Skin Blood Flow Laser Doppler Research Articles

Thermo-haemodynamic coupling during regional thigh heating: Insight into the importance of local thermosensitive mechanisms in blood circulation.

A positive relationship between local tissue temperature and perfusion exists, with isolated limb-segment hyperthermia stimulating hyperaemia in the heated region without affecting the adjacent, non-heated limb segment. However, whether partial-limb segment heating evokes a heightened tissue perfusion in the heated region without directly or reflexly affecting the non-heated tissues of the same limb segment remains unknown. This study investigated, in 11 healthy young adults, the lower limb temperature and haemodynamic responses to three levels of 1h upper-leg heating, none of which alter core temperature: (1) whole-thigh (WTH; water-perfused garment), (2) quadriceps (QH; water-perfused garment) and (3) partial-quadriceps (PQH; pulsed shortwave diathermy) heating. It was hypothesised that perfusion would only increase in the heated regions. WTH, QH and PQH increased local heated tissue temperature by 2.9±0.6, 2.0±0.7 and 2.9±1.3°C (P<0.0001), respectively, whilst remaining unchanged in the non-heated hamstrings and quadriceps tissues during QH and PQH. WTH induced a two-fold increase in common femoral artery blood flow (P<0.0001) whereas QH and PQH evoked a similar ∼1.4-fold elevation (P≤0.0018). During QH and PQH, however, tissue oxygen saturation and laser-Doppler skin blood flow in the adjacent non-heated hamstrings or quadriceps tissues remained stable (P>0.5000). These findings in healthy young humans demonstrate a tight thermo-haemodynamic coupling during regional thigh heating, providing further evidence of the importance of local heat-activated mechanisms on the control of blood circulation.

Neck cooling induces blood pressure increase and peripheral vasoconstriction in healthy persons

IntroductionNoninvasive temperature modulation by localized neck cooling might be desirable in the prehospital phase of acute hypoxic brain injuries. While combined head and neck cooling induces significant discomfort, peripheral vasoconstriction, and blood pressure increase, localized neck cooling more selectively targets blood vessels that supply the brain, spares thermal receptors of the face and skull, and might therefore cause less discomfort cardiovascular side effects compared to head- and neck cooling. The purpose of this study is to assess the effects of noninvasive selective neck cooling on cardiovascular parameters and cerebral blood flow velocity (CBFV).MethodsEleven healthy persons (6 women, mean age 42 ± 11 years) underwent 90 min of localized dorsal and frontal neck cooling (EMCOOLS Brain.Pad™) without sedation. Before and after cooling onset, and after every 10 min of cooling, we determined rectal, tympanic, and neck skin temperatures. Before and after cooling onset, after 60- and 90-min cooling, we monitored RR intervals (RRI), systolic, diastolic blood pressures (BPsys, BPdia), laser Doppler skin blood flow (SBF) at the index finger pulp, and CBFV at the proximal middle cerebral artery (MCA). We compared values before and during cooling by analysis of variance for repeated measurements with post hoc analysis (significance: p < 0.05).ResultsNeck skin temperature dropped significantly by 9.2 ± 4.5 °C (minimum after 40 min), while tympanic temperature decreased by only 0.8 ± 0.4 °C (minimum after 50 min), and rectal temperature by only 0.2 ± 0.3 °C (minimum after 60 min of cooling). Index finger SBF decreased (by 83.4 ± 126.0 PU), BPsys and BPdia increased (by 11.2 ± 13.1 mmHg and 8.0 ± 10.1 mmHg), and heart rate slowed significantly while MCA-CBFV remained unchanged during cooling.ConclusionsWhile localized neck cooling prominently lowered neck skin temperature, it had little effect on tympanic temperature but significantly increased BP which may have detrimental effects in patients with acute brain injuries.

Cutaneous Vascular Responses of the Hands and Feet to Cooling, Rewarming, and Hypoxia in Humans

This study investigated skin vasomotor responses in the fingers and toes during cooling and rewarming with and without normobaric hypoxia. Fourteen volunteers (8 males and 6 females) were exposed to gradual air cooling (mean±SD: -0.4±0.1oC·min-1) followed by rewarming (+0.5±0.1oC·min-1) while breathing normoxic air (FIO2 0.21 at 761±3 mm Hg) or hypoxic gas (FIO2 0.12, at 761±3 mm Hg, equivalent to ~5000 m above sea level). Throughout the gradual cooling and rewarming phases, rectal temperature was measured, and skin temperatures and laser Doppler skin blood flow were measured on the thumb, little finger, and great and little toe pads. During gradual cooling, skin temperature but not deep body temperature decreased. No differences in cutaneous vascular conductance were found for the toes or thumb (P=0.169 great toe; P=0.289 little toe; P=0.422 thumb). Cutaneous vascular conductance was reduced in the little finger to a greater extent at the same mean skin temperatures (34.5-33.5oC) in the hypoxic compared with normoxic conditions (P=0.047). The onset of vasoconstriction and release of vasoconstriction in the thumb and little finger occurred at higher mean skin temperatures in hypoxia compared with normoxia (P<0.05). The onset of vasoconstriction and release of vasoconstriction in the toes occurred at similar skin temperatures (P=0.181 and P=0.132, respectively). The earlier vasoconstrictor response and later release of vasoconstriction in the finger during hypoxic conditions may result in a greater dose of cold to that digit, taking longer to rewarm following the release of vasoconstriction.

Effect of bariatric surgery on microvascular dysfunction associated to metabolic syndrome: a 12-month prospective study

To prospectively evaluate the effect of weight loss after bariatric surgery on microvascular function in morbidly obese patients with and without metabolic syndrome (MetS). A cohort of morbidly obese patients with and without MetS was studied before surgery and after 12 months of surgery. Healthy lean controls were also examined. Microvascular function was assessed by postocclusive reactive hyperemia (PORH) at forearm skin evaluated by laser Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was calculated from laser-Doppler skin blood flow and blood pressure. Regression analysis was performed to assess the contribution of different clinical, metabolic and biochemical parameters to microvascular function. Before surgery, 62 obese patients, 39 with MetS and 23 without MetS, and 30 lean control subjects were analyzed. The absolute area under the hyperemic curve (AUC(H)) CVC of PORH was significantly decreased in obese patients compared with lean control subjects. One year after surgery, AUC(H) CVC significantly increased in patients free of MetS, including patients that had MetS before surgery. In contrast, AUC(H) CVC did not significantly change in patients in whom MetS persisted after surgery. Stepwise multivariate regression analysis showed that only changes in HDL cholesterol (HDL-C) and oxidized LDL (oxLDL) independently predicted improvement of AUC(H) after surgery. These two variables together accounted for 40.9% of the variability of change in AUC(H) CVC after surgery. Bariatric surgery could significantly improve microvascular dysfunction in obese patients, but only in patients free of MetS after surgery. Improvement of microvascular dysfunction is strictly associated to postoperative increase in HDL-C levels and decrease in oxLDL levels.

Power spectral analysis of the effects of epinephrine, norepinephrine, dobutamine and dopexamine on microcirculation following free tissue transfer

The use of pressor drugs after microsurgical free tissue transfer remains controversial because of potential vasoconstrictor effects on the free flap. Noninvasive monitoring of free flaps with laser Doppler flowmetry may provide further information regarding the local regulation of blood flow in the flap tissues during pressor infusions. This study evaluated the effects of four commonly used pressor agents. Twenty four patients (25 data sets) undergoing head and neck cancer resection and free flap reconstruction were recruited. Epinephrine, norepinephrine, dopexamine, and dobutamine were infused in a random order at four infusion rates, after surgery, with free flap and control area (deltoid region) laser Doppler skin blood flow monitoring. Frequency analysis of the Doppler waveform was performed utilizing the time period immediately before the first drug infusion for each patient as baseline. At baseline there was less power at the 0.002-0.6 Hz frequency in the flap compared with control tissue consistent with surgical denervation. At maximum epinephrine infusion rates, the control of blood flow moved toward (i.e., proportion of power increased in) the lower frequencies, as smooth muscle mediated (myogenic) control began to dominate blood flow, an effect most marked with norepinephrine. Dobutamine and dopexamine had little effect on control of blood flow. Denervation of free flap tissue is demonstrable using spectral analysis of laser Doppler blood flow signals. With norepinephrine the control of blood flow shifts toward low frequency vasomotion where blood flow depends mostly on average blood pressure, making it potentially the most suitable agent following free tissue transfer.

Head and Neck Cooling Decreases Tympanic and Skin Temperature, But Significantly Increases Blood Pressure

Localized head and neck cooling might be suited to induce therapeutic hypothermia in acute brain injury such as stroke. Safety issues of head and neck cooling are undetermined and may include cardiovascular autonomic side effects that were identified in this study. Ten healthy men (age 35±13 years) underwent 120 minutes of combined head and neck cooling (Sovika, HVM Medical). Before and after onset of cooling, after 60 and 120 minutes, we determined rectal, tympanic, and forehead skin temperatures, RR intervals, systolic and diastolic blood pressures (BP), laser-Doppler skin blood flow at the index finger and cheek, and spectral powers of mainly sympathetic low-frequency (0.04-0.15 Hz) and parasympathetic high-frequency (0.15-0.5 Hz) RR interval oscillations and sympathetic low-frequency oscillations of BP. We compared values before and during cooling using analysis of variance with post hoc analysis; (significance, P<0.05). Forehead skin temperature dropped by 5.5±2.2°C with cooling onset and by 12.4±3.2°C after 20 minutes. Tympanic temperature decreased by 4.7±0.7°C within 40 minutes, and rectal temperature by only 0.3±0.3°C after 120 minutes. Systolic and diastolic BP increased immediately on cooling onset and rose by 15.3±20.8 mm Hg and 16.5±13.4 mm Hg (P=0.004) after 120 minutes, whereas skin blood flow fell significantly during cooling. RR intervals and parasympathetic RR interval high-frequency powers increased with cooling onset and were significantly higher after 60 and 120 minutes than they were before cooling. Head and neck cooling prominently reduced tympanic temperature and thus might also induce intracerebral hypothermia; however, it did not significantly lower body core temperature. Profound skin temperature decrease induced sympathetically mediated peripheral vasoconstriction and prominent BP increases that are not offset by simultaneous parasympathetic heart rate slowing. Prominent peripheral vasoconstriction and BP increase must be considered as possibly harmful during head and neck cooling.

Human sympathetic outflows to skin and muscle target organs fluctuate concordantly over a wide range of time‐varying frequencies

Frequency-domain analyses of simultaneously recorded skin and muscle sympathetic nerve activities may yield unique information on otherwise obscure central processes governing human neural outflows. We used wavelet transform and wavelet phase coherence methods to analyse integrated skin and muscle sympathetic nerve activities and haemodynamic fluctuations, recorded from nine healthy supine young men. We tested two null hypotheses: (1) that human skin and muscle sympathetic nerve activities oscillate congruently; and (2) that whole-body heating affects these neural outflows and their haemodynamic consequences in similar ways. Measurements included peroneal nerve skin and tibial nerve muscle sympathetic activities; the electrocardiogram; finger photoplethysmographic arterial pressure; respiration (controlled at 0.25 Hz, and registered with a nasal thermistor); and skin temperature, sweating, and laser-Doppler skin blood flow. We made recordings at ∼27°C, for ∼20 min, and then during room temperature increases to ∼38°C, over 35 min. We analysed data with a wavelet transform, using the Morlet mother wavelet and wavelet phase coherence, to determine the frequencies and coherences of oscillations over time. At 27°C, skin and muscle nerve activities oscillated coherently, at ever-changing frequencies between 0.01 and the cardiac frequency (∼1 Hz). Heating significantly augmented oscillations of skin sympathetic nerve activity and skin blood flow, arterial pressure, and R-R intervals, over a wide range of low frequencies, and modestly reduced coordination between skin and muscle sympathetic oscillations. These results suggest that human skin and muscle sympathetic motoneurones are similarly entrained by external influences, including those of arterial baroreceptors, respiration, and other less well-defined brainstem oscillators. Our study provides strong support for the existence of multiple, time-varying central sympathetic neural oscillators in human subjects.

Topiramate improves neurovascular function, epidermal nerve fiber morphology, and metabolism in patients with type 2 diabetes mellitus

Topiramate improves neurovascular function, epidermal nerve fiber morphology, and metabolism in patients with type 2 diabetes mellitus Amanda L Boyd, Patricia M Barlow, Gary L Pittenger, Kathryn F Simmons, Aaron I VinikDepartment of Internal Medicine, Eastern Virginia Medical School, Norfolk, VA, USAPurpose: To assess the effects of topiramate on C-fiber function, nerve fiber morphology, and metabolism (including insulin sensitivity, obesity, and dyslipidemia) in type 2 diabetes.Patients and methods: We conducted an 18-week, open-label trial treating patients with topiramate. Twenty subjects with type 2 diabetes and neuropathy (61.5 &plusmn; 1.29 years; 15 male, 5 female) were enrolled and completed the trial. Neuropathy was evaluated by total neuropathy scores, nerve conduction studies, quantitative sensory tests, laser Doppler skin blood flow, and intraepidermal nerve fibers in skin biopsies.Results: Topiramate treatment improved symptoms compatible with C-fiber dysfunction. Weight, blood pressure, and hemoglobin A1c also improved. Laser Doppler skin blood flow improved significantly after 12 weeks of treatment, but returned to baseline at 18 weeks. After 18 weeks of treatment there was a significant increase in intraepidermal nerve fiber length at the forearm, thigh, and proximal leg. Intraepidermal nerve fiber density was significantly increased by topiramate in the proximal leg.Conclusion: This study is the first to demonstrate that it is possible to induce skin intraepidermal nerve fiber regeneration accompanied by enhancement of neurovascular function, translating into improved symptoms as well as sensory nerve function. The simultaneous improvement of selective metabolic indices may play a role in this effect, but this remains to be determined.Keywords: diabetic neuropathy, skin blood flow, skin biopsy, diabetes

Topiramate improves neurovascular function, epidermal nerve fiber morphology, and metabolism in patients with type 2 diabetes mellitus.

PurposeTo assess the effects of topiramate on C-fiber function, nerve fiber morphology, and metabolism (including insulin sensitivity, obesity, and dyslipidemia) in type 2 diabetes.Patients and methodsWe conducted an 18-week, open-label trial treating patients with topiramate. Twenty subjects with type 2 diabetes and neuropathy (61.5 ± 1.29 years; 15 male, 5 female) were enrolled and completed the trial. Neuropathy was evaluated by total neuropathy scores, nerve conduction studies, quantitative sensory tests, laser Doppler skin blood flow, and intraepidermal nerve fibers in skin biopsies.ResultsTopiramate treatment improved symptoms compatible with C-fiber dysfunction. Weight, blood pressure, and hemoglobin A1c also improved. Laser Doppler skin blood flow improved significantly after 12 weeks of treatment, but returned to baseline at 18 weeks. After 18 weeks of treatment there was a significant increase in intraepidermal nerve fiber length at the forearm, thigh, and proximal leg. Intraepidermal nerve fiber density was significantly increased by topiramate in the proximal leg.ConclusionThis study is the first to demonstrate that it is possible to induce skin intraepidermal nerve fiber regeneration accompanied by enhancement of neurovascular function, translating into improved symptoms as well as sensory nerve function. The simultaneous improvement of selective metabolic indices may play a role in this effect, but this remains to be determined.

Monitoring cortical hemodynamic changes after sumatriptan injection during migraine attack by near-infrared spectroscopy

The aim of the present study is to provide effective tools for monitoring hemodynamic changes in the cortical and scalp surface during migraine attack and treatment. Using near-infrared spectroscopy system (NIRS) and laser Doppler skin blood flow (SkBF) devices in combination, we monitored changes in extra- and intra-cranial vasculature states upon sumatriptan injection during spontaneous migraine attack. We examined 4 control subjects and 4 migraine patients. Multi-channel NIRS probes were placed over the temporoparietal area bilaterally and oxygenated hemoglobin (oxy-Hb) was analyzed. Laser Doppler SkBF was simultaneously recorded to measure scalp surface blood flow changes. All patients were treated with a sumatriptan injection (3 mg), and all control subjects received a saline injection as a control for oxy-Hb/SkBF signals caused by injection pain over the monitoring period. There was a marked reduction of oxy-Hb/SkBF in all patients after sumatriptan injection, consistent with pain relief. Moreover, the changes in oxy-Hb/SkBF were significantly correlated. By contrast, saline injection did not cause any significant changes. These data suggest that sumatriptan induces blood vessel contraction at both cortical and scalp surfaces. Simultaneous oxy-Hb/SkBF recording enables real-time continuous monitoring of the effects of sumatriptan treatment in clinical situations.

The progress on risk assessment for pressure ulcer

The accurate risk-assessment scales (RASs) is considerable for instituting strategy for prevention and management of pressure ulcers (PU) . In the current, the values achieved within each risk factor are summed to derive the total score. The equal -weighting scoring technique is too simplistic and subjective leads to limitations. It shows that properly trained, experienced nurses should conduct PU risk assessments, whilst more robust data -driven RASs should be developed using the computation pressure monitoring, skin blood flow laser-Doppler and differential weighting scoring method together with advanced statistical techniques. Key words: Pressure ulcer; Etiopathogenisis; Risk-assessment scales

Spectral analysis of laser Doppler skin blood flow oscillations in human essential arterial hypertension

The aim of this study was to investigate whether human essential arterial hypertension (EHT) is associated with modification of the skin blood flowmotion (SBF), which could be a sign of skin microcirculatory impairment. Forearm skin perfusion was measured by laser Doppler flowmetry (LDF) in conventional perfusion units (PU) before and after ischemia in 20 middle-age newly diagnosed EHT untreated patients, in 20 middle-age long standing EHT treated patients and in 30 age and sex matched healthy normotensive subjects (NS). Power spectral density (PSD) of SBF total spectrum (0.009–1.6 Hz), as well of five different frequency intervals (FI), each of them related to endothelial (0.009–0.02 Hz), sympathetic (0.02–0.06 Hz), myogenic (0.06–0.2 Hz), respiratory (0.2–0.6) or cardiac (0.6–1.6) activity, was also measured in PU 2/Hz before and after ishemia, using Fourier analysis of LDF signal. The three studied groups did not differ in basal and post-ischemic skin perfusion or in basal SBF parameters considered. However, while a significant post-ischemic increase in PSD of total spectrum SBF ( P < 0.001) and of its different FI, with the only exception of respiratory FI, was observed in NS, a significsnt post-ischemic increase in PSD was observed only for total spectrum ( P < 0.01) and for endothelial FI ( P < 0.001) in newly diagnosed EHT patients and only for myogenic FI ( P < 0.05) in long standing EHT patients. These findings suggest that the mechanisms which mediate the post-ischemic increment of SBF are perturbed earlier in human EHT than the mechanisms which mediate the skin post-ischemic hyperaemia. The same findings also suggest that the impairment of the endothelial mechanism involved in SBF control occurs by the time in the course of EHT.

Effects of Apneic Events on Skin Microcirculation in Preterm Newborns: Applications of Laser-Doppler-Flowmetry

Apnea is one of the most common neonatal respiratory disorders and consist in pauses in respiratory movements lasting more than 20 seconds. The objective of this study was to determine the characteristics of skin blood flow microcirculation in preterm newborn with frequent apneic events with Laser-Doppler-Flowmetry. We have studied 20 preterm newborns with a mean weight of 1560 g (range 1140 – 2150) and a mean post-conceptional age of 31,2 weeks (range 28 – 33). The laser Doppler skin blood flow was measured during 88 apneic events. The newborns were divided into two different groups: GROUP 1 concerning apneic spells in the first 5 days of life; GROUP 2 concerning apneic events in the same newborns from 6 to 10 days of life. We included in our study only 13 of 20 newborns, in which there were apneic events during both periods. A statistically significant difference (p&lt;0.01) was found considering the percentage reduction of skin blood flow perfusion (SBFP). A remarkable increase of mean SBFP reduction was noted in every newborn older than five days. LDF can assume an important role during apneic events suggesting that the newborn is more capable of contrasting the negative effects of apneic spells, centralizing the circle in favour of vital organs.

Pressure ulcer prevention.

The purpose of this collective review is to outline the predisposing factors in the development of pressure ulcers and to identify a pressure ulcer prevention program. The most frequent sites for pressure ulcers are areas of skin overlying bony prominences. There are four critical factors contributing to the development of pressure ulcers: pressure, shearing forces, friction, and moisture. Pressure is now viewed as the single most important etiologic factor in pressure ulcer formation. Prolonged immobilization, sensory deficit, circulatory disturbances, and poor nutrition have been identified as important risk factors in the development of pressure ulcer formation. Among the clinical assessment scales available, only two, the Braden Scale and Norton Scale, have been tested extensively for reliability and/or validity. The most commonly used risk assessment tools for pressure ulcer formation are computerized pressure monitoring and measurement of laser Doppler skin blood flow. Pressure ulcers can predispose the patient to a variety of complications that include bacteremia, osteomyelitis, squamous cell carcinoma, and sinus tracts. The three components of pressure ulcer prevention that must be considered in any patient include management of incontinence, nutritional support, and pressure relief. The pressure relief program must be individualized for non-weight-bearing individuals as well as those that can bear weight. For those that can not bear weight and passively stand, the RENAISSANCE Mattress Replacement System is recommended for the immobile patient who lies supine on the bed, the stretcher, or operating room table. This alternating pressure system is unique because it has three separate cells that are not interconnected. It is specifically designed so that deflation of each individual cell will reach a ZERO PRESSURE during each alternating pressure cycle. The superiority of this system has been documented by comprehensive clinical studies in which this system has been compared to the standard hospital bed as well as to two other commercially available pressure relief mattresses. The most recent advance in pressure ulcer prevention is the development of the ALTERN8* seating system. This seating system provides regular periods of pressure relief and stimulation of blood flow to skin areas while users are seated. By offering the combination of pressure relief therapy and an increase in blood flow, the ALTERN8* reportedly creates an optimum pressure ulcer healing environment. Foam is the most commonly used material for pressure reduction and pressure ulcer prevention and treatment for the mobile individual. For those immobilized individuals who can achieve a passive standing position, a powered wheelchair that allows the individual to achieve a passive standing position is recommended. The beneficial effects of passive standing have been documented by comprehensive scientific studies. These benefits include reduction of seating pressure, decreased bone demineralization, increased blander pressure, enhanced orthostatic circulatory regulation, reduction in muscular tone, decrease in upper extremity muscle stress, and enhanced functional status in general. In the absence of these dynamic alternating pressure seating systems and mattresses, there are enormous medicolegal implications to the healthcare facility. Because there is not sufficient staff to provide pressure relief to rotate the patient every 2 hours in a hospital setting, with the exception of the intensive care unit, the immobile patient is prone to develop pressure ulcers. The cost of caring for these preventable pressure ulcers may now be as high as 60,000 dollars per patient. The occupational physical strain sustained by nursing personnel in rotating their patients has led to occupational back pain in nurses, a major source of morbidity in the healthcare environment.

COLD PRESSOR TEST DEMONSTRATES RESIDUAL SYMPATHETIC CARDIOVASCULAR ACTIVATION IN FAMILIAL DYSAUTONOMIA

In familial dysautonomia (1713), i.e. Riley‐Day‐syndrome, sympathetic cardiovascular function, as well as afferent temperature and pain mediating neurons, are significantly reduced. Thus, it was questioned if cold pressor test (CPT), which normally enhances sympathetic outflow and induces peripheral vasoconstriction by the activation of thermo‐ and nociceptive system activation, could be used to assess sympathetic function in FD. To evaluate whether CPT can be used to assess sympathetic activation in FD, we performed CPT in 15 FD patients and IS controls. After a 35‐min resting period, participants immersed their right hand and arm up to the elbow into 0‐1°C cold water while we monitored heart rate (HR), respiration, beat‐to‐beat radial artery blood pressure (BP), and laser Doppler skin blood flow (SBF) at the right index finger pulp. From these measurements, heart rate variability parameters were calculated: root mean square of successive differences (RMSSD), coefficient of variation (CV), low and high frequency (LF, HF) power spectra of the electrocardiogram (ECG). All participants perceived cold stimulation and indicated discomfort. In controls, SBF decreased and HR and BP increased rapidly upon CPT. After 60 s, SBF indicated secondary vasodilatation in six controls, BP rise attenuated and HR returned to baseline in all controls. In the patients, SBF remained unchanged, HR and BP increased significantly, but after 50‐60 s of CPT and changes were lower than in controls (p*LT0.05). RMSSD and CV decreased and LF increased significantly only in the controls. We conclude that CPT activates sympathetic HR and BP modulation despite impaired pain and temperature perception in FD patients. BP increase in the presence of almost unchanged SBF might be due to HR increase and to nociceptive arousal and emotionally induced catecholamine release as seen in emotional crises of FD patients. CPT assesses sympathetic cardiovascular responses independently from baroreflex function, which is compromised in FD.

Effects of increased ambient temperature on skin sympathetic nerve activity and core temperature in humans

The strength of sympathetic vasoconstrictor nerve traffic to the skin has an important role in human thermoregulation since it controls heat loss from the skin by constricting or dilating cutaneous blood vessels. This study sought to clarify the time relationship between a reduction of the vasoconstrictor activity induced by elevating the ambient temperature (Ta), and subsequent change of core temperature (Tty). For this purpose, we recorded peroneal skin sympathetic nerve activity (SSNA), laser Doppler skin blood flow, skin and core (tympanic) temperatures in 11 subjects while increasing Ta from 15 to 30°C during ∼30 min. We observed a significant suppression of SSNA 7.7 min after Ta rise with marked interindividual variations. Tty displayed an increase with a peak after 8.2 min followed by a successive decrease, which became significant 14 min after the Ta rise. The rate of decrease of vasoconstrictor SSNA correlated both with the rate of decrease of Tty (P<0.01) and the magnitude of the Tty decrease (P<0.0005). A cross-correlogram between SSNA and Tty showed a peak at 7 min (r=0.52). We conclude that a Ta rise-induced reduction of skin vasoconstrictor nerve traffic leads to a core temperature decrease after 7–8 min.

Cold pressor test demonstrates residual sympathetic cardiovascular activation in familial dysautonomia

In familial dysautonomia (FD), i.e. Riley–Day-syndrome, sympathetic cardiovascular function, as well as afferent temperature and pain mediating neurons, are significantly reduced. Thus, it was questioned if cold pressor test (CPT), which normally enhances sympathetic outflow and induces peripheral vasoconstriction by the activation of thermo- and nociceptive system activation, could be used to assess sympathetic function in FD. To evaluate whether CPT can be used to assess sympathetic activation in FD, we performed CPT in 15 FD patients and 18 controls. After a 35-min resting period, participants immersed their right hand and arm up to the elbow into 0–1 °C cold water while we monitored heart rate (HR), respiration, beat-to-beat radial artery blood pressure (BP), and laser Doppler skin blood flow (SBF) at the right index finger pulp. From these measurements, heart rate variability parameters were calculated: root mean square of successive differences (RMSSD), coefficient of variation (CV), low and high frequency (LF, HF) power spectra of the electrocardiogram (ECG). All participants perceived cold stimulation and indicated discomfort. In controls, SBF decreased and HR and BP increased rapidly upon CPT. After 60 s, SBF indicated secondary vasodilatation in six controls, BP rise attenuated and HR returned to baseline in all controls. In the patients, SBF remained unchanged, HR and BP increased significantly, but after 50–60 s of CPT and changes were lower than in controls ( p<0.05). RMSSD and CV decreased and LF increased significantly only in the controls. We conclude that CPT activates sympathetic HR and BP modulation despite impaired pain and temperature perception in FD patients. BP increase in the presence of almost unchanged SBF might be due to HR increase and to nociceptive arousal and emotionally induced catecholamine release as seen in emotional crises of FD patients. CPT assesses sympathetic cardiovascular responses independently from baroreflex function, which is compromised in FD.

Cold face test demonstrates parasympathetic cardiac dysfunction in familial dysautonomia.

In familial dysautonomia (FD), i.e., Riley-Day syndrome, parasympathetic dysfunction has not been sufficiently evaluated. The cold face test is a noninvasive method of activating trigeminal brain stem cardiovagal and sympathetic pathways and can be performed in patients with limited cooperation. We performed cold face tests in 11 FD patients and 15 controls. For 60 s, cold compresses (0-1 degrees C) were applied to the cheeks and forehead while we monitored heart rate, respiration, beat-to-beat radial artery blood pressure, and laser-Doppler skin blood flow at the first toe pulp. From these measurements heart rate variability parameters were calculated: root mean square of successive differences (RMSSD), coefficient of variation (CV), low- and high-frequency (LF and HF, respectively) power spectra of the electrocardiogram, and the LF transfer function gain between blood pressure and heart rate. All patients perceived cold stimulation and acknowledged discomfort. In controls, heart rate and skin blood flow decreased significantly during cold face test; in patients, both parameters decreased only briefly and not significantly. In controls, blood pressure, RMSSD, CV, and heart rate HF-power spectra increased but remained unchanged in patients. Respiration, as well as heart rate LF power spectra, did not change in either group. In controls, LF transfer function gain between blood pressure and heart rate indicated that bradycardia was not secondary to blood pressure increase. We conclude that the cold face test demonstrated that patients with FD have a reduced cardiac parasympathetic response, which implies efferent parasympathetic dysfunction.

Skin Vasomotor Reflex as a Measure of Depth of Anesthesia

Department of Anesthesiology; Kumamoto University School of Medicine; Kumamoto, Japan;shimoda@kaiju.medic.kumamoto-u.ac.jpIn Reply:-Thank you for the opportunity to comment on the report by Ezri et al. and their very interesting observations. We are gratified with the concept “anesthesia management by evaluating autonomic reactivity,” because it may provide important information regarding the depth of anesthesia, as Dr. Anderson pointed out. [1]Laser-Doppler (LD) flowmetry measures superficial cutaneous microcirculation under the probe, whereas plethysmography evaluates changes in the whole blood volume in the finger. The basic wave in LD skin blood flow wave is coincident with the simultaneously recorded baseline fluctuation in the plethysmographic wave. [2]It has not been confirmed whether a linear, quantitative correlation exists between the amplitude of the skin vasomotor reflex measured by LD flowmetry and the pulse amplitude of the plethysmography. The report of Ezri et al. suggests that the changes in the pulse amplitude of plethysmography may also reflect sympathetically mediated vasomotion. Any progress toward an inexpensive and simpler autonomic monitor will prove to be beneficial to the spread of patient-by-patient-based anesthesia management.Analyses of pulse waves (e.g., arterial blood flow, LD skin blood flow, and plethysmography wave) have a common weak point. For example, anesthesia induction with propofol and anaphylactoid reactions increases the pulse amplitude of the plethysmography and LD skin blood flow. This problem has limited the application of pulse wave analysis in assessing the depth of anesthesia. For reducing this problem, we prefer to evaluate autonomic reactivity using a known quantitative stimulus before anesthesia, surgical procedures, or both, rather than to evaluate the changes in autonomic indicators induced by the procedures.Osamu Shimoda, M.D.Department of Anesthesiology; Kumamoto University School of Medicine; Kumamoto, Japan;shimoda@kaiju.medic.kumamoto-u.ac.jp(Accepted for publication June 18, 1998.)

The Relationship of Laser–Doppler Skin Blood Flow Measurements to the Cutaneous Microvascular Anatomy

The hairless plantar paw surface of the rat shows high skin blood flow with a substantial response to thermal stimulation. This contrasts with hair-covered areas such as the back, where there is much lower basal flow and thermal response. These properties are similar to the differences seen in humans between skin sites which have a high density of arterioles and venules (AV areas) and sites with predominantly nutritive (NUTR) capillary perfusion. However, there has been no previous study of the microvascular anatomy of rodent skin. We used NIH Image, a quantitative imaging program, to count the capillaries, arterioles, and venules in the skin of the plantar paw surface and the back of 14 Wistar–Kyoto rats. We also used laser–Doppler techniques to determine skin blood flow at these sites. We found significantly more vessels per unit area at the paw. There were twice as many capillaries in the paw (19.6 ± 2.4 per mm2) compared to the back (9 ± 1.5 per mm2) (P< 0.001). Similarly, there were three times as many venules (11.8 ± 1.2 per mm2vs 3.48 ± 0.45 per mm2;P< 0.001). The largest difference was in the number of arterioles (7.76 ± 0.74 per mm2vs 0.79 ± 0.13 per mm2at the back;P< 0.001). The greater microvascular density at the paw was reflected in a threefold higher basal blood flow (6.6 ± 0.44 ml/min/100 g) compared to that in the back (1.99 ± 0.07 ml/min/100 g) (P< 0.001). Microvascular volume at the back was 0.14 ± 0.01 × 106RBC/ml in the basal state compared to 0.31 ± 0.01 × 106RBC/ml at the paw. Thus, the increased number of vessels at the paw resulted in a twofold increase in microvascular volume. The plantar paw surface has considerably more vessels than the back. As might be expected, there is a higher proportion of arterioles and venules compared to capillaries at the paw than at the back. Thus, the plantar paw surface is an AV site compared to the back, which is a NUTR site. Although our prior studies have largely assumed that we could use the paw and back as contrast sites comparable to AV and NUTR sites in humans, we have now for the first time conclusively established this fact. The increased microvascular density at the paw results in higher skin blood flow at this site.