Blood pressure is measured in a comparison of systolic, which is blood pressure when the heart is pumping, and diastolic, which is blood pressure when the heart is at rest. A normal blood pressure reading is about 120/80mm Hg. If either number rises above 140/90mm Hg, there may be a problem with high blood pressure, or hypertension, while a reading of below 90/60mm Hg is low, or hypotensive, and causes symptoms of dizziness, weakness and fainting. Some changes in blood pressure may occur when a person goes from lying down to sitting or standing up.
Aging and Blood Pressure Changes
As people age, the central nervous system has increased difficulty regulating blood pressure. ChemoCare states that a quick change from sitting to standing may cause orthostatic hypotension, a sudden drop in blood pressure that may cause dizziness as the blood pressure drops below normal.
Knee Bending Changes Blood Pressure
Standing with knees bent and performing static contraction of the large leg muscles, also called isometric exercises, can increase blood pressure as much as strenuous, active exercise. The difference in blood pressure is due to nerve impulses from the veins, the blood vessels that return blood to the heart. Also called afferent impulses, these nerve impulses from the lower limbs cause your blood pressure to rise. Experimental Physiology states that a sharp rise in both systolic and diastolic blood pressure results because of the knees-bent body positioning.
Unexpected Blood Pressure Changes in Body Position
A six-year Atherosclerosis Risk in Communities, or ARIC, study of hypertension published in the 2002 "Journal of Human Hypertension," found that those with the lowest baseline systolic blood pressure, or SBP, were at highest risk of a cardiac event. Changes in blood pressure when going from supine, or lying down with face up, to standing showed both increases and decreases in SBP. Those whose blood pressure decreased upon standing, experiencing orthostatic hypotension, were most at risk of heart disease. That group also had the lowest starting baseline SBP when at rest. The report, headed by Dr. K. M. Rose of University of North Carolina School of Public Health's department of epidemiology stated that those with the lowest baseline SBP of 90 mmHg were twice as likely to have a coronary event as those who began with the highest baseline SBP of 130 mmHg.
Highest SBP Changes Show Highest Risk
Those with the most change in blood pressure when going from sitting to standing are at greatest risk of coronary disease. A report by the American Heart Association on the six-year ARIC study showed that those who either had a marked increase or decrease in blood pressure when changing body position were most likely to have a heart attack. The 1999 report stated that those whose blood pressure dropped the most upon standing tended to be older, have more years of cigarette smoking and had more high blood pressure and peripheral vascular disease than those with little blood pressure change when standing. Those whose blood pressure increased the most upon standing were also at high risk of heart disease.
References
- Experimental Physiology: Postural Effects on Heart Rate and Blood Pressure
- Chemo Care: Managing Blood Pressure
- Journal of Human Hypertension: Association Between the Blood Pressure Response to a Change in Posture
- American Heart Association: Descriptive Epidemiology of Blood Pressure Response to Change in Body Position
