Skin Blood Flow Research Articles

Using Wavelet Analysis of Blood Flow Oscillations to Investigate Differences in Skin Blood Flow Regulations Between the Upper and Lower Limbs.

The objective of this study was to investigate the differences in skin blood flow regulations between the upper and lower limbs in healthy adults using wavelet analysis of skin blood oscillations. To the best of our knowledge, this is the first study investigating the dominant skin blood flow control of the upper and lower limbs in healthy adults. Skin blood flow of the forearm and leg was simultaneously measured by laser Doppler flowmetry (LDF) in 17 healthy adults. Skin blood flow oscillations were analyzed using wavelet analysis to assess the dominant control among the metabolic endothelial (0.0095-0.02Hz), neurogenic (0.02-0.05Hz), myogenic (0.05-0.15Hz), respiratory (0.15-0.4Hz), and cardiac (0.4-2Hz) origins. Skin blood flow in the leg (11.13 ± 4.90 perfusion unit) was significantly higher than in the forearm (6.90 ± 2.50 perfusion unit, p < 0.001). The metabolic endothelial control is more dominant in the forearm (1.19 ±0.51 au) compared to the leg (0.73 ± 0.41 au, p < 0.01). The myogenic control is more dominant in the leg (1.18 ± 0.28 au) compared to the forearm (0.96±0.18 au, p < 0.05). Through wavelet analysis of skin blood flow oscillations, the results indicate that metabolic endothelial control is more dominant in the forearm (upper limbs) and myogenic control is more dominant in the leg (lower limbs).

Micro- and macrovascular function in the highest city in the world: a cross sectional study

Since vascular responses to hypoxia in both healthy high-altitude natives and chronic mountain sickness (a maladaptive high-altitude pathology characterised by excessive erythrocytosis and the presence of symptoms-CMS) remain unclear, the role of inflammation and oxidative/nitrosative stress on the endothelium-dependent and -independent responses in both the micro- and macrocirculation, in healthy Andeans at different altitudes and in CMS patients, was examined. 94 men were included: 18 lowlanders (LL), 38 healthy highlanders permanently living at 3800m (n=21-HL-3800) or in La Rinconada, the highest city in the world (5100-5300m) (n=17-HL-5100/No CMS). Moreover, 14 participants with mild (Mild CMS) and 24 with moderate to severe CMS (Mod/Sev CMS) were recruited. All undertook two reactivity tests: i) local thermal hyperaemia (microcirculation) and ii) flow-mediated dilation (macrocirculation). Endothelium-independent function (glyceryl trinitrate) was also assessed only in La Rinconada. Conductance and skin blood flow velocity during the microcirculation test, as well as macrocirculation progressively decreased with altitude (LL>HL-3800 > HL-5100/No CMS). CMS also induced a decrease in macrocirculation (HL-5100/No CMS>Mild CMS= Mod/Sev CMS), while glyceryl trinitrate restored vascular function. Both oxidative stress and nitric oxide metabolites increased with altitude only. Principal component analysis revealed that increasing inflammation with altitude was associated with a progressive decline in both micro- and macrovascular function in healthy highlanders. Both micro and macrovascular function are affected by chronic exposure to hypoxia, the latter being further compounded by CMS. The "Fonds de dotation AGIR pour les maladies chroniques", the "Air Liquide Foundation", and the "French National Research Agency".

Multifunctional carbomer based ferulic acid hydrogel promotes wound healing in radiation-induced skin injury by inactivating NLRP3 inflammasome

BackgroundRadiation-induced skin injury is a significant adverse reaction to radiotherapy. However, there is a lack of effective prevention and treatment methods for this complication. Ferulic acid (FA) has been identified as an effective anti-radiation agent. Conventional administrations of FA limit the reaching of it on skin. We aimed to develop a novel FA hydrogel to facilitate the use of FA in radiation-induced skin injury.MethodsWe cross-linked carbomer 940, a commonly used adjuvant, with FA at concentrations of 5%, 10%, and 15%. Sweep source optical coherence tomography system, a novel skin structure evaluation method, was applied to investigate the influence of FA on radiation-induced skin injury. Calcein-AM/PI staining, CCK8 assay, hemolysis test and scratch test were performed to investigate the biocompatibility of FA hydrogel. The reducibility of DPPH and ABTS radicals by FA hydrogel was also performed. HE staining, Masson staining, laser Doppler blood flow monitor, and OCT imaging system are used to evaluate the degree of skin tissue damage. Potential differentially expressed genes were screened via transcriptome analysis.ResultsGood biocompatibility and in vitro antioxidant ability of the FA hydrogels were observed. 10% FA hydrogel presented a better mechanical stability than 5% and 15% FA hydrogel. All three concentrations of FA remarkably promoted the recovery of radiation-induced skin injury by reducing inflammation, oxidative conidiation, skin blood flow, and accelerating skin tissue reconstruction, collagen deposition. FA hydrogel greatly inhibiting the levels of NLRP3, caspase-1, IL-18, pro-IL-1β and IL-1β in vivo and vitro levels through restraining the activation of NLRP3 inflammasome. Transcriptome analysis indicated that FA might regulate wound healing via targeting immune response, inflammatory response, cell migration, angiogenesis, hypoxia response, and cell matrix adhesion.ConclusionsThese findings suggest that the novel FA hydrogel is a promising therapeutic method for the prevention and treatment of radiation-induced skin injury patients.Graphical

Abstract 44: Transcutaneous hydrogen sulfide measurement as a way to evaluate skin blood flow

Hydrogen sulfide (H 2 S) generated in the endothelium of small arteries has been shown to contribute to vasodilation, angiogenesis, and antioxidant properties. We have developed a non-invasive way to measure H 2 S emitted by the skin (TAGS™) and have shown that the ratio of leg:arm emitted levels correlate with severity of microvascular impairment in subjects with diabetes. This study evaluated the correlation of transdermal H 2 S ratios with the current gold standard method of evaluating leg skin blood flow, transcutaneous oxygen pressures (tcpO 2 ). TAGS™ measurements were made on the forearm and lower limbs in subjects to calculate the leg:arm ratio while tcpO 2 was recorded only from legs. Other measurements included ankle brachial index (ABI), fasting blood glucose, HbA1c, plasma lipids, blood pressure, and BMI. We observed that TAGS™ ratios correlated strongly with HbA1c (p = 0.0002) and with tcpO 2 (p = 0.0009). In addition, TAGS ratios were significantly lower in subjects with diabetes (0.69 +/- 0.18) compared to healthy controls (1.13 +/- 0.40) (p = &lt;0.0001). These results suggest lower leg:arm ratios of transdermal H 2 S measurements are indicative of impaired microvascular function and that the TAGS™ measurements may be a simpler way than tcpO 2 to detect and monitor diminished skin blood flow that leads to PAD complications.

Hyperthermia and Exertional Heatstroke During Running, Cycling, Open Water Swimming, and Triathlon Events.

Few previous epidemiological studies, sports medicine position statements, and expert panel consensus reports have evaluated the similarities and differences of hyperthermia and exertional heatstroke (EHS) during endurance running, cycling, open water swimming, and triathlon competitions. Accordingly, we conducted manual online searches of the PubMed and Google Scholar databases using pre-defined inclusion criteria. The initial manual screenings of 1192 article titles and abstracts, and subsequent reviews of full-length pdf versions identified 80 articles that were acceptable for inclusion. These articles indicated that event medical teams recognized hyperthermia and EHS in the majority of running and triathlon field studies (range, 58.8 to 85.7%), whereas few reports of hyperthermia and EHS appeared in cycling and open water swimming field studies (range, 0 to 20%). Sports medicine position statements and consensus reports also exhibited these event-specific differences. Thus, we proposed mechanisms that involved physiological effector responses (sweating, increased skin blood flow) and biophysical heat transfer to the environment (evaporation, convection, radiation, and conduction). We anticipate that the above information will help race directors to distribute pre-race safety advice to athletes and will assist medical directors to better allocate medical resources (eg, staff number and skill sets, medical equipment) and optimize the management of hyperthermia and EHS.

Nicotine exacerbates exertional heat strain in trained men: a randomized, placebo-controlled, double-blind study.

To determine whether using nicotine exacerbates exertional heat strain through an increased metabolic heat production (Hprod) or decreased skin blood flow (SkBF), 10 nicotine-naïve trained males [37 ± 12 yr; peak oxygen consumption (V̇o2peak): 66 ± 10 mL·min-1·kg-1] completed four trials at 20°C and 30°C following overnight transdermal nicotine (7 mg·24 h-1) and placebo use in a crossover, double-blind design. They cycled for 60 min (55% V̇o2peak) followed by a time trial (∼75% V̇o2peak) during which measures of gastrointestinal (Tgi) and mean weighted skin ([Formula: see text]sk) temperatures, SkBF, Hprod, and mean arterial pressure (MAP) were made. The difference in ΔTgi between nicotine and placebo trials was greater during 30°C (0.4 ± 0.5°C) than 20°C (0.1 ± 0.7°C), with [Formula: see text]sk higher during nicotine than placebo trials (0.5 ± 0.5°C, P = 0.02). SkBF became progressively lower during nicotine than placebo trials (P = 0.01) and progressively higher during 30°C than 20°C trials (P < 0.01); MAP increased from baseline (P < 0.01) and remained elevated in all trials. The difference in Hprod between 30°C and 20°C trials was lower during nicotine than placebo (P = 0.01) and became progressively higher during 30°C than 20°C trials with exercise duration (P = 0.03). Mean power output during the time trial was lower during 30°C than 20°C trials (24 ± 25 W, P = 0.02), and although no effect of nicotine was observed (P > 0.59), two participants (20%) were unable to complete their 30°C nicotine trials as one reached the ethical limit for Tgi (40.0°C), whereas the other withdrew due to "nausea and chills" (Tgi = 39.7°C). These results demonstrate that nicotine use increases thermal strain and risk of exertional heat exhaustion by reducing SkBF.NEW & NOTEWORTHY In naïve participants, acute nicotine use exerts a hyperthermic effect that increases the risk of heat exhaustion during exertional heat strain, which is driven by a blunted skin blood flow response. This has implications for 1) populations that face exertional heat strain and demonstrate high nicotine use (e.g., athletes and military, 25%-50%) and 2) study design whereby screening and exclusion for nicotine use or standardization of prior use (e.g., overnight abstinence) is encouraged.

Neuromuscular electrical stimulation for facial wrinkles and sagging: The 8-week prospective, split-face, controlled trial in Asians.

This study aims to fill the knowledge gap regarding the effects of high frequency facial neuromuscular electrical stimulation (fNMES) on facial aging, using a device equipped with CERTEC (Cell Energy Regeneration Technology) operating between 40 and 190 kHz. This prospective split-face study was conducted at Tokyo University Hospital between March and May 2023 with 24 healthy adult women aged 30-59. The intervention group used the fNMES device along with basic skin care on one side of the face, and basic skin care alone on the other side for 8 weeks. Evaluations included changes in skin wrinkles, sagging, and blood flow. This study found significant improvements in skin elasticity and degree of wrinkles in the areas intervened with fNMES (p < 0.05, respectively). In addition, the intervention resulted in significant improvements in jawline angle (p < 0.01), submental volume (p < 0.05), cheek volume (p < 0.05), maximum nasolabial fold depth (p = 0.03), and total volume of the nasolabial folds (p = 0.03). The fNMES intervention also showed improvement in blood flow (p < 0.05). These improvements were also subjectively assessed by the participants in subject questionnaires at 8 weeks after the intervention (p < 0.05). This study suggests that high frequency fNMES effectively improves facial skin elasticity, reduces wrinkles and sagging, promotes blood flow, and contributes to overall facial appearance rejuvenation. Although further studies are needed, high frequency fNMES appeared promising as a noninvasive anti-aging therapy.

Influence of sustained mild dehydration on thermoregulatory and cognitive functions during prolonged moderate exercise

PurposeThe current study investigated whether sustained mild dehydration affects thermoregulatory function and cognitive performance during prolonged exercise.MethodsTwelve young adults performed a test consisting of three sets of 20-min exercise with 2-min intervals under euhydrated (control, CON) and mildly dehydrated conditions (MDEH) at an ambient temperature of 30 °C and 60% relative humidity. MDEH was established by restricting water intake for 24 h, resulting in urine specific gravity of ≥ 1.020. Heart rate (HR), mean arterial blood pressure (MAP), skin blood flow (SkBF), sweat rate (SR) on the chest and forearm, and ear canal and mean skin surface temperatures (Tear and mean Tskin, respectively) were continuously recorded. For each exercise set, thermal and humid sensations and thermal discomfort were assessed using visual analog scales (VAS), and the rating of perceived exertion (RPE) was estimated. Cognitive performance on the Go/No-Go (easy) and incongruent Stroop (difficult) tasks was assessed before and after the test.ResultsNo differences were observed in HR, MAP, SkBF, SR, Tear, and mean Tskin between the CON and MDEH. Thermal and humidity sensations, thermal discomfort, and RPE were higher in MDEH than in CON. Moreover, response time to the Stroop task was prolonged in MDEH.ConclusionThese findings suggest that sustained mild dehydration does not affect autonomic thermoregulation during exercise. Augmented thermal perception and perceived exertion, which are necessary for behavioral thermoregulation, were noted; however, cognitive function may be attenuated under MDEH.

Coagulation depth estimation using a line scanner for depth-resolved laser speckle contrast imaging.

Partial-thickness burn wounds extend partially through the dermis, leaving many pain receptors intact and making the injuries very painful. Due to the painfulness, quick assessment of the burn depth is important to not delay surgery of the wound if needed. Laser speckle imaging (LSI) of skin blood flow can be helpful in finding severe coagulation zones with impaired blood flow. However, LSI measurements are typically too superficial to properly reach the full depth of the adult dermis and cannot resolve the flow in depth. Diffuse correlation spectroscopy (DCS) uses varying source-detector separations to allow differentiation of flow depths but requires time-consuming 2D scanning to form an image of the burn area. We here present a prototype for a hybrid DCS and LSI technique called speckle contrast diffuse correlation spectroscopy (scDCS) with the novel approach of using a laser line as a source and using the speckle contrast of averaged images to obtain an estimate of static scattering in the tissue. This will allow for fast non-contact 1D scanning to perform 3D tomographic imaging, making quantitative estimates of the depth and area of the coagulation zone from burn wounds. Simulations and experimental results from a volumetric flow phantom and a gelatin wedge phantom show promise to determine coagulation depth. The aim is to develop a method that, in the future, could provide more quantitative estimates of coagulation depth in partial thickness burn wounds to better estimate when surgery is needed.

Altered Microvascular Reactivity During a Skin Thermal Challenge Is Associated With Organ Dysfunction and Slow Recovery After Cardiac Surgery

ObjectivesTo assess microvascular reactivity during a skin thermal challenge early post-cardiac surgery and its association with outcome. DesignNon-invasive physiological study. SettingThirty-five-bed department of intensive care. ParticipantsPatients admitted to the ICU post-cardiac surgery. InterventionsThermal challenge. Measurements and Main ResultsForty-six patients were included; 14 needed vasoactive support or ventilatory support for at least 48 hours (slow recovery) and 32 had a more rapid recovery. Skin blood flow (SBF) was measured on the anterior proximal forearm using skin laser Doppler (SLD). A thermal challenge was performed by abruptly increasing local skin temperature from 37°C to 43°C while monitoring SBF. The ratio between the SBFs at 43°C and 37°C was calculated as a measure of microvascular reactivity. SBF at 37°C was not significantly different in patients with a slow recovery and those with a rapid recovery, but SBF after 9 min at 43°C was lower [48.5 (17.3-69.0) vs 85.1 (45.2-125.7), p<0.01], resulting in a lower SBF ratio [2.8 (1.5-4.7) vs 4.8 (3.7-7.8), p<0.01]. Patients with lower SBF ratios were more likely to have dysfunction of at least 1 organ (as assessed using the sequential organ dysfunction [SOFA] score) 48 hours post-cardiac surgery than those with higher ratios: 88% vs 40% vs 27% (p<0.01), respectively, for the lowest, middle, and highest tertiles of SBF ratio. In multivariable analysis, lower SBF ratio was an independent risk factor for slow recovery. ConclusionsEarly alterations in microvascular reactivity as evaluated by a skin thermal challenge are correlated with organ dysfunction. These observations may help in the development of new, simple, non-invasive monitoring systems in postoperative patients.

Dynamic Microcirculation Characteristics of Plantar Skin Under Metatarsal Head of Human Foot in Response to Life-Like Pressure Stimulus.

Diabetic foot ulcer (DFU) is a severe complication with high mortality. High plantar pressure and poor microcirculation are considered main causes of DFU. The specific aims were to provide a novel technique for real-time measurement of plantar skin blood flow (SBF) under walking-like pressure stimulus and delineate the first plantar metatarsal head dynamic microcirculation characteristics because of life-like loading conditions in healthy individuals. Twenty young healthy participants (14 male and 6 female) were recruited. The baseline (i.e., unloaded) SBF of soft tissue under the first metatarsal head were measured using laser Doppler flowmetry (LDF). A custom-made machine was utilized to replicate daily walking pressure exertion for 5 min. The exerted plantar force was adjusted from 10 N (127.3 kPa) to 40 N (509.3 kPa) at an increase of 5 N (63.7 kPa). Real-time SBF was acquired using the LDF. After each pressure exertion, postload SBF was measured for comparative purposes. Statistical analysis was performed using the R software. All levels of immediate-load and postload SBF increased significantly compared with baseline values. As the exerted load increased, the postload and immediate-load SBF tended to increase until the exerted load reached 35 N (445.6 kPa). However, in immediate-load data, the increasing trend tended to level off as the exerted pressure increased from 15 N (191.0 kPa) to 25 N (318.3 kPa). For postload and immediate-load SBF, they both peaked at 35 N (445.6 kPa). However, when the exerted force exceeds 35 N (445.6 kPa), both the immediate-load and postload SBF values started to decrease. Our study offered a novel real-time plantar soft tissue microcirculation measurement technique under dynamic conditions. For the first metatarsal head of healthy people, 20 N (254.6 kPa)-plantar pressure has a fair microcirculation stimulus compared with higher pressure. There might be a pressure threshold at 35 N (445.6 kPa) for the first metatarsal head, and soft tissue microcirculation may decrease when local pressure exceeds it.

Spectral changes in skin blood flow during pressure manipulations or sympathetic stimulation.

Skin blood flow is commonly determined by laser Doppler flowmetry (LDF). It has been suggested that pathophysiological conditions can be assessed by analysis of specific frequency domains of the LDF signals. We tested whether physiological stimuli that activate myogenic and neurogenic mechanisms would affect relevant portions of the laser Doppler spectrum. LDF sensors were placed on the right forearm of 14 healthy volunteers for myogenic (six females) and 13 for neurogenic challenge (five females). Myogenic responses were tested by positioning the arm ∼50° above/below heart level. Neurogenic responses were tested by immersing the left hand into an ice slurry with and without topical application of local anaesthetic. Short-time Fourier analyses were computed over the range of 0.06 to 0.15Hz for myogenic and 0.02 to 0.06Hz for neurogenic. No significant differences in spectral density were observed (P=0.40) in the myogenic range with arm above (7±54×10-4dB) and below heart (7±14×10-4dB). Neurogenic spectral density showed no significant increase from baseline to cold pressor test (0.0017±0.0013 and 0.0038±0.0039dB; P=0.087, effect size 0.47). After application of anaesthetic, neurogenic spectral density was unchanged between the baseline and cold pressor test (0.0014±0.0025 and 0.0006±0.0005dB; P=0.173). These results suggest that changes in the myogenic and neurogenic spectral density of LDF signals did not fully reflect the skin vascular function activated by pressure manipulation and sympathetic stimulation. Therefore, LDF myogenic and neurogenic spectral density data should be interpreted with caution.

The impact of irritant challenge on the skin barrier and myeloid-resident immune cells in women who are postmenopausal is modulated by hormone replacement therapy.

Sex hormone changes during menopausal transition contribute to declining skin health. However, how menopause and its treatment by hormone replacement therapy (HRT) impact the skin barrier and immune system is unclear. To examine how menopause and HRT affect the skin barrier and immune cell composition in postmenopausal women following irritant challenge. Two cohorts of postmenopausal women were recruited to the study. The first cohort consisted of 10 untreated women [HRT-; mean (SEM) age 56.5 (1.6) years (range 48-63)] and the second was composed of 8 women receiving HRT [HRT+; mean (SEM) age 54.0 (2.1) years (range 48-63)]. Skin irritation was induced by applying topical sodium lauryl sulfate (SLS) 1.25% to occluded buttock skin for 48 h. Clinical assessment was conducted after 24 h, followed by biopsy of both SLS-challenged and unchallenged skin for analysis of skin barrier proteins and immune cell distribution using immunofluorescence. Clinically, there were no significant differences in skin irritant responses between those taking or not taking HRT (including increased skin redness and blood flow). In response to SLS challenge a significant increase in transepidermal water loss (P < 0.05), filaggrin deposition and cytokeratin 10 (K10)+ cell layers (P < 0.01) was observed in individuals receiving HRT compared with the HRT- group. Following SLS challenge in individuals taking HRT, a significant (P < 0.01) reduction in CD207+ cells in the epidermis was observed, accompanied by an increase of CD207+ cells in the dermis, indicative of migrating Langerhans cells (LCs). Significantly fewer migrating LCs were found in those who were not receiving HRT (P < 0.01). Furthermore, the numbers of dermal dendritic cells (DCs), macrophages, and CD11c+CD206- and CD68+CD206- subsets were found to be significantly (P < 0.05) higher in those taking HRT following SLS challenge. Individuals receiving HRT displayed enhanced skin barrier response to SLS challenge with thicker filaggrin and increased K10+ epidermal cell layers. Following challenge, HRT users exhibited elevated LC, inflammatory DC and macrophage counts in the dermis. These may render skin both more prone to inflammation and more capable of resolving it, while also promoting skin repair.

Immunomodulating effects of the single bacterial strain therapy EDP1815 on innate and adaptive immune challenge responses — a randomized, placebo-controlled clinical trial

The gut microbiome can modulate systemic inflammation and is therefore target for immunomodulation. Immunomodulating effects of EDP1815, a bacterial commensal strain of Prevotella histicola, were studied in healthy participants. Effects on adaptive immunity were evaluated by a neo-antigen challenge with keyhole limpet haemocyanin (KLH), while effects on innate immunity were evaluated by topical toll-like receptor 7 (TLR7) agonist imiquimod. Capsules with two enteric coating levels (EC1, EC2) were compared. Thirty-six healthy participants were included and received a daily dose of 8 × 1010 cells EDP1815-EC1, EDP1815-EC2 or placebo (randomization 1:1:1) for 60 days. They received KLH vaccinations at days 8, 24 and 36, with intradermal skin challenge at day 57. KLH challenge outcomes were antibody levels, and skin blood flow and erythema after skin challenge, measured by imaging techniques. Imiquimod administration started at day 57, for 72 h. Outcomes consisted of imaging measurements similar to the KLH challenge, and the influx of inflammatory cells and cytokines in blister fluid. There was no effect of EDP1815 treatment on the KLH challenge, neither on the imaging outcomes of the imiquimod challenge. There was a consistently lower influx of inflammatory cells in the blister fluid of EDP1815-treated participants (neutrophils, p = 0.016; granulocytes, p = 0.024), more pronounced in EC1. There was a lower influx of interleukin [IL]-1β, IL-6, IL-8, IL-10, interferon [IFN]-γ and tumour necrosis factor in blister fluid of EDP1815-treated participants. EDP1815 had immunomodulatory effects on the innate immune response driven by imiquimod, but no effect on the KLH challenge was observed. Trial registration number: NCT05682222; date: 22 July 2022.

An evaluation of the effects of localised skin cooling on microvascular, inflammatory, structural, and perceptual responses to sustained mechanical loading of the sacrum: A study protocol.

This study protocol aims to investigate how localised cooling influences the skin's microvascular, inflammatory, structural, and perceptual tolerance to sustained mechanical loading at the sacrum, evaluating factors such as morphology, physiology, and perceptual responses. The protocol will be tested on individuals of different age, sex, skin tone and clinical status, using a repeated-measure design with three participants cohorts: i) young healthy (n = 35); ii) older healthy (n = 35); iii) spinal cord injured (SCI, n = 35). Participants will complete three testing sessions during which their sacrum will be mechanically loaded (60 mmHg; 45 min) and unloaded (20 min) with a custom-built thermal probe, causing pressure-induced ischemia and post-occlusive reactive hyperaemia. Testing sessions will differ by the probe's temperature, which will be set to either 38°C (no cooling), 24°C (mild cooling), or 16°C (strong cooling). We will measure skin blood flow (via Laser Doppler Flowmetry; 40 Hz); pro- and anti-inflammatory biomarkers in skin sebum (Sebutape); structural skin properties (Optical Coherence Tomography); and ratings of thermal sensation, comfort, and acceptance (Likert Scales); throughout the loading and unloading phases. Changes in post-occlusive reactive hyperaemia will be considered as the primary outcome and data will be analysed for the independent and interactive effects of stimuli's temperature and of participant group on within- and between-subject mean differences (and 95% Confidence Intervals) in peak hyperaemia, by means of a 2-way mixed model ANOVA (or Friedman). Regression models will also be developed to assess the relationship between absolute cooling temperatures and peak hyperaemia. Secondary outcomes will be within- and between-subject mean changes in biomarkers' expression, skin structural and perceptual responses. This analysis will help identifying physiological and perceptual thresholds for the protective effects of cooling from mechanically induced damage underlying the development of pressure ulcers in individuals varying in age and clinical status.

Using wavelet phase coherence of heart rate variability and blood flow oscillations to compare mechanisms of action between Tai Chi mind-body exercise and brisk walking aerobic exercise

Tai Chi exercise has been demonstrated to be beneficial for health and quality of life. However, the mind–body effect of Tai Chi on modulating interactions of the cardiovascular components has not been investigated. This study aimed to differentiate the effect of Tai Chi (mind–body exercise) and brisk walking (aerobic exercise) on modulating skin blood flow oscillations (BFO) of the upper and lower limbs and heart rate variability (HRV). Bafa Wubu of Tai Chi for 15 min and brisk walking for 15 min were performed by 30 adults in two different days. Wavelet phase coherence was employed to assess the coordination between HRV and BFO before and after exercise. Two indices were proposed to quantify the coherence, i.e., the area (Aϕ) and maximal difference (dmax) between the coherence function and the threshold obtained by surrogate test. The results demonstrated that Tai Chi resulted in a significant decrease in phase coherence between HRV and BFO of the upper limb in the frequency interval 0.05–0.15 Hz (Aϕ baseline 0.1600 ± 0.0288, post-exercise 0.0486 ± 0.0220, p < 0.001; dmax baseline 0.3222 ± 0.0220, post-exercise 0.2578 ± 0.0219, p < 0.005), but not between HRV and BFO of the lower limb. Brisk walking resulted in a significant increase in phase coherence between HRV and BFO of the lower limb in the frequency interval 0.05–0.15 Hz (Aϕ baseline 0.0455 ± 0.0251, post-exercise 0.1190 ± 0.0241, p < 0.05; dmax baseline 0.2191 ± 0.0225, post-exercise 0.3103 ± 0.0208, p < 0.05) but not between HRV and BFO of the upper limb. Our finding indicates that mind–body exercise and aerobic exercise modulate cardiovascular regulations through different mechanisms of action.

Skin Wetting Attenuates the Thermal Strain of Older Adults Exposed to Very Hot and Dry Heat with Accompanying Activities of Daily Living

Heat waves cause more deaths and hospitalizations in the elderly relative to any other age group. Indoor cooling with an air conditioner is an effective strategy to prevent the deleterious health effects of heat. However, air conditioning may not be available to some due to limited access, rising energy costs, power outages, and/or industry/government-imposed rolling blackouts. Thus, there is a clear need to identify non-air conditioning dependent cooling strategies to attenuate excessive elevations in body temperature and associated physiological strain in the elderly during heat wave conditions. Purpose: We tested the hypothesis that supplemental skin wetting via water spray attenuates elevations in core temperature and the accompanying physiological strain in older adults exposed to very hot and dry heat with accompanying activities of daily living. Methods: In a randomized order, 10 older adults (4 Females/6 Males; 74 ± 5 years) were exposed to 3-hours of ambient heating, replicating peak environmental conditions during the 2018 Los Angeles heat wave (47 ºC, 15% relative humidity), with (water spray) or without (control) skin-wetting via tap temperature water (~40 g applied every 10-minutes). To simulate heat generation associated with activities of daily living, participants performed six 5-minute periods of light exercise (~3 METS; metabolic heat production: 2.93 ± 0.42 W/kg in control and 2.95 ± 0.44 W/kg in water spray) dispersed throughout the heat exposure. To maintain euhydration, participants consumed 3 mL/kg/hr of tap-temperature water. We assessed core and skin temperatures, heart rate, whole-body sweat rate, and forearm blood flow (as a surrogate of changes in skin blood flow). We compared data between control and water spray trials using one-tailed paired t-tests. Results: When compared to control, water spray reduced the increase in core temperature by 0.33 ± 0.43 °C (p=0.020), ending skin temperature by 1.83 ± 0.73 °C (p&lt;0.001), and ending heart rate by 6 ± 9 bpm (p=0.033). Whole-body sweat rate was 2.12 ± 1.08 g/min lower with water spray compared to control (p&lt;0.001). However, the increase in forearm blood flow was not different between control (154 ± 74 mL/min) and water spray (149 ± 93 mL/min) trials (p=0.400). Conclusion: These preliminary data show that supplemental skin-wetting via water spray attenuates the thermal (core and skin temperature) and associated physiological strain (heart rate and fluid-loss) of older adults exposed to extreme heat with accompanying activities of daily living. The downstream impact of this reduced thermal strain on cardiac and renal stress should be examined, as these are two of the main causes of heat-related morbidity and mortality. Supported by NIH R01AG069005 (CGC) and AHA 23POST1023065 (ZJM). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Use of Infrared Thermography and Heart Rate Variability to Evaluate Autonomic Activity in Domestic Animals.

Most of the responses present in animals when exposed to stressors are mediated by the autonomic nervous system. The sympathetic nervous system, known as the one responsible for the "fight or flight" reaction, triggers cardiovascular changes such as tachycardia or vasomotor alterations to restore homeostasis. Increase in body temperature in stressed animals also activates peripheral compensatory mechanisms such as cutaneous vasodilation to increase heat exchange. Since changes in skin blood flow influence the amount of heat dissipation, infrared thermography is suggested as a tool that can detect said changes. The present review aims to analyze the application of infrared thermography as a method to assess stress-related autonomic activity, and their association with the cardiovascular and heart rate variability in domestic animals.

Topically Applied N,N-Dimethylglycine Sodium Salt Enhances Human Skin Blood Flow by Inducing Endothelial Nitric Oxide Release

Topically Applied N,N-Dimethylglycine Sodium Salt Enhances Human Skin Blood Flow by Inducing Endothelial Nitric Oxide Release

Caffeine ingestion compromises thermoregulation and does not improve cycling time to exhaustion in the heat amongst males

PurposeCaffeine is a commonly used ergogenic aid for endurance events; however, its efficacy and safety have been questioned in hot environmental conditions. The aim of this study was to investigate the effects of acute caffeine supplementation on cycling time to exhaustion and thermoregulation in the heat.MethodsIn a double-blind, randomised, cross-over trial, 12 healthy caffeine-habituated and unacclimatised males cycled to exhaustion in the heat (35 °C, 40% RH) at an intensity associated with the thermoneutral gas exchange threshold, on two separate occasions, 60 min after ingesting caffeine (5 mg/kg) or placebo (5 mg/kg).ResultsThere was no effect of caffeine supplementation on cycling time to exhaustion (TTE) (caffeine; 28.5 ± 8.3 min vs. placebo; 29.9 ± 8.8 min, P = 0.251). Caffeine increased pulmonary oxygen uptake by 7.4% (P = 0.003), heat production by 7.9% (P = 0.004), whole-body sweat rate (WBSR) by 21% (P = 0.008), evaporative heat transfer by 16.5% (P = 0.006) and decreased estimated skin blood flow by 14.1% (P < 0.001) compared to placebo. Core temperature was higher by 0.6% (P = 0.013) but thermal comfort decreased by − 18.3% (P = 0.040), in the caffeine condition, with no changes in rate of perceived exertion (P > 0.05).ConclusionThe greater heat production and storage, as indicated by a sustained increase in core temperature, corroborate previous research showing a thermogenic effect of caffeine ingestion. When exercising at the pre-determined gas exchange threshold in the heat, 5 mg/kg of caffeine did not provide a performance benefit and increased the thermal strain of participants.