The vascular underfilling stimulates the release of hormones that decrease the amount of salt and fluid excreted from the kidneys, which increases plasma volume. The greater plasma volume increases total circulating blood volume. As a result of these adjustments to the cardiovascular and circulatory systems, blood pressure tends to be lower, there is a 15 to 20% increase in chamber volume and stroke volume, up to a 40% increase in cardiac output, and a 30 to 60% increase in blood volume.