Assessment of skeletal muscle microcirculation in type 2 diabetes mellitus using dynamic contrast-enhanced ultrasound: a pilot study

An exercise stress test for contrast-enhanced duplex ultrasound assessment of lower limb muscle perfusion in patients with peripheral arterial disease

OBJECTIVE

The aim of the present study was to develop a standardized contrast-enhanced duplex ultrasound (CE-DUS) protocol to assess lower-extremity muscle perfusion before and after exercise and determine relationships of perfusion with clinical and functional measures.

METHODS

CE-DUS (EPIQ 5G, Philips) was used before and immediately after a 10-minute, standardized bout of treadmill walking to compare microvascular perfusion of the gastrocnemius muscle in older (55-82 years) patients with peripheral arterial disease (PAD) (n = 15, mean ankle-brachial index, 0.78 ± 0.04) and controls (n = 13). Microvascular blood volume (MBV) and microvascular flow velocity (MFV) were measured at rest and immediately following treadmill exercise, and the Modified Physical Performance Test (MPPT) was used to assess mobility function.

RESULTS

In the resting state (pre-exercise), MBV in patients with PAD was not significantly different than normal controls (5.17 ± 0.71 vs 6.20 ± 0.83 arbitrary units (AU) respectively; P = .36); however, after exercise, MBV was ∼40% lower in patients with PAD compared with normal controls (5.85 ± 1.13 vs 9.53 ± 1.31 AU, respectively; P = .04). Conversely, MFV was ∼60% higher in patients with PAD compared with normal controls after exercise (0.180 ± 0.016 vs 0.113 ± 0.018 AU, respectively; P = .01). There was a significant between-group difference in the exercise-induced changes in both MBV and MFV (P ≤ .05). Both basal and exercise MBV directly correlated with MPPT score in the patients with PAD (r = 0.56-0.62; P < .05).

CONCLUSIONS

This standardized protocol for exercise stress testing of the lower extremities quantifies calf muscle perfusion and elicits perfusion deficits in patients with PAD. This technique objectively quantifies microvascular perfusion deficits that are related to reduced mobility function and could be used to assess therapeutic efficacy in patients with PAD.

Metformin attenuates high glucose-induced injury in islet microvascular endothelial cells

As one of the most frequently prescribed antidiabetic drugs, metformin can lower glucose levels, improve insulin resistance manage body weight. However, the effect of metformin on islet microcirculation remains unclear. In the present study, to explore the effect of metformin on islet endothelial cells and investigated the underlying mechanism, we assessed the effects of metformin on islet endothelial cell survival, proliferation, oxidative stress and apoptosis. Our results suggest that metformin stimulates the proliferation of pancreatic islet endothelial cells and inhibits the apoptosis and oxidative stress caused by high glucose levels. By activating farnesoid X receptor (FXR), metformin increases the expression of vascular endothelial growth factor-A (VEGF-A) and endothelial nitric oxide synthase (eNOS), improves the production of nitric oxide (NO) and decreases the production of ROS. After the inhibition of FXR or VEGF-A, all of the effects disappeared. Thus, metformin appears to regulate islet microvascular endothelial cell (IMEC) proliferation, apoptosis and oxidative stress by activating the FXR/VEGF-A/eNOS pathway. These findings provide a new mechanism underlying the islet-protective effect of metformin.

Insulin protects against type 1 diabetes mellitus-induced ultrastructural abnormalities of pancreatic islet microcirculation

Pancreatic islet microcirculation, consisting of pancreatic islet microvascular endothelial cells (IMECs) and pericytes (IMPCs), provides crucial support for the physiological function of pancreatic islet. Emerging evidence suggests that pancreatic islet microcirculation is impaired in type 1 diabetes mellitus (T1DM). Here, we investigated the potential ultrastructural protective effects of insulin against streptozotocin (STZ)-induced ultrastructural abnormalities of the pancreatic islet microcirculation in T1DM mouse model. For this purpose, pancreatic tissues were collected from control, STZ-induced T1DM and insulin-treated mice, and a pancreatic IMECs cell line (MS1) was cultured under control, 35 mM glucose with or without 10⁻⁸ M insulin conditions. Transmission and scanning electron microscopies were employed to evaluate the ultrastructure of the pancreatic islet microcirculation. We observed ultrastructural damage to IMECs and IMPCs in the type 1 diabetic group, as demonstrated by destruction of the cytoplasmic membrane and organelles (mainly mitochondria), and this damage was substantially reversed by insulin treatment. Furthermore, insulin inhibited collagenous fiber proliferation and alleviated edema of the widened pancreatic islet exocrine interface in T1DM mice. We conclude that insulin protects against T1DM-induced ultrastructural abnormalities of the pancreatic islet microcirculation.

Quantitative Musculoskeletal Ultrasound

Ultrasound (US) imaging plays a crucial role in the assessment of musculoskeletal (MSK) disorders. Several quantitative tools are offered by US systems and add information to conventional US imaging. This article reviews the quantitative US imaging tools currently available in MSK radiology, specifically focusing on the evaluation of elasticity with shear-wave elastography, perfusion with contrast-enhanced US and noncontrast superb microvascular imaging, and bone and muscle mass with quantitative US methods. Some of them are well established and already of clinical value, such as elasticity and contrast-enhanced perfusion assessment in muscles and tendons. MSK radiologists should be aware of the potential of quantitative US tools and take advantage of their use in everyday practice, both for clinical and research purposes.

[CEUS-application possibilities in the musculoskeletal system]

METHODICAL ISSUE

Contrast-enhanced ultrasound (CEUS) offers easily accessible visualization and quantification of the skeletal muscle microcirculation and other tissues in vivo and in real-time with almost no side effects.

AIM

The aim of this review is to present the increasing number of musculoskeletal CEUS applications.

METHODICAL INNOVATIONS/PERFORMANCE

CEUS applications regarding the musculoskeletal system include applications at bone and joints extending beyond the visualization of only the muscular microcirculation. Besides basic muscle physiology, impaired microcirculation in patients with peripheral artery disease or diabetes mellitus and the diagnosis of inflammatory myopathies have been the subject of previous CEUS studies. More recent studies in orthopedics and traumatology have focused on osseous and muscular perfusion characteristics, e. g., in differentiating infected and aseptic non-unions or the impact of different types of implants and prostheses on muscular microcirculation as a surrogate marker of clinical success.

PRACTICAL RECOMMENDATIONS

CEUS of the musculoskeletal system is used in clinical trials or off-label. Therefore, it is not well established in clinical routine. However, considering the increasing number of musculoskeletal CEUS applications, this could change in the future.

Utility of Contrast-Enhanced Ultrasound for the Assessment of Skeletal Muscle Perfusion in Diabetes Mellitus: A Meta-Analysis

BACKGROUND This study evaluated the effectiveness of contrast-enhanced ultrasonography for the assessment of skeletal muscle perfusion in diabetes mellites. MATERIAL AND METHODS Electronic databases (Embase, Google Scholar, Ovid, and PubMed) were searched for required articles, and studies were selected by following pre-determined eligibility criteria. Meta-analyses of mean differences or standardized mean differences (SMD) were performed to evaluate the significance of difference in contrast-enhanced ultrasonography measured muscle perfusion indices between patients with diabetes and healthy individuals or between basal and final values of perfusion indices after insulin manipulation or physical exercise in patients with diabetes or healthy individuals. RESULTS There were 15 studies included, with 279 patients with diabetes and 230 healthy individuals in total. The age of the study patients with diabetes mellitus was 55.8 years (95% CI: 49.6 years, 61.9 years) and these patients had disease for 11.4 years (95% CI: 7.7 years, 15.1 years). The percentage of males in group of patients with diabetes was 66% (95% CI: 49%, 84%), body mass index was 29.4 kg/m² (95% CI: 26.5 kg/m², 32.3 kg/m²), hemoglobin A1c was 7.3% (95% CI: 6.7%, 7.9%), and fasting plasma glucose was 149 kg/m² (95% CI: 118 kg/m², 179 kg/m²). Time to peak intensity after provocation was significantly higher in patients with diabetes than in healthy individuals (SMD 1.18 [95% CI: 0.60, 1.76]; P<0.00001). In patients with diabetes, insulin administration did not improve contrast-enhanced ultrasonography measured muscle perfusion indices but exercise improved muscle perfusion but at a level that was statistically non-significant (SMD between basal and post-exercise values (1.03 [95% CI: -0.14, 2.20]; P=0.08). In healthy individuals, lipids in addition to insulin administration was associated with significantly reduced blood volume and blood flow. CONCLUSIONS Our review showed that the use of contrast-enhanced ultrasonography showed that diabetes mellitus was associated with altered muscle perfusion in which insulin-mediated metabolic changes played an important role.

Pancreatic-islet microvascular vasomotion dysfunction in mice with spinal cord injury

Patients with spinal cord injury (SCI) have an increased risk for developing type 2 diabetes. It is unknown whether the pancreatic-islet microvascular vasomotion is involved. We used female C57BL/6 mice and a 100-kilodyne T10 Infinite Horizons contusion SCI (or T10 laminectomy) to detect blood glucose and pancreatic-islet microvascular vasomotion. Blood glucose obtained from tail vein was detected using one Touch UltraEasy glucometer. Glucose tolerance test was performed by d-glucose administration intraperitoneally. Functional status of pancreatic-islet microvascular vasomotion was determined by laser Doppler monitoring. Expressions of insulin and glucagon were determined by immunohistochemistry. Expression of VEGF-A was determined by immunohistochemistry and Western blotting. Our result demonstrated that blood glucose was significantly increased at 4 h postinjury compared to that in sham group, with continuous higher blood glucose until 4 days postinjury (p < 0.05). SCI mice at day 7 and day 14 had significantly impaired glucose tolerance following glucose administration (p < 0.01). Average blood perfusion, amplitude, frequency, and relative velocity of vasomotion were significantly lower at 6 h postinjury than those in the sham group (p < 0.05), which were gradually upregulated over time. The expression of insulin was decreased, while the expression of glucagon was increased at 6 h postinjury. Similarly, the expression of VEGF-A was significantly decreased at 6 h postinjury, compared to that in sham group (p < 0.05), with slight increases by 14 days postinjury. Our study suggests that the functional status of pancreatic-islet microvascular vasomotion is impaired after injury, which may have implications for developing effective therapeutic interventions for SCI.

Cardiovascular aging and the microcirculation of skeletal muscle: using contrast-enhanced ultrasound

Skeletal muscle is the largest and most important site of capillary-tissue exchange, especially during high-energy demand tasks such as exercise; however, information regarding the role of the microcirculation in maintaining skeletal muscle health is limited. Changes in microcirculatory function, as observed with aging, chronic and cardiovascular diseases, and exercise, likely precede any alterations that arise in larger vessels, although further investigation into these changes is required. One of the main barriers to addressing this knowledge gap is the lack of methodologies for quantifying microvascular function in vivo; the utilization of valid and noninvasive quantification methods would allow the dynamic evaluation of microvascular flow during periods of clinical relevance such as during increased demand for flow (exercise) or decreased demand for flow (disuse). Contrast-enhanced ultrasound (CEUS) is a promising noninvasive technique that has been used for diagnostic medicine and more recently as a complementary research modality to investigate the response of the microcirculation in insulin resistance, diabetes, and aging. To improve the reproducibility of these measurements, our laboratory has optimized the quantification protocol associated with a bolus injection of the contrast agent for research purposes. This brief report outlines the assessment of microvascular flow using the raw time-intensity curve incorporated into gamma variate response modeling. CEUS could be used to compliment any macrovascular assessments to capture a more complete picture of the aging vasculature, and the modified methods presented here provide a template for the general analysis of CEUS within a research setting.

Prospects of Contrast-Enhanced Ultrasonography for the Diagnosis of Peripheral Arterial Disease: A Meta-analysis

OBJECTIVES

Contrast-enhanced ultrasonography (CEUS) is a modern diagnostic method that can also be used to study microperfusion. This study compared the time to peak intensity measured by CEUS in patients with peripheral arterial disease (PAD) and healthy control participants.

METHODS

After a comprehensive literature search in multiple electronic databases and study selection, a random-effect meta-analysis was performed to compare the time to peak intensity measured by CEUS in patients with PAD and healthy controls, which followed meta-regression analyses for identification of factors affecting the outcomes.

RESULTS

Fourteen studies (data for 322 patients with PAD and 314 healthy individuals) were used for the meta-analysis. The age of this sample of patients with PAD was 64.92 (95% confidence interval, 62.53, 67.31) years, and that of the healthy controls was 55.32 (51.67, 58.98) years. The times to peak intensity were 18.55 (15.62, 21.48) seconds in healthy controls, 33.40 (27.65, 39.15) seconds in patients with PAD, and 76.22 (36.23, 116.22) seconds in patients with PAD and diabetes mellitus. The difference between patients with PAD and healthy controls in the time to peak intensity was statistically significant (mean difference, 24.80 [10.16, 39.44] seconds; P < .00009). The ABI was not significantly associated with the time to peak intensity in patients with PAD. Age and sex were also not significantly associated with the time to peak intensity.

CONCLUSIONS

Contrast-enhanced ultrasonography is a valuable tool for the diagnosis of PAD based on its ability to differentiate the time to peak intensity between patients with PAD and healthy individuals, but little data are yet available to assess its diagnostic ability in clinical practice.

Evidence for congruent impairment in micro and macrovascular function in type 1 diabetes

Diabetes affects large and small vessels through mechanisms only partially known. In the present study, we evaluated the function of capillaries and large arteries in subjects with type 1 diabetes mellitus (T1DM) to study the effect of chronic hyperglycemia in the absence of other cardiovascular risk factors. Twenty-five subjects with T1DM and 12 healthy age-matched controls were enrolled. Nine patients had mild or moderate retinopathy. Contrast enhanced ultrasound was used to measure perfusion of the deep forearm flexor muscle of the non-dominant arm at rest (baseline) and after an ischemic stimulus (reactive hyperemia). Perfusion was expressed as Video Intensity (VI) in arbitrary unit (a.u.)/mm². The time to reach peak VI after ischemia was also recorded. The function of large arteries was evaluated using flow-mediated vasodilation (FMD). VI was significantly lower in T1DM compared to control subjects both at baseline (0.22±0.16 vs 0.44±0.35 a.u./mm², p<0.05), and after ischemia (0.33±0.24 vs 0.68±0.46 a.u./mm², p<0.05). The time to reach peak VI after ischemia was markedly longer in T1DM (5.6±2.2 vs 4.0±1.7 seconds, p<0.02). These differences were more marked in T1DM subjects with retinopathy. FMD was lower in TIDM patients compared to controls (5.4±6.4 vs 10.7±4.5%, p<0.01). The present findings demonstrate that T1DM patients have defective peripheral skeletal muscle perfusion both at rest and after ischemia compared with control subjects. Low muscle perfusion associates with low FMD of the brachial artery. Furthermore, T1DM subjects with retinopathy have the least muscle perfusion and blunted response to hyperemia compared to T1DM without retinopathy.

Insulin treatment restores islet microvascular vasomotion function in diabetic mice

BACKGROUND

The microcirculation plays an important role in the pathogenesis of diabetes and its complications. We hypothesized that pancreatic islet microvascular (PIM) vasomotion, as a parameter of pancreatic islet microcirculation function, is abnormal in diabetic mice and that insulin treatment may reverse this dysfunction.

METHODS

Mice were randomly assigned to non-diabetic control, untreated diabetic, and insulin-treated diabetic groups (n = 6 in each group). Separate groups of streptozotocin (STZ)-induced diabetic and high-fat diet-fed mice were used as a model of hyperglycemia. Insulin-treated diabetic mice were treated with 1-1.5 IU/day insulin for 1 week. Laser Doppler monitors were used to evaluate PIM vasomotion. Morphological and ultrastructural changes in islet endothelial cells were determined by immunohistochemistry and transmission electron microscopy. Glucagon, insulin, vascular endothelial growth factor (VEGF)-A, and platelet endothelial cell adhesion molecule (PECAM-1) expression was determined by immunohistochemistry and Western blotting.

RESULTS

In both untreated diabetic groups, the pancreatic islet microcirculation was unable to regulate PIM vasomotion. The rhythm of vasomotion was irregular, and the average blood perfusion, amplitude, frequency, and relative velocity of vasomotion were significantly lower than in non-diabetic controls. Insulin treatment restored the functional status of PIM vasomotion. In islet endothelial cells from both untreated diabetic groups, the mitochondria were swollen with disarrangement of the cristae, and the distribution of PECAM-1 was discontinuous. Insulin treatment significantly increased the reduced expression of PECAM-1 in both untreated diabetic groups and VEGF-A expression in untreated STZ-diabetic mice.

CONCLUSION

The results suggest that the functional status of PIM vasomotion is impaired in diabetic mice but can be restored by insulin.

Contrast-Enhanced Ultrasound Reveals Exercise-Induced Perfusion Deficits in Claudicants

Background

Contrast-Enhanced Ultrasonography (CEUS) is an imaging modality allowing perfusion quantification in targeted regions of interest of the lower extremity that has not been possible with color-flow imaging or with measurement of ankle brachial indices. We developed a protocol to quantify lower extremity muscle perfusion impairment in PAD patients in response to exercise.

Methods and findings

Thirteen patients with Rutherford Class I-III Peripheral Arterial Disease (PAD) and no prior revascularization procedures were recruited from the Baltimore Veterans Affairs Medical Center and compared with eight control patients without PAD. CEUS interrogation of the index limb gastrocnemius muscle was performed using an intravenous bolus of lipid-stabilized microsphere contrast before and after a standardized treadmill protocol. Peak perfusion (PEAK) and time to peak perfusion (TTP) were measured before and after exercise. Between and within group differences were assessed. Control subjects demonstrated a more rapid TTP (p<0.01) and an increase in peak perfusion (PEAK, p=0.02) after exercise, when compared to their baseline measures. Patients with PAD demonstrated TTP and PEAK measures equivalent to controls at baseline (p=0.39, p=0.71, respectively). However, they exhibited no significant exercise-induced changes in perfusion (TTP p=0.49 and PEAK 0.67, respectively compared to baseline). After exercise, normal subjects had significantly shorter TTP (p=0.04) and greater PEAK (p=0.02) than PAD patients.

Conclusion

Consistent with their lack of ischemic symptoms at rest, class I to III claudicant PAD patients showed similar perfusion measures (TTP and PEAK) at rest. PAD patients, however, were unable to increase perfusion in response to exercise, whereas controls increased perfusion significantly. This corresponds with claudication and limited walking capacity observed in PAD. CEUS with bolus injection offers a convenient, objective, quantitative and visual physiologic assessment of perfusion limitation in specific muscle groups of PAD patients. This has the potential for substantial clinical and research utility.

Quantitative correlational study of microbubble-enhanced ultrasound imaging and magnetic resonance imaging of glioma and early response to radiotherapy in a rat model

PURPOSE

Radiotherapy remains a major treatment method for malignant tumors. Magnetic resonance imaging (MRI) is the standard modality for assessing glioma treatment response in the clinic. Compared to MRI, ultrasound imaging is low-cost and portable and can be used during intraoperative procedures. The purpose of this study was to quantitatively compare contrast-enhanced ultrasound (CEUS) imaging and MRI of irradiated gliomas in rats and to determine which quantitative ultrasound imaging parameters can be used for the assessment of early response to radiation in glioma.

METHODS

Thirteen nude rats with U87 glioma were used. A small thinned skull window preparation was performed to facilitate ultrasound imaging and mimic intraoperative procedures. Both CEUS and MRI with structural, functional, and molecular imaging parameters were performed at preradiation and at 1 day and 4 days postradiation. Statistical analysis was performed to determine the correlations between MRI and CEUS parameters and the changes between pre- and postradiation imaging.

RESULTS

Area under the curve (AUC) in CEUS showed significant difference between preradiation and 4 days postradiation, along with four MRI parameters, T2, apparent diffusion coefficient, cerebral blood flow, and amide proton transfer-weighted (APTw) (all p < 0.05). The APTw signal was correlated with three CEUS parameters, rise time (r = - 0.527, p < 0.05), time to peak (r = - 0.501, p < 0.05), and perfusion index (r = 458, p < 0.05). Cerebral blood flow was correlated with rise time (r = - 0.589, p < 0.01) and time to peak (r = - 0.543, p < 0.05).

CONCLUSIONS

MRI can be used for the assessment of radiotherapy treatment response and CEUS with AUC as a new technique and can also be one of the assessment methods for early response to radiation in glioma.

Modulation of endothelial cell phenotype by physical activity: impact on obesity-related endothelial dysfunction

Increased levels of physical activity are associated with reduced cardiovascular disease (CVD) risk and mortality in obesity and diabetes. Available evidence suggests that local factors, including local hemodynamics, account for a significant portion of this CVD protection, and numerous studies have interrogated the therapeutic benefit of physical activity/exercise training in CVD. Less well established is whether basal differences in endothelial cell phenotype between/among vasculatures related to muscle recruitment patterns during activity may account for reports of nonuniform development of endothelial dysfunction in obesity. This is the focus of this review. We highlight recent work exploring the vulnerability of two distinct vasculatures with established differences in endothelial cell phenotype. Specifically, based largely on dramatic differences in underlying hemodynamics, arteries perfusing soleus muscle (slow-twitch muscle fibers) and those perfusing gastrocnemius muscle (fast-twitch muscle fibers) in the rat exhibit an exercise training-like versus an untrained endothelial cell phenotype, respectively. In the context of obesity, therefore, arteries to soleus muscle exhibit protection from endothelial dysfunction compared with vulnerable arteries to gastrocnemius muscle. This disparate vulnerability is consistent with numerous animal and human studies, demonstrating increased skeletal muscle blood flow heterogeneity in obesity coincident with reduced muscle function and exercise intolerance. Mechanistically, we highlight emerging areas of inquiry exploring novel aspects of hemodynamic-sensitive signaling in endothelial cells and the time course of physical activity-associated endothelial adaptations. Lastly, further exploration needs to consider the impact of endothelial heterogeneity on the development of endothelial dysfunction because endothelial dysfunction independently predicts CVD events.

Contrast-enhanced ultrasonography to assess blood perfusion of skeletal muscles in normal dogs

This study evaluated perfusion of skeletal muscle using contrast enhanced ultrasonography in humerus, radius, femur and tibia in normal dogs. Contrast enhanced ultrasonography for each region was performed after injecting 0.5 mL and 1 mL of contrast medium (SonoVue) in every dog. Blood perfusion was assessed quantitatively by measuring the peak intensity, time to the peak intensity and area under the curve from the time-intensity curve. Vascularization in skeletal muscle was qualitatively graded with a score of 0-3 according to the number of vascular signals. A parabolic shape of time-intensity curve was observed from muscles in normal dogs, and time to the peak intensity, the peak intensity and area under the curve of each muscle were not significantly different according to the appendicular regions examined and the dosage of contrast agent administered. This study reports that feasibility of contrast enhanced ultrasonography for assessment of the muscular perfusion in canine appendicular regions.

Reliability of contrast-enhanced ultrasound for the assessment of muscle perfusion in health and peripheral arterial disease

We investigated the reliability of contrast-enhanced ultrasound (CEUS) in assessing calf muscle microvascular perfusion in health and disease. Response to a post-occlusive reactive hyperaemia test was repeated on two occasions >48 h apart in healthy young (28 ± 7 y) and elderly controls (70 ± 5 y), and in peripheral arterial disease patients (PAD, 69 ± 7 y; n = 10, 9 and 8 respectively). Overall, within-individual reliability was poor (coefficient of variation [CV] range: 15-87%); the most reliable parameter was time to peak (TTP, 15-48% CV). Nevertheless, TTP was twice as long in elderly controls and PAD compared to young (19.3 ± 10.4 and 22.0 ± 8.6 vs. 8.9 ± 6.2 s respectively; p < 0.01), and area under the curve for contrast intensity post-occlusion (a reflection of blood volume) was ∼50% lower in elderly controls (p < 0.01 versus PAD and young). Thus, CEUS assessment of muscle perfusion during reactive hyperaemia demonstrated poor reliability, yet still distinguished differences between PAD patients, elderly and young controls.

Assessing the end-organ in peripheral arterial occlusive disease-from contrast-enhanced ultrasound to blood-oxygen-level-dependent MR imaging

Peripheral arterial occlusive disease (PAOD) is a result of atherosclerotic disease which is currently the leading cause of morbidity and mortality in the western world. Patients with PAOD may present with intermittent claudication or symptoms related to critical limb ischemia. PAOD is associated with increased mortality rates. Stenoses and occlusions are usually detected by macrovascular imaging, including ultrasound and cross-sectional methods. From a pathophysiological view these stenoses and occlusions are affecting the microperfusion in the functional end-organs, such as the skin and skeletal muscle. In the clinical arena new imaging technologies enable the evaluation of the microvasculature. Two technologies currently under investigation for this purpose on the end-organ level in PAOD patients are contrast-enhanced ultrasound (CEUS) and blood-oxygen-level-dependent (BOLD) MR imaging (MRI). The following article is providing an overview about these evolving techniques with a specific focus on skeletal muscle microvasculature imaging in PAOD patients.

A pilot study of regional perfusion and oxygenation in calf muscles of individuals with diabetes with a noninvasive measure

OBJECTIVE

To assess alterations in the regional perfusion and oxygenation of the calf muscles in individuals with diabetes.

METHODS

Age-matched individuals with (n = 5) and without diabetes (n = 6) were investigated. Skeletal muscle perfusion, oxygen extraction fraction, and oxygen consumption rate were measured by newly developed noncontrast magnetic resonance imaging (MRI) techniques. The subjects lay supine on the MRI table with their foot firmly strapped to a custom-built isometric exercise device. The measurements were performed at rest and during an isometric plantar flexion muscle contraction.

RESULTS

Individuals without diabetes had up to a 10-fold increase in muscle perfusion, 25% elevation in muscle oxygen extraction fraction, and a 12-fold increase in oxygen consumption rate in the calf during the plantar flexion isometric contraction. In patients with diabetes, the increases in these parameters were only up to sixfold, 2%, and sixfold, respectively. Exercise oxygen consumption rate was inversely associated with blood HbA1c levels (r(2) = .91).

CONCLUSIONS

This is the first study to quantify regional skeletal muscle oxygenation in patients with diabetes using noncontrast MRI and warrants additional study. Attenuation of perfusion and oxygenation during exercise may have implications for understanding diabetic complications in the lower extremities.