PAT Signal

PAT™ Technology (Peripheral Arterial Tone)

PAT™ technology is a non-invasive window to the cardiovascular system and autonomic nervous system. Peripheral Arterial Tone (PAT™) signal is a proprietary technology used for non-invasively measuring arterial tone changes in peripheral arterial beds.

ThePAT™ signal is measured from the fingertip by recording finger arterial pulsatile volume changes.
Based on PAT™ technology, the non-invasive EndoPAT system comprises a measurement apparatus that supports a pair of modified plethysmographic bio-sensors. The unique feature of the PAT™ bio-sensors is that they impart a uniform sub-diastolic pressure field to the distal two-thirds of the fingers including their tips. Applying the pressure in this way is extremely important as it:

  • Prevents distal venous blood pooling, that can induce a veno-arteriolar vasoconstriction reflex
  • Unloads arterial wall tension which generates a greater dynamic range of the measured PAT™ signal
  • Fixates thePAT™ bio-sensor to the finger, which reduces movement artifacts


Endothelial Function

EndoPAT assesses digital flow-mediated dilation during reactive hyperemia using measurements from both arms – occluded side and control side.
EndoPAT provides an index of endothelial function in two forms: RHI and LnRHI

RHI (Reactive Hyperemia Index) is the post-to-pre occlusion PAT™ signal ratio in the occluded side, normalized to the control side and further corrected
for baseline vascular tone.
Normal: RHI > 1.67
Abnormal: RHI ≤ 1.67

LnRHI is a similar index after natural log transformation with a matched cutoff:
Normal: LnRHI > 0.51
Abnormal: LnRHI ≤ 0.51

Natural log is a monotonic transformation therefore it does not change the dichotomous diagnosis for any individual test.
LnRHI provides a better double-sided distribution than RHI that is closer to normal distribution. It offers better separation between disease states.

Risk Score Calculator

The EndoPAT™ Risk Score Calculator provides the 3 most commonly used cardiovascular risk assessment methods:

  • Framingham Risk Score: Estimates 10 year risk of Coronary Heart Disease, MI or cardiac death (Adults treatment panel III, JAMA 2001). Applies to subjects without known heart disease or diabetes. Utilities different models for men and women using the following predictors: age, total cholesterol, HDL, systolic blood pressure, treatment for hypertension and smoking.
  • Score: The European estimate of a 10 year risk of fatal CVD (EHJ, 2003). Charts are divided to low-risk regions (Belgium, France, Greece, Italy, Luxemburg, Spain and Portugal) and high-risk regions (all other European countries) using the following predictors: gender, age, total cholesterol, systolic blood pressure, and smoking.
  • Reynolds Risk Score: Provides 10 years’ risk of MI, stroke, revascularization or cardiac death (JAMA 2007, Circ 2008). Reynolds risk score uses the following predictors: gender, age, total cholesterol, HDL, systolic blood pressure, hsCRP, and parent MI before age 60.

Additional tests provided (not for clinical use in USA)

Augmentation Index (AI)

Measures arterial stiffness is calculated via pulse waveform analysis of the PAT™ signal and is considered an independent risk factor for CVD not necessarily correlated to endothelial function.

AI is calculated from PAT™ pulses recorded at the base-line period.
The result is further normalized to heart rate of 75bpm ([email protected]).

Lower AI values (including negative results) reflect better arterial elasticity.
The AI result is provided relative to gender matched, non-selective populations.

Heart rate variability (HRV)

A measure of heart beat-to-beat variability in either time or frequency domain.
HRV reflects the status of the autonomic nervous system (ANS) and is associated with the balance between sympathetic and parasympathetic activities that may reflect various pathological conditions.

The HRV is calculated from the baseline period, based on the ESC and North American Society of Pacing Electrophysiology task force standards.
Results are available in various time and frequency domain formats.