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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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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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.

D. Estimated Metabolic Inflection Indicator.

What is "Estimated Metabolic Inflection Indicator": this is a multisensor fusion algorithm that evaluates, in real time, the direction of blood glucose fluctuation (rising, stable, or rapidly falling). Without requiring blood sampling or subcutaneous sensors, the method monitors the neurovascular and autonomic footprint that metabolic changes leave on the body.

How is working: the algorithm relies on the involuntary reaction of the sympathetic nervous system (SNS) and the cardiovascular response to glucose fluctuations:
- During rapid drops in blood glucose (risk of hypoglycemia): The body releases adrenaline, triggering an acute "fight-or-flight" response. This manifests as cold sweating (a sudden rise in skin conductance/GSR), compensatory tachycardia (increased heart rate/HR), and peripheral vasoconstriction (a drop in the perfusion index/PI).
- During postprandial states (rise in blood glucose): The reaction is more gradual, characterized by incremental adjustments in skin temperature and GSR, without sudden adrenergic surges.

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

// ==========================================
// 6. ALGORITM pentru Indicator Estimat de Inflexiune Metabolica
// ==========================================
// Declarare variabile interne pentru stocare stare anterioara memorare esantion
float gsr_prev;
float hr_prev;

// Calculul variatiei rapide (derivata discreta)
float delta_gsr = gsr - gsr_prev;
float delta_hr = hr - hr_prev;

// Initializare scor: 0 = Stabil / Homeostazie
glycemic_trend = 0; 
glycemic_alert = 0;

// Verificare validitate date (evita alarme false la deconectare)
if (spo2 > 0.0 && hr > 0.0) {

    // 1. Trend de Scadere Rapida / Stres Metabolic Sympathetic (Risc Hipoglicemic)
    // Caracterizat prin: crestere brusca GSR (transpiratie) + accelerare HR + PI scazut (vasoconstructie)
    if (delta_gsr > 15.0 && delta_hr > 3.0 && pi < 1.0) {
        glycemic_trend = -1; // Trend descrescator (Scadere rapida)
        glycemic_alert = 1;  // Declansare alerta vizuala
    }
    
    // 2. Trend de Crestere / Raspuns Postprandial
    // Caracterizat prin: crestere lenta Temp/GSR fara peak-uri sau fluctuatii majore de HR
    else if (delta_gsr < -5.0 && temp > 36.6 && delta_hr >= -2.0 && delta_hr <= 2.0) {
        glycemic_trend = 1;  // Trend crescator
        glycemic_alert = 0;
    }
    
    // 3. Stare Stabila / Homeostazie
    else {
        glycemic_trend = 0;  // Stare neutra / stabila
        glycemic_alert = 0;
    }
}

// Salvare valori curente pentru esantionul urmator
gsr_prev = gsr;
hr_prev = hr;

The front panel in Labview (no video provided, see last note):

OBS: The metabolic trend monitoring method integrated into the EdgeCare system is based on the multisensory fusion hypothesis validated in the scientific literature.

According to recent studies on autonomic responses to metabolic imbalances, a drop in glucose levels triggers acute sympathetic activation, manifested as rapid variations in electrodermal conductance (GSR) and peripheral hemodynamic adjustments derived from the PPG signal (HR, PI).

The algorithm developed in LabVIEW utilizes these discrete metrics to classify the trend of variation without requiring invasive devices.

IMPORTANT: With this final feature, I aimed to create a device capable of indicating potential rises, falls, or periods of stability in estimated blood glucose levels. To generate this estimate, I utilized GSR, HR, PI, and temperature parameters. This device is not intended to replace a standard glucometer, as the goal is to provide a rough estimate of the trend rather than a precise blood glucose reading; consequently, it should be regarded as an experimental device.

Note: this last module is purely theoretical and experimental; calibrating the algorithm requires a significant number of measurements taken at various times of the day, such as in the morning, after breakfast, before and after lunch, before and after dinner, and at night.
Therefore, this module will be updated once I have created the final hardware version: the wristband with the sensors and power supply installed.

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.