We built Pulseline to help you build a calm, daily relationship with your heart and overall wellness. That means being honest about how the app works and where our ideas come from. This page is a friendly tour of the science behind each feature, with links to the public health sources we lean on.
Important: Pulseline is a wellness and lifestyle app, not a medical device. The information here is provided for transparency and general education only. It is not medical advice and is not a substitute for diagnosis, treatment, or monitoring by a qualified healthcare professional. If something about your health worries you — please talk to a doctor.
1. Camera-Based Heart Rate (PPG)
When you cover your iPhone's rear camera with your fingertip and turn on the flash, the camera sees tiny color changes in your skin as blood pulses through it. This technique is called photoplethysmography, or PPG. It's the same general principle used by the green LEDs on the back of fitness watches — just with your phone's camera instead of dedicated sensors.
Smartphone PPG has been studied for over a decade. Results are best when you're sitting still, warm, and pressing gently and consistently on the lens. Cold fingers, motion, or low light reduce accuracy. Pulseline's reading is an estimate, not a clinical measurement.
- MedlinePlus (NIH) — overview of pulse and what it tells you: medlineplus.gov/ency/article/003399.htm
- American Heart Association — All About Heart Rate (Pulse): heart.org — All About Heart Rate
- U.S. National Library of Medicine, PubMed Central — open-access research on smartphone PPG and signal quality: ncbi.nlm.nih.gov/pmc — smartphone photoplethysmography
2. Heart Rate Zones
The four zones you see in Pulseline — resting, fat burn, cardio, and peak — follow the same framework popularized by the American Heart Association. They are calculated from an estimate of your maximum heart rate, which depends on your age. We use these as a general guide, not a prescription for training. Your real maximum can vary, especially if you take certain medications or have a known heart condition; in those cases, please ask your doctor.
- American Heart Association — Target Heart Rates Chart: heart.org — Target Heart Rates
- American Heart Association — Know Your Target Heart Rate for Exercise: heart.org — Know Your Target Heart Rate
- Centers for Disease Control and Prevention — Target Heart Rate and Estimated Maximum Heart Rate: cdc.gov — Measuring Physical Activity Intensity
3. Breathing Exercises
Pulseline includes three guided breathing patterns: Box Breathing (4-4-4-4), 4-7-8 Relaxation, and Coherent Breathing (5-5). Slow-paced breathing — generally around 5–6 breaths per minute — is one of the most-studied ways to help your body settle down. It nudges the part of your nervous system responsible for "rest and digest" and can support a calmer, more focused state.
These exercises are a wellness tool, not a treatment. If you live with anxiety, panic episodes, or any breathing condition, please work with a healthcare professional alongside any self-care practice.
- NIH National Center for Complementary and Integrative Health — Relaxation Techniques: What You Need To Know: nccih.nih.gov — Relaxation Techniques
- NIH National Center for Complementary and Integrative Health — Meditation and Mindfulness: nccih.nih.gov — Meditation and Mindfulness
- American Heart Association — How to Manage Stress: heart.org — Stress Management
4. BMI (Body Mass Index)
BMI is a simple screening number based on your height and weight. It's useful as a general reference for trends over time, but it doesn't account for muscle mass, bone density, age, ethnicity, or where on your body fat is stored. Treat the categories Pulseline shows as a starting point for a conversation with a clinician, not a label.
- World Health Organization — A Healthy Lifestyle: WHO Recommendations (includes BMI ranges): who.int — A Healthy Lifestyle
- Centers for Disease Control and Prevention — About Body Mass Index (BMI): cdc.gov — About BMI
- NIH National Heart, Lung, and Blood Institute — BMI Calculator: nhlbi.nih.gov — BMI
5. Why Keeping a Wellness Diary Helps
Pulseline lets you write down your own blood pressure, blood oxygen (SpO₂), blood sugar, and water intake. The app does not measure any of these — you enter them yourself, from a real device or routine. Keeping a tidy log over time helps you and your doctor spot patterns that a single reading can't.
Blood Pressure
Many cardiology organizations recommend monitoring blood pressure at home with a validated upper-arm cuff and bringing the log to medical visits. Pulseline is the log; the cuff is the measurement.
- American Heart Association — Monitoring Your Blood Pressure at Home: heart.org — Home BP Monitoring
- American Heart Association — Understanding Blood Pressure Readings: heart.org — BP Readings
Blood Oxygen (SpO₂)
SpO₂ in Pulseline is also a manual log. Consumer pulse oximeters have known limitations, especially in low-perfusion or low-light conditions, and the FDA notes that readings should be interpreted alongside how you actually feel.
- U.S. Food and Drug Administration — Pulse Oximeter Accuracy and Limitations: fda.gov — Pulse Oximeter Accuracy
- U.S. Food and Drug Administration — Pulse Oximeters and Oxygen Concentrators: What to Know About At-Home Oxygen Therapy: fda.gov — Pulse Oximeters & Oxygen Concentrators
Blood Sugar
Self-monitoring of blood glucose is a routine part of life with diabetes, and a written log helps clinicians see what a single fingerstick can't. Pulseline does not advise on insulin dosing or medication — please follow your care plan.
- Centers for Disease Control and Prevention — Manage Blood Sugar: cdc.gov — Manage Blood Sugar
- NIH National Institute of Diabetes and Digestive and Kidney Diseases — Diabetes Tests & Diagnosis: niddk.nih.gov — Diabetes Tests
Water Intake
General hydration guidance for healthy adults comes from public dietary references. Individual needs vary with body size, activity, climate, and medical conditions — Pulseline's daily goal is a starting point, not a rule.
- U.S. National Academies of Sciences, Engineering, and Medicine — Dietary Reference Intakes for Water: nap.nationalacademies.org — DRI for Water
- Centers for Disease Control and Prevention — Water and Healthier Drinks: cdc.gov — Water & Healthier Drinks
6. General Heart & Wellness Guidelines We Follow
Whenever Pulseline frames a number, a category, or a piece of advice, we try to keep it in line with these big, well-regarded public health resources. They're worth a bookmark.
- World Health Organization — Cardiovascular Diseases (CVDs): who.int — Cardiovascular Diseases
- American Heart Association — Life's Essential 8 (healthy lifestyle framework): heart.org — Life's Essential 8
- Centers for Disease Control and Prevention — Heart Disease: cdc.gov — Heart Disease
- NIH MedlinePlus — Heart Diseases: medlineplus.gov — Heart Diseases
7. A Note on Limitations
No phone-based heart rate reading is as accurate as a medical-grade ECG or oximeter. No app is a substitute for a clinician who knows your history. Pulseline is best thought of as a gentle daily companion — a way to notice changes and start better conversations about your health, not a way to replace them.
8. Questions or Corrections
If you spot something on this page that looks out of date, or if you'd like to suggest an additional source, we'd love to hear from you.
Reminder: Pulseline is not a medical device. Measurements and information in the app are for general wellness and educational purposes only. They are not a diagnosis, treatment, or substitute for advice from a qualified healthcare professional. If you experience chest pain, shortness of breath, fainting, or any concerning symptom, contact emergency services or a doctor right away.