Components of SVR

 Q: Systemic Vascular Resistance (SVR) is determined by all of the following EXCEPT? (select one)

A) Afterload 

 B) Vessel length 

C) Vessel tone 

D) Vessel diameter 

E) Blood viscosity

Answer: A

Hemodynamic stability vs instability is basically determined at bedside by the vital of systemic blood pressure (BP)

BP = CO X SVR 

 Where BP is Blood-Pressure, CO is Cardiac-Output and SVR is Systemic Vascular Resistance. 

 On further refinement 

 CO = HR X SV 

 Where HR is Heart Rate and SV is Stroke Volume 

 The stroke volume is determined by three entities 

•  Preload 
•  Myocardial contractility 
•  Afterload 

 and SVR is determined by: 

•  Vessel length 
•  Blood viscosity 
•  Vessel diameter, and 
•  Vessel tone

Afterload (choice A) is more of a determinant of SV than SVR.

#hemodynamics

References:

1. Bighamian R, Hahn JO. Relationship between stroke volume and pulse pressure during blood volume perturbation: a mathematical analysis. Biomed Res Int. 2014;2014:459269. doi:10.1155/2014/459269 

2. Reynolds HR, Hochman JS. Cardiogenic shock current concepts and improving outcomes. Circulation. 2008;117(5):686–697