Reactive Hyperemia Index ∞ Area

Reactive Hyperemia Index

Meaning

The Reactive Hyperemia Index (RHI) quantifies peripheral arterial dilation following brief induced ischemia. This non-invasive metric reflects microvascular endothelial function, specifically the endothelium’s ability to produce vasodilatory substances in response to metabolic demand. It offers objective assessment of vascular health and vessel lining integrity.

Context

Within the cardiovascular system, RHI primarily assesses microcirculation, focusing on the endothelial layer. This critical interface regulates vascular tone, blood flow, and inflammatory responses. The index is relevant for systemic vascular health, as endothelial dysfunction often precedes overt clinical disease.

Significance

The practical importance of RHI lies in its utility as an early indicator of cardiovascular risk. An impaired RHI can signal subclinical endothelial dysfunction, a foundational defect in conditions like hypertension, diabetes, and atherosclerosis. Early detection allows for timely interventions, potentially influencing patient symptoms and improving long-term health outcomes through guided therapeutic strategies.

Mechanism

The underlying mechanism of reactive hyperemia involves a physiological cascade initiated by transient arterial occlusion. During ischemia, metabolic byproducts like adenosine and carbon dioxide accumulate. Upon cuff release, these vasodilatory mediators, along with endothelium-derived nitric oxide, trigger a rapid, pronounced increase in blood flow. A robust RHI signifies healthy endothelial response.

Application

In clinical practice, RHI is applied as a non-invasive diagnostic tool to assess endothelial health. It is measured using specialized peripheral arterial tonometry (PAT) devices, recording pulsatile volume changes in the fingertip before and after brachial artery occlusion. This protocol allows clinicians to evaluate vascular function, valuable in preventive cardiology and for monitoring intervention effectiveness.

Metric

The Reactive Hyperemia Index is precisely measured through the ratio of peripheral arterial pulsatile volume after cuff release (hyperemic phase) to the baseline volume (pre-occlusion phase). This ratio, calculated by the PAT device, serves as a quantitative biomarker of endothelial function. A higher RHI value generally indicates more robust endothelial responsiveness, while lower values suggest compromised vascular health.

Risk

While RHI measurement is generally safe and non-invasive, potential risks primarily involve misinterpretation. The procedure carries minimal risk, but inaccurate readings can occur in patients with severe peripheral artery disease or conditions altering peripheral perfusion. Solely relying on RHI without a comprehensive clinical profile could lead to incomplete assessment or inappropriate management, underscoring integrated clinical judgment.