Laser Doppler Perfusion Monitoring Research Articles

Repeatability of the evaluation of systemic microvascular endothelial function using laser doppler perfusion monitoring: clinical and statistical implications

OBJECTIVE:An awareness of the repeatability of biological measures is required to properly design and calculate sample sizes for longitudinal interventional studies. We investigated the day-to-day repeatability of measures of systemic microvascular reactivity using laser Doppler perfusion monitoring.METHODS:We performed laser Doppler perfusion monitoring in combination with skin iontophoresis using acetylcholine and sodium nitroprusside as well as post-occlusive reactive and thermal hyperemia twice within two weeks. The repeatability was assessed by calculating the within-subject standard deviations, limits of agreement, typical errors and intra-class correlation coefficients between days 1 and 2. The ratio of the within-subject standard deviation to the mean values obtained on days 1 and 2 (within-subject standard deviation/GM) was used to determine the condition with the best repeatability.RESULTS:Twenty-four healthy subjects, aged 24.6±3.8 years, were recruited. The area under the curve of the vasodilatory response to post-occlusive reactivity showed marked variability (within-subject standard deviation/GM = 0.83), while the area under the curve for acetylcholine exhibited less variability (within-subject standard deviation/GM = 0.52) and was comparable to the responses to sodium nitroprusside and thermal treatment (within-subject standard deviations/GM of 0.67 and 0.56, respectively). The area under the blood flow/time curve for vasodilation during acetylcholine administration required the smallest sample sizes, the area under the blood flow/time curve during post-occlusive reactivity required the largest sample sizes, and the area under the blood flow/time curves of vasodilation induced by sodium nitroprusside and thermal treatment required intermediate sizes.CONCLUSIONS:In view of the importance of random error related to the day-to-day repeatability of laser Doppler perfusion monitoring, we propose an original and robust statistical methodology for use in designing prospective clinical studies.

324 Skin Microcirculation in Healthy Newborns - Assessments of Morphology, Perfusion and Oxygenation

Background and aims: Measurements of central hemodynamics, blood gases and urinary output are commonly used to monitor patients, but values within reference range do not guarantee adequate cellular nutrition and oxygenation. We have examined skin microvascular perfusion, morphology and oxygenation in healthy newborns. Material and Methods: Twenty-five healthy newborns (gestational age >37 weeks) were enrolled within 24 hours after delivery. Skin microvascular assessments were performed day one, two and three, on the chest and the hand, using three different techniques: Computer-assisted video microscopy, CAVM (morphology); Laser Doppler Perfusion Monitoring, LDPM (perfusion); Diffuse Reflectance Spectroscopy, DRS (oxygen saturation of capillary erythrocytes). Results: (Mean with SD) CAVM: Microvascular density (number of microvessels crossing a grid of lines/mm line): Chest: 11.3 (1.5), 11.0 (1.7), 10.7 (1.6). Hand: 13.2 (2.0), 13.2 (1.9), 12.4 (1.6).LDPM: Perfusion (arbitrary units): Chest: 110.4 (32.1), 102.7 (27.8), 100.5 (28.1). Hand: 58.5 (26.2), 55.1 (17.5), 46.6 (14.9).DRS: Microvascular oxygen saturation (%): Chest: 71.9 (7.3), 73.5 (12.2), 74.5 (9.2). Hand: 68.3 (11.5), 63.1 (11.6), 65.5 (11.7). Conclusions: We were able to obtain noninvasive reproducible data for skin microvascular morphology, perfusion and oxygen saturation. The number of skin vessels is fewer in chest than in hand, with a slight reduction from day 1 to day 3. There is higher perfusion in the chest than in the hand, probably due to higher skin temperature (+2.8°). Since all the infants has arterial oxygenation >97%, oxygen extraction in the skin microvessels were approximately 20% in the chest and 30% in the hand.

Sensation evoked by esophageal distension in functional chest pain patients depends on mechanical stress rather than on ischemia

Functional chest pain is commonly reproduced by bag distension in the esophageal body. It is unknown whether such pain is primarily associated with mechanical stress and strain (force-deformation) or with changes in mucosal perfusion. Fourteen patients (6M, 8F, average age 55.9 years) underwent ramp bag distension before and after injection of 20 mg butylscopolamine bromide (BS) using a novel bag catheter incorporating endosonography and laser Doppler perfusion monitoring. Healthy subjects served as controls. Mucosal perfusion was evaluated and stress and strain were computed and related to the sensation. The symptom score increased with bag volume (P < 0.001). Volume as a function of pressure was higher in patients than in controls (P < 0.001), both before and during BS. The stress-strain relationship was exponential and indicated a stiffer esophageal wall in patients especially before BS (P < 0.01). The stress-strain curves indicate increased muscle tone in the functional chest pain patients. The perfusion decreased with increasing symptom score from visual analog scale 1-7 during BS. The decrease was on average 18.9% in patients and 19.7% in controls (P = ns). Multiple regression analysis from distensions during BS showed that the discomfort/pain sensations depended on stress and strain (P < 0.001) and with stress as the largest contributor. Perfusion did not contribute. Pain evoked by bag distension in patients with functional chest pain is stress-dependent rather than dependent on mucosal perfusion. Furthermore, the esophagus of the patients was characterized by more pronounced muscle tone during the distensions.

Mucosal blood flow measurements using laser Doppler perfusion monitoring

Perfusion of individual tissues is a basic physiological process that is necessary to sustain oxygenation and nutrition at a cellular level. Ischemia, or the insufficiency of perfusion, is a common mechanism for tissue death or degeneration, and at a lower threshold, a mechanism for the generation of sensory signalling including pain. It is of considerable interest to study perfusion of peripheral abdominal tissues in a variety of circumstances. Microvascular disease of the abdominal organs has been implicated in the pathogenesis of a variety of disorders, including peptic ulcer disease, inflammatory bowel disease and chest pain. The basic principle of laser Doppler perfusion monitoring (LDPM) is to analyze changes in the spectrum of light reflected from tissues as a response to a beam of monochromatic laser light emitted. It reflects the total local microcirculatory blood perfusion, including perfusion in capillaries, arterioles, venules and shunts. During the last 20-25 years, numerous studies have been performed in different parts of the gastrointestinal (GI) tract using LDPM. In recent years we have developed a multi-modal catheter device which includes a laser Doppler probe, with the intent primarily to investigate patients suffering from functional chest pain of presumed oesophageal origin. Preliminary studies show the feasibility of incorporating LDPM into such catheters for performing physiological studies in the GI tract. LDPM has emerged as a research and clinical tool in preference to other methods; but, it is important to be aware of its limitations and account for them when reporting results.

Time Development Models for Perfusion Provocations Studied with Laser-Doppler Flowmetry, Applied to Iontophoresis and PORH

Clinical acceptance of laser-Doppler perfusion monitoring (LDPM) of microcirculation suffers from lack of quantitatively reliable signal data, due to varying tissue constitution, temperature, hydration, etc. In this article, we show that a novel approach using physiological models for response upon provocations provides quantitatively and clinically relevant time constants. We investigated this for two provocation protocols: postocclusive reactive hyperemia (PORH) and iontophoresis shots, measured with LDPM on extremities. PORH experiments were performed on patients with peripheral arterial occlusive disease (PAOD) or diabetes mellitus (DM), and on healthy controls. Iontophoresis experiments were performed on pre-eclamptic patients and healthy controls. We developed two dynamical physical models, both based on two characteristic time constants: for PORH, an "arterial" and a "capillary" time constant and, for iontophoresis, a "diffusion" and a "decay" time constant. For the different subject groups, we could extract time constants that could probably be related to physiological differences. For iontophoresis, a shot saturation constant was determined, with very different values for different groups and administered drugs. With these models, the dynamics of the provocations can be investigated and quantitative comparisons between experiments and subject groups become available. The models offer a quantifiable standard that is independent of the type of LDPM instrumentation.

Electroacupuncture Induces Differential Effects between Yin and Yang: A Study using Cutaneous Blood Flow and Temperature Recordings of the Hand's Dorsum and Palm

The underlying theory of traditional Chinese Medicine (TCM) considers that Yin and Yang are in the opposition with each other and play different roles in physiological responses. Several studies have reported that electroacupuncture (EA) produces a greater effect than manual acupuncture (MA), and that the effect of EA is similar to transcutaneous electric nerve stimulation (TENS). Therefore, the purpose of the present study was to investigate the differences between Yin and Yang induced by acupuncture. A total of 20 healthy volunteers were studied. The cutaneous blood flow and temperature were recorded by a laser doppler perfusion and temperature monitoring system on the dorsum and palm of the right hand. Four sessions of sham acupuncture (SA), MA, 2 Hz EA, and 2 Hz TENS were bilaterally applied to Zusanli (ST36) and Shangjuxu (ST37) acupoints. Each of the subjects received four sessions in a random manner. The treatment interval was at least three days between sessions in order to prevent overlapping residual effects. Each of the four sessions was divided into pre-acupuncture period (BP), acupuncture period (AP), and post-acupuncture (PP) periods. Each treatment period was 15 min. Results indicated that the cutaneous blood flow recorded from the palm of the hand were greater than that recorded from the dorsum at the pre-acupuncture period; while the difference in the cutaneous temperature from the dorsum of the hand between AP and BP was greater in the 2 Hz EA session than in the SA and MA sessions. In conclusion, the results of the present study were consistent with the underlying theory of TCM that considers the fundamental differences between Yin and Yang.

Activation of Somatosensory Afferents Elicit Changes in Vaginal Blood Flow and the Urethrogenital Reflex Via Autonomic Efferents

We examined the effects of pudendal sensory nerve stimulation and urethral distention on vaginal blood flow and the urethrogenital reflex, and the relationship between somatic and autonomic pathways regulating sexual responses. Distention of the urethra and stimulation of the pudendal sensory nerve were used to evoke changes in vaginal blood flow (laser Doppler perfusion monitoring) and pudendal motor nerve activity in anesthetized, spinally transected female rats. Bilateral cuts of either the pelvic or hypogastric nerve or both autonomic nerves were made, and blood flow and pudendal nerve responses were reexamined. Stimulation of the pudendal sensory nerve or urethral distention elicited consistent increases in vaginal blood flow and rhythmic firing of the pudendal motor nerve. Bilateral cuts of the pelvic plus hypogastric nerves significantly reduced vaginal blood flow responses without altering pudendal motor nerve responses. Pelvic nerve cuts also significantly reduced vaginal blood flow responses. In contrast, hypogastric nerve cuts did not significantly change vaginal blood flow. Bilateral cuts of the pudendal sensory nerve blocked pudendal motor nerve responses but stimulation of the central end evoked vaginal blood flow and pudendal motor nerve responses. Stimulation of the sensory branch of the pudendal nerve elicits vasodilatation of the vagina. The likely mechanism is via activation of spinal pathways that in turn activate pelvic nerve efferents to produced changes in vaginal blood flow. Climatic-like responses (firing of the pudendal motor nerve) occur in response to stimulation of the pudendal sensory nerve and do not require intact pelvic or hypogastric nerves.

Evaluation of microvascular endothelial function in patients with type 1 diabetes using laser-Doppler perfusion monitoring: Which method to choose?

The evaluation of microvascular function is essential in the investigation of the pathophysiology of cardiometabolic diseases [ Struijker-Boudier, H.A. et al., 2007. Evaluation of the microcirculation in hypertension and cardiovascular disease. Eur. Heart J. 28, 2834–2840]. In clinical research and practice, the study of microcirculation is of great value in the assessment of the effects of medical interventions and monitoring disease progression. It is well-known that patients with type 1 and 2 diabetes have microvascular dysfunction that results from numerous factors including hyperglycemia, oxidative stress and insulin resistance [ Schalkwijk, C.G., Stehouwer, C.D., 2005. Vascular complications in diabetes mellitus: the role of endothelial dysfunction. Clin. Sci. (Lond). 109, 143–159]. Moreover, skin microvascular dysfunction in type 1 diabetes precedes symptoms of end-organ microvascular disease [Khan, F. et al., 2000. Impaired skin microvascular function in children, adolescents, and young adults with type 1 diabetes. Diabetes Care 23, 215–220]. In this study, we assessed skin microvascular function of patients with type 1 diabetes using laser-Doppler perfusion monitoring (LDPM) coupled with physiological and pharmacological local vasodilator stimuli.

2,3,7,8-TCDD exposure, endothelial dysfunction and impaired microvascular reactivity

Vascular function was examined in subjects with long-term high level of serum 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) during their follow-up visits. Their earlier mean peak TCDD level at the time of exposure in 1965-1968 was estimated in the range of 3300-74 000 pg/g lipids. Ten former pesticide production workers heavily exposed to TCDD (age 57 +/- 2 years, TCDD about 170 pg/g lipids) were examined in 2001. Extended group of 15 TCDD-exposed men (age 59 +/- 3 years, TCDD about 130 pg/g lipids) underwent the same examination in 2004. Findings were compared with a control group of 14 healthy men (age 54 +/- 2 years). Skin microvascular reactivity (MVR) was measured by laser Doppler perfusion monitoring in the forearm during post-occlusive reactive hyperemia (PORH) and thermal hyperemia (TH). Several parameters of MVR in men exposed to TCDD were significantly impaired, compared with the control group and further progression of the impairment of MVR has been observed between years 2001 and 2004. Serum concentration of E-selectin and inhibitor of tissue plasminogen activator 1 (PAI-1) was significantly higher in exposed subjects (56.0 +/- 18.4 ng/mL versus 40.0 +/- 12.0 ng/mL, P = 0.022 and 90.9 +/- 33.3 ng/mL versus 45.0 +/- 18.0, P = 0.002, respectively). In addition, PORH in the forearm was significantly negatively associated with SOD activity (r = -0.77, P = 0.009) as well as the velocity of perfusion increase during TH (r = -0.68, P = 0.03) and TH% (r = -0.78, P = 0.008). Our data document the presence of endothelial dysfunction in TCDD-exposed men.

Intracerebral Microvascular Measurements during Deep Brain Stimulation Implantation using Laser Doppler Perfusion Monitoring

The aim of the study was to investigate if laser Doppler perfusion monitoring (LDPM) can be used in order to differentiate between gray and white matter and to what extent microvascular perfusion can be recorded in the deep brain structures during stereotactic neurosurgery. An optical probe constructed to fit in the Leksell® Stereotactic System was used for measurements along the trajectory and in the targets (globus pallidus internus, subthalamic nucleus, zona incerta, thalamus) during the implantation of deep brain stimulation leads (n = 22). The total backscattered light intensity (TLI) reflecting the grayness of the tissue, and the microvascular perfusion were captured at 128 sites. Heartbeat-synchronized pulsations were found at all perfusion recordings. In 6 sites the perfusion was more than 6 times higher than the closest neighbor indicating a possible small vessel structure. TLI was significantly higher (p < 0.005) and the perfusion significantly lower (p < 0.005) in positions identified as white matter in the respective MRI batch. The measurements imply that LDPM has the potential to be used as an intracerebral guidance tool.

Laser Doppler perfusion monitoring and imaging: novel approaches

Laser Doppler flowmetry (LDF) is a non invasive method enabling the monitoring of microvascular blood flow, a very important marker of tissue health. This article gives an overview on the concept of LDF for microvascular perfusion monitoring and imaging. It first describes the theoretical background of the technique. Then, the benefits of LDF signal processing are shown through clinical examples: use of time-frequency representations and wavelets. Afterwards, the paper introduces novel approaches of velocity components. For that purpose, a work providing the determination of the velocities relative contribution in physiologically relevant units (mm/s) is presented. Imaging perfusion is also reviewed through methods based on laser speckle. The most prominent disadvantage of the latter devices being the time needed to produce a perfusion image, solutions are proposed in the last part of the paper.

Path-length-resolved optical Doppler perfusion monitoring

We report the first path-length-resolved perfusion measurements on human skin measured with a phase-modulated low-coherence Mach-Zehnder interferometer with spatially separated fibers for illumination and detection. Optical path lengths of Doppler shifted and unshifted light and path-length-dependent Doppler broadening of multiply scattered light from skin are measured from the Doppler broadened interference peaks appearing in the power spectrum. Perfusion and its variations during occlusion are measured in real time for a given optical path length, and the results are compared with the perfusion signal obtained with a conventional laser Doppler perfusion monitor.

Endothelium -dependent and -independent vasodilatation in preeclampsia and HELLP syndrome

PREECLAMPSIA AND HELLP SYNDROME JUDITH BLAAUW, MARIA G. VAN PAMPUS, GERHARD RAKHORST, JAN G. AARNOUDSE, University Medical Center Groningen, Obstetrics and Gynaecology, Groningen, Netherlands, University Medical Center Groningen, Biomedical Engineering, Groningen, Netherlands OBJECTIVE: Systemic vascular dysfunction is thought to play an important role in preeclampsia (PE) and HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome. Vasodilatory reactivity was found to be different in women with PE compared to HELLP syndrome, thereby suggesting different alterations of the vasculature (Fisher et al, AJOG 2000). We studied endothelium-dependent and -independent microvascular reactivity in women with PE, with and without HELLP syndrome. STUDY DESIGN: Skin perfusion, denoted as flux, was measured on the middle finger using laser Doppler perfusion monitoring in 5 pregnant women with PE, in 7 pregnant women with HELLP syndrome, in 12 women with a recent history of PE, and in 13 women with a recent history of HELLP syndrome. Postpartum measurements were performed during a time period of 3-11 months after delivery. Endothelium-dependent and -independent vasodilatation of the skin microcirculation was induced by iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP). Microvascular vasodilatation was calculated as percentage increase from baseline to plateau flux. RESULTS: For both pregnancy and postpartum studies, clinical characteristics such as maternal age, body mass index and blood pressures were similar between the 2 groups. No significant differences in baseline and plateau fluxes, or in ACh-mediated vasodilatation were noticed. Although SNP-mediated vasodilatation in HELLP syndrome during pregnancy was higher, it did not reach statistical significance (table, meanG SEM).

Integrated Optoelectronic Probe Including a Vertical Cavity Surface Emitting Laser for Laser Doppler Perfusion Monitoring

An integrated optoelectronic probe with small dimensions, for direct-contact laser Doppler blood flow monitoring has been realized. A vertical cavity surface emitting laser (VCSEL), and a chip with photodetectors and all necessary electronics are integrated in a miniature probe head connected to a laptop computer. The computer sound processor is utilized for acquisition and digital signal processing of the incoming Doppler signal. In this paper, the design of the laser Doppler perfusion monitor is described and its performance is evaluated. We demonstrate our perfusion monitor to be less sensitive to subject motion than a commercial fiber-optic device. For medium and high perfusion levels, the performance of our integrated probe is comparable to the fiberoptic flowmeter containing a normal edge-emitting laser diode. For very low perfusion levels, the signal-to-noise ratio of the fiber-optic device is higher. This difference can mainly be attributed to the shorter coherence length of the VCSEL compared with the edge-emitting laser diode.

Intraoperative measurement of pharynx/esophagus retraction during anterior cervical surgery. Part II: perfusion

Early postoperative dysphagia after anterior cervical surgery is a well-known phenomenon with so far unknown etiology. We hypothesised that direct pressure induced by the medial retractor blade on pharynx/esophagus mucosal wall leads to local ischemia. Subsequently postoperative hyperemia and swelling of the pharynx/esophagus may result in swallowing disturbance. To prove the hypothesis local blood flow inside the pharynx/esophagus wall during anterior cervical surgery was measured using a laser Doppler (LD) perfusion monitor unit. Fifteen patients underwent standard anterior cervical discectomy and fusion (ACDF). The LD probe was placed underneath the medial retractor blade in order to gain information at the maximum point of pressure applied onto the pharynx/esophagus wall. Local perfusion was measured prior to retractor opening (5 min), during spreading of the retractor and after its closure (5 min). Perfusion was measured semiquantitatively in perfusion units (PU). Local perfusion ranged from 30 to 210 PU (mean 107) prior to retractor opening, from 7 to 60 PU (mean 30) with open retractor and from 15 to 280 PU (mean 117) after retractor closure. In all 15 patients the open retractor led to hypoperfusion ranging from 21 to 93% compared to the baseline level. In seven patients a reactive hyperemia at the end of the procedure was detected (32-89% compared to baseline level). In four patients after hypoperfusion during spreading of the retractor the baseline levels were reached again and in four patients perfusion remained diminished even after retractor closure. To best of our knowledge, this is the first report on intraoperative measurement of local perfusion of the pharynx/esophagus wall during anterior cervical surgery. Diminished local perfusion was observed in all patients during spreading of the retractor and post-procedure hyperemia was recorded in 46% of the patients. The local ischemia of the pharynx/esophagus wall may be a crucial step in the development of postoperative dysphagia.

The influence of wavelength and probe configuration on findings of a skin vasoconstriction test when using laser Doppler perfusion devices

The aim of this study was to establish the degree to which a standardized test based on laser Doppler blood flow measurement is dependent on the particular equipment set-up being used. For this purpose, we examined finger skin blood flow with laser Doppler instruments in 20 healthy subjects. In laser Doppler perfusion monitoring (LDPM), we used a custom-made probe with two detecting fibers placed 0.25 and 1.2 mm from the illuminating fiber, respectively, and two laser Doppler perfusion imagers (LDPI) with a wavelength of 632.8 nm and 780 nm, respectively. Warming of the hand was achieved with a Peltier element, and reflex vasoconstriction was induced by immersing the other hand for 3 min into a water bath kept at 15°C. As a measure for the change in skin blood flow, a vasoconstriction index (VAC: cooling/before cooling) was calculated and used for the comparison of the different devices. VAC values gathered around 0.6 for all devices. However, LDPI with a wavelength of 632.8 nm showed a slightly higher VAC index, and the difference was significant. We conclude that using a standardized test is the most appropriate for monitoring changes in blood flow rather than recording and comparing discrete values in intermittent recordings. Although a difference was noted when comparing the devices, different fiber separations and wavelengths seem then to be of little consequence.

Myocardial perfusion monitoring during coronary artery bypass using an electrocardiogram-triggered laser Doppler technique

Electrocardiogram (ECG)-triggered laser Doppler perfusion monitoring (LDPM) was used to assess myocardial perfusion, with minimum myocardial tissue motion influence, during coronary artery bypass grafting (CABG). Thirteen subjects were investigated at six phases: pre- and post-CABG; post aorta cross-clamping; pre and post left internal mammary artery (LIMA) graft declamping; and post aorta declamping. The perfusion signal was calculated in late systole and late diastole, with expected minimum tissue motion, and compared with arrested heart measurements. Patient conditions or artifacts caused by surgical activity made it impossible to perform and analyse data in all six phases for some patients. No significant (n = 5) difference between perfusion signals pre- and post-CABG was found. Diastolic perfusion signal levels were significantly (p < 0.02) lower compared with systolic levels. After aorta cross-clamping, the signal level was almost zero. A distinct perfusion signal increase after LIMA and aorta declamping, compared with pre-LIMA declamping, was found in ten cases out of 13. A significantly (p < 0.04) lower perfusion signal in the arrested heart compared with in the beating heart was registered. Influence from mechanical ventilation was observed in 14 measurements out of 17. In conclusion, ECG-triggered LDPM can be used to assess myocardial perfusion during CABG. Perfusion signals were lower in the arrested heart compared with in the beating heart and in late diastole compared with late systole. No significant difference between pre- and post-CABG was found.

Clinical microneedle injection of methyl nicotinate: stratum corneum penetration

In recent years, microneedles were proposed as a method to painlessly deliver drugs past the stratum corneum. Microneedles have been fabricated in several designs, but limited studies have tested microneedle injections in humans. In this work, we compare microneedle injections with topical application (TA) to investigate if microneedles enhance in vivo drug delivery past the stratum corneum. In vitro tests were used to measure microneedle pressures and injection volumes. In vivo microneedle injections were performed on the volar forearm of 11 healthy volunteers. Two sets of microneedles, pointed and symmetric, were used to develop microneedle/syringe apparatuses that were used to inject approximately 1 microL of 0.1 M methyl nicotinate, and were compared against TA. A Laser Doppler Perfusion Monitor was used to record maximum blood flow and the time to maximum blood flow at the treatment sites. Pointed and symmetric microneedle-injected sites showed a significantly faster time to maximum blood flow than TA. The pointed microneedle injections also resulted in a higher maximum blood flux. Volunteers reported feeling pressure but no pain from the microneedles during the injections. The microneedles aid in bypassing the stratum corneum and enhance drug delivery through it. The design of the microneedle influences its delivery capabilities, because the pointed microneedles seem to be less susceptible to clogging during the injection.

A Model for Post-Occlusive Reactive Hyperemia as Measured With Laser-Doppler Perfusion Monitoring

To facilitate the quantitative analysis of post-occlusive reactive hyperaemia (PORH), measured with laser-Doppler perfusion monitoring (LDPM) on extremities, we present a flow model for the dynamics of the perfusion of the tissue during PORH, based on three parameters: two time constants (tau1 and tau2) and the ratio of the maximum flux and the resting flux. With these three constants quantitative comparisons between experiments will be possible and, therefore, we propose to adopt this approach as future standard. For this reason, we also developed a computer program to perform the fit of the model to measured data.

How to assess post-occlusive reactive hyperaemia by means of laser Doppler perfusion monitoring: Application of a standardised protocol to patients with peripheral arterial obstructive disease

The standardisation of manoeuvres to perform clinically discriminative microvascular flow reserve tests is still poorly developed, as well as the response analysis. The aim of this study was to establish a reproducible analysis method for the post-occlusive reactive hyperaemia (PORH) test measured using laser Doppler perfusion monitoring (LDPM). LDPM data were measured from the PORH response of 24 Fontaine class II–III peripheral atherosclerotic/arterial obstructive disease (PAOD) patients and 30 healthy subjects. The PORH response was recorded from the dorsum of the foot after 3 min of arterial occlusion at the thigh. The resulting tracings were analysed by describing their morphology through five defined parameters: resting flux (RF), time to RF level ( t RF), maximum flux (MF) during reactive hyperaemia, time to maximum flux ( t MF), and time to half recovery ( t HR). While the time parameters were discriminative between patients and controls, flux parameters were not. The time to resting flux ( t RF) led to the most discriminative model that correctly predicted 88.5% of the cases. Hence, we concluded that obtaining t RF with the presented procedures provides an optimal model to quantify the patient's microvascular condition from the PORH response.