Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site sdcc6.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!hao!hplabs!sdcrdcf!sdcsvax!sdcc6!07077090 From: 07077090@sdcc6.UUCP (07077090) Newsgroups: net.med Subject: Re: blood pressure Message-ID: <1779@sdcc6.UUCP> Date: Wed, 10-Oct-84 02:28:31 EDT Article-I.D.: sdcc6.1779 Posted: Wed Oct 10 02:28:31 1984 Date-Received: Fri, 12-Oct-84 05:44:18 EDT References: <3778@tektronix.UUCP>, <127@logico.UUCP> Organization: U.C. San Diego, Computer Center Lines: 27 As you imply, blood pressure is a complex phenomenon. In the most basic terms, it is determined by cardiac output and vascular impedance which has both resistive and capacitance components. The pulse pressure (systolic-diastolic) increases with increased stroke volume and decreased vessel compliance (capacitance) while mean arterial pressure depends on cardiac output and vascular resistance. BP of 120/100 (vs 120/90) implies a higher resistance (or higher output) and more work for the heart. As far as we know, there is no lower limit for the beneficial effects of low blood pressure, until low pressure itself becomes symptomatic (e.g. with lightheadedness or fainting). There is a complex feedback system as you suggest, involving hormones etc, which is one reason BP is hard to control. For example, one cause of high BP could be thought of as the body (kidneys?) "thinking" there is low intravascular blood volume, and thus "conserving" as much water in the circulation as possible. Mikc Blyth ..sdcc3!sdcc6!07077090 UCSD Medical School