Displaying all 11 publications

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  1. Cheng RW, Yusof F, Tsui E, Jong M, Duffin J, Flanagan JG, et al.
    J Physiol, 2016 Feb 01;594(3):625-40.
    PMID: 26607393 DOI: 10.1113/JP271182
    KEY POINTS: Vascular reactivity, the response of the vessels to a vasoactive stimulus such as hypoxia and hyperoxia, can be used to assess the vascular range of adjustment in which the vessels are able to compensate for changes in PO2. Previous studies in the retina have not accurately quantified retinal vascular responses and precisely targeted multiple PaO2 stimuli at the same time as controlling the level of carbon dioxide, thus precluding them from modelling the relationship between retinal blood flow and oxygen. The present study modelled the relationship between retinal blood flow and PaO2, showing them to be a combined linear and hyperbolic function. This model demonstrates that the resting tonus of the vessels is at the mid-point and that they have great vascular range of adjustment, compensating for decreases in oxygen above a PETCO2 of 32-37 mmHg but being limited below this threshold. Retinal blood flow (RBF) increases in response to a reduction in oxygen (hypoxia) but decreases in response to increased oxygen (hyperoxia). However, the relationship between blood flow and the arterial partial pressure of oxygen has not been quantified and modelled in the retina, particularly in the vascular reserve and resting tonus of the vessels. The present study aimed to determine the limitations of the retinal vasculature by modelling the relationship between RBF and oxygen. Retinal vascular responses were measured in 13 subjects for eight different blood gas conditions, with the end-tidal partial pressure of oxygen (PETCO2) ranging from 40-500 mmHg. Retinal vascular response measurements were repeated twice; using the Canon laser blood flowmeter (Canon Inc., Tokyo, Japan) during the first visit and using Doppler spectral domain optical coherence tomography during the second visit. We determined that the relationship between RBF and PaO2 can be modelled as a combination of hyperbolic and linear functions. We concluded that RBF compensated for decreases in arterial oxygen content for all stages of hypoxia used in the present study but can no longer compensate below a PETCO2 of 32-37 mmHg. These vessels have a great vascular range of adjustment, increasing diameter (8.5% arteriolar and 21% total venous area) with hypoxia (40 mmHg P ETC O2; P < 0.001) and decreasing diameter (6.9% arteriolar and 23% total venous area) with hyperoxia (500 mmHg PETCO2; P < 0.001) to the same extent. This indicates that the resting tonus is near the mid-point of the adjustment ranges at resting PaO2 where sensitivity is maximum.
    Matched MeSH terms: Regional Blood Flow/physiology*
  2. Tayyari F, Yusof F, Vymyslicky M, Tan O, Huang D, Flanagan JG, et al.
    Invest Ophthalmol Vis Sci, 2014 Dec;55(12):7716-25.
    PMID: 25335983 DOI: 10.1167/iovs.14-14430
    The purpose of this study was to determine the within-session variability and between-session repeatability of spectral Fourier-domain optical coherence tomography (Doppler FD-OCT) Doppler retinal blood flow measurements in young and elderly subjects.
    Matched MeSH terms: Regional Blood Flow/physiology
  3. Tee GB, Rasool AH, Halim AS, Rahman AR
    J Pharmacol Toxicol Methods, 2004 Jul-Aug;50(1):73-8.
    PMID: 15233971 DOI: 10.1016/j.vascn.2004.02.002
    Human postocclusive forearm skin reactive hyperemia is not only a potential means of identifying early signs of cardiovascular diseases, it can also be used in the assessment of local microvascular response to topically applied compounds on skin. The method is not fully characterized. In this study, we investigated the influence of occlusion time on postocclusive forearm skin reactive hyperemia using laser Doppler fluximetry (LDF).
    Matched MeSH terms: Regional Blood Flow/physiology
  4. Ismail A, Chen HC, Faye I, Tang TB
    Sci Rep, 2020 09 28;10(1):15829.
    PMID: 32985560 DOI: 10.1038/s41598-020-72556-9
    Real-time impairment of ocular blood flow (OBF) under common carotid artery stenosis (CCAS) has not been ascertained. We aimed to longitudinally assess the impact of CCAS on OBF using a rabbit model. About 75% stenosis was created by tying the common carotid artery with a plastic mandrel using a nylon suture. The plastic mandrel was gently removed, leaving a ligature. Neurological and behavioral assessments were recorded as the clinical indicator of stroke severity. With laser speckle flowgraphy, the pulse waveform parameters namely mean blur rate (MBR), blowout score (BOS), blowout time (BOT), rising rate, S1-area, falling rate (FR), S2-area, flow acceleration index (FAI), acceleration time index, resistive index (RI) and the difference between the maximum and minimum values of MBR (AC) were assessed in overall, vessel, and tissue regions of the optic nerve head (ONH). Longitudinally, BOS significantly increased until day 19 post-surgery, whereas FAI, RI, and AC significantly decreased. Beyond day 19, BOS, BOT, FR, FAI, RI, and AC significantly decreased. We defined two stages representing impaired vessel conditions, namely the vessel resistance phase, where BOS increases and FAI, RI, and AC decrease, and the vessel elasticity phase where BOS, BOT, FR, FAI, RI and AC decrease. These stages provide information about atherosclerosis, assessable non-invasively through the eye.
    Matched MeSH terms: Regional Blood Flow/physiology
  5. Alsemiry RD, Sarifuddin, Mandal PK, Sayed HM, Amin N
    Biomed Res Int, 2020;2020:7609562.
    PMID: 32090110 DOI: 10.1155/2020/7609562
    The simultaneous effect of flexible wall and multiple stenoses on the flow and mass transfer of blood is investigated through numerical computation and simulations. The solution is obtained using the Marker and Cell technique on an axisymmetric model of Newtonian blood flow. The results compare favorably with physical observations where the pulsatile boundary condition and double stenoses result in a higher pressure drop across the stenoses. The streamlines, the iso-concentration lines, the Sherwood number, and the mass concentration variations along the entire wall segment provide a comprehensive analysis of the mass transport characteristics. The double stenoses and pulsatile inlet conditions increase the number of recirculation regions and effect a higher mass transfer rate at the throat, whereby more mass is expected to accumulate and cause further stenosis.
    Matched MeSH terms: Regional Blood Flow/physiology*
  6. Yapp JH, Raja Ahmad RMK, Mahmud R, Mohtarrudin N, Mohamad Yusof L, Abdul Rahim E, et al.
    Wound Repair Regen, 2019 05;27(3):225-234.
    PMID: 30667138 DOI: 10.1111/wrr.12698
    Frequent repositioning is important to prevent pressure ulcer (PU) development, by relieving pressure and recovering damages on skin areas induced by repetitive loading. Although repositioning is the gold standard to prevent PU, there is currently no strategy for determining tissue condition under preventive approaches. In this study, the peak reactive hyperemia (RH) trends and ultrasonographic (US) features are compared with the tissue condition under histopathological examination to determine the potential use of these features in determining the tissue condition noninvasively. Twenty-one male Sprague-Dawley rats (seven per group), with body weight of 385-485 g, were categorized into three groups and subjected to different recovery times, each with three repetitive loading cycles at skin tissues above of right trochanter area. The first, second, and third groups were subjected to short (3 minutes), moderate (10 minutes), and prolonged (40 minutes) recovery, respectively, while applying fixed loading time and pressure (10 minutes and 50 mmHg, respectively), to provide different degree of recovery and tissue conditions (tissue damage and tissue recovery). Peak RH was measured in the three cycles to determine RH trend (increasing, decreasing, and inconsistent). All rat tissues were evaluated using ultrasound at pre- and post-experiment and rated by two raters to categorize the severity of tissue changes (no, mild, moderate, and severe). The tissue condition was also evaluated using histopathological examination to distinguish between normal and abnormal tissues. Most of the samples with increasing RH trend is related to abnormal tissue (71%); while inconsistent RH trends is more related to normal tissue (82%). There is no relationship between the tissue conditions evaluated under ultrasonographic and histopathological examination. Peak RH trend over repetitive loading may serve as a new feature for determining the tissue condition that leading to pressure ulcer.
    Matched MeSH terms: Regional Blood Flow/physiology*
  7. Ismail A, Bhatti MS, Faye I, Lu CK, Laude A, Tang TB
    Graefes Arch Clin Exp Ophthalmol, 2018 Sep;256(9):1711-1721.
    PMID: 29876732 DOI: 10.1007/s00417-018-4030-9
    PURPOSE: To evaluate and compare the temporal changes in pulse waveform parameters of ocular blood flow (OBF) between non-habitual and habitual groups due to caffeine intake.

    METHOD: This study was conducted on 19 healthy subjects (non-habitual 8; habitual 11), non-smoking and between 21 and 30 years of age. Using laser speckle flowgraphy (LSFG), three areas of optical nerve head were analyzed which are vessel, tissue, and overall, each with ten pulse waveform parameters, namely mean blur rate (MBR), fluctuation, skew, blowout score (BOS), blowout time (BOT), rising rate, falling rate, flow acceleration index (FAI), acceleration time index (ATI), and resistive index (RI). Two-way mixed ANOVA was used to determine the difference between every two groups where p 

    Matched MeSH terms: Regional Blood Flow/physiology
  8. Yapp JH, Kamil R, Rozi M, Mohtarrudin N, Loqman MY, Ezamin AR, et al.
    J Tissue Viability, 2017 Aug;26(3):196-201.
    PMID: 28438463 DOI: 10.1016/j.jtv.2017.03.002
    Tissue recovery is important in preventing tissue deterioration, which is induced by pressure and may lead to pressure ulcers (PU). Reactive hyperaemia (RH) is an indicator used to identify people at risk of PU. In this study, the effect of different recovery times on RH trend is investigated during repetitive loading. Twenty-one male Sprague-Dawley rats (seven per group), with body weight of 385-485 g, were categorised into three groups and subjected to different recovery times with three repetitive loading cycles. The first, second, and third groups were subjected to short (3 min), moderate (10 min), and prolonged (40 min) recovery, respectively, while fixed loading time and pressure (10 min and 50 mmHg, respectively). Peak hyperaemia was measured in the three cycles to determine trends associated with different recovery times. Three RH trends (increasing, decreasing, and inconsistent) were observed. As the recovery time is increased (3 min vs. 10 min vs. 40 min), the number of samples with increasing RH trend decreases (57% vs. 29% vs. 14%) and the number of samples with inconsistent RH trend increases (29% vs. 57% vs. 72%). All groups consists of one sample with decreasing RH trend (14%). Results confirm that different recovery times affect the RH trend during repetitive loading. The RH trend may be used to determine the sufficient recovery time of an individual to avoid PU development.
    Matched MeSH terms: Regional Blood Flow/physiology*
  9. Munajat I, Yoysefi M, Nik Mahdi NM
    Foot (Edinb), 2017 Aug;32:30-34.
    PMID: 28672132 DOI: 10.1016/j.foot.2017.05.003
    BACKGROUND: Arterial deficiency in congenital clubfoot or congenital talipes equinovarus (CTEV) was postulated as either the primary cause of deformity or secondary manifestation of other bony and soft tissue abnormalities. The objectives of the study were to find any association between arterial deficiency with severity of CTEV and its treatment.

    METHOD: This prospective study conducted on 24 feet with CTEV (18 babies) with Pirani score ranging between 2 to 6. Eighteen normal babies (36 feet) were selected as control. We used Color Doppler Ultrasound to assess dorsalis pedis and posterior tibial arteries before initiating the treatment. Second ultrasound was performed in study group upon completion of Ponseti treatment.

    RESULTS: The patients were from one week to 15 weeks of life. Dorsalis pedis arterial flows were absent in 7 clubfeet (29.1%) while the remaining 17 clubfeet (70.8%) had normal flow. There was a significant association between Pirani severity score and vascular status in congenital clubfoot. There was a higher proportion of clubfeet having abnormal vascularity when the Pirani severity score was 5 and more. In study group, posterior tibial arteries were detectable and patent in all feet. All normal feet in control group had normal arterial flow. There was a significant difference in vascular flow before and after the Ponseti treatment (p 0.031).

    CONCLUSION: The study concludes that there is an association between Pirani severity score and arterial deficiency in CTEV. Ponseti treatment is safe in CTEV with arterial deficiency and able to reconstitute the arterial flow in majority of cases.

    Matched MeSH terms: Regional Blood Flow/physiology
  10. Shariati NH, Zahedi E, Jajai HM
    Physiol Meas, 2008 Mar;29(3):365-74.
    PMID: 18367811 DOI: 10.1088/0967-3334/29/3/007
    Bilateral PPG signals have been used for comparative study of two groups of healthy (free from any cardiovascular risk factors) and diabetic (as cardiovascular disease risk group) subjects in the age-matched range 40-50 years. The peripheral blood pulsations were recorded simultaneously from right and left index fingers for 90 s. Pulses have been modeled with the ARX440 model in the interval of 300 sample points with 100 sample points overlap between segments. Model parameters of three segments based on the highest fitness (higher than 80%) of modeled segments were retained for each subject. Subsequently, principal component analysis (PCA) was applied to the parameters of retained segments to eliminate the existing correlation among parameters and provide uncorrelated variables. The first principal component (contains 78.2% variance of data) was significantly greater in diabetic than in control groups (P < 0.0001, 0.74 +/- 2.01 versus -0.53 +/- 1.66). In addition the seventh principal component, which contains 0.02% of the data variance, was significantly lower in diabetic than in control groups (P < 0.05, -0.007 +/- 0.03 versus 0.005 +/- 0.03). Finally, linear discrimination analysis (LDA) was used to classify the subjects. The classification was done using the robust leaving-one-subject-out method. LDA could classify the subjects with 71.7% sensitivity and 70.2% specificity while the male subjects resulted in a highly acceptable result for the sensitivity (81%). The present study showed that PPG signals can be used for vascular function assessment and may find further application for detection of vascular changes before onset of clinical diseases.
    Matched MeSH terms: Regional Blood Flow/physiology
  11. Ampomah K, Amano S, Wages NP, Volz L, Clift R, Ludin AFM, et al.
    Med Sci Sports Exerc, 2019 Sep;51(9):1817-1827.
    PMID: 30913160 DOI: 10.1249/MSS.0000000000001984
    PURPOSE: The goal of this trial was to determine whether low-load blood flow-restricted (BFR) exercise of appendicular muscles induces a cross-transfer of effect to the trunk extensor (TE) muscles, such that low-load TE exercise would enhance TE size and function to a greater extent than standard low-load exercise in people with recurrent low back pain (LBP). We also investigated the direct effects of BFR exercise in the appendicular muscles.

    METHODS: Thirty-two adults with recurrent, nonspecific LBP were randomized into two groups: Appendicular BFR exercise (BFR exercise) or control exercise (CON exercise). All participants trained (two times per week) for 10 wk, with a 12-wk follow-up. Participants performed three sets of leg extension (LE), plantar flexion (PF), and elbow flexion (EF) exercises followed by low-load TE exercise without BFR. Outcome measures included magnetic resonance imaging-derived muscle size (quadriceps and TE), strength (LE, PF, EF, and TE), and endurance (LE and TE).

    RESULTS: There was no evidence for a cross-transfer of effect to the TE. There was also no statistically significant enhancement of limb skeletal muscle size or function of BFR relative to CON exercise at any time point; though, moderate effect sizes for BFR exercise were observed for enhanced muscle size and strength in the leg extensors.

    CONCLUSIONS: Low-load BFR exercise of the appendicular muscles did not result in a cross-transfer of effect to the TE musculature. There was also no significant benefit of low-load BFR exercise on the appendicular muscle size and function, suggesting no benefit from low-load BFR exercise in adults with recurrent, nonspecific LBP.

    Matched MeSH terms: Regional Blood Flow/physiology*
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