Basic Voo exhalation

Exhale slowly on a sustained "Voooo" sound, feeling the vibration in your chest and belly.

Why it works

The extended exhalation activates the parasympathetic nervous system directly through respiratory sinus arrhythmia: slowing exhalation increases vagal tone and lowers heart rate. Simultaneously, the voiced "Voo" (low-frequency resonance) vibrates the thorax, stimulating vagal afferents in the chest wall and bronchi. Together, the slow exhale and resonance give the vagus two concurrent inputs to shift state — more than either would alone.

How to do it

1. Sit comfortably with your feet on the floor and your spine roughly upright.
2. Take a natural breath in through the nose.
3. As you exhale, voice a low, resonant "Voooooo" — pitched low enough to feel it vibrate in the sternum and belly, not in the throat.
4. Let the sound last for the entire exhalation, then pause briefly before inhaling again.
5. Repeat 3–5 times, then sit quietly for a moment and notice what has shifted.

Evidence

Extended exhalation is well established to increase vagal tone via respiratory sinus arrhythmia. Humming and chanting have preliminary evidence of increasing heart rate variability (HRV). The Voo sound specifically is Levine’s practice and has not been tested in a controlled trial. A systematic review of slow-breathing psychophysiology, a controlled study isolating a longer exhale-to-inhale ratio, and fMRI imaging of "OM" chanting each independently support the two components the Voo combines — the extended exhale and the resonant vocalization. (mechanistic)

The extended-exhalation mechanism is supported; the additional benefit of the resonant tone over a plain slow exhale is plausible but not independently demonstrated.

Sources

• Jerath et al. (2006), physiology of slow breathing, Medical Hypotheses — on extended exhalation and autonomic balance
• Zaccaro, A., Piarulli, A., Laurino, M., Garbella, E., Menicucci, D., Neri, B., & Gemignani, A. (2018). How Breath-Control Can Change Your Life: A Systematic Review on Psycho-Physiological Correlates of Slow Breathing. Frontiers in Human Neuroscience, 12, 353.
• Van Diest, I., Verstappen, K., Aubert, A. E., Widjaja, D., Vansteenwegen, D., & Vlemincx, E. (2014). Inhalation/Exhalation Ratio Modulates the Effect of Slow Breathing on Heart Rate Variability and Relaxation. Applied Psychophysiology and Biofeedback, 39(3-4), 171-180.
• Kalyani, B. G., Venkatasubramanian, G., Arasappa, R., Rao, N. P., Kalmady, S. V., Behere, R. V., Rao, H., Vasudev, M. K., & Gangadhar, B. N. (2011). Neurohemodynamic correlates of 'OM' chanting: A pilot functional magnetic resonance imaging study. International Journal of Yoga, 4(1), 3-6.

Common mistake

Pitching the "Voo" too high — in the throat rather than the chest — which reduces the thoracic vibration that is the functional element of the practice. Aim for a foghorn, not a hum.