The first aim of the present study was to test the influence of body posture on the indirectly measured BP values when the arm was placed at the right atrium level. The second aim of our study was to test the effect of the level of the arm on the indirectly measured BP values in the supine position: arm on the bed surface and arm at half distance between the sternum and the bed. Of these, 50 patients were on antihypertensive drug treatment. The arm was placed at the approximated right atrium level using a levelling instrument.
In all, 25 subjects 16 hypertensive patients, 11 males, mean age All BP readings were taken simultaneously at both arms, with the subject comfortably supine on an examination bed with one small cushion under the head. To test for BP differences between the two arms, one BP reading was first performed with the patients in the described supine position and both arms placed on the bed, with the palms upwards.
One arm at random right or left was then supported with a specially designed pillow with the cubital fossa and upper arm at half-distance between the bed and the sternum approximation of the right atrium level , whereas the other arm remained on the bed Figure 1.
The arm position was switched thereafter, with the arm first supported on the pillow now being placed on the bed and vice versa. Computerised tomography illustrating the difference between the arm levels used in the present study right arm supported at the right atrium level and left arm supported on the examination bed.
R: right arm; L: left arm; RA: right atrium. In both studies, all BP measurements were performed by the same trained observer RTN , in a quiet room, with comfortable temperature.
Every patient that agreed to participate in our study received detailed explanation before the procedure commenced and talking was avoided during the measurements. The mean of three readings of BP and HR obtained, respectively, in each position was considered representative for that position. Paired t -test was used to compare the differences between the BP and HR, respectively, in different positions.
The main results are given in Table 1. The HR was slightly, but significantly, higher in the sitting than supine position Table 2 presents the BP and HR readings taken in the supine position with the arm on the examination bed and with the arm supported at the right atrium level. As seen in Table 2 , no difference was found in the initial BP readings between the two arms. However, significantly higher BP readings were recorded when the arm was placed on the bed than when the arm was supported at right atrium level.
Statistical significance was not reached for the SBP in the right arm but the trend of the results was similar to that in the left arm. In our group of hypertensive patients, in an outpatient setting, we found significantly lower BP readings in the sitting than in the supine position when the patient's arms were supported at the right atrium level as exactly as possible in both positions.
This confirms previous observations in normo-tensive subjects. The BP measurement in sitting position is most often used in the general physician's office, whereas in some hospitals BP is often measured in supine position.
Both diagnostic and therapeutic decisions are based on BP readings taken sometimes in sitting and sometimes in supine positions, since they are often regarded as equivalent. The differences we found using the Hawksley Random Zero sphygmomanometer are sustained by those found with the automatic instrument. The explanation of the slight differences in results between the two instruments could be the different measurement principle.
One should realise that with the oscillometric method the mean arterial pressure is determined by the maximal amplitude of the oscillations, and SBP and DBP are subsequently computed from this value. Another factor that is often neglected during BP measurement is the position of the arm of the patient. We and others 7 , 8 , 9 have shown that this induces a consistent difference between BP readings taken with the arm in different positions.
Such differences may result in large errors in BP readings that could obscure or even inverse the difference in BP readings between the sitting and supine position. The effect of the arm position on BP readings in the supine position was especially observed during nocturnal BP registration in ambulatory BP measurement ABPM studies 10 , 11 , 12 , 13 and in pregnant women, 14 , 15 , 16 when the BP was measured in the lateral recumbent position.
The BP values recorded when the arm was placed above the heart level were significantly lower than those recorded when the arm was situated below the heart level. When the patient is lying on the examination bed, one assumes that the arms of the patient rest at the level of the right atrium. Our results in a group of patients with a wide range of BP values, show that even such a small variation in the arm position can result in significant BP differences.
To obtain a double control of the results and to avoid observer bias, we used automated devices, and we performed simultaneous readings in both arms and for each arm in both sequences of the two positions. The results showed similar trends in both arms and were independent of the sequence of the two positions and of the BP level. The magnitude of differences we obtained was slightly smaller ranging from 2.
A possible explanation for the difference between these two studies could be the fact that oscillometric instruments were used in the present study, whereas standard mercury sphygmomanometers were used in the study of Ljungvall et al. In conclusion, the present study shows that the assumption that blood pressure in sitting and supine position can be considered similar is incorrect even when the arm of the patient is placed at the correct right atrium level in both positions, as officially recommended.
Supporting the arm of the patient on the arm support of a common chair in the sitting position could partially correct and potentially reverse the differences between sitting and supine positions. In consequence, such practice is incorrect and should be discouraged. Guyton A. Textbook of Medical Physiology. WB Saunders: Philadelphia. Google Scholar. Hypertension ; 22 : — Several older studies found that blood pressure was higher among study participants while they were lying down compared to sitting.
One of these, a study , included 6, healthy volunteers. However, the results of several newer studies have suggested blood pressure may be lower while lying down than when sitting:. Lower blood pressure while lying down makes sense when you think of your heart as a pump. So why are there variations in the findings, especially with the older studies?
Investigators suggest that the variations could be due to differences in the populations studied, such as age or underlying health conditions. The technique and order of the blood pressure measurements could also play a role. The only exception may be in situations where someone has an underlying health condition. For consistency, medical experts suggest that your blood pressure readings should always be taken in the same position.
This makes it easier to compare your readings and to notice any changes. Your blood pressure can also change as you move from one position to another. This may be particularly noticeable when you move from a sitting or lying position to a standing position. When you stand, gravity causes blood to pool in your lower body. This can cause a temporary drop in blood pressure. However, your body has a way to adjust to this change.
Certain reflexes in your body send a signal to your brain when a drop in blood pressure is detected. Your brain then tells your heart to beat faster in order to pump more blood.
This works to stabilize your blood pressure. However, sometimes this process can be interrupted, causing the drop in blood pressure to last longer than normal. As a result, you may feel lightheaded , dizzy , or faint for a short while after you stand.
This condition is called orthostatic hypotension or postural hypotension. It can be caused by a variety of factors, including:. The American Heart Association recommends sitting down to take your blood pressure. They also note that while there are differences in the right arm versus the left arm, these are small and only cause a variation of 10 mm Hg or less.
Additional posture-related factors can also affect your blood pressure readings. Although there are more information on arm position in blood pressure measurement, surprisingly little information can be found in the literature with respect to the influence of body position on the blood pressure readings in healthy young people. Methods: A total of healthy young students who had accepted to participate in the study were randomly selected.
In all subjects the blood pressure was measured subsequently in four positions: Sitting blood pressure was taken from the left arm, which was flexed at the elbow and supported at the heart level on the chair. After at least one minute of standing, the blood pressure was then taken standing, with the arm supported at the elbow and the cuff at the heart level. After one minute of rest, the blood pressure was subsequently taken supine position.
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