Displaying publications 1 - 20 of 33 in total

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  1. 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*
  2. 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*
  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. 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
  5. Tan AE, Norizah WM, Rahman HA, Aziz BA, Cheah FC
    J Obstet Gynaecol Res, 2005 Aug;31(4):296-301.
    PMID: 16018775 DOI: 10.1111/j.1447-0756.2005.00291.x
    Aim: To determine the incidence of an abnormal umbilical artery resistance index (UARI) in diabetic pregnancies and the relation to fetal outcome and the development of neonatal septal hypertrophic cardiomyopathy.

    Methods: A case-control study with subjects comprising 50 randomly selected diabetic mothers and a matched control group of 50 non-diabetic pregnancies. Doppler studies of the UARI were carried out at least once per week, beginning from 36 weeks' gestation for both groups. Within 48 h post delivery, echocardiograms were carried out on the newborn infants to identify those with hypertrophic cardiomyopathy, particularly asymmetrical septal hypertrophy.

    Results: The numbers of patients with abnormal UARI were similar in both the diabetic and control groups. A higher proportion of operative deliveries for intrapartum fetal distress was seen in patients with an abnormal UARI in the diabetic group. However, the groups did not differ in the numbers of infants who were small for gestational age, who had low Apgar scores or umbilical artery acidosis, and who required admission to the special care nursery. Six infants of diabetic mothers (12%) had septal hypertrophy, but none of these were associated with abnormal antenatal UARI.

    Conclusion: Diabetic pregnancy is not associated with a significantly higher incidence of abnormal UARI on Doppler study than non-diabetic pregnancy. UARI is not a useful single indicator by which to predict subsequent fetal outcome or the development of neonatal septal hypertrophic cardiomyopathy in diabetic pregnancies.
    Matched MeSH terms: Regional Blood Flow
  6. Sia SF, Zhao X, Li R, Zhang Y, Chong W, He L, et al.
    Proc Inst Mech Eng H, 2016 Nov;230(11):1051-1058.
    PMID: 28095764 DOI: 10.1177/0954411916671752
    BACKGROUND: Internal carotid artery stenosis requires an accurate risk assessment for the prevention of stroke. Although the internal carotid artery area stenosis ratio at the common carotid artery bifurcation can be used as one of the diagnostic methods of internal carotid artery stenosis, the accuracy of results would still depend on the measurement techniques. The purpose of this study is to propose a novel method to estimate the effect of internal carotid artery stenosis on the blood flow based on the concept of minimization of energy loss.

    METHODS: Eight internal carotid arteries from different medical centers were diagnosed as stenosed internal carotid arteries, as plaques were found at different locations on the vessel. A computational fluid dynamics solver was developed based on an open-source code (OpenFOAM) to test the flow ratio and energy loss of those stenosed internal carotid arteries. For comparison, a healthy internal carotid artery and an idealized internal carotid artery model have also been tested and compared with stenosed internal carotid artery in terms of flow ratio and energy loss.

    RESULTS: We found that at a given common carotid artery bifurcation, there must be a certain flow distribution in the internal carotid artery and external carotid artery, for which the total energy loss at the bifurcation is at a minimum; for a given common carotid artery flow rate, an irregular shaped plaque at the bifurcation constantly resulted in a large value of minimization of energy loss. Thus, minimization of energy loss can be used as an indicator for the estimation of internal carotid artery stenosis.

    Matched MeSH terms: Regional Blood Flow
  7. 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
  8. Rasyada AR, Sha'ban M, Azhim A
    Cardiovasc J Afr, 2018;29(3):146-149.
    PMID: 30067273 DOI: 10.5830/CVJA-2018-001
    INTRODUCTION: The aim of this study was to evaluate the impact of different visceral fat (VF) and blood pressure (BP) levels on changes in blood flow velocity (BFV) among non-obese subjects, using a cross-sectional study approach.

    METHODS: A total of 110 putatively healthy and non-obese subjects were divided into three groups according to their level of VF and BP. Common carotid artery BFV was measured using a developed portable Doppler ultrasound measurement system.

    RESULTS: The most pronounced peak systolic velocity (S1) was lower (p < 0.05) in the hypertensive group and the peak diastolic velocity (D) was significantly lower in the pre-hypertensive group than in the normotensive group. There were differences in velocity reflection and resistive indices between the hypertensive and other two BP groups. The higher VF group had significantly lower S1 and D velocities and resistive and vascular elasticity indices. By contrast, the velocity reflection index was larger in the higher VF group.

    CONCLUSIONS: We confirmed that there were significant differences in the BFV among non-obese subjects who differed in level of VF and BP. This study confirms that a putatively increasing VF and BP level is associated with the development of hypertension.

    Matched MeSH terms: Regional Blood Flow
  9. Peh SC, Lindop GB
    J Pathol, 1991 Apr;163(4):343-9.
    PMID: 2033493
    Hypertension complicates chronic pyelonephritis. Since arterial narrowing is common in the damaged kidney, activation of the renin-angiotensin system due to renal ischaemia has been suggested as a pathogenetic mechanism. We used an antiserum to human renin and an immunoperoxidase technique to study the anatomy of renin-containing cells (RCC) in 18 kidneys removed for pyeloneophritis. We independently assessed the degree of arterial narrowing and correlated these variables with the clinical findings. There was histological evidence of hyperplasia of RCC in 5 of the 6 hypertensive patients and in 7 of the 12 non-hypertensive cases. There was no difference in the apparent number or distribution of RCC between the hypertensive and the non-hypertensive cases. Also, the degree of arterial narrowing did not correlate with either the hyperplasia of RCC or the blood pressure of the patients. Our results do not support the hypothesis that narrowing of the intrarenal arteries is important in the pathogenesis of hypertension in pyelonephritis. In our cases, the renal veins were more severely damaged than the arteries and their lumina were often obliterated by organized thrombus. We suggest that such widespread obliteration of the renal venous tree could impair blood flow and contribute to the tissue damage in the pyelonephritic kidney.
    Matched MeSH terms: Regional Blood Flow
  10. Omar KZ, Ariffin H, Abdullah WA, Chan LL, Lin HP
    Med. Pediatr. Oncol., 2000 May;34(5):377-8.
    PMID: 10797367
    Matched MeSH terms: Regional Blood Flow/drug effects
  11. Neoh HS, Kumarasamy S, Raman S
    Med J Malaysia, 1990 Mar;45(1):37-41.
    PMID: 2152067
    This report deals with the use of a relatively new investigative technique (Doppler ultrasound) in the management of a case of early onset pre-eclampsia and discusses the benefit of this new technique over conventional methods of fetal monitoring.
    Matched MeSH terms: Regional Blood Flow
  12. 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
  13. Mokhtar S, Azizi ZA, Govindarajanthran N
    Asian J Surg, 2008 Jul;31(3):124-9.
    PMID: 18658010
    OBJECTIVE: This study investigated the effects of posture and also intermittent foot and calf compression on peak systolic flow of the popliteal artery in a normal population.

    METHODS: This was a prospective study carried out in normal subjects at the Vascular Laboratory, Department of Surgery, Hospital Kuala Lumpur, from March 2006 to September 2006. The study compared the popliteal artery blood flow during change of posture from the horizontal (supine) to the sitting position and the effect of intermittent pneumatic compression (IPC) of the foot and calf on popliteal artery blood flow immediately and 10 minutes after cessation of compression.

    RESULTS: A total of 15 subjects involving 30 limbs were examined in this study. On comparing flows between the horizontal and sitting position, there was a mean reduction in blood flow of 23% (p < 0.005). Immediately after compression of the foot and calf, there was an increase in blood flow of between 4% and 35% with a mean of 15% (p < 0.05). Peak systolic flows at 10 minutes postcompression were 536 +/- 95 mL/min, which was still significantly higher than precompression measurements.

    CONCLUSION: There is a significant reduction in popliteal artery blood flow on changing from the supine to the sitting position. Popliteal artery blood flow is higher than baseline after 15 minutes of intermittent pneumatic foot and calf compression. The increase in popliteal artery blood flow is still present 10 minutes after cessation of IPC.

    Matched MeSH terms: Regional Blood Flow
  14. Li S, Shaharudin S, Abdul Kadir MR
    Am J Phys Med Rehabil, 2021 Apr 01;100(4):337-344.
    PMID: 33727516 DOI: 10.1097/PHM.0000000000001567
    BACKGROUND: Due to the pain caused by knee injuries, low-load resistance training with blood flow restriction (L-BFR) may be a potential adjuvant therapeutic tool in the rehabilitation of knee injuries. This review aimed to analyze the effectiveness of L-BFR training modality in knee rehabilitation.

    DESIGN: A meta-analysis was conducted to determine the potential impact of blood flow restriction on patients with knee injuries. PubMed, EBSCO, and Web of Science databases were searched for eligible studies from January 2000 until January 2020. The mean differences of the data were analyzed using Revman 5.3 software with a 95% confidence interval.

    RESULTS: Nine studies fulfilled the inclusion criteria. These studies involved 179 patients who received L-BFR, 96 patients who underwent high-load resistance training, and another 94 patients who underwent low-load resistance training. The analysis of pooled data showed that patients in both the L-BFR (standardized mean difference, 0.83 [0.53, 1.14], P < 0.01) and high-load resistance training (standardized mean difference, -0.09 [-0.43, 0.24], P = 0.58) groups experienced an increase in muscle strength after the training. In addition, pain score was significantly reduced in the L-BFR group compared with the other two groups (standardized mean difference, -0.61 [-1.19, -0.03], P = 0.04).

    CONCLUSIONS: Muscle strength increased after L-BFR and high-load resistance training compared with low-load resistance training. Furthermore, pain score was significantly reduced after L-BFR. Hence, L-BFR is a potential intervention to be applied in rehabilitation of knee injuries.

    Matched MeSH terms: Regional Blood Flow
  15. 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/drug effects*; Regional Blood Flow/physiology
  16. 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
  17. Hiong LC, Voon KL, Abdullah NA, Sattar MA, Rahman NA, Khan AH, et al.
    Acta Pharmacol Sin, 2008 Apr;29(4):451-7.
    PMID: 18358091 DOI: 10.1111/j.1745-7254.2008.00772.x
    The aim of the present study was to investigate the effectiveness of transforming growth factor (TGF)-beta1 antisense oligodeoxynucleotides (ODN) in ameliorating deteriorated kidney function in rats with puromycin-induced chronic renal failure (CRF).
    Matched MeSH terms: Regional Blood Flow/drug effects
  18. Ghani AR, John JT, Idris Z, Ghazali MM, Murshid NL, Musa KI
    Malays J Med Sci, 2008 Oct;15(4):48-55.
    PMID: 22589638 MyJurnal
    A prospective cohort study was done to evaluate the role of surgery in patients with spontaneous supratentorial intracerebral haemorrhage (SICH) and to identify predictors of outcome including the use of invasive regional cortical cerebral blood flow (rCoBF) and microdialysis. Surgery consisted of craniotomy or decompressive craniectomy. The ventriculostomy for intracranial pressure (ICP) monitoring and drainage and regional cortical cerebral blood flow (rCoBF) and microdialysis were performed in all subjects. Pre and post operative information on subjects were collected. The study end points was functional outcome at 6 months based on a dichotomised Glasgow Outcome Scale (GOS).The selected clinical, radiological, biochemical and treatment factors that may influence the functional outcome were analysed for their significance. A total of 36 patients were recruited with 27(75%) patients had Glasgow Coma Score (GCS) between 5 to 8 on admission and 9(25%) were admitted with GCS of 9. At 6 months, 86 % had a poor or unfavourable outcome (GOS I-III) and 14% had good or favourable outcome (GOS IV-V). The mortality rate at 6 months was 55%. Univariate analysis for the functional outcome identified 2 significant variables, the midline shift (p=0.013) and mean lactate:pyruvate ratio (p=0.038). Multivariate analysis identified midline shift as the single significant independent predictor of functional outcome (p=0.013).Despite aggressive regional cortical cerebral blood flow (rCoBF) and microdialysis study for detection of early ischemia, surgical treatment for spontaneous intracerebral haemorrhage only benefited a small number of patients in terms of favourable outcome (14%) and in the majority of patients (86%), the outcome was unfavourable. Patients with midline shift > 5mm has almost 21 times higher chances (adj) OR 20.8 of being associated with poor outcome (GOS I-III).
    Matched MeSH terms: Regional Blood Flow
  19. Chia TY, Sattar MA, Abdulla MH, Rathore HA, Ahmad Fu, Kaur G, et al.
    Ren Fail, 2013 Aug;35(7):978-88.
    PMID: 23822648 DOI: 10.3109/0886022X.2013.809563
    This study investigated the effects of tempol, a superoxide dismutase (SOD) mimetic and L-NAME, a nitric oxide (NO) synthase inhibitor on the renal function and hemodynamics in cyclosporine A (CsA) induced renal insufficiency rats. Male Sprague-Dawley rats were treated with either vehicle (C), tempol (T, 1 mmol/L in drinking fluid), L-NAME (L, 1 mmol/L in drinking fluid), CsA (Cs, 25 mg/kg/day via gavage), CsA plus tempol (TCs), CsA plus L-NAME (LCs) or CsA plus a combination of tempol and L-NAME (TLCs) for 21 consecutive days. At the end of treatment regimen, the renal responses to noradrenaline (NA), phenylephrine (PE), methoxamine and angiotensin II (Ang II) were determined. Cs and LCs rats had lower creatinine clearance (0.7 ± 0.1 and 0.6 ± 0.5 vs. 1.3 ± 0.2 mL/min/kg) and fractional excretion of sodium (0.12 ± 0.02 and 0.17 ± 0.01 vs. 0.67 ± 0.04%) but higher systolic blood pressure (145 ± 2 and 178 ± 4 vs. 116 ± 2) compared to the control (all p blood pressure and improved creatinine clearance and sodium excretion compared to untreated Cs. The renal vasoconstriction in Cs or LCs to NA, PE and Ang II were lower than control by ∼35-48% (all p 
    Matched MeSH terms: Regional Blood Flow/drug effects
  20. 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*
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