Signal Collection Best Practices

This guide helps you obtain high-quality ECG and PPG physiological signals to ensure subsequent analysis is accurate, reliable, and repeatable.

---

ECG signal collection guidance

1. Environment preparation

Measurement environment requirements

Item	Recommended	Reason
Temperature	20–25°C	Too cold can cause vasoconstriction and muscle tremor
Humidity	40–60%	Too dry may reduce electrode contact; too humid increases sweat interference
Lighting	Soft, natural light	Avoids patient stress
Noise	Quiet environment	Reduces psychological stress
Electromagnetic environment	Keep away from strong equipment	Prevents power-frequency interference (50/60Hz)

Equipment check list

Before measurement:

☑️ Device battery is sufficient (recommended > 50%)
☑️ Electrodes/sensors are clean and uncontaminated
☑️ Lead wires are securely connected
☑️ Proper grounding (medical-grade devices)
☑️ Sampling rate is configured correctly (recommended 500Hz)
☑️ Time synchronization is accurate

2. Skin preparation

Correct skin preparation can significantly improve signal quality.

Standard workflow

Detailed steps

1. Clean the skin 🧼

   - Use warm water and a mild soap
   - Thoroughly remove sweat, dirt, and cosmetics
   - Pat dry with a clean towel

2. Remove hair ✂️

   - If hair is dense, shaving is recommended
   - Avoid depilatory creams (may irritate skin)
   - Avoid accidental cuts

3. Light abrasion 🔧

   - Use medical sandpaper or gentle exfoliating gel
   - Lightly abrade to remove dead skin
   - Reduce skin impedance
   - Note: do not over-abrade

4. Remove oil 🧴

   - Wipe with 75% alcohol pad
   - Wait until it fully evaporates and dries

5. Electrode attachment 📍

   - Peel off electrode protective film
   - Press from center outward to avoid air bubbles
   - Ensure conductive gel makes good skin contact

3. Electrode placement

Standard 12-lead system

Limb lead electrode positions:
🔴 RA (Right Arm): inside right forearm or below right clavicle
🟡 LA (Left Arm): inside left forearm or below left clavicle
🟢 LL (Left Leg): inside left calf or over left iliac crest
⚫ RL (Right Leg / ground): inside right calf or over right iliac crest

Precordial (chest) lead electrode positions:
🔵 V1: right sternal border, 4th intercostal space
🔵 V2: left sternal border, 4th intercostal space
🔵 V3: midpoint between V2 and V4
🔵 V4: left midclavicular line, 5th intercostal space
🔵 V5: same horizontal level as V4, anterior axillary line
🔵 V6: same horizontal level as V4, mid-axillary line

Simplified single-lead / three-lead systems

Single-lead (Lead II)

Most common monitoring lead
🔴 RA: right shoulder or below right clavicle
⚫ RL: lower left abdomen or left iliac crest
Reference electrode: lower right abdomen or right iliac crest

Three-lead (standard configuration)

Can obtain Leads I, II, III
🔴 RA: right arm or right shoulder
🟡 LA: left arm or left shoulder
🟢 LL: left leg or lower left abdomen

4. Patient preparation and instructions

Pre-measurement explanation to the patient

Explain clearly:

✅ Measurement purpose and process
✅ Duration (usually 5–10 minutes)
✅ Painless, safe, non-invasive
✅ Stay calm and relaxed
✅ Avoid speaking and moving

Patient positioning options

Position	Advantages	Disadvantages	Best for
Supine (lying on back)	Most stable/standard	Some patients may feel uncomfortable	Routine exams & diagnosis
Semi-supine	Comfortable, less affected by breathing	Slight body-position changes	Elderly or breathing difficulty
Sitting	Convenient and natural	Slightly less stable	Quick screening / dynamic monitoring
Standing	Real-life state	More interference	Exercise testing / special assessments

Recommended: supine position, arms relaxed at sides, palms facing down.

Patient do’s & don’ts

During measurement:

✅ Stay relaxed, avoid tension
✅ Normal breathing (do not hold breath)
✅ Don’t speak or cough
✅ Don’t move the body or limbs
✅ Tell us immediately if you feel discomfort

Avoid before measurement:

❌ Intense exercise (rest at least 10 minutes)
❌ Smoking (at least 30 minutes before)
❌ Stimulants like coffee/tea (at least 1 hour before)
❌ Full meal (at least 1 hour before)
❌ Excessive anxiety or strong emotional excitation

5. Acquisition parameter settings

Recommended configuration

{
  "sampling_rate": 500,        // Sampling rate (Hz), standard clinical use
  "resolution": 12,            // ADC resolution (bits)
  "gain": 1000,               // Gain multiplier
  "filter_settings": {
    "highpass": 0.05,          // High-pass filter (Hz), removes baseline drift
    "lowpass": 100,            // Low-pass filter (Hz), anti-aliasing
    "notch": 50                // Notch filter (Hz), remove power-frequency interference
  },
  "duration": 60,             // Recording duration (seconds), at least 30 seconds
  "lead_config": "standard_12" // Lead configuration
}

Parameter selection by scenario

Routine monitoring

• Sampling rate: 250–500 Hz
• Duration: 30–60 seconds
• Leads: Lead II or 12-lead

Arrhythmia detection

• Sampling rate: 500 Hz
• Duration: at least 2 minutes (recommended 5–10 minutes)
• Leads: 12-lead

HRV (heart rate variability) analysis

• Sampling rate: ≥ 250 Hz
• Duration: 5 minutes (short-term) or 24 hours (long-term)
• Leads: single-lead is sufficient

Exercise test

• Sampling rate: 500–1000 Hz
• Duration: full exercise + recovery period
• Leads: 12-lead, with focus on V5

---

Quick diagnosis of common ECG signal issues

---

PPG signal collection guidance

1. Device selection

Measurement method selection

Transmissive PPG

Suitable sites: fingertip, earlobe
Advantages:
✅ stronger signal and higher SNR
✅ good accuracy
Limitations:
❌ less convenient to wear
❌ not ideal for long-term monitoring
Recommended scenarios: medical pulse oximetry, SpO2 measurement

Reflective PPG

Suitable sites: wrist, forehead, chest
Advantages:
✅ convenient to wear
✅ suitable for long-term monitoring
✅ preferred for wearables
Limitations:
❌ weaker signal
❌ more prone to interference
Recommended scenarios: daily health monitoring, exercise tracking

Wavelength selection

Use case	Recommended wavelength	Notes
Heart rate monitoring	Green light (525nm)	Highest absorption; suitable for wrist
SpO2 measurement	Red (660nm) + Infrared (940nm)	Dual-wavelength pairing
Deeper vessels	Infrared (940nm)	Greater penetration depth

2. Measurement sites and preparation

Wrist (most common)

📍 Position: 2–3 cm behind the wrist bone
📏 Tightness: can fit one finger
🤚 Recommended: non-dominant hand
⌚ Orientation: sensor flat on skin; screen facing up

Skin preparation:

1. Clean the wrist skin
2. Remove lotion/sunscreen
3. Wipe away sweat
4. Remove excessive hair if needed

Fitting check:

✅ Sensor back is fully in contact with skin
✅ No obvious light leakage (check in a dark area)
✅ No excessive pressure; circulation is not affected
✅ Even illumination with green light

Fingertip (medical-grade)

Recommended fingers:

• Best: index finger or middle finger
• Alternative: ring finger
• Avoid: thumb (more muscle), little finger (lower blood flow)

Insertion depth:

✅ Insert to the fingertip fully
✅ Nail stays above the sensor
✅ Fingertip pad makes full contact with the sensor

Notes:

❌ Avoid nail polish / fake nails
❌ Don’t squeeze too hard
❌ Keep finger warm
❌ Don’t move the finger during measurement

3. Posture and environment

Resting measurement

Best posture

Sitting or lying down:
✅ relaxed body
✅ measurement site at the same height as the heart
✅ arm supported (avoid letting it hang)
✅ don’t cross legs (can affect circulation)

Duration

• Adaptation: 30 seconds
• Measurement: at least 60 seconds
• Recommended: 2–5 minutes

Exercise measurement

Device requirements:

✅ supports exercise mode
✅ accelerometer assistance
✅ water/sweat resistant
✅ firmly worn

Wearing advice:

Wear slightly tighter than resting measurement
Ensure no wobbling
Wear 5 minutes before exercise so skin adapts

4. Signal quality optimization techniques

Hardware-side

✅ Use multiple LEDs and detectors (redundancy)
✅ Adaptive light emphasis regulation
✅ Add accelerometer (motion compensation)
✅ Improve enclosure design (light shielding + better fit)

Software-side

✅ Real-time signal quality assessment
✅ Motion artifact detection & removal
✅ Adaptive filtering
✅ Multi-sensor data fusion

Usage habits:

✅ Clean sensors regularly
✅ Keep skin clean and dry
✅ Wear correctly (proper tightness)
✅ Avoid extreme temperature
✅ Rest 2–5 minutes before measurement

---

Common PPG questions diagnosis

---

Data recording & management

1. Record metadata

For each acquisition, record complete metadata:

{
  "measurement_info": {
    "timestamp": "2025-11-17T10:30:00Z",
    "duration": 300,
    "signal_type": "ECG",
    "device_id": "AIECG-2024-001",
    "software_version": "v2.1.0"
  },
  "subject_info": {
    "subject_id": "SUBJ_001",
    "age": 45,
    "gender": "male",
    "height": 175,
    "weight": 70
  }
}