Identifier: textbookofphysio1916howe (find matches)
Title: A text-book of physiology : for medical students and physicians
Year: 1916 (1910s)
Authors: Howell, William H. (William Henry), 1860-1945
Subjects: Physiology Medicine
Publisher: Philadelphia and London : W. B. Saunders Company
Contributing Library: Yale University, Cushing/Whitney Medical Library
Digitizing Sponsor: Open Knowledge Commons and Yale University, Cushing/Whitney Medical Library

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essure in the large arteries, as influenced by VELOCITY AND PRESSURE OF BLOOD-FLOW. 493 the heart beat. These arteries are, in fact, subject to very rapid andvery extensive changes in pressure at each beat of the heart, andthese changes are naturally more pronounced when the force of theheart beat is increased,—for instance, 1 y muscular exercise. Systolic, Diastolic, and Mean Arterial Pressure.—As statedin the last paragraph, the arterial pressure in the larger arteriesundergoes extensive variations with each heart beat. The maxi-mum pressure caused by the systole of the heart, the apex of thepulse wave, is spoken of as systolic pressure; the minimum pressurein the artery—that is, the pressure at the end of the diastole of theheart, or the bottom of the pulse-wave, is known as the diastolicpressure. In a dog under ordinary conditions of experimentationthe systolic (lateral) pressure in the aorta may be as much as 168mms., while the diastolic pressure is only 100 mms. In man the
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Fig. 194.—Schematic representation of the pressure change caused by each heartbeat. The schema represents three heart beats supposed to be recorded on a rapidly movingsurface by a manometer delicate enough to follow the pressure changes accurately. Thetop of the pulse wave measures the systolic pressure; the bottom the diastolic pressure. systolic pressure as measured in the brachial artery may be takenin round numbers as equal to 110 to 116 mms., while the diastolicpressure is only 65 to 75 mms. The difference between thesystolic and the diastolic pressure has been designated con-veniently as the pulse pressure. It measures, of course, thevariation in pressure in any given artery caused by the heart beat,and so far as that artery is concerned it gives the force of theheart beat except for the small component used to acceleratethe movement of the blood. From the figures given above itwill be seen that the pulse pressure in the brachial artery ofman averages 45 mms. Hg. Each systole

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