Once upon a time I was a physiologist

These days I study environmental issues, but my first degree and DPhil were in physiology. I’m still fascinated by how the body works, although it’s not an area of reserach I expect to go back to in the future.

During my DPhil I studied the way in which the brain controls breathing during exercise. At rest, the stimulus to breathe is the level of carbon dioxide in the bloodstream. If the level goes up, it is sensed by the carotid bodies (sensing organs in the arteries in the neck), which send a signal to the brain to increase breathing. If the level of carbon dioxide goes down, the carotid bodies sense this, and send a signal to the brain to decrease breathing. This is how a lot of systems in the body work; we have sensors that detect a change from the normal condition (i.e. an error signal), and the sensor is linked to a means for correcting the difference, so we have a feedback mechansim.

One of the things that has fascinated exercise physiologists for years, is the mechanism responsible for increased breathing during exercise. We need to breathe more when we exercise, in order to supply the muscles with oxygen and remove the metabolites that muscles produce when they exercise. The reason for the physiologists fascination is the lack of error signal; the level of carbon dioxide in the blood doesn’t change, so the usual mechanism for regulating breathing does not seem to be responsible. Other potential error signals such as oxygen level in the blood, or levels of metabolites from exercising muscles also seem to be absent. An alternative theory is that the brain directly controls the level of breathing via a ‘feedforward’ mechanism, rather than via feedback from an error signal. In other words, the part of the brain that tells the muscles to start working (telling the legs to spin on a bicycle for example), also tells the breathing muscles to increase the level of breathing. This theory is known as central command.

My work involved hypnotising people and asking them to imagine themselves exercising, whilst we recorded their breathing, heart rate and blood pressure. We also got people to undertake actual exercise under hypnosis and changed their perception of how hard the exercise was. Our aim was to manipulate central command, independently of any peripheral feedback mechanism.

We then went on to scan hypnotised people’s brains whilst they were imagining themselves exercising in order to better understand which bits of the brain are involved in the exercise response.

At the time, a new surgical intervention for Parkinsons Disease patients was being undertaken in Oxford, and I was fortunate enough to be able to study these patients whilst they underwent brain surgery; the part of the brain being operated on is implicated in the control of breathing during exercise, so we were able to study the effect that electrically stimulating these areas of the brain had on breathing, heart rate and blood pressure.

I wrote a few journal papers about all of this, links below in case anyone is interested.

 

I also worked with some colleagues on ventricular arrhythmias, the paper from which is here.

Thornton, J. M., Guz, A., Murphy, K., Griffith, A. R., Pedersen, D. L., Kardos, A., Leff, A., Adams, L., Casadei, B. and Paterson, D. J. (2001), Identification of higher brain centres that may encode the cardiorespiratory response to exercise in humans. The Journal of Physiology, 533: 823–836. doi:10.1111/j.1469-7793.2001.00823.x

 

Thornton, J. M., Aziz, T., Schlugman, D. and Paterson, D. J. (2002), Electrical stimulation of the midbrain increases heart rate and arterial blood pressure in awake humans. The Journal of Physiology, 539: 615–621. doi:10.1113/jphysiol.2001.014621

[the journal papers are behind a paywall, if you would like copies, please email me via the contact page].

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