Local Thermal Impact on Microcirculation Assessed by Imaging Photoplethysmography (original) (raw)
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Microvascular Research, 2002
We compared the results of skin blood flow (SBF) measurements, obtained simultaneously in adjacent fingertips by laser Doppler flowmetry (LDF) and thermal clearance (TC) probes, having approximately the same spatial and temporal characteristics. Experiments were performed in nine healthy volunteers during rest at room temperature (26 -28°C). A time resolution equal to about a second was achieved by speeding up the response of the thermal measurement circuit by applying the computer simulation software of the MATLAB package. The comparison revealed that the frequency-corrected TC signal correlated well with the multiprobe LDF signal (median correlation coefficient ؍ 0.90, range ؍ 0.84 to 0.96). At the same time the individual slope values of the regression equation ranged from 0.58 to 1.61, revealing the difficulties encountered in obtaining the invariant scaling factor between the TC and LDF measurements. The relationship between the frequency-corrected TC signal and the multiprobe LDF signal was found to be linear in the range of SBF changes of about three-to fourfold. In the case of larger fluctuations in SBF, excessive acceleration at high SBF rates was noted. © 2002 Elsevier Science (USA)
Medical Engineering & Physics, 2001
We compared two different techniques for non-invasive registration of fingertip skin blood flow patterns in 15 healthy volunteers during a rest at room temperature 26-28°C. The large area probes of a two-channel laser Doppler flowmeter (LDF) and an experimental probe of a thermal clearance (TC) instrument provided approximately the same sample volume of the studied tissue. The laser Doppler probes were attached to the pulp of the index (LDF1) and ring (LDF2) fingers, while the TC probe to the pulp of the middle finger. A computer simulation method, provided by the MATLAB package, was introduced to speed up the frequency response of the TC probe. By calculating the correlation coefficients and applying the least squares criterion, we evaluated the similarity of the 3-min samples having time resolution of 1 s. The group-averaged value of the correlation coefficient (median with a 99% confidence interval) for LDF2 versus LDF1 equalled 0.95 (0.92-0.97). After an introduction of the computer-based frequency correction, the correlation coefficient for TC versus LDF1 increased from 0.81 (0.61-0.85) till 0.92 (0.84-0.95), while the root mean squared error between TC and LDF1 diminished by 33% (pϽ0.001).
Contactless Monitoring of Microcirculation Reaction on Local Temperature Changes
Applied Sciences, 2019
Assessment of skin blood flow is an important clinical task which is required to study mechanisms of microcirculation regulation including thermoregulation. Contactless assessment of vasomotor reactivity in response to thermal exposure is currently not available. The aim of this study is to show the applicability of the imaging photoplethysmography (IPPG) method to measure quantitatively the vasomotor response to local thermal exposure. Seventeen healthy subjects aged 23 ± 7 years participated in the study. A warm transparent compress applied to subject’s forehead served as a thermal impact. A custom-made IPPG system operating at green polarized light was used to monitor the subject’s face continuously and simultaneously with skin temperature and electrocardiogram (ECG) recordings. We found that the thermal impact leads to an increase in the amplitude of blood pulsations (BPA) simultaneously with the skin temperature increase. However, a multiple increase in BPA remained after the c...
Microvascular Research, 2012
Objectives: Laser speckle contrast imaging (LSCI) is a novel non-invasive microvascular imaging modality. The present study evaluates the validity and reliability of LSCI by comparison with infrared thermography (IRT) for the dynamic assessment of digital microvascular function in healthy volunteers. Methods: Subjects attended on 3 occasions. Simultaneous assessment of cutaneous perfusion at 3 distinct regions of interest (ROI) within the hands was undertaken using LSCI and infrared thermography (IRT) at baseline, and at 13 s intervals over 15 min following a standardised local cold challenge. Endpoints for evaluation included absolute measurements at baseline and following cold stress, in addition to the characteristics of the re-warming curves (maximum % recovery and maximum gradient). Visits 1 and 2 were undertaken in identical conditions (ambient temperature 23°C) to assess reproducibility, whereas visit 3 was undertaken at a lower ambient room temperature of 18°C to evaluate responsiveness to reduction in ambient room temperature. Results: Fourteen healthy participants completed the study. There was greater variability in the data generated using LSCI compared with the highly damped IRT, reflecting greater sensitivity of LSCI to physiological variation and movement artefact. LSCI and IRT correlated well at baseline and following cold challenge for all endpoints (r s for pooled data between 0.5 and 0.65, p b 0.00005). Reproducibility of both IRT and LSCI was excellent (ICCs N 0.75) for absolute assessments but lower for re-warming curve characteristics. LSCI provides greater spatial resolution than IRT identifying variation in cutaneous perfusion within the hands most likely associated with the presence of arteriovenous anastamoses. Both techniques were responsive to reduction in ambient room temperature. Effect sizes were greatest for IRT than LSCI (e.g. − 1.17 vs. − 0.85 at ROI 1 at baseline) although this may represent heat transfer rather than altered vascular perfusion. Discussion: In the dynamic assessment of digital vascular perfusion, LSCI correlates well with IRT, is reproducible and responsive to reduction in ambient room temperature. Absolute measurements appear preferable to parameters derived from re-warming curve characteristics when assessing digital perfusion following cold challenge. The greater temporal and spatial resolution of LSCI compared with IRT may facilitate the development of novel assessment tools of autonomic function and digital cutaneous perfusion.
Thermography Quantification of Human Perfusion Thermal Signature
Blood perfusion quantification is important vital parameters in different diagnostic procedure, using infrared thermography imaging; it is reliable to use this technique as non-contact, non-invasive blood flow measurement method. Therefore, we developed a measurement protocol for blood flow over the arm's anterior surface. By using the superficial brachial and radial veins to be monitored under the impact of cold-excitation of (2 °C to 5 °C), the blood perfusion signal was detected using thermal imager of long-wave infrared spectral range (LWIR, 7μm - 14 μm). The simulation of Penne's bioheat transfer equation was performed to be compared with results obtained from the infrared thermography. Furthermore, the proposed blood flow monitoring using external adjusting of the excitation temperature, by using (cold-compress, or cold air-stream) applied to the region under testing. The signal detected resembles to the hemodynamic pulse of the superficial veins, in the ...
2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2009
The noninvasive measurement of peripheral vascular reactivity, as an indicator of vascular function, provides a valuable tool for cardiovascular screening of at-risk populations. Practical and economical considerations demand that such a test be low-cost and simple to use. To this end, it is advantageous to substitute digital thermal monitoring (DTM) for the more costly and complex Doppler system commonly used for this measurement. A signal processing model was developed to establish the basis for the relationship between finger temperature reactivity and blood flow reactivity following a transient brachial artery occlusion and reperfusion protocol (reactive hyperemia). Flow velocity signals were acquired from the radial artery of human subjects via an 8 MHz Doppler probe while simultaneous DTM signals were acquired from a distal fingertip via DTM sensors. The model transforms the DTM temperature signals into normalized flow signals via a deconvolution method which employs an exponential impulse function.
The Journal of Hand Surgery, 1993
Isolated cold stress testing applies cold thermal stress to an extremity for noninvasive study of skin surface temperature as an index of digital microcirculation. In this study, laser Doppler fluxmetry was combined with isolated cold stress testing to examine the relationship between digital thermoregulation (measured by isolated cold stress testing) and digital microcirculatory blood flow (measured by laser Doppler fluxmetry) in 50 healthy men and women. After a 5 minute baseline period, both hands were subjected to cold stress (average, 8" C) for 20 minutes and then returned to room temperature for 20 minutes. Digital temperatures and laser Doppler measurements were graphed to document individual responses. The 25 women had lower digital temperatures, lower laser Doppler fluxmetry values, and less average rewarming than the 25 men. Statistical cluster analysis revealed a cold pattern, found predominantly in women, and a warm pattern, found predominantly in men. These patterns of response may help to elucidate the pathogenesis of the vascular occlusive syndromes occurring predominantly in women.
Physiological Measurement, 2012
Using a small, but very instructive experiment, it is demonstrated that laser-Doppler flowmetry (LDF) at large interoptode spacing represents a unique tool for new investigations of thermoregulatory processes modulating the blood flow of small muscle masses in humans. It is shown on five healthy subjects that steady-state values of blood flow (perfusion) in the thenar eminence muscle group depend in
Physiology International, 2020
Microvascular function has been assessed by determining the rhythmic oscillations in blood flow induced by the vasomotion of resistance vessels. Although laser-Doppler flowmetry (LDF) allows simple, non-invasive evaluation of this flow-motion in the cutaneous microcirculation, the temporal and spatial reproducibility of such assessments remains unclear.In the present study, we investigated cutaneous flow-motion in three consecutive years in eight skin regions using LDF in six healthy young volunteers. The characteristic flow-motion frequency was determined using fast-Fourier transformation. Additionally, in two years a more traditional measure of microvascular reactivity, postocclusive reactive hyperemia (PORH) was evoked in the forearm after transient brachial artery occlusion (1–2–3 min) induced by cuff inflation.Well-defined flow-motion was found in six regions showing significant differences in frequency: the highest flow-motion frequency was found in the frontal and temporal re...