SVR

Q: Systemic Vascular Résistance (SVR) is primarily governed by all of the following EXCEPT? (select one)

A) Extravascular edema

B) Vessel length

C) Blood viscosity

D) Vessel diameter

E) Vessel tone

Answer: A

The formula to understand hemodynamics is relatively simple. The three significant determinants are:

• systemic blood pressure (BP)
• cardiac output (CO), and 
• systemic vascular resistance (SVR)

The simple formula is: BP = CO X SVR

Where CO = HR X SV

HR = Heart rate

SV = Stroke Volume

The stroke volume depends on the following:

• Preload
• Myocardial contractility
• Afterload

SVR is governed by:

• Vessel length
• Blood viscosity
• Vessel diameter and tone 

Alteration in any of the above may cause hemodynamic instability or may be a reactive process to an insult in a body.

Extravascular edema (choice A) has no primary role in determining SVR.

#hemodynamics

References:

1. Secomb TW. Hemodynamics. Compr Physiol. 2016 Mar 15;6(2):975-1003. doi: 10.1002/cphy.c150038. PMID: 27065172; PMCID: PMC4958049.

2. De Hert S. Physiology of hemodynamic homeostasis. Best Pract Res Clin Anaesthesiol. 2012 Dec;26(4):409-19. doi: 10.1016/j.bpa.2012.10.004. PMID: 23351228.

3. Chawla LS, Ince C, Chappell D, Gan TJ, Kellum JA, Mythen M, Shaw AD; ADQI XII Fluids Workgroup. Vascular content, tone, integrity, and haemodynamics for guiding fluid therapy: a conceptual approach. Br J Anaesth. 2014 Nov;113(5):748-55. doi: 10.1093/bja/aeu298. Epub 2014 Sep 17. PMID: 25231767.