Validation of diffuse correlation spectroscopy measurements of rodent cerebral blood flow with simultaneous arterial spin labeling MRI; towards MRI-optical continuous cerebral metabolic monitoring.

Cerebral blood flow (CBF) during stepped hypercapnia was measured simultaneously in the rat brain using near-infrared diffuse correlation spectroscopy (DCS) and arterial spin labeling MRI (ASL). DCS and ASL CBF values agree very well, with high correlation (R=0.86, p< 10(-9)), even when physiological instability perturbed the vascular response. A partial volume effect was evident in the smaller magnitude of the optical CBF response compared to the MRI values (averaged over the cortical area), primarily due to the inclusion of white matter in the optically sampled volume. The 8.2 and 11.7 mm mid-separation channels of the multi-distance optical probe had the lowest partial volume impact, reflecting ~75 % of the MR signal change. Using a multiplicative correction factor, the ASL CBF could be predicted with no more than 10% relative error, affording an opportunity for real-time relative cerebral metabolism monitoring in conjunction with MR measurement of cerebral blood volume using super paramagnetic contrast agents.

Dynamic functional and mechanical response of breast tissue to compression.

Physiological tissue dynamics following breast compression offer new contrast mechanisms for evaluating breast health and disease with near infrared spectroscopy. We monitored the total hemoglobin concentration and hemoglobin oxygen saturation in 28 healthy female volunteers subject to repeated fractional mammographic compression. The compression induces a reduction in blood flow, in turn causing a reduction in hemoglobin oxygen saturation. At the same time, a two phase tissue viscoelastic relaxation results in a reduction and redistribution of pressure within the tissue and correspondingly modulates the tissue total hemoglobin concentration and oxygen saturation. We observed a strong correlation between the relaxing pressure and changes in the total hemoglobin concentration bearing evidence of the involvement of different vascular compartments. Consequently, we have developed a model that enables us to disentangle these effects and obtain robust estimates of the tissue oxygen consumption and blood flow. We obtain estimates of 1.9+/-1.3 micromol/100 mL/min for OC and 2.8+/-1.7 mL/100 mL/min for blood flow, consistent with other published values.

Determination of root canal curvatures before and after canal preparation (part II): A method based on numeric calculus.

The aim of this paper is to present a new method based on numeric calculus to provide data on any type of root canal curvature at any point of the long axis of the canal. Twenty severely curved, simulated root canals were prepared with rotary FlexMaster and Profile instruments in the crown-down technique and manually in the step-back technique. The inner and outer curvatures were registered in a system of coordinates before and after preparation in increments of 0.5 mm. Using an equalising function, the curvatures were first represented in graphic and algebraic form. The maximum and the mean curvature as well as the length of the arc from the apical foramen to the point of maximum curvature were determined mathematically. An increase in maximum curvature was registered for all four shaping systems investigated. The radius of the inner curvature decreased by 0.5-1.2 mm in the manual systems as a result of the preparation. The Profile system displayed the smallest changes in radius (-0.9 mm) even with the outer curvature, and manual preparation with stainless steel files the most pronounced change (-1.8 mm). The point of maximum curvature at the inner curvature was displaced by 1.6 mm to the apical foramen through manual preparation with Ni-Ti files. At the outer curvature, the maximum displacement (1.8 mm) recorded was also the result of preparation with Ni-Ti hand files, while a displacement of only 0.3 mm to the apical foramen was recorded with the other systems. The method offers a means of determining curvatures precisely without random specification of reference points. The method is also capable of registering only minor changes in curvature in the two-dimensional long axis of the canal.

Determination of root canal curvatures before and after canal preparation (part 1): a literature review.

The continuing development of methods and materials for root canal preparation is resulting in enhanced preparation techniques with only minor alterations to the canal morphology. Improved evaluation methods are required for differentiated assessment of these innovations. One criterion for assessment of the preparation quality of curved root canals is preparation-induced straightening of the canal. The first canal curvature measurements served to divide teeth into different curvature classes. However, their actual execution represented mere angular measurement rather than root curvature assessment. This purely graphic method lacked precision, nor could it be readily applied to all tooth groups. Further developments of that method resulted in it being applicable to molars and to canals with multiple curvatures. Some years ago, the graphically determined curvature radius was added as a further parameter to measurement of the canal deviation angle, thus permitting a curvature to be correctly described for the first time in geometric and analytic terms. The first mathematically accurate description was presented by Dobó-Nagy et al., who correctly described the mean canal curvature in a two-dimensional image in concrete terms by means of fourth-degree polynomial functions. Recent developments in the application of microcomputed tomography of extracted teeth permit non-destructive three-dimensional assessment of root canal configurations. It remains to be seen whether this resource-intensive form of in vitro examination can assert itself.

Rational modification of protein stability by the mutation of charged surface residues.

Continuum methods were used to calculate the electrostatic contributions of charged and polar side chains to the overall stability of a small 41-residue helical protein, the peripheral subunit-binding domain. The results of these calculations suggest several residues that are destabilizing, relative to hydrophobic isosteres. One position was chosen to test the results of these calculations. Arg8 is located on the surface of the protein in a region of positive electrostatic potential. The calculations suggest that Arg8 makes a significant, unfavorable electrostatic contribution to the overall stability. The experiments described in this paper represent the first direct experimental test of the theoretical methods, taking advantage of solid-phase peptide synthesis to incorporate approximately isosteric amino acid substitutions. Arg8 was replaced with norleucine (Nle), an amino acid that is hydrophobic and approximately isosteric, or with alpha-amino adipic acid (Aad), which is also approximately isosteric but oppositely charged. In this manner, it is possible to isolate electrostatic interactions from the effects of hydrophobic and van der Waals interactions. Both Arg8Nle and Arg8Aad are more thermostable than the wild-type sequence, testifying to the validity of the calculations. These replacements led to stability increases at 52.6 degrees C, the T(m) of the wild-type, of 0.86 and 1.08 kcal mol(-)(1), respectively. The stability of Arg8Nle is particularly interesting as a rare case in which replacement of a surface charge with a hydrophobic residue leads to an increase in the stability of the protein.

Effects of granulocyte-macrophage colony-stimulating factor on wound contraction.

The effect of topical recombinant murine and human GM-CSF, 1 or 10 micrograms/cm2 for one to ten days, on the contraction and healing of acute and chronic granulating wounds infected with Escherichia coli was studied in Sprague-Dawley rats. Bacterial contamination of wounds produced significant inhibition of wound contraction. Application of GM-CSF at either dose level to infected wounds markedly increased the rate of wound closure compared to the rate in infected untreated controls. Ten days treatment was found to be more effective than a single application. An advanced stage of wound healing was observed at ten days in the GM-CSF-treated rats compared with controls. Bacterial counts decreased in the GM-CSF-treated wounds which may suggest bactericidal activity. Topical treatment with GM-CSF was shown to effectively inhibit the retardation of wound closure produced by bacterial contamination and may therefore be useful in the management of patients with infected wounds.

Does inhalation injury limit exercise endurance in children convalescing from thermal injury?

The cardiopulmonary performance levels in children who are convalescing from thermal injury are unknown. This investigation was designed to evaluate cardiopulmonary function in children with and without inhalation injury. Forty children with a mean time since burn injury of 2.6 +/- 1.9 years and a mean burn size of 44% +/- 22% total body surface area were selected for the study and divided into two groups: inhalation injury (group 1) and non-inhalation injury (group 2). Pulmonary function studies and cardiopulmonary stress testing were completed on all patients. Both groups reached the same endurance level on the treadmill; however, patients in group 1 did so with an increased expired volume, respiratory rate, and ratio of dead space ventilation to total ventilation which indicated that there were greater demands on the respiratory system. Spirometry and lung volumes at rest showed that 64% of patients in group 1 had abnormal lung function compared with only 27% of patients in group 2.

Pseudomonas aeruginosa exotoxin A: its role in retardation of wound healing: the 1992 Lindberg Award.

Bacterial concentrations greater than 10(5) colony-forming units/gm of tissue prevent wound healing. However, it has not been determined whether it is the number of bacteria or a toxin produced by these organisms that impedes the wound healing process. Pseudomonas aeruginosa (PSAR), a burn wound pathogen, produces a dermonecrotic toxin, exotoxin A. Studies have indicated a role for exotoxin A in the pathogenicity of PSAR. We investigated the role of exotoxin A in the retardation of contraction. Acute granulating wounds were created on 90 Sprague-Dawley rats. The animals were equally divided into six groups and were treated topically as follows: group 1, sham: no infection, no treatment; group 2, exotoxin A; group 3, exotoxin A and antiexotoxin; group 4, autoclaved PSAR 10(6); group 5, 10(6) viable PSAR inoculated in the wound; group 6, 10(6) viable PSAR and antiexotoxin. Wound contraction was measured with the use of planimetry twice a week. Serial biopsies were performed on all wounds. Contraction rates revealed significantly (p < 0.05) retarded closure in the animals treated with exotoxin A and in the viable PSAR group when compared with the rates of the noninfected control groups. Animals treated with exotoxin A plus antiexotoxin A and those treated with live PSAR and antiexotoxin showed contraction rates identical to the control groups. These data suggest that exotoxin A in PSAR infections retards wound healing and that neutralization of the toxin restores the normal healing process.

Local infiltration of an angiogenic growth factor does not stimulate the delay phenomenon.

The role of angiogenesis in the delay phenomenon is unclear. In this study a potent angiogenic growth factor, basic fibroblast growth factor (bFGF) was used to ascertain the importance of angiogenesis in this phenomenon. bFGF (100 micrograms) was infiltrated beneath the panniculus carnosus on the dorsum of 50 rats. Another 50 rats received saline vehicle infiltration only. Ten days later a modified McFarlane flap (10 x 3 cm) was elevated and biopsies collected. Flap blood flow was determined by laser Doppler before and after elevation. The mean surviving length (Group I--71.3 +/- 4.6 mm and Group II--73.4 +/- 5.5 mm) and Doppler flow measurements were comparable between the two groups. Animals treated with bFGF showed marked perivascular changes and proliferation of fibroblasts, but no increase in the number or size of capillaries was seen. This lack of angiogenesis suggests pharmacologically mediated delay may require more than just an angiogenic stimulus.