Impacts of Rhythmic and Hypoxic Breathwork on EEG, Mood, Sleep, and Physiology

Breathwork. Breathwork simply means consciously manipulating the breath to achieve a desired result. There are many kinds of breathwork for different goals. An entire segment of yoga, called pranayama, harnesses the power of breath manipulation for various health benefits. The current study does not use a specific technique from ancient traditions but combines two basic techniques grounded in Western literature: slow-paced breathing and hypoxic breath-hold training.

Breathwork: slow-paced breathing. The study of slow-paced breathing (SPB) emerged from the observation that heart rate follows the breath: heart rate increases during inhale and decreases during exhale. Multiple physiological processes come into alignment when breathing is maintained at a constant rate of about 0.1 Hz (6 breaths per minute). Since slower breathing necessitates larger tidal volume, SPB causes rhythmic changes in blood pressure, which triggers the baroreflex response. The baroreflex involves communication from the body to the brain stem and higher brain centers via vagal nerve afferents. The brain projects back through the vagus nerve to the heart, releasing acetylcholine, to cause temporary heart slowing. Because typical breath (in our culture anyway) is usually much faster and less regular, this resonance is not achieved in normal daily living, leading to reduced parasympathetic function. Practicing SPB can help to restore health by recovery of proper autonomic balance. For example, blood pressure is acutely reduced during SPB, along with increased baroreflex sensitivity. Systolic blood pressure was reduced in hypertensive patients after 8 and 12 weeks of SPB practice. It can also reduce blood pressure and increase oxygen absorption in sea level dwellers exposed to high altitudes.

In addition to brain stem targets of vagal afferents, dorsal pons, periaqueductal grey matter, cerebellum, hypothalamus, thalamus, and lateral and anterior insular cortices also show activity on functional magnetic resonance imaging (fMRI) during SPB (Critchley et al., 2015). A regular practice of SPB for 8 weeks has also been shown to increase functional connectivity between the ventromedial prefrontal cortex and the insula, amygdala, middle cingulate, and lateral prefrontal cortex compared to controls (Schumann et al., 2021).

Breathwork: breath hold. Various research avenues have shown the surprising benefits of intermittent low oxygen. Throughout the ages, different cultures have had some level of awareness about breathing less or moving to altitude for health reasons. Specific studies began to be performed when humans began high altitude activities like hot air ballooning and mountaineering and from there many discoveries have been made about the benefits of low oxygen. For example, high altitude living for athletes confers advantages for training and competition at sea level, and yogi masters have taught pranayama (breathing techniques) that limit oxygen exposure for various benefits like stress reduction or clearing the mind. But these are only the most obvious sequelae of lowered oxygen. More surprising is that hypoxic preconditioning protects against subsequent ischemic challenge that would normally result in neuronal death. Reduced oxygen has also been shown to boost growth factors, increase neurogenesis, improve blood flow to the brain and increase antioxidant activity. The mechanism of such benefits is thought to mostly involve hypoxia-inducible factors (HIFs), which lead to downstream effectors such as heme-oxygenase-1, heat-shock proteins, growth factors, erythropoietin and more. Thus, as counter-intuitive as it might seem, limiting oxygen, either by reduced oxygen gas mixtures, altitude, or breath-holding, is an effective way to stimulate the body's natural abilities to increase health-promoting factors.

EEG brain imaging of breathwork. In this study, we will use a 128-channel EEG cap to record whole-head EEG that will allow for decomposition into cortical source activity using independent component analysis (ICA). This technique has the advantage of separating activities emanating from different areas of the brain (instead of scalp locations) and then observing their transient interactions during specific tasks. In this study, we will examine source activity during guided rhythmic breathing and breath-hold sequences to observe the frequency power and coherences that characterize these states. The effect of hypoxia on the EEG has not been extensively studied, and preliminary reports are varied, partly because of varied techniques for inducing hypoxia. For example, hypobaric hypoxia has been shown to increase in alpha (~8-12 Hz) and theta (~4-7 Hz) frequencies in one study, but decrease alpha in two other studies, though these both did find a consistent increase in theta power. Normobaric breath holding has also been shown to decrease alpha activity. Furthermore hypercapnia, or increased carbon dioxide (CO2) (which also occurs during breath hold), has also been noted to decrease alpha, as well as beta (~13-30 Hz) and low gamma (~30-50 Hz) using magnetoencephalography.