Transient BP spikes coupled to learning in brain

There is no known cause for hypertension—persistently high blood pressure (BP)—in roughly half of all people. One plausible theory is, however, that hypertension might be the result of a long period of many recurrent BP peaks. Hundreds of thousands of micro-stress events may occur daily—the telephone ringing, a car horn sounding in the street—with BP spiking every time as a result.

For nearly twenty years, a University of Gothenburg research group has been investigating how this kind of micro-stress affects nerve signals to our muscles and the throughput (perfusion) of blood in their vessels (muscle vasculature). In half of the over 150 men included in the group’s studies to date, the pattern of their reaction system leads to BP peaks, while for the other half, the reactions taking place in their bodies do not change BP.

Ultramodern brain-imaging techniques

The latest results are published in Scientific Reports. For the study, 20 men aged 19–45 were examined. The experiment involved triggering a response in the nervous system with unexpected electric shocks that emulate the sudden and stressful stimuli we are exposed to daily. The researchers combined two measurement methods. In one, a traditional research technique called microneurography, thin needle electrodes are used to probe the signalling in nerve fibres (specifically, muscle sympathetic nerve activity, MSNA) directed to the muscles' vascular bed (blood vessels). The other was a modern brain-imaging technique known as magnetoencephalography (MEG).

For the first time, the researchers can link the increased susceptibility to micro-stress to a reflex-like signal in the brain. The brain area (the “rolandic area”) that activates the signal controls several conscious brain functions. This finding opens the question of whether the BP peaks may be learned and could, therefore, also, with training, be eliminated.

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“We see a surprisingly strong connection between the peripheral autonomic vascular reaction, which takes place subconsciously, and a reaction pattern — already known — in a part of the brain where emotional impressions and motor skills undergo conscious interpretation. This raises questions about how independently the ‘autonomic nervous system’ really works, as it’s called,” says Mikael Elam, Professor of Clinical Neurophysiology at Sahlgrenska Academy, University of Gothenburg.

Long road ahead to clinical use

The idea that the discovery might come to be used to prevent hypertension is not unrealistic, but much research remains to be done.

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“If we can develop ways of boosting the signal-to-noise ratio, in the future, it may be possible to extract the relevant brain signals from a regular electroencephalogram [EEG], available in every hospital. That would enable us, at an early stage, to identify people who react to BP spikes before they develop hypertension. Many other opportunities for preventive measures and research would follow,” says Justin Schneiderman, Senior Lecturer in experimental multimodal neuroimaging at Sahlgrenska Academy, University of Gothenburg.

Environmental factors decisive

Interestingly, our environment seems to matter more than our genetic code regarding which reaction pattern we develop and, thus, whether we experience many daily BP spikes or not. An earlier study by the research group on identical twins showed that activity in the twins’ blood-vessel-regulating autonomic nervous systems was similar, while their stress-triggered reactions diverged.

“One may speculate that today, many people have learned to suppress the primitive fight-or-flight response since it’s irrelevant in modern society. It’s an impulse that prepares us for action by reducing the vasoconstrictor nerve activity, thereby increasing blood flow in the muscles. In terms of long-term health consequences, preserving the old flight-or-fight impulse might be beneficial in response to sudden stressors,” Elam ponders.

A wide-ranging collaboration

The research group hopes to facilitate studies at the population level, monitoring large groups of people over a long period. This would enable the investigation of, first, whether individuals with reaction patterns that cause many peaks in blood pressure during the day are indeed at increased risk of developing hypertension later in life and, second, whether influencing this reaction pattern is feasible.

Research mapping the biological processes and signals controlling the autonomic regulation of our blood vessels is being conducted in collaboration with the University of Gothenburg, Sahlgrenska University Hospital, and Chalmers University of Technology.