What is the optimal management of potentially resectable stage III-N2 NSCLC? Results of a fixed-effects network meta-analysis and economic modelling

Introduction

There is a critical need to understand the optimal treatment regimen in patients with potentially resectable stage III-N2 nonsmall cell lung cancer (NSCLC).

Methods

A systematic review of randomised controlled trials was carried out using a literature search including the CDSR, CENTRAL, DARE, HTA, EMBASE and MEDLINE bibliographic databases. Selected trials were used to perform a Bayesian fixed-effects network meta-analysis and economic modelling of treatment regimens relevant to current-day treatment options: chemotherapy plus surgery (CS), chemotherapy plus radiotherapy (CR) and chemoradiotherapy followed by surgery (CRS).

Findings

Six trials were prioritised for evidence synthesis. The fixed-effects network meta-analyses demonstrated an improvement in disease-free survival (DFS) for CRS versus CS and CRS versus CR of 0.34 years (95% CI 0.02-0.65) and 0.32 years (95% CI 0.05-0.58) respectively, over a 5-year period. No evidence of effect was observed in overall survival although point estimates favoured CRS. The probabilities that CRS had a greater mean survival time and greater probability of being alive than the reference treatment of CR at 5 years were 89% and 86% respectively. Survival outcomes for CR and CS were essentially equivalent. The economic model calculated that CRS and CS had incremental cost-effectiveness ratios of £19 000/quality-adjusted life-year (QALY) and £78 000/QALY compared to CR. The probability that CRS generated more QALYs than CR and CS was 94%.

Interpretation

CRS provides an extended time in a disease-free state leading to improved cost-effectiveness over CR and CS in potentially resectable stage III-N2 NSCLC.

Cost-effectiveness of topical pharmacological, oral pharmacological, physical and combined treatments for acne vulgaris

BACKGROUND

Acne vulgaris is a common skin condition that may cause psychosocial distress. There is evidence that topical treatment combinations, chemical peels and photochemical therapy (combined blue/red light) are effective for mild-to-moderate acne, while topical treatment combinations, oral antibiotics combined with topical treatments, oral isotretinoin and photodynamic therapy are most effective for moderate-to-severe acne. Effective treatments have varying costs. The National Institute for Health and Care Excellence (NICE) in England considers cost-effectiveness when producing national clinical, public health and social care guidance.

AIM

To assess the cost-effectiveness of treatments for mild-to-moderate and moderate-to-severe acne to inform relevant NICE guidance.

METHODS

A decision-analytical model compared costs and quality-adjusted life-years (QALYs) of effective topical pharmacological, oral pharmacological, physical and combined treatments for mild-to-moderate and moderate-to-severe acne, from the perspective of the National Health Service in England. Effectiveness data were derived from a network meta-analysis. Other model input parameters were based on published sources, supplemented by expert opinion.

RESULTS

All of the assessed treatments were more cost-effective than treatment with placebo (general practitioner visits without active treatment). For mild-to-moderate acne, topical treatment combinations and photochemical therapy (combined blue/red light) were most cost-effective. For moderate-to-severe acne, topical treatment combinations, oral antibiotics combined with topical treatments, and oral isotretinoin were the most cost-effective. Results showed uncertainty, as reflected in the wide confidence intervals around mean treatment rankings.

CONCLUSION

A range of treatments are cost-effective for the management of acne. Well-conducted studies are needed to examine the long-term clinical efficacy and cost-effectiveness of the full range of acne treatments.

A systematic review and network meta-analysis of topical pharmacological, oral pharmacological, physical and combined treatments for acne vulgaris

BACKGROUND

Various treatments for acne vulgaris exist, but little is known about their comparative effectiveness in relation to acne severity.

OBJECTIVES

To identify best treatments for mild-to-moderate and moderate-to-severe acne, as determined by clinician-assessed morphological features.

METHODS

We undertook a systematic review and network meta-analysis of randomized controlled trials (RCTs) assessing topical pharmacological, oral pharmacological, physical and combined treatments for mild-to-moderate and moderate-to-severe acne, published up to May 2020. Outcomes included percentage change in total lesion count from baseline, treatment discontinuation for any reason, and discontinuation owing to side-effects. Risk of bias was assessed using the Cochrane risk-of-bias tool and bias adjustment models. Effects for treatments with ≥ 50 observations each compared with placebo are reported below.

RESULTS

We included 179 RCTs with approximately 35 000 observations across 49 treatment classes. For mild-to-moderate acne, the most effective options for each treatment type were as follows: topical pharmacological - combined retinoid with benzoyl peroxide (BPO) [mean difference 26·16%, 95% credible interval (CrI) 16·75-35·36%]; physical - chemical peels, e.g. salicylic or mandelic acid (39·70%, 95% CrI 12·54-66·78%) and photochemical therapy (combined blue/red light) (35·36%, 95% CrI 17·75-53·08%). Oral pharmacological treatments (e.g. antibiotics, hormonal contraceptives) did not appear to be effective after bias adjustment. BPO and topical retinoids were less well tolerated than placebo. For moderate-to-severe acne, the most effective options for each treatment type were as follows: topical pharmacological - combined retinoid with lincosamide (clindamycin) (44·43%, 95% CrI 29·20-60·02%); oral pharmacological - isotretinoin of total cumulative dose ≥ 120 mg kg^-1 per single course (58·09%, 95% CrI 36·99-79·29%); physical - photodynamic therapy (light therapy enhanced by a photosensitizing chemical) (40·45%, 95% CrI 26·17-54·11%); combined - BPO with topical retinoid and oral tetracycline (43·53%, 95% CrI 29·49-57·70%). Topical retinoids and oral tetracyclines were less well tolerated than placebo. The quality of included RCTs was moderate to very low, with evidence of inconsistency between direct and indirect evidence. Uncertainty in findings was high, in particular for chemical peels, photochemical therapy and photodynamic therapy. However, conclusions were robust to potential bias in the evidence.

CONCLUSIONS

Topical pharmacological treatment combinations, chemical peels and photochemical therapy were most effective for mild-to-moderate acne. Topical pharmacological treatment combinations, oral antibiotics combined with topical pharmacological treatments, oral isotretinoin and photodynamic therapy were most effective for moderate-to-severe acne. Further research is warranted for chemical peels, photochemical therapy and photodynamic therapy for which evidence was more limited. What is already known about this topic? Acne vulgaris is the eighth most common disease globally. Several topical, oral, physical and combined treatments for acne vulgaris exist. Network meta-analysis (NMA) synthesizes direct and indirect evidence and allows simultaneous inference for all treatments forming an evidence network. Previous NMAs have assessed a limited range of treatments for acne vulgaris and have not evaluated effectiveness of treatments for moderate-to-severe acne. What does this study add? For mild-to-moderate acne, topical treatment combinations, chemical peels, and photochemical therapy (combined blue/red light; blue light) are most effective. For moderate-to-severe acne, topical treatment combinations, oral antibiotics combined with topical treatments, oral isotretinoin and photodynamic therapy (light therapy enhanced by a photosensitizing chemical) are most effective. Based on these findings, along with further clinical and cost-effectiveness considerations, National Institute for Health and Care Excellence (NICE) guidance recommends, as first-line treatments, fixed topical treatment combinations for mild-to-moderate acne and fixed topical treatment combinations, or oral tetracyclines combined with topical treatments, for moderate-to-severe acne.

A non-parametric approach for jointly combining evidence on progression free and overall survival time in network meta-analysis

Randomised controlled trials of cancer treatments typically report progression free survival (PFS) and overall survival (OS) outcomes. Existing methods to synthesise evidence on PFS and OS either rely on the proportional hazards assumption or make parametric assumptions which may not capture the diverse survival curve shapes across studies and treatments. Furthermore, PFS and OS are not independent: OS is the sum of PFS and post-progression survival (PPS). Our aim was to develop a non-parametric approach for jointly synthesising evidence from published Kaplan-Meier survival curves of PFS and OS without assuming proportional hazards. Restricted mean survival times (RMST) are estimated by the area under the survival curves (AUCs) up to a restricted follow-up time. The correlation between AUCs due to the constraint that OS>PFS is estimated using bootstrap re-sampling. Network meta-analysis models are given for RMST for PFS and PPS and ensure that OS=PFS + PPS. Both additive and multiplicative network meta-analysis models are presented to obtain relative treatment effects as either differences or ratios of RMST. The methods are illustrated with a network meta-analysis of treatments for Stage IIIA-N2 Non-Small Cell Lung Cancer. The approach has implications for health economic models of cancer treatments which require estimates of the mean time spent in the PFS and PPS health-states. The methods can be applied to a single time-to-event outcome, and so have wide applicability in any field where time-to-event outcomes are reported, the proportional hazards assumption is in doubt, and survival curve shapes differ across studies and interventions. This article is protected by copyright. All rights reserved.

Spie charts for quantifying treatment effectiveness and safety in multiple outcome network meta-analysis: a proof-of-concept study

BACKGROUND

Network meta-analysis (NMA) simultaneously synthesises direct and indirect evidence on the relative efficacy and safety of at least three treatments. A decision maker may use the coherent results of an NMA to determine which treatment is best for a given outcome. However, this evidence must be balanced across multiple outcomes. This study aims to provide a framework that permits the objective integration of the comparative effectiveness and safety of treatments across multiple outcomes.

METHODS

In the proposed framework, measures of each treatment's performance are plotted on its own pie chart, superimposed on another pie chart representing the performance of a hypothetical treatment that is the best across all outcomes. This creates a spie chart for each treatment, where the coverage area represents the probability a treatment ranks best overall. The angles of each sector may be adjusted to reflect the importance of each outcome to a decision maker. The framework is illustrated using two published NMA datasets comparing dietary oils and fats and psoriasis treatments. Outcome measures are plotted in terms of the surface under the cumulative ranking curve. The use of the spie chart was contrasted with that of the radar plot.

RESULTS

In the NMA comparing the effects of dietary oils and fats on four lipid biomarkers, the ease of incorporating the lipids' relative importance on spie charts was demonstrated using coefficients from a published risk prediction model on coronary heart disease. Radar plots produced two sets of areas based on the ordering of the lipids on the axes, while the spie chart only produced one set. In the NMA comparing psoriasis treatments, the areas inside spie charts containing both efficacy and safety outcomes masked critical information on the treatments' comparative safety. Plotting the areas inside spie charts of the efficacy outcomes against measures of the safety outcome facilitated simultaneous comparisons of the treatments' benefits and harms.

CONCLUSIONS

The spie chart is more optimal than a radar plot for integrating the comparative effectiveness or safety of a treatment across multiple outcomes. Formal validation in the decision-making context, along with statistical comparisons with other recent approaches are required.

Empirical evaluation of SUCRA-based treatment ranks in network meta-analysis: quantifying robustness using Cohen's kappa

OBJECTIVE

To provide a framework for quantifying the robustness of treatment ranks based on Surface Under the Cumulative RAnking curve (SUCRA) in network meta-analysis (NMA) and investigating potential factors associated with lack of robustness.

METHODS

We propose the use of Cohen's kappa to quantify the agreement between SUCRA-based treatment ranks estimated through NMA of a complete data set and a subset of it. We illustrate our approach using five published NMA data sets, where robustness was assessed by removing studies one at a time.

RESULTS

Overall, SUCRA-based treatment ranks were robust to individual studies in the five data sets we considered. We observed more incidences of disagreement between ranks in the networks with larger numbers of treatments. Most treatments moved only one or two ranks up or down. The lowest quadratic weighted kappa estimate observed across all networks was in the network with the smallest number of treatments (4), where weighted kappa=40%. In the network with the largest number of treatments (12), the lowest observed quadratic weighted kappa=89%, reflecting a small shift in this network's treatment ranks overall. Preliminary observations suggest that a study's size, the number of studies making a treatment comparison, and the agreement of a study's estimated treatment effect(s) with those estimated by other studies making the same comparison(s) may explain the overall robustness of treatment ranks to studies.

CONCLUSIONS

Investigating robustness or sensitivity in an NMA may reveal outlying rank changes that are clinically or policy-relevant. Cohen's kappa is a useful measure that permits investigation into study characteristics that may explain varying sensitivity to individual studies. However, this study presents a framework as a proof of concept and further investigation is required to identify potential factors associated with the robustness of treatment ranks using more extensive empirical evaluations.

Clinical impact of improved point-of-care glucose monitoring in neonatal intensive care using Nova StatStrip: Evidence for improved accuracy, better sensitivity, and reduced test utilization

OBJECTIVES

Studies have demonstrated improved analytical performance of the Nova StatStrip glucose meter, but limited data is available on its clinical performance in critically ill neonates in the neonatal intensive care unit (NICU).

DESIGN AND METHODS

A retrospective charge review was conducted on 651 neonates admitted to the NICU over 2 years. Demographics, sample collection information, and clinical details were recorded. Glucose measurements were performed at the bedside using either the Nova StraStrip or LifeScan SureStep Flexx meters as well as corresponding measurements of laboratory venous plasma glucose. Performance was analyzed by receiver operator characteristic (ROC) curves for detecting hypoglycemia and critical glucose levels.

RESULTS

Linear regression analysis comparing StatStrip and laboratory venous plasma glucose samples demonstrated significantly tighter agreement (r(2)=0.7994) and accuracy (mean bias=0.13mmol/L) than SureStep (r(2)=0.6845 and mean bias=0.53mmol/L). StatStrip also showed improved sensitivity for detecting critical low glucose values ≤3.0mmol/L (80.9 vs 68.9%, p<0.05). ROC curve analysis further demonstrated excellent performance of StatStrip at this cutoff with an AUC of 0.98. Overall, neonates were also tested significantly less frequently with the StatStrip meter by 24% compared to SureStep.

CONCLUSIONS

Implementation of StatStrip led to better agreement with venous plasma glucose, improved detection of critical low glucose results, and more efficient test utilization. This study demonstrates the importance of accurate and sensitive glucose monitoring in the NICU.

Closing the gaps in pediatric laboratory reference intervals: a CALIPER database of 40 biochemical markers in a healthy and multiethnic population of children

BACKGROUND

Pediatric healthcare is critically dependent on the availability of accurate and precise laboratory biomarkers of pediatric disease, and on the availability of reference intervals to allow appropriate clinical interpretation. The development and growth of children profoundly influence normal circulating concentrations of biochemical markers and thus the respective reference intervals. There are currently substantial gaps in our knowledge of the influences of age, sex, and ethnicity on reference intervals. We report a comprehensive covariate-stratified reference interval database established from a healthy, nonhospitalized, and multiethnic pediatric population.

METHODS

Healthy children and adolescents (n = 2188, newborn to 18 years of age) were recruited from a multiethnic population with informed parental consent and were assessed from completed questionnaires and according to defined exclusion criteria. Whole-blood samples were collected for establishing age- and sex-stratified reference intervals for 40 serum biochemical markers (serum chemistry, enzymes, lipids, proteins) on the Abbott ARCHITECT c8000 analyzer.

RESULTS

Reference intervals were generated according to CLSI C28-A3 statistical guidelines. Caucasians, East Asians, and South Asian participants were evaluated with respect to the influence of ethnicity, and statistically significant differences were observed for 7 specific biomarkers.

CONCLUSIONS

The establishment of a new comprehensive database of pediatric reference intervals is part of the Canadian Laboratory Initiative in Pediatric Reference Intervals (CALIPER). It should assist laboratorians and pediatricians in interpreting test results more accurately and thereby lead to improved diagnosis of childhood diseases and reduced patient risk. The database will also be of global benefit once reference intervals are validated in transference studies with other analytical platforms and local populations, as recommended by the CLSI.

The effect of pressure loading on the blood flow rate in human skin

The effect of pressure on the blood flow in skin is of considerable clinical interest. Methods are described for the estimation of skin blood flow from the disappearance rate of an injection of 133Xe in saline. The flow rate may be monitored for a period long enough to establish the normal flow and the reduced flow resulting from a constant pressure load. Initial results indicate that the flow is reduced greatly by pressures up to 10 mmHg. This result is interpreted as a demonstration of an auto regulatory mechanism of skin blood flow. Above 30 mmHg the flow continues to decrease essentially to zero as systolic pressure is approached.

Interface pressures and shear stresses: sagittal plane angular alignment effects in three trans-tibial amputee case studies

Interface pressures and shear stresses at different sagittal plane angular alignment settings were measured on 3 trans-tibial amputee subjects ambulating with patellar-tendon-bearing total contact prostheses. Substantial socket-shank angular alignment modifications in the sagittal plane had minimal effect on stance phase peak interface pressures, though more substantial effects on stance phase peak resultant shear stresses. No consistent trend of a greater stress at misaligned vs nominally aligned settings was identified. Changes in interface stresses from session to session tended to be greater than those for different alignment settings, suggesting that subjects compensated well for misalignments but less well for session differences.

Fatigue life of a Nd:YAG laser-welded metal ceramic alloy

Fifteen laser-welded Olympia alloy samples were divided into three groups of five samples each, with different gap distances between the welded halves. The first group was welded with a 0.0-mm gap distance. The second and third groups had Olympia shims placed in 0.3- and 1.0-mm gaps, respectively, prior to laser welding. Each of the samples was tested to failure in load fatigue at 30 Hz in a fatigue testing device using an applied stress of 35,000 psi (241.4 MPa). The means and standard deviations for the number of cycles required to produce fatigue failure for each group was 494,618 +/- 118,311 cycles for the group welded with 0.0-mm gap distance, and 242,741 +/- 44,623 and 232,021 +/- 55,877 cycles for the 0.3- and 1.0-mm specimens, respectively. A one-way analysis of variance showed that the 0.0-mm gap specimens had the greatest number of cycles to failure (P < or = 0.05). There was no significant difference between the other two groups. With the exception of two specimens that failed at the weld center, all failures occurred at the edge of the weld.

Load fatigue performance of two implant-abutment combinations

The load fatigue performance of the CeraOne and EsthetiCone implant systems was investigated. Three torques (standard torque, standard torque + 20%, and standard torque -20%) were used to tighten the screws. A rotating-beam fatigue model was used. A 70-N load was applied to the specimens at a 30-degree angle to the long axis. Two-way analysis of variance revealed (1) no statistically significant difference between the three torques for each system, and (2) a statistically significant difference between the implant systems. Implant failure occurred in 10 of 15 CeraOne specimens. In the EsthetiCone system, only abutment screw failure occurred.

Influence of reinforcement design on the loss of marginal seal of provisional fixed partial dentures

Loss of marginal cement seal, initial fracture, and stiffness of three four-unit provisional restorations were tested. Loss of marginal cement seal was monitored using strain gauges located occlusogingivally at the distal of the second molar abutment and the mesial of the first premolar abutment of a four-unit posterior fixed provisional restoration with two pontics. The provisional restorations were then placed in an Instron testing machine and loaded to initial fracture. Stiffness was calculated from the Instron recordings. The provisional designs were permachrome band-reinforced, wire-reinforced, and a nonreinforced control. Analysis showed: (1) the band-reinforced design withstood a significantly greater load before loss of cement seal (P< or =.05); (2) the band-reinforced design had a significantly higher stiffness (P< or =.05); and (3) there was no difference between the three designs for load at initial fracture. Within the same sample it was found that for both band- and wire-reinforced designs the premolar abutment lost the marginal cement seal at a significantly lower load than the molar (P< or =.05). For the control there was no significant difference for load at marginal cement seal loss between abutments.

Comparison of residual stability in thoracolumbar spine fractures using neutral zone measurements

Because treatment algorithms for spinal injuries depend largely on the clinical assessment of stability after injury, this study both quantified and compared the mechanical stability after three different patterns of injury in the thoracolumbar spine. We created compression fractures, burst fractures, and flexion-distraction injuries in 26 thoracolumbar specimens from human cadavers in order to compare residual stability as a function of type of injury. Spinal stability was evaluated using measurements of the boundaries of the neutral zone, which provide a measure of spinal laxity in various directions of motion. An increase after injury was indicative of greater spinal laxity and hence reduced residual stability. Geometric characteristics (or parameters) of the neutral zone boundaries were used for statistical comparison between the types of injury. Of the three groups, burst fractures retained the least residual stability and compression fractures, the greatest. The angular ranges of motion in the neutral zone for burst fractures demonstrated increases (compared with average values for intact specimens) of 154% in flexion-extension, 134% in lateral bending, and 108% in torsion after injury. The results for flexion-distraction injuries were similar to those for burst fractures in flexion-extension (126%) and torsion (62%); however, more residual stability was retained in lateral bending than was seen for burst fractures (48%). Compression fractures retained the most residual stability, with increases in motion of 40% in flexion-extension, 56% in lateral bending, and 3% in torsion. These findings may be useful in determining the necessity for surgical stabilization of the spine and selection of the appropriate system of fixation.

How does vacuum forming affect Pelite mechanical properties?

Pelite is a polyethylene closed cell foam commonly used as an interface material in prosthetics. Both normal and vacuum-formed Pelite were tested under compression and under shear loading. For shear testing, the results were not significantly different for normal and vacuum-formed Pelite. For normal Pelite, the slope of the stress-strain curve was 1.17MPa (+/- 0.14) while for vacuum-formed Pelite it was 1.24MPa (+/- 0.22). Compressive results, however, were significantly different. Below 80kPa of applied compression, the slope of the stress-strain curve for normal Pelite was 0.99MPa (+/- 0.11) while for vacuum formed Pelite it was 0.72MPa (+/- 0.12). Between 80kPa and 200kPa of applied compression, the slope of the stress-strain curve for normal Pelite was 0.45MPa (+/- 0.03) while for vacuum formed Pelite it was 0.55MPa (+/- 0.05). Reasons for the differences and their significance to interface mechanics and computer-aided prosthesis design are discussed.

Clinical measurement of normal and shear stresses on a trans-tibial stump: characteristics of wave-form shapes during walking

Stresses on the surface of a stump within a prosthetic socket during walking can potentially traumatize stump tissues. To gain insight into stresses and design parameters that affect them, normal and shear interface stresses were measured on three unilateral trans-tibial amputee subjects during walking trials. During stance phase repeated characteristics in wave-form shapes from different subjects were apparent. They included "loading delays", "high frequency events (HFE's)", "first peaks", "valleys", "second peaks", and "push-off". Characteristics did not necessarily occur at the same time from one step to the next but their timings matched well with events in shank force and moment data which were collected simultaneously. For "plantarflexion" and "dorsiflexion" alignment changes, the above wave-form characteristics were still present but their timings within the stance phase changed. The physical meaning and relevance of the characteristics to stump tissue mechanics are discussed.

Fatigue life of porcelain repair systems

Eight intraoral porcelain repair systems, ie, Oral Ceram-Etch (Gresco), Scotchprime (3M), Rocatec (ESPE), Command Ultrafine (Kerr), Silistor (Kulzer), Clearfil Porcelain Bond (J Morita), All-Bond (Bisco), and Monobond S (Vivadent) were used in this study. The control specimens consisted of unetched porcelain surfaces onto which a resin composite was polymerized without the use of an adhesive. Load fatigue was used as the testing method to simulate the repetitive action of mastication. The peak stress applied to each test specimen was 1500 psi (10.34 MPa), and an upper limit on the number of load cycles applied to any specimen was set at 2,000,000 cycles. Statistical analysis revealed two significant subsets. Only Clearfil Porcelain Bond and All-Bond did not fail before reaching the 2,000,000-cycle upper limit.

Interface shear stresses during ambulation with a below-knee prosthetic limb

Shear stresses on a residual limb in a prosthetic socket are considered clinically to contribute to tissue breakdown in below-knee amputees. When applied simultaneously with normal stresses, they can cause injury within the skin or can generate an abrasion on the surface. To gain insight into shear stresses and parameters that affect them, interface stresses were recorded on below-knee amputee subjects during walking trials. On the tibial flares, resultant shear ranged from 5.6 kPa to 39.0 kPa, while on the posterior surface it ranged from 5.0 kPa to 40.7 kPa. During stance phase, anterior resultant shears on a socket were directed toward the apex while posterior resultant shears were directed downward approximately perpendicular to the ground. Waveform shapes were usually double-peaked, with the first peak at 25% to 40% into stance phase and the second peak at 65% to 85% into stance. Application of these results to residual limb tissue mechanics and prosthetic design is discussed.

An angular alignment measurement device for prosthetic fitting

A device to measure socket/shank angular alignment in a prosthesis equipped with a Berkeley Adjustable Leg is described. Angular alignment in the sagittal plane can be measured over the entire 20-degree range with a repeatability of 1 degree. This device can be a useful prosthetics fitting, teaching, and research tool.

Biomechanical properties of dermis

Data obtained from a wide variety of test methods both in vitro and in vivo and histological studies of stressed skin have led to an understanding of the mechanical properties of the dermis and the relation of these properties to the structure of the collagen and elastin fiber networks of the dermis. The mechanical properties are found to be well adapted to the mechanical function of the dermis. The viscoelastic nature of the skin shows that a simple structural model based only on collagen and elastin is not adequate for a full understanding of this tissue. The role of proteoglycans in bonding collagen fibrils into large fibers and in connecting these fibers into the fibrous net of the dermis is not well understood. Mechanical testing can yield information on the nature of bonds at this level of structure.

The effect of vasopressin on gastric wound healing

The gastric incisions of rabbits intra-arterially infused with vasopressin were analyzed for collagen synthesis, tensile strength and inflammatory reaction for five, ten and 20 days from the time of wounding. Significant differences were looked for in the collagen content of treated and untreated wounds. Tensile strength of a strip of gastric wound with sutures removed was tested on a motor driven tensiometer. The breaking point of the strip in grams of weight required was used as the end point. A portion of tissue from the wound site of each of the 36 rabbits was processed for microscopic examination, and the resulting slides were labeled with code numbers to preserve blind conditions. The effect of vasopressin on the healing of a standard gastric incision in the rabbit was studied. When compared with those rabbits in the control study which were infused with a saline solution alone, no significant difference was found in tensile strength, inflammatory response or synthesis of new collagen, as determined by the hydroxyproline ratio. There would appear to be no adverse effects upon gastric wound healing as a result of intra-arterially infused vasopressin in the concentrations used in this experiment.

Age-related changes in the mechanical properties of human skin

The mechanical properties of skin have been studied both in vivo and in vitro by a variety of test methods. These properties are well matched to the function of the skin, and they depend on the geometry of the collagen and elastin networks of the dermis. The time dependence of these properties is thought to be related to the "ground substance" components of the dermis. Age-related changes in the mechanical properties are a function of the degradation of the elastin network and of some as yet undefined changes in the viscoelastic properties of the "ground substance."

Indicator pastes: their behavior and use

Indicator pastes were subjected to a laboratory investigation and a clinical trail. The tests showed: 1. An increase in temperature increased the rate of flow of the pastes. 2. An increase in applied pressure increased the rate of the flow of the pastes. 3. Pastes containing a small percentage of filler were compressed to a smaller thickness than those containing a greater percentage of filler. 4. The zinc oxide-hydrogenated oil mixture demonstrated a biphasic flow pattern. Pressure Indicator Paste demonstrated a simple flow pattern. 5. Similar tests did not give identical results. However, the characteristics of flow curves for similar tests were consistent. 6. A clinical trial using eight subjects showed no marked differences between three indicator pastes but did show significant differences between the interpretations of paste patterns by four dentists. This evidence suggests that the nature of the suspension medium affects both the type of flow and the rate of flow of an indicator paste. The percentage composition of filler affects both the final film thickness and the rate of flow. Improved criteria for the interpretation of paste patterns must be developed before clinical differences in paste behavior are noted.

Bone-titanium implant response to mechanical stress

The purpose of this study was to investigate the nature and strength of any bond which may develop between alveolar bone and titanium allow implants. Implants were placed in a previously prepared edentulous region in the mandibles of dogs. The implants were conical in shape with circumferential grooves to provide axial retention. Five months later the implants were rotated. No indication was found of an adhesive bond being broken.

Effects of external pressure loading on human skin blood flow measured by 133Xe clearance

Forearm skin blood flow was measured during external pressure loading in normal human subjects using 133Xe washout from intracutaneous injection sites. Pressures ranging between 5 and 150 mmHg were applied through a 3-cm-diameter disc placed over the site of flow determination. The pressure was maintained constant by a servo-controlled loading mechanism. Flow decreased with pressures from 5 to 10 and 30 to 150 mmHg, but remained constant with pressures from 10 to 30 mmHg. Reactive hyperemia occurred following removal of pressures of 90 mmHg or greater, but did not occur following removal of lower pressures. The pressure-flow curve for parasacral skin of paraplegic subjects closely paralleled the pressure-flow curve of normal skin at pressures tested: 5-15 mmHg. These data are interpreted to demonstrate autoregulation of skin blood flow. Autoregulation in parasacral skin of paraplegic subjects suggests a peripheral mechanism. The occurrence of hyperemia at pressures which exceed the ability of skin to autoregulate suggests that both autoregulation and post occlusion hyperemia may have the same mechanism.

Root surface measurement using a digital computer

An accurate method is presented for the determination of the area of the periodontal ligament attached to teeth. This method requires the use of digitizing equipment for an accurate determination of tooth cross sections and a digital computer for final manipulation of the area calculations. The procedure is general and is not restricted to single-rooted teeth.