Modulation of the thermoregulatory sweating response to mild hyperthermia during activation of the muscle metaboreflex in humans.
(1/911)
1. To investigate the effect of the muscle metaboreflex on the thermoregulatory sweating response in humans, eight healthy male subjects performed sustained isometric handgrip exercise in an environmental chamber (35 C and 50 % relative humidity) at 30 or 45 % maximal voluntary contraction (MVC), at the end of which the blood circulation to the forearm was occluded for 120 s. The environmental conditions were such as to produce sweating by increase in skin temperature without a marked change in oesophageal temperature. 2. During circulatory occlusion after handgrip exercise at 30 % MVC for 120 s or at 45 % MVC for 60 s, the sweating rate (SR) on the chest and forearm (hairy regions), and the mean arterial blood pressure were significantly above baseline values (P < 0.05). There were no changes from baseline values in the oesophageal temperature, mean skin temperature, or SR on the palm (hairless regions). 3. During the occlusion after handgrip exercise at 30 % MVC for 60 s and during the occlusion alone, none of the measured parameters differed from baseline values. 4. It is concluded that, under mildly hyperthermic conditions, the thermoregulatory sweating response on the hairy regions is modulated by afferent signals from muscle metaboreceptors. (+info)
Absorption of solar radiation by an ellipsoid sensor simulated the human body.
(2/911)
Assessment of heat gain in man caused by solar radiation is one of the most important problems in research of the human heat balance outdoors. The purpose of the present study was to investigate a new method for estimation of solar heat income. Absorption of short wave radiation (direct, diffuse and reflected) was measured with an ellipsoid sensor representing a simple, physical model of man. Measurements were performed in climatic chamber with the use of an iodide CSI solar lamp. The absorbed quantity of solar radiation varied as a result of sun altitude as well as of a colour and insulation of fabric covering the ellipsoid sensor. The new coefficients derived from our investigations for estimating doses of absorbed solar radiation should be applicable for a standing man. They correlate better with mean skin temperature observed on subjects outdoor than previous results obtained based on a cylinder as an analogue model of man. The ellipsoid sensor covered by a black fabric absorbed about 6 times more of solar radiation than when covered by a white textile. (+info)
Perfusion of the human finger during cold-induced vasodilatation.
(3/911)
We have investigated the effect of severe local cooling on the vasomotor activity of the arteriovenous anastomoses (AVAs) and other finger vessels. The right third finger was subjected to local cooling (3 degrees C) for 30-45 min in 21 healthy, thermoneutral subjects. Blood velocity in the third finger arteries of both hands was simultaneously recorded using ultrasound Doppler, and skin temperature and laser-Doppler flux from the pulp of the cooled finger were also recorded. The results demonstrate that the initial cold-induced vasoconstriction during severe local cooling involves constriction of the AVAs as well as the two main arteries supplying this finger. During cold-induced vasodilatation (CIVD), the maximum velocity values were not significantly different from those before cooling. Furthermore, the velocity fluctuations in the cooled finger were in most subjects found to be synchronous with the velocity fluctuations in the control finger. This indicates that the large blood flow to the finger and the high skin temperature during CIVD are caused by relaxation of the smooth muscle cells of the AVAs. (+info)
Paradoxical heat sensation in healthy subjects: peripherally conducted by A delta or C fibres?
(4/911)
Paradoxical heat sensation upon cooling of the skin has been reported in central as well as in peripheral neurological conditions. In our study, we examined this phenomenon in 35 naive healthy test subjects, of whom 23 experienced paradoxical heat sensation under test conditions. We measured the peripheral conduction velocities of cold sensation, warm sensation and of paradoxical heat sensation by using a quantitative sensory testing model of indirect peripheral conduction velocity measurement. This was based on comparison of measurements at a proximal and a distal site using two measurement methods, one inclusive and the other exclusive of reaction time. We found that the conduction velocity of paradoxical heat sensation (0.70 m/s) was similar to that of warm sensation (0.68 m/s), and that the conduction velocity of cold sensation (7.74-8.01 m/s) was considerably faster. Thus, we conclude that paradoxical heat sensation in healthy subjects is conducted peripherally via slow unmyelinated C fibres and not via the faster A delta fibres. Consequently, we propose that paradoxical heat sensation is encoded via the heat sensing pathway, in accordance with the labelled-line code theory. The mechanisms proposed suggest a malfunctioning cold-sensing pathway disinhibiting the heat-sensing pathway, at peripheral, central or both levels, thus facilitating a paradoxical heat sensation. (+info)
Peripheral blood flow rates and microvascular responses to orthostatic pressure changes in claudicants before and after revascularisation.
(5/911)
OBJECTIVES: To study the effect of arterial reconstruction for occlusive atherosclerotic disease with intermittent claudication on blood flow rate during rest and on microvascular responses to orthostatic pressure changes in the pulp skin of the first toe where arteriovenous anastomoses are numerous. MATERIAL: Eleven patients with Fontaine IIa claudication (ankle blood pressure index > 0.30) before and 7 (range: 2-11) months after intervention. METHODS: Blood flow rate was measured by the heat washout method with the toe at heart level and after passive lowering to 50 cm below this level using a Clark type electrode with thermostatically controlled cap that was fixed to the pulp of the first toe by adhesive tape. RESULTS: At heart level, blood flow rate was lower in claudicants before reconstruction as compared to a group of previously published control subjects (p = 0.0076, Wilcoxon), blood flow rate increased in claudicants from before to after intervention (p = 0.0128), and postoperative blood flow rate was like that of normals (N.S.). Before surgery, blood flow rate in claudicants increased in median with a factor of 1.79 during lowering (p < 0.0051). CONCLUSIONS: The disturbance of the microcirculatory responses to orthostatically induced pressure changes in claudicants reverted towards normal after arterial reconstruction. (+info)
Role of nitric oxide in the vascular effects of local warming of the skin in humans.
(6/911)
Local warming of skin induces vasodilation by unknown mechanisms. To test whether nitric oxide (NO) is involved, we examined effects of NO synthase (NOS) inhibition with NG-nitro-L-arginine methyl ester (L-NAME) on vasodilation induced by local warming of skin in six subjects. Two adjacent sites on the forearm were instrumented with intradermal microdialysis probes for delivery of L-NAME and sodium nitroprusside. Skin blood flow was monitored by laser-Doppler flowmetry (LDF) at microdialysis sites. Local temperature (Tloc) of the skin at both sites was controlled with special LDF probe holders. Mean arterial pressure (MAP; Finapres) was measured and cutaneous vascular conductance calculated (CVC = LDF/MAP = mV/mmHg). Data collection began with a control period (Tloc at both sites = 34 degrees C). One site was then warmed to 41 degrees C while the second was maintained at 34 degrees C. Local warming increased CVC from 1.44 +/- 0.41 to 4.28 +/- 0.60 mV/mmHg (P < 0.05). Subsequent L-NAME administration reduced CVC to 2.28 +/- 0.47 mV/mmHg (P < 0.05 vs. heating), despite the continued elevation of Tloc. At a Tloc of 34 degrees C, L-NAME reduced CVC from 1.17 +/- 0.23 to 0.75 +/- 0.11 mV/mmHg (P < 0.05). Administration of sodium nitroprusside increased CVC to levels no different from those induced by local warming. Thus NOS inhibition attenuated, and sodium nitroprusside restored, the cutaneous vasodilation induced by elevation of Tloc; therefore, the mechanism of cutaneous vasodilation by local warming requires NOS generation of NO. (+info)
How dolphins use their blubber to avoid heat stress during encounters with warm water.
(7/911)
Dolphins have been observed swimming in inshore tropical waters as warm as 36-38 degrees C. A simple protocol that mimicked the thermal conditions encountered by a dolphin moving from cool pelagic to warm inshore water was used to determine how dolphins avoid hyperthermia in water temperatures (Tw) at and above their normal core temperature (Tc). Tw (2 sites), rectal temperature (Tre; 3 depths), and skin temperature (Tsk; 7 sites) and rate of heat flow (4-5 sites) between the skin and the environment were measured while the dolphin rested in a chamber during a 30-min baseline and 40-60 min while water was warmed at approximately 0.43 degrees C/min until temperatures of 34-36 degrees C were attained. Instead of the expected increase, Tre consistently showed declines during the warming ramp, sometimes by amounts that were remarkable both in their magnitude (1.35 degrees C) and rapidity (8-15 min). The reduction in Tre occurred even while heat loss to the environment was prevented by continued controlled warming of the water that kept Tw slightly above Tsk and while metabolic heat production alone should have added 1.6-2 degrees C/h to the Tc. This reduction in Tc could only be due to a massive redistribution of heat from the core to the blubber layer. (+info)
Relative contribution of core and cutaneous temperatures to thermal comfort and autonomic responses in humans.
(8/911)
Subjective thermal comfort plays a critical role in body temperature regulation since this represents the primary stimulus for behavioral thermoregulation. Although both core (Tc) and skin-surface (Tsk) temperatures are known afferent inputs to the thermoregulatory system, the relative contributions of Tc and Tsk to thermal comfort are unknown. We independently altered Tc and Tsk in human subjects while measuring thermal comfort, vasomotor changes, metabolic heat production, and systemic catecholaminergic responses. Multiple linear regression was used to determine the relative Tc/Tsk contribution to thermal comfort and the autonomic thermoregulatory responses, by using the ratio of regression coefficients for Tc and Tsk. The Tc/Tsk contribution ratio was relatively lower for thermal comfort (1:1) than for vasomotor changes (3:1; P = 0.008), metabolic heat production (3.6:1; P = 0.001), norepinephrine (1.8:1; P = 0.03), and epinephrine (3:1; P = 0.006) responses. Thus Tc and Tsk contribute about equally toward thermal comfort, whereas Tc predominates in regulation of the autonomic and metabolic responses. (+info)