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Biomedical subjects

R R Gonzalez

Publications and source records attributed to R R Gonzalez.

At least 19 recordsLinked to original sources

The effect of Portuguese Man-of-war (Physalia physalis) venom on calcium, sodium and potassium fluxes of cultured embryonic chick heart cells.

Portuguese Man-of-war venom markedly increases calcium (45Ca2+) influx into primary, cultured, embryonic chick heart cells. This action is dose-dependent, but is unaffected by organic calcium blockers (diltiazem, verapamil, nifedipine, nimodipine and mibefradil). On the other hand, certain trivalent (La3+, Gd3+) and divalent (Zn2+, Ni2+, Cu2+, Mn2+) metals inhibit venom-induced calcium influx. Sodium (22Na+) influx into chick heart cells is also significantly increased by Man-of-war venom. Flecainide does not block venom-induced sodium influx. The efflux of the potassium analogue, 86Rb+, from heart cells is also significantly increased by the venom. The venom, however, has little or no effect on rubidium (86Rb+) or 2-deoxy-D-[2-3H] glucose influx.

Animals↗

Physiological problems associated with wearing NBC protective clothing during cold weather.

This report considers how thermal balance of soldiers wearing nuclear, biological and chemical (NBC) protective clothing in combination with the Extreme Cold Weather Clothing System (ECWCS) is affected during work in cold weather. A review of published reports concerning physiological consequences of wearing NBC protective clothing during cold exposure was completed. The findings reported in the experimental literature were too limited to adequately forecast the effects of adding NBC clothing to ECWCS. To remedy the information gap, simulation modeling was employed to predict body temperature changes during alternating bouts of exercise and rest throughout 8 h of exposure to three different severely cold conditions. Published findings indicate that NBC protective clothing may inadequately protect against hand and finger cooling, especially during rest following strenuous activity. No evidence substantiates suggestions that wearing NBC protective masks increases susceptibility to facial frostbite. Collectively, the limited experimental work and the results of simulation modeling argue against any increased risk of hypothermia associated with wearing NBC protective clothing while working in the cold. However, wearing NBC protective clothing during strenuous activity in cold weather may increase the risk of hyperthermia, and cause sweat accumulation in clothing which may compromise insulation and increase the risk of hypothermia during subsequent periods of inactivity.

Body Temperature↗

Benefit of heat acclimation is limited by the evaporative potential when wearing chemical protective clothing.

Heat acclimation-induced sweating responses have the potential of reducing heat strain for chemical protective garment wearers. However, this potential benefit is strongly affected by the properties of the garment. If the clothing ensemble permits sufficient evaporative heat dissipation, then heat acclimation becomes helpful in reducing heat strain. On the other hand, if the garment creates an impenetrable barrier to moisture, no benefit can be gained from heat acclimation as the additional sweating cannot be evaporated. Ten subjects were studied exercising on a treadmill while wearing two different chemical protective ensembles. Skin heat flux, skin temperature, core temperature, metabolic heat production and heart rate were measured. It was found that the benefit of heat acclimation is strongly dependent on the ability of the body to dissipate an adequate amount of heat evaporatively. The evaporative potential (EP), a measure of thermal insulation modified by moisture permeability, of the clothing ensemble offers a quantitative index useful to determine, a priori, whether heat acclimation would be helpful when wearing protective clothing system. The data show that when EP is < 15%, heat acclimation affords no benefit. An evaporative potential graph is created to aid in this determination.

Acclimatization↗

A quantitative evaluation of alpha1, alpha4, alphaV and beta3 endometrial integrins of fertile and unexplained infertile women during the menstrual cycle. A flow cytometric appraisal.

The expression of integrin molecules alpha1beta1, alpha4beta1 and alphaVbeta3 within endometrial tissue has been proposed as a marker of uterine receptivity during the implantation window. The present investigation examines by flow cytometric analysis the concentrations of alpha1, alpha4, alphaV and beta3 integrin subunits in endometrial stromal (ESC) and epithelial cells (EEC) in two groups of women throughout the menstrual cycle: normal fertile women (n = 27) and women with unexplained infertility (n = 26). Integrin concentrations in endometrial cells were calculated in relative fluorescence units against a negative cellular control. The assessment of integrin subunits detected the protein in ESC and EEC from the late proliferative to the late secretory phase. In both groups of women, the alpha1 was the highest integrin expressed in ESC and EEC throughout the menstrual cycle. All women exhibited low concentrations of alpha4-EEC at the time of the implantation window. Infertile women expressed lower concentrations of the alpha4-ESC during the proliferative and early secretory phase while lower concentrations of the alpha1-ESC were seen during the late secretory phase. Interestingly, the infertile women expressed lower concentrations of beta3-EEC in the early, mid-secretory and late secretory phases (P < 0.05). Infertile women also expressed lower concentrations of alpha1-EEC and alphaV-EEC during the late secretory phase (P < 0.05). It can be concluded that the quantitative determination of beta3-EEC by flow cytometry confirmed its potential feature as a marker of endometrial receptivity at the time of the implantation window. In addition, the defective expression of the alpha1-ESC found in the late secretory phase might be associated with the poor fertility outcome of women with unexplained infertility.

Adult↗

Characterization of a three-phase response in gloved cold-stressed fingers.

Seven gloves were studied worn by eight sedentary subjects (six men and two women) exposed to cold-dry, C D, (mean dry bulb temperature Tdb = -17.2 degrees C; mean dew point temperature Tdp = -25.1 degrees C), and cold-wet, C-W, (Tdh = 0 degrees C; Tdp = -8.4 degrees C) conditions. Mean endurance times were 75 min for the C-D and 162 min for the C W conditions. A three-phase response pattern of the temperature in the fingers was characterized. Phase I comprised an initial period during which finger temperature remained close to the pre-exposed level, due to delayed vasoconstriction in the finger. Phase II involved an exponential-like decrease of finger temperature indicative of the onset of vasoconstriction in the finger. Phase III manifested periodic finger temperature changes due to cold induced vasodilatation (CIVD). Mean wave patterns for phase III indicated approximately 3.5 waves x h(-1) in the C D but only about 2 waves x h(-1) in the C-W condition. Extension of endurance time, due to CIVD, was defined as the difference in time between the actual end of the experiment and the time the finger-tip would have reached the set temperature endurance limit as extrapolated by a continued exponential drop. Three overall response patterns of fingers in the cold were characterized: type A exhibiting all 3 phases; type B1 or B2 exhibiting either phases I+ II or phases II+ III; and type C showing only phase II. Considerable inter- and intra-subject variability was found. In both test conditions the final physiological thermal states of the subjects were between comfortable and slightly uncomfortable but acceptable and thus did not correlate with the responses in the fingers.

Adult↗

Evaluation of clothing systems to determine heat strain.

This article describes the basic evaluation process and test methodology employed when temperature extremes for clothing systems must be considered as part of the U.S. Army's Health Hazard Assessment for material in the development and acquisition process. The goals of the evaluation are to select clothing systems that minimize the hazards of heat strain and to predict the heat strain for persons wearing such clothing. Clothing evaluations begin with biophysical assessments that determine the thermal characteristics (vapor permeability and insulation) for textiles via guarded hot plate tests and for clothing systems via thermal manikin tests. The results from biophysical tests can be used to select the textile and/or clothing with the best thermal characteristics. The data from manikin evaluations also can be used in prediction modeling. Human physiological testing is best done in a controlled laboratory environment, although for realism and user acceptability field trials may also be conducted. Proven test and measurement methods must be employed, and tests must control for confounding variables; subjects serve as their own controls, and test environment and procedures are consistent between trials. The process and test methodology described can be applied to the evaluation of civilian clothing systems as well as to the military systems for which they were developed.

Hot Temperature↗

Simulation of a cold-stressed finger including the effects of wind, gloves, and cold-induced vasodilatation.

The thermal response of fingers exposed to cold weather conditions has been simulated. Energy balance equations were formulated, in a former study, for the tissue layers and the arterial, venous, and capillary blood vessels. The equations were solved by a finite difference scheme using the Thomas algorithm and the method of alternating directions. At this stage of development the model does not include any autonomic control functions. Model simulations assumed an electrical heating element to be embedded in the glove layers applied on the finger. A 1.3 W power input was calculated for maintaining finger temperatures at their pre-cold exposure level in a 0 degree C environment. Alternate assumptions of nutritional (low) and basal (high) blood flows in the finger demonstrated the dominance of this factor in maintaining finger temperatures at comfortable levels. Simulated exposures to still and windy air, at 4.17 m/s (15 km/h), indicated the profound chilling effects of wind on fingers in cold environments. Finally, the effects of variable blood flow in the finger, known as "cold-induced vasodilatation," were also investigated. Blood flow variations were assumed to be represented by periodic, symmetric triangular waves allowing for gradual opening-closing cycles of blood supply to the tip of the finger. Results of this part of the simulation were compared with measured records of bare finger temperatures. Good conformity was obtained for a plausible pattern of change in blood flow, which was assumed to be provided in its entirety to the tip of the finger alone.

Algorithms↗

Thermoregulatory responses to cold transients: effects of menstrual cycle in resting women.

Effects of the menstrual cycle on heat loss and heat production (M) and core and skin temperature responses to cold were studied in six unacclimatized female nonsmokers (18-29 yr of age). Each woman, resting supine, was exposed to a cold transient (ambient temperature = mean radiant temperature = 20 to -5 degrees C at -0.32 degrees C/min, relative humidity = 50 +/- 2%, wind speed = 1 m/s) in the follicular (F) phase (days 2-6) and midluteal (L) phase (days 19-23) of her menstrual cycle. Clothed in each of two ensembles with different thermal resistances, women performed multiple experiments in the F and L phases. Thermal resistance was 0.2 and 0.4 m2 . K . W-1 for ensembles A and B, respectively. Esophageal temperature (Tes), mean weighted skin temperature (Tsk), finger temperature (Tfing), and area-weighted heat flux were recorded continuously. Rate of heat debt (-S) and integrated mean body temperature (Tb,i) were calculated by partitional calorimetry throughout the cold ramp. Extensive peripheral vasoconstriction in the F phase during early periods of the ramp elevated Tes above thermoneutral levels. Shivering thermogenesis (DeltaM = M - Mbasal, W /m2) was highly correlated with declines in Tsk and Tfing (P <0.0001). There was a reduced slope in M as a function of Tb,i in the L phase with ensembles A (P < 0.02) and B (P < 0.01). Heat flux was higher and -S was less in the L phases with ensemble A (P < 0.05). An analytic model revealed that Tsk and Tes contribute as additive inputs and Tfing has a multiplicative effect on the total control of DeltaM during cold transients (R2 = 0.9). Endogenous hormonal levels at each menstrual cycle phase, core temperature and Tsk inputs, vascular responses, and variations in body heat balance must be considered in quantifying thermoregulatory responses in women during cold stress.

Adult↗

Body temperature and thermoregulation during submaximal exercise after 115-day spaceflight.

BACKGROUND: Altered thermoregulation has been reported following spaceflight simulations (bed rest and water immersion) but has never been examined after actual spaceflight. HYPOTHESIS: We tested the null hypothesis that body temperatures and heat loss responses during exercise would be similar before and after spaceflight. METHODS: Two male crewmembers of the 115-d Mir 18 mission performed supine submaximal cycle exercise (20 min at 40% and 20 min at 65% of preflight VO2peak) once at 145-146 d preflight and once at 5 d postflight (R + 5). RESULTS: After flight neither crewmember could complete the exercise protocol, stopping after 28-29 min. The core temperature (Tin, ingestible telemetry pill) at test termination was similar (37.8 degrees C for both subjects) pre- and postflight despite shorter postflight test duration. The slopes of the skin blood flow (laser Doppler)/Tin relationship (subject 1: 396 vs. 214; subject 2: 704 vs. 143% change Perfusion Unit/degree C), and the sweating rate (dew point hygrometry)/Tin relationship (subject 1: 6.3 vs. 2.0; subject 2: 4.6 vs. 0.7 mg.min-1.cm-2.degree C-1), were both reduced postflight without appreciable change in the Tin thresholds for sweating or skin blood flow. CONCLUSION: In this preliminary report for two crewmembers, the sensitivity of the heat loss responses were reduced after long-duration spaceflight, resulting in a faster rate of rise in core temperature.

Adult↗

Thermoregulatory responses to cold: effects of handwear with multi-layered clothing.

BACKGROUND: Thermoregulatory responses were studied during rest and exercise in men wearing diverse handwear with an extended cold-weather clothing system [ECWCS]. The ECWCS (thermal insulation = 3.6 clo (1 clo = thermal resistance approximately 0.155 m2.K.W(-1)); weight = 10.1 kg) incorporates skin-tight polypropylene underwear, polyester/cotton fatigues, polyester-insulated liners, balaclava, vapor-barrier boots, and polytetrafluroethylene [PTFE]-lined outer garments. METHODS: Six fit males each rested (M = 71 W.m(-2) and performed treadmill exercise (M = 171 W.m(-2)) while wearing the following handwear with the ECWCS: a light duty glove (LD, clo = 0.86), a heavy duty glove (HD, clo = 1.05), or an Arctic mitten (AM, clo = 1.46). Cold exposures were at Ta = 0 degrees C, -20 degrees C, and -30 degrees C; rh = 20%; wind speed = 10.34 m.s(-1). Exposure was a target period of 120 min designated as maximal endurance time (ET, min). All experiments were performed on separate days. Rectal (Tre), middle finger (Tmf), and mean weighted skin (Tsk) temperatures were recorded continuously; oxygen uptake and heart rate were measured periodically and total body weight loss msw, g.h(-1)) was determined after each run. RESULTS: During rest at 0 degrees C, the ECWCS maintained Tre at 37 degrees C for the maximal ET with all handwear configurations; for each lower ambient condition, steady-state Tre dropped -0.2 degrees C per each 10 C decrease in Ta.Tmf at or near 5 degrees C prior to the maximal ET was the basis for premature attrition; Tsk of 29.4 degrees C was associated with subjective thermal discomfort. ET was predicted adequately by combining Tmf, heat production, Tre and Tsk. CONCLUSIONS: The ECWCS with specific handwear furnish adequate ET in cold-dry ambients provided that ventilation and removal of extra layers is an option during heavy exercise and thermal insulation is not decreased by body moisture.

Adult↗

Endothelium-dependent vascular smooth muscle relaxation activated by electrical field stimulation.

Electrical field stimulation (EFS) produced relaxation of contracted arteries in the presence of tetrodotoxin. In the present study the contributions of vascular smooth muscle repolarization and endothelial release of nitric oxide to the relaxation response were investigated using isolated rat tail arteries and bovine aortic endothelial cells (BAEC). Intact and endothelium-denuded rings or intact, pressurized artery segments were contracted with either phenylephrine or KCl prior to EFS. Electrical field stimulation induced a small relaxation in denuded, phenylephrine contracted rings that was inhibited by the K+ channel blockers glibenclamide and BaCl2. In intact, phenylephrine-contracted rings, EFS induced significantly larger relaxations that were inhibited by BaCl2 as well as by L-NAME, an inhibitor of nitric oxide (NO) synthase, and methylene blue. EFS-induced relaxations were completely inhibited when BaCl2 and L-NAME or methylene blue were combined. Exposure to Ca(2+)-free buffer or diltiazem also inhibited the relaxation while ascorbic acid had no effect. Effluent from electrically stimulated BAEC caused denuded, phenylephrine contracted rings to relax. The ability of the effluent to cause relaxation was almost completely blocked by exposure of the BAEC to L-NAME or exposure of the recipient vascular smooth muscle to methylene blue; glibenclamide caused partial blockade. Simultaneous measurements of membrane potential and intraluminal pressure showed that EFS-induced membrane repolarization preceded changes in steady-state pressure. It is concluded that (1) the smooth muscle cells possess an endothelium-independent repolarization mechanism, (2) EFS causes endothelial cells of intact arteries to release NO and possibly a hyperpolarizing factor, (3) EFS of BAEC causes release of NO, and (4) EFS-induced relaxation depends on vascular smooth muscle cell membrane repolarization and endothelial cell release of vasoactive substances.

Animals↗

Numerical analysis of an extremity in a cold environment including countercurrent arterio-venous heat exchange.

A model of the thermal behavior of an extremity, e.g., a finger, is presented. The model includes the effects of heat conduction, metabolic heat generation, heat transport by blood perfusion, heat exchange between the tissue and the large blood vessels, and arterio-venous heat exchange. Heat exchange with the environment through a layer of thermal insulation, depicting thermal handwear, is also considered. The tissue is subdivided into four concentric layers simulating, from the center outward, core, muscle, fat, and skin. Differential heat balance equations are formulated for the tissue and for the major artery and the major vein traversing the finger. These coupled equations are solved numerically by a finite-difference, alternating direction method employing a Thomas algorithm. The numerical scheme was extensively tested for its stability and convergence. This paper presents the model equations and results of the convergence tests, and shows plots of blood and tissue temperatures along the axis of the model for combinations of parameters including the effect of countercurrent heat exchange between the artery and the vein.

Algorithms↗

Heat strain models applicable for protective clothing systems: comparison of core temperature response.

Core temperature (Tc) output comparisons were analyzed from thermal models applicable to persons wearing protective clothing. The two models evaluated were the United States (US) Army Research Institute of Environmental Medicine (USARIEM) heat strain experimental model and the United Kingdom (UK) Loughborough (LUT25) model. Data were derived from collaborative heat-acclimation studies conducted by three organizations and included an intermittent-work protocol (Canada) and a continuous-exercise/heat stress protocol (UK and US). Volunteers from the US and the UK were exposed to a standard exercise/heat stress protocol (ambient temperature 35 degrees C/50% relative humidity, wind speed 1 m/s, level treadmill speed 1.34 m/s). Canadian Forces volunteers did an intermittent-work protocol (15 min moderate work/15 min rest at ambient temperature of 40 degrees C/30% relative humidity, wind speed approximately 0.4 m/s). Each model reliably predicted Tc responses (within the margin of error determined by 1 root mean square deviation) during work in the heat with protective clothing. Models that are analytically similar to the classic Stolwijk-Hardy model serve as robust operational tools for prediction of physiological heat strain when modified to incorporate clothing heat-exchange factors.

Acclimatization↗

Applications of predictive environmental strain models.

Researchers at the U.S. Army Research Institute of Environmental Medicine have developed and validated numerical models capable of predicting the extent of physiologic strain and adverse terrain and weather-related medical consequences of military operations in harsh environments. A descriptive historical account is provided that details how physiologic models for hot and cold weather exposure have been integrated into portable field advisory devices, computer-based meteorologic planning software, and combat-oriented simulation systems. It is important that medical officers be aware of the existence of these types of decision support tools so that they can assure that outputs are interpreted in a balanced and medically realistic manner. Additionally, these modeling applications may facilitate timely preventive medicine planning and efficient dissemination of appropriate measures to prevent weather- and altitude-related illnesses and performance decrements. Such environmental response modeling applications may therefore be utilized to support deployment preventive medicine planning by field medical officers.

Algorithms↗

Lumped-parameter tissue temperature-blood perfusion model of a cold-stressed fingertip.

A lumped-parameter model of a fingertip is presented. The semispherical model includes the effects of heat storage, heat exchange with the environment, and heat transport by blood perfusion. The thermal insulation on the surface of the fingertip is represented by the overall heat transfer coefficient that is calculated by common engineering formulas. The model is solved analytically for the simple case of constant blood perfusion rate. The general case of variable blood perfusion rates is solved by an Euler finite difference technique. At this stage, the model does not include active control mechanisms of blood perfusion. Thus the effects of cold-induced vasodilatation have to be superimposed and are modeled by symmetrical triangular waveforms because these were found to best depict the behavior of fingers exposed to cold environments. Results of this model were compared with experimental data obtained in two separate studies. One included 60-min infrared thermograms of the dorsal surface of bare hands of sedentary subjects horizontally suspended on a fish net in a 0 degree C environment. Another study, on gloved finger temperatures, involved 0 and -6.7 degrees C environments. Fingertip (nail bed) temperatures of both these studies were compared with model predictions. Blood perfusion rates were assumed and adjusted within physiologically reasonable limits. Comparison of measured and computed temperature records showed very good conformity in both cases studied.

Body Temperature Regulation↗

Metabolic and thermal adaptations from endurance training in hot or cold water.

Metabolic and thermal adaptations resulting from endurance training in hot vs. cold water were compared. It was hypothesized that training in hot water would have greater effects on muscle glycogen use and blood lactate accumulation during exercise than training in cold water. Eighteen men exercised at 60% of maximal oxygen uptake while immersed in hot (n = 9) or cold water (n = 9) for 1 h, 5 days/wk, for 8 wk. Training in hot water (35 degrees C) potentiated body temperature increases during exercise, and training in cold water (20 degrees C) blunted body temperature increases during exercise. Before and after training, cardiorespiratory and thermoregulatory responses and muscle glycogen and blood lactate changes were assessed during a 1-h exercise trial in hot water and, on a separate day using the same intensity, in cold water. Oxygen uptake was similar for all trials, averaging 2.0 +/- 0.1 l/min. It was observed that 1) training reduced glycogen use and lactate accumulation during exercise, with no difference between cold and hot water training groups in the magnitude of this effect; 2) lactate accumulation during exercise was the same in hot water as in cold water; and 3) skin temperature decreased more rapidly during cold-water exercise after than before training, with no difference between cold and hot water training groups in the magnitude of this effect. Thus, exercise-induced body temperature increases are not an important stimulus for glycogen-sparing effects and blunted lactate accumulation associated with endurance training.

Adaptation, Physiological↗

Predicting human heat strain and performance with application to space operations.

This Institute has developed a USARIEM Heat Strain Prediction Model for predicting physiological responses and soldier performance in the heat, which has been programmed for use by hand-held calculators and personal computers, and incorporated into the development of a heat strain decision aid. This model is demonstrated to predict accurately (generally within +/- 1 SD/SEM) rectal temperature (Tre) responses for soldiers wearing various military clothing ensembles during U.S. or non-U.S. military scenarios in the heat at home or abroad. The value of this model is shown presently for three NASA scenarios involving the Launch and Entry Suit (LES). The LES (ventilated or unventilated) is modeled during pre-launch/launch, re-entry/landing, and emergency egress after re-entry/landing scenarios, predominately to evaluate heat acclimation and hydration state effects. During the pre-launch/launch scenario, predicted final Tre closely agrees with observed values suggesting minimal heat strain (Tre approximately 38.0 degrees C). In contrast, dehydrated (3%) unacclimated individuals show moderate levels of heat strain (Tre approximately 38.5 degrees C) for this same scenario. During the re-entry/landing and emergency egress scenarios, dehydrated unacclimated individuals are predicted to exhibit excessive heat strain (Tre > 39.0 degrees C). Thermal tolerance time is predicted to be only 6 min during emergency egress if individuals are dehydrated and unacclimated to heat while wearing the LES. If heat transfer values for space operations clothing are known, NASA can use this prediction model to help avoid undue heat strain involving astronauts for most scenarios during spaceflight.

Acclimatization↗

Human thermoregulatory responses during heat exposure after artificially induced sunburn.

Thermoregulatory responses in the heat (ambient temperature 49 degrees C, 20% relative humidity, 1 m/s wind) were investigated in 10 unacclimated men during 50 min of cycle ergometer exercise (approximately 53% of maximal aerobic power) after a 10-min rest before as well as 24 h and 1 wk after twice the minimal erythemal dose of UV-B radiation that covered approximately 85% of the body surface area. In 7 subjects esophageal temperature (Tes) was recorded while in all 10 subjects five-site skin and rectal temperatures, heart rate, and back, left forearm, and shielded (12 cm2 area) right forearm sweating rates (msw) were recorded at 15-s intervals. Venous blood was collected before and after exercise-heat stress. Mean skin temperature, Tes, rectal temperature, heart rate, and total body sweating rate were not significantly (P greater than 0.05) affected by sunburn. Pre- and postexercise values of hematocrit, hemoglobin, plasma protein, plasma volume, and plasma osmolality were also not affected (P greater than 0.05) by sunburn. Analysis of presunburn and post-sunburn data showed that the Tes intercept for sweating (degrees C) was unaffected (P greater than 0.05), but msw/Tes and final msw from the left forearm (msw/Tes 0.24 +/- 0.02 vs. 0.17 +/- 0.01 mg.cm-2.min-1. degrees C-1, P less than 0.05; msw 0.60 +/- 0.05 vs. 0.37 +/- 0.02, mg.cm-2.min-1, P less than 0.05) and back (msw/Tes 0.43 +/- 0.03 vs. 0.36 +/- 0.01 mg.cm-2.min-1. degrees C-1, P = 0.052; msw 1.08 +/- 0.09 vs. 0.74 +/- 0.05 mg.cm-2.min-1, P less than 0.05) were significantly reduced 24 h postsunburn.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗