Cardiac output and vasodilatation in the vasovagal response: an analysis of the classical papers.
Heart Rhythm(2016)
摘要
The simple faint is secondary to hypotension and bradycardia resulting in transient loss of consciousness. According to Ohm's Law applied to the circulation: BP = SVR*CO, hypotension can result from a decrease in SVR (Systemic vascular resistance) or CO (Cardiac output) or both. It is important to understand that when blood pressure (BP) is falling, SVR and CO do not change reciprocally as they do in the steady state. In 1932, Lewis, assuming that decreased SVR alone accounted for hypotension defined "the vasovagal response" along pathophysiological lines to denote the association of vasodilatation with vagal induced bradycardia in simple faint. Studies performed by Barcroft and Sharpey Schafer between 1940 and 1950 used volume-based plethysmography to demonstrate major forearm vasodilatation during extreme hypotension and concluded that the main mechanism for hypotension was vasodilatation. Plethysmographic measurements were intermittent and not frequent enough to capture rapid changes in blood flow during progressive hypotension. However, later investigations by Weissler, Murray and Stevens performed between 1950 and 1970, used invasive beat-to-beat BP measurements and more frequent measurements of CO using the Fick principle. They demonstrated that CO significantly fell before syncope and little vasodilatation occurred until very late in the vasovagal reaction Thus, since the 1970s', decreasing cardiac output rather than vasodilation has been regarded as the principal mechanism for the hypotension of vasovagal syncope.
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关键词
BP,CBV,CO,FBF,HR,LBNP,SBP,SV,SVR
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