Chapter

Pressure and Its Measurement

James R. Munis

in Just Enough Physiology

Published on behalf of © Mayo Foundation for Medical Education and Research

Published in print December 2011 | ISBN: 9780199797790
Published online June 2012 | e-ISBN: 9780199929665 | DOI: http://dx.doi.org/10.1093/med/9780199797790.003.0001

Series: Mayo Clinic Scientific Press

Pressure and Its Measurement

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In physiologic terms, we are exposed to 3 main sources of pressure: 1) the weight of the atmosphere; 2) hydrostatic forces exerted by the weight of body fluids; and 3) mechanical pressure generated by the heart or other muscles that contract around those fluids. Because cardiopulmonary physiology deals so much with pressure measurements, let's start by defining what pressure really is. Simply put, pressure is force divided by area. It's also important to understand what pressure is not. For example, pressure is not energy. Only when pressure is coupled to a volume change (ie, movement or pressure-volume work) is it a component of energy. This is more than just a semantic point. Although we're fond of saying that fluids move from high to low pressure, that isn't always true. The reason why highlights a fundamental difference between pressure and energy. Pressure is surprisingly difficult to measure. Often, when we think we are measuring pressure, we are actually measuring stretch or movement.

Chapter.  2307 words.  Illustrated.

Subjects: Professional Development in Medicine

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