Modulation of the thermoregulatory sweating response to mild hyperthermia during activation of the muscle metaboreflex in humans.
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)
Stroke volume decline during prolonged exercise is influenced by the increase in heart rate.
This study determined whether the decline in stroke volume (SV) during prolonged exercise is related to an increase in heart rate (HR) and/or an increase in cutaneous blood flow (CBF). Seven active men cycled for 60 min at approximately 57% peak O2 uptake in a neutral environment (i.e., 27 degrees C, <40% relative humidity). They received a placebo control (CON) or a small oral dose (i.e., approximately 7 mg) of the beta1-adrenoceptor blocker atenolol (BB) at the onset of exercise. At 15 min, HR and SV were similar during CON and BB. From 15 to 55 min during CON, a 13% decline in SV was associated with an 11% increase in HR and not with an increase in CBF. CBF increased mainly from 5 to 15 min and remained stable from 20 to 60 min of exercise in both treatments. However, from 15 to 55 min during BB, when the increase in HR was prevented by atenolol, the decline in SV was also prevented, despite a normal CBF response (i.e., similar to CON). Cardiac output was similar in both treatments and stable throughout the exercise bouts. We conclude that during prolonged exercise in a neutral environment the decline in SV is related to the increase in HR and is not affected by CBF. (+info)
Respiratory and cardiac modulation of single sympathetic vasoconstrictor and sudomotor neurones to human skin.
1. The firing of single sympathetic neurones was recorded via tungsten microelectrodes in cutaneous fascicles of the peroneal nerve in awake humans. Studies were made of 17 vasoconstrictor neurones during cold-induced cutaneous vasoconstriction and eight sudomotor neurones during heat-induced sweating. Oligounitary recordings were obtained from 8 cutaneous vasconstrictor and 10 sudomotor sites. Skin blood flow was measured by laser Doppler flowmetry, and sweating by changes in skin electrical resistance within the innervation territory on the dorsum of the foot. 2. Perispike time histograms revealed respiratory modulation in 11 (65 %) vasoconstrictor and 4 (50 %) sudomotor neurones. After correcting for estimated conduction delays, the firing probability was higher in inspiration for both classes of neurone. Measured from the oligounitary recordings, the respiratory modulation indices were 67. 7 +/- 3.9 % for vasoconstrictor and 73.5 +/- 5.7 % for sudomotor neurones (means +/- s.e.m.). As previously found for sudomotor neurones, cardiac rhythmicity was expressed by 7 (41 %) vasoconstrictor neurones, 5 of which showed no significant coupling to respiration. Measured from the oligounitary records, the cardiac modulation of cutaneous vasoconstrictor activity was 58.6 +/- 4.9 %, compared with 74.4 +/- 6.4 % for sudomotor activity. 3. Both vasoconstrictor and sudomotor neurones displayed low average firing rates (0.53 and 0.62 Hz, respectively). The percentage of cardiac intervals in which units fired was 38 % and 35 %, respectively. Moreover, when considering only those cardiac intervals when a unit fired, vasoconstrictor and sudomotor neurones generated a single spike 66 % and 67 % of the time. Rarely were more than four spikes generated by a single neurone. 4. We conclude that human cutaneous vasoconstrictor and sudomotor neurones share several properties: both classes contain subpopulations that are modulated by respiration and/or the cardiac cycle. The data suggest that the intensity of a multi-unit burst of vasoconstrictor or sudomotor impulses is probably governed primarily by firing incidence and the recruitment of additional neurones, rather than by an increase in the number of spikes each unit contributes to a burst. (+info)
Responses of sympathetic outflow to skin during caloric stimulation in humans.
We previously showed that caloric vestibular stimulation elicits increases in sympathetic outflow to muscle (MSNA) in humans. The present study was conducted to determine the effect of this stimulation on sympathetic outflow to skin (SSNA). The SSNA in the tibial and peroneal nerves and nystagmus was recorded in nine subjects when the external meatus was irrigated with 50 ml of cold (10 degrees C) or warm (44 degrees C) water. During nystagmus, the SSNA in tibial and peroneal nerves decreased to 50 +/- 4% (with baseline value set as 100%) and 61 +/- 4%, respectively. The degree of SSNA suppression in both nerves was proportional to the maximum slow-phase velocity of nystagmus. After nystagmus, the SSNA increased to 166 +/- 7 and 168 +/- 6%, respectively, and the degree of motion sickness symptoms was correlated with this SSNA increase. These results suggest that the SSNA response differs from the MSNA response during caloric vestibular stimulation and that the SSNA response elicited in the initial period of caloric vestibular stimulation is different from that observed during the period of motion sickness symptoms. (+info)
Physical activity assessment in population surveys: can it really be simplified?
BACKGROUND: Several studies have used a simplified approach for the assessment of physical activity such as the frequency of exercise-induced sweating. In this study leisure-time physical activity has been assessed using this and another more detailed measure. SUBJECTS AND METHODS: A sample of 4171 adults answered the Health Interview Survey of Barcelona in 1992. The respondents were classified into categories depending on participation in moderate and/or intense physical activity (> or =20 min) and also according to the frequency of exercise-induced sweating: 0, 1-2 and > or =3 times/week. Agreement between the two measures was calculated using the weighted Kappa (Kw) statistic with 95% confidence intervals (95% CI). Stratified analyses were performed. RESULTS: Prevalence of physical activity > or =3 times/week was lower with the sweat question (12.5%) than with the questions about the frequency of performance of selected activities (19.6%). The physical activity patterns by age, gender and overweight were similar for the two measures, but differed by month of the year. Agreement was lower among the older age categories and was higher among males (Kw = 0.59, 95% CI: 0.57-0.62) than among females (Kw = 0.48, 95% CI: 0.46-0.50). Overall, the agreement was higher in the hotter months (Kw = 0.72 among males and 0.58 among females). CONCLUSIONS: In the assessment of physical activity in the population by means of the sweat question there can be interference from other variables, apart from the intensity of the activity, which influence sweating during the exercise. Further assessments of the validity of exercise-induced sweating in representative samples of the general population would be useful. (+info)
Core temperature and sweating onset in humans acclimated to heat given at a fixed daily time.
The thermoregulatory functions of rats acclimated to heat given daily at a fixed time are altered, especially during the period in which they were previously exposed to heat. In this study, we investigated the existence of similar phenomena in humans. Volunteers were exposed to an ambient temperature (Ta) of 46 degrees C and a relative humidity of 20% for 4 h (1400-1800) for 9-10 consecutive days. In the first experiment, the rectal temperatures (Tre) of six subjects were measured over 24 h at a Ta of 27 degrees C with and without heat acclimation. Heat acclimation significantly lowered Tre only between 1400 and 1800. In the second experiment, six subjects rested in a chair at a Ta of 28 degrees C and a relative humidity of 40% with both legs immersed in warm water (42 degrees C) for 30 min. The Tre and sweating rates at the forearm and chest were measured. Measurements were made in the morning (0900-1100) and afternoon (1500-1700) on the same day before and after heat acclimation. Heat acclimation shortened the sweating latency and decreased the threshold Tre for sweating. However, these changes were significant only in the afternoon. The results suggest that repeated heat exposure in humans, limited to a fixed time daily, alters the core temperature level and thermoregulatory function, especially during the period in which the subjects had previously been exposed to heat. (+info)
The results of thoracoscopic sympathetic trunk transection for palmar hyperhidrosis and sympathetic ganglionectomy for axillary hyperhidrosis.
OBJECTIVES: To review our total experience of thoracoscopic sympathetic trunk transection for the treatment of palmar hyperhidrosis and second and third thoracic sympathetic ganglionectomy for axillary hyperhidrosis. DESIGN: Longitudinal cohort study following up consecutive patients for 0.3 to 5.5 years. SUBJECTS: Fifty-four consecutive patients undergoing thoracoscopic sympathectomy for hyperhidrosis. METHODS: Prospective evaluation of immediate technical success, complications, late recurrence of hyperhidrosis and patient acceptability. RESULTS: 100% initial cure for palmar hyperhidrosis, 91% of sympathetic ganglionectomies for axillary hyperhidrosis were technically successful and initially curative. Compensatory sweating 44% patients, most severe after bilateral sympathetic ganglionectomy. Complications occurred in 14% patients, all resolving without further intervention. There were no cases of Horner's syndrome. 13% patients reported a return of some palmar sweating. 5.4% patients developed recurrent palmar hyperhidrosis at 6, 15 and 21 months postoperatively. CONCLUSION: Transection of the sympathetic trunk between the first and second thoracic sympathetic ganglia initially cures 100% of patients treated primarily for palmar hyperhidrosis. Technically successful 2nd and 3rd thoracic sympathetic ganglionectomy initially cures 100% of patients with axillary hyperhidrosis. Compensatory sweating is common after bilateral sympathectomy. Recurrent palmar hyperhidrosis occurs in 5.4% of cases, but can be cured by a second thoracoscopic sympathectomy. Horner's syndrome is an avoidable complication of thoracoscopic sympathectomy. (+info)
Altered reflex control of cutaneous circulation by female sex steroids is independent of prostaglandins.
We tested the hypothesis that the shift in the cutaneous vasodilator response to hyperthermia seen with elevated female reproductive hormones is a prostaglandin-dependent resetting of thermoregulation to higher internal temperatures, similar to that seen in the febrile response to bacterial infection. Using water-perfused suits to control body temperature, we conducted heat stress experiments in resting women under conditions of low and high progesterone and estrogen and repeated these experiments after an acute dose of ibuprofen (800 mg). In six women the hormones were exogenous (oral contraceptives); three women had regular menstrual cycles and were tested in the early follicular and midluteal phases. Resting oral temperature (Tor) was significantly elevated with high hormone status (P < 0.05); this was not affected by ibuprofen treatment (P > 0.2). The Tor threshold for cutaneous vasodilation was significantly increased by high hormone status (+0.27 +/- 0.07 degrees C, P < 0. 02); the shift was not affected by ibuprofen treatment (with ibuprofen: +0.29 +/- 0.08 degrees C, P > 0.2 vs. control experiments). The Tor threshold for sweating was similarly increased by high hormone status (+0.22 +/- 0.05 degrees C, P < 0.05); this shift was not influenced by ibuprofen (with ibuprofen: +0.35 +/- 0. 05, P > 0.1 vs. control experiments). Thus the shift in thermoregulatory control of skin blood flow and sweating mediated by female reproductive steroids is not sensitive to ibuprofen; it therefore appears that this shift is independent of prostaglandins. (+info)