Carbohydrate saving or biomass maintenance: which is the main determinant of the plant's long-term submergence tolerance?

It is hypothesized that plant submergence tolerance could be assessed from the decline of plant biomass due to submergence, as biomass integrates all eco-physiological processes leading to fitness. An alternative hypothesis stated that the consumption rate of carbohydrate is essential in differing tolerance to submergence. In the present study, the responses of biomass, biomass allocation, and carbohydrate content to simulated long-term winter submergence were assessed in four tolerant and four sensitive perennials. The four tolerant perennials occur in a newly established riparian ecosystem created by The Three Gorges Dam, China. They had 100% survival after 120 days' simulated submergence, and had full photosynthesis recovery after 30 days' re-aeration, and the photosynthetic rate was positively related to the growth during the recovery period. Tolerant perennials were characterized by higher carbohydrate levels, compared with the four sensitive perennials (0% survival) at the end of submergence. Additionally, by using a method which simulates posterior estimates, and bootstraps the confidence interval for the difference between strata means, it was found that the biomass response to post-hypoxia, rather than that to submergence, could be a reliable indicator to assess submergence tolerance. Interestingly, the differences of changes in carbohydrate content between tolerant and sensitive perennials during submergence were significant, which were distinct from the biomass response, supporting the hypothesis that tolerant perennials could sacrifice non-vital components of biomass to prioritize the saving of carbohydrates for later recovery. Our study provides some insight into the underlying mechanism(s) of perennials' tolerance to submergence in ecosystems such as temperate wetland and reservoir riparian.

Warm water immersion in patients with chronic heart failure: a pilot study : Shah immerse: HF.

BACKGROUND: Patients with chronic conditions, such as heart failure, swim regularly and most rehabilitation exercises are conducted in warm hydrotherapy pools. However, little is known about the acute effects of warm water immersion (WWI) on cardiac haemodynamics in patients with chronic heart failure (CHF). METHODS: Seventeen patients with CHF (NYHA I and II; mean age 67 years, 88% male, mean left ventricular ejection fraction 33%) and 10 age-matched normal subjects were immersed up to the neck in a hydrotherapy pool (33-35 °C). Cardiac haemodynamics were measured non-invasively, and echocardiography was performed at baseline, during WWI, 3 min after kicking in the supine position and after emerging. RESULTS: In patients with CHF, compared to baseline, WWI immediately increased stroke volume (SV, mean ± standard deviation; from 65 ± 21 to 82 ± 22 mL, p < 0.001), cardiac output (CO, from 4.4 ± 1.4 to 5.7 ± 1.6 L/min, p < 0.001) and cardiac index (CI, from 2.3 ± 0.6 to 2.9 ± 0.70 L/min/m², p < 0.001) with decreased systemic vascular resistance (from 1881 ± 582 to 1258 ± 332 dynes/s/cm5, p < 0.001) and systolic blood pressure (132 ± 21 to 115 ± 23 mmHg, p < 0.001). The haemodynamic changes persisted for 15 min of WWI. In normal subjects, compared to baseline, WWI increased SV (from 68 ± 11 to 80 ± 18 mL, p < 0.001), CO (from 5.1 ± 1.9 to 5.7 ± 1.8 L/min, p < 0.001) and CI (from 2.7 ± 0.9 to 2.9 ± 1.0 L/min/m², p < 0.001).In patients with CHF, compared to baseline, WWI caused an increase in left atrial volume (from 57 ± 44 to 72 ± 46 mL, p = 0.04), without any changes in left ventricular size or function or amino terminal pro B-type natriuretic peptide. CONCLUSIONS: In patients with CHF, WWI causes an acute increase in cardiac output and a fall in systemic vascular resistance. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov (Identifier: NCT02949544) https://clinicaltrials.gov/ct2/show/NCT02949544?cond=NCT02949544&rank=1 .

[Immersion in the world of hyperbaric medicine with two specialist nurses]. / Immersion dans le monde de l'hyperbarie avec deux infirmiers spécialisés.

The speciality of the hyperbaric nurse, whether practised in the civil or military setting, has a wide-reaching scope. Two teams of professionals from Lyon and Toulon share their motivations and demonstrate, through the words of two nurses, a real collective passion for this original and highly technical practice.

Lower-limb hot-water immersion acutely induces beneficial hemodynamic and cardiovascular responses in peripheral arterial disease and healthy, elderly controls.

Passive heat induces beneficial perfusion profiles, provides substantive cardiovascular strain, and reduces blood pressure, thereby holding potential for healthy and cardiovascular disease populations. The aim of this study was to assess acute responses to passive heat via lower-limb, hot-water immersion in patients with peripheral arterial disease (PAD) and healthy, elderly controls. Eleven patients with PAD (age 71 ± 6 yr, 7 male, 4 female) and 10 controls (age 72 ± 7 yr, 8 male, 2 female) underwent hot-water immersion (30-min waist-level immersion in 42.1 ± 0.6°C water). Before, during, and following immersion, brachial and popliteal artery diameter, blood flow, and shear stress were assessed using duplex ultrasound. Lower-limb perfusion was measured also using venous occlusion plethysmography and near-infrared spectroscopy. During immersion, shear rate increased (P < 0.0001) comparably between groups in the popliteal artery (controls: +183 ± 26%; PAD: +258 ± 54%) and brachial artery (controls: +117 ± 24%; PAD: +107 ± 32%). Lower-limb blood flow increased significantly in both groups, as measured from duplex ultrasound (>200%), plethysmography (>100%), and spectroscopy, while central and peripheral pulse-wave velocity decreased in both groups. Mean arterial blood pressure was reduced by 22 ± 9 mmHg (main effect P < 0.0001, interaction P = 0.60) during immersion, and remained 7 ± 7 mmHg lower 3 h afterward. In PAD, popliteal shear profiles and claudication both compared favorably with those measured immediately following symptom-limited walking. A 30-min hot-water immersion is a practical means of delivering heat therapy to PAD patients and healthy, elderly individuals to induce appreciable systemic (chronotropic and blood pressure lowering) and hemodynamic (upper and lower-limb perfusion and shear rate increases) responses.

Acute hot water immersion is protective against impaired vascular function following forearm ischemia-reperfusion in young healthy humans.

Ischemia-reperfusion (I/R) injury is a primary cause of poor outcomes following ischemic cardiovascular events. We tested whether acute hot water immersion protects against forearm vascular I/R. Ten (5 male, 5 female) young (23 ± 2 yr), healthy subjects participated in two trials in random order 7-21 days apart, involving: 1) 60 min of seated rest (control), or 2) 60 min of immersion in 40.5°C water (peak rectal temperature: 38.9 ± 0.2°C). I/R was achieved 70 min following each intervention by inflating an upper arm cuff to 250 mmHg for 20 min followed by 20 min of reperfusion. Brachial artery flow-mediated dilation (FMD) and forearm postocclusive reactive hyperemia (RH) were measured as markers of macrovascular and microvascular function at three time points: 1) preintervention, 2) 60 min postintervention, and 3) post-I/R. Neither time control nor hot water immersion alone affected FMD (both, P > 0.99). I/R reduced FMD from 7.4 ± 0.7 to 5.4 ± 0.6% (P = 0.03), and this reduction was prevented following hot water immersion (7.0 ± 0.7 to 7.7 ± 1.0%; P > 0.99). I/R also impaired RH (peak vascular conductance: 2.6 ± 0.5 to 2.0 ± 0.4 ml·min-1·mmHg-1, P = 0.003), resulting in a reduced shear stimulus (SRAUC·10-3: 22.5 ± 2.4 to 16.9 ± 2.4, P = 0.04). The post-I/R reduction in peak RH was prevented by hot water immersion (2.5 ± 0.4 to 2.3 ± 0.4 ml·min-1·mmHg-1; P = 0.33). We observed a decline in brachial artery dilator function post-I/R, which may be (partly) related to damage incurred downstream in the microvasculature, as indicated by impaired RH and shear stimulus. Hot water immersion was protective against reductions in FMD and RH post-I/R, suggesting heat stress induces vascular changes consistent with reducing I/R injury following ischemic events.

Use of Cold-Water Immersion to Reduce Muscle Damage and Delayed-Onset Muscle Soreness and Preserve Muscle Power in Jiu-Jitsu Athletes.

CONTEXT: Cold-water immersion (CWI) has been applied widely as a recovery method, but little evidence is available to support its effectiveness. OBJECTIVE: To investigate the effects of CWI on muscle damage, perceived muscle soreness, and muscle power recovery of the upper and lower limbs after jiu-jitsu training. DESIGN: Crossover study. SETTING: Laboratory and field. PATIENTS OR OTHER PARTICIPANTS: A total of 8 highly trained male athletes (age = 24.0 ± 3.6 years, mass = 78.4 ± 2.4 kg, percentage of body fat = 13.1% ± 3.6%) completed all study phases. INTERVENTION(S): We randomly selected half of the sample for recovery using CWI (6.0°C ± 0.5°C) for 19 minutes; the other participants were allocated to the control condition (passive recovery). Treatments were reversed in the second session (after 1 week). MAIN OUTCOME MEASURE(S): We measured serum levels of creatine phosphokinase, lactate dehydrogenase (LDH), aspartate aminotransferase, and alanine aminotransferase enzymes; perceived muscle soreness; and recovery through visual analogue scales and muscle power of the upper and lower limbs at pretraining, postrecovery, 24 hours, and 48 hours. RESULTS: Athletes who underwent CWI showed better posttraining recovery measures because circulating LDH levels were lower at 24 hours postrecovery in the CWI condition (441.9 ± 81.4 IU/L) than in the control condition (493.6 ± 97.4 IU/L; P = .03). Estimated muscle power was higher in the CWI than in the control condition for both upper limbs (757.9 ± 125.1 W versus 695.9 ± 56.1 W) and lower limbs (53.7 ± 3.7 cm versus 35.5 ± 8.2 cm; both P values = .001). In addition, we observed less perceived muscle soreness (1.5 ± 1.1 arbitrary units [au] versus 3.1 ± 1.0 au; P = .004) and higher perceived recovery (8.8 ± 1.9 au versus 6.9 ± 1.7 au; P = .005) in the CWI than in the control condition at 24 hours postrecovery. CONCLUSIONS: Use of CWI can be beneficial to jiu-jitsu athletes because it reduces circulating LDH levels, results in less perceived muscle soreness, and helps muscle power recovery at 24 hours postrecovery.

Analysis of the neuromuscular activity during rising from a chair in water and on dry land.

PURPOSE: The purpose of the present study was to analyze the neuromuscular responses during the performance of a sit to stand [STS] task in water and on dry land. SCOPE: 10 healthy subjects, five males and five females were recruited for study. Surface electromyography sEMG was used for lower limb and trunk muscles maximal voluntarty contraction [MVC] and during the STS task. RESULTS: Muscle activity was significantly higher on dry land than in water normalized signals by MVC from the quadriceps-vastus medialis [17.3%], the quadriceps - rectus femoris [5.3%], the long head of the biceps femoris [5.5%], the tibialis anterior [13.9%], the gastrocnemius medialis [3.4%], the soleus [6.2%]. However, the muscle activity was higher in water for the rectus abdominis [-26.6%] and the erector spinae [-22.6%]. CONCLUSIONS: This study for the first time describes the neuromuscular responses in healthy subjects during the performance of the STS task in water. The differences in lower limb and trunk muscle activity should be considered when using the STS movement in aquatic rehabilitation.

Consecutive days of cold water immersion: effects on cycling performance and heart rate variability.

We investigated performance and heart rate (HR) variability (HRV) over consecutive days of cycling with post-exercise cold water immersion (CWI) or passive recovery (PAS). In a crossover design, 11 cyclists completed two separate 3-day training blocks (120 min cycling per day, 66 maximal sprints, 9 min time trialling [TT]), followed by 2 days of recovery-based training. The cyclists recovered from each training session by standing in cold water (10 °C) or at room temperature (27 °C) for 5 min. Mean power for sprints, total TT work and HR were assessed during each session. Resting vagal-HRV (natural logarithm of square-root of mean squared differences of successive R-R intervals; ln rMSSD) was assessed after exercise, after the recovery intervention, during sleep and upon waking. CWI allowed better maintenance of mean sprint power (between-trial difference [90 % confidence limits] +12.4 % [5.9; 18.9]), cadence (+2.0 % [0.6; 3.5]), and mean HR during exercise (+1.6 % [0.0; 3.2]) compared with PAS. ln rMSSD immediately following CWI was higher (+144 % [92; 211]) compared with PAS. There was no difference between the trials in TT performance (-0.2 % [-3.5; 3.0]) or waking ln rMSSD (-1.2 % [-5.9; 3.4]). CWI helps to maintain sprint performance during consecutive days of training, whereas its effects on vagal-HRV vary over time and depend on prior exercise intensity.

The influence of concentration/meditation on autonomic nervous system activity and the innate immune response: a case study.

OBJECTIVE: In this case study, we describe the effects of a particular individual's concentration/meditation technique on autonomic nervous system activity and the innate immune response. The study participant holds several world records with regard to tolerating extreme cold and claims that he can influence his autonomic nervous system and thereby his innate immune response. METHODS: The individual's ex vivo cytokine response (stimulation of peripheral blood mononuclear cells with lipopolysaccharide [LPS]) was determined before and after an 80-minute full-body ice immersion during which the individual practiced his concentration/meditation technique. Furthermore, the individual's in vivo innate immune response was studied while practicing his concentration/mediation technique during human endotoxemia (intravenous administration of 2 ng/kg LPS). The results from the endotoxemia experiment were compared with a historical cohort of 112 individuals who participated in endotoxemia experiments in our institution. RESULTS: The ex vivo proinflammatory and anti-inflammatory cytokine response was greatly attenuated by concentration/meditation during ice immersion, accompanied by high levels of cortisol. In the endotoxemia experiment, concentration/meditation resulted in increased circulating concentrations of catecholamines, and plasma cortisol concentrations were higher than in any of the previously studied participants. The individual's in vivo cytokine response and clinical symptoms after LPS administration were remarkably low compared with previously studied participants. CONCLUSIONS: The concentration/meditation technique used by this particular individual seems to evoke a controlled stress response. This response is characterized by sympathetic nervous system activation and subsequent catecholamine/cortisol release, which seems to attenuate the innate immune response.

Role of CD38, a cyclic ADP-ribosylcyclase, in morphine antinociception and tolerance.

Our previous studies have demonstrated that an increase in intracellular levels of Ca(2+) in neurons is an important component of both the antinociception produced by morphine and morphine's tolerance. The present study tested the hypothesis that the Ca(2+) signaling second messenger, cyclic ADP-ribose (cADPR), derived from CD38 activation participates in morphine antinociception and tolerance. We first showed that morphine's antinociceptive potency was increased by the intracerebroventricular injection of CD38 substrate beta-NAD(+) in mice. Furthermore, morphine tolerance was reversed by intracerebroventricular administration of each of three different inhibitors of the CD38-cADPR-ryanodine receptor Ca(2+) signaling pathway. These inhibitors were the ADP-ribosylcyclase inhibitor nicotinamide, cADPR analog 8-bromo-cADPR, and a large dose of ryanodine (>50 muM) that blocks the ryanodine receptor. In CD38 gene knockout [CD38(-/-)] mice, the antinociceptive action of morphine was found to be less potent compared with wild-type (WT) mice, as measured by tail-flick response, hypothermia assay, and observations of straub tail. However, there was no difference in locomotor activation between CD38(-/-) and WT animals. It was also found that less tolerance to morphine developed in CD38(-/-) mice compared with WT animals. These results indicate that cADRP-ryanodine receptor Ca(2+) signaling associated with CD38 plays an important role in morphine tolerance.

Cold immersion recovery responses in the diabetic foot with neuropathy.

The aim of this article was to investigate the effectiveness of testing cold immersion recovery responses in the diabetic foot with neuropathy using a contact thermography system based on thermochromic liquid crystals. A total of 81 subjects with no history of diabetic foot ulceration were assigned to neuropathy, non neuropathy and healthy groups. Each group received prior verbal and written description of the test objectives and subsequently underwent a comprehensive foot care examination. The room temperature and humidity were consistently maintained at 24 degrees C and less than 50%, respectively, with air conditioning. The right foot for each subject was located on the measurement platform after cold immersion in water at 18-20 degrees C. Whole-field thermal images of the plantar foot were recorded for 10 minutes. Patients with diabetes with neuropathy show the highest 'delta temperature', that is difference between the temperature after 10-minute recovery period and baseline temperature measured independently at all the three sites tested, that is first metatarsal head (MTH), second MTH and heel. This clinical study showed for the first time the evidence of poor recovery times for the diabetic foot with neuropathy when assessing the foot under load. A temperature deficit (because of poor recovery to baseline temperature) suggests degeneration of thermoreceptors, leading to diminished hypothalamus-mediated activity in the diabetic neuropathic group.

[Dry immersion effects on the mechanisms of metabolic-reflex regulation of hemodynamics during muscular work].

Effects of 4-d dry immersion on metabolic-reflex regulation of hemodynamics were evaluated during local static work (30% of maximum voluntary effort) of the talocrural extensors. One group of immersed test-subjects received low-frequency electrostimulation of leg muscles to offset the immersion effect on EMG of working muscles. Metabolic-reflex regulation was evaluated through comparison of cardiovascular responses to physical tests with and w/o post-exercise vascular occlusion. Immersion vaguely increased heart rate and reduced systolic arterial pressure in resting subjects; however, it did not have a distinct effect on arterial pressure and HR during muscular work or metabolic-reflex potentiation of hemodynamic shifts.

Breath-hold performance during cold water immersion: effects of psychological skills training.

INTRODUCTION: Accidental cold water immersion (CWI) is a significant cause of death, particularly in those who are immersed in rough water or forcibly submerged such as in a ditched and inverted helicopter. The marked reduction in maximal breath-hold time associated with CWI, part of the 'cold shock' response, significantly increases the risk of drowning. However, the response is highly variable between subjects. This experiment tested the hypothesis that part of this variability is due to psychological factors. METHODS: There were 32 subjects who completed 2 2.5-min, head-out immersions in 11 degrees C water, separated by 7 d. Between immersions, subjects were matched on initial maximum breath-hold time on immersion (BHwater) and allocated to either a psychological intervention group (PIG) or control group (CG). PIG (n=16) subjects each undertook a psychological skills intervention comprising 4 interlinked training sessions covering goal-setting, arousal regulation, mental imagery, and positive self-talk; CG (n=16) continued normal daily activity. RESULTS: Psychological intervention significantly increased BHwater on immersion in the PIG vs. the CG [mean (SD); CG BHwater immersion 1:24.01 (6.72) s; immersion 2: 21.34 (16.31) s; PIG: BHwater immersion 1: 24.66 (14.60) s; immersion 2: 44.25 (31.63) s]. The difference in maximum voluntary BHwater between immersion 1 and 2 in the PIG averaged 19.59 s, equating to an 80% increase following psychological intervention. CONCLUSION: Psychological influences may account for a significant amount of the variability in the respiratory responses during CWI, and may be a key factor in determining the chances of survival following accidental immersion.

Cardiorespiratory effects of warm water immersion in elderly patients with chronic heart failure.

BACKGROUND: Hydrotherapy might be included in the rehabilitation of patients with chronic heart failure (CHF), but little is known about the acute cardiorespiratory reaction in warm water. The aim of this study was to assess the acute cardiorespiratory effect of immersion in warm water, in a clinical setting, in elderly patients with CHF compared with healthy age and sex matched persons. METHODS: Twelve patients (three females) with CHF, NYHA II-III, age 64 +/- 6 years, and 12 healthy subjects were studied. Cardiorespiratory changes, on land and in a temperature-controlled swimming pool (33-34 degrees C) were assessed during rest and exercise, in a sitting position, using continuous gas analyses. RESULTS: There were no significant differences, land versus water, in carbon dioxide production, total ventilation, respiratory frequency, respiratory exchange ratio, heart rate or blood pressure in either of the groups. A significant difference was found in oxygen uptake, at rest, land versus water in patients with CHF in comparison with healthy subjects (-0.2 +/- 0.4 versus +0.3 +/- 0.6 ml kg(-1) min(-1), P < 0.01). Oxygen kinetics (tau) increased significantly (P = 0.01) in both groups during exercise in water. CONCLUSION: Hydrotherapy was well tolerated and the vast majority of the cardiorespiratory responses, during warm water immersion in a clinical setting, are similar in patients with CHF compared with healthy subjects. However, further larger studies, are needed to better understand the physiological reactions during hydrotherapy.

[Comparative evaluation of different methods for normalizing heat state of persons exposed to cold water]. / Sravnitel'naia otsenka razlichnykh sposobov normalizatsii teplovogo sostoianiia cheloveka posle okhlazheniia ego v vodnoi srede.

Decrease of deep body temperature in humans due to exposure to cold water continues after the exposure ends and carries major danger for human health and life. The article covers data characterizing human heat state parameters after rejection of cold (10 +/- 1 degree C) water environment. This rejection was proved to take place in more severely decreased "core" and "capsule" temperature vs that in air environment. Studies of heat state in 38 volunteers practicing winter swimming demonstrated comparative evaluation of various heating methods among which the most effective are immersion into warm (38 degrees C) water with simultaneous hydromassage and being in sauna at air temperature of 65 +/- 5 degrees C.

Clinical analysis of breathing exercise during immersion in 38 degrees C water for obstructive and constrictive pulmonary diseases.

Breathing exercises during immersion in 38 degrees C water were performed in 22 patients with bronchial asthma, pulmonary emphysema and constrictive pulmonary diseases. The patients entered a pool filled with 38 degrees C water to shoulder level. While standing, they breathed in deeply and breathed out slowly through the mouth into water while sinking the nose below the water level. This breathing method was repeated for 20 min. with a 5-min. rest out of water and this cycle was performed twice a day for two months. Respiratory function test and arterial blood gas analysis were examined before and after the two-month exercise program. FEV1.0% was significantly increased in patients with asthma and emphysema (p = 0.042 and 0.032, respectively) but did not change in patients with constrictive pulmonary diseases. %FVC, PF and Vmf25 did not change in any of the diseases. PaO2 was significantly increased in emphysematous patients (p = 0.0002) and PaCO2 was significantly decreased in asthmatic and emphysematous patients (p = 0.034 and 0.046, respectively). These results suggest that our breathing exercise by immersion is useful in patients with asthma and emphysema but is less effective in patients with constrictive pulmonary diseases.

Does capsaicin affect physiologic and thermal responses of males during immersion in 22 degrees C?

BACKGROUND: Capsaicin alters thermoregulation in adult rats by producing a dose-dependent fall in body temperature and metabolism. The present investigation examined the thermal and metabolic responses in males who were fed capsaicin (CAP: 2 mg.kg(-1) body weight) vs. a placebo (PL: a maltodextrin capsule) prior to immersion in cold water. METHODS: Seven Caucasian males aged 20-28 yr were immersed in 22 degrees C twice (PL vs. CAP), for 120 min. The following were examined: metabolism (M; W.m(-2)), rectal temperature (Tre; degrees C), mean skin temperature (Tsk; degrees C), tissue insulation (I; degrees C.m(-2).W(-1) and proportion of energy derived from carbohydrate (%CHO). RESULTS: For M, Tre, I, and Tsk there was no significant differences between treatments (PL vs. CAP) when the variables were pooled jointly over time. However, significant differences across time was detected for Tre (p = 0.0003), Tsk (p = 0.0147), and M (p = 0.0036). Values for %CHO demonstrate a main effect for treatment (p = 0.0210) suggesting the CAP (46.7-/+25.9%) treatment demonstrated a decreased reliance on carbohydrate utilization for energy provision as compared to the PL (75.0+/-21.9%) treatment. Additionally, the treatment x time interaction was significant (p = 0.0096) whereby, PL differed from CAP at 5 min only. CONCLUSION: From these data it appears that while M, Tre, and Tsk differed across time, a CAP (which differentially affected percent of energy derived from carbohydrate) feeding did not differentially affect the thermal and metabolic responses of males during acute cold water immersion.

Comparison of responses of men to immersion in circulating water at 40.0 and 41.5 degrees C.

BACKGROUND: The recommended maximum water temperature for public hot tubs has been set at 40.0 degrees C, but no research has been published on human immersion in hot water at higher temperatures. HYPOTHESIS: We hypothesized that thermoregulatory and cardiovascular responses at two water temperatures would be proportional to the water:blood temperature gradients. METHODS: Six healthy men were immersed for 21 min in circulating hot water at 40.0 and 41.5 degrees C in separate trials in random order 1-3 wk apart. Measurements included heart rate, systolic BP, esophageal, rectal, and non-immersed skin temperatures, sweat rate, and perceived comfort. RESULTS: The rise in all body temperatures, sweat rate, and heart rate were significantly greater in the 41.5 vs. 40.0 degrees C water. Peak esophageal temperatures were 38.3 +/- 0.2 degrees C vs. 37.8 +/- 0.03 degrees C, peak sweat rates were 0.48 +/- 0.05 vs. 0.32 +/- 0.03 kg x m(-2) x h(-1), and peak heart rates were 123 +/- 7 vs. 108 +/- 5 bpm, respectively. Systolic BPs followed different patterns of response in each trial, whereas diastolic pressures were not different between trials. Comfort at each level of immersion was reduced during the 41.5 degrees C trial compared with the 40.0 degrees C in excess of that predicted by difference in esophageal temperature between the trials. CONCLUSIONS: These results suggest that risks of hyperthermia or adverse cardiovascular effects in hot tubs may not be greater in water above 40.0 degrees C unless perceptual judgment is impaired. Hypotension when standing to exit the tub occurred in both trials and may represent a potential hazard to hot tub use.

Hyperammonemia reduces water immersion--restraint stress gastric ulcers in rats.

1. The influence of hyperammonemia (produced by the continuous intraperitoneal infusion of ammonium acetate for 6 days) on stress-induced gastric ulcer formation was investigated in conscious rats. 2. Continuous ammonium acetate infusion significantly reduced stress-induced gastric ulceration concomitant with an increase in gastric blood flow, as determined using radioactive microspheres. The serum levels of L-arginine as well as nitrite and nitrate (oxidative byproducts of nitric oxide) were increased by ammonium acetate infusion. 3. Prior administration of N omega-nitro-L-arginine methyl ester, a competitive nitric oxide synthase inhibitor, substantially attenuated the increase in gastric blood flow caused by ammonium acetate infusion and diminished the protective effect on gastric ulceration. 4. These findings suggest that the synthesis of endogenous nitric oxide from L-arginine is accelerated by continuous ammonium acetate infusion when the urea cycle remains intact and has a substantial cytoprotective effect on the stomach, probably through maintaining the gastric mucosal microcirculation.