EdgeCare: phase 3 - bracelet with two dry electrodes placed on the skin for the dielectric profile and more

The function used in Labview for all above calculatiuon is this (in formula node):

// Intrari: gsr, tau, temp
// Iesiri: hydratation_index, c_skin_nF, status_code

if (gsr >= 9999.0 || tau == 0) {
    c_skin_nF = 0.0;
    hydratation_index = 0.0;
    status_code = 0; // Deconectat
} else {
    // 1. Compensare termica pentru GSR (Referinta: 33.0 °C, Coeficient: 2% per °C)
    float t_ref = 33.0;
    float alpha = 0.02;
    
    // Corectam GSR-ul daca temperatura este valida
    float gsr_corr = gsr;
    if (temp > 25.0 && temp < 42.0) {
        gsr_corr = gsr * (1.0 + alpha * (temp - t_ref));
    }

    // 2. Calcul capacitate dielectrici compensata
    c_skin_nF = tau / gsr_corr;
    // 3. Scalare Indice de Hidratare (0 - 100%)
    float c_min = 0.5; // nF
    float c_max = 3.0; // nF
    
    float raw_index = ((c_skin_nF - c_min) / (c_max - c_min)) * 100.0;
    
    if (raw_index < 0.0) raw_index = 0.0;
    if (raw_index > 100.0) raw_index = 100.0;
    
    hydratation_index = raw_index;

    // 4. Clasificare stare
    if (gsr_corr < 40.0) {
        status_code = 4; // Transpiratie / Hiperhidroza
    } else if (hydratation_index >= 60.0) {
        status_code = 3; // Hidratat / Optim
    } else if (hydratation_index >= 30.0) {
        status_code = 2; // Hidratare Moderata
    } else {
        status_code = 1; // Deshidratat / Uscat
    }
}

Demo: 

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EdgeCare: phase 3 - bracelet with two dry electrodes placed on the skin for the dielectric profile and more

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OBS: The EdgeCare system utilizes the parallel RC equivalent model for epidermal impedance described by Geddes & Baker (1989) and Martinsen & Grimnes (2011).

The determination of the dielectric capacitance (Cskin = Tau / R) and its scaling to derive the hydration index follow the dynamics of electrodermal activity (EDA) variation established by Boucsein (2012),

with a thermal correction using an alpha coefficient of 0.02°C applied in accordance with Wenig & Martinsen (2000).

B. Cardiorespiratory efficiency and tissue perfusion; apnea detection

This module assesses in real time how efficiently the cardiovascular system delivers oxygen to peripheral tissues and how the body reacts to stress or hypoxia.

To achive this, an new parameter is introduced: PI (Tissue Perfusion Index).

How it is working: PI it represents the ratio between the pulsatile alternating component (AC, pulsating arterial blood) and the non-pulsatile continuous component (DC, tissue, bone, static venous blood)

The formula used is this: PI = (AC / DC ) * 100%

Interpretation: 

- PI >=1.0%  - indicates good tissue perfusion in the finger;

- PI < 0.5% - indicates peripheral vasoconstriction, cold fingers, or a weak signal.

SpO2 and HR are both displayed on the same Waveform Chart with double Y-axes:

- on the left side is displayed HW that monitors variations in ventricular rate (40 --180 BPM), in pink colour;

-  on the right side is displayed SpO2 that mMonitors arterial oxygenation levels (70-100\%).

Apnea detection: the algorithm runs inside the Formula Node block in LabVIEW and evaluates the conditions for an episode of obstructive or central sleep apnea.

The algorithm and Labview implementation:

// Intrari: gsr, tau, temp, pi, spo2
// Iesiri: hydratation_index, c_skin_nF, status_code, low_perfusion, cardio_status, apnea_alert

// ==========================================
// 1. EVALUARE PROFIL DIELECTRIC (GSR + TAU)
// ==========================================

if (gsr >= 9999.0 || tau == 0) {
    c_skin_nF = 0.0;
    hydratation_index = 0.0;
    status_code = 0; // Deconectat
} else {
    // 1. Compensare termica pentru GSR (Referinta: 33.0 °C, Coeficient: 2% per °C)
    float t_ref = 33.0;
    float alpha = 0.02;
    
    // Corectam GSR-ul daca temperatura este valida
    float gsr_corr = gsr;
    if (temp > 25.0 && temp < 42.0) {
        gsr_corr = gsr * (1.0 + alpha * (temp - t_ref));
    }

    // 2. Calcul capacitate dielectrici compensata
    c_skin_nF = tau / gsr_corr;
    // 3. Scalare Indice de Hidratare (0 - 100%)
    float c_min = 0.5; // nF
    float c_max = 3.0; // nF
    
    float raw_index = ((c_skin_nF - c_min) / (c_max - c_min)) * 100.0;
    
    if (raw_index < 0.0) raw_index = 0.0;
    if (raw_index > 100.0) raw_index = 100.0;
    
    hydratation_index = raw_index;

    // 4. Clasificare stare
    if (gsr_corr < 40.0) {
        status_code = 4; // Transpiratie / Hiperhidroza
    } else if (hydratation_index >= 60.0) {
        status_code = 3; // Hidratat / Optim
    } else if (hydratation_index >= 30.0) {
        status_code = 2; // Hidratare Moderata
    } else {
        status_code = 1; // Deshidratat / Uscat
    }
}

// ==========================================
// 2. EVALUARE INDICE DE PERFUZIE (PI)
// ==========================================
int low_perfusion = 0;
if (pi > 0.0 && pi < 0.5) {
    low_perfusion = 1; // Vasoconstruc?ie / Degete reci
}

// ==========================================
// 3. STARE CARDIORESPIRATORIE
// ==========================================
// 0: Deconectat | 1: Normal | 2: Hipoxie | 3: Aritmie/Anormal
if (spo2 == 0 || hr == 0) {
    cardio_status = 0;
} else if (spo2 >= 95.0 && hr >= 50.0 && hr <= 100.0) {
    cardio_status = 1; 
} else if (spo2 < 90.0) {
    cardio_status = 2; 
} else {
    cardio_status = 3; 
}

// ==========================================
// 4. ALGORITM ALERTA APNEE ÎN SOMN
// Scadere SpO2 <= 92% corelata cu micro-trezire (HR >= 85 BPM)
// ==========================================
int apnea_alert;
if (spo2 > 0 && spo2 <= 92.0 && hr >= 85.0) {
    apnea_alert = 1; // Alerta apnee / desaturare
} else {
    apnea_alert = 0;
}

Working mechanism:

- Respiratory pause (Apnea): During the cessation of breathing, blood oxygen levels begin to drop progressively;

- Desaturation (SpO_2 <= 92\%): When the SpO_2 level falls below the critical threshold of 92\%, the body enters a state of mild hypoxia;

- Micro-arousal / Sympathetic stress response (HR >= 85 BPM): The brain detects the lack of oxygen and activates the sympathetic nervous system, triggering a sudden increase in heart rate (compensatory tachycardia) to circulate the remaining oxygenated blood more rapidly;

- Signal validation (SpO_2 > 0): Prevents false alarms from triggering when the sensor is removed from the finger (disconnected state).

OBS: The perfusion index (PI) was evaluated according to the methodology described by Allen [5], while the arterial desaturation thresholds for apnea follow the recommendations of Penzel et al. [7].

C. Detection of febrile conditions or heat shock.

The Temp + GSR (Body Thermoregulatory Response) module complements the EdgeCare biometric system by adding the component of metabolic and autonomic nervous system (ANS) assessment.

If oximetry (HR, SpO_2, PI) measures cardiorespiratory function, the combination Temperature + GSR monitors heat stress and electrodermal reactivity.

The role of parameters:
a. Peripheral/Skin Temperature (Temp):
- Febrile State / Hyperthermia (Temp > 37.5C): The body tries to eliminate excessive heat through peripheral vasodilatation and sweating.
- Heat Shock / Hypothermia / Vasoconstriction (Temp < 35.0C): The body redirects blood from the periphery to the vital organs (fingers become cold, correlated with a massive drop in PI).
b. Galvanic Skin Response (GSR / Electrodermal Conductance)
- The eccrine sweat glands are innervated exclusively by the sympathetic nervous system.
- In case of intense physical exertion, thermal shock, pain or emotional stress, sweat activity increases instantly.
- Water and minerals in sweat remove skin resistance and increase GSR conductance.

Code for this module (this code will be added in Formula node from Labview):

// Detectie Soc Termic sau Stare Febrila
if (temp > 38.0) {
    fever_alert = 1; // Indicator Febrăa/ Hipertermie
} else if (temp < 35.0 && pi < 0.5) {
    shock_alert = 1; // Indicator Posibil Soc Termic / Hipotermie
} else {
    fever_alert = 0;
    shock_alert = 0;
}

Demo:

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EdgeCare: phase 3 - bracelet with two dry electrodes placed on the skin for the dielectric profile and more

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OBS: to simulate fever in "The Body's termoregulatory Response" area I heated the temperature sensor a little above the trigger threshold of the alert.

Bibliography:

- Geddes, L. A., & Baker, L. E. (1989). Principles of Applied Biomedical Instrumentation (3rd ed.). John Wiley & Sons.

- Martinsen, O. G., & Grimnes, S. (2011). Bioimpedance and Bioelectricity Basics (3rd ed.). Academic Press.

- Wenig, P. B., & Martinsen, O. G. (2000). Thermal influence on skin bioimpedance measurements. Annals of Biomedical Engineering, 28(5), 582–588.

- Boucsein, W. (2012). Electrodermal Activity (2nd ed.). Springer Science & Business Media.

- J. Allen, „Photoplethysmography and its application in clinical physiological measurement”, Physiological Measurement, vol. 28, no. 3, pp. R1–R39, 2007.

- MAXIM Integrated, „MAX30100: Pulse Oximeter and Heart-Rate Sensor IC”, Datasheet & Application Notes, Rev. 0, 2014.

- T. Penzel, et al., „The apnea-hypopnea index: history, clinical use, and future potential”, Journal of Clinical Sleep Medicine, 2012.

I will continue here with the implementations...