Effect of non-uniform skin temperature on thermoregulatory response during water immersion

The present study investigated the effect of non-uniform skin temperature distribution on thermoregulatory responses and subjective thermal sensation during water immersion. Ten healthy male subjects carried out 60 min water immersion twice, once with uniform (UST) and once with non-uniform (NUST) skin temperature. In UST condition, subjects immersed at 29 degrees C in naked condition, while in NUST condition, subjects immersed at 26 degrees C with partial coverage wetsuit (PCWS). The PCWS covers trunk region, upper arms, and thighs. The non-uniform skin temperature distribution, higher at trunk and lower at distal extremities, was observed in NUST condition. Shivering thermogenesis was not influenced by the skin temperature distribution at the experimental condition of this study. On the other hand, the tissue insulation (I (tissue)) was significantly higher in NUST condition compared to the UST condition. The increment of I (tissue) might have been caused by the peripheral vasoconstriction induced by the cold input from the distal extremities in NUST condition. The higher I (tissue) in NUST condition might lead to the significantly higher esophageal temperature compared to UST condition. No difference was observed in thermal sensation between the two conditions. Subjects felt slightly more comfortable in NUST condition than in UST condition. In conclusion, the non-uniform skin temperature distribution, higher at trunk and lower at distal extremities, might affect the peripheral vasoconstriction to increase the I (tissue). On the other hand, shivering thermogenesis and subjective thermal sensation were not affected by the non-uniform skin temperature distribution at the present experimental condition.     

Influence of cold pain in the hand on skin impedance, heart rate and skin temperature

Twenty-one healthy volunteers took part in the study, the aim of which was to determine the influence of acute pain on skin impedance, skin temperature and heart rate. Acute pain was induced by cold exposure. Skin impedance, heart rate and facial skin temperature were recorded before, during and after the painful stimulation. The skin impedance increased during the stimulation by 24%, heart rate by 6% and skin temperature by 6%. The results show that changes in skin impedance as a result of acute pain can easily be recorded and could be a useful tool in monitoring acute pain. The technique is better than monitoring heart rate or skin temperature.     

Frequency tuning of the contralateral medial olivocochlear reflex in humans

Activation of the medial olivocochlear (MOC) efferents attenuates cochlear gain and reduces the amplitudes of mechanical, electrical, and neural cochlear outputs. The functional roles of the MOC efferents are not fully understood, especially in humans, despite postulations that they are involved in protection against acoustic trauma, facilitation of transient-sound perception, etc. Delineating the frequency tuning properties of the MOC efferents would provide critical evidence to support or refute these postulated functional roles. By utilizing spontaneous otoacoustic emissions (SOAEs), a cochlear measure sensitive to MOC modulation, we systematically demonstrate in humans that the contralateral MOC reflex is tuned to a fixed frequency band between 500 and 1,000 Hz independent of SOAE frequency. Our results question the role of the MOC reflex in protection against acoustic trauma or facilitation of transient-sound perception.     

Infrared thermography for examination of skin temperature in the dorsal hand of office workers

Reduced blood flow may contribute to the pathophysiology of upper extremity musculoskeletal disorders (UEMSD), such as tendinitis and carpal tunnel syndrome. The study objective was to characterize potential differences in cutaneous temperature, among three groups of office workers assessed by dynamic thermography following a 9-min typing challenge: those with UEMSD, with (n=6) or without (n=10) cold hands exacerbated by keyboard use, and control subjects (n=12). Temperature images of the metacarpal region of the dorsal hand were obtained 1 min before typing, and during three 2-min sample periods [0–2 min (early), 3–5 min (middle), and 8–10 min (late)] after typing. Mean temperature increased from baseline levels immediately after typing by a similar magnitude, 0.7 (0.3)°C in controls and 0.6 (0.2)°C in UEMSD cases without cold hands, but only by 0.1 (0.3)°C in those with cold hands. Using paired t-tests for within group comparisons of mean dorsal temperature between successive imaging periods, three patterns of temperature change were apparent during 10 min following typing. Controls further increased mean temperature by 0.1°C (t-test, P=0.001) at 3–5 min post-typing before a late temperature decline of –0.3°C (t-test, P=0.04), while cases without cold hands showed no change from initial post-typing mean temperature rise during middle or late periods. In contrast, subjects with keyboard-induced cold hands had no change from initial post-typing temperature until a decrease at the late period of –0.3°C (t-test, P=0.06). Infrared thermography appears to distinguish between the three groups of subjects, with keyboard-induced cold hand symptoms presumably due, at least partially, to reduced blood flow.     

Ipsilateral foot and contralateral hand anomalies in a patient with Poland-Moebius syndrome

This report describes a patient who had bilateral facial nerve paralysis, external ophthalmoplegia, absence of pectoralis major muscle at right side, ipsilateral hand and foot, and contralateral hand anomalies. To our knowledge, this is the first patient with Poland syndrome reported in combination with Moebius syndrome, presenting with contralateral hand and ipsilateral foot anomalies.     

Anemia causes a relative decrease in blood lactate concentration during exercise

Summary The purpose of the present study was to examine to what degree a reduction in systemic oxygen transport capacity influences the absolute and relative levels (% of maximal oxygen uptake) of submaximal blood lactate accumulation. Anemia was induced by repeated venesections in eight healthy males. After 9–10 weeks of anemia, hemoglobin concentration [Hb] was restored by retransfusion of packed erythrocytes. The [Hb] values obtained were, before venesections, in control (C)=145±10, in the anemic state (A)=110±8, and after retransfusion (R)=143+-8 g · l^–1 respectively. In all states, muscle biopsies were taken and measurements made of and at a running velocity corresponding to a blood lactate concentration of 4 mM (v _{Hla 4.0}). In the A condition decreased by 19% as compared to C (P<0.01). v _{Hla 4.0}. v _{Hla 4.0} was 14% lower in A as compared to C and R (p<0.01). at v _{Hla 4.0} was 13% lower in A as compared to C (P<0.01). However, at v _{Hla 4.0} expressed as a percentage of was increased (P<0.01) in the anemic state, the values obtained being C=83.3%, A=89.8% and R=84.8%. Ventilation at v _{Hla 4.0} was higher in A as compared to C and R (P<0.05). R and C values were not significantly different for any of the values presented above. The maximal activity of citrate synthase in muscle did not differ between the three different conditions. It is concluded that a reduction in systemic oxygen transport leads to an absolute decrease in the fixed anaerobic threshold. However, peripheral factors modified this decrease. As a consequence there was a marked shift to the right, relative to , in the submaximal lactate accumulation upon induction of anemia.     

Viewing the hand prior to movement improves accuracy of pointing performed toward the unseen contralateral hand

 It is now well established that the accuracy of pointing movements to visual targets is worse in the full open loop condition (FOL; the hand is never visible) than in the static closed loop condition (SCL; the hand is only visible in static position prior to movement onset). In order to account for this result, it is generally admitted that viewing the hand in static position (SCL) improves the movement planning process by allowing a better encoding of the initial state of the motor apparatus. Interestingly, this wide-spread interpretation has recently been challenged by several studies suggesting that the effect of viewing the upper limb at rest might be explained in terms of the simultaneous vision of the hand and target. This result is supported by recent studies showing that goal-directed movements involve different types of planning (egocentric versus allocentric) depending on whether the hand and target are seen simultaneously or not before movement onset. The main aim of the present study was to test whether or not the accuracy improvement observed when the hand is visible before movement onset is related, at least partially, to a better encoding of the initial state of the upper limb. To address this question, we studied experimental conditions in which subjects were instructed to point with their right index finger toward their unseen left index finger. In that situation (proprioceptive pointing), the hand and target are never visible simultaneously and an improvement of movement accuracy in SCL, with respect to FOL, may only be explained by a better encoding of the initial state of the moving limb when vision is present. The results of this experiment showed that both the systematic and the variable errors were significantly lower in the SCL than in the FOL condition. This suggests: (1) that the effect of viewing the static hand prior to motion does not only depend on the simultaneous vision of the goal and the effector during movement planning; (2) that knowledge of the initial upper limb configuration or position is necessary to accurately plan goal-directed movements; (3) that static proprioceptive receptors are partially ineffective in providing an accurate estimate of the limb posture, and/or hand location relative to the body; and (4) that static visual information significantly improves the representation provided by the static proprioceptive channel. Received: 23 July 1996 / Accepted: 13 December 1996     

Stiffness regulation by reflex action in the normal human hand

1. The torque and electromyographic (EMG) responses to stretch of the first dorsal interosseous muscle (externally imposed joint rotation) were recorded in five normal human subjects. The total measured stiffness was decomposed into three individual stiffness components; passive, intrinsic, and reflex. 2. The passive component was measured with the subject relaxed. Compared with the total response at the height of short latency reflex action, the passive component comprised 6-32% of the total stiffness recorded at an initial torque level of 20 N-cm [15-39% maximum voluntary contraction (MVC)]. The passive response also reflected a significant acceleration component during rapid joint rotation due primarily to digit inertia. 3. The intrinsic stiffness component, attributed to the mechanical properties of the active muscle fibers, was estimated by recording the response to joint rotation with the muscle activated in a distributed manner using a single intramuscular electrode. The dynamic stiffness (measured at the end of a ramp displacement) and the static stiffness (measured 1 s after onset of the displacement) both scaled in a straight-line manner with the initial torque level. This relationship held whether the initial torque level was varied by changes in recruitment or temporal summation. 4. The reflex component was calculated by subtracting the passive and the estimated intrinsic component from the total response. The timing of the EMG signal recorded during measurement of the total response and the fact that the estimated intrinsic component matched the total active response over the first 65-100 ms after displacement onset supported the case that this was the true reflex component. The peak of the reflex activity occurred 155-360 ms after displacement onset and, at this peak, accounted for 18-44% of the total stiffness (at an initial torque level of 20 N-cm). 5. Over the low to intermediate torque range employed, we observed that both intrinsic muscle stiffness and total stiffness increased with initial torque. Because total stiffness increased more rapidly than intrinsic stiffness, the difference between them (equal to reflex stiffness) also increased with initial torque. Furthermore, when the total active response trials (passive stiffness removed) were shifted vertically so that the initial torque levels matched, it was seen that reflex action did not reduce the stiffness range to less than the stiffness range encountered for the intrinsic response alone.(ABSTRACT TRUNCATED AT 400 WORDS)     

Oxytocin causes a sustained decrease in plasma levels of corticosterone in rats.

The aim of this study was to investigate how oxytocin (OXT) influences plasma levels of ACTH and corticosterone in rats. A single injection of OXT (1 mg/kg s.c.) caused a transient increase in ACTH and corticosterone. In contrast, 1 mg/kg OXT (but not 10-100 microg/kg) decreased corticosterone, but not ACTH levels, 6 h after the injection. OXT (1 mg/kg s.c.) administered once a day for 5 days, decreased cortiocosterone for 10 days after the last injection. An acute challenge with ACTH increased corticosterone to the same level in rats pretreated with OXT and controls. Dexamethasone decreased corticosterone to equal levels in both groups. Thus, OXT seems to be able to stimulate as well as to inhibit the activity within the HPA-axis within a short- and a long-term perspective, respectively.     

Sympathetic activity influences the vascular axon reflex in the skin

The interaction between changes of skin blood flow evoked by centrally mediated reflexes and local axon reflexes was studied in healthy subjects. Axon reflexes were evoked on the dorsum of the hand by transcutaneous electrical stimulation and reflex changes of blood flow by changes of ambient temperature, deep breath and emotional changes of blood flow by changes of ambient temperature, deep breath and emotional stress. Skin blood flow was measured by two laser-Doppler flowmeters, the probes of which were situated 6-8 mm from the stimulating electrode (monitoring net flow responses) and several centimetres away (monitoring generalized reflex responses only). The axon reflex responses were markedly diminished by body cooling but did not change during body warming. In warm subjects, a deep breath and emotional stress caused transient reductions of the flow response evoked by the electrical stimulation. Regional anaesthesia of the nerve(s) innervating the stimulated skin area led to marked increases of axon reflex responses in cold subjects, but no changes occurred in warm subjects. The anaesthesia also eliminated the transient flow reductions evoked by deep breaths and emotional stress. Since the applied stimuli are known to change skin sympathetic activity, it is concluded that sympathetic (presumably vasoconstrictor) impulses destined for the skin may reduce axon reflex responses.     

The veno-arteriolar reflex in free skin flaps

The veno-arteriolar reflex was measured in 10 subjects in whom an area of denervated skin was present in the lower limb following free flap transfer of skin and subcutaneous tissue 3 weeks to 2 years previously. The vasoconstrictor response to dependency was measured in the skin of the flap, in adjacent innervated skin and after chemical dilatation of cutaneous vessels in the skin of the flap. This veno-arteriolar reflex resulting in a reduction of blood flow of 30-40% was present and equal in both normal and denervated skin. The response was abolished by chemical vasodilatation. The results indicate that sympathetic innervation is not essential for the veno-arteriolar reflex, and suggest that myogenic mechanisms may be more important than previously believed.     

Cyclic intramuscular temperature fluctuations in the human forearm during cold-water immersion

Summary The purpose of the present study was to investigate the intramuscular temperature fluctuations in the human forearm immersed in water at 15°C. Tissue temperature (T _t) was continuously monitored by a calibrated multi-couple probe during 3 h immersion of the forearm. The probe was implanted approximately 90 mm distal from the olecranon process along the ulnar ridge. T _t was measured every 5 mm, from the longitudinal axis of the forearm (determined from computed tomography scanning) to the skin surface. Along with T _t, rectal temperature, skin temperature and heat loss of the forearm were measured during the immersions. Five of the six subjects tested showed evidence of cyclic temperature fluctuations in the forearm limited to the muscle tissue. The first increase of the muscle temperature was observed 75 (SE 6) min after the onset of the immersion, and the duration of the cycle averaged 36 (SE 3) min. The maximum increase of the muscle temperature, which ranged between 0.4°C and 1.0°C, was measured at the axis of the forearm, and was inversely correlated to the circumference of the subject's forearm (P< 0.05). No corresponding increases of the skin temperature and heat loss of the forearm were observed for the complete duration of the immersion. These data support the hypothesis of a significant contribution of the muscle vessels during cold-induced vasodilatation in the forearm.     

Unilateral eye enucleation in adult rats causes neuronal loss in the contralateral superior colliculus

Several studies have reported the morphological changes induced by unilateral enucleation during early neonatal life on the developing visual system. This study has examined cellular changes in the superior colliculi by removal of a single eye in adult rats. Anaesthetised male hooded rats aged 90 d had their right eyes removed. Groups of nonenucleated control and enucleated rats were killed when aged either 150 or 390 d. The brains were removed and both the right and left superior colliculi dissected out. The volume of the stratum griseum superficiale (SGS) within these colliculi was estimated stereologically by light microscopy, as well as the numerical density and total number of neurons within this cell layer. The volume of the cell layer was reduced by about 40% on the side contralateral to the enucleated eye but not on the ipsilateral side at both survival periods examined. The numerical density of neurons within the SGS was unaffected by the enucleation so that the colliculi contralateral to the enucleated eye showed a substantial loss of neurons within this cell layer. This study demonstrates the importance of the retinal ganglion cell input, even in adult animals, for maintaining the viability of neurons in the SGS layer of the superior colliculus.     

Nitric oxide and noradrenaline contribute to the temperature threshold of the axon reflex response to gradual local heating in human skin

The initial skin blood flow response to rapid local heating is an axon reflex, which may be mediated by calcitonin gene-related peptide and substance P released from C-fibres. We investigated the role of nitric oxide (NO) and noradrenaline on the temperature threshold for the axon reflex during gradual local heating. 36 subjects participated in two studies. Using microdialysis, we examined the following interventions: NO synthase inhibition (10 m m N ^G-nitro- l -arginine methyl ester, l -NAME); low-dose NO infusion (1.0 μ m sodium nitroprusside, SNP); adrenergic blockade (10 m m bretylium tosylate); and low-dose (0.1 μ m ) noradrenaline infusion. Laser-Doppler flowmetry was used to measure red blood cell flux. Skin was heated at a rate of 0.1°C min⁻¹ from 33°C to 40°C. Compared to control skin sites, the axon reflex response was shifted to a higher temperature in 4 subjects in the l -NAME sites (control, 37.0 ± 0.3°C, n = 16; l -NAME, 39.8 ± 0.1°C, n = 4; P < 0.001) and absent in 12 subjects. The response was also absent in l -NAME plus low-dose SNP sites and not altered by low-dose SNP infusion alone. Adrenergic blockade, with and without low-dose noradrenaline infusion, also abolished the axon reflex response in all subjects. Low-dose noradrenaline infusion alone shifted the axon reflex to a significantly lower temperature threshold compared to control sites (control, 38.2 ± 0.5°C; noradrenaline, 37.7 ± 0.4°C, P < 0.05, n = 5). These results suggest that endogenous NO and noradrenaline contribute to the temperature threshold of the axon reflex response during gradual local heating of the skin.     

Effects of intrathecal substance P and a substance P antagonist on a reflex to noxious heat are independent of changes in tail skin temperature

Substance P or the substance P receptor antagonist (d-Arg¹, d-Trp^{7, 9}, Leu¹¹)-substance P (Spantide) was injected into the lumbar subarachnoid space in mice, and the ability to change the tail-flick reflex and the tail skin temperature was investigated. Tail-flick latency (the time needed to evoke the tail-flick reflex by noxious radiant heat) was reduced for 1–4 min after intrathecal administration of substance P (5 μg), but the tail skin temperature was not significantly changed. Nor was the tail skin temperature significantly changed after intrathecal injection of Spantide (5 pg), but this compound significantly increased tail-flick latencies 5–30 min after injection. Analysis of co-variance showed that the effects of substance P or Spantide on tail-flick latency were significant, whereas the influence of tail skin temperature on tail-flick latency was nonsignificant. Thus, intrathecal substance P induces a short-lasting increase in nociceptive sensitivity, and intrathecal Spantide produces an antinociceptive effect of longer duration. The results seem not to be the result of changes in tail skin temperature.