Central venous pressure can be measured by placing the tip of a catheter in the right atrium. Changes in central venous pressures are a good indicator of central blood volume because the compliance of the intrathoracic vessels tends to be constant. In certain situations, however, the physiological meaning of central venous pressure is changed. For example, if the tricuspid valve is incompetent, right ventricular pressure is transmitted to the right atrium during ventricular systole. In general, the use of central venous pressure to assess changes in central blood volume depends on the assumption that the right heart is capable of pumping normally. Also, central venous pressure does not necessarily reflect left atrial or left ventricular filling pressure. Abnormalities in right or left heart function or in pulmonary vascular resistance can make it difficult to predict left atrial pressure from central venous pressure.
Unfortunately, measurements of the peripheral venous pressure, such as the pressure in an arm or leg vein, are subject to too many influences (e.g., partial occlusion caused by positioning or venous valves) to be helpful in most clinical situations.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.