Evaluation of the dynamic cutaneous post-ischaemic hyperaemia and thermal response in elderly subjects and in an area at risk for pressure sores

Summary. The response of skin blood cell flux (SBF) to locally applied pressure was evaluated with the laser-Doppler technique in the areas of the sacrum and the gluteus maximus muscle of geriatric patients and healthy young and elderly subjects. The SBF over the sacrum stopped at a lower external skin pressure than over the gluteus muscle in all groups studied (P<0·05·0·001). The SBF at rest was lower among geriatric patients and over the sacrum, with men showing the lowest value (P<0·001). The initial slope of the SBF curve and the peak SBF during the post-occlusive reactive hyperaemia (PRH) were lower among geriatric patients compared to younger healthy subjects (P<0·05·0·01) over both areas studied. During the last part of the PRH response rhythmic oscillations started, known as vasomotion. The mean skin temperature at rest was higher over the sacrum (P<0·001) than over the gluteus area, but no difference was found between the groups. The temperature increase during the PRH was larger over the gluteus muscle (P<0·01) than over the sacrum area in the healthy subjects. Among the patients the temperature increase was larger over the gluteus only during the first half of the PRH, after which the temperature increased most over the sacrum. It is concluded that SBF and skin temperature show different responses in microvascular reactivity to external pressure in elderly vs. younger subjects and also between sexes. The described technique may be useful in clinical practice for predicting the risk of pressure sores in different areas and subjects.     

Effect of a warm footbath before bedtime on body temperature and sleep in older adults with good and poor sleep: An experimental crossover trial

Background

The decrease in core body temperature before sleep onset and during sleep is associated with dilation of peripheral blood vessels, which permits heat dissipation from the body core to the periphery. A lower core temperature coupled with a higher distal (hands and feet) temperature before sleep are associated with shorter sleep latency and better sleep quality. A warm foot bath is thought to facilitate heat dissipation to improve sleep outcomes.

Objectives

This study examined the effect of a warm footbath (40 °C water temperature, 20-min duration) on body temperature and sleep in older adults (≥55 years) with good and poor sleep.

Design

Two groups and an experimental crossover design was used.

Setting and participants

Forty-three adults responded to our flyer and 25 participants aged 59.8 ± 3.7 years (poor sleeper with a Pittsburgh Sleep Quality Index score ≥ 5 = 17; good sleepers with a Pittsburgh Sleep Quality Index score < 5 = 8) completed this study.

Methods

All participants had body temperatures (core, abdomen, and foot) and polysomnography recorded for 3 consecutive nights. The first night was for adaptation and sleep apnea screening. Participants were then randomly assigned to either the structured foot bathing first (second night) and non-bathing second (third night) condition or the non-bathing first (second night) and foot bathing second (third night) condition.

Results

A footbath before sleep significantly increased and retained foot temperatures in both good and poor sleepers. The pattern of core temperatures during foot bathing was gradually elevated (poor sleepers vs. good sleepers = +0.40 ± 0.58 °C vs. +0.66 ± 0.17 °C). There were no significant changes in polysomnographic sleep and perceived sleep quality between non-bathing and bathing nights for both groups.

Conclusion

A footbath of 40 °C water temperature and 20-min duration before sleep onset increases foot temperatures and distal–proximal skin temperature gradients to facilitate vessel dilatation and elevates core temperature to provide heat load to the body. This footbath does not alter sleep in older adults with good and poor sleep.     

Regional variations in nocturnal fluctuations in subcutaneous blood flow rate in the lower leg of man

The purpose of the study was to investigate possible regional variations in recently discovered nocturnal fluctuations in subcutaneous blood flow rates. Approximately 90 min after going to sleep, a 100% blood flow rate increment, lasting about 100 min, has been demonstrated in the distal and medial aspect of the right lower leg of normal human subjects. In the present study subcutaneous adipose tissue blood flow rates were measured simultaneously in the right and left lower legs of 16 normal human subjects over 12–20 h ambulatory conditions. The ¹³³Xe wash-out technique, portable CdTe(Cl) detectors and a portable data storage unit were used. The tracer depots were applied on the medial aspects of the right lower leg and on the medial (series 1) and lateral (series 2) aspect of the left lower leg 10 cm proximal to the malleolar level by means of the epicutaneous, atraumatic labelling technique. A nocturnal hyperaemic response was demonstrated at both the medial and lateral aspect of the leg. As for the degree of hyperaemia and the absolute blood flow rates in the different phases, there were some deviations between the medial and the lateral locations. However, a highly significant positive correlation was observed in both series concerning the duration of the period from going to bed until the hyperaemia phase (P< 0·001). The mechanisms involved in the nightly subcutaneous hyperaemia are at present unknown. The sudden, synchronized increase in nocturnal subcutaneous blood flow points to a central nervous or humoral elicitation, although local metabolic factors might participate as well.     

Effects of local forearm skin heating on skin properties

This study investigated impacts of local skin heating on skin properties and tested whether skin changes depended on heat‐induced hyperaemia. It was reasoned that heat‐induced vasodilation impacts accompanying interstitial fluid changes. Forearm skin was locally heated from a baseline of 35°C to 40–42°C in 30 young adults (15 females, 15 males, 24.9 ± 2.1 years) and non‐heated in 10 others (5 females, 5 males, 25.2 ± 1.3 years. Skin blood flow (SBF) was continuously measured using a laser Doppler method and skin tissue dielectric constant (TDC), stratum corneum capacitance (SCC) and transepidermal water loss (TEWL) were measured before and after maintained heat for 12 min. TDC values were determined to effective measurement depths of 1.5 mm (TDC15) and 2.5 mm (TDC25). Results showed a large heat‐induced hyperaemia, with SBF increasing on average 8.8‐fold from its baseline of 35°C. Heating also caused significant increases in TDC, SCC and TEWL that, compared to preheating, increased approximately 1.1‐fold, 3.1‐fold and 4.5‐fold. None of these skin changes correlated with the magnitude of the SBF hyperaemic response. Absence of this correlation may indicate that in young healthy adults, increased capillary filtration due to heat‐induced arteriolar vasodilation is rapidly accommodated by postcapillary reabsorption, enhanced lymphatic activity and TEWL processes. An alternate explanation is that heating caused increased red cell oscillations that were detected as part of the laser Doppler increase without representing increased capillary flux. The major determinant of the Increases in TDC, SCC and TEWL is likely a consequence of heat‐induced eccrine gland activation. Studies of older persons or those with depressed function are warranted.     

Maximization of skin capillaries during intravital video-microscopy in essential hypertension: comparison between venous congestion, reactive hyperaemia and core heat load tests.

Intravital capillary video-microscopy is a dynamic method for studying skin capillaries. The technique of direct intravital microscopy (without dyes) depends on the presence of red blood cells inside capillaries for their identification. The aim of the present study was to compare different techniques to try to establish the best method for maximizing the number of visible perfused capillaries during intravital capillary microscopy. We compared the effects of venous congestion with those of post-occlusive reactive hyperaemia (Study 1). We also investigated venous congestion followed first by post-occlusive reactive hyperaemia and then by a core heat load test (Study 2). Finally we investigated venous congestion followed by post-occlusive reactive hyperaemia combined with venous congestion (Study 3). In Study 1, capillary density increased with venous congestion from a baseline value of 74+/-2 (mean+/-S.E.M.) per field to 82+/-3 per field (P<0.0001; analysis of variance). With reactive hyperaemia, there was an apparent decrease in visible capillary density to 69+/-2 per field. In Study 2, baseline capillary density was 69+/-4 per field, and this increased significantly with venous congestion to 74+/-4 per field (P=0.01). With both reactive hyperaemia and core heat load, the apparent density was 62+/-4 per field. In Study 3 the baseline density was 70+/-2 per field, and this increased significantly with venous congestion to 80+/-3 per field (P<0.0001). With reactive hyperaemia combined with venous congestion, the density was 81+/-3 per field (P=0.328 compared with venous congestion alone). The results show that venous congestion at 60 mmHg for 2 min is the most effective method for visualization of the maximal number of perfused skin capillaries during intravital video-microscopy.     

Forearm skin tissue dielectric constant measured at 300 MHz: effect of changes in skin vascular volume and blood flow

Skin tissue dielectric constant (TDC) values measured via the open‐ended coaxial probe method are useful non‐invasive indices of local skin tissue water. However, the effect of skin blood flow (SBF) or skin blood volume (SBV) on TDC values is unknown. To determine the magnitude of such effects, we decreased forearm SBV via vertical arm raising for 5 min (test 1) and increased SBV by bicep cuff compression to 50 mmHg for 5 min (test 2) in 20 healthy supine subjects (10 men). TDC values were measured to a depth of 1·5 mm on anterior forearm, and SBF was measured with laser‐Doppler system simultaneously on forearm and finger. Results indicate that decreasing vascular volume (test 1) was associated with a small but statistically significant reduction in TDC (3·0 ± 4·3%, P = 0·003) and increasing vascular volume (test 2) was associated with a slight but statistically significant increase in TDC (3·5 ± 3·0%, P<0·001). SBF changes depended on test and measurement site. For forearm, test 1 significantly increased SBF (102·6 ± 156·2%, P<0·001) and test 2 significantly decreased it (39·5 ± 13·1%, P<0·001). In finger, SBF was significantly reduced by both tests: in test 1 by 55·3 ± 32·1%, P<0·001 and in test 2 by 53·3 ± 27·6%, P<0·001. We conclude that the small percentage changes in TDC values (3·0–3·5%) over the wide range of induced SBV and SBF changes suggest a minor effect on clinically determined TDC values because of SBV or SBF changes or differences when comparing TDC longitudinally over time or among individuals of different groups in a research setting.     

Laser Doppler measurements of skin blood flow before,during, and after lumbar sympathetic blockade in children and young adults with reflex sympathetic dystrophy syndrome

Changes in the skin capillary blood flow (SBF) and temperature before, during, and 1 hour after unilateral lumbar paravertebral sympathetic blockade (LSB) were studied simultaneously with laser Doppler flowmetry and thermometry in patients with reflex sympathetic dystrophy syndrome. The baseline flow measurements in the toes on the affected limb were significantly lower than in the contralateral limb (p<0.01). During LSB, a 10-fold increase in SBF was detected within 4 minutes after injection of a local anesthetic agent when the sympathetic blockade was effective; an increase of more than 1°C in the skin temperature occurred within 11 minutes. Measurements 1 hour after blockade showed an 18-fold (mean) increase in SBF in the toes (p<0.0001) and a 2-fold (mean) increase in SBF in the thighs (p<0.001). There was a significant decrease in the skin blood flow in the contralateral toes after the sympathetic blockade (p<0.01). We conclude that laser Doppler flow measurements can be used to detect immediate onset of sympathetic blockade in patients under general anesthetic or conscious sedation.     

Ambulatory measurement of nocturnal fluctuations in subcutaneous blood flow rate in the lower leg of man during 12-h periods with the portable CdTe(C1) detector. Methodological considerations

Summary. Possible sources of error during long-term measurements of subcutaneous blood flow rate with the portable CdTe(Cl) detector system were ruled out in the present study. Local blood flow rates were recorded in the lower legs of normal human subjects by means of the ¹³³Xe wash-out technique. A good correlation was found between the portable CdTe(Cl) and stationary NaI(Tl) detector systems both prior to (r = 0·88, P<0·0001) and after (r = 0·68, P = 0·07) day over night (12 h) measurements. Identical post-ischaemic reactive hyperaemia could be demonstrated by both detector systems 12 h after the application of the isotope depot. This indicates that blood flow rates and vascular reactivity can be measured over 12 h by the portable CdTe(Cl) detector. Identical results were obtained during the 12-h measurements performed with the portable CdTe(Cl) detector attached directly to the skin surface and with the detector elevated above the skin surface. Therefore, geometrical changes were without any influence on our measurements. We conclude that measurements of subcutaneous blood flow rates in the lower leg of human subjects can be performed under out-patients conditions by means of the ¹³³Xe wash-out technique and portable CdTe(Cl) detectors. A skin area≥4 cm should be labelled by means of the atraumatic, epicutaneous labelling technique and the detector attached directly to the skin surface with a single layer of a 20-μm thick gas-tight Mylar membrane interposed between the skin surface and the detector. The investigation of the subcutaneous blood flow rate should not be initiated until at least 90 min after labelling. Measurements over depots emitting < 1000 counts per sampling period should be avoided unless background activity is subtracted.     

Local skin pressure and its effects on skin microcirculation as evaluated by laser—Doppler fluxmetry

Summary. The effect of prolonged local pressure on the skin microcirculation was investigated in the regions of the sacrum and gluteus maximus muscle to determine the aetiology of pressure sores. Thirty normal subjects (15 female, 15 male) were investigated. The subjects were divided into three age groups: group 1, ≤ 35 years; group 2, 36–64 years; and group 3, ≥ 65 years. Local pressure was applied with a specially designed instrument according to the sequence 0→ 110→ 0→ 110→ 0→ mmHg. Skin blood cell flux (SBF) was measured with a laser–Doppler technique and the local skin temperature measured with a thermistor. No significant differences were seen in SBF due to sex or age. However, differences between the two areas studied were observed. SBF was maximal over the sacrum at 12–50 mmHg (1.6–6.7 kPa) applied pressure. With further pressure increases, the SBF signal decreased successively, reaching minimum level at 110 mmHg (14.6 kPa), where it was approximately 43% below the initial value. The SBF in the gluteus region showed a more stable pattern, with a maximum SBF at 13–60 mmHg (1.7–8.0 kPa). At both locations, an increased SBF at zero pressure was seen when the pressure was decreased from 110 to 0 mmHg. The skin temperature (n = 7) increased by 2.7°C (range 1.9–3.5°C) over the gluteus and by 1.3°C (range 0.8–2.5°C) over the sacrum. This increase was more rapid over the gluteus region. Concomitantly a temperature-dependent increase of SBF could be seen. It is concluded that a cause for the greater frequency of pressure sores over the sacrum than over the gluteus region is the comparatively poorer regulation of microvascular flow in this area.     

Development of gangrene during sleep

A method for continuous measurement of subcutaneous adipose tissue blood flow in the forefoot over 24 h (SBF) is described. The method is based on the radioisotope wash-out principle using 133-Xenon (133Xe). A portable semiconductor detector is placed just above a local depot of 37-74 kBq 133Xe in 0.1 ml isotonic saline, injected into the subcutaneous adipose tissue in the forefoot. The detector is connected to a memory unit allowing for storage of data. Because of the short distance, the recorded elimination rate constant must be corrected for combined convection and diffusion of the radioactive indicator. Characteristic 24-h blood flow patterns were unveiled in patients with normal peripheral circulation and in patients having ischaemic nocturnal rest pain. In normal subjects, SBF doubled from day to night. This is ascribed to the local veno-arteriolar sympathetic axon reflex, which induces vasoconstriction when the transmural pressure of the veins exceeds approximately 25 mmHg. In patients having ischaemic rest pains SBF was reduced by 37% on the average from day to night. This was caused by nocturnal hypotension, which is reflected proportionally in the foot. As the resistance vessels most probably are fully dilatated in feet with rest pain, the blood pressure drop during sleep causes the perfusion pressure and, therefore, blood flow to drop below a certain critical limit. There was a pronounced correlation between the reduction systemic mean arterial blood pressure and SBF. The patients complaining of intermittent claudication, but no rest pains, demonstrated a variety of changes in SBF compatible with the continuous spectrum of peripheral arteriosclerotic disease. The reduced blood flow during sleep in patients having ischaemic rest pains give rise to the concept of the development of gangrene during sleep.     

Changes in plasma volume, in transcapillary escape rate of albumin and in subcutaneous blood flow during hypoglycaemia in man

Hypoglycaemia was induced by insulin injected intravenously (0.15 i.u./kg body weight) in seven healthy young males. Plasma volume was measured before and during hypoglycaemia by intravenous injection of 125I before hypoglycaemia and of 131I during hypoglycaemia. Plasma volume decreased and transcapillary escape rate increased significantly during hypoglycaemia. Skin temperature and local subcutaneous adipose tissue blood flow were measured in four different regions. Both tended to decrease during hypoglycaemia and decreased significantly 2 h after hypoglycaemia. There was no correlation between changes in the two measurements, suggesting that there is no simple relationship between subcutaneous blood flow and skin temperature during hypoglycaemia.     

Mild mental stress in diabetes: changes in heart rate and subcutaneous blood-flow

Summary. A TV-game of tennis of 20 min duration was used to study the influence of mild mental stress on subcutaneous blood-flow (SBF), blood-pressure and heart rate in nine insulin-dependent diabetics and nine healthy subjects. SBF was measured on the thigh by local clearance of xenon-133. Measurements were made before, during and after the period of stress. During stress, SBF increased significantly by 26% in the healthy subjects, while SBF remained unchanged in the diabetics. The difference between the two groups was significant (P<0–05). Following stress, SBF returned to pre-stress level in the healthy subjects, while a significant decrease of 33% was observed in the diabetics. The pre-stress heart rate level was higher and the stress-induced increase in heart rate was less in the diabetics compared with the healthy subjects (P<005). During the stress a slight–but insignificant–increase in blood-pressure was observed in both groups. In conclusion, we found that even mild mental strain influences SBF in both normal subjects and in diabetics. The induced alterations in the two groups are different, probably because of a slight parasympathetic dysfunction in the diabetics.     

Ephedrine-induced thermogenesis in man: no role for interscapular brown adipose tissue

The warmest interscapular skin areas were located by thermography in six healthy subjects during ephedrine-induced thermogenesis. In these interscapular areas, and in lumbar control areas, the skin temperature, subcutaneous temperature and adipose tissue blood flow were measured before and during ephedrine-induced thermogenesis. The skin and subcutaneous temperatures increased in the interscapular area as well as in the lumbar area, by about 0.7-1.2 degrees C. The interscapular skin temperature remained about 1 degree C higher than the lumbar; the subcutaneous temperatures in the two areas were identical during the experiments. Although the interscapular subcutaneous adipose tissue blood flow increased about sixfold and the lumbar increased twofold, the absolute flows were higher in the lumbar area. The oxygen uptake increased to a maximum of 30% above control level. Plasma glucose and glycerol concentrations remained unchanged, and plasma non-esterified fatty acids, lactate and noradrenaline concentrations increased slightly but significantly. Biopsies taken from the hot interscapular areas did not contain brown adipose tissue. It is concluded that the high interscapular skin temperature may be due to a lower insulating fat thickness and that the increases in skin and subcutaneous temperatures during ephedrine-induced thermogenesis are caused by an increased blood flow. These observations weigh against the hypothesis that the interscapular temperature increase is due to functional, interscapular brown adipose tissue.     

Effects of thermal applications on the abdominal temperature of rats.

The results of thermal applications to the abdomens of restrained, unanesthetized rats are reported. A silicone envelope through which water at 0. 10, 20, 30, 40, or 50°C circulated was applied while skin surface, subcutaneous, intraperitoneal, and colonic temperatures were measured. Pad applications at 0°C significantly lowered tissue temperature at all four locations measured. Pad applications at 10 and 20°C significantly lowered skin surface, subcutaneous, and intraperitoneal temperatures. Pad applications at 30°C significantly lowered skin surface and subcutaneous temperatures. Pad applications at 40 and 50°C significantly increased skin surface and subcutaneous temperatures, and applications at 50°C also increased intraperitoneal temperature. lntraperitoneal and colonic temperatures were insignificantly affected by pad applications of 30 and 40°C, and colonic temperatures were not significantly altered by any thermal application other than that at 0°C. The findings indicate that application of mild heat or cold (30–40°C) to the abdominal skin of the rat does not alter deep abdominal temperatures, indicating no deep vasomotor response to these thermal applications. The question can be raised whether these results suggest that a similar response may occur in humans.     

Effect of foot bathing on distal-proximal skin temperature gradient in elders

Increased distal (foot)-proximal (abdominal) skin temperature gradient (DPG) has been associated with better sleep initiation. Warm foot bath can affect distal skin temperature to change DPG. However, the optimum water temperature and duration necessary to raise DPG has not been established. This study explored the effects of 1-h foot bathing at two water temperatures of 40 and 41 degrees C, respectively, on DPG in Taiwanese elders (n=6, ages 60-73 years). Each subject's feet and legs were immersed in a temperature-controlled water tub to 20 cm above the ankles for 60 min in each of two water temperatures. Oral, abdominal, and foot temperatures were taken during (at 10-min intervals), and after (at 1-min intervals) foot bathing. DPG was calculated by subtracting abdominal temperature from foot temperature. Results showed the value of DPG was significantly increased in the 10th min bathing at both water temperatures and maintained above 0 degrees C. DPG gradually declined after bathing at both water temperatures. The value of DPG with 41 degrees C water was slightly higher than 40 degrees C. All subjects tolerated both bathing temperatures well for 1h. Both 40 and 41 degrees C foot bathing for 1h can increase the DPG and may be an effective way to affect whole body skin blood flow and trigger heat dissipation.     

Effect of local warming on forearm reactive hyperaemia

Summary. Measurement of minimal vascular resistance has proved useful in quantifying structural changes in regional circulations. Accurate measurement of minimal vascular resistance requires full relaxation of all resistance vessels within the region under examination. The usual procedure in humans involves the measurement of maximal forearm blood-flow following 6–10 min of forearm ischaemia. We conducted this study to find whether forearm skin was fully vasodilated by this procedure. Peak forearm blood-flow was measured by plethysmography in six healthy subjects following 10 min of ischaemia while the arm was at a neutral temperature (33°C) and while the arm was locally warmed to 42°C. Peak reactive hyperaemia blood-flow was significantly elevated by local heating (P<0·001) to 79·6 ml100ml^-1min^-1 from a value of 50·2 ml100ml^-1min^-1 during normothermia. Peak reactive hyperaemia blood-flow in the contralateral unheated forearm showed no significant change between the two periods of ischaemia (P>0·05). These findings were confirmed in four subjects by laser Doppler velocimetry, which gives a linear index of skin blood-flow. In normothermic conditions, this index rose to 0·89 V following 10 min of ischaemia and to 1·26 V with local warming to 42°C (P<0·001). Ischaemia plus local warming did not cause a further significant rise in this index of skin blood-flow (1·35 V, P>0·05). These data suggest that 10 min of ischaemia during normothermia is insufficient to relax fully cutaneous resistance vessels and that maximal forearm blood-flow is underestimated by this procedure.     

Why do patients with severe arterial insufficiency get pain during sleep?

Simultaneous measurement during 24 h of mean arterial blood pressure (MABP) and forefoot subcutaneous adipose tissue blood flow (SBF) was undertaken in eight patients (15 feet) with different degrees of arterial insufficiency. The recordings were undertaken with the patients in the supine position only. The MABP decreased by 19 +/- 9% from awake to asleep independently of symptomatology. In two limbs with normal circulation, SBF decreased by 8 +/- 7%. In five limbs with arterial insufficiency but no rest pain SBF decreased by 16 +/- 8%, and in eight limbs with ischaemic nocturnal rest pain, SBF was reduced by 32 +/- 12% during sleep. It is concluded that nocturnal hypotension is the major aethiological factor for the symptom ischaemic nocturnal rest pain.     

Increased sympathetic tone in forearm subcutaneous tissue in primary hypothyroidism

Summary. Sympathetic reflex regulation of subcutaneous blood flow (SBF) in the forearm was studied in eight patients with primary hypothyroidism. Diastolic arterial pressure was ≥95 mmHg in five patients. SBF was determined by local clearance of Na^99mTcO₄. Sympathetic vasoconstriction normally seen after lowering the forearm 40 cm below heart level was absent since SBF only decreased by 4% (± 7%, P > 0·1) during these conditions. In head-up vertical position we noticed a diminished baroreceptor response as SBF at heart level was reduced by 11% (±7%, P < 0·1) compared to supine position. After proximal local anaesthesia SBF increased by 351% (±81%, P < 0·01) and disclosed a normal vasoconstrictor response as SBF was reduced by 53% (±5%, P < 0·01) during arm lowering. Five of the treated patients were restudied in the euthyroid state. Mean arterial pressure was reduced in mean by 20 mmHg (± 6 mmHg, P < 0·02) during treatment and a significant vasoconstriction was observed both during arm lowering (SBF =-52% (±6%, P<0·02)) and in head-up vertical position (SBF= -45% (± 11%, P<0·02)). In conclusion sympathetic vasoconstrictor activity in adipose tissue is markedly increased in primary hypothyroidism. Sympathetic tone and arterial pressure are reduced during treatment.     

Comparison of digital infrared thermal imaging (DITI) with contact thermometry: pilot data from a sleep research laboratory

Body temperature regulation is associated with changes in sleep propensity; therefore, sleep research often necessitates concomitant assessment of core and skin surface temperatures. Attachment to thermistors may limit the range of movement and comfort, introducing a potential confound that may prolong sleep initiation or increase wakefulness after sleep onset. It has been suggested that contact thermometry may artificially increase temperatures due to insulation. We report here on a method of remote sensing skin temperatures using a digital infrared thermal imaging (DITI) system, which can reduce these potential confounds. Using data from four healthy young adult volunteers (age = 26.8 +/- 2.2 years; mean +/- SEM), we compared measures of skin temperature using a DITI system with contact thermometry methods already in use in our sleep laboratory. A total of 416 skin temperature measurements (T(sk)) were collected from various sites, resulting in an overall correlation coefficient of R = 0.99 (p < 0.0001) between both methods. Regression analyses for individuals resulted in correlation coefficients between 0.80 and 0.97. These pilot results suggest that DITI can assess skin surface temperatures as accurately as contact thermometry, provided the interest is in relative and not absolute temperature changes. This and some other important limitations are discussed in more detail hereafter.     

Skin microcirculatory and thermal changes in elderly subjects with early stage of pressure sores

Summary. Elderly subjects are prone to develop pressure sores over the sacrum area mainly due to external pressure and shear effects which negatively affect the skin microcirculation. The aim of the study described here was to measure skin microcirculatory and thermal changes in twelve elderly patients with an early stage of pressure sore and in ten elderly subjects without pressure sore. The total skin microcirculation at a damaged risk area, the sacrum, and a reference area of undamaged skin over the gluteal region, was evaluated using the laser Doppler fluxmetry. The nutritive transport of small solutes, characterized by the transcapillary exchange of sodium fluorescein, was evaluated using the fluorescein flowmetry technique. The skin temperature was measured with a thermoelement. The skin microcirculation at the area with an early stage of pressure sore was significantly higher than at undamaged skin as measured by both techniques. The total microcirculatory blood flow increased > 16 times (P < 0–001) and the nutritive transport 5 times (P < 0–01) compared to the reference value, and the calculated blood flow of subpapillary tissue layers increased 17–19 times (P < 0–001). However, the skin temperatures in damaged and undamaged skin did not differ significantly. These results show an increased skin microcirculation in the early stage of pressure sores but no increase in skin temperature. The more strongly increased skin blood flow in subpapillary tissue layers effectively conducts away the heat caused by the damage and the increased metabolic activity.