HRV Breathing
Breathing that reads your HRV in real time
Vayu is a biofeedback breathing platform that measures heart rate variability (RMSSD) from your Apple Watch or WearOS device during every session. Your HRV tells the app how your nervous system is responding. The app guides your breath through haptic pulses on your wrist.
Pilot study, N=199, 4-6 weeks. Adhia et al., Human Factors in revision. SFU Metacreation Lab, NRC IRAP supported.
What is HRV biofeedback breathing?
Heart rate variability (HRV) is the variation in time between consecutive heartbeats, measured in milliseconds. It reflects how well your autonomic nervous system adapts to stress and recovery. Higher HRV generally indicates a healthy, resilient nervous system. Lower HRV is associated with stress, fatigue, and poor recovery.
HRV biofeedback breathing uses real-time HRV data to guide your practice. Instead of following a fixed timer, you receive feedback on whether your breath is actually moving your HRV. This closes the loop: you breathe, your HRV responds, the app adjusts guidance.
Vayu reads RMSSD (root mean square of successive differences), the standard clinical measure for short-term HRV, directly from your Apple Watch or WearOS device during sessions. You see your HRV changing live as you breathe.
Breathing techniques and HRV
Resonance frequency breathing
5-6 breaths/min
Largest acute HRV increase. Synchronizes breathing with cardiovascular oscillation frequency. Personalized to each user's RMSSD response.
Best for: Stress recovery, HRV improvement
Box breathing (4:4:4:4)
~3.75 breaths/min
Activates parasympathetic nervous system. Equal timing for inhale, hold, exhale, hold. Strong HRV response with hold phases.
Best for: Focus, calm under pressure
4-7-8 breathing
~3 breaths/min
Extended exhale activates vagal tone. The 7-count hold increases CO2 tolerance. Pronounced parasympathetic activation.
Best for: Sleep, anxiety, acute stress
Wim Hof method
Cyclic hyperventilation + retention
Acute sympathetic activation followed by deep parasympathetic recovery. High HRV during retention phases.
Best for: Energy, resilience training
Frequently asked questions
What is HRV biofeedback breathing?
HRV biofeedback breathing is a practice where you receive real-time feedback on your heart rate variability while performing breathing exercises. Vayu uses Apple Watch to read RMSSD live and delivers haptic guidance on your wrist based on your actual HRV response.
Which breathing technique improves HRV the most?
Resonance frequency breathing (5 to 6 breaths per minute) consistently produces the largest acute HRV increases in research. It synchronizes breathing with the natural oscillation frequency of the cardiovascular system. Vayu includes resonance frequency breathing with real-time HRV feedback.
How much can breathing exercises improve HRV?
In a pilot study of 199 Vayu users over 4 to 6 weeks, average HRV improved by 28.6% (Cohen's d=0.68). Individual results vary based on baseline HRV, practice consistency, and other health factors.
Start improving your HRV today
Real-time HRV biofeedback on Apple Watch and WearOS. Free to start.
Download VayuSee the research: pilot study data
