What happens inside your body when you're tired, out of breath, or oxygen-deprived? A new study by researchers at the University of Portsmouth and University College London (UCL) has mapped how different parts of the body communicate during stress, potentially paving the way for earlier illness diagnosis.
The study , conducted on healthy volunteers, used a new approach which studies how different organs and body systems communicate with each other. When a person faces physiological stress, different parts of the body have to work together to adapt and keep us functioning.
This study used a brand new way to map how systems talk to each other, moment by moment, in real-time. Instead of just checking whether the heart rate or breathing rate goes up or down (which is what doctors typically do), this team mapped out how one body signal influences another - like which signal is giving the most instructions and which is doing the most listening.
By analysing recorded signals from the body (such as heart rate, respiratory rate, blood oxygen saturation, and the concentration of exhaled oxygen and carbon dioxide), the team tracked the transfer of information between these systems under conditions of low oxygen (hypoxia), sleep deprivation, and physical moderate intensity exercise (cycling).
The team used wearable sensors to monitor key physiological signals in 22 healthy volunteers during different stress scenarios at the University of Portsmouth's Extreme Environment Labs . A face mask measured breathing gases, while a pulse oximeter tracked blood oxygen levels.
Researchers monitor physiological signals while participant cycles in hypoxic state at the University of Portsmouth's Extreme Environment Labs. Credit: University of Portsmouth
The study, published in the Journal of Physiology , is a continuation of earlier research that showed just 20 minutes of moderate exercise can improve brain performance after a bad night's sleep .
"This time, we wanted to understand how physiological stressors affect the body together, not just on their own," said Dr Joe Costello , from the University's School of Psychology, Sport and Health Sciences .
"This approach lets us see how the body's internal systems communicate with each other when they're pushed to respond and adapt. And that kind of insight could be a game-changer for spotting when something starts to go wrong."
The unique method of monitoring these body signals is called 'transfer entropy'. The result was a complex network of maps that show which body parts act as 'information hubs' under different stress conditions.
Dr Costello explained: "What makes our approach so unique is that it doesn't pigeonhole our data into one system or variable - it looks at how everything is connected in real time. Rather than just measuring a heart rate or a breathing rate on its own, it helps us understand the dynamic relationships between them. It's a whole-body approach to human physiology, and that's crucial if we want to see the bigger picture."
The team discovered that different stresses cause different parts of the body to take the lead in managing the situation:
- During exercise, your heart becomes the main responder. It receives the most input from other systems because it's working hard to pump blood to your muscles.
- During low oxygen, it's your blood oxygen levels that become the central player, working closely with breathing to adjust to the lack of air.
When sleep deprivation is added, the changes are more subtle - but if low oxygen is also involved, your breathing rate suddenly steps up and takes the lead.
These information maps show early, hidden signs of stress that wouldn't be obvious just by looking at heart rate or oxygen levels alone. That means this could one day help spot health problems before symptoms appear.
Associate Professor Alireza Mani , head of the Network Physiology Lab at UCL, said: "These maps show that our body isn't just reacting to one thing at a time. 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.
"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."
Dr Thomas Williams from the University of Portsmouth''s School of Psychology, Sport and Health Sciences , added: "Extreme environments give us a safe and controlled way to replicate the kinds of physiological stress seen in illness or injury. By studying how the body responds and adapts under these conditions, we can begin to develop tools to detect early warning signs - often before symptoms appear - in clinical, athletic, and occupational settings."
With further investigation, the researchers hope the method could one day help doctors identify early warning signs of illness or poor recovery, especially in settings like intensive care, where vital signs are already being monitored. It could also be useful for athletes, military personnel, and people working in extreme environments.
The paper encourages more scientists to take a "whole-body" view of physiology rather than focusing on isolated measurements.
It also recognises only healthy, young people were included in this study, and several individuals were withdrawn due to adverse events. The paper recommends further investigation into the relationship between physiological stressors and the body, with a broader mix of participants.
