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(Stroke. 2001;32:275-a.)
© 2001 American Heart Association, Inc.

Letters to the Editor

Stress-Related Intracerebral Hemorrhage and the Water-Hammer Effect

Johan Ahlqvist, MD

Department of Physiology, University of Turku, Turku, Finland, (retired at Sibbvik, Västanfjärd, Finland)

To the Editor:

Lammie et al¹ described thalamic hemorrhage following emotional upset in an elderly man with old lacunar infarcts in other parts of the brain. The case supported Caplan’s hypothesis that acute rises in blood pressure or cerebral blood flow may cause rupture of the small perforating arteries,¹ which branch at almost right angles from the middle and posterior cerebral arteries to supply, among others, the thalamus and basal ganglia.

At autopsy of cases of not only infarct but also hemorrhage, I paid attention to the frequent occurrence of potential sources of small arterial emboli in the heart or at carotid artery atheromatous plaques. That emboli might be related to hemorrhage made no sense until, as a retiree, I began to poke into the physiology² and physics^{3 4} of flow.

A water-hammer phenomenon was studied in the late 19th century.³ When flow of fluid in a pipe is stopped by sudden closure of a valve, the kinetic energy of the upstream fluid is reduced to zero very rapidly, creating a high pressure at the valve and causing a pressure wave to move upstream from it. Downstream, momentum reduces pressure. The primary waves are followed by secondary ("bouncing") ones, until the fluid comes to rest.⁴ The theory^{3 4} is complicated, but the brief upstream rise of pressure (p) at rapid closure of valves may be calculated (G.A. Öhman, personal communication, 2000) from the rather simple equation

View larger version (4K): [in this window] [in a new window]   Figure 1.

I use it to calculate a theoretical rise in pressure in the middle cerebral . . . [Full Text of this Article]