The Importance of Central Blood Pressure as a Predictor of Future Cardiovascular Events

I have been doing research in blood pressure diagnostics for the last 30 years, mostly focusing on oscillometric methods of measurement and diagnosis. Over the last couple of years I have been doing more and more research on what is unfortunately a very often misunderstood parameter, which is Central Blood Pressure (CBP). There is more and more evidence that central pressure is better related to future cardiovascular events than is brachial pressure. I strongly believe that the automatic measurement of central blood pressure will be integrated in future home measurements devices and will be displayed as a parameter next to the traditional systolic and diastolic values.

What is Central Blood Pressure?

Central blood pressure (CBP) refers to the pressure within the aorta, the largest artery in the body, which delivers oxygen-rich blood from the heart to the rest of the circulatory system. Unlike brachial blood pressure, which is measured at the arm using a cuff and represents the pressure in peripheral arteries, central blood pressure provides a direct assessment of the hemodynamic load on vital organs such as the heart, brain, and kidneys.

CBP reflects the actual pressure experienced by these organs and is influenced by factors such as arterial stiffness and wave reflections within the arterial system. This distinction is significant because brachial blood pressure can often underestimate or overestimate the true cardiovascular load. Measuring central blood pressure allows for a more precise evaluation of cardiovascular health and provides a clearer understanding of an individual’s risk for future cardiovascular events.

Key Characteristics of Central Blood Pressure

1. Proximity to the Heart: CBP measures pressure closer to the heart and vital organs, offering a more direct insight into the effects of blood pressure on these structures.
2. Wave Reflections: Central pressure accounts for wave reflections from the arterial system that impact the aorta more significantly than peripheral arteries.
3. Pulse Pressure Amplification: The difference between central and brachial pulse pressures highlights how blood pressure values can vary across the arterial tree, making central measurements more physiologically relevant.

A Brief History of Central Blood Pressure

The concept of central blood pressure has roots in the early 20th century when researchers first recognized the differences between central and peripheral blood pressures. Initial studies were limited by the lack of advanced measurement techniques, relying on invasive catheterization to assess central aortic pressure. Despite its accuracy, invasive measurement was impractical for widespread clinical use.

Early Techniques: Invasive Catheterization

In 1828, Jean Leonard Marie Poiseuille introduced the mercury manometer as a tool for estimating blood pressure. In Poiseuille’s experiment, a cannula was inserted into an artery and attached to a manometer on the other end. With every pulse, blood displaced mercury inside the manometer.? Blood pressure was identified by measuring the mercury displacement. It was essentially a reproduction on humans of the experiments of Stephen Hales who, in the 18th century, conducted invasive blood pressure measurements in animals.

In the mid-19th century, the French surgeon Jean Faivre made significant contributions to the measurement of human blood pressure. In 1856, during a surgical procedure, Faivre connected an artery to a mercury manometer, enabling direct readings of systolic pressure. This pioneering method provided some of the earliest quantitative data on human blood pressure, with Faivre recording brachial artery systolic pressures between 115 and 120 mmHg.

These foundational experiments paved the way for the development of more refined techniques and instruments in cardiovascular physiology. The evolution of invasive blood pressure measurement was instrumental in enhancing our understanding of hemodynamics and the pathophysiology of cardiovascular diseases.

In the 1920s and 1930s, researchers began to investigate arterial pressure profiles using catheter-based methods. These techniques involved inserting a catheter directly into the aorta via a peripheral artery, such as the femoral or brachial artery, to measure central pressure. While these methods provided highly accurate measurements, they were invasive, carried significant risks, and were reserved primarily for research settings or critical care applications.

Emergence of Non-Invasive Methods

The limitations of invasive techniques drove the development of non-invasive methods in the latter half of the 20th century. In the 1970s, the advent of tonometry marked a significant breakthrough. Tonometry involves placing pressure sensors over a superficial artery, such as the radial artery, to capture pulse waveforms. These waveforms were then analyzed and mathematically transformed to estimate central aortic pressure.

Key Technological Advances

1. Pulse Wave Analysis (PWA): This method uses tonometry-derived data to reconstruct central aortic pressure waveforms. Mathematical models correct for wave reflections and pulse pressure amplification, making the technique accurate and non-invasive.
2. SphygmoCor System: Introduced in the 1990s, the SphygmoCor device became one of the most widely used systems for non-invasive central blood pressure measurement. It integrates tonometry with pulse wave analysis and provides detailed assessments of arterial stiffness and wave reflections.
3. Oscillometric Methods: More recently, some oscillometric devices, commonly used for brachial blood pressure measurement, have been adapted to estimate central blood pressure. These devices simplify the process by applying algorithms to standard cuff measurements, making CBP assessments more accessible in routine clinical practice.

Widespread Recognition and Research

As non-invasive methods have became reliable and user-friendly, they have opened the door to large-scale studies on central blood pressure. Pioneering trials like the Conduit Artery Function Evaluation (CAFé) study and the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) leveraged these technologies to demonstrate the clinical relevance of CBP. These studies established central pressure as a key marker of cardiovascular health, distinct from brachial pressure.

Integration into Clinical Practice

Since the early 21st century, CBP measurement devices have become compact, automated, and cost-effective, allowing for integration into clinical practice and research worldwide. Modern devices now combine CBP assessment with measurements of arterial stiffness, such as pulse wave velocity (PWV), further enhancing their utility in cardiovascular risk stratification.

Central vs. Brachial Blood Pressure: A Better Predictor of Cardiovascular Risk

For decades, brachial blood pressure has been the cornerstone of hypertension diagnosis and management. However, accumulating evidence suggests that central blood pressure provides a more accurate assessment of cardiovascular risk. Several factors contribute to this distinction.

The Relationship Between Central Blood Pressure and Cardiovascular Events

1. Prognostic Value: Central blood pressure is more closely associated with adverse cardiovascular outcomes, including myocardial infarction, stroke, and heart failure. This is because CBP reflects the hemodynamic stress on the heart and aorta, which are critical in the pathogenesis of these events.
2. Impact of Arterial Stiffness: Arterial stiffness, a hallmark of aging and hypertension, disproportionately affects central arteries. CBP captures the impact of stiffness more effectively than brachial pressure, providing a better marker of vascular health.
3. Drug Effects: Antihypertensive medications often reduce central and brachial pressures differently. Central pressure provides a clearer picture of the therapeutic benefits on cardiovascular outcomes.

Evidence from Clinical Studies

The CAFé Study

The Conduit Artery Function Evaluation (CAFé) study was a landmark investigation that highlighted the importance of CBP. It demonstrated that certain antihypertensive therapies, despite having similar effects on brachial pressure, had differing impacts on central pressure. Patients with greater reductions in CBP experienced better cardiovascular outcomes, emphasizing its prognostic relevance.

ASCOT and Beyond

The Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) also underscored the value of CBP in predicting cardiovascular events. It showed that CBP measurements provided additional insights into cardiovascular risk beyond brachial pressure, particularly in high-risk populations.

Clinical Implications

1. Targeting Central Pressure in Treatment: Therapies aimed at reducing central pressure may offer superior protection against cardiovascular events compared to those focusing solely on brachial pressure. For instance, drugs like calcium channel blockers and renin-angiotensin system inhibitors are more effective at lowering CBP.
2. Improved Risk Stratification: Incorporating CBP into clinical practice allows for more precise risk assessment, particularly in patients with borderline or resistant hypertension.
3. Personalized Medicine: By identifying individuals with elevated CBP but normal brachial pressure, clinicians can tailor interventions to address hidden risks.

Why Central Pressure Outperforms Brachial Pressure

Physiological Relevance

Central blood pressure directly affects the heart and brain, making it a more relevant measure of the forces that drive cardiovascular damage. Brachial pressure, while convenient to measure, does not fully capture the dynamics of arterial wave reflections and stiffness.

Superior Correlation with End-Organ Damage

Studies consistently show that CBP correlates more strongly with markers of end-organ damage, such as:

• Left Ventricular Hypertrophy (LVH): CBP has a stronger relationship with LVH compared to brachial pressure, reflecting its role in determining cardiac workload.
• Carotid Intima-Media Thickness: CBP is a better predictor of atherosclerosis progression in the carotid arteries.
• Microvascular Damage: CBP correlates with damage to the renal and retinal microvasculature, linking it to chronic kidney disease and retinopathy.

Refining Cardiovascular Risk Models

Traditional risk models, such as the Framingham Risk Score, rely heavily on brachial blood pressure. Adding CBP to these models has been shown to improve their predictive accuracy, particularly in populations with high cardiovascular risk.

Future Directions in Central Blood Pressure Research

As the evidence supporting CBP continues to grow, several areas warrant further investigation:

1. Standardization of Measurement: Establishing standardized protocols for CBP measurement will enhance its utility in clinical practice.
2. Integration with Wearable Technology: Advances in wearable sensors may enable continuous monitoring of central pressure, providing dynamic insights into cardiovascular health.
3. Cost-Effectiveness Studies: Demonstrating the economic benefits of incorporating CBP into routine care will be essential for widespread adoption.
4. Longitudinal Studies: Large-scale, long-term studies are needed to confirm the superiority of CBP in predicting hard cardiovascular outcomes.

Central blood pressure represents a paradigm shift in our understanding and management of cardiovascular risk. By focusing on the pressure exerted on central arteries, CBP provides a more accurate reflection of the hemodynamic forces that drive cardiovascular disease. Its superior correlation with end-organ damage and adverse events positions it as a valuable tool for risk stratification and treatment optimization.

While brachial blood pressure remains a cornerstone of hypertension management, the integration of central blood pressure into clinical practice has the potential to revolutionize cardiovascular care. As measurement techniques become more accessible and evidence continues to accumulate, CBP is likely to play an increasingly prominent role in preventing and managing cardiovascular disease.

Discover the history of blood pressure on www.bloodpressurehistory.com

Uwe DIEGEL, [email protected]

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