Interplay in human nervous system
Motor functions of our body can be performed as a voluntary or involuntary response. When the response to the stimulus is performed consciously, it is supervised by a so-called somatic nervous system. The autonomic nervous system, on the other hand, is responsible for processes related to uncontrollable responses, such as cardiovascular adaptation to exercise, body temperature regulation, or breathing.
Autonomic nervous system is sub-divided into two components with contradictory roles. The sympathetic nervous system is activated in the face of threat or stress. The time intervals between the successive heart beats become then shorter, more blood is pumped per unit time and blood pressure spikes. Once the stressful situation is gone, the parasympathetic nervous system is activated to restore the impaired balance and induce the state of relaxation.
Heart rate variability (HRV)
The sympathetic and parasympathetic nervous systems work in a carefully harmonized manner. The energy-consuming ‘fight or flight’ state governed by the sympathetic nervous system should be naturally followed by a shift towards the ‘rest and digest’ parasympathetic response. A prolonged deviation from the equilibrium, however, may pose a threat to human health.
To monitor the balance between the two extreme states of autonomic nervous activity, a notion of heart rate variability was developed. HRV is a measure of changes in the duration of time intervals between the successive heart beats.
The variation in beat-to-beat intervals yields information on how the autonomic nervous system modulates heart muscle activity. It is a valid non-invasive indicator of the general health of the patient.
Lack of balance between the sympathetic and parasympathetic nervous systems, often caused by stress or anxiety, is typically reflected in low HRV. The link between decreased HRV and certain types of cardiovascular or autonomic pathologies is so strong, that HRV can serve as a diagnostic tool for evaluating the prognosis of patients with many chronic cardiovascular conditions.
HRV in hypertension
A decreased HRV is commonly reported in patients with elevated blood pressure. What many people do not realize, however, is that it is possible to somewhat influence your HRV level with the use of certain conscious practices, including meditation [1], contemplative training [2], or breathing exercises [3]. As a consequence, one should observe an increase in the fitness level, stress adaptation and emotional stability possibly disturbed by hypertension.
This relationship is often employed by designers of smart wearables. Electronic watches occasionally ask their users to slow down and breathe calmly for a minute. Although this method will not cure hypertension per se, it can largely improve the quality of everyday life of patients with elevated blood pressure [4].
Slow breathing exercises repeated periodically throughout the day act as triggers activating the parasympathetic nervous system in a way similar to how it works on its own. Repeated daily, such a training to balance the distorted HRV can help decrease blood pressure and live a better life with hypertension.
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