Factors That Affect Blood Pressure Readings

The following factors affect the results of blood pressure measurement:

1. Anxiety, stress, and/or pain Sometimes the mere fact of having the blood pressure taken by a physician can cause a nervous and anxious patient to experience a significant rise in the blood pressure (so-called white coat syndrome) (21,22).

2. Exercise, such as climbing a couple of flights of stairs, and even mild activity involving bending or stooping in the elderly could raise the pressure. It should be noted that the transfer of energy of pulse pressure wave to the periphery is greater at low frequencies (<2.5 Hz) in patients at rest because of slower heart rates and longer ejection time. With exercise and the associated faster heart rates and shorter ejection time, the energy transfer occurs at higher frequencies (>2.5 Hz). Because higher frequencies are amplified more, the systolic brachial pressure will be elevated and may not necessarily reflect the true central aortic systolic pressure (23-25).

3. Exposure to cold by causing sympathetic vasoconstriction will raise the pressures.

4. Postprandial state will tend to lower the pressure. In addition to increased vagal tone necessary for increased peristalsis, the lower pressure is likely related to vasodilatation in the mesenteric vessels diverting more blood to the gut for the purpose of proper digestion. This probably also relates to the increase in angina or postprandial decrease in exercise tolerance in patients with exertional angina. The increased demand of blood supply to the gut, increasing the work load of the heart coupled with the decreased diastolic pressure (coronary perfusion pressure), leads to mismatch between the oxygen demand and the coronary blood supply, resulting in angina.

5. Alcohol acutely will lower the pressure, whereas chronic alcohol consumption raises the pressures.

6. Both chronic and acute cigarette smoking tend to cause elevated pressures.

7. Use of illicit drugs such as cocaine may cause significant elevations in blood pressure.

8. Excessive use of liquorice can lead to sustained hypertension.

9. Distension of viscus organs, such as the urinary bladder, gall bladder, and bowels, can cause severe increase in pressures.

10. Significant drop in blood pressure may be noted on postural change from a supine to an erect position (postural hypotension) in patients with hypovolemia, following use of certain antihypertensive drugs, and in patients with diabetes with autonomic dysfunction. This is more common in type 1 diabetics.

11. During pregnancy the uterus can compress the inferior vena cava in the supine position and cause decreased venous return, thereby lowering the blood pressure. It is therefore always advisable to measure the blood pressure in a pregnant woman in the sitting position.

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