Methodological Tests of Sweating Activity Measurement for Research

1. Methodological Tests of Sweating Activity Measurement for Research

2. Barbara J. Holtzclaw, PhD, RN, FAAN Associate Dean, College of Nursing D.W. Reynolds Center for Geriatric Nursing Excellence James W. Mold, MD, MPH College of Medicine, Dept. of Family and Preventive Medicine M EDICINE

3. Let talk about sweat! • Types of sweat glands: • Eccrine (thermoregulatory, cover most of body) • Apocrine (non-thermoregulatory, emotion responsive, in specific regions) • Apoeccrine (newly identified, function not known).

4. Epithelial cells lining the coiled portion of the sweat gland produce a precursor secretion containing concentrations of sodium = 142 mEq/L and chloride = 104 mEq/L. • Cholinergic sympathetic nerve fibers supplying glandular cells evoke secretion. • Electrolytes flow through ductal portion of sweat gland to be reabsorbed at a rate dependent on sweat rate.

5. Light SNS stimulation of sweat gland lets precursor fluid flow through duct slowly allowing reabsorption and concentration of most of the Na+ and Cl+ ions. Low osmotic pressure of sweat reduces reabsorption of water and urea; lactate and K+ remain concentrated. • Strong SNS stimulation of sweat gland by exercise produces large amounts of precursor secretion, little reabsorption of ions, and dilute sweat (50-60 mEq/L). Rapid tubular transit of sweat prevents low reabsorption.

6. Physiological Mechanisms • Thermoregulatory • Increased heat generation • External heat exposure (hot room) • Reduced heat dissipation (e.g. blankets) • Elevation of set point/thermo-neutral zone (e.g. fever) • Reduced sweat threshold (e.g. night time*) • Early phase of acclimatization • Circadian rhythm disturbances (e.g. depression) • Non-thermoregulatory • Autonomic non-thermoregulatory responses • Direct sweat gland stimulation • Osmotic mechanisms

7. Sweat measurement appears as a study variable in a variety of investigations. Measurement requirements depend on need to determine: • Body distribution of sweat • Amount of sweat production • Consistency and contents of sweat • Circadianicity of perceptible sweating

8. Sweat as a study variable • Fever • Exercise • Night sweats • Hot flashes • Heat stress • Mental stress

9. Sweat as a diagnostic biomarker • Cystic Fibrosis • Hyper- or Hypohidrosis • Metabolic disorders • C-fiber dysfunction • Complex pain disorders

10. Questions & Measurements: Typical sweating-related research questions: • When does it occur? = time it occurs • Thermal causal factors = thermometry • How much water loss? = change in weight • What is being secreted? = sweat analysis

11. Questions & Measurements: Questions related to cause and mechanisms: • Sudomotor function? = ability of sweat glands to release chloride ions • Sudomotor activity = what stimulates sweat glands? • Autonomic activity = general distribution [ANS contribution is complex]

12. Critical factors dictating selection of measurement methods: • Mechanisms underlying sweat production and secretion • Relationship of sweat to the research question Precision and accuracy of sudomotor components are important when inferential questions or correlates are proposed.

13. Research situation: Interdisciplinary researchers planning clinical research to study factors related to night sweats in adult men and women from unknown cause. • Prevalence estimates range from 10% - 41% • Commonly under-reported Underlying question: • Are night sweats associated with adverse health outcomes

14. Autonomic, non-thermoregulatory mechanisms that Induce Sweating • Increased sympathetic activity, central • Disturbed sleep stages • Vagal stimulation (gustatory, gastrointestinal distention or cardiac pain) • Autonomic nervous system dysfunction/instability • Medullary and spinal cord abnormalities • Anxiety states

15. Methodological aims of this pilot study were to: • determine an accurate, feasible strategy to measure sweat frequency and intensity in adults • test feasibility, ease of measurement, and seek potential predictive correlates associated with sweat activity for a future study of idiopathic night sweats

16. Methods: Systematic search of existing or historically documented sweat measurement techniques: • Search included data from scientific literature, instrument vendors, and reports. • Preliminary categorization done to describe/compare/contrast capabilities of extant techniques to measure sweating activity.

17. Results from Search: • Measurements included sweating intensity, amount, ion concentrations, and excitation frequency were found. • Over a dozen methods in historical reviews included galvanic responses; electrodermal conductance measurements, and sweat distribution by starch-iodine compounds.

18. Results from Search: • Newer investigators found that electrode configuration, type of electrodes, excitation frequency and signal extraction, influenced other factors that could dominate the measurement of sweating activity. • Skin conductance levels did not directly correlate with sweat production or evaporation from skin, but instead with the filling of the sweat ducts and the reabsorption process.

19. Measurements include sweat rates, amount, content, excitation frequency

20. Results from Search: • Despite, the number of methods and analyses of electrodermal measurements, no established unit relating electrical measurements to sweat activity has been fully validated. • We selected a newly developed instrument measuring parameters from skin conductance curves, calibrated to measure quantity of sweat production in perceptible sweating.

21. Tronstad, C., Gjein, G.E., Grimnes, S., Martinsen, O.G., Krogstad, A.-L., & Fosse, E. (2008). Electrical measurement of sweat activity. Physiological Measurement, 29(6), S407-415.

22. Tronstad, C., Gjein, G.E., Grimnes, S., Martinsen, O.G., Krogstad, A.-L., & Fosse, E. (2008). Electrical measurement of sweat activity. Physiological Measurement, 29(6), S407-415.

23. Instrumentation Methods: • 7 adults underwent polysomnography (PSG) in a sleep lab. • We selected a newly developed instrument measuring parameters from skin conductance curves, calibrated to measure quantity of sweat production in perceptible sweating by electrical impedance (Sudlogger). • Variables included history of night sweats severity/frequency, sleep-related symptoms.=

24. Instrumentation Methods: • PSG readings tracked with biological signals: core temperatures (VitalSense, ingested disposable temperature probe), skin temperatures (chest thermistor), and sweating frequency and amplitude from forehead, chest, arm, and palm (Sudologger).

25. Core Temp Surface Temp Sweat Volume Sweat “Freq” Sleep Stage Arousals PLMs Apnea/Hypop

26. Results: • Sweating (frequency, amplitude, and area under the curve) was defined as > 1,000 impulses per 30 minute interval. • Two subjects reported prior night sweats but only 1 actually sweated during study. • Two had sweating during the study but were unaware of it.

27. Results [continued]: • Subjective reports of night time sweating did not predict objective sweating during the sleep studies, and there were no other reliable predictors. • Sweating episodes were associated with higher body temperature, earlier sleep stage and periodic limb movements, but not with skin temperature, apeneic/hypopneic episodes, or brief spontaneous arousals.

28. Conclusions: • No associations were found between subjective and objective evidence of night sweats, nor obstructive sleep apnea. • Plans are to specifically enroll patients who complain of severe and frequent night sweats and to add measurements of heart rate variability to our set of variables. • The newly developed Sudologger was selected to meet upcoming study needs.

29. References: Mold, J. W., Mathew, M. K., Belgore, S., & DeHaven, M. (2002). Prevalence of night sweats in primary care patients: an OKPRN and TAFP-Net collaborative study. J FamPract, 51(5), 452-456. Ohhashi, T., Sakaguchi, M., & Tsuda, T. (1998). Human perspiration measurement. Physiological Measurement, 19(4), 449-461. Provitera, V., Nolano, M., Caporaso, G., Stancanelli, A., Santoro, L., & Kennedy, W. R. (2010). Evaluation of sudomotor function in diabetes using the dynamic sweat test. Neurology, 74(1), 50-56. Tronstad, C., Gjein, G. E., Grimnes, S., Martinsen, O. G., Krogstad, A.-L., & Fosse, E. (2008). Electrical measurement of sweat activity. Physiological Measurement, 29(6), S407-415.