Lec 4 Notes

Relationship between Arterial Stiffness, Wave Reflection, and Micro-Circulation

  • Overview
    • Focus on the interconnection between arterial stiffness, wave reflection, and pulsatile flow in managing hypertension and diabetes.

Micro-Circulatory Problems in Diabetics

  • Background
    • Diabetics show a higher incidence of micro-circulatory issues compared to non-diabetics.
    • Common complications include:
      • Retinopathy
      • Stroke
      • Nephropathy
    • Increased risk of macrovascular complications in diabetics:
    • Higher rates of cardiovascular (CV) events such as:
      • Myocardial Infarction (MI)
      • Cardiac Failure
      • Peripheral Vascular Disease (PVD)
    • Studies (ACCT data) reveal that diabetics have noticeably higher arterial stiffness than healthy controls (Reference: McDonnell et al., ESH Milan, 2007).

Arterial Stiffness Measurements

  • Indicators of Arterial Stiffness
    • Carotid-Femoral Pulse Wave Velocity (C-F PWV): Indicates stiffness levels (statistical significance p < 0.001).

UKPDS Study Insights

  • Blood Pressure vs. Glycemic Control
    • Tight blood pressure control is more effective than strict glycemic control in reducing microvascular complications in diabetes patients.

Large Artery Stiffness Effects

  • Pathophysiology
    • Increased stiffness of large arteries diminishes their buffering capacity, resulting in higher pulsatile flow/pressure transmission to microcirculation.

Pulsatility and Wave Reflection

  • Effects on Microcirculation
    • Changes in arterial parameters like aPWV (aortic pulse wave velocity) and AIx (Augmentation Index) impact both macrovascular and microvascular health.
    • An increased AIx could reflect higher pressure waves that might affect the microcirculation uniquely, potentially having beneficial effects.

Aims of the Research Study

  • Objectives
    • Investigate the relationship among aPWV, AIx, and pulsatility in retinal arteries.
    • Examine if high PWV and low AIx correlate with increased microcirculation pulsatility compared to low PWV and high AIx.

Methodology Overview

  • Participant Profile
    • 106 individuals (ages 39-83) free from cardiovascular disease (CVD) and ocular disorders.
    • Excluded those on sympathomimetic compounds.
  • Measurement Techniques
    • Macrovascular assessments:
    • Peripheral and Central Blood Pressure
    • Augmentation Index (SphygmoCor)
    • Aortic PWV (using SphygmoCor)
    • Microvascular assessments:
    • Retinal Artery Pulsatility Ratio (PR)
    • Retinal Artery Resistance Index (RI) via Doppler Ultrasound.

Doppler Ultrasound Parameters

  • Functional Measurements
    • Pulsatility Ratio (PR):
    • Defined as peak systolic velocity divided by end diastolic velocity.
    • Resistance Index (RI):
    • Calculated as (Peak Systolic Velocity - End Diastolic Velocity) / Peak Systolic Velocity.

Study Group Characteristics

  • Two groups based on aPWV and AIx:
    • Group 1 (Lowest PWV, Highest AIx)
    • Group 2 (Highest PWV, Lowest AIx)

Conclusions Drawn

  • Implications of Findings
    • Increased large artery stiffness is associated with elevated pulsatility in the microcirculation, posing risks for microvascular damage.
    • While increased wave reflection may serve as a protective mechanism against high pulsatility transmission, reducing blood pressure and stiffness while maintaining wave reflection may potentially mitigate microvascular impairment.
    • Care should be exercised in reducing wave reflection in patients with already high aPWV, as it might lead to negative outcomes for microvasculature.