Validating sweat ammonia as physiological parameter for wearable devices in sports science

Abstract

The measurement of physiological parameters in sweat has long been assumed to offer a non-invasive alternative to conventional blood testing. Recently, advances in sensor technology enable the production of printed sweat sensors applicable for the use in wearable devices. However, the remaining challenge is the determination of the physiological correlation between blood and sweat components. In this study, we conducted ammonia measurements in blood and sweat during a stepwise incremental cycle ergometer test in 40 subjects under completely controlled conditions in a clinical environment to determine the correlation between the ammonium concentrations in blood and sweat. Samples were taken for each workload step separately. Sweat was sampled directly from the upper body, blood was taken from an indwelling cannula at the end of each workload step, respectively. For meaningful classification of the measured quantities, blood lactate and heart rate were monitored additionally. The results for blood ammonium concentration show increasing behavior in good accordance with the established indicators for physical exhaustion, whereas sweat ammonium concentration seems to decrease with workload. This is found to be due to dilution, as sweat rate increases. The presented results provide insight in the correlation between blood and sweat parameters and therefore are of high importance for further development of wearable devices. Clinical Relevance-Sweat sensing opens up new possibilities for non-invasive, continuous in-situ monitoring of physiological parameters for healthcare and sports science applications.

A Comprehensive Review of the Recent Developments in Wearable Sweat-Sensing Devices

“…Electrolytes are often popular biomarkers that have been used in sweat applications, especially in sports performance and the diagnosis of some diseases. For instance, sodium [ 32 , 33 , 34 ], chloride [ 35 ], potassium [ 32 ], and ammonium [ 33 , 36 ] ions are the most frequent sweat ions detected by electrochemical sensors during physical exercise. It is important to monitor these ion measurements because they decrease over time during physical training.…”

State of Sweat: Emerging Wearable Systems for Real-Time, Noninvasive Sweat Sensing and Analytics

“…Establishing a strong correlation between regional and whole-body sweat-based measurements represents a key step for developing new insights into the physiological relevance of sweat biochemical signals. In addition to fluid and chloride loss, the concentration of glucose, , lactate, , ammonia, and cortisol in sweat has value for monitoring athletic training and conditioning. Varying dynamically with physiological status (diet, stress, overall health) and activity, biomarker concentrations also correspond to dynamic variations in instantaneous sweat rate. , Recent efforts (Figure B–D) offer the requisite temporal resolution of instantaneous sweat rate to deconvolve this variability with real-time continuous sensing strategies.…”

The Evolving Role of Proteins in Wearable Sweat Biosensors

“…Ammonia is a byproduct of protein catabolism during exercise, and its accumulation in blood can have physiological repercussions . Blood ammonia is also secreted through sweat, and the correlations between its concentrations in blood and sweat have been well-established . Ammonia is usually detected through ion-selective electrodes or polymers. , However, a recent epidermal device reported the use of two enzymes (ammonium monooxygenase and hydroxylamine oxidoreductase) for enzymatic detection.…”

“…Ammonia is a byproduct of protein catabolism during exercise, and its accumulation in blood can have physiological repercussions. 61 Blood ammonia is also secreted through sweat, and the correlations between its concentrations in blood and sweat have been well-established. 61 Ammonia is usually detected through ion-selective electrodes or polymers.…”