The Predictive Value of Heart Rate Variability for the Prognosis of Patients With Mild to Moderate Traumatic Brain Injury

Glasgow Outcome Score

• Dead: As a direct result of brain trauma, or due to secondary complications, or other complications
• Vegetative State: Patients who remain unresponsive and speechless…. 3， Severe Disability: The patient is conscious but needs the assistance of another person for some activities of daily living every day 4， Moderate Disability: Such a patient can look after himself at home, get out and about to the shops, and travel by public transport. However, some previous activities, either at work or in social life, are now no longer possible because of either physical or mental deficit 5， Good Recovery: This indicates the capacity to resume normal occupational and social activities, although minor physical or mental deficits may exist. Social outcomes should be included in the assessment here, such as leisure activities and family relationships.

This metric measures the standard deviation of normal beat-to-beat intervals (SDNN) present within the heart rhythm. It is a time domain measure of heart rate variability（HRV）, and it serves as a marker of overall adaptability of the nervous system.

The average of all 5-minute standard deviations of NN intervals across 24 hours (SDNN index). Reflects combined parasympathetic and sympathetic modulation

The Root Mean Square of Successive Differences between NN intervals (RMSSD) quantifies the variability in time intervals between consecutive normal heartbeats (NN intervals) on an electrocardiogram (ECG). Reflects parasympathetic (vagal) tone, as it captures rapid, beat-to-beat changes in heart rate mediated by the autonomic nervous system. A higher RMSSD indicates greater HRV and adaptability of the cardiovascular system, often associated with better stress resilience and recovery.

A higher pNN50 indicates greater parasympathetic dominance. A lower pNN50 suggests reduced vagal tone, common in stress, aging, or pathologies.

The Triangle Index is a global measure of heart rate variability derived from the geometric properties of an NN interval histogram. A higher value indicates greater overall HRV, reflecting healthy autonomic nervous system function.

Baseline level of High Frequency HRV power (0.15-0.4 Hz) measured in ms2/Hz recorded on day 1 of TBI

Low-frequency (LF) power (typically 0.04-0.15 Hz) is a spectral component of HRV reflecting mixed sympathetic and parasympathetic influences on heart rate, with potential contributions from baroreflex activity.

VLF (Very-Low-Frequency) power is a spectral component of heart rate variability (HRV) in the 0.0033-0.04 Hz range (or sometimes <0.05 Hz). VLF is linked to long-term autonomic and neurohormonal control.

Its values range from 3 to 15. 13 to 15: Mild traumatic brain injury (mTBI). 9 to 12: Moderate TBI.3 to 8: Severe TBI.

White Blood Cell (WBC) count refers to the measurement of the total number of white blood cells (leukocytes) per microliter (µL) or cubic millimeter (mm³) of blood. These cells are a crucial component of the immune system, playing essential roles in defending the body against infections, foreign substances, and diseases.

Hemoglobin (Hb or Hgb) is an iron-containing protein found in red blood cells (RBCs) that binds oxygen in the lungs and delivers it to tissues throughout the body while also transporting carbon dioxide back to the lungs for exhalation.

Platelets (thrombocytes) are small, colorless cell fragments in the blood that play a crucial role in clotting and stopping bleeding. The platelet count (PLT) measures the number of platelets per microliter (μL) of blood.

C-reactive protein (CRP) is a liver-produced protein that increases rapidly in response to inflammation, infection, or tissue damage. It is a key acute-phase reactant used to detect and monitor inflammatory conditions.