The calculation of left ventricular mass has been made by echocardiography for a number of years. This has become an established mode of measurement and is often used serially in studies to determine the effects of drugs (e.g., antihypertensive agents) on the mass of the heart. However, the formula used makes specific assumptions about the geometric shape of the ventricle; It is possible that volume-related changes in the shape of the ventricle may be inaccurately reflected as a change in left ventricular mass as calculated by the standard formula. It is of interest that patients prescribed diuretics for hypertension seem to develop a decrease in left ventricular mass, which is greater than that observed with many other antihypertensive agents. Whether this is a true decrease or is related to change in circulating plasma volume with a secondary change in the geometry of the heart is unknown. We therefore propose to study the effects of acute changes in the volume of the heart on calculated left ventricular mass. Since these changes are acute they will have no effect on the true mass and any changes in calculated mass will reflect a flaw in the formula. It is important to know this information in order to assess the value of serial echocardiography in antihypertensive studies. Normal subjects will be asked to participate in this study. They will undergo echocardiography in the supine position in a normal resting state. They will then be subjected to lower body negative pressure. This is a technique that has been used for many years in physiology laboratories and consists of placing the body (from waist down) in an enclosed space from which the air is gradually removed under controlled conditions. Previous studies have shown that lower body negative pressure sustained for 8-21 minutes is safe and can decrease left ventricular volume by approximately 30%. We propose to repeat the echocardiogram after gradual lower body suction to -40mmHg and to calculate various parameters including the left ventricular mass.
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