Forehead Skin Blood Flow Research Articles

Prefrontal NIRS signal is unaffected by forehead Doppler flux during incremental cycling exercise.

Near-infrared spectroscopy (NIRS) is used to measure tissue concentrations of oxyhemoglobin (O2 Hb) and deoxyhemoglobin (HHb). In the context of exercise, NIRS confers a higher signal-to-noise ratio than other neuroimaging techniques. However, part of the signal may be influenced by thermoregulatory hyperemia in the superficial cutaneous capillaries of the forehead. The degree to which NIRS signals during exercise reflect cerebral or extracerebral hemodynamic changes is a continuing source of controversy. However, the influence of skin blood flow may be attenuated depending on the NIRS technique (e.g., frequency domain machines with maximal optode separation distances >3.5 cm). The purpose of this study was to compare the changes in forehead skin blood flow and cerebral hemoglobin concentration during incremental exercise versus direct vasodilation of the forehead skin induced by gradual local heating. Thirty participants (12 females, 18 males; age: 20.8 ± 3.2 years; body mass index: 23.8 ± 3.7 kg·m-2 ) participated in the study. Forehead skin blood flow was quantified laser Doppler flux and absolute concentrations of cerebral O2 Hb and HHb were measured by NIRS. Local heating significantly increased the Doppler flux signal across time and these changes were significantly correlated with skin temperature. During incremental exercise, skin temperature, Doppler flux, O2 Hband HHb increased however, the only significant change that was consistently correlated with Doppler flux was skin temperature. Therefore, a significant change in forehead skin blood flow may not significantly the NIRS hemoglobin data, depending on the type of NIRS device used.

Laser Speckle Contrast Imaging-based diagnosis of severe mesenteric traction syndrome: Hemodynamics and prostacyclin - A prospective cohort study.

Today, the diagnosis and grading of mesenteric traction syndrome relies on a subjective assessment of facial flushing. However, this method has several limitations. In this study, Laser Speckle Contrast Imaging and a predefined cut-off value are assessed and validated for the objective identification of severe mesenteric traction syndrome. Severe mesenteric traction syndrome (MTS) is associated with increased postoperative morbidity. The diagnosis is based on an assessment of the developed facial flushing. Today this is performed subjectively, as no objective method exists. One possible objective method is Laser Speckle Contrast Imaging (LSCI), which has been used to show significantly higher facial skin blood flow in patients developing severe MTS. Using these data, a cut-off value has been identified. This study aimed to validate our predefined LSCI cut-off value for identifying severe MTS. A prospective cohort study was performed on patients planned for open esophagectomy or pancreatic surgery from March 2021 to April 2022. All patients underwent continuous measurement of forehead skin blood flow using LSCI during the first hour of surgery. Using the predefined cut-off value, the severity of MTS was graded. In addition, blood samples for prostacyclin (PGI2) analysis and hemodynamics were collected at predefined time points to validate the cut-off value. Sixty patients were included in the study. Using our predefined LSCI cut-off value, 21 (35%) patients were identified as developing severe MTS. These patients were found to have higher concentrations of 6-Keto-PGFaα (p=0.002), lower SVR (p<0.001), lower MAP (p=0.004), and higher CO (p<0.001) 15min into surgery, as compared with patients not developing severe MTS. This study validated our LSCI cut-off value for the objective identification of severe MTS patients as this group developed increased concentrations of PGI2 and more pronounced hemodynamic alterations compared with patients not developing severe MTS.

The effect of a mesenteric traction syndrome on internal carotid artery blood flow

PurposeDuring abdominal surgery, manipulation of internal organs may induce a “mesenteric traction syndrome” (MTS) including a triad of flushing, hypotension, and tachycardia that lasts for approximately 30 min. We evaluated whether MTS affects internal carotid artery blood flow.MethodsThis prospective cohort study included 27 patients aged 65 ± 11 years (mean ± SD) undergoing stomach resection (n = 12), esophageal resection (n = 14), or gastro-entero anastomosis (n = 1) during propofol-remifentanil and thoracic epidural anesthesia. Duplex ultrasound determined internal carotid artery blood flow, laser Doppler flowmetry assessed forehead skin blood flow, and near-infrared spectroscopy determined cerebral oxygenation. Development of MTS was defined by flushing within 60 min after incision.ResultsSeven patients developed MTS 22 [20–26; median (IQR)] min after incision and at that time the change in heart rate (to 87 ± 13 vs. 70 ± 11 bpm; P = 0.0007) and skin blood flow (to 214 (134–269) vs. 84 (59-112 PU; P = 0.0044) was higher in the patients who developed MTS as compared to those who did not, while mean arterial pressure (63 ± 13 vs. 64 ± 14 mmHg; P = 0.1433), cerebral oxygenation (69 ± 9% vs. 63 ± 10%; P = 0.2485), and internal carotid artery flow (225 ± 53 vs. 203 ± 69 ml/min; P = 0.9529) were similar.ConclusionHemodynamic perturbations are observed in some patients in response to manipulation of the viscera, but the development of MTS appears not to influence internal carotid artery flow.Clinical trial registrationhttps://clinicaltrials.gov/ct2/show/NCT02951273?term=NCT02951273&amp;amp;rank=1, identifier: NCT02951273.

Dynamic Exercise Elicits Dissociated Changes Between Tissue Oxygenation and Cerebral Blood Flow in the Prefrontal Cortex: A Study Using NIRS and PET.

Neuronal activity causes changes in both cerebral metabolic rate of oxygen (CMRO2) and cerebral blood flow (CBF). Since the relationship between tissue oxygenation and regional CBF (rCBF) during exercise has not been elucidated, we compared the data obtained using near-infrared spectroscopy (NIRS) and rCBF examined using positron emission tomography (PET). Participants in this study comprised 26 healthy young men. Changes in concentration of oxygenated hemoglobin (ΔO2Hb) and deoxygenated hemoglobin (ΔHHb) in the prefrontal cortex (PFC) were measured using NIRS continuously during a 15-min bout of the constant-load low-intensity cycling exercise (n=14). Under the same protocol as the NIRS study, rCBF was measured using H215O and PET by the autoradiographic method at baseline (Rest) and at 3 min (Ex1) and 13 min (Ex2) after starting exercise (n=12). As systematic factors influenced by exercise, heart rate, end-tidal pressure of carbon dioxide (PETCO2) and blood pressure (BP) were monitored. For each region investigated by NIRS, rCBF was analyzed quantitatively using PET-MRI co-registered standardized images. Despite inter-individual differences, changing patterns of ΔO2Hb and ΔHHb in the PFC were similar between channels. Significant main effects for time point were identified in ΔO2Hb, ΔHHb and changes in rCBF. While rCBF increased from rest, ΔO2Hb was not changed at Ex1. Conversely, rCBF was unchanged from rest but ΔO2Hb was significantly increased at Ex2. Fluctuations of PETCO2 and BP evoked by exercise were not in accordance with changes in ΔO2Hb, ΔHHb and rCBF, while BP may affect the forehead skin blood flow. Given that NIRS data are a mixture of skin and brain effects, our results suggest that CMRO2 may differ between the phases in a bout of dynamic exercise. The present study indicates the utility of NIRS to examine the relationship between CMRO2 and rCBF during exercise.

A mesenteric traction syndrome affects near-infrared spectroscopy evaluated cerebral oxygenation because skin blood flow increases.

During abdominal surgery manipulation of internal organs may induce a "mesenteric traction syndrome" (MTS) including a triad of flushing, hypotension, and tachycardia that lasts for about 30min. We evaluated whether MTS affects near-infrared spectroscopy (NIRS) assessed frontal lobe oxygenation (ScO2) by an increase in forehead skin blood flow (SkBF). The study intended to include 10 patients who developed MTS during pancreaticoduodenectomy and 22 patients were enrolled (age 61 ± 8 years; mean ± SD). NIRS determined ScO2, laser Doppler flowmetry determined SkBF, cardiac output (CO) was evaluated by pulse-contour analysis (Modelflow), and transcranial Doppler assessed middle cerebral artery mean flow velocity (MCA Vmean). MTS was identified by flushing within 60min after start of surgery. MTS developed 20min (12-24; median with range) after the start of surgery and heart rate (78 ± 16 vs. 68 ± 17bpm; P = 0.0032), CO (6.2 ± 1.4 vs. 5.3 ± 1.1L min-1; P = 0.0086), SkBF (98 ± 35 vs. 80 ± 23 PU; P = 0.0271), and ScO2 (71 ± 6 vs. 67 ± 8%; P < 0.0001), but not MCA Vmean (32 ± 8 vs. 32 ± 7; P = 0.1881) were largest in the patients who developed MTS. In some patients undergoing abdominal surgery NIRS-determined ScO2 is at least temporarily affected by an increase in extra-cranial perfusion independent of cerebral blood flow as indicated by MCA Vmean. Thus, NIRS evaluation of ScO2 may overestimate cerebral oxygenation if patients flush during surgery.

Ultrasound tagged near infrared spectroscopy does not detect hyperventilation-induced reduction in cerebral blood flow

Introduction: Continuous non-invasive monitoring of cerebral blood flow (CBF) may be important during anaesthesia and several options are available. We evaluated the CerOx monitor that employs ultrasound tagged near infrared spectroscopy to estimate changes in a CBF index (CFI).Methods: Seven healthy males (age 21–26 years) hyperventilated and were administered phenylephrine to increase mean arterial pressure by 20–30 mmHg. Frontal lobe tissue oxygenation (ScO2) and CFI were obtained using the CerOx and mean blood flow velocity in the middle cerebral artery (MCAvmean) was determined by transcranial Doppler. Blood flow in the internal and external carotid artery (ICAf and ECAf) was determined using duplex ultrasonography and forehead skin blood flow (SkBF) and oxygenation (SskinO2) by laser Doppler and white light spectroscopy.Results: During hyperventilation MCAvmean and ICAf decreased by 44% (median; interquartile range 40–49; p = 0.016) and 46% (40–53; p = 0.03), respectively. Conversely, CFI increased by 9% (2–31; p = 0.016), while no significant change was observed in ScO2. SkBF increased by 19% (9–53; p = 0.016) and SskinO2 by 6% (1–7; p = 0.047), although ECAf was unchanged. Administration of phenylephrine was not associated with any changes in MCAvmean, ICAf, ECAf, ScO2, SkBF, SskinO2, or CFI.Conclusion: The CerOx was able to detect a stable CBF during administration of phenylephrine. However, during hyperventilation MCAvmean and ICAf decreased while CFI increased, likely due to an increase in superficial tissue oxygenation. Thus, CFI does not provide an unbiased evaluation of changes in CBF.

Augmented supraorbital skin sympathetic nerve activity responses to symptom trigger events in rosacea patients.

Facial flushing in rosacea is often induced by trigger events. However, trigger causation mechanisms are currently unclear. This study tested the central hypothesis that rosacea causes sympathetic and axon reflex-mediated alterations resulting in trigger-induced symptomatology. Twenty rosacea patients and age/sex-matched controls participated in one or a combination of symptom triggering stressors. In protocol 1, forehead skin sympathetic nerve activity (SSNA; supraorbital microneurography) was measured during sympathoexcitatory mental (2-min serial subtraction of novel numbers) and physical (2-min isometric handgrip) stress. In protocol 2, forehead skin blood flow (laser-Doppler flowmetry) and transepithelial water loss/sweat rate (capacitance hygrometry) were measured during sympathoexcitatory heat stress (whole body heating by perfusing 50°C water through a tube-lined suit). In protocol 3, cheek, forehead, forearm, and palm skin blood flow were measured during nonpainful local heating to induce axon reflex vasodilation. Heart rate (HR) and mean arterial pressure (MAP) were recorded via finger photoplethysmography to calculate cutaneous vascular conductance (CVC; flux·100/MAP). Higher patient transepithelial water loss was observed (rosacea 0.20 ± 0.02 vs. control 0.10 ± 0.01 mg·cm(-2)·min(-1), P < 0.05). HR and MAP changes were not different between groups during sympathoexcitatory stressors or local heating. SSNA during early mental (32 ± 9 and 9 ± 4% increase) and physical (25 ± 4 and 5 ± 1% increase, rosacea and controls, respectively) stress was augmented in rosacea (both P < 0.05). Heat stress induced more rapid sweating and cutaneous vasodilation onset in rosacea compared with controls. No axon reflex vasodilation differences were observed between groups. These data indicate that rosacea affects SSNA and that hyperresponsiveness to trigger events appears to have a sympathetic component.

A Decrease in Spatially Resolved Near-Infrared Spectroscopy-Determined Frontal Lobe Tissue Oxygenation by Phenylephrine Reflects Reduced Skin Blood Flow

Spatially resolved near-infrared spectroscopy-determined frontal lobe tissue oxygenation (ScO2) is reduced with administration of phenylephrine, while cerebral blood flow may remain unaffected. We hypothesized that extracranial vasoconstriction explains the effect of phenylephrine on ScO2. We measured ScO2 and internal and external carotid as well as vertebral artery blood flow in 7 volunteers (25 [SD 4] years) by duplex ultrasonography during IV infusion of phenylephrine, together with middle cerebral artery mean blood velocity, forehead skin blood flow, and mean arterial blood pressure. During phenylephrine infusion, mean arterial blood pressure increased, while ScO2 decreased by -19% ± 3% (mean ± SE; P = 0.0005). External carotid artery (-27.5% ± 3.0%) and skin blood flow (-25.4% ± 7.8%) decreased in response to phenylephrine administration, and there was a relationship between ScO2 and forehead skin blood flow (Pearson r = 0.55, P = 0.042, 95% confidence interval [CI], = 0.025-0.84; Spearman r = 0.81, P < 0.001, 95% CI, 0.49-0.94) and external carotid artery conductance (Pearson r = 0.62, P = 0.019, 95% CI, 0.13 to 0.86; Spearman r = 0.64, P = 0.012, 95% CI, 0.17-0.88). These findings suggest that a phenylephrine-induced decrease in ScO2, as determined by INVOS-4100 near-infrared spectroscopy, reflects vasoconstriction in the extracranial vasculature rather than a decrease in cerebral oxygenation.

Skin blood flow influences cerebral oxygenation measured by near-infrared spectroscopy during dynamic exercise

Near-infrared spectroscopy (NIRS) is widely used to investigate cerebral oxygenation and/or neural activation during physiological conditions such as exercise. However, NIRS-determined cerebral oxygenated hemoglobin (O2Hb) may not necessarily correspond to intracranial blood flow during dynamic exercise. To determine the selectivity of NIRS to assess cerebral oxygenation and neural activation during exercise, we examined the influence of changes in forehead skin blood flow (SkBF(head)) on NIRS signals during dynamic exercise. In ten healthy men (age: 20 ± 1 years), middle cerebral artery blood flow velocity (MCA V mean, via transcranial Doppler ultrasonography), SkBF(head) (via laser Doppler flowmetry), and cerebral O2Hb (via NIRS) were continuously measured. Each subject performed 60 % maximum heart rate moderate-intensity steady-state cycling exercise. To manipulate SkBF(head), facial cooling using a mist of cold water (~4 °C) was applied for 3 min during steady-state cycling. MCA V mean significantly increased during exercise and remained unchanged with facial cooling. O2Hb and SkBF(head) were also significantly increased during exercise; however, both of these signals were lowered with facial cooling and returned to pre-cooling values with the removal of facial cooling. The changes in O2Hb correlated significantly with the relative percent changes in SkBF(head) in each individual (r = 0.71-0.99). These findings suggest that during dynamic exercise NIRS-derived O2Hb signal can be influenced by thermoregulatory changes in SkBF(head) and therefore, may not be completely reflective of cerebral oxygenation or neural activation.

Brachial and middle cerebral artery blood flow responses during sinusoidal leg cycling exercise

To examine the control of peripheral circulation to non‐active muscle and brain during leg cycling exercise, we measured the dynamics of brachial artery (BA) and middle cerebral artery (MCA) blood flow (BF) to sinusoidal (sine) work rate (WR) forcing. Nine healthy subjects performed upright leg cycle exercise with a constant WR for 30 min followed by 16‐min sine WR exercises of 4‐min period fluctuated between 20 W to 60% VO2max. During protocol, we measured pulmonary gas exchange [breath‐by‐breath], heart rate (HR) and mean arterial blood pressure (MAP) [Photoplethysmograph], blood velocity (BV) and cross sectional area of BA [Ultrasound Pulsed‐Doppler], BV of MCA [Transcranial Doppler Ultrasonograph], and forearm and forehead skin BF (SBF) [Laser Doppler] and sweating rate (SR) [Capacitance Hygrometry]. The variable was fitted as y(t)=M+A*sin((2π/T)*t‐θ), where t: time, A/M: relative amplitude, T: period, θ: phase shift. Almost variables traced the sine wave adequately. The phase of variables regarding O2‐transport such as VO2, HR followed sine WR with similar delays (the mean: VO2; 51, HR; 45 °). While the BV in MCA showed the similar phase (73 °), its A/M was small (4.5 %). Contrarily, the response of BA displayed an anti‐phase (175 °) and a large A/M (30 %). The peripheral circulatory responses to nonactive limb and brain is quite different. (Support: JSPS‐KAKENHI, 22370091, 23650390, 24700701, 24247046)

Augmented supraorbital skin sympathetic nerve activity responses to symptom trigger events in rosacea patients

To investigate if rosacea alters skin sympathetic nerve activity (SSNA) and end‐organ responses, 12 patients and age‐ and sex‐matched controls underwent 2 symptom triggering stressors (mental and physical stress). Subjects performed 2‐min mental arithmetic and 2‐min isometric handgrip (35% of maximal voluntary contraction). SSNA (supraorbital microneurography), forehead skin blood flow (laser‐Doppler flowmetry), and forehead sweat rate (capacitance hygrometry) were measured. Heart rate and mean arterial pressure (MAP) were recorded via finger photoplethysmography. Cutaneous vascular conductance (CVC) was calculated by flux/MAP, and SSNA was normalized to baseline. Heart rate and MAP changes from baseline were not different between patients and controls during either stressor. Rosacea patients showed higher baseline sweat rate than controls (0.20±0.02 vs. 0.10±0.02 mg/cm2/min, p&gt;0.05), and CVC trended higher compared to controls. SSNA during mental stress was higher in patients compared to controls (39±12% vs. 9±3%, p&gt;0.05); similar augmented SSNA responses were observed during handgrip (rosacea = 31±13% and controls = 2±1%, p&gt;0.05). These data identify trigger induced hyper‐responsiveness of sympathetic outflow in the face of rosacea patients and thus may be part of the etiology of the disease.Funded by a grant from the National Rosacea Society.

An evaluation of the role of skin temperature during heat adaptation.

This project sought to evaluate the importance of skin temperature during heat acclimation, using an isothermal-strain model. Two groups of seven matched males, participated (1 h per day, 10 days) in one of two conditions: (i) temperate physical training (TEMP: 22.4 +/- 0.7 degrees C, relative humidity (r.h.) 41.0 +/- 0.9%); or (ii) combined physical training and heat acclimation (HEAT: 38.2 +/- 0.7 degrees C, r.h. 39.7 +/- 1.3%). Isothermal strain was induced in both groups by rapidly elevating rectal temperature by 1 degree C (cycling), then holding it constant by manipulating external work. Subjects completed two three-phase heat stress tests (39.8 +/- 0.1 degrees C, r.h. 38.6 +/- 1.2), consisting of 20 min rest, then 20 min cycling at each of 30% and 45% of peak power, before and after each regimen. While there was a difference of 4.2 degrees C in mean skin temperature between treatments, both regimens elicited a similar peripheral sudomotor increase, indicating a core temperature dependent adaptation. However, based on significant pre- vs. post-acclimation decreases in average auditory canal temperature (0.4 +/- 0.1 degree C), average forehead skin blood flow (26%), average perceived exertion (11%), and a 5% increase in average forehead sweat rate (0.1 +/- 0.04 mg cm-2 min-1), the HEAT regimen elicited a more complete acclimation. While elevation in core temperature is critical to acclimation, it also appears necessary to expose subjects to an external thermal stress. This observation has not been previously demonstrated under conditions of isothermal strain, and verifies the importance of skin temperature elevation in the acclimation process.

Skin blood flow oscillations respond more effectively to rhythmic thermal stimulation than to continuous or periodic breathing in newborn infants.

Effect of continuous (n = 30) and periodic (n = 5) breathing on forehead skin blood flow (SBF) oscillations was studied in healthy 3-day-old preterm and term infants. Femoral SBF was measured in 10 of the term infants during continuous breathing. Respiratory and SBF signals were analysed by power spectrum during the control period. The signal analysis was repeated during rhythmic thermal stimulation which was applied to the skin of each infant in order to synchronise spontaneous SBF oscillations. During the control period, the forehead and femoral SBF of all the studied infants oscillated at frequencies corresponding to the frequency of regular continuous breathing. External thermal stimulation decreased these high-frequency oscillations of forehead SBF in both preterm and term infants. Oscillations in femoral SBF of term infants remained unchanged. During periodic breathing, the spontaneous forehead SBF oscillation was synchronised to the frequency of respiratory amplitude variation. Despite periodic breathing, thermal stimulation was able to resynchronise the SBF oscillation to the stimulation frequency in 4/5 infants. Forehead SBF oscillates at the frequency of both continuous and periodic breathing in preterm as well as in term infants on postnatal day 3. Rhythmic thermal stimulation synchronises SBF and affects SBF more effectively than continuous or periodic breathing. These results suggest functional neural control of cutaneous vasculature at birth.

Physical dilatation of the nostrils lowers the thermal strain of exercising humans.

Increased nasal air flow during exercise was examined as a possible heat loss avenue contributing to selective brain cooling in hyperthermic humans. On 2 separate days, eight subjects [mean (SE) age, 26.4 (1.2) years] exercised on a cycle ergometer in a warm room [28 (0.2) degrees C; 28 (5)% relative humidity] to induce a moderate level of hyperthermia. In one session the nostrils were physically dilatated [average dilatation 1.55 (0.17) times] and in the other they were not (control). Both sessions started with a 5-min resting period; then subjects pedaled at 60 W for 5 min, 100 W for 15 min, and 150 W for 20 min. During dilatation both tympanic temperature (Tty) and forehead skin blood flow, estimated by laser doppler velocimetry, were significantly lower than during the control exercise of 150 W. Rates of increase of Tty during the 100-W exercise were the same in both conditions; however, during the 150-W exercise with dilatated nostrils Tty increased at a rate significantly lower than during control [1.1 (0.3) degrees C.h-1 vs 1.5 (0.4) degrees C.h-1]. The change in the rate of increase of Tty between conditions was significantly correlated to the degree of nostril dilatation (r = -0.77, P = 0.02), suggesting that the lower Tty observed was due to nostril dilatation. Facial skin temperature was not significantly different between sessions. The results suggest that the nasal cavity may act as a heat exchanger in selective brain cooling of exercising humans.

Effect of dialysis on the power spectra of heart rate, blood pressure and forehead skin blood flow in patients with chronic renal failure

Effect of dialysis on the power spectra of heart rate, blood pressure and forehead skin blood flow in patients with chronic renal failure

Skin blood flow changes, measured by laser Doppler flowmetry, in the first week after birth

Changes in forehead skin blood flow were determined in 17 healthy, term newborns, using a fiberless diode laser Doppler flow meter (Diodopp). Measurements were carried out three times on each infant, at postnatal ages of 16.8 ± 7.4 h, 58.9 ± 6.2 h and 121.5 ± 14.2 h (mean ± S.D.), respectively. Skin blood flow, respiration, heart rate and skin temperature were recorded simultaneously, while the newborns were asleep. During the recordings, the behavioural state of the newborns was observed and environmental temperature and humidity were kept constant. Postocclusive hyperaemia of the skin blood flow was obtained by pressing the laser Doppler probe against the skull for 30 or 60 s. The following parameters changed significantly between the first and third measurements (t-test for paired samples): the basal skin blood flow during active and quiet sleep decreased, the average decrease being 29.4% ( P = 0.002) and 25.9% ( P = 0.01), respectively; skin blood flow during postocclusive hyperaemia also changed: the time taken to reach maximum hyperaemia increased from 17.3 to 22.7 s ( P = 0.01), while the halftime recovery increased from 46.1 to 57.1 s ( P = 0.02). The changes in skin blood flow between the first and second measurements and between the second and third measurements did not reach the level of statistical significance.

Forehead skin blood flow in normal neonates during active and quiet sleep, measured with a diode laser Doppler instrument.

Changes in forehead skin blood flow during active and quiet sleep were determined in 16 healthy neonates using a recently developed semi-conductor laser Doppler flow meter with-out light conducting fibres. Measurements were carried out at a postnatal age varying from 5 hours to 7 days. The two sleep states could be distinguished in 17 recordings. The mean skin blood flow values during active sleep were significantly higher (p less than 0.01) than those during quiet sleep, the mean increase being 28.1%. The variability of the flow signal, expressed as the coefficient of variation, changed significantly from 23.1% during active sleep to 18.2% during quiet sleep.

Drug- and temperature-induced changes in peripheral circulation measured by laser-Doppler flowmetry and digital-pulse plethysmography.

We measured the effects of a new transdermal nitroglycerin patch (25 mg, 10 cm2) applied for 24 h, norphenephrine (6 mg), prazosin (1 mg) as well as local heat and cold provocation on blood pressure, heart rate, skin blood flow (measured by laser-Doppler flowmetry, L-D) and peripheral arterial resistance (assessed by digital pulse plethysmography, D-P) in 15 healthy volunteers (aged 21-31 years). Heat provocation induced a three-fold increase in skin blood flow in the hand (p less than 0.001) and cold provocation a decrease in flow (p less than 0.05) of about 20%. Forehead skin blood flow did not change. Peripheral arterial resistance showed less consistent changes during the provocation tests. Prazosin increased the forehead skin blood flow (p less than 0.01) and decreased peripheral arterial resistance, while norphenephrine showed an opposite effect. Transdermal nitroglycerin induced an increase of 25% in forehead skin blood flow (p less than 0.05) which persisted for 24 h and a decrease in peripheral arterial resistance (p less than 0.02), but this effect was evident up to 8 h only. We conclude that (1) local heat and cold provocation mainly affected skin blood flow, (2) vasodilative and vasoconstrictive drugs showed marked changes in peripheral arterial resistance, but at different points in time from subject to subject, and (3) transdermal nitroglycerin patches induced haemodynamic changes persisting for up to 8-24 h.