use are different (mechanical or electronic), but they are all designed for self-checking blood pressure.

Tonometer shows different pressure

There are situations when tonometers show different pressure. This may be due to the peculiarity of the device itself, with the time of day, and also its readings are highly dependent on its incorrect use or non-compliance with the instructions.
For example, after a walk in the fresh air, a tonometer will show a higher pressure for any person than after 5 or 10 minutes of rest. This is normal, even doctors suggest that the patient sit quietly before measuring pressure.
If you take measurements several times in a row, the tonometer may show different pressures. This is due to the fact that after the first check, the vessel walls squeezed by the device did not have time to recover, the blood flow is still difficult. In this regard, it is recommended to re-measure only after 3-5 minutes. It should be borne in mind that for some people, especially in the elderly, it takes 10-15 minutes to restore blood vessels.
Very often people ask why there is a difference in values between the measurements of an electronic and mechanical tonometer. On the first one, they are 15–20 mm Hg higher. Art. even with parallel measurement of blood pressure. The explanation is simple: the electronic device is too sensitive to many changes.

The automatic blood pressure monitor responds to such factors:

third-party interference, even air movement;
muscle tension, imperceptible movement of the arm or body; emotional condition.
The sensitive sensor reacts even to the movement of air. Be calm, don't talk, keep your back straight. The cuff of the tonometer, fixed on the arm, should be at the level of the heart. If you remove all the interference, follow the instructions, the result will be correct.
If you need to get a more accurate result, you can take measurements three times with the necessary break between them. After that, it is important to derive the arithmetic mean. It must be remembered that the first indicator and the last may differ due to the artery getting used to compression or any involuntary movement, so triple measurements will give more accurate data.
It must be remembered that a decrease, as well as an increase in pressure beyond the norm, is an alarm signal. It is necessary to find out the reason by contacting a cardiologist.
Very often, blood pressure monitors may not give out at all or show an incorrect result, as well as show different pressure for various technical reasons:
forgot to insert batteries;
the device is not used correctly;
low-quality batteries that quickly fail.
In order for electronic blood pressure monitors to work well, it is necessary to change the batteries on time. It is recommended to use for meters blood pressure only alkaline (ALKALINE) batteries LR. They are more energy intensive and guarantee a long service life, which is from 200 to 400 measurement cycles. Here, the word cycle means 2-3 times a day. Batteries LR, regardless of the manufacturer, will ensure the operation of the tonometer for 4-6 months.
When the tonometer is turned on, the display is tested, and if the device showed a symbol that indicates insufficient power, this means that the batteries are low - it's time to take care of new batteries.
In addition to errors associated with the measurement of blood pressure by the device, and technical reasons, different pressures can be quite physiological. It is worth remembering that active movements, transferred loads, even sneezing and coughing increase blood pressure. This is a natural reaction and does not require medication. Blood pressure rises for a short time, and if you repeat the measurements a little later, the indicators will drop significantly.

When buying a blood pressure monitor for home use, be sure to study the operating instructions for this device in detail. At misuse errors may occur, for example, when the tonometer does not show pressure. Understanding the cause of the malfunction is quite simple if you know the features of measuring pressure with a specific device.

If the tonometer shows different values, it is too early to sound the alarm and blame the device for lying, since the person himself may take the measurement incorrectly. The most common reasons for changing values when remeasuring pressure are:

incorrect cuff placement;
arrhythmia;
dead batteries of the tonometer;
incorrect body position.

Most often, the reason is the incorrect installation of the cuff. For shoulder tonometers, this is not typical, although when the cuff slips, a change in indicators can be observed. This is due to a change in the compression of the artery.

This problem is more typical for carpal tonometers. The narrow cuff should be positioned directly over the radial artery. If it is displaced, rotated or loosely installed, there will be a problem in performance.

Electronic blood pressure monitors, regardless of type, can show different values \u200b\u200bfor arrhythmia. There is only one way to correct the situation - by replacing the device with a device equipped with an arrhythmia indicator. In this case, the device will take a series of measurements and display the average value. With arrhythmia, small discrepancies, by 2-3 mm Hg, are not an error and should not cause concern about a malfunction of the device.

In about half of the cases of an error, the reason is quite banal - it's a weak battery. This problem is typical only for devices that are powered by AA batteries. In the budget segment, often mobile automatic blood pressure monitors are not equipped with a charge indicator, and the battery life is calculated by the number of measurements.

To avoid failures due to weak batteries, it is better to buy a mains-operated blood pressure monitor.

Incorrect body position greatly affects the measurement results. Traditionally, blood pressure is measured in a sitting position. In this case, the arm on which the cuff is installed should be strictly at the level of the heart. This rule is the same for all tonometers - both shoulder and carpal. The electronic tonometer shows different results in different positions. Taking a measurement while lying down leads to an error, which is about 10 mm Hg. If the hand is raised above the level of the heart, the pressure will be approximately 5-7 mm Hg. below. Moreover, the higher the hand is raised, the lower the indicators will be.

Why is the device dropping indicators?

If the tonometers do not show pressure, but begin to drop indicators, the cause should be sought in the malfunction of the device itself or in the characteristics of the patient's state of health. In the first case, we are talking about a serious breakdown, in which the device must be replaced, but not repaired.

Resetting the measurement results may be due to an arrhythmia. This is due to the fact that the device cannot correctly measure due to violations heart rate. If the tonometer is equipped with an arrhythmia indicator, it requires at the software level the need to conduct a series of measurements and display the average values of arterial pressure on the screen. In cheap models, there is no such indicator, so the device simply cannot display the results of the measurements taken. This will lead to the fact that the tonometer will not be able to show the result, it will constantly reset the received data and start the process of air injection into the cuff again.

The answer to the question of why the tonometer does not show pressure, but resets the results, may be hidden in random movements of the hand on which the cuff is installed. In this case, the pressure of the cuff on the artery will be unevenly distributed. The device will not be able to fix the exact measurement result and will simply reset them. Solving such a problem is quite simple - you just need to fix your hand in one position and take a second measurement.

On the monitor of the device, indicators of the arrhythmia indicator and battery charge are visible

Common device failures

To understand why the tonometer shows an error, you should first carefully study the instructions. Usually, error codes are listed in the table in the operating instructions, which allows you to quickly determine the cause of the device malfunction.

Common breakdowns of home devices:

compressor failure;
malnutrition;
failure in the algorithm of the oscillometric method.

If the compressor fails, the tonometer will not work. In this case, a certain error may appear on the screen. If the error code is not displayed on the screen, it is very easy to figure out such a breakdown, since in this case air will not be pumped into the cuff, and it will not compress the artery. In addition to the breakdown of the compressor, such a problem may be associated with a kink and rupture of the hose that connects the cuff to the body of the device.

You also need to inspect the cuff and check for integrity. They, unfortunately, are short-lived, but if the cuff is torn, it will not be difficult to replace it.

Power failure and battery failure is a common reason that the tonometer throws off the pressure measurement results. If the device is powered by batteries, before taking it in for repair, you should replace them. In the event that the problem still remains when changing the batteries, the cause must be sought directly in the contacts of the device that provide power.

Automatic blood pressure monitors can be powered by a rechargeable battery. Such devices are usually equipped with a special charger. If such a battery fails, usually there is no error, but the device simply stops turning on. Diagnostics is needed to solve the problem. The problem may lie in both the failure of the battery and the charger itself.

The operation of an automatic tonometer is based on the oscillometric method of measurement. In case of violations in the operation of this algorithm, errors and errors occur in the measurement. This may be evidenced by both a discrepancy in the measurement results, and a constant reset of indicators and the beginning of a new air injection cycle.

It is important to understand that some breakdowns can lead to a complete failure of the tonometer, while the device will not turn on and respond to any actions. Some breakdowns are quite successfully corrected in the service center, but the device may also not be repairable. It is difficult to understand the reasons for the malfunction of the tonometer, it is better to give the device for troubleshooting to a specialized service center. Also, don't forget about the warranty. If the warranty period has not yet expired, the tonometer can be replaced by contacting a service center.

Errors in the operation of tonometers

When wondering what to do with the difference in indicators for hypertension and why the tonometer shows different pressures, many people do not pay attention to the violation of the rules for operating this device.

The discrepancy in the indicators during the measurement can be caused by:

too narrow or wide cuff;
incorrect installation of the cuff;
incorrect body position when measuring pressure;
too frequent measurements.

If everything is simple enough with the problems of choosing and installing a cuff, the problems of too frequent measurements should be considered in more detail. Many people make the mistake of taking a series of pressure measurements without interruption in an attempt to get the most accurate result.

Cardiologists warn that blood pressure should be measured no more than once every 15 minutes. When re-measured after 1-2 minutes, there may be a significant discrepancy in the results. Sometimes the difference can reach 30-40 mm Hg. This is due to the fact that after the first procedure, the artery on which the cuff presses adapts to the changed conditions. When recompressed, the pressure data will be distorted due to the adaptation of the body to the air pressure in the cuff.

How to check the tonometer for accuracy?

It is recommended to do an initial check of measurement accuracy at the time of purchase. To do this, you can measure the pressure with the selected device, and then repeat the measurement after a while using a mechanical tonometer. It is the mechanical models, when working with which a phonendoscope is used, that are considered the most accurate. This will allow you to identify possible discrepancies and inaccuracies.

Another method, more reliable, is to connect two pressure measuring devices to the cuff at once. Both devices will record the indicator at the same moment. Then the data should be compared and a conclusion about possible errors should be made. To get the most accurate information, you should use a blood pressure monitor and a reference device that was calibrated by the master.

Each tonometer can be customized. This procedure is called calibration and is carried out only by a specialist. As a result of the adjustment, the buyer will receive a guaranteed accurate device that will not distort the results. There are only two downsides to this approach. The first is the high cost of setting, which can exceed the price of the tonometer itself. The second disadvantage is the lack of specialists. You can calibrate the tonometer only in specialized medical equipment stores, while setting up the device will take a lot of time.

Automatic blood pressure monitors are in demand for frequent measurement of blood pressure in the elderly. But often the devices fail to work.

The most common question from users: why does the tonometer pump air a second time. This situation often occurs for no apparent reason. Consider the features of the automatic device and understand the problem.

About the principle of operation of an automatic tonometer

In work automatic blood pressure monitor the oscillometric method is laid down, which allows you to quickly and accurately measure pressure indicators. The method was introduced back in 1876 and consists in determining the oscillations in the cuff of the device. Fluctuations occur due to the passage of blood through the squeezed area. It is formed as a result of pumping air into the cuff when it is properly positioned.

Automatic blood pressure monitor

The advantage of the oscillometric method lies in the possibility of reducing the influence external factors. The result is a much more accurate measurement.

The basis of the automatic tonometer is the same principle as in other types of devices. With the only difference in the distribution of vibrations by a specially designed automatic system. The clamped area determines the blood flow with its main indicators, which are converted into numerical values on the tonometer display.

The principle of operation of the device

An automatic blood pressure monitor is convenient in that it is not necessary to inflate the cuffs for measurement. But due to simplicity, frequent breakdowns of the device occur, one of which is re-inflation, which occurs after deflation and the beginning of the conversion of the blood flow into numerical values.

Why does the tonometer pump air a second time after partial blowing?

Often the device begins to take air again after a partial descent due to improper operation of the device. The reason may be as follows:

the arm on which the cuff is worn is on weight;
the cuff is incorrectly positioned in relation to the cubital fossa - too high or low;
the bracelet was incorrectly positioned - the hose was knocked off the mark, which should be on the inner surface of the shoulder;
too weak fit of the cuff to the skin;
the man whose blood pressure is being measured moved his arm sharply.

In all cases, the reason for the redialing is determined by a weak probing of the flow of blood in the veins. As a result, the automatic device takes the situation for its own mistake and begins to correct it by pumping air a second time.

Dangerous is the reason for re-pumping air, which consists in high blood pressure. The principle of operation of the automatic system of the device is that at first the device pumps air in accordance with the standards of indicators. As a rule, for a person it is 120/80 mm Hg. For accurate measurement, the system pumps the sleeve up to a maximum of 170-180 mm Hg for the upper indicator. If a person has high blood pressure, the device has to pump air again to make an accurate measurement.

How to troubleshoot?

The bracelet-type tonometer often pumps air a second time

An automatic blood pressure monitor is sensitive to any fluctuations, so you should be especially careful when measuring pressure. Comply with all the conditions and recommendations specified in the instructions should be those who carry out the measurement on their own. In this case, the following rules must be observed:

Instructions for correct measurement

sit comfortably in a chair, leaning on the back;
hold the arm so that the cuff is at the level of the heart;
it is impossible to support the cuff with the second hand;
you can not strain your wrist or hand;
the wrist should be on the same straight line with the hand;
you can not clamp your hand into a fist;
it is not recommended to move at the time of measuring pressure and even talk;
place a hand with a cuff over the stomach, you can put it on the table in front of you;
the cuff should be 3-4 cm above the ulnar socket of the joint;
the hose should be in the middle of the cubital hole;
the cuff is gently tightened on the arm, with partial compression.

Correct location

Any extraneous movements can distort the indicators, as a result of which pumping up a second time often occurs. If blood pressure measurement is carried out with a bracelet-type device, then it is necessary to follow the rules and recommendations specified in the instructions.

Re-inflating the blood pressure monitor is not a serious malfunction in the device, but may indicate significant health problems. To achieve the correct result, it is recommended to measure the pressure several times and take the average value.

Semi-automatic and automatic devices.

Previously, the main devices were mercury. The cuffs of blood pressure monitors in the process of measuring blood pressure can be located on the wrist or forearm. Blood pressure is measured in millimeters of mercury (mm Hg). But what if the tonometer does not show pressure, or gives different readings? And how to check the tonometer for accuracy?

To estimate blood pressure, you need to know the initial data, which look like this:

lowered Blood pressure is considered in cases where the upper indicator is 100-110, and the lower one is 70-60 mm Hg. Art.;
optimal- 120/80 mm Hg. Art.;
slightly elevated- 130-139 / 85-89 mm Hg. Art.;
high- 140/90 mm Hg. Art.

With age, blood pressure, as a rule, changes upward due to changes in vascular throughput.

Normal pressure is considered at the following values:

in 16 - 20 year olds- 100-120 / 70-80 mm Hg. Art.;
in 20-40 year olds- 120-130 / 70-80 mm Hg. Art.;
in 40 - 60 year olds- less than 140/90 mm Hg. Art.;
over 60 years old- less than 150/90 mm Hg. Art.

For the correct determination of blood pressure, the following rules must be observed:

at least 5 minutes the patient should be in a calm and comfortable environment;
an hour before the procedure, he should not eat, drink or, as well as smoke;
his bladder does not have to be complete;
after emotional outbursts, you need to wait at least an hour;
during the measurement, do not talk, sit straight and have support under your back;
do not cross your legs so as not to pinch large vessels and not interfere with the flow of blood;
the cuff should not hang out or pinch the arm tightly;
The cuff should be at heart level and two centimeters above the elbow.

Violation of the elementary conditions for measuring blood pressure leads to erroneous values. The error can reach 20-25 mm Hg. Art.

Users sometimes encounter situations where the tonometer does not show pressure. The reasons that the tonometer does not show pressure can only be found out by a specialist, how to answer certain questions regarding the operation of the device.

Tonometer shows different pressure

If you can put up with the difference in the readings of the device after measuring blood pressure at long intervals, explaining them by different conditions under which measurements are taken (time of day, physical state person, etc.), then the discrepancy between the results when measured after 5-7 minutes makes you think.

Meanwhile, there are reasons for this.

Errors may occur due to the characteristics of the device itself, its improper use, measurements with different devices, the position of the cuff relative to the heart, the state of the power supply of the electronic device, physiological features body (vessels are located deep, large body fat, low elasticity of blood vessels, etc.), as well as the posture of the patient and his behavior during the procedure.

The readings also change due to the fact that the walls of the blood vessel, squeezed by the cuff during the previous measurement of blood pressure, adapt to decompression and do not have time to return to their original state, which affects the blood flow and its parameters.

If in young people the restoration of arteries occurs in a few minutes, then in the elderly this time increases to 10-15 minutes.

Therefore, blood pressure measurements must be carried out strictly according to the instructions, with one device, and also taking into account age, and keeping calm while waiting for a second procedure.

The most accurate results are obtained after three measurements at set intervals and averaging the instrument readings.

Why does the tonometer take off when measuring pressure?

Sometimes in the process of measuring blood pressure, a sharp zeroing of the tonometer readings occurs. The reasons for this are:

failure of the device;
failure (error) of the oscillometric method of measurement, which is the basis for the operation of the vast majority of electronic semi-automatic and automatic tonometers;
involuntary movement of the arm, on which the cuff of the electronic device is fixed, the operation of which is based on the oscillometric method of measurement;
arrhythmia, when the heart works irregularly, and the time interval between individual “beats” may not be enough for the sensor to trigger electronic tonometer;
characteristics of the patient's body, as mentioned above.

Regardless of the type of tonometer used, if there is any doubt about the accuracy of its operation, it is necessary to contact the metrological laboratory for verification. All sold devices undergo such control during pre-sale preparation.

The oscillometric principle of measuring blood pressure is associated with the pressure in the cuff, which changes during the pulse push and its absence. Under the influence of this pressure, the volume of the limb under the cuff changes, which is detected by the sensor located in it.

The signal from the sensor enters the "brain" of the device, where it is processed and converted into visible numbers that tell us about the actual blood pressure. Since this method is associated with the pulse, then its value is also given by the device. The movements of the patient or his arm, on which the measurement is carried out, affect the pressure in the cuff, which affects the operation of the device and the accuracy of its readings.

The principle of measuring blood pressure according to Korotkov (auscultatory method)

Such a phenomenon is impossible in mechanical devices, the operation of which is based on the auscultatory method of measurement. Its essence lies in listening to the noise associated with the movement of blood. In the process of forcing air into the cuff of the device and bleeding it, noises arise, grow, weaken and disappear, which are captured by the phonendoscope.

The specialist at a certain moment records the readings of the device corresponding to the upper and lower pressure values. He must have good hearing and experience in the use of such a device. The accuracy of measurement largely depends on his abilities.

Why are there different readings when measuring pressure?

The tonometer, like any measuring device, has errors associated with the method underlying its operation.

The accuracy of determining blood pressure is affected by:

the rate of air pumping into the cavity of the cuff and its bleed;
the amount of pressure created in the cuff;
natural fluctuation in blood pressure, which can change quite quickly;
time between measurements;
use of different devices;
measurement on different hands;
type of cuff and more offset relative to the heart;
the behavior of the patient during the procedure (talking, sneezing, raising the arm with the cuff and his emotions, changing the position of the body, etc.).

When using a conventional (mechanical) tonometer, the measurement accuracy also depends on the professionalism of the person conducting the procedure, since not everyone is able to catch noises and their changes in a phonendoscope. Especially striking differences in the readings of a mechanical device are observed when the pressure is independently determined.

Here, the applied efforts, the tension of attention and the regulation of the rate of pressure release in the cuff affect. The influence of the human factor is significantly reduced when using an electronic tonometer, which explains its increased accuracy.

Human emotions cannot be discounted. If his first measurement showed an increased (lower) pressure value, then involuntary excitement sets in, which will certainly affect the result of the repeated measurement.

The pressure can rise even at the sight of a person in a white coat taking measurements.

While waiting for the second measurement, the patient calms down, his blood pressure returns to normal, which is shown by the repeated procedure. Related to this is that many people are trying to get rid of non-existent.

Rules for measuring pressure with an electronic tonometer

Here is the correct course of action:

Prepare for the study: it is advisable to conduct it after you rest (sit quietly) for 5 minutes. This requirement can be neglected if the patient's condition requires emergency medical care.
If a person undergoing tonometry with an electronic tonometer smoked or drank coffee 1-2 hours before the study, the pressure readings may be overestimated.
Sit or seat the subject on a chair with a back, make sure that the body position is correct - the back is relaxed with support on the back of the chair, the legs are lowered, not tense and not crossed.
Release your left or right shoulder from clothing. Make sure that it does not cause compression and does not interfere with the application of the cuff. Ideally, the measurement should be taken on both hands. Of course, if you are right-handed, it will be more convenient to do this on your left hand. But if the pressure difference on the left and right exceeds 10 mm Hg, it is better to measure on the arm on which the indicators are higher.
Place your hand on a support (for example, on a table) so that it is bent at the elbow, lying on the surface of the support with the extensor surface of the forearm and completely relaxed.
Take an electronic blood pressure monitor, make sure that there is no obvious damage to the device, kinks and kinks in the hose.
Unfasten the cuff and, using a circular wrap, put it on your shoulder so that it is located 2 cm higher above the elbow bend, the pneumatic hose leading to the device is directed towards the hand, located in the center of the cubital fossa (along the imaginary line connecting it with middle finger).
If there is a mark on the cuff, make sure that it is located in the middle part of the inner surface of the upper arm.
Press the power button on the machine.
Wait for the automatic inflation and exhaust air to take place. Do nothing during this time.
Numbers will appear on the electronic display of the device - the upper one displays systolic pressure, the lower one - diastolic. Most of the devices also show the pulse rate, the indicator of which is located below the rest. In this case, the numbers will be located above the pulse (middle column).
Press the button, turn off the device and wait for the automatic shutdown.
Remove the cuff - the measurement is completed.

Rules for measuring pressure with an electronic tonometer

Rules for imposing a tonometer cuff on the arm

Features of measurement by a semi-automatic electronic tonometer

A semi-automatic tonometer is a device that independently determines the numbers of blood pressure, but you need to pump the air yourself with a pear. According to some reports, its results are more reliable than a fully automatic device. In general, you need to measure according to the same algorithm, the differences are only in such moments:

After you have put the cuff on your upper arm correctly, turn on the blood pressure monitor by pressing the start button on its body.
Take the rubber bulb of the device in your free hand and inflate the cuff to a level of 20–30 mm Hg. Art. higher than the usual or expected pressure. If you do not know these numbers, you can blow air up to 200 mm Hg. st., it will not be a mistake.
After forcing the desired pressure in the cuff, press the button near the pear so that the air slowly begins to leave it. At this time, the device will determine the pressure itself.
The results will appear on the digital display, similar to the numbers described in the section “Rules for measuring with an automatic electronic tonometer - point 11”.
To complete the procedure, once again press the start button of the device and the button near the pear, remove the cuff.

Common mistakes

Typical errors distorting results:

Failure to comply with the requirements for taking measurements in a state of complete physical and psycho-emotional rest is a false overestimation of the device.
The arm on which the cuff is worn is tense or is located on weight.
The cuff is worn over the garment.
The shoulder is incorrectly released from clothing - it squeezes the tissues, the cuff grabs its edge.
High or too low position of the cuff in relation to the antecubital fossa.
The device is turned on before applying the cuff.
Incorrect position of the hoses (along the outer surface of the shoulder) or mismatch of the mark on the cuff in the middle of the inner surface of the shoulder.
Too tight or, on the contrary, too weak fit of the cuff to the shoulder.
Conversation or any tension during the measurement.
A pause of 1-2 minutes between several changes on one hand was not maintained.

If you have any doubts about the results of measuring pressure with an electronic tonometer (the indicators do not correspond to your well-being), be sure to take a control measurement with a classic mechanical tonometer!

If you constantly measure blood pressure with an electronic blood pressure monitor, keep a record of the indicators of each study, noting the date, time and value of the indicators.
Be sure to periodically check the pressure with a mechanical tonometer. It is better that this is done by a specialist (preferably the attending physician).
If the indicators of a mechanical and electronic tonometer differ, you must trust the first one.
For greater reliability, it is better to measure the pressure several times on both hands during one session, pause for 1-2 minutes between changes.
The results of three measurements are considered reliable, the difference between which does not exceed 5 mm Hg. Art.