HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 98/1/356    most recent 00535.2004v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Reddi, B. A. J. Articles by Carpenter, R. H. S. Search for Related Content PubMed PubMed Citation Articles by Reddi, B. A. J. Articles by Carpenter, R. H. S.

INVITED COMMENTARY

Venous excess: a new approach to cardiovascular control and its teaching

The Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom

ABSTRACT

The circulatory control system is driven partly by factors relating to the arterial side and partly by factors relating to the venous side. Students are generally provided with a conceptually clear account of the arterial side, based on sound homeostatic mechanisms of negative feedback from a well-defined error signal, arterial pressure. However, on the venous side, teaching is often based on the notion of venous return, a concept that, as normally presented, is imprecise and intangible, a frequent cause of confusion that may lead to errors of clinical practice. Although one can trace these misconceptions back to some of Guyton's publications, Guyton himself was well aware of the complexities of venous resistance and capacitance but has not always been well served by subsequent misinterpretation. The fundamental problem with venous return that makes it inappropriate for controlling the circulation is that it lacks the essential requirement of being an error signal. We propose instead a new variable, venous excess, which represents the accumulation of any mismatch between the rate of blood entering the great veins and the rate of leaving, the cardiac output. As well as being directly observable without intervention (in a patient's jugular vein), it meets all of the requirements of an error signal: via the Starling mechanism it stimulates cardiac output, regulates venous compliance, and in the longer term is an important determinant of fluid intake and excretion, and these effects act to reduce the original perturbation. Based on this concept, we suggest a simple and secure basis for teaching the control of the circulation that avoids undue reliance on entities that are difficult to specify or measure and emphasizes the role of feedback and the similarities between the arterial and venous mechanisms.

feedback; homeostasis

This article has been cited by other articles:

				T. M. Zidon and D. D. Sheriff Diversion of blood flow from noncompliant to compliant vasculature in awake dogs: mechanical impact on right atrial pressure Am J Physiol Heart Circ Physiol, January 1, 2006; 290(1): H217 - H223. [Abstract] [Full Text] [PDF]