The most advanced biosensor ever created for monitoring the environment is the human brain. While we are unable to introspect about the early presence or progression of cardiovascular disease, diabetes, multiple sclerosis or cancer, the brain may nonetheless reflect the status of health and disease in the body through its communications and interactions with the sympathetic and parasympathetic branches of autonomic nervous system (ANS).
The parasympathetic vagal nerve wanders through the body allowing the brain to assess and intervene throughout the viscera, including the heart, lungs, stomach, liver, pancreas and small and large intestines, among other targets. Eighty percent of the vagal nerve is incoming information, reporting on the state of our organs to the brain. By the nature of its wandering route through the body, the vagal nerve provides an effective early warning system as a source of feedback to the brain and the immune system. Walter Cannon, the great American physiologist who characterized how sensory signals from the organs are sent to the brain, called this the “wisdom of the body.” Advances in biosensing should tap into this wisdom for health assessment and management.
ANS measurement from breath to heart to brain
Rather than walking around with unwieldy brain scanners on our heads, measuring the brain’s regulation of the ANS is best where they come together. The ANS can be assessed with great effectiveness from the combined activity of the respiratory and cardiovascular systems. These metrics tend to fall in the larger class of analytics termed Heart Rate Variability (HRV), a family of over 100 indices to assess heartbeat dynamics and their relation to respiration.
Cardiorespiratory dynamics not only reflect the health of the heart and lungs, but also serve as a proxy for the entire ANS. Even after controlling for heart disease and other potential confounders, HRV can track an impressive variety of risk factors and disease progression from metabolic factors such as triglycerides and blood glucose levels to inflammatory markers of cancer progression, and the list keeps growing. HRV not only can track severity and progression but also recovery after intervention. Much more than a marker of the heart and lungs, HRV tracks what the brain knows about the body.
Breathing life into HRV
The degree of parasympathetic activity, indexed through high-frequency changes in HRV as reflected in Respiratory Sinus Arrhythmia (RSA), serves as an excellent proxy of health and disease. The magnitude of RSA reflects the waxing and waning of heart rate with inhalation and exhalation and it has a tight relationship with breathing frequency and volume. To appropriately assess HRV, the frequency and depth of respiration has to be tracked because of moment-to-moment changes in respiratory variables and mental activity. Across conditions and diseases, greater parasympathetic RSA is a protective factor.
New breath sensitive MEMS (microelectromechanical systems) chips have been developed to measure breathing quality directly from airflow, affording more specific parameters with greater diagnostic potential for breathing assessment than chest and abdomen displacement. There is exciting potential in combining MEMS breath sensing technology with cardiovascular measurement. Fingertip pulse, under low activity, is an excellent stand in for ECG to calculate heart rate variability. So breathing into a handheld device that collects fingertip pulse can assess cardiorespiratory dynamics. State of the art measurement of HRV to assess the brain’s knowledge about the body is literally at our fingertips.
HRV-related cardiorespiratory components, can be reliably measured in as little as 15s, with 5 minutes recommended as the standard by the Task Force of the European Society of Cardiology and the North American Society of Pacing Electrophysiology. This opens up a world of possibility for building brief challenges that encourage daily repeated assessments through fun games, to assess the presence and progression of disease. Development of new diagnostic tests may then occur not only on the sensor and analytic side, but also with the development of administered mental challenges. The latter opportunity could reveal different facets of cardiorespiratory dynamics that are diagnostic for specific diseases.
Simultaneous assessment and management
Being administered an A1c test does not lower your blood sugar, nor does a lipid screen decrease your triglycerides. By contrast, standard measurement protocols for accurate assessment of HRV and RSA increase parasympathetic activity, which is protective against disease. Rigorous assessment of HRV controls and slows down breathing to limit respiratory parameters on HRV. Studies have shown that repeated daily practice of 0.1 Hz breathing (6 breaths a minute) increases the magnitude of RSA and overtime increases underlying parasympathetic strength. Accordingly, the testing for parasympathetic strength itself can enhance it, predicting decreased morbidity and mortality. At a minimum, there is significant potential in longitudinal tracking of these cardiorespiratory dynamics. This could also provide further diagnostic power. Those resistant to this parasympathetic intervention may need more monitoring or other more focused condition specific interventions.
From population to individual health management
While it is important, and trendy, to consider population health management for more efficient and effective health care, each of us is a population of one. That is, none of us are the “average” person, and we have our own idiosyncratic variation in biological variables. Daily controlled measurement of cardiorespiratory dynamics allows each of us to put flesh on the bones of our own personal model of health and wellbeing through repeated and controlled assessments. Such controlled longitudinal assessment of what the brain knows about the body can test the effectiveness of interventions, whether traditional behavioral (diet, exercise, smoking cessation) or technology based gaming for health. This approach will allow a new rigorous assessment of what is normal and abnormal not only in reference to a larger peer group, but also to ourselves. Less than a cost of a single blood test, ANS monitoring via cardiorespiratory dynamics can usher in a much needed and cost effective era of personalized health tracking and management.
