Biomedical subjects

Q X Yang

Publications and source records attributed to Q X Yang.

At least 19 recordsLinked to original sources

PubMed2005

Regional activation in the rat brain during visceral stimulation detected by c-fos expression and fMRI.

AIM: The aim of the study was to determine and compare the areas of brain activated in response to colorectal distention (CRD) using functional magnetic resonance imaging (fMRI) and c-fos protein expression. METHODS: For fMRI study (3.0 T magnet), anaesthetized rats underwent phasic CRD, synchronized with fMRI acquisition. Stimulation consisted of eight cycles of balloon deflation (90 s) and inflation (30 s), at 40, 60 or 80 mmHg of pressure. For c-fos study two sets of experiments were performed on anaesthetized rats: comparing (A) brain activation in rats with the inserted colorectal balloon (n = 5), to the rats without the balloon (n = 5); and (B) rats with inserted balloon (n = 10), to the rats with inserted and distended balloon (n = 10). The pressure of 80 mmHg was applied for 2 h of 30 s inflation and 90 s deflation, alternating cycles. RESULTS: Functional MRI revealed significant activation in the amygdala, hypothalamus, thalamus, cerebellum and hippocampus. Significant increase in c-fos expression was observed in amygdala and thalamus in the first set of experiments, and hypothalamus and parabrachial nuclei in the second. CONCLUSION: The two methods are not interchangeable but appeared to be complementary: fMRI was more sensitive, whereas c-fos had much greater resolution.

Animals↗

PubMed2003

Biosorption of reactive dyes by the mycelium pellets of a new isolate of Penicillium oxalicum.

Three reactive dyes were rapidly adsorbed by the mycelium pellets of Penicillium oxalicum. Dye removal of Reactive Blue 19 was up to 60% in 10 min and 91% in 80 min. Dye adsorption isotherms fitted Langmuir model well and the maximum adsorption capacities at 20 degrees C were calculated to be 160 mg g(-1) for Reactive Blue 19, 122 mg g(-1) for Reactive Red 241 and 137 mg g(-1) for Reactive Yellow 145, respectively. The pellets exhibited a high dye adsorption capacity (80-180 mg g(-1)) for all of the 3 dyes over a wide pH range (pH 2-10), and the maximum adsorption was obtained at pH 2. The adsorption capacity was mildly increased by increasing salinity.

Adsorption↗

PubMed2002

Removal of local field gradient artefacts in BOLD contrast imaging of head and neck tumours.

Monitoring of oxygenation in tumours is an important issue in predicting the success of anti-cancer treatments such as radiotherapy. Gradient echo (GE) imaging sequences can be used for monitoring changes in tumour blood flow and oxygenation. However, the application of this method in head and neck tumours is hampered by significant artefacts and losses of the MR signal near air-tissue interfaces. We investigated the usefulness of a gradient-echo slice excitation profile (GESEPI) sequence that should keep the oxygen contrast while recovering the signal loss caused by susceptibility artefacts. A tumour model was implanted in the neck and in the leg of mice. MR imaging was performed at 4.7 T. GE and GESEPI sequences were used for monitoring the blood oxygen level dependent (BOLD) contrast after carbogen breathing. The pO2 was also monitored in tumours using an OxyLite probe (Oxford Optronics). Using the tumours implanted in the leg, we found that the variations of signal intensity after carbogen breathing were similarin both sequences. In the tumour implanted in the neck, it was possible, using GESEPI sequences, to recover the signal loss caused by susceptibility artefacts and to monitor the effect of carbogen-induced changes in the tumour.

Animals↗

PubMed2002

Different excitation and reception distributions with a single-loop transmit-receive surface coil near a head-sized spherical phantom at 300 MHz.

Calculations and experiments were used to examine the B(1) field behavior and signal intensity distribution in a 16-cm diameter spherical phantom excited by a 10-cm diameter surface coil at 300 MHz. In this simple system at this high frequency very complex RF field behavior exists, resulting in different excitation and reception distributions. Included in this work is a straightforward demonstration that coil receptivity is proportional to the magnitude of the circularly polarized component of the B(1) field that rotates in the direction opposite to that of nuclear precession. It is clearly apparent that even in very simple systems in head-sized samples at this frequency it is important to consider the separate excitation and reception distributions in order to understand the signal intensity distribution.

Head↗

PubMed2001

Spatial variation in cartilage T2 of the knee.

Technical limitations imposed by resolution and B1 homogeneity have thus far limited quantitative in vivo T2 mapping of cartilage to the patella. The purpose of this study is to develop T2 mapping of the femoral/tibial joint and assess regional variability of cartilage T2 in the knee. Quantitative in vivo T2 mapping of the knee was performed on 15 asymptomatic adults (age, 22-44) using a 3T MR scanner. There is a consistent pattern of spatial variation in cartilage T2 with longer values near the articular surface. The greatest variation occurs in the patella, where T2 increases from 45.3 +/- 2.5 msec at a normalized distance of 0.33-67 +/- 5.5 msec at a distance of 1.0. These results demonstrate feasibility of performing in vivo T2 mapping of femoral tibial cartilage. Except for the superficial 15% where T2 values are lower, the spatial variation in T2 of femoral and tibial cartilage is similar to patellar cartilage.

Adult↗

PubMed2000

Effects of forearm bier block with bretylium on the hemodynamic and metabolic responses to handgrip.

We tested the hypothesis that a reduction in sympathetic tone to exercising forearm muscle would increase blood flow, reduce muscle acidosis, and attenuate reflex responses. Subjects performed a progressive, four-stage rhythmic handgrip protocol before and after forearm bier block with bretylium as forearm blood flow (Doppler) and metabolic (venous effluent metabolite concentration and (31)P-NMR indexes) and autonomic reflex responses (heart rate, blood pressure, and sympathetic nerve traffic) were measured. Bretylium inhibits the release of norepinephrine at the neurovascular junction. Bier block increased blood flow as well as oxygen consumption in the exercising forearm (P < 0.03 and P < 0.02, respectively). However, despite this increase in flow, venous K(+) release and H(+) release were both increased during exercise (P < 0.002 for both indexes). Additionally, minimal muscle pH measured during the first minute of recovery with NMR was lower after bier block (6.41 +/- 0.08 vs. 6.20 +/- 0.06; P < 0.036, simple effects). Meanwhile, reflex effects were unaffected by the bretylium bier block. The results support the conclusion that sympathetic stimulation to muscle during exercise not only limits muscle blood flow but also appears to limit anaerobiosis and H(+) release, presumably through a preferential recruitment of oxidative fibers.

Adult↗

PubMed2000

Ischemic exercise and the muscle metaboreflex.

In exercising muscle, interstitial metabolites accumulate and stimulate muscle afferents. This evokes the muscle metaboreflex and raises arterial blood pressure (BP). In this report, we examined the effects of tension generation on muscle metabolites and BP during ischemic forearm exercise in humans. Heart rate (HR), BP, P(i), H(2)PO(4)(-), and pH ((31)P-NMR spectroscopy) data were collected in 10 normal healthy men (age 23 +/- 1 yr) during rhythmic handgrip exercise. After baseline measurements, the subjects performed rhythmic handgrip for 2 min. At 2 min, a 250-mmHg occlusion cuff was inflated, and ischemic handgrip exercise was continued until near fatigue (Borg 19). Measurements were continued for an additional 30 s of ischemia. This protocol was performed at 15, 30, 45, and 60% of the subjects' maximum voluntary contraction (MVC) in random order. As tension increased, the time to fatigue decreased. In addition, mean arterial pressure and HR were higher at 60% MVC than at any of the other lower tensions. The NMR data showed significantly greater increases in H(2)PO(4)(-), P(i), and H(+) at 60% than at 15 and 30% MVC. Therefore, despite the subjects working to the same perceived effort level, a greater reflex response (represented by BP and HR data) was elicited at 60% MVC than at any of the other ischemic tensions. These data are consistent with the hypothesis that, as tension increases, factors aside from insufficient blood flow contribute to the work effect on muscle metabolites and the magnitude of the reflex response.

Adult↗

PubMed1999

Multiple echo frequency-domain image contrast: improved signal-to-noise ratio and T2 (T2*) weighting.

Conventional T2- and T2*-weighted image contrasts are produced by waiting a TE period for the transverse magnetic resonance (MR) signals to decay to differentiate tissue types with distinct relaxation rates. Significant image signal-to-noise ratio (SNR) is compromised by this contrast-producing process. In this report, a multiple echo frequency-domain image contrast (MEFIC) method is presented. During the conventional TE period, a multiple echo train modulated by T2 or T2* decay is acquired. A third Fourier transform along the echo direction produces an image set with pixel signal intensity modulated by the spectrum of the decay curve. This method simultaneously enhances image contrast with a large increase in SNR. Experimental studies of cerebral vasogenic edema in immature rats and functional MR imaging studies of the human motor cortex have demonstrated that the MEFIC method produces superior image quality over conventional methods for generating T2- and T2* weighted images.

Animals↗

PubMed1999

Microimaging at 14 tesla using GESEPI for removal of magnetic susceptibility artifacts in T(2)(*)-weighted image contrast.

In magnetic resonance imaging (MRI), T(2)(*)-weighted contrast is significantly enhanced by extremely high magnetic field strength, offering broad potential applications. However, the T(2)(*)-weighted image contrast distortion and signal loss artifact arising from discontinuities of magnetic susceptibility within and around the sample are also increased, limiting utilization of high field systems for T(2)(*)-weighted contrast applications. Due to the B(0) dependence of the contrast distortions and signal losses, and the heterogeneity of magnetic susceptibility in biological samples, magnetic susceptibility artifacts worsen dramatically for in vivo microimaging at higher fields. Practical applications of T(2)(*)-sensitive techniques enhanced by higher magnetic fields are therefore challenged. This report shows that magnetic susceptibility artifacts dominate T(2)(*)-weighted image contrast at 14 T, and demonstrates that the GESEPI (gradient echo slice excitation profile imaging) technique effectively reduces or eliminates these artifacts at long TE in the highest field (14 T) currently available for (1)H imaging.

Algorithms↗

PubMed1998

Removal of local field gradient artifacts in T2*-weighted images at high fields by gradient-echo slice excitation profile imaging.

Development of high magnetic field MRI techniques is hampered by the significant artifacts produced by B0 field inhomogeneities in the excited slices. A technique, gradient-echo slice excitation profile imaging (GESEPI), is presented for recovering the signal lost caused by intravoxel phase dispersion in T2*-weighted images. This technique superimposes an incremental gradient offset on the slice refocusing gradient to sample k-space over the full range of spatial frequencies of the excitation profile. A third Fourier transform of the initial two-dimensional image set generates an image set in which the artifacts produced by the low-order B0 inhomogeneity field gradients in the sample are separated and removed from the high-order microscopic field gradients responsible for T2* contrast. Application to high field brain imaging, at 3.0 T for human and at 9.4 T for immature rat imaging demonstrates the significant improvement in quality of the T2*-weighted contrast images.

Algorithms↗

PubMed1998

Altered mechanisms of sympathetic activation during rhythmic forearm exercise in heart failure.

In congestive heart failure (CHF), the mechanisms of exercise-induced sympathoexcitation are poorly defined. We compared the responses of sympathetic nerve activity directed to muscle (MSNA) and to skin (SSNA, peroneal microneurography) during rhythmic handgrip (RHG) at 25% of maximal voluntary contraction and during posthandgrip circulatory arrest (PHG-CA) in CHF patients with those of an age-matched control group. During RHG, the CHF patients fatigued prematurely. At end exercise, the increase in MSNA was similar in both groups (CHF patients, n = 12; controls, n = 10). However, during PHG-CA, in the controls MSNA returned to baseline, whereas it remained elevated in CHF patients (P < 0.05). Similarly, at end exercise, the increase in SSNA was comparable in both groups (CHF patients, n = 11; controls, n = 12), whereas SSNA remained elevated during PHG-CA in CHF patients but not in the controls (P < 0.05). In a separate control group (n = 6), even high-intensity static handgrip was not accompanied by sustained elevation of SSNA during PHG-CA. 31P-nuclear magnetic resonance spectroscopy during RHG demonstrated significant muscle acidosis and accumulation of inorganic phosphate in CHF patients (n = 7) but not in controls (n = 9). We conclude that in CHF patients rhythmic forearm exercise leads to premature fatigue and accumulation of muscle metabolites. The prominent PHG-CA response of MSNA and SSNA in CHF patients suggests activation of the muscle metaboreflex. Because, in contrast to controls, in CHF patients both MSNA and SSNA appear to be under muscle metaboreflex control, the mechanisms and distribution of sympathetic outflow during exercise appear to be different from normal.

Adult↗

PubMed1998

Effects of the ovarian cycle on sympathetic neural outflow during static exercise.

We compared reflex responses to static handgrip at 30% maximal voluntary contraction (MVC) in 10 women (mean age 24.1 +/- 1.7 yr) during two phases of their ovarian cycle: the menstrual phase (days 1-4) and the follicular phase (days 10-12). Changes in muscle sympathetic nerve activity (MSNA; microneurography) in response to static exercise were greater during the menstrual compared with follicular phase (phase effect P = 0.01). Levels of estrogen were less during the menstrual phase (75 +/- 5.5 vs. 116 +/- 9.6 pg/ml, days 1-4 vs. days 10-12; P = 0.002). Generated tension did not explain differences in MSNA responses (MVC: 29.3 +/- 1.3 vs. 28.2 +/- 1.5 kg, days 1-4 vs. days 10-12; P = 0.13). In a group of experiments with the use of 31P-NMR spectroscopy, no phase effect was observed for H+ and H2PO-4 concentrations (n = 5). During an ischemic rhythmic handgrip paradigm (20% MVC), a phase effect was not observed for MSNA or H+ or H2PO-4 concentrations, suggesting that blood flow was necessary for the expression of the cycle-related effect. The present studies suggest that, during static handgrip exercise, MSNA is increased during the menstrual compared with the follicular phase of the ovarian cycle.

Adult↗

PubMed1997

Multi-gradient echo with susceptibility inhomogeneity compensation (MGESIC): demonstration of fMRI in the olfactory cortex at 3.0 T.

Short image acquisition times and sensitivity to magnetic susceptibility favor the use of gradient echo imaging methods in functional MRI (fMRI). However, magnetic susceptibility effects attributed to air-tissue interfaces also lead to severe signal loss in images of the large inferior frontal and lateral temporal cortices of the human brain, which renders these regions inaccessible to fMRI. The signal loss is caused by the local field gradients in the silce selection direction. A multigradient echo with magnetic susceptibility inhomogeneity compensation method (MGESIC) is proposed to overcome this problem. The MGESIC method effectively corrects the susceptibility artifacts and maintains the advantages of gradient echo methods to both BOLD sensitivity and fast image acquisition. The effectiveness of the MGESIC method is demonstrated by fMRI experimental results within the olfactory cortex.

Humans↗

PubMed1997

Augmented sympathetic tone alters muscle metabolism with exercise: lack of evidence for functional sympatholysis.

It is unclear whether sympathetic tone opposes dilator influences in exercising skeletal muscle. We examined high levels of sympathetic tone, evoked by lower body negative pressure (LBNP, -60 mmHg) on intramuscular pH and phosphocreatine (PCr) levels (31P-nuclear magnetic resonance spectroscopy) during graded rhythmic handgrip (30 contractions/min; approximately 17, 34, 52 and 69% maximal voluntary contraction). Exercise was performed with LBNP and without LBNP (Control). At the end of exercise, LBNP caused lower levels of muscle pH (6.59 +/- 0.09) compared with Control (6.78 +/- 0.05; P < 0.05). PCr recovery, an index of mitochondrial respiration, was less during the recovery phase of the LBNP trial. Exercise mean arterial pressure was not altered by LBNP. The protocols were repeated with measurements of forearm blood flow velocity and deep venous samples (active forearm) of hemoglobin (Hb) saturation, pH, and lactate. With LBNP, mean blood velocity was reduced at rest, during exercise, and during recovery compared with Control (P < 0.05). Also, venous Hb saturation and pH levels during exercise and recovery were lower with LBNP and lactate was higher compared with Control (P < 0.05). We conclude that LBNP enhanced sympathetic tone and reduced oxygen transport. At high workloads, there was a greater reliance on nonoxidative metabolism. In other words, sympatholysis did not occur.

Adult↗

PubMed1996

Three-dimensional mapping of the static magnetic field inside the human head.

Finite element analysis was used to calculate the static magnetic field within the three-dimensional head model. Localized field distributions were evaluated by using the magnetic field histogram technique. Experimental field maps and histograms of the human head were also obtained to validate the simulation results. Field deviations and gradients inside the human head cause NMR signal frequency shifts and line broadening, respectively. Voxels 2 x 2 x 0.5 cm may have frequency differences of more than 2.0 ppm. The linewidth of a single voxel may be broadened by more than 0.5 ppm. Calculated and experimental field maps are in excellent agreement. The global field distortion in the human head is primarily due to the susceptibility difference between air and tissues and their corresponding geometrical shapes.

Computer Simulation↗

PubMed1996

Double-sampled echo-planar imaging at 3 tesla.

A persistent artifact in the images acquired by the echo-planar imaging (EPI) method is the Nyquist or N/2 ghost which interferes with the image and reduces the signal-to-noise ratio (SNR). The Nyquist ghost is the result of the time-reversal asymmetry between the even and odd echoes. To eliminate this artifact, the authors present a double-sampled EPI (DSEPI) method in which echoes from each even and odd echo pair are equally phase encoded. The even and odd echoes are separately reconstructed into two distinct images which are then added together. The DSEPI method has been applied to human brain at 3.0 T and shown to be a simple and effective way to eliminate the Nyquist ghost and restore image SNR loss.

Brain↗

PubMed1996

Dynamics of trimethoprim bound to dihydrofolate reductase--a deuterium NMR study.

We have employed deuterium NMR techniques to determine the dynamics of trimethoprim (TMP) in a binary complex with dihydrofolate reductase (DHFR) or in a ternary complex with DHFR and cofactor NADP+ in the fully hydrated state. TMP was deuterated at the following positions: (2',6'-D2)TMP, (3'-Ome-D3)TMP and (3',4'-Ome-D6)TMP. Dynamics of TMP were deduced from lineshape simulation and relaxation measurements of the deuterium NMR powder spectra of the three samples obtained at various temperatures. The results showed that in the polycrystalline state the TMP molecule is very rigid. The only detectable motion is the methyl group rotation at a rate of 10(10) s-1 at 25 degrees C, as determined from simulation of the partially relaxed powder patterns. When bound to DHFR a residual deuterium quadrupole splitting of 140 kHz was observed for (2',6'-D2)TMP at temperatures up to 30 degrees C, suggesting that the benzyl ring in the bound state is also very rigid. In contrast, in the binary complex with DHFR the methoxyl groups of TMP undergo librational motion of 10(7) s-1 about the C3-O bond at an amplitude of 54 degrees for the meta methoxyl group and about the C4-O bond at an amplitude of 70 degrees and similar rate for the para methoxyl group at 30 degrees C. The presence of the cofactor, NADP+, appears to tighten up the binding pocket such that the motion freedom of TMP is more restricted. The rigidity of TMP in a protein complex as revealed by our deuterium NMR results is in accord with the tight binding of TMP to DHFR.

Deuterium↗

PubMed1996

Influences of gender on sympathetic nerve responses to static exercise.

We compared reflex responses to static handgrip at 30% maximal voluntary contraction (MVC) in 26 untrained men (mean age 35 +/- 3 yr) and 23 untrained women (mean age 39 +/- 4 yr). Women demonstrated attenuated increases in blood pressure and muscle sympathetic nerve activity (MSNA; by microneurography) compared with men. This difference was also observed during a period of posthandgrip circulatory arrest. 31P-nuclear magnetic resonance (NMR) spectroscopy studies demonstrated attenuations in the production of diprotonated phosphate and the development of cellular acidosis in women compared with men. Subjects also performed ischemic handgrip to fatigue. During this paradigm, MSNA responses were similar in the two groups, suggesting that freely perfused conditions are necessary for the full expression of the gender effect. Finally, we examined MSNA responses to adductor pollicus exercise in 7 men (26 +/- 1 yr) and 6 women (25 +/- 2 yr). MVC values and times to fatigue were similar in the two groups (MVC: men, 4.3 +/- 0.4 kg; women, 4.0 +/- 0.3 kg; not significant. Time to fatigue: men, 209 +/- 16 s; women, 287 +/- 50 s; not significant). At periods of end exercise and postexercise circulatory arrest, MSNA responses were attenuated in the women compared with the men. We conclude that, during nonischemic static exercise, sympathetic neural outflow is less in women compared with men. This response is due to an attenuated metaboreflex in women. Finally, on the basis of the adductor pollicus experiments, this effect appears independent of muscle mass, workload, and the level of training.

Acidosis↗