'Map' of how body parts interact under stress created

A new study has mapped how different body parts communicate with each other under physiological stress, such as during exercise or sleep deprivation, which researchers say could one day help diagnose an illness earlier.

Researchers at the University of Portsmouth and University College London, UK, said the study encourages a "whole-body" view of physiology, instead of focusing on isolated measurements such as heart or breathing rate.

Using 'transfer entropy' — a method of monitoring body signals — a complex network of maps was created showing which body parts act as 'information hubs' under different stress conditions, the team explained.

For example, during exercise, the heart — which is working hard to pump blood to muscles —receives the most input from other systems and therefore, "takes the lead" in helping the body adapt, the researchers said.

Described in a study published in the Journal of Physiology, the maps "show that our body isn't just reacting to one thing at a time," said author Alireza Mani, associate professor and head of the network physiology lab at University College London.

"It's responding in an integrated, intelligent way. And by mapping this, we're learning what normal patterns look like, so we can start spotting when things go wrong," Mani said.

Organ systems are known to work together to help one adapt and function under conditions that produce stress in the body.

The study looked at 22 healthy volunteers who were monitored using wearable sensors during exposure to three stressed environments — low oxygen (hypoxia), sleep deprivation and physical moderate intensity exercise (cycling).

A face mask measured the participants' breathing gases, while a pulse oximeter tracked blood oxygen levels.

The researchers analysed the signals recorded — heart and respiratory rate, blood oxygen levels, and concentration of oxygen and carbon dioxide in exhaled breath — and tracked how information was being transferred between the organ systems.

In a low oxygen environment, blood oxygen becomes the "central player", working closely with breathing to adjust to the lack of air, the researchers said.

They explained that when sleep deprivation is added, the changes are more subtle, with information shifting between organ systems — if low oxygen is also involved, breathing rate suddenly steps up and takes the lead.

The maps indicate early, hidden signs of stress that would not be obvious from heart rate or oxygen levels alone, meaning that the findings could one day help spot health problems before symptoms appear, the team said.

"This matters in healthcare because early signs of deterioration, especially in intensive care units or during the onset of complex conditions like sepsis or COVID-19, often show up not in the average numbers but in the way those numbers relate to each other," Mani said.

The authors wrote, "During exercise, heart rate emerged as the primary recipient of information, whereas (blood oxygen) served as the main disseminator. Hypoxia led to the engagement of (blood oxygen) as a hub in the network." "Sleep deprivation was associated with a shift in the flow of information between the nodes during hypoxia," they wrote.