Every term you need to read the science fluently — physiology, techniques, assessments.
A–Z (29 of 29 terms)
Technique
4-7-8 breathing
A 4-second inhale, 7-second hold, 8-second exhale — a long-exhale downshift pattern.
Sensation
Air hunger
The subjective feeling of needing to breathe, driven primarily by CO₂ chemoreceptor activation.
Physiology
Apnea
A pause in breathing. Voluntary apnea (breath hold) trains CO₂ tolerance; involuntary apnea during sleep is a medical concern.
Assessment
BOLT
Body Oxygen Level Test — a subjective post-exhale, first-urge breath-hold baseline; it does not directly measure oxygen or CO₂.
Technique
Box breathing
Equal-count inhale, hold-in, exhale, hold-out — the canonical version is 4-4-4-4.
Assessment
Breath hold time
The duration of a voluntary breath hold. Distinct from BOLT (which stops at first urge, not at strain).
Technique
Buteyko method
A family of practices that reduce minute ventilation to raise CO₂ tolerance. Originated the BOLT test.
Physiology
Chemoreceptors
Sensors that monitor blood chemistry to regulate breathing. Central chemoreceptors watch CO₂ and pH; peripheral ones watch oxygen.
Physiology
CO₂ tolerance
Practical comfort with rising respiratory drive and mild air hunger during controlled breathing.
Technique
Coherence (breathing)
Paced breathing near five to six breaths per minute, commonly used to increase respiratory-linked HRV during a session.
Physiology
Dead space
Air that reaches the airway but does not participate in gas exchange (roughly 150 ml in adults).
Anatomy
Diaphragm
The dome-shaped primary breathing muscle attaching to the lower ribs and lumbar spine.
Physiology
Functional residual capacity (FRC)
The volume of air left in the lungs after a normal (not forced) exhale.
Physiology
HRV
Heart rate variability — variation in time between consecutive heartbeats. Interpretation depends on the metric, rhythm, person, and measurement context.
Physiology
Hypercapnia
Elevated CO₂ in the blood. It can occur in controlled respiratory research, but clinically significant hypercapnia can be dangerous.
Physiology
Hyperventilation
Breathing in excess of metabolic need. Lowers blood CO₂, raises pH, and can produce tingling, dizziness, and lightheadedness.
Anatomy
Intercostals
Muscles between the ribs. External intercostals assist inhale; internal intercostals assist forced exhale.
Physiology
Minute ventilation
The total volume of air moved into and out of the lungs per minute. Tidal volume × breath rate.
Habit
Mouth breathing
Breathing through the mouth instead of the nose. Common at rest and during sleep; typically a habit that can be retrained.
Biochemistry
Nasal nitric oxide (nNO)
Nitric oxide produced continuously in the paranasal sinuses and inhaled with nasal breathing.
Technique
Physiological sigh
A nasal inhale, smaller top-up inhale, and long relaxed exhale based on a normal spontaneous sigh pattern.
Technique
Resonance frequency breathing (RFB)
Breathing at the individual's cardiovascular resonance frequency to maximise HRV. Typically 5–6.5 BPM.
Physiology
Respiratory drive
The neural signal that triggers each breath. Modulated by chemoreceptor input, cortical influence, and metabolic demand.
Assessment
Resting breath rate
Breaths per minute at rest, interpreted with age, health, symptoms, medication, and measurement conditions.
Physiology
RSA (Respiratory Sinus Arrhythmia)
The normal variation in heart rate across the breath cycle — faster on inhale, slower on exhale.
Physiology
Sighing
A single deep breath (roughly twice tidal volume) that reinflates collapsed alveoli. Occurs spontaneously every few minutes.
Physiology
Tidal volume
The volume of air moved with each normal breath. Normal adult tidal volume is roughly 500 ml.
Physiology
Vagal tone
A functional description of parasympathetic cardiac modulation. It can be estimated in context, but is not directly read from one wearable score.
Technique
Wim Hof method
A three-pillar protocol combining active breathing, cold exposure, and commitment.