Listening to the river

April 21, 2000

The Medical Research Council's Max Perutz Essay Prize 2000 attracted 39 entries from young scientists eager to explain their work to a wide audience.The competition, held to encourage and recognise good communication, drew a particularly high-quality response. Judges included Steve Farrar, science correspondent of The THES. This is the winning entry, 'Decomposing a Shocking Sound' by Paul Dark, an MRC clinical training fellow at the MRC Trauma Group, University of Manchester.

Bang! Backfire or car-bomb? My heart pounds, eyes stare and cold sweat forms on my skin. Momentarily frozen, anticipating danger, my muscles primed for action. Manon, my youngest child, emerges from behind the kitchen door, clutching the burst balloon. We laugh. In this calming moment, I reflect on my body's immediate, automatic, complex responses that daily defend me from danger and keep me alive.

A sudden event like this, sometimes distressing, is often thought of as a "shock". Medical doctors use the word shock, or circulatory shock, to mean something very specific: a failure of the circulation to supply enough oxygen to support the body's fight for life. In the emergency room this defines "triage code red", a patient whose life is immediately threatened. During my medical training I have learnt how to recognise circulatory shock immediately. Comforted by this, I begin life-saving anti-shock treatments, knowing that these will fail as often as they succeed. There is no magic bullet. Circulatory shock is the twilight zone between life and death, the body balancing on a knife-edge. Heart attacks, internal bleeding following injury and severe blood infections are all examples of common diseases that can lead inexorably to shock and death.

When a sudden serious illness begins, our bodies respond by concentrating on defence. Subconsciously, we divert blood flow towards the main battlefields where local defence mechanisms need an abundant supply of oxygen. Maintenance of blood flow to our power generator (heart muscle) and our coordinating computer (brain) is crucial. Automatically, we reduce blood flow to other areas, less essential to our immediate needs. As a doctor, I cannot see or touch these subtle pattern changes of blood flow inside the body, an early warning sign that all is not well. Eventually, defences can be overwhelmed and, quite suddenly and unexpectedly, the system fails and circulatory shock ensues. A terrifying event to witness.

If I could actually see these subtly changing patterns of blood flow, how they develop towards catastrophe and improve with treatment, I could help my patients avoid shock. My dream is to beat this lottery that is "triage code red".

In 1842, Christian Doppler was the first to realise that light waves are changed subtly when reflected by moving objects. Sound waves exhibit identical behaviour, easily demonstrated by the changing pitch of a pas-sing ambulance siren. The vehicle's speed determines the size of this pitch change. I can focus inaudible sound waves (ultrasound) from outside the body onto the main artery leaving the heart (the aorta). Every blood cell rushing through this beam reflects waves back to a detector. A variety of blood cell speeds exist in the aorta at any moment. Imagine a wide motorway with thousands of ambulances, sirens blazing, moving past at different speeds. The noise would be very complicated but would contain the tint signals that refer to the speed of each ambulance.

The detected ultrasound is equally complex. Electronic processing known as "de-modulation" can produce an audible signal from the detected ultrasound. Whooshing sounds are created, representing the speeds of the blood cells present. If this sound could be described perfectly, we would see the patterns of blood cell movements within the aorta. Unfortunately, modern digital ultrasound machines can only produce profiles from the fastest moving cells, not a complete picture.

Following a series of chance encounters with three experienced engineers (Jon Purdy, John Atherton and Dennis Dodds), we recognised that this important clinical problem raised interesting engineering questions. I was particularly excited when introduced to a new mathematical technique known as wavelet analysis, originally developed to understand seismological shock waves.

Wavelet analysis can untangle complicated signals into component parts and help detect pattern changes. We believe that wavelet analysis of the ultrasound signal will produce the speed pattern of blood cells and reveal emerging changes. Imagine we can hear the whooshing sound, the orchestral score already composed but hidden from sight. We do not know which notes are being played and when. Wavelet analysis will help us discover these notes and their timing.

We have built our first machine and monitored the circulation during small blood losses at operations and during blood re-infusion. We are tremendously excited, in front of us beautiful patterns of blood cell movements, never seen before. They evolve throughout a single pulse, change during early blood loss and recover during re-infusion. Now we are characterising these changes and developing an explanation for why they occur. Then we can disseminate our work, canvassing for valuable opinion from our colleagues, presently known or unknown.

Scientific advances have outstripped developments in the practice of medicine. I believe that seemingly impossible medical problems are best approached by teams of investigators with a wide range of medical practice, biology and technology. However, to do this successfully, we must communicate.

All of the winning entries can be read at http://www.mrc.ac.uk/whats_new/perutz_2000/Perutz.htm

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