Understanding what happens inside the body during states of fatigue, breathlessness, or oxygen deprivation is crucial for early detection of physiological deterioration, but existing diagnostic methods often rely on isolated measurements like heart or breathing rates. These basic indicators may miss the subtle, early signs of stress when multiple systems in the body begin to compensate or falter. The body responds to physiological stress—such as low oxygen, sleep deprivation, or physical exertion—through complex internal coordination across organs and systems, which standard measurements fail to capture. Researchers have now developed a new way to track how body systems interact in real-time, providing insights that could help detect health problems before symptoms appear.

In a new study, researchers from the University of Portsmouth (Hampshire, UK) and University College London (London, UK) used a method called ‘transfer entropy’ to monitor how different physiological systems interact, moment to moment, in real-time. Instead of examining individual metrics like heart rate or respiratory rate in isolation, this approach tracked how one body signal influences another, identifying which systems send or receive the most information. The study involved 22 healthy volunteers and was conducted at the University of Portsmouth’s Extreme Environment Labs. Participants underwent different stress scenarios, including moderate-intensity cycling, low oxygen (hypoxia), and sleep deprivation. Wearable sensors recorded data such as heart rate, respiratory rate, blood oxygen saturation, and exhaled gas concentrations. A face mask measured breathing gases, while a pulse oximeter tracked blood oxygen levels. This allowed researchers to generate real-time information maps showing how organs and systems communicate under various stress conditions.

The findings, published in the Journal of Physiology, revealed that different stressors shift the body’s central information hubs. During exercise, the heart emerged as the primary responder. Under low oxygen conditions, blood oxygen levels played the lead role, working in close coordination with respiration. When sleep deprivation was added to low oxygen exposure, breathing rate became the dominant system. These dynamic interrelationships would not be evident through traditional monitoring. The researchers suggest this approach could lead to new diagnostic tools in clinical, athletic, and occupational settings by identifying early warning signs of illness or poor recovery. The study also emphasizes the need to adopt a “whole-body” view of human physiology. While this study focused on healthy young individuals, the team recommends expanding the research to include a broader participant pool for further validation.

“These maps show that our body isn’t just reacting to one thing at a time. It’s responding in an integrated, intelligent way,” said Associate Professor Alireza Mani, Head of the Network Physiology Lab, University College London, and co-lead of the study. “And by mapping this, we’re learning what normal patterns look like, so we can start spotting when things go wrong.”

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