Respiratory
Lung function and blood oxygenation. Metrics that track your respiratory health and oxygen delivery efficiency.
Inhaler Usage
Definition
A count of inhaler actuations (puffs), typically tracking rescue inhaler use for asthma or COPD management.
Why It Matters
Inhaler usage patterns reveal respiratory control: - Rescue inhaler frequency - High use indicates poor control - Treatment adherence - Tracking controller medication use - Trigger identification - Usage patterns correlate with triggers - Medical conversations - Objective data for healthcare visits - Asthma action plan - Usage informs zone assessment
How It's Tracked
- Smart inhalers - Connected devices that log each actuation
- Manual logging - User-entered data in health apps
- Third-party apps - Asthma management apps syncing to HealthKit
Reference Guidance
| Inhaler Type | Typical Use Pattern |
|---|---|
| Controller (daily) | Regular schedule, 1-2x daily |
| Rescue (as needed) | <2x per week indicates good control |
| Rescue | >2x per week may indicate poor control |
Asthma Control Assessment
| Rescue Use | Interpretation |
|---|---|
| ≤2 days/week | Well-controlled |
| >2 days/week | Not well-controlled |
| Daily or multiple times daily | Poorly controlled |
Based on standard asthma guidelines.
Confounders & Limitations
- Manual entry - Depends on user consistency
- Technique issues - Puff counted even if poorly administered
- Different medications - Rescue vs controller not always distinguished
- Priming puffs - May be counted incorrectly
Use Cases
- Symptom tracking - Correlate usage with triggers
- Doctor visits - Provide objective usage data
- Action plan compliance - Track response to symptoms
- Long-term trends - Seasonal patterns, trigger identification
When to Discuss with Doctor
- Needing rescue inhaler more than 2x per week
- Waking at night due to symptoms
- Using rescue inhaler before exercise every time
- Running out of rescue inhaler frequently
- Any increase from your baseline pattern
References
Respiratory Rate
Definition
The number of breaths taken per minute, a fundamental vital sign.
Why It Matters
Respiratory rate is sensitive to many conditions: - Vital sign - One of the four classic vital signs (with HR, BP, temperature) - Illness indicator - Elevations can signal infection, fever, stress - Cardiopulmonary status - Reflects lung and heart function - Sleep quality - Breathing patterns during sleep reveal health info - Fitness context - Recovery breathing after exercise
How It's Measured
- Clinical - Counted by healthcare provider observing chest movements
- Apple Watch (sleep) - Estimated during sleep using accelerometer and heart rate
- Third-party devices - Some wearables track respiratory rate continuously
Reference Ranges
| Category | Respiratory Rate |
|---|---|
| Normal adult (awake) | 12-20 breaths/min |
| Normal adult (asleep) | 10-18 breaths/min |
| During exercise | Increases with intensity |
| Children | Higher than adults (varies by age) |
Confounders & Limitations
- Activity level - Exercise increases rate
- Talking - Affects breathing pattern
- Anxiety/stress - Can elevate rate
- Sleep position - May affect measurements
- Altitude - Higher elevation increases rate
- Measurement accuracy - Wearable estimates less precise than clinical
Use Cases
- Sleep monitoring - Trends in nighttime breathing
- Illness detection - Elevated rate may precede other symptoms
- Recovery tracking - Post-exercise breathing normalization
- Stress awareness - Chronic elevation may indicate stress
When to Be Concerned
- Resting rate consistently above 20/min
- Sudden increase from personal baseline
- Accompanied by shortness of breath
- Associated with chest pain or discomfort
References
Spirometry: FVC, FEV1, Peak Expiratory Flow
Definition
Pulmonary function test measurements that assess lung capacity and airflow:
- FVC (Forced Vital Capacity) - Total volume of air you can forcibly exhale after maximum inhalation
- FEV1 (Forced Expiratory Volume in 1 second) - Volume exhaled in the first second of forced exhalation
- PEF (Peak Expiratory Flow) - Maximum speed of exhalation
Why It Matters
Spirometry values are essential for: - Asthma diagnosis and monitoring - Detecting airway obstruction - COPD assessment - Measuring disease severity - Treatment effectiveness - Tracking response to medications - Surgical preparation - Assessing respiratory reserve - Occupational health - Monitoring exposure effects
How It's Measured
Spirometry requires specialized equipment: - Clinical spirometer - Laboratory-grade device - Portable spirometers - Home devices (some connect to HealthKit) - Peak flow meters - Simple PEF measurement devices
Technique matters: 1. Maximum deep breath in 2. Seal lips around mouthpiece 3. Blast air out as hard and fast as possible 4. Continue until lungs are empty
Reference Values
Values are expressed as percentage of predicted, based on: - Age - Sex - Height - Ethnicity
| Measurement | Normal Range |
|---|---|
| FVC | ≥80% of predicted |
| FEV1 | ≥80% of predicted |
| FEV1/FVC ratio | ≥70% (or lower limit of normal) |
| PEF | Varies; personal best used as reference |
Key Patterns
| Pattern | FEV1 | FVC | FEV1/FVC |
|---|---|---|---|
| Normal | Normal | Normal | Normal |
| Obstructive (asthma, COPD) | ↓ | Normal or ↓ | ↓ |
| Restrictive (fibrosis) | ↓ | ↓ | Normal or ↑ |
Confounders & Limitations
- Technique-dependent - Poor effort affects results
- Acute conditions - Colds, infections alter baseline
- Medications - Bronchodilators affect readings
- Time of day - Values may vary throughout day
- Device calibration - Home devices less accurate than clinical
Use Cases
- Asthma action plans - PEF zones (green/yellow/red)
- COPD staging - Disease severity classification
- Treatment monitoring - Before/after bronchodilator response
- Long-term trends - Tracking lung function over time
References
Blood Oxygen (SpO2)
What Is SpO2?
Peripheral Capillary Oxygen Saturation (SpO2) measures the percentage of hemoglobin in your red blood cells that is carrying oxygen from the lungs to the rest of the body.
- 95-100%: Normal saturation.
- 90-95%: Mild hypoxemia (may be normal during sleep or high altitude).
- < 90%: Clinically significant hypoxemia (often requires supplemental oxygen).
How HealthKit Measures It
The Apple Watch uses a specialized Blood Oxygen sensor: 1. Red & Infrared LEDs shine into your wrist. 2. Photodiodes measures the reflected light. 3. Color Analysis: Oxygen-rich blood is bright red (absorbs infrared); oxygen-poor blood is dark red (absorbs red light). The watch calculates saturation based on this ratio.
Scientific Background
Oxygen Transport
Oxygen is the fuel for every cell. Without it, cellular metabolism switches to anaerobic pathways, producing lactic acid and eventually failing (cell death). * Hemoglobin: The "taxi caps" for oxygen molecules. * Saturation: Tells you how full those taxis are. 100% means every binding site is full.
Silent Hypoxia
Conditions like COVID-19 brought attention to "Silent Hypoxia," where patients have dangerously low SpO2 (<80%) but do not feel short of breath. Regular monitoring can catch this decline early.
Clinical Significance
Factors Affecting Readings
Consumer pulse oximeters (including Apple Watch) can be affected by: * Perfusion (Blood Flow): Cold hands or vasoconstriction cause low readings. * Motion: You must be perfectly still. * Skin Pigmentation: High levels of melanin can sometimes reduce signal strength, though algorithms try to correct for this. * Tattoos: Ink can block the light path.
High Altitude
At higher elevations, the air is thinner (less partial pressure of oxygen). * Sea Level: SpO2 98-100% * Denver (5,280 ft): SpO2 ~95-98% * Aspen (8,000 ft): SpO2 ~91-94%
This drop is physiological and expected. It triggers the body to produce more red blood cells (acclimatization).
Recommendations
Getting a Good Measure
- Placement: Watch should be snug but not tight.
- Position: Rest your arm on a table with the watch face up.
- Stillness: Do not move for the full 15-second countdown.
When to Seek Help
If you repeatedly get readings < 90% while at rest and at sea level, especially if accompanied by shortness of breath, confusion, or chest pain, consult a healthcare provider immediately.
References
- Luks AM, Swenson ER. (2011) Pulse Oximetry at High Altitude. High Altitude Medicine & Biology.
- Jubran A. (2015) Pulse oximetry. Critical Care.
- Apple Inc. (2020) Blood Oxygen App Feature Paper.