Effects of aging and degeneration on the human intervertebral disc during the diurnal cycle: a finite element study

A significant biochemical change that takes place in intervertebral disc degeneration is the loss of proteoglycans in the nucleus pulposus. Proteoglycans attract fluid, which works to reduce mechanical stresses in the solid matrix of the nucleus and provide a hydrostatic pressure to the annulus fibrosus, whose fibrous nature accommodates this stress. Our goals are to develop an osmo-poroelastic finite element model to study the relationship between proteoglycan content and the stress distribution within the disc and to analyze the effects of degeneration on the disc's diurnal mechanical response. Stress in the annulus increased with degeneration from ∼0.2 to 0.4 MPa, and an increase occurred in the center of the nucleus from 1.2 to 1.6 MPa. The osmotic pressure in the central nucleus region decreased the most with degeneration, from ∼0.42 to ∼0.1 MPa in a severely dehydrated disc. A 3% decrease in diurnal fluid lost with degeneration equated to ∼21% decrease in fluid exchange, and hence a decrease in nutrients that require convection to enter the disc. We quantified the increases in internal stresses in the nucleus and annulus throughout the various stages of degeneration, suggesting that these changes lead to further remodeling of the tissue.

Large-scale survey of naturally occurring HBV polymerase mutations associated with anti-HBV drug resistance in untreated patients with chronic hepatitis B

Drug resistance is a major limitation for the long-term efficacy of antiviral therapy with nucleos(t)ide analogues (NAs) in chronic hepatitis B (CHB). Antiviral resistance mutations may pre-exist in the overall viral population of untreated patients. We aimed to assess the prevalence of such hepatitis B virus (HBV) variants in a large cohort of NAs-naïve patients with CHB and to explore possible association with viral and host variables. Serum samples from 286 NAs-naïve consecutive patients with CHB were tested for serum HBV-DNA, and 255 of them having HBV-DNA > 1000 IU/mL were further analysed for drug resistance mutations by INNO-LiPA HBV DRv2/v3. NAs-naïve patients analysed were mainly men (73%), Caucasians (85%), hepatitis B e Antigen (HBeAg) negative (79%) and genotype D (69%), with a mean age of 43.2 ± 13.4 years. HBV mutations associated with antiviral drug resistance were detected in 13 (5%) patients: three patients infected with HBV genotype C had the rtM204V + rtL180M mutations associated with lamivudine (LMV) resistance. Four patients had the rtI233V mutation that may reduce sensitivity to adefovir, and three patients had the rtM250L/V mutation typical of entecavir resistance. LMV compensatory mutations rtL80V and rtV173L were seen in two and one patients, respectively. No relationship was seen between presence of resistant or compensatory mutations and HBV-DNA levels, HBeAg/anti-HBe status or previous IFN therapy. These results confirm that HBV mutations, which confer resistance against currently available anti-HBV NAs, may already exist in patients who have never received the drug.

Osteoblast Attachment on Biomaterials as a Function of Surface Charge

Bioactive materials such as calcium phosphate ceramics and bioactive glasses enhance bone tissue formation and then bond to bone tissue. In our work, we question what particular surface feature or features of bioactive materials are responsible for the bone tissue response. In this study we have uncoupled surface charge from surface chemistry, energy, and topography and have examined osteoblast adhesion to titanium surfaces of varying surface charge. We have shown that a negative surface charge promotes osteoblast adhesion by approximately 60% over a neutral surface and that conversely, a positive surface charge inhibits osteoblast adhesion by about 20%. Continued examination of surface characteristics that control cellular responses are warranted with the eventual goal of applying those desirable surface characteristics to any structural biomaterial for bone implant or tissue engineering applications.

Hyperinsulinaemia reduces the 24-h virological response to PEG-interferon therapy in patients with chronic hepatitis C and insulin resistance

Insulin resistance (IR) reduces response to pegylated-interferon (PEG-IFN)/ribavirin in chronic hepatitis C (CHC), but the mechanisms are still undefined. We examined the relationship between baseline insulin levels, the main component affecting homeostasis model of assessment - insulin resistance (HOMA-IR) for assessment of IR in non-diabetic patients, and the 'acute' virological response to PEG-IFN measured 24 h after the first injection and taken as correlate of intracellular interferon signalling. In 62 patients treated with PEG-IFN/Ribavirin, serum insulin and HOMA-IR were assessed at baseline, while hepatitis C virus (HCV)-RNA was measured at baseline and 24 h, 1, 2, 4 and 12 weeks after treatment initiation. Sustained virological response was examined 24 weeks after therapy discontinuation. Mean baseline insulin was 11.52 +/- 8.51 U/L and mean HOMA-IR was 2.65 +/- 2.01 both being significantly higher with advanced liver fibrosis. Hepatitis C virus-RNA decay observed 24 h after the first injection of PEG-IFN was significantly lower (0.7 +/- 0.8 log) in patients with HOMA > or =3 compared with those with HOMA <3 (1.7 +/- 0.8, P = 0.001). A highly significant (r = -0.42) inverse correlation was observed between baseline insulin levels and the 24-h HCV-RNA decay. The difference in early viral kinetics between patients with HOMA > or =3 or <3 resulted in a significant difference in the percentage of patients achieving rapid (week 4) and sustained virological response. Multivariate analysis, inclusive of patient age, HCV genotype and fibrosis stage, identified baseline insulin levels as the main independent variable affecting the 24-h response to PEG-IFN. Hyperinsulinaemia reduces the cellular response to Pegylated-interferon in CHC with IR. Strategies to reduce insulin levels before initiation of treatment should be pursued to improve efficacy of anti-viral treatment.

Synthesis and recovery characteristics of branched and grafted PNIPAAm-PEG hydrogels for the development of an injectable load-bearing nucleus pulposus replacement

A family of injectable poly(N-isopropyl acrylamide) (PNIPAAm) copolymer hydrogels has been fabricated in order to tune mechanical properties to support load-bearing function and dimensional recovery for possible use as load-bearing medical devices, such as a nucleus pulposus replacement for the intervertebral disc. PNIPAAm-polyethylene glycol (PEG) copolymers were synthesized with varying hydrophilic PEG concentrations as grafted or branched structures to enhance dimensional recovery of the materials. Polymerizations were confirmed with attenuated total reflectance-Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy studies. Incorporation of PEG was effective in raising water content of pure PNIPAAm hydrogels (29.3% water for pure PNIPAAm vs. 47.7% for PEG branches and 39.5% for PEG grafts). PNIPAAm with 7% grafted as well as 7% branched PEG had significantly reduced compressive modulus compared to that of pure PNIPAAm. Initially recovered compressive strain was significantly increased for 7% PEG branches after pre-testing immersion in PBS for up to 33 days, while 7% PEG grafts decreased this value. Sample height recovery for pure PNIPAAm was limited to 31.6%, while PNIPAAm with 7% branches was increased to 71.3%. When mechanically tested samples were allowed to recover without load over 30 min, each composition was able to significantly recover height, indicating that the time to recovery is slower than the unloading rates typically used in testing. While the incorporation of hydrophilic PEG was expected to alter the mechanical behavior of the hydrogels, only the branched form was able to significantly enhance dimensional recovery.

The effect of nucleus implant parameters on the compressive mechanics of the lumbar intervertebral disc: a finite element study

A simplified finite element model of the human lumbar intervertebral disc was utilized for understanding nucleus pulposus implant mechanics. The model was used to assess the effect of nucleus implant parameter variations on the resulting compressive biomechanics of the lumbar anterior column unit. The effects of nucleus implant material (modulus and Poisson's ratio) and geometrical (height and diameter) parameters on the mechanical behavior of the disc were investigated. The model predicted that variations in implant modulus contribute less to the compressive disc mechanics compared to the implant geometrical parameters, for the ranges examined. It was concluded that some threshold exists for the nucleus implant modulus, below which little variations in load-displacement behavior were shown. Compressive biomechanics were highly affected by implant volume (under-filling the nucleus cavity, line-to-line fit, or over-filling the nucleus cavity) with a greater restoration of compressive mechanics observed with the over-filled implant design. This work indicated the effect of nucleus implant parameter variations on the compressive mechanics of the human lumbar intervertebral disc and importance of the "fit and fill" effect of the nuclear cavity in the restoration of the human intervertebral disc mechanics in compression. These findings may have clinical significance for nucleus implant design.

Comparison of periprosthetic tissue digestion methods for ultra-high molecular weight polyethylene wear debris extraction

There is considerable interest in characterization of wear debris from polyethylene (UHMWPE) bearing components used in total joint replacement. To isolate UHMWPE wear debris, tissue samples must be excised from regions adjacent to revised UHMWPE implant components, followed by exposure to one of many available tissue digestion methods. Numerous studies demonstrate successful digestion, but the relative efficiency of each method is not clear. The purpose of this study was to evaluate a variety of conditions for tissue digestion to provide a quantitative comparison of methods. Porcine and human hip tissues were exposed for 24 h to basic, acidic or enzymatic agents, filtered and digestion efficiency calculated based on the percentage of initial to final tissue weight. Of the conditions tested, 5 M NaOH, 5 M KOH, 15 M KOH or 15.8 M HNO(3) yielded the most complete porcine hip tissue digestion (<1% residual tissue weight; p < 0.05). Proteinase K and Liberase Blendzyme 3 did not effectively digest tissue in a 24 h period. Similar to results from the porcine dataset, human tissues digestion was most efficient using 5 M NaOH, 5 M KOH or 15.8 M HNO(3) (<1% residual tissue weight; p < 0.05). To verify that particle surface modifications did not occur after prolonged reagent exposure, GUR415 and Ceridust 3715 particles were immersed in each solution for 24 h. Overall, this study provides a framework for thorough and efficient digestive methods for UHMWPE wear debris extraction.

23Na TQF NMR imaging for the study of spinal disc tissue

A method for acquiring triple quantum filtered (TQF) (23)Na NMR images is proposed that takes advantage of the differences in transverse relaxation rates of sodium to achieve positive intensity, PI, NMR signal. This PITQF imaging sequence has been used to obtain spatially resolved one-dimensional images as a function of the TQF creation time, tau, for two human spinal disc samples. From the images the different parts of the tissue, nucleus pulposus and annulus fibrosus, can be clearly distinguished based on their signal intensity and creation time profiles. These results establish the feasibility of (23)Na TQF imaging and demonstrate that this method should be applicable for studying human disc tissues as well as spinal disc degeneration.

The application of 23Na double-quantum-filter (DQF) NMR spectroscopy for the study of spinal disc degeneration

Degenerative disc disease is an irreversible process that leads to a loss of mechanical integrity and back pain in millions of people. In this report, (23)Na double-quantum-filtered (DQF) NMR spectroscopy is used to study disc tissues in two stages of degeneration. Initial results indicate that the (23)Na DQF signal may be useful for determining the degree of degeneration. The spectral analysis reveals the presence of sodium environments with different residual quadrupolar couplings and T(2) relaxation times that we attribute to different regions, or compartments, corresponding to different biochemical regions in the tissue. In general it is found that there are compartments with no residual quadrupolar couplings, compartments with moderate couplings (200 to 1000 Hz), and compartments with couplings ranging from 1500 to 3000 Hz. The results indicate that (23)Na DQF NMR spectroscopy provides a probe of the degenerative state of the intervertebral disc tissues, and might hold potential as a novel diagnostic method for detection of disc degeneration.

2H double quantum filtered (DQF) NMR spectroscopy of the nucleus pulposus tissues of the intervertebral disc

Deuterium (2H) double-quantum filtered (DQF) NMR spectroscopy of nucleus pulposus (NP) tissues from human intervertebral discs is reported. The DQF spectral intensities, DQ build-up rates, and DQF-detected rotating-frame spin-lattice relaxation times are sensitive to the degree of hydration of the NP tissue, and display a monotonous correlation with age between 15 and 80 years. The implications of this work are that the changes in water dynamics as detected via DQF NMR spectroscopy may be used as a probe of tissue degeneration in NP, particularly in the early stages of degeneration to which most standard NMR methods are not sensitive.

Synthesis and characterization of an injectable hydrogel with tunable mechanical properties for soft tissue repair

Injectable polymers are attractive materials for the fixation or augmentation of soft tissues. Thermosensitive hydrogels, especially poly(N-isopropylacryamide), have been investigated for these applications to exploit the lower critical solution temperature (LCST) which falls between room and body temperatures. One limitation to the material is the ability to withstand loading. In this work, we evaluated an injectable material system, poly(N-isopropylacryamide)-co-poly(ethyleneglycol) dimethacrylate, with the addition of trimethacryloxypropyltrimethoxysilane (MPS). Our goal was to investigate the potential to tune the mechanical behavior of the injectable hydrogel. Addition of MPS to the hydrogel increased the compressive modulus but did not affect the LCST of the hydrogel. An increase in ion concentration of the immersion media resulted in less solution uptake by the hydrogels, regardless of MPS presence in the system. The challenge of this material system is to balance the network-forming and modulus-enhancing MPS while maintaining an injectable hydrogel for potential soft tissue repair.

In situ apatite forming injectable hydrogel

Injectable polymers are attractive materials for tissue augmentation or replacement. Thermosensitive hydrogels, especially poly(N-isopropylacryamide), have been investigated for these applications to exploit the lower critical solution temperature (LCST) which falls between room and body temperatures. Some practical limitations to the material are the load-bearing capabilities and the ability to bond to the host tissue. In this work, we evaluated a novel, injectable apatite-forming material system: poly(N-isopropylacryamide)-co-poly(ethyleneglycol) dimethacrylate, with the addition of tri-methacryloxypropyltrimethoxysilane (MPS). We have previously reported that MPS concentration permits the material system to be tuned to different compressive moduli ranging from 50-700 kPa without altering the LCST of the material. Here, we explore the apatite formation of this material system in protein-free and protein-containing SBF. The MPS-containing hydrogel system exhibited apatite formation throughout the gel thickness. The apatite formation was inhibited by the presence of proteins. This mechanism is likely controlled by the silanol groups (Si-OH) in MPS, which provided attachment sites for calcium and initiated mineral dissolution from the simulated biological environments. The challenge of this material system is to balance the network-forming and modulus-enhancing MPS while maintaining an injectable hydrogel for potential tissue regeneration.

Friction and wear behavior of poly(vinyl alcohol)/poly(vinyl pyrrolidone) hydrogels for articular cartilage replacement

Many hydrogels have been proposed as articular cartilage replacements as an alternative to partial or total joint replacements. In the current study, poly(vinyl alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) hydrogels were investigated as potential cartilage replacements by investigating their in vitro wear and friction characteristics in a pin-on-disk setup. A three-factor variable-level experiment was designed to study the wear and friction characteristics of PVA/PVP hydrogels. The three different factors studied were (a) polymer content of PVA/PVP hydrogels, (b) load, and (c) effect of lubricant. Twelve tests were conducted, with each lasting 100,000 cycles against Co-Cr pins. The average coefficient of friction for synovial fluid lubrication was a low 0.035 compared with 0.1 for bovine serum lubrication. Frictional behavior of PVA/PVP hydrogels did not follow Amonton's law of friction. Wear of the hydrogels was quantified by measuring their dry masses before and after the tests. Higher polymer content significantly reduced the wear of hydrogel samples with 15% PVA/PVP samples, showing an average dry polymer loss of 4.74% compared with 6.05% for 10% PVA/PVP samples. A trend change was observed in both the friction and wear characteristics of PVA/PVP hydrogels at 125 N load, suggesting a transition in the lubricating mechanism at the pin-hydrogel interface at the critical 125 N load.

2006 Otto Aufranc Award Paper: significance of in vivo degradation for polyethylene in total hip arthroplasty

Our research group developed an implant retrieval program to study in vivo degradation of polyethylene. We now have evidence to support our hypothesis that degradation of radiation-sterilized polyethylene occurs in the body for not only historical gamma air sterilized liners, but also for conventional gamma inert sterilized (ArCom) and annealed highly crosslinked polyethylene (Crossfire) liners as well. Our research has also led to the discovery that the most severe manifestations of in vivo oxidation typically occur in regions of the liner experiencing minimal wear, such as the rim of the component, where the body fluids (containing oxidizing species) have access to the polyethylene. Our data from historical, ArCom, and Crossfire retrievals all point to a similar scenario in which the femoral head limits the in vivo oxidation of polyethylene at the bearing surface. Consequently, provided rim impingement does not occur, and the polyethylene locking mechanisms remain relatively isolated from oxidizing fluid, in vivo oxidation does not seem to be clinically important in the first 10 years of implantation for conventional gamma sterilized polyethylene. We conclude that in vivo degradation should be included among the list of potential long-term failure modes for modular polyethylene components for total hip arthroplasty.

The Role of Interfacial Mechanics in the Prediction of Global Mechanical Behavior of a Bioactive Composite: An In Vitro Study

A bioactive bone-tissue substitute, hydroxyapatite (HA)-polymethylmethacrylate (PMMA) with the addition of a copolymer coupling agent, was examined in vitro to determine the influence of the coupling agent on the local mechanical properties of the system before and after simulated biologic conditions. Nano-indentation of the cross-sectional interface between the HA and PMMA of the composite was studied. The fracture mechanism and position of each indent mark were analyzed at up to 5000× magnification under field-emission, environmental-scanning electron microscopy. The local interfacial results were compared with global quasistatic compression test results. It was found that nano-indentation of the interface could predict changes in global mechanical behavior of the composite. Both interfacial and global Young's moduli were reduced after immersion in the simulated biologic media. Although the coupling agent improved the interfacial and global mechanical properties before and after 24 hours in in vitro immersion, it did not affect the surface bioactivity of the system, as shown in the measurement of calcium and phosphate concentration uptake. Thus, nano-indentation is a sensitive technique for examining interfacial mechanics and mechanical consequences of biologic reactivity of composite materials.

Functional compressive mechanics of a PVA/PVP nucleus pulposus replacement

Emerging techniques as an alternative to the current treatments of lower back pain include nucleus replacement by an artificial material, which aims to relieve pain and restore the normal spinal motion. The compressive mechanical behavior of the PVA/PVP hydrogel nucleus implant was assessed in the present study. PVA/PVP hydrogels were made with various PVP concentrations. The hydrogels were loaded statically under unconfined and confined conditions. Hydrogels were tested dynamically up to 10 million cycles for a compression fatigue. Also, hydrogel nucleus implants with a line-to-line fit, were implanted in the human cadaveric intervertebral discs (IVD) to determine the compressional behavior of the implanted discs. Hydrogel samples exhibited typical non-linear response under both unconfined and confined compressions. Properties of the confinement ring dictated the observed response. Hydrogel moduli and polymer content were not different pre- and post-fatigues. Slight geometrical changes (mostly recoverable) were observed post-fatigue. In cadavers, hydrogels restored the compressive stiffness of the denucleated disc when compared with equivalent condition of the IVD. The results of this study demonstrate that PVA/PVP hydrogels may be viable as nucleus pulposus implants. Further studies under complex loading conditions are warranted to better assess its potential as a replacement to the degenerated nucleus pulposus.

The effect of protein-free versus protein-containing medium on the mechanical properties and uptake of ions of PVA/PVP hydrogels

The effect of two simulated biological environments (protein-free and protein-containing) on ion uptake and physical properties of PVA/PVP hydrogels were explored in this work. It was found that over the immersion period in both media, wet mass of the hydrogels decreased and compressive moduli increased, likely due to increased polymer content with water loss as the hydrogels equilibrated with water. These changes were independent of polymer content and immersion medium. However, dry mass of the hydrogels increased dramatically when immersed in protein-free medium, changing only moderately in protein-containing medium. The increase in dry mass was attributed to ion uptake from immersion medium, as confirmed by EDXA. We postulate that differences between ion uptake in protein-free versus protein-containing medium is likely the result of serum proteins in the protein-containing medium adsorbing to the surface, inhibiting transport of ions into the hydrogel.

Prevalence, clinical spectrum and atypical symptoms of gastro-oesophageal reflux in Argentina: a nationwide population-based study

BACKGROUND

Population-based data on gastro-oesophageal reflux in Latin America are lacking.

AIM

To assess gastro-oesophageal reflux symptom prevalence, clinical spectrum and association with the atypical symptoms in our country.

METHODS

Gastro-oesophageal reflux self-report questionnaires validated at Mayo Clinic, USA, were submitted to a sample of 1000 residents (aged 18-80 years) from 17 representative geographical areas of Argentina. The samples were selected and stratified according to age, gender, geographical areas and size of town of residence provided by the Argentine Bureau of Statistics and Census.

RESULTS

The overall prevalence of any typical gastro-oesophageal reflux symptom experienced in the previous year was 61.2% (95% CI, 57.9-64.6), the prevalence of frequent gastro-oesophageal reflux symptoms was 23.0% (95% CI, 20.1-25.9) and the prevalence of gastro-oesophageal reflux disease was 11.9% (95% CI, 9.6-14.1). Frequent gastro-oesophageal reflux symptoms were associated with dysphagia (OR 2.12, 95% CI, 1.27-3.54, P < 0.01), globus (OR 2.22, 95% CI, 1.35-3.66, P < 0.01) and non-cardiac chest pain (OR 1.55, 95% CI, 1.04-2.31, P < 0.05).

CONCLUSIONS

In Argentina, typical symptoms of gastro-oesophageal reflux are highly prevalent at the national level, and frequent gastro-oesophageal reflux symptoms are significantly associated with dysphagia, globus and non-cardiac chest pain.

Effect of coupling agents on the local mechanical properties of bioactive dental composites by the nano-indentation technique

OBJECTIVES

To examine the use of nano-indentation as a method of determining the interfacial mechanics of bioactive composites for mandibular bone substitutes.

METHODS

Three coupling agents (PMMA-MAA, PMMA-MA and silane) were used to treat hydroxyapatite (HA) particles before incorporation into a polymethylmethacrylate (PMMA) matrix. Nano-indentation was used to determine the hardness and Young's modulus on the HA particle surface, at the HA/PMMA interface and in the PMMA matrix region for each of the four groups. In addition bulk four-point bending tests were conducted on each of the four groups as a comparison.

RESULTS

The findings resulted in significant differences in the local interfacial Young's modulus between the polymer-treated composites and the uncoupled control specimens with a marked improvement (50%) in modulus with either polymertreated group. Similarly, the bending modulus of the polymer-treated groups was significantly higher than the un-treated control group; however, these differences were not as pronounced (approximately 15%).

SIGNIFICANCE

The co-polymer-treated composites resulted in improved interfacial modulus as compared to the un-treated controls and that the nano-indentation technique is a powerful tool for understanding the local interfacial mechanics of bioactive composites.

In vivo degradation of polyethylene liners after gamma sterilization in air

BACKGROUND

Ultra-high molecular weight polyethylene degrades during storage in air following gamma sterilization, but the extent of in vivo degradation remains unclear. The purpose of this study was to quantify the extent to which the mechanical properties and oxidation of conventional polyethylene acetabular liners treated with gamma sterilization in air change in vivo.

METHODS

Fourteen modular cementless acetabular liners were revised at an average of 10.3 years (range, 5.9 to 13.5 years) after implantation. All liners, which had been machined from GUR 415 resin, had been gamma-sterilized in air; the average shelf life was 0.3 year (range, 0.0 to 0.8 year). After removal, the components were expeditiously frozen to minimize ex vivo changes to the polyethylene prior to characterization. The average duration between freezing and testing was 0.6 year. Mechanical properties and oxidation were measured with use of the small-punch test and Fourier transform infrared spectroscopy, respectively, in the loaded and unloaded regions of the liners.

RESULTS

There was substantial regional variation in the mechanical properties and oxidation of the retrieved liners. The ultimate load was observed to vary by >90% near the surface. On the average, the rim and the unloaded bearing showed evidence of severe oxidation near the surface after long-term in vivo aging, but these trends were not typically observed on the loaded bearing surface or near the backside of the liners.

CONCLUSIONS

The mechanical properties of polyethylene that has been gamma-sterilized in air may decrease substantially in vivo, depending on the location in the liner. The most severe oxidation was observed at the rim, suggesting that the femoral head inhibits access of oxygen-containing body fluids to the bearing surface. This is perhaps why in vivo oxidation has not been associated with clinical performance to date.

Nucleus Implant Parameters Significantly Change the Compressive Stiffness of the Human Lumbar Intervertebral Disc

Nucleus replacement by a synthetic material is a recent trend for treatment of lower back pain. Hydrogel nucleus implants were prepared with variations in implant modulus, height, and diameter. Human lumbar intervertebral discs (IVDs) were tested in compression for intact, denucleated, and implanted condition. Implantation of nucleus implants with different material and geometric parameters into a denucleated IVD significantly altered the IVD compressive stiffness. Variations in the nucleus implant parameters significantly change the compressive stiffness of the human lumbar IVD. Implant geometrical variations were more effective than those of implant modulus variations in the range examined.