Kiwis developing a stomach pacemaker

Electrical impulses generate powerful contractions that ripple from the top to bottom of the stomach. These impulses can be disordered and cause nausea.


Electrical impulses generate powerful contractions that ripple from the top to bottom of the stomach. These impulses can be disordered and cause nausea.

The stomach’s job is to break down our food into very small pieces – less than 2 millimetres – using a combination of muscular agitation and strong acids. Once the food is sufficiently processed, the sphincter at the bottom of the stomach acts as a sieve, allowing the contents through into the small intestine. The capacity of the human stomach is up to about 4 litres, a limit tested by some!

If the stomach had stars for energy efficiency, like fridges and washing machines, it would surely have the maximum number. Electrical impulses – about one every 20 seconds – generate powerful contractions that ripple from the top to bottom of the stomach, using just one thousandth the voltage of an AA battery. The power of these contractions is evident when you are sick and the contractions reverse.

Typically, the stomach takes three-four hours to digest a meal. The stomach is in constant communication with the brain, suggesting what and when to eat. If we eat something very fatty, the duodenum acts independently to put the brakes on and holds up the release of stomach contents into the small intestine. We don’t always heed the signals and stop eating, or choose to eat what our brain is telling us our body needs.

Professor Leo Cheng​ and Dr Nira Paskaranandavadivel​ are Riddet Institute researchers at the University of Auckland and studying stomach motion, specifically to understand how different foods are digested.

* Drink coffee and tea for their valuable antioxidants
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They are also supervising the development of a pacemaker for those unfortunate people who have disordered contractions, resulting in delayed emptying of the stomach and chronic nausea. These stomach disorders are likely underestimated because they are hard to diagnose – the symptoms could be attributed to any number of maladies.

The stomach pacemaker, analogous to a heart pacemaker, would monitor, restore and regulate the stomach’s contractions. PhD students in the team, Nima Hosseini​ and Saeed Alighale,​ have been tackling two different aspects of the research.

To know what is abnormal, you first have to understand what’s normal in a healthy stomach. Nima is studying the stomach’s contractions with magnetic resonance imaging (MRI). He has discovered that pineapple juice is a perfect natural contrast fluid to clearly show the outline of the stomach in the otherwise murky MRI image.

He then creates mathematical models of stomach contraction patterns and uses fluid dynamics to simulate flows within the stomach – the same mathematical physics that underpinned our America’s Cup triumph.

Saeed’s mission is to apply this knowledge to fabrication of the stomach pacemaker. Preliminary trials in patients at Auckland City Hospital have been successful, but the instalment of a final product in people with gastric disorders needs more research and is still a way off.

Part of their scientific pursuit is to develop simple ways of diagnosing disordered contractions in the first place. The research may also inform surgeries that limit stomach size, which in many cases remove the stomach’s natural pacemaker.

Banding of the stomach is no longer practised – instead the stomach is divided length-wise, but how much this interferes with the stomach’s natural rhythm remains a mystery.

Another question arises about weight control: what would happen if you used the pacemaker to slow down the rate of contractions, and therefore digestion, making you feel full for longer? Could this be a weight control therapy, less invasive and radical than surgery?

Professor Leo Cheng and Dr Nira Paskaranandavadivel are with the Riddet Institute and Bioengineering Institute at the University of Auckland, and Glenda Lewis is a science writer.