Real-Time Hydration Monitoring During Exercise Using Ultrasound Imaging

Aim: Accurate assessment of human hydration status is crucial for maintaining physiological homeostasis and optimising performance. Traditional assessment methods require invasive blood sampling or time-consuming laboratory procedures for urine analysis. This study explores whether intermittent inferior vena cava (IVC) ultrasound (US) measurements respond to exercise-associated body mass loss and subsequent water intake. Methods: A cohort of 33 healthy young adults (17 females, 16 males) underwent a controlled experimental protocol comprising moderate-intensity exercise to induce dehydration, followed by a rehydration phase. Longitudinal US scans of the IVC were acquired at 10-min intervals during dehydration (five times) and at 2-min intervals after rehydration (three times). Quantitative physiological parameters, IVC diameter (D), caval index (CI), cardiac caval index (CCI), and respiratory caval index (RCI), were extracted from US data. Body mass was recorded at each dehydration sub-phase, with equivalent water volumes administered during rehydration to match mass loss. Results: At the group level, IVC diameter was lower after 10 min of exercise than at baseline and higher 4 min after water intake than at the end of exercise (both p < 0.01). Moreover, a Random Forest (RF) classifier achieved 76% leave-one-out accuracy in categorising subjects according to rehydration rate, utilising biometric data and IVC features obtained at the 10-min dehydration checkpoint. Conclusion: This investigation demonstrates that IVC US imaging offers a promising, non-invasive methodology for rapid hydration assessment. If validated in an extended cohort, it could have significant implications for personalised monitoring in sports medicine.