Pneumococcal infections are caused by Streptococcus pneumoniae, a gram-positive, catalase-negative organism commonly referred to as pneumococcus.
Blood pressure is a measure of the changing fluid pressure within the circulatory system. It varies. from a peak pressure produced by contraction of the left ventricle, to a low pressure, which is. maintained by closure of the aortic valve and elastic recoil of the arterial system. The peak.
â¢ To understand how vessel elasticity, blood volume, and cardiac output affect blood pressure. Page 3. Sources of Peripheral Resistance. â¢ One of the main factors that affects blood pressure is peripheral resistance. â¢ Blood cells and plasma encounter resistance when they contact blood vessel walls.