The Prior Hypothesis at the first Edinburgh Conversation

Posted by | 29 Nov 2017

On Friday 17th November, the Resuscitation Research Group held the first of the new series of Edinburgh Conversations.

The theme of the Conversation was the ‘Prior Hypothesis’. Experts met to discuss the effects of capillary pore size, pulse waves and osmotic pressure on fluid exchange, with a view to thinking about implications for future research and clinical practice.

It was the opportunity to release the initials results of the Prior Study, which was led by Allan MacRaild, Senior Research Nurse in EMERGE.

Dr Frank Prior was joined by Dr Colin Robertson, Dr Gordon Drummond, Mr Peter Jones, Mr Allan MacRaild and Dr Gareth Clegg. Discussions from the event will help strengthen the hypothesis and uncover unexplored areas.

The Prior Hypothesis – an update to the Starling Hypothesis – offers a new model of fluid balance and exchange.

Fluid balance and exchange are driven by the balance of two opposing pressures, the blood pressure which filters fluid out of the capillary and the osmotic pressure which draws fluid back into the plasma. Our physico chemical studies show that osmotic pressure is dependent on both concentration and membrane pore size. Increasing the concentration increases the osmotic pressure. Increasing pore size causes a fall in osmotic pressure. These three major factors determine osmosis. A knowledge of two of them should enable the third to be calculated. To test this concept we have measured membrane osmotic pressures (MOPx) and calculated capillary pore sizes during lying and standing, temperature stress, arm occlusion and simulated dives in human volunteers. We have also calculated pore size during anaesthetic induction, throughout Major GI surgery, and during pulsatile and non pulsatile cardiac bypass.


These results are included in our book entitled The Prior Hypothesis, which is in the final proof reading phase.