Plasma hyperosmolality attenuates skin sympathetic nerve activity during passive heat stress in humans
Bibliographic record
Abstract
KEY POINTS: Plasma hyperosmolality delays the onset for sweat production and cutaneous vasodilatation during heat stress in humans; however, the mechanism by which hyperosmolality exerts this effect remains unknown. This study examined if plasma hyperosmolality exerts a central and/or peripheral modulation of thermoregulatory function in humans. The main findings are that plasma hyperosmolality delays the increase in skin sympathetic nerve activity during whole-body passive heat stress in humans. In contrast, local intradermal infusion of hyperosmotic saline did not affect sweating or cutaneous vasodilatation. These results suggest that plasma hyperosmolality delays the onset threshold for sweating and cutaneous vasodilatation by inhibiting efferent thermoregulatory activity in humans. ABSTRACT: In humans, plasma hyperosmolality delays the onset of sweating and cutaneous vasodilatation during heat stress. However, it remains unknown if hyperosmolality exerts this effect through a central (i.e. CNS) and/or peripheral (i.e. effector organ) modulation of thermoregulatory activity. We examined if intravenous infusion of hyperosmotic saline affects skin sympathetic nerve activity (SSNA) during whole-body passive heating in healthy humans. Furthermore, we examined if local intradermal infusion of hyperosmotic saline affects sweating and cutaneous vasodilatation during passive heating. Following intravenous infusion of either 0.9% (ISO) or 3.0% (HYPER) NaCl saline, 12 subjects were passively heated until core temperature increased by ∼0.6°C. During each condition, sweating and cutaneous vascular conductance were measured over two intradermal microdialysis probes, one perfused with ISO saline and the other with HYPER saline. Intravenous infusion of HYPER saline increased plasma osmolality (294 ± 3 to 316 ± 5 mOsm kg(-1) H2O, P ≤ 0.01), which remained greater than ISO throughout heating. Plasma hyperosmolality delayed the mean body temperature onset of sweating (+1.24 ± 0.18 vs. +1.60 ± 0.18°C, P ≤ 0.01) and cutaneous vasodilatation (+1.15 ± 0.18 vs. +1.53 ± 0.22°C, P ≤ 0.01), and attenuated the increase in SSNA during heating (+147 ± 178 vs. +427 ± 281%, P ≤ 0.01). Intradermal infusion of HYPER saline increased baseline cutaneous vascular conductance (P ≤ 0.01), which did not increase further during the subsequent heating period (P = 0.11). In contrast, intradermal infusion of HYPER saline did not affect sweating (P = 0.99). These results provide direct evidence that plasma hyperosmolality exerts a central modulatory effect governing efferent thermoregulatory activity in humans.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".