Systemic Vascular Resistance (SVR) and Cardiac Function

Introduction

Systemic Vascular Resistance (SVR) is a key parameter in cardiovascular physiology. It refers to the resistance that the systemic circulation offers to blood flow. SVR is crucial in determining afterload—the pressure the heart must work against to pump blood into the arteries.

Key Concepts:

1. Definition of SVR:

   • SVR is the total resistance exerted by the systemic vasculature.
   • It is influenced by arterial tone, blood viscosity, and vessel diameter.

2. SVR and Cardiac Output Relationship:

   • Cardiac output (CO) is the volume of blood pumped by the heart per minute.
   • SVR and CO are inversely related: if SVR increases, the heart must pump harder to maintain blood flow.

3. Causes of Increased SVR:

   • Hypertension
   • Vasoconstriction (caused by stress, hormones like catecholamines)
   • Atherosclerosis and arterial stiffness
   • Chronic kidney disease

4. Causes of Decreased SVR:

   • Sepsis and anaphylaxis (leading to vasodilation)
   • Shock states (distributive and neurogenic shock)
   • Use of vasodilatory drugs (e.g., nitrates)

5. SVR and Heart Failure:

   • In heart failure with reduced ejection fraction (HFrEF), SVR tends to be increased due to compensatory vasoconstriction.
   • In heart failure with preserved ejection fraction (HFpEF), SVR may also be high due to arterial stiffness.

6. Clinical Measurement and Management:

   • SVR is not directly measured but is estimated using the formula:

     SVR = (Mean Arterial Pressure - Central Venous Pressure) / Cardiac Output × 80

   • Management strategies include:
     • Vasodilators (e.g., ACE inhibitors, calcium channel blockers) to lower SVR in hypertension or heart failure.
     • Fluids and vasopressors in cases of low SVR due to sepsis or shock.

Conclusion

Understanding SVR is essential in managing various cardiovascular conditions. It directly affects heart workload and is a central consideration in heart failure, hypertension, and shock management.

Source recommendations

1. European Society of Cardiology (ESC) Guidelines on Heart Failure

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Acute-and-Chronic-Heart-Failure
2. https://academic.oup.com/eurheartj/article/42/36/3599/6358045
3. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Focused-Update-on-Heart-Failure-Guidelines
4. https://academic.oup.com/eurheartj/article/44/37/3627/7246292
5. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines

2. American Heart Association (AHA) Guidelines on Hypertension

1. https://www.ahajournals.org/doi/10.1161/hyp.0000000000000065
2. https://www.heart.org/en/health-topics/high-blood-pressure
3. https://professional.heart.org/en/science-news/2017-hypertension-clinical-guidelines
4. https://www.heart.org/en/health-topics/high-blood-pressure/understanding-blood-pressure-readings/monitoring-your-blood-pressure-at-home
5. https://www.acc.org/Latest-in-Cardiology/Articles/2024/02/05/11/43/2023-ESH-Hypertension-Guideline-Update

3. American College of Cardiology (ACC) Guidelines on Shock Management

1. https://www.acc.org/Latest-in-Cardiology/Journal-Scans/2025/03/17/18/39/ACCs-First-Concise-Clinical-Guidance-Focuses-on-Evaluation-and-Management-of-Cardiogenic-Shock
2. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001063
3. https://www.acc.org/
4. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001309
5. https://pubmed.ncbi.nlm.nih.gov/35363499/