Resting Respiratory Resistance in Female Teenage Athletes With and Without Exercise-Induced Laryngeal Obstruction

OBJECTIVE

Exercise-induced laryngeal obstruction (EILO) occurs with paradoxical vocal fold motion or supraglottic collapse during moderate to vigorous exercise. Previously, Gallena et al (2015) reported lower-than-normal inspiratory (Ri) and expiratory (Re) resistances during resting tidal breathing (RTB) in female teenage athletes with EILO. This study aimed to replicate that unexpected result.

METHOD

The Airflow Perturbation Device measured Ri and Re during three 1-minute trials of RTB in 16 teenage female athletes with EILO and 16 sex-, age-, and height-matched controls. Multiple linear regression examined group, age, height, and weight as predictors of Ri and Re.

RESULTS

Ri and Re tended to be lower in the EILO group than the control group [Ri: F(1,30) = 3.58, P = 0.068, d = 0.686; Re: F(1,30) = 3.28, P = 0.080, d = 0.640], but there was no statistically significant difference in the overall effect [F(2,29) = 1.75, P = 0.192]. After one outlier for Re from the EILO group and her matched control were removed, the overall difference was statistically significant, F(2,27) = 3.38, P = 0.049, with Re primarily contributing to the difference [Ri: F(1,28) = 3.66, P = 0.066, d = 0.719; Re: F(1,28) = 5.69, P = 0.024, d = 0.899].

CONCLUSION

These results did not replicate the robust differences found previously between Ri and Re during RTB in teenage girls with and without EILO, but the results trended in the same direction and met criterion for statistical significance once an outlier was removed from analysis. Overall, the observation that resting respiratory resistances were lower in most teenage girls with EILO suggests that reduced tone of the laryngeal and/or lower airways may predispose young athletes to EILO.

A Rapid, Handheld Device to Assess Respiratory Resistance: Clinical and Normative Evidence

INTRODUCTION

Following reports of respiratory symptoms among service members returning from deployment to South West Asia (SWA), an expert panel recommended pre-deployment spirometry be used to assess disease burden. Unfortunately, testing with spirometry is high cost and time-consuming. The airflow perturbation device (APD) is a handheld monitor that rapidly measures respiratory resistance (APD-Rr) and has promising but limited clinical data. Its speed and portability make it ideally suited for large volume pre-deployment screening. We conducted a pilot study to assess APD performance characteristics and develop normative values.

MATERIALS AND METHODS

We prospectively enrolled subjects and derived reference equations for the APD from those without respiratory symptoms, pulmonary disease, or tobacco exposure. APD testing was conducted by medical technicians who received a 10-min in-service on its use. A subset of subjects performed spirometry and impulse oscillometry (iOS), administered by trained respiratory therapists. APD measures were compared with spirometry and iOS.

RESULTS

The total study population included 199 subjects (55.8% males, body mass index 27.7 ± 6.0 kg/m2, age 49.9 ± 18.7 yr). Across the three APD trials, mean inspiratory (APD-Ri), expiratory (APD-Re), and average (APD-Ravg) resistances were 3.30 ± 1.0, 3.69 ± 1.2, and 3.50 ± 1.1 cm H2O/L/s. Reference equations were derived from 142 clinically normal volunteers. Height, weight, and body mass index were independently associated with APD-Ri, APD-Re, and APD-Ravg and were combined with age and gender in linear regression models. APD-Ri, APD-Re, and APD-Ravg were significantly inversely correlated with FEV1 (r = -0.39 to -0.42), FVC (r = -0.37 to -0.40), and FEF25-75 (r = -0.31 to -0.35) and positively correlated with R5 (r = 0.61-0.62), R20 (r = 0.50-0.52), X5 (r = -0.57 to -0.59), and FRES (r = 0.42-0.43). Bland-Altman plots showed that the APD-Rr closely approximates iOS when resistance is normal.

CONCLUSION

Rapid testing was achieved with minimal training required, and reference equations were constructed. APD-Rr correlated moderately with iOS and weakly with spirometry. More testing is required to determine whether the APD has value for pre- and post-deployment respiratory assessment.

Short-Term Intensive Therapy and Outcomes for Athletes With Paradoxical Vocal Fold Motion Disorder

Purpose The aim of the study was to develop a treatment for athletes with paradoxical vocal fold motion disorder (PVFMD) based on exercise physiology and learning theory principles and administer it over a preestablished time frame. Method A prospective, repeated-measures, within-subject group design was used. Eleven adolescent/teen athletes diagnosed with PVFMD via laryngoscopy received short-term intensive (STI) therapy. Eight of the athletes returned for extended follow-up. Changes in postexercise inspiratory ( R _i) and expiratory ( R _e) resistances and Modified Borg Dyspnea Scale (MBDS) ratings collected at baseline were compared immediately posttreatment and at extended follow-up. Dyspnea Index scores were collected at baseline and at extended follow-up. Two no-treatment control athletes with PVFMD participated in two exercise challenges-baseline and 6 weeks later. Results Immediately after STI therapy, athletes attained significant improvement in R _i, R _e, and MBDS ratings. These changes were maintained at extended follow-up as well as a significant change in Dyspnea Index scores. The 2 control athletes who were reassessed 6 weeks after baseline experienced negative changes in postexercise R _i and MBDS ratings. Conclusion STI therapy that incorporated individuality, specificity, and variable practice effectively changed outcome measures posttreatment with further improvement observed at extended follow-up. These results provide preliminary evidence for STI therapy for PVFMD.

The Effect of Exercise on Respiratory Resistance in Athletes With and Without Paradoxical Vocal Fold Motion Disorder

PURPOSE

An investigational, portable instrument was used to assess inspiratory (R(i)) and expiratory (R(e)) resistances during resting tidal breathing (RTB), postexercise breathing (PEB), and recovery breathing (RB) in athletes with and without paradoxical vocal fold motion disorder (PVFMD).

METHOD

Prospective, controlled, repeated measures within-subject and between-groups design. Twenty-four teenage female athletes, 12 with and 12 without PVFMD, breathed into the Airflow Perturbation Device for baseline measures of respiratory resistance and for two successive 1-min trials after treadmill running for up to 12 min. Exercise duration and dyspnea ratings were collected and compared across groups.

RESULTS

Athletes with PVFMD had lower than control R(i) and R(e) values during RTB that significantly increased at PEB and decreased during RB. Control athletes' R(e) decreased significantly from RTB to PEB but not from PEB to RB, whereas R(i) did not change from RTB to PEB but decreased from PEB to RB. Athletes without PVFMD ran longer, providing lower dyspnea ratings.

CONCLUSION

Immediately following exercise, athletes with PVFMD experienced increased respiratory resistance that affected their exercise performance. The difference in resting respiratory resistances between groups is intriguing and could point to anatomical differences or neural adaptation in teenagers with PVFMD. The Airflow Perturbation Device appears to be a clinically feasible tool that can provide insight into PVFMD and objective data for tracking treatment progress.

Test-retest reliability of respiratory resistance measured with the airflow perturbation device

PURPOSE

In this study, the authors aimed to determine reliability of the airflow perturbation device (APD) to measure respiratory resistance within and across sessions during resting tidal (RTB) and postexercise breathing in healthy athletes, and during RTB across trials within a session in athletes with paradoxical vocal fold motion (PVFM) disorder.

METHOD

Prospective, repeated-measures design. The APD measured respiratory resistance during 3 baseline assessments in 24 teenage female athletes, 12 with and 12 without PVFM. Control athletes provided data at rest and following a customized exercise challenge during each of 3 sessions. Intraclass correlation coefficient (ICC) analysis assessed strength of relationships, and repeated-measures analysis of variance assessed differences across trials and sessions.

RESULTS

ICC analyses confirmed strong correlations across RTB trials for inspiratory, expiratory, and mean respiratory resistance in both groups. Inspiratory resistance decreased ~5% between sessions for control participants; expiratory and mean respiratory resistances were stable. Data from control athletes across sessions and following rigorous exercise were strongly correlated when taken at comparable intervals.

CONCLUSIONS

APD-measured respiratory resistance, including separate assessments for the inspiratory and expiratory phases, has strong test-retest reliability during RTB and after exercising. This suggests that the APD is a useful measurement tool for the assessment of airway function in patients suspected of having PVFM.

Validity of a new respiratory resistance measurement device to detect glottal area change

OBJECTIVE

To determine the correlation between respiratory resistance (Rr) values measured with the Airflow Perturbation Device (APD) to laryngoscopic images of glottal area (GA) in feigned paradoxical vocal fold motion (PVFM), also known as vocal cord dysfunction.

HYPOTHESIS

There is a strong inverse relationship between Rr and GA such that laryngeal constriction can be detected and quantified by APD-measured Rr.

STUDY DESIGN

Prospective, single subject study.

METHODS

A healthy adult feigned breathing that was characteristic of PVFM. Rr and GA were simultaneously recorded, synchronized, and analyzed for three complete breathing cycles with significant glottal constriction occurring during inspiration.

RESULTS

Cross-correlation analysis revealed a strong negative correlation (-0.824) between GA and Rr during feigned PVFM breathing such that Rr increased when GA decreased.

CONCLUSION

APD-measured Rr appears to be a viable noninvasive method for diagnostic screening and monitoring of treatment outcomes for individuals presenting with dyspnea related to PVFM.

Variation of respiratory resistance suggests optimization of airway caliber

Physiologically optimized processes, such as respiration, walking, and cardiac function, usually show a range of variability about the optimized value. Airway resistance has, in the past, been noted as variable, and this variability has been connected to pulmonary disease (e.g., asthma). A hypothesis was presented many years ago that postulated airway resistance as an optimized parameter in healthy individuals, and we have noticed that respiratory measurements made with the airflow perturbation device (APD) tend to be variable in nature. It was posited that this variability indicates that respiratory resistance is optimized similarly to other physiological processes. Fifty subjects with a wide range of demographics volunteered to have 100 measurements made of their respiratory resistances. Resistances were separated into inhalation and exhalation phases. These were plotted and shown to have frequency distributions that were consistent with expectations for an optimized process. The frequency distributions were not quite symmetrical, being skewed slightly toward upper resistances. Comparison between subject data and data from a mechanical respiratory analog showed that subject resistance variation is overwhelmingly from the respiratory system and not from the APD.

Low-power laser irradiation increases cyclic GMP synthesis in penile smooth muscle cells in vitro

OBJECTIVE

The objective of the present study was to determine the effect of low-power laser irradiation (LPLI) on cyclic guanosine monophosphate (cGMP) produced by human corpus cavernosum smooth muscle cells (HCC SMC) in vitro.

BACKGROUND DATA

Numerous reports suggest that LPLI is capable of affecting cellular processes in the absence of significant thermal effect

METHODS

HCC SMC cultures were irradiated with single-dose LPLI using a He-Ne continuous wave laser (632 nm) with different energy densities (0.52-2.1 J/cm2). Assessment of effect on cell viability was performed utilizing Alamar Blue assay. Effect of LPLI on cGMP production was studied by radioimmunoassay.

RESULTS

We observed that: (1) LPLI of HCC SMC results in a statistically significant increase of cGMP synthesis in culture and is dose dependent (maximal effect was observed with LPLI irradiance of 1.57 J/cm2. (2) There were no changes in Normalized Viability Index (NVI) immediately after and 24 h following laser irradiation.

CONCLUSION

Our studies demonstrate that LPLI irradiation stimulates elevation of cGMP in vitro.

Photoactivation of vascular iNOS and elevation of cGMP in vivo: possible mechanism for photovasorelaxation and inhibition of restenosis in an atherosclerotic rabbit models

Recently, intravascular low-power red laser light (LPRLL) therapy has been proposed for the prevention of postangioplasty restenosis due to the observed inhibition of experimental neointimal formation. The objective of this study was to determine the impact of endoluminal LPRLL on vascular levels of inducible nitric oxide synthase (iNOS) and cyclic guanosine monophosphate (cGMP) to help define the mechanism of this effect. Eight atherosclerotic male adult New Zealand White rabbits weighing 4-6 kg were used in these studies. The iliac arteries were treated in separate zones with: (1) balloon inflation only; (2) laser illumination only; and (3) balloon inflation + laser illumination. An uninjured zone of the iliac artery served as a control. Laser irradiation (630 nm) was delivered to the vessel wall via a Cold laser Illuminator (Cook, Inc., Bloomington, IN), with a 3 mm-diameter balloon. Experiments demonstrated that vascular cGMP levels obtained immediately following treatment in the balloon only group was the lowest (0.29 +/- 0.05 pmol/mg protein) and significantly lower compared with the uninjured controls (1.01 +/- 0.07 pmol/ mg protein) (P < 0.001). In the laser only treated group cGMP levels were significantly increased (2.87 +/- 0.12 pmol/mg protein) compared with the uninjured control (P < 0.001) and the balloon only group (P < 0.001). Vascular cGMP levels in the balloon + laser group (2.09 +/0.07 pmol/mg protein) was also increased compared to the balloon only (P < 0.001) and control (P < 0.001) groups. Qualitative analysis of Western blot demonstrated that laser illumination induces iNOS. In contrast balloon dilatation did not induce iNOS. Balloon + laser treatment, however, tended to restore the expression of iNOS. Our study demonstrated that intravascular low dose laser irradiation induces iNOS and elevates vascular cGMP in an in vivo atherosclerotic rabbit model.

Altered compliance and residual strain precede angiographically detectable early atherosclerosis in low-density lipoprotein receptor deficiency

BACKGROUND

This study was performed to detect changes in vascular biomechanical properties early in atherogenesis.

METHODS AND RESULTS

Age- and weight-matched LDL-receptor deficient Watanabe hypercholesterolemic male rabbits (Group I: n = 11) and normal rabbits (Group II: n = 11) were studied. Fasting plasma lipoprotein concentrations, aortic angiography and intravascular ultrasound, in vivo aortic compliance evaluation, ex vivo aortic residual strain measurements, aortic lipid content and histopathology were determined. Plasma cholesterol was increased 9.8 fold and aortic cholesterol content was increased from 20 to 43 fold in Group I compared to Group II, respectively (P < .00005). Angiography revealed no stenoses in either group, whereas intravascular ultrasound and histological studies of Group I showed small circumferential plaques with < 10% cross-sectional area involvement. The residual strain in Group I was significantly increased in the ascending thoracic aorta (22.1 +/- 6.9% versus 10.4 +/- 3.2% in Group II, P < .0001), descending thoracic aorta (15.7 +/- 7.2% versus 4.8 +/- 1.3% in Group II, P < .0001), and abdominal aorta (18.0 +/- 4.8% versus 8.3 +/- 6.3% in Group II, P < .005). Changes in residual strain were inversely correlated with the aortic cholesterol content in the ascending thoracic aorta (r = -.72; P = -.001), descending thoracic aorta (r = -.95; P < .001), and abdominal aorta (r = -.51; P = .019).

CONCLUSIONS

Early atherosclerosis in LDL-receptor deficient rabbits, undetectable by angiography yet observed by intravascular ultrasound imaging and histology, is associated with marked changes in ex vivo residual strain. Alterations in vascular biomechanical properties, associated with changes in cholesterol content, may have physiologic consequences and may be useful in detecting and quantitating early atherosclerosis.

Wound healing. Tensile strength vs healing time for wounds closed under tension

OBJECTIVES

To measure tensile strength of wounds closed with and without tension in rats, delineating the postoperative time interval when tensile strength is equal. To study patterns of growth in tensile strength.

DESIGN

Transverse incisions on the backs of control rats were closed with minimal tension. In experimental animals, after excision of skin from the back, wounds were closed with closing tensions in excess of 70 g. Animals were killed at designated healing intervals for tensile-strength testing of wounds.

SUBJECTS

One hundred Sprague-Dawley rats were divided into 5 groups days 5, 7, 10, 14, and 21, with equal numbers of control and experimental animals in each group. Wounds from 94 animals were available for breakload testing.

INTERVENTION

Closing tensions were measured for transverse incisions on the backs of control animals before closure and after removal of 50 to 60 mm of skin from the backs of experimental animals.

RESULTS

Tensile strength was not significantly different on day 5. However, wounds closed under tension showed significantly higher tensile strength on 7, 10, 14, 21. Polynomial regression suggests a cubic relationship between healing time and tensile strength.

CONCLUSIONS

Results suggest that tensile strength of wounds closed under tension exceeds that of tensionless wounds as early as day 7 following surgery. This study also illustrates the 2 periods of rapid increase in wound tensile strength that probably coincide with specific stages of wound healing.

Wound healing: effects of closing tension, zyplast, and platelet-derived growth factor

Previous studies have shown that beginning 5 to 7 days from wounding, the tensile strength of wounds closed under tension in rats is significantly higher than the tensile strength of wounds closed without tension. This study evaluated the effects of increased closing tension, zyplast implant (ZI), and human recombinant platelet-derived growth factor (PDGF) on the tensile strength of wounds. Six groups of 12 rats each were divided into two main subsets: wounds were closed without tension in three groups and with high tension of approximately 100 g in the three other groups. In both no-tension and high-tension groups, one subgroup received no intervention (controls), one subgroup received ZI (zyplast controls), and one subgroup received ZI-PDGF (ZI used as a carrier for PDGF). Healing was evaluated by tensile strength determinations at 5 days. For the controls, wounds closed under tension showed a trend toward higher tensile strength, but statistical significance was not reached. Compared with controls, tensile strength was 45% lower in the wounds with ZI and closure with tension (P = .0063) and 38% lower in the wounds with ZI and closure without tension (P = .007). Treatment with ZI-PDGF resulted in 69% higher tensile strengths (P = .049) as compared with ZI controls for wounds closed with tension. This study demonstrated the beneficial effect of PDGF in accelerating healing in wounds closed under tension. Although ZI was able to deliver PDGF to the wound, the use of this substance as a carrier is questioned since it was detrimental to healing.

Vascular effects of diet-induced hypercalcemia after balloon artery injury in giant Flemish rabbits

To determine whether metastatic calcification during neointima formation can result in neointimal calcification that simulates advanced human atherosclerosis, 32 giant Flemish rabbits (weight 5.5 +/- 0.6 kg) underwent overstretch balloon injury of bilateral iliac arteries and received diet therapy for 8 weeks: high cholesterol (2%) and low calcium-vitamin D2 regimen (250 mg of calcium carbonate orally 5 times weekly and 50,000 U of calciferol intramuscularly 3 times weekly; group 1; n = 5); low cholesterol (0.5%) and high calcium-vitamin D2 regimen (500 mg of calcium carbonate orally 5 times weekly and 100,000 U of calciferol intramuscularly three times weekly; group 2; n = 19); or 0% cholesterol and high calcium-vitamin D2 regimen (group 3; n = 8). The incidence of vascular calcification was highest (71.4%) in group 2. Eighty-one percent of calcification was medial. Residual strain measurements of 7 thoracic aortas from group 2 compared to normal thoracic aortas from 8 control rabbits showed that residual strain was significantly increased in the calcified atherosclerotic aortas (12.3% vs 5.2%; p = 0.001). We conclude that diet-induced hypercalcemia predominantly affects the media despite the presence of concomitant neointima formation from balloon artery injury with or without hypercholesterolemia and increases the residual strain more than twofold compared to normal thoracic aortas.

Mechanical characteristics of vascular tissue and their role in brain injury modeling: a review

A review of the mechanical characterization of vascular tissue is presented in the context of its relevance to the computational modeling of traumatic brain injury (TBI). Mathematical representations of experimentally observed vascular behavior are described. Several material models, for large vessels, and their applicability to blood vessels in the brain are discussed. Integration of vascular tissue behavior into an existing computational model of the brain, to account for the anisotropic effects they produce, is discussed.

Somatotropin alters collagen metabolism in growing pigs

Treatment of pigs with porcine somatotropin (pST) is associated with altered nutrient partitioning. The aim of this investigation was to determine the role of pST in protein and collagen deposition in growing pigs. Barrows were treated daily with buffer or pST when they weighed between 30 and 64 kg (n = 8 pigs/group). Pigs were restrictively fed such that the average feed intake for both groups was 1.86 kg/d. Treatment with pST was associated with 25, 55, 78 and 31% higher growth rates for carcass, skin, viscera and head, respectively. Total protein depositions (g/d) were 52, 60, 81, 42 and 54% greater in carcass, skin, viscera, head and empty body, respectively, of pST-treated pigs. Collagen represented approximately 70, 15 and 43% of total protein in skin, viscera and head; pST did not influence this ratio. However, collagen relative to total protein was 16% lower in the carcass of pST-treated pigs. Deposition rate of collagen was higher in all components of empty body, except carcass, as a result of pST treatment. The ratio of non-collagen protein to collagen deposition rate was 49% greater in the carcass of pST-treated pigs. The deposition rate of acid-soluble collagen was approximately 2-fold higher in skin but was 25% lower in carcass of pST-treated pigs. Depositions of insoluble collagen in viscera and head of pST-treated pigs were 74 and 46% greater, respectively, than for controls. These data show that pST treatment enhances collagen deposition in skin, head and viscera, whereas non-collagen protein deposition and collagen maturation are enhanced in the carcass.

Comparison of the Howmedica and Synthes military external fixation frames

To direct the U.S. military purchase of deployable external fixation gear, a project was designed to compare the biomechanical properties and ease of clinical application of military external fixators developed by Synthes and Howmedica. The project assessed (a) ease of application, (b) biomechanics, (c) heat stability, and (d) product line compatibility. Pretrained general surgery residents were provided with fresh cadaver limbs with simulated grade IIIB tibial fractures and 5-cm middiaphyseal defects. All chose the Howmedica Ultra-X for its ease of application but, on manual testing, noted that the Synthes Trauma-Fix was more stable. The frames were biomechanically tested in a previously validated model with strictly controlled parameters. The Howmedica Ultra-X demonstrated only 75% of the compressive stiffness, 29% of the anteroposterior bending stiffness, and 51% of the torsional stiffness of the Synthes Trauma-Fix. The Ultra-X failed to withstand steam sterilization and was significantly weaker than, and incompatible with, Howmedica's commercially available product. The Trauma-Fix demonstrated no statistically significant difference from Synthes' commercially available product. The Howmedica Ultra-X is unsuitable for military external fixation: The biomechanical properties are not equivalent to those of the unilateral Hoffmann frame, it is incompatible with commercially available Howmedica external fixators, and it fails to withstand heat sterilization.

Torque generated by handheld screwdrivers and mechanical torquing devices for osseointegrated implants

This study evaluated the ability of practitioners experienced in the use of Brãnemark implant components to impart a desired torque using handheld screwdrivers. The torque output and variability of mechanical torque devices was also examined. For clinicians using handheld screwdrivers, values ranged from 0.7 to 18.1 Ncm, 1.4 to 33.7 Ncm, and 8.2 to 36.2 Ncm for the 10-Ncm, 20-Ncm, and 32-Ncm torques respectively. The manually operated mechanical torquing devices produced torque values within the tolerances specified by their respective manufacturers at all levels. Significant variation from the manufacturer's set values were noted as a function of tightening speed with the electronic torquing device. The data indicate that there is wide variation in the ability of clinicians to perceive adequate torquing forces applied to implant components. Calibrated torquing devices are mandatory if proper torquing procedures are to be accomplished.

A comparison of obsidian and surgical steel scalpel wound healing in rats

There are several anecdotal clinical articles claiming wound healing and scar superiority using obsidian (volcanic glass) scalpels. In order to determine if skin incisions made with obsidian were superior to those made with standard surgical steel, wound tensile strength, scar width, and histology were assessed in 40 adult male Sprague-Dawley rats. Each rat received two parallel 8-cm dorsal skin incisions, one with an obsidian scalpel and the other with a surgical steel scalpel (no. 15 blade). Data were analyzed by ANOVA. Tensile strength of the two wound types was not different at 7, 14, 21, and 42 days. Scar width, however, was significantly less in the obsidian wounds at 7, 10, and 14 days (p < 0.005). At 21 days, scar width was not different in the two groups. At 42 days, all wounds were barely detectable, thus precluding scar width analysis. A blinded histologic review suggested that obsidian wounds contained fewer inflammatory cells and less granulation tissue at 7 days.

Copper deficiency alters collagen types and covalent cross-linking in swine myocardium and cardiac valves

Dietary copper deficiency induces alterations of connective tissue metabolism that are associated with lesions in cardiovascular and other organ systems. To determine the impact of copper deficiency on characteristics of collagen in porcine myocardium and cardiac valves, weaned pigs were fed diets with adequate or deficient levels of copper. Although dietary copper did not affect the concentration of collagen in either myocardium or bicuspid valves, the degree of collagen cross-linking, as assessed by the level of hydroxylysylpyridinoline, was lower in both tissues of copper-deficient pigs. Proportions of type III collagen were increased in the left ventricle and bicuspid valves of copper-deficient pigs. Copper deficiency induced extensive remodeling, however, of the collagen fraction of cardiac interstitium. Reduction in left ventricular collagen cross-linking may provide the stimulus for the development of cardiac hypertrophy, which characterizes severe copper deficiency, by increasing the compliance of the ventricular wall. The shift in the phenotypic profile of collagen that is associated with this cardiac hypertrophy indicates synthesis of new collagen, which could affect collagen cross-linking irrespective of copper status.

Wound healing. Relationship of wound closing tension to scar width in rats

A study was conducted to better define the relationship between closing tension and the resulting scar width of incisional wounds. Five groups of 10 hairless rats each were studied. Transverse wounds were created and closed on the back of each rat, with closing tension varied by excising amounts of skin in widths of 0 (control), 15, 30, 45, and 60 mm. At 28 days, the scar width was measured by three methods: digital caliper, photographically, and histologically. Results showed that wounds closed under the highest tension (60-mm excision group) had significantly wider scars than controls by all three measurement techniques. Regression analysis of the caliper scar width as determined by squaring the closing tension resulted in a nonlinear equation resembling an exponential curve that "best fit" the variables.

Effect of hypertension on elasticity and geometry of aortic tissue from dogs

Inflation-extension experiments were carried out on segments of the descending thoracic aortas from 4 normotensive and 4 hypertensive dogs rendered hypertensive using either unilateral or bilateral renal artery constriction. Intravascular pressures up to 200 mm Hg and axial forces up to 200 g were used. The external diameter of the segment and the distance between two longitudinally spaced gage marks were recorded photographically at each pressure-force level combination. Dimensions in the underformed configuration were measured at the end of the inflation-extension experiment. Data were analyzed for changes in geometry and force-deformation response. Results indicate that: 1. Under sustained hypertension the wall thickness in the underformed configuration increases with a concurrent reduction in the in-situ longitudinal extension ratio. 2. This dual tissue response accomplishes substantial reductions in the circumferential and longitudinal stresses from the levels that would be reached at equivalent pressures in the absence of these geometric changes. 3. At comparable intravascular pressures the extensibility in the circumferential direction is slightly greater for the hypertensive aortas as compared to normals. However, the stress-extension ratio relationship in the circumferential direction is similar in the two groups. 4. The stress-extension ratio relationship in the longitudinal direction indicates that the hypertensive aorta is stiffer than its normotensive counterpart.

Structural stiffness of the Hoffmann simple anterior tibial external fixation frame

Tibial external fixation frames were constructed on aluminum tube simulating tibia bone. A 20-mm gap was left at the fracture site in order to measure the structural stiffness of the frame rather than the aluminum tube. The performance of the frames were experimentally evaluated and quantified using tests which simulated the loading conditions encountered in normal walking. These included axial compression, anteroposterior (AP) bending, lateral bending and torsional loading of the frame. The parameters studied were (a) number of fixation pins, (b) number of connecting rods and (c) location of clamps on the pins. Four constants were evaluated from these tests using various structural configurations of the frames; these resulted in four stiffness coefficients in compression, AP bending, lateral bending and torsion. Stiffnesses of various frames with different geometric configurations were compared by comparing their appropriate stiffness coefficients. Such comparison can set forth a quantitative guideline in selecting a suitable frame configuration for the type of injury and condition of fracture pattern. This type of quantitative analysis can also be useful in modifying the frame during the postoperative bone healing process.

Residual stress and strain in aortic segments

In the study of stresses and strains in vascular segments, it is generally assumed that the traction-free configuration assumed by a segment when there is no axial force and there are no intravascular and extravascular pressures is stress-free. To investigate the degree of validity of this assumption, 286 oval shaped rings were excised from three bovine and six porcine aortas and photographed. Radial cuts were made in these rings which opened up into horseshoe shapes and were also photographed. Smoothed boundary lengths at intimal and adventitial levels in the rings and their cut open configurations were measured from the photographs and the residual strains in the annular configuration relative to the open configuration were computed. It was found that: the average maximum residual intimal engineering strain in the uncut configuration was -0.082 for all nine aortas and -0.096 and -0.077 for the bovine and porcine aortas alone, respectively; the average maximum residual adventitial strain was 0.085 for all aortas, and 0.102 and 0.078 for the bovine and porcine aortas alone, respectively; an estimated average beneficial compressive stress of -0.188 X 10(5) Pa (corresponding to a strain level of -0.082) is available at the intimal level to counteract the in vivo tensile stress due to the intravascular pressure; an estimated average initial tensile stress of 0.195 X 10(5) Pa (corresponding to a strain level of 0.085) exists at the adventitial level which adds to the in vivo tensile stress due to the intravascular pressure. Although these stress levels are not large in comparison with the in vivo stress in the arterial wall, a detailed stress analysis must take into account these initial stresses.

Incremental formulations in vascular mechanics

The pulsatile deformations of the large arteries can be viewed as small time-varying deformations superposed on large deformations. This motivates the study of the incremental deformations of the vascular tissue. Unfortunately, because of the variety of possible choices of definitions of stresses and strains, the choice of the characterizing incremental moduli is not unique, which has led to much ambiguity and confusion in the literature. This communication systematically presents some of the options available for characterization of orthotropic incremental deformations of the vascular tissue, and provides explicit formulas for interconversions of incremental elastic moduli for uniaxial tests on strips of incompressible tissue. Relative merits of various choices are discussed.

Determination of the local erosion stress of the canine endothelium using a jet impingement method

A method to determine local endothelial erosion stress is presented. Freshly excised segments of middle descending thoracic aortas of dogs were slit open longitudinally and stretched in a specially designed rack to various circumferential and longitudinal dimensions. Jets of physiological saline were impinged normally on the endothelium of these segments. Lesions caused by the jet were made visible by staining the tissue with Evans blue dye. The dye solution was absorbed by regions where the endothelial layer had been damaged or destroyed. Characteristically, the lesions were annular in shape. This indicates that the endothelium can withstand large normal stresses where the jet impinges, but is eroded by the shear stress resulting from the jet efflux. Erosion stress of the endothelium was determined by correlating the external radius of a lesion with the shear stress expected at that radial distance from the center of the jet. Results from 185 lesions created in 17 aortic segments indicate that: 1) the in-vitro endothelial erosion stress as measured by a 30-s duration of exposure to shear stress is 7761 ± 155 (SEM) dynes/cm2 at room temperature (23° C) and 2645 ± 155 (SEM) dynes/cm2 at body temperature (37°C); 2) the erosion stress decreases markedly with an increase in the duration of exposure to shear stress; 3) the results for long-duration exposure are consistent with those of the well-known in-vivo study of Fry on endothelial erosion stress. The importance of the method is its ability to measure local endothelial erosion stress which is of particular significance in the study of the discrete process of atherogenesis.