Toshiyuki Itoh

Effects of near-infrared low-level laser irradiation on microcirculation.

Recently, there has been an increase in the clinical application of low‐level laser irradiation (LLLI) in various fields. The present study was conducted to explore the effects of LLLI on microcirculation.

Effect of an exercise-heat acclimation program on body fluid regulatory responses to dehydration in older men.

We examined if an exercise-heat acclimation program improves body fluid regulatory function in older subjects, as has been reported in younger subjects. Nine older (Old; 70 +/- 3 yr) and six younger (Young; 25 +/- 3 yr) male subjects participated in the study. Body fluid regulatory responses to an acute thermal dehydration challenge were examined before and after the 6-day acclimation session. Acute dehydration was produced by intermittent light exercise [4 bouts of 20-min exercise at 40% peak rate of oxygen consumption (VO(2 peak)) separated by 10 min rest] in the heat (36 degrees C; 40% relative humidity) followed by 30 min of recovery without fluid intake at 25 degrees C. During the 2-h rehydration period the subjects drank a carbohydrate-electrolyte solution ad libitum. In the preacclimation test, the Old lost approximately 0.8 kg during dehydration and recovered 31 +/- 4% of that loss during rehydration, whereas the Young lost approximately 1.2 kg and recovered 56 +/- 8% (P < 0.05, Young vs. Old). During the 6-day heat acclimation period all subjects performed the same exercise-heat exposure as in the dehydration period. Exercise-heat acclimation increased plasma volume by approximately 5% (P < 0.05) in Young subjects but not in Old. The body fluid loss during dehydration in the postacclimation test was similar to that in the preacclimation in Young and Old. The fractional recovery of lost fluid volume during rehydration increased in Young (by 80 +/- 9%; P < 0.05) but not in Old (by only 34 +/- 5%; NS). The improved recovery from dehydration in Young was mainly due to increased fluid intake with a small increase in the fluid retention fraction. The greater involuntary dehydration (greater fluid deficit) in Old was accompanied by reduced plasma vasopressin and aldosterone concentrations, renin activity, and subjective thirst rating (P < 0.05, Young vs. Old). Thus older people have reduced ability to facilitate body fluid regulatory function by exercise-heat acclimation, which might be involved in attenuation of the acclimation-induced increase in body fluid volume.We examined if an exercise-heat acclimation program improves body fluid regulatory function in older subjects, as has been reported in younger subjects. Nine older (Old; 70 ± 3 yr) and six younger (Young; 25 ± 3 yr) male subjects participated in the study. Body fluid regulatory responses to an acute thermal dehydration challenge were examined before and after the 6-day acclimation session. Acute dehydration was produced by intermittent light exercise [4 bouts of 20-min exercise at 40% peak rate of oxygen consumption (V˙o 2 peak) separated by 10 min rest] in the heat (36°C; 40% relative humidity) followed by 30 min of recovery without fluid intake at 25°C. During the 2-h rehydration period the subjects drank a carbohydrate-electrolyte solution ad libitum. In the preacclimation test, the Old lost ∼0.8 kg during dehydration and recovered 31 ± 4% of that loss during rehydration, whereas the Young lost ∼1.2 kg and recovered 56 ± 8% ( P < 0.05, Young vs. Old). During the 6-day heat acclimation period all subjects performed the same exercise-heat exposure as in the dehydration period. Exercise-heat acclimation increased plasma volume by ∼5% ( P < 0.05) in Young subjects but not in Old. The body fluid loss during dehydration in the postacclimation test was similar to that in the preacclimation in Young and Old. The fractional recovery of lost fluid volume during rehydration increased in Young (by 80 ± 9%; P < 0.05) but not in Old (by only 34 ± 5%; NS). The improved recovery from dehydration in Young was mainly due to increased fluid intake with a small increase in the fluid retention fraction. The greater involuntary dehydration (greater fluid deficit) in Old was accompanied by reduced plasma vasopressin and aldosterone concentrations, renin activity, and subjective thirst rating ( P < 0.05, Young vs. Old). Thus older people have reduced ability to facilitate body fluid regulatory function by exercise-heat acclimation, which might be involved in attenuation of the acclimation-induced increase in body fluid volume.

Chapter 24 Thermoregulation and body fluid in hot environment

Publisher Summary This chapter explores the effect of thermoregulatory responses on body fluid and circulation. Modifications of thermoregulatory control induced by dehydration are discussed concerning the influence of hyperosmolality and hypovolemia. The chapter also deals with the effect of hyperosmolality and hypovolemia on hypothalamic thermoregulatory mechanisms and the competition between body temperature cardiovascular and body fluid homeostasis. The physiological responses to a heat load in homeothermic animals include cutaneous vasodilation to transfer heat from the body core to the body surface by circulation and evaporative heat loss from the body surface. Heat stress causes dehydration due to sweating, leading to hyperosmolality of body fluid and hypovolemia. Dehydration impairs thermoregulation, reducing both sweating and cutaneous vasodilation, while dehydration-induced hyperosmolality causes a shift of body fluid from intracellular fluid to extracellular fluid and stimulates drinking behavior, which counteracts the decrease in blood volume. The redistribution of blood flow for thermoregulation causes a lowering of central venous pressure, which serves as an input signal for drinking behavior and circulatory regulation, including the increases in total peripheral resistance and vascular compliance.

Thermoregulation and body fluid osmolality.

Thermoregulatory responses induce dehydration, and dehydration itself raises body temperature, causing an increase in the threshold temperature for cutaneous vasodilatation and sweating, the sensitivity of cutaneous vasodilatation in response to a unit rise in body temperature, and the maximum attainable level of cutaneous circulation, and sweat rate. The reduction of these thermoregulatory responses has been related to hypovolemia and hyperosmolality. Evidence showing the involvement of cardiopulmonary baroreceptors is discussed along with an introduction on the effect of hyperosmolality on skin blood flow and sweating and the involvement of central nervous mechanisms. Heat induced hyperosmolality triggers regulatory responses maintaining blood volume and circulatory function, including a fluid shift between body fluid compartments and the control of fluid intake. Evidence showing the importance of the osmotic regulation of body fluid by drinking is also presented. Finally, the effect of hypovolemia and hyperosmolality under thermal stress due to hot environment or physical activity is discussed from the viewpoint of the interaction between circulation, thermoregulation and body fluid homeostasis.

Changes in vascular compliance during hyperthermia

Abstract 1. 1. The effect of acute hyperthermia on the relationship between the cardiovascular responses and blood volume (BV) change was assessed on splenectomized dogs using continuous determination of BV and simulation analysis. 2. 2. A decrease in vascular compliance during hyperthermia was observed. 3. 3. An increase in unstressed BV was also evident. 4. 4. These results were discussed in relation to the cardiovascular regulation during hyperthermia.

Mechanism Underlying the Changes in Plasma Potassium Concentration during Infusion of Isosmotic Nonelectrolyte Solution

Generally, during infusion of an isosmotic nonelectrolyte solution that permeates the cell membrane, plasma K+ concentration ([K+]pl) either does not change or it increases slightly. The mechanism underlying this [K+]pl change has not been clarified. We continuously monitored the [K+]pl and plasma Na+ concentration ([Na+]pl) for 10 min during isosmotic mannitol infusion of 1.6 ml/100 g body weight in rats with intact kidney function (intact mannitol group). In addition, in nephrectomized rats, we compared the [K+]pl change during infusion with isosmotic mannitol (which permeates the cell membrane; mannitol nephrectomized group) with that during infusion with isosmotic sucrose (which does not permeate the cell membrane; sucrose nephrectomized group) to evaluate the effect of cell volume regulation. In the intact mannitol group, [Na+]pl decreased with dilution, and [K+]pl remained relatively constant. In the sucrose nephrectomized group, [K+]pl decreased by the same percentage as [Na+]pl and gradually increased to greater than the control level. In the mannitol nephrectomized group, however, [K+]pl increased immediately after the beginning of the infusion and reached the same level as that in the sucrose nephrectomized group. To confirm that the difference in [K+]pl between the mannitol and sucrose nephrectomized groups was dependent on cell volume regulation, we investigated the changes in mean corpuscular volume of red blood cells, using a Coulter counter. This value remained constant during isosmotic sucrose infusion but increased during isosmotic mannitol infusion, returning to the original volume after the infusion. We kept [HCO3-] and pH constant throughout the experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Global Warming and Deaths from Heat Stroke

For the past two decades, the number of heat-related deaths in Japan has been increasing along with the global warming trend. To assess the effect of hot weather on human health, we investigated heat-related deaths in Japan from 1968 through 1997, analyzing the data with reference to the distribution of the deaths by age and the incidence of hot days in summer. Vital Statistics of Japan, published by the Ministry of Health and Welfare of Japan, was the source of the heat-related mortality data employed in this study. Meteorological data were obtained from the District Meteorological Observatories in Tokyo and Osaka, the two largest cities in Japan. Heat-related deaths were most prone to occur on days with a peak daily temperature greater than 38°C, and the incidence of these deaths showed an exponential dependence on the number of hot days. Thus, even a small rise in atmospheric temperature may lead to a considerable increase in heat-related mortality, indicating the importance of combating global warming. Furthermore, half (50.1%) of the heat-related deaths occurred in children (≤4 years of age) and the elderly (≥70 years) irrespective of gender, indicating the vulnerability of these age groups to heat. More comprehensive measures should be adopted for children 4 years of age or less and the elderly to prevent heat-related deaths in these age groups.

Reversed behavioral effect of cholecystokinin after frontal decortication in rats

Cholecystokinin tetrapeptide (CCK-4) is likely to possess opposite central action against cholecystokinin octapeptide (CCK-8). In the present study, the behavioral effects of CCK-4 and CCK-8 were compared in frontal decorticated rats. In sham-operated rats, CCK-4 produced marked excitatory responses, while CCK-8 had no stimulatory effects. In frontal decorticated rats, CCK-4 did not cause any excitatory behaviors, while CCK-8 produced markedly enhanced responses. We speculate that an appropriate balance of these CCK peptides might be involved in the maintenance of normal mental states.