Mechanical damage characterization in human femoropopliteal arteries of different ages

Endovascular treatment of Peripheral Arterial Disease (PAD) is notorious for high failure rates, and interaction between the arterial wall and the repair devices plays a significant role. Computational modeling can help improve clinical outcomes of these interventions, but it requires accurate inputs of elastic and damage characteristics of the femoropopliteal artery (FPA) which are currently not available. Fresh human FPAs from n = 104 tissue donors 14-80 years old were tested using planar biaxial extension to capture elastic and damage characteristics. Damage initiation stretches and stresses were determined for both longitudinal and circumferential directions, and their correlations with age and risk factors were assessed. Two and four-fiber-family invariant-based constitutive models augmented with damage functions were used to describe stress softening with accumulating damage. In FPAs younger than 50 years, damage began accumulating after 1.51 ± 0.13 and 1.49 ± 0.11 stretch, or 196 ± 110 kPa and 239 ± 79 kPa Cauchy stress in the longitudinal and circumferential directions, respectively. In FPAs older than 50 years, damage initiation stretches and stresses decreased to 1.27 ± 0.09 (106 ± 52 kPa) and 1.26 ± 0.09 (104 ± 59 kPa), respectively. Damage manifested primarily as tears at the internal and external elastic laminae and within the tunica media layer. Higher body mass index and presence of diabetes were associated with lower damage initiation stretches and higher stresses. The selected constitutive models were able to accurately portray the FPA behavior in both elastic and inelastic domains, and properties were derived for six age groups. Presented data can help improve fidelity of computational models simulating endovascular PAD repairs that involve arterial damage. STATEMENT OF SIGNIFICANCE: This manuscript describes inelastic, i.e. damage, behavior of human femoropopliteal arteries, and provides values for three constitutive models simulating this behavior computationally. Using a set of 104 human FPAs 14-80 years old, we have investigated stress and stretch levels corresponding to damage initiation, and have studied how these damage characteristics change across different age groups. Presented inelastic arterial characteristics are important for computational simulations modeling balloon angioplasty and stenting of peripheral arterial disease lesions.

Limb flexion-induced axial compression and bending in human femoropopliteal artery segments

BACKGROUND

High failure rates of femoropopliteal artery (FPA) interventions are often attributed in part to severe mechanical deformations that occur with limb movement. Axial compression and bending of the FPA likely play significant roles in FPA disease development and reconstruction failure, but these deformations are poorly characterized. The goal of this study was to quantify axial compression and bending of human FPAs that are placed in positions commonly assumed during the normal course of daily activities.

METHODS

Retrievable nitinol markers were deployed using a custom-made catheter system into 28 in situ FPAs of 14 human cadavers. Contrast-enhanced, thin-section computed tomography images were acquired with each limb in the standing (180 degrees), walking (110 degrees), sitting (90 degrees), and gardening (60 degrees) postures. Image segmentation and analysis allowed relative comparison of spatial locations of each intra-arterial marker to determine axial compression and bending using the arterial centerlines.

RESULTS

Axial compression in the popliteal artery (PA) was greater than in the proximal superficial femoral artery (SFA) or the adductor hiatus (AH) segments in all postures (P = .02). Average compression in the SFA, AH, and PA ranged from 9% to 15%, 11% to 19%, and 13% to 25%, respectively. The FPA experienced significantly more acute bending in the AH and PA segments compared with the proximal SFA (P < .05) in all postures. In the walking, sitting, and gardening postures, average sphere radii in the SFA, AH, and PA ranged from 21 to 27 mm, 10 to 18 mm, and 8 to 19 mm, whereas bending angles ranged from 150 to 157 degrees, 136 to 147 degrees, and 137 to 148 degrees, respectively.

CONCLUSIONS

The FPA experiences significant axial compression and bending during limb flexion that occur at even modest limb angles. Moreover, different segments of the FPA appear to undergo significantly different degrees of deformation. Understanding the effects of limb flexion on axial compression and bending might assist with reconstructive device selection for patients requiring peripheral arterial disease intervention and may also help guide the development of devices with improved characteristics that can better adapt to the dynamic environment of the lower extremity vasculature.

Limb flexion-induced twist and associated intramural stresses in the human femoropopliteal artery

High failure rates of femoropopliteal artery (FPA) interventions are often attributed to severe mechanical deformations that occur with limb movement. Torsion of the FPA likely plays a significant role, but is poorly characterized and the associated intramural stresses are currently unknown. FPA torsion in the walking, sitting and gardening postures was characterized in n = 28 in situ FPAs using intra-arterial markers. Principal mechanical stresses and strains were quantified in the superficial femoral artery (SFA), adductor hiatus segment (AH) and the popliteal artery (PA) using analytical modelling. The FPA experienced significant torsion during limb flexion that was most severe in the gardening posture. The associated mechanical stresses were non-uniformly distributed along the length of the artery, increasing distally and achieving maximum values in the PA. Maximum twist in the SFA ranged 10-13° cm^-1, at the AH 8-16° cm^-1, and in the PA 14-26° cm^-1 in the walking, sitting and gardening postures. Maximum principal stresses were 30-35 kPa in the SFA, 27-37 kPa at the AH and 39-43 kPa in the PA. Understanding torsional deformations and intramural stresses in the FPA can assist with device selection for peripheral arterial disease interventions and may help guide the development of devices with improved characteristics.

Comparison of femoropopliteal artery stents under axial and radial compression, axial tension, bending, and torsion deformations

High failure rates of Peripheral Arterial Disease (PAD) stenting appear to be associated with the inability of certain stent designs to accommodate severe biomechanical environment of the femoropopliteal artery (FPA) that bends, twists, and axially compresses during limb flexion. Twelve Nitinol stents (Absolute Pro, Supera, Lifestent, Innova, Zilver, Smart Control, Smart Flex, EverFlex, Viabahn, Tigris, Misago, and Complete SE) were quasi-statically tested under bench-top axial and radial compression, axial tension, bending, and torsional deformations. Stents were compared in terms of force-strain behavior, stiffness, and geometrical shape under each deformation mode. Tigris was the least stiff stent under axial compression (6.6N/m axial stiffness) and bending (0.1N/m) deformations, while Smart Control was the stiffest (575.3N/m and 105.4N/m, respectively). Under radial compression Complete SE was the stiffest (892.8N/m), while Smart Control had the lowest radial stiffness (211.0N/m). Viabahn and Supera had the lowest and highest torsional stiffness (2.2μNm/° and 959.2μNm/°), respectively. None of the 12 PAD stents demonstrated superior characteristics under all deformation modes and many experienced global buckling and diameter pinching. Though it is yet to be determined which of these deformation modes might have greater clinical impact, results of the current analysis may help guide development of new stents with improved mechanical characteristics.

The choice of a constitutive formulation for modeling limb flexion-induced deformations and stresses in the human femoropopliteal arteries of different ages

Open and endovascular treatments for peripheral arterial disease are notorious for high failure rates. Severe mechanical deformations experienced by the femoropopliteal artery (FPA) during limb flexion and interactions between the artery and repair materials play important roles and may contribute to poor clinical outcomes. Computational modeling can help optimize FPA repair, but these simulations heavily depend on the choice of constitutive model describing the arterial behavior. In this study finite element model of the FPA in the standing (straight) and gardening (acutely bent) postures was built using computed tomography data, longitudinal pre-stretch and biaxially determined mechanical properties. Springs and dashpots were used to represent surrounding tissue forces associated with limb flexion-induced deformations. These forces were then used with age-specific longitudinal pre-stretch and mechanical properties to obtain deformed FPA configurations for seven age groups. Four commonly used invariant-based constitutive models were compared to determine the accuracy of capturing deformations and stresses in each age group. The four-fiber FPA model most accurately portrayed arterial behavior in all ages, but in subjects younger than 40 years, the performance of all constitutive formulations was similar. In older subjects, Demiray (Delfino) and classic two-fiber Holzapfel-Gasser-Ogden formulations were better than the Neo-Hookean model for predicting deformations due to limb flexion, but both significantly overestimated principal stresses compared to the FPA or Neo-Hookean models.

Abstract 506: Intramural Structural Changes in Human Femoropopliteal Arteries With Age

Introduction: Femoropopliteal artery (FPA) disease is common and therapeutic interventions and reconstructions leave significant room for improvement. Models of arterial growth and remodeling can help better understand the pathophysiology of FPA disease, but they require detailed data on arterial structural composition to produce accurate predictions. The goal of this work was to quantify intramural collagen and elastin in human FPAs and determine how these constituents change with age.

Methods: FPAs were obtained from 32 tissue donors without hallmarks of peripheral artery disease (average age 50±18 years, age range 15-72 years). Longitudinal pre-stretch, wall thickness and lumen diameter were used to calculate in situ volume of tissue in a 1cm-long arterial segment. Arteries were fixed in formalin and sectioned in both transverse and longitudinal directions. Elastin and collagen contents were quantified with image analysis using Verhoeff-Van Gieson and Masson’s Trichrome stained slides scanned at 10x.

Results: Ageing was associated with an increase in in situ tissue volume of 31mm 3 per decade of life, and increases in the overall wall and tunica media thicknesses of 94μm and 19μm per decade of life respectively (p=0.01). Volume fraction of elastin did not change with age (p=0.49) and remained at 4.8±1.6%, although elastic fibers did become more fragmented (p<0.01). Amorphous medial collagen increased with age from occupying 35±11% of the media at ages younger than 30 years, to 54±9% of the media at ages older than 60 years. This translated into an increase of 4.1% in medial collagen per decade of life (p<0.01). Volume fraction of fibrillar adventitial collagen did not change with age (p=0.09) and remained at 34±7%.

Conclusions: In human FPAs, arterial walls thicken and collagen content increases with age. Though total elastin content remains stable, elastic fiber architecture deteriorates with aging. Quantification of intramural structural changes in human FPAs across age groups can be instrumental for developing models of arterial growth and remodeling that can help better understand the pathophysiology of peripheral artery disease.

Constitutive description of human femoropopliteal artery aging

Femoropopliteal artery (FPA) mechanics play a paramount role in pathophysiology and the artery's response to therapeutic interventions, but data on FPA mechanical properties are scarce. Our goal was to characterize human FPAs over a wide population to derive a constitutive description of FPA aging to be used for computational modeling. Fresh human FPA specimens ([Formula: see text]) were obtained from [Formula: see text] predominantly male (80 %) donors 54±15 years old (range 13-82 years). Morphometric characteristics including radius, wall thickness, opening angle, and longitudinal pre-stretch were recorded. Arteries were subjected to multi-ratio planar biaxial extension to determine constitutive parameters for an invariant-based model accounting for the passive contributions of ground substance, elastin, collagen, and smooth muscle. Nonparametric bootstrapping was used to determine unique sets of material parameters that were used to derive age-group-specific characteristics. Physiologic stress-stretch state was calculated to capture changes with aging. Morphometric and constitutive parameters were derived for seven age groups. Vessel radius, wall thickness, and circumferential opening angle increased with aging, while longitudinal pre-stretch decreased ([Formula: see text]). Age-group-specific constitutive parameters portrayed orthotropic FPA stiffening, especially in the longitudinal direction. Structural changes in artery wall elastin were associated with reduction of physiologic longitudinal and circumferential stretches and stresses with age. These data and the constitutive description of FPA aging shed new light on our understanding of peripheral arterial disease pathophysiology and arterial aging. Application of this knowledge might improve patient selection for specific treatment modalities in personalized, precision medicine algorithms and could assist in device development for treatment of peripheral artery disease.

Treatment patterns from 647 patients with Gaucher disease: An analysis from the Gaucher Outcome Survey

The Gaucher Outcome Survey (GOS) is an international disease-specific registry established in 2010 for patients with a confirmed diagnosis of Gaucher disease (GD), regardless of GD type or treatment status. For insight into how GD management varies among countries, we analyzed treatment patterns in GOS. As of October 30, 2015, data on GD-specific treatment (enzyme replacement therapy, substrate reduction therapy, or chemical chaperone therapy) received at any time were available for 647 patients. At analysis, velaglucerase alfa (316/573, 55.1%) and imiglucerase (184/573, 32.1%) were the treatments most widely used. Of the 647 treated patients, 446 (68.9%) had been treated for >5years and 368 (56.9%) had received only one GD-specific drug therapy. There were 377 patients who received velaglucerase alfa. Velaglucerase alfa was most widely used at 60U/kg every other week (134/492 dose entries, 27.2%), but there were differences in dosing between the three highest-enrolling countries (defined as >100 GOS patients enrolled in each), with most patients in Israel receiving <20U/kg, most patients in the United Kingdom receiving 20 to <40U/kg, and most in the United States receiving 60U/kg. This analysis provides a foundation upon which to examine real-life outcomes data from different treatment regimens globally.

Abstract 121: Effects of Tethering Branches on Limb Flexion-induced Deformations of the Human Femoropopliteal Artery

Introduction: High failure rates of femoropopliteal artery (FPA) interventions are commonly attributed to severe mechanical deformations that occur with limb movement. Recent data demonstrate large variability in FPA bending and torsion. We hypothesize that FPA branch tethering significantly influences arterial deformations.

Methods: Under fluoroscopic guidance, nitinol markers were endovascularly deployed into 22 limbs of 11 human cadavers. Dilute contrast was injected into the FPA, and thin-section CT images were acquired with the limbs in straight (180°) and acutely bent (60°) postures. Image segmentation and 3D reconstruction were used to measure bending and torsion of the FPA by tracking spatial movement of the artery and markers. FPA bends were measured as radii of inscribed spheres, while torsion was calculated by measuring the angle of twist between each pair of consecutive markers in the straight and bent leg configurations. FPA branches were mapped and Pearson correlation r was used to assess whether bending and torsion values correlated with the distance to the nearest branch.

Results: At the adductor hiatus the FPA demonstrated a bending radius of 3.43±9.14 mm with 15.03±9.95 °/cm twist, while below the knee the most acute bending radius was 2.21±7.03 mm and the maximum twist was 32.03±10.68 °/cm. Bending and torsion below the knee were more severe than at the adductor hiatus (p<0.01). On average, large branches were observed 6.82± 8.26 mm in proximity to the bend and 5.29± 5.16 mm to the twist in the adductor hiatus and 7.96± 6.52 mm and 6.31± 6.06 mm to the bend and twist below the knee. There was no correlation ( r =-0.22, p=0.32) between bending and branch proximity at the adductor hiatus or in the below the knee arterial segments ( r =-0.11, p=0.30). Similarly, no correlation was observed between twist and branch proximity ( r =0.02, p=0.91 at the adductor hiatus; r =-0.02, p=0.87 below the knee).

Conclusions: Limb flexion-induced deformations of the FPA demonstrate severe bending and torsion at the adductor hiatus and below the knee; however, neither bending nor torsion appear to be affected by the proximity of the FPA branches. These data suggest that tethering branches have minimal effect on limb flexion-induced bending and torsion of the FPA.

In situ longitudinal pre-stretch in the human femoropopliteal artery

In situ longitudinal (axial) pre-stretch (LPS) plays a fundamental role in the mechanics of the femoropopliteal artery (FPA). It conserves energy during pulsation and prevents buckling of the artery during limb movement. We investigated how LPS is affected by demographics and risk factors, and how these patient characteristics associate with the structural and physiologic features of the FPA. LPS was measured in n=148 fresh human FPAs (14-80 years old). Mechanical properties were characterized with biaxial extension and histopathological characteristics were quantified with Verhoeff-Van Gieson Staining. Constitutive modeling was used to calculate physiological stresses and stretches which were then analyzed in the context of demographics, risk factors and structural characteristics. Age had the strongest negative effect (r=-0.812, p<0.01) on LPS and could alone explain 66% of LPS variability. Male gender, higher body mass index, hypertension, diabetes, coronary artery disease, dyslipidemia and tobacco use had negative effects on LPS, but only the effect of tobacco was not associated with aging. FPAs with less pre-stretch had thicker medial layers, but thinner intramural elastic fibers with less dense and more fragmented external elastic laminae. Elastin degradation was associated with decreased physiological tethering force and longitudinal stress, while circumferential stress remained constant. FPA wall pathology was negatively associated with LPS (r=-0.553, p<0.01), but the effect was due primarily to aging. LPS in the FPA may serve as an energy reserve for adaptive remodeling. Reduction of LPS due to degradation and fragmentation of intramural longitudinal elastin during aging can be accelerated in tobacco users.

STATEMENT OF SIGNIFICANCE

This work studies in situ longitudinal pre-stretch (LPS) in the human femoropopliteal artery. LPS has a fundamental role in arterial mechanics, but is rather poorly studied due to lack of direct in vivo measurement method. We have investigated LPS in the n=148 human femoropopliteal arteries in the context of subject demographics and risk factors, and structural and physiologic characteristics of the artery. Our results demonstrate that LPS reduces with age due to degradation and fragmentation of intramural elastin. LPS may serve as an energy reserve for adaptive remodeling, and reduction of LPS can be accelerated in tobacco users.

Quantifying the Erlenmeyer flask deformity

OBJECTIVE

Erlenmeyer flask deformity is a common radiological finding in patients with Gaucher's disease; however, no definition of this deformity exists and the reported prevalence of the deformity varies widely. To devise an easily applied definition of this deformity, we investigated a cohort of knee radiographs in which there was consensus between three experienced radiologists as to the presence or absence of Erlenmeyer flask morphology.

METHODS

Using the presence or absence of Erlenmeyer flask morphology as a benchmark, we measured the diameter of the femur at the level of the physeal scar and serially at defined intervals along the metadiaphysis.

RESULTS

A measured ratio in excess of 0.57 between the diameter of the femoral shaft 4 cm from the physis to the diameter of the physeal baseline itself on a frontal radiograph of the knee predicted the Erlenmeyer flask deformity with 95.6% sensitivity and 100% specificity in our series of 43 independently diagnosed adults with Gaucher's disease. Application of this method to the distal femur detected the Erlenmeyer flask deformity reproducibly and was simple to carry out.

CONCLUSION

Unlike diagnostic assignments based on subjective review, our simple procedure for identifying the modelling deformity is based on robust quantitative measurement: it should facilitate comparative studies between different groups of patients, and may allow more rigorous exploration of the pathogenesis of the complex osseous manifestations of Gaucher's disease to be undertaken.

Age adjusting severity scores for Anderson-Fabry disease

Anderson-Fabry Disease (AFD) is a life-threatening X-linked lysosomal storage disorder, caused by a deficiency of alpha galactosidase A. The disease affects males and females, and may present in childhood or adulthood. In the absence of a biomarker of disease burden or therapeutic response, scoring systems based on clinical manifestations, have been developed. Such global scores e.g. the Mainz Severity Score Index (MSSI) are confounded by the natural history of disease that deteriorates with age, making comparisons across age groups invalid. In this study the baseline MSSI, as adapted for data collected in the Fabry Outcome Survey (FOS) database (FOS-MSSI), was calculated for 655 females and 617 males with confirmed AFD. Using an ANCOVA model, equations for the predicted FOS-MSSI based on age were derived for males and females from data where patients from the UK or outside Europe were excluded. The initially excluded patients were used for validation. The predicted severity scores of UK and non-Europe-cohorts of adult and paediatric patients were found to follow the model produced for the European cohort thereby providing validation of the methodology. Deviation of the actual FOS-MSSI from the predicted was calculated and termed the age-adjusted score. Examples of the use of the age-adjusted score in individual patients, in comparison of mutations and in investigation of early factors which may impact on later severity of Fabry disease are given. This validated age and gender adjusted scoring system allows the comparison of disease severity in different subgroups such as genotypes without age or sex as confounding factors.

Community-acquired pneumonia: doctors do not follow national guidelines

OBJECTIVES

Appropriate assessment of community-acquired pneumonia (CAP) allows accurate severity scoring and hence optimal management, leading to reduced morbidity and mortality. British Thoracic Society (BTS) guidelines provide an appropriate score. Adherence to BTS guidelines was assessed in our medical assessment unit (MAU) in 2001/2 and again in 2005/6, 3 years after introducing an educational programme.

METHODS

A retrospective case-note study, comparing diagnosis, documentation of severity, management and outcome of CAP during admission to MAU during 3 months of each winter in 2001/2 and 2005/6.

RESULTS

In 2001/2, 65/165 patients were wrongly coded as CAP and 100 were included in the study. In 2005/6 43/130 were excluded and 87 enrolled. In 2005/6, 87% did not receive a severity score, a significant increase from 48% in 2001/2 (p<0.0001). Parenteral antibiotics were given to 79% of patients in 2001/2 and 77% in 2005/6, and third generation cephalosporins were given to 63% in 2001/2 and 54% in 2005/6 (p = NS). In 2001, 15 different antibiotic regimens were prescribed, increasing to 19 in 2005/6.

CONCLUSIONS

Coding remains poor. Adherence to CAP management guidelines was poor and has significantly worsened. Educational programmes, alone, do not improve adherence. Restriction of antibiotic prescribing should be considered.

Reversible hypertension following coeliac disease treatment: the role of moderate hyperhomocysteinaemia and vascular endothelial dysfunction

The vascular endothelium maintains a relatively vasodilated state via the release of nitric oxide (NO), a process that could be disrupted by hyperhomocysteinaemia. Since endothelial dysfunction is associated with increased systemic vascular resistance that is the hallmark of sustained arterial hypertension, we hypothesised that in patients with both hypertension and coeliac disease with hyperhomocysteinaemia (via malabsorption of essential cofactors), treatment of the latter disease could improve blood pressure (BP) control. A single patient with proven sustained hypertension and newly-diagnosed coeliac disease had baseline and post-treatment BP and endothelial function assessed by ambulatory BP monitoring (ABPM) and brachial artery forearm occlusion plethysmography respectively. This 49 year-old woman had uncomplicated sustained hypertension proven on repeated ABPM carried out 6 weeks apart (daytime mean 151/92 mm Hg and 155/95 mm Hg), and sub-clinical coeliac disease (gluten-sensitive enteropathy). Initial assessments revealed raised homocysteine levels with low normal vitamin B(12) level. It was likely that she had impaired absorption of essential cofactors for normal homocysteine metabolism. She adhered to a gluten-free diet and was give oral iron, folate and B(6) supplementations as well as B(12) injections for 3 months. Her BP had improved by 6 months and normalised by 15 months (daytime ABPM mean 128/80 mm Hg). There was parallel restoration of normal endothelial function with normalisation of her homocysteine levels. These observations suggest that sub-clinical coeliac disease related hyperhomocysteinaemia might cause endothelial dysfunction, potentially giving rise to a reversible form of hypertension. In addition, this case study supports the notion that irrespective of aetiology, endothelial dysfunction may be the precursor of hypertension. This highlights the need to resolve co-existing vascular risk factors in patients with hypertension.

Association between low-density lipoprotein composition and its metabolism in non-insulin-dependent diabetes mellitus

Atheroma is related to low-density lipoprotein (LDL) composition. LDL in diabetic patients-a group with increased risk of severe atheroma-has been shown by our group and others to have various compositional alterations that are potentially atherogenic. Little is known about the relationship between LDL turnover and composition. This study examined the relationship between LDL composition and turnover in non-insulin-dependent diabetes mellitus (NIDDM) patients. Twenty-two NIDDM patients with a mean plasma cholesterol of 6.6+/-1.5 mmol/L were studied. Twelve subjects were hypercholesterolemic (mean cholesterol, 7.7+/-0.8 mmol/L), and eight of these agreed to be studied a second time after 4 weeks of treatment with simvastatin. LDL was isolated by density gradient ultracentrifugation, iodinated, and reinjected into the patient. LDL turnover was determined by measuring the clearance of [125I]-LDL from plasma over a 10-day period. The LDL residence time, determined using a biexponential model, correlated negatively with the body mass index (BMI) (r = -.73, P<.001) and serum triglycerides (r = - .57, P<.01). There was a significant inverse correlation between LDL residence time and the LDL esterified to free cholesterol ratio in hypercholesterolemic subjects (r = -.94, P<.001). There was a significant inverse relationship between LDL residence time and both hemoglobin A1c (HbA1c) and fasting blood glucose in these subjects before treatment (P<.005). After simvastatin therapy, the relationships were no longer significant. Simvastatin treatment was associated with a shorter LDL residence time (P<.01) and a decrease in LDL glycation (P<.001) with virtually no change in diabetic control (HbA1c, 6.0%+/-3.1% v. 6.3%+/-3.3%, NS). This study suggests that a decrease in residence time by upregulation of the LDL receptor with simvastatin alters LDL composition in a way that is likely to render the particle less atherogenic.

Efficacy of nasal continuous positive airway pressure therapy in chronic heart failure: importance of underlying cardiac rhythm

BACKGROUND

Some previous reports have indicated beneficial cardiac effects of nasal continuous positive airway pressure (NCPAP) in patients with severe congestive heart failure (CHF), but others have reported deleterious cardiac effects, particularly among patients in atrial fibrillation (AF). The aim of this study was to determine if differences in cardiac rhythm influence the acute cardiac response to NCPAP.

METHODS

Eleven consecutive patients with CHF were recruited, six in atrial fibrillation (AF) and five with sinus rhythm (SR). Cardiac index was measured during awake NCPAP application by the thermodilution technique during cardiac catheterisation. NCPAP was applied in a randomised sequence at pressures of 0, 5, and 10 cm H2O with three 30 minute applications separated by 20 minute recovery periods without NCPAP.

RESULTS

Significant differences were found between the AF and SR groups for cardiac index responses to NCPAP (p = 0.004, ANOVA) with a fall in cardiac index in the AF group (p = 0.02) and a trend towards an increase in the SR group (p = 0.10). Similar differences were seen between the groups in stroke volume index responses but not in heart rate responses. Changes in systemic vascular resistance were also significantly different between the two groups (p < 0.005, ANOVA), rising in the AF group but falling in the SR group.

CONCLUSIONS

These data indicate an important effect of underlying cardiac rhythm on the awake haemodynamic effects of NCPAP in patients with CHF.

Reversible hypercapnia in chronic obstructive pulmonary disease: a distinct pattern of respiratory failure with a favorable prognosis

PURPOSE

Hypercapnia is regarded as a poor prognostic indicator in chronic obstructive pulmonary disease (COPD), but many patients hospitalized with hypercapnia associated with an acute exacerbation of COPD revert to normocapnia during recovery. We wished to determine if this reversible hypercapnia represents a distinct pattern of respiratory failure in COPD, or simply a stage in the progression to chronic hypercapnia. We therefore compared the long-term clinical progression and survival of COPD patients with reversible hypercapnic respiratory failure (defined as type 2.1) to those with normocapnic (PaCO2 < 50 mm Hg; type 1) and also to those patients with chronic hypercapnic (PaCO2 > 50 mm Hg) respiratory failure (defined as type 2.2).

PATIENTS AND METHODS

We prospectively followed for 5 years a cohort of 85 patients who had been admitted as emergencies during a 1-year period to the respiratory unit of a University teaching hospital with an exacerbation of COPD complicated by respiratory failure (PaO2 < 60 mm Hg). The main long-term outcome measures were survival and blood gas changes.

RESULTS

Sixty-eight (80%) patients survived the initial admission, and 17 (27%) survived 5 years. PaCO2 rose substantially more during exacerbations in type 2.1 patients (mean 15.8 mm Hg), compared with type 2.2 (mean 6.8 mm Hg) and type 1 patients (mean 1.5 mm Hg). We analyzed 149 subsequent admissions among the survivors over the following 5 years. Type 2.1 patients had a better 5-year survival (28%) than type 2.2 (11% survival; P < 0.05), and similar to type 1 patients (33% 5-year survival). Only 24% of reversible hypercapnic patients developed chronic hypercapnia during long-term followup.

CONCLUSIONS

The data support reversible hypercapnia being a distinct manifestation of respiratory failure in COPD, with a similar prognosis to that of normocapnic respiratory failure.

Elevated triglyceride-rich lipoproteins in diabetes. A study of apolipoprotein B-48

The role of the intestine in cholesterol metabolism in human diabetes is unclear, although abnormalities have been demonstrated in cholesterol synthesis and absorption in diabetic animals. This study examines the relationship between fasting and post-prandial apolipoprotein B-48 in type 2 (non-insulin-dependent) diabetic and non-diabetic subjects. Eight type 2 diabetic patients and ten healthy non-diabetic control subjects were given a high-fat meal (1300 kcal), and the triglyceride-rich lipoprotein fraction was isolated by ultracentrifugation (d < 1.006 g/ml) from fasting and post-prandial plasma. Apolipoprotein B-48 and apo B-100 were separated on 4%-15% gradient gels and quantified by densitometric scanning with reference to a purified low-density lipoprotein (LDL) apo B-100 preparation. Diabetic patients had significantly higher concentrations of apo B-48 and apo B-100 in both the fasting (P < 0.05) and post-prandial (P < 0.001) triglyceride-rich lipoprotein samples compared with non-diabetic subjects. The diabetic patients also exhibited a significantly different post-prandial profile for apo B-48 and apo B-100, with a prolonged increase and a later post-prandial peak, than the non-diabetic subjects (P < 0.01). These results suggest that the raised fasting triglyceride-rich lipoproteins, often found in diabetes, are associated with apo B-48 and may be derived from increased intestinal chylomicron production. The post-prandial pattern suggests an abnormality in intestinal production as well as hepatic clearance of apo B-48 in type 2 diabetes.

Intestinally derived lipoprotein particles in non-insulin-dependent diabetic patients with and without hypertriglyceridaemia

We have previously demonstrated alterations in apolipoprotein B-48 metabolism in the post-prandial state in patients with non-insulin-dependent diabetes mellitus. This study investigates the relationship between hypertriglyceridaemia and post-prandial lipoprotein metabolism. Four groups of patients were examined: non-insulin-dependent diabetic patients, with normal serum triglyceride levels (serum triglyceride < 2.1 mmol l-1; haemoglobin HbA1c 5.5% +/- 0.4%); poorly controlled, non-insulin-dependent diabetic patients with hypertriglyceridaemia (serum triglyceride > 2.1 mmol l-1; HbA1c 8.8% +/- 0.9%); non-diabetic subjects with serum triglycerides < 2.1 mmol l-1; and non-diabetic subjects with hypertriglyceridaemia (serum triglyceride > 2.1 mmol l-1). Subjects were studied fasting and following a high-fat meal (1300 kcal). The triglyceride-rich lipoprotein fraction was isolated by ultracentrifugation (d < 1.006 g ml-1). Apoprotein B-48, apoprotein B-100 and apoprotein E were separated on 4%-15% gradient gels and quantified as a percentage of the fasting concentration by densitometric scanning. Triglyceride-rich lipoprotein apolipoprotein B-48 and apolipoprotein B-100 post-prandial profiles demonstrated a maximum increase either at 2 h or rising still further to a peak at 6 h before falling in the diabetic groups and hypertriglyceridaemic non-diabetic subjects when compared with the normotriglyceridaemic control subjects whose levels decreased after 2 h (P < 0.05). A significantly different triglyceride-rich lipoprotein apolipoprotein E profile was also exhibited by the diabetic patients (P < 0.05). Levels of triglyceride-rich lipoprotein, cholesterol, triglyceride, total protein and apoprotein B were elevated in the hypertriglyceridaemic subjects, both diabetic and non-diabetic. These results indicate that hypertriglyceridaemia is associated with altered metabolism and composition of post-prandial triglyceride-rich lipoprotein particles in both poorly controlled diabetic and non-diabetic subjects.

Alterations in apolipoprotein B-48 in the postprandial state in NIDDM

The intestine is a major site of cholesterol synthesis and produces apolipoprotein B-48, which is critical for intestinal cholesterol absorption and secretion. The purpose of this study was to examine postprandial changes in apolipoprotein B-48 in diabetes. Six non-insulin-dependent diabetic patients and six non-diabetic control subjects were given a high-fat meal (1300 kcal) and blood samples were taken pre- and postprandially, from which the triglyceride-rich lipoprotein fraction was isolated by ultracentrifugation (density < 1.006 g/ml). Apolipoprotein B-48 was separated on 4-15% gradient gels and quantified as a percentage of the fasting concentration by densitometric scanning. Total protein, triglyceride and cholesterol in the triglyceride-rich lipoprotein fraction, blood glucose, and serum insulin were also measured. Diabetic patients exhibited a postprandial triglyceride-rich apolipoprotein B-48 profile significantly different from that of control subjects (p < 0.05). The triglyceride and total protein concentration in the triglyceride-rich lipoprotein fraction mirrored the post-prandial profile and apolipoprotein B-48 in both groups. Significantly different patterns for triglyceride (p < 0.02) and total protein (p < 0.05) following the fat-rich meal were observed in the two groups. Fasting and postprandial triglyceride-rich lipoprotein cholesterol and total apolipoprotein B were significantly higher in diabetic patients than in control subjects (p < 0.05). Since apolipoprotein B-48 is the structural protein of intestinally-derived lipoprotein particles, these studies suggest an abnormality in intestinal lipoprotein metabolism in diabetes.

Short report: the effect of omeprazole on Helicobacter pylori and associated gastritis

Twenty-one patients with endoscopically confirmed duodenal ulceration, who had failed to heal with an H2-antagonist, were given omeprazole 20 mg o.m. for four weeks. Four antral biopsies from each patient were taken at endoscopy before, at the end of, and four weeks after treatment. Rapid urease test, culture, histopathology and transmission electron microscopy were carried out on these biopsies to determine the presence of Helicobacter pylori and improvement of gastritis. After four weeks of treatment, duodenal ulceration was healed in 16 (79%) of the patients; H. pylori was not detected by culture in 11 (50%) of the patients, and the associated gastritis improved in 12 (54%) patients. Four weeks after cessation of treatment the organism was cultured from antral biopsies of 18 (86%) of the patients and all of these had gastritis. Omeprazole treatment healed duodenal ulceration, improved gastritis temporarily, and suppressed but did not eradicate H. pylori.

Prediction of human analgesic dosages of nonsteroidal anti-inflammatory drugs (NSAIDs) from analgesic ED50 values in mice

The oral analgesic activities (ED50's) of 15 NSAIDs were determined in the phenylquinone-induced writhing test in mice. ED50 values (mg/kg) were: acetylsalicylic acid (182), fenclofenac (168), phenylbutazone (129), ibuprofen (82.2), diflunisal (55.6), benoxaprofen (25.4), naproxen (24.1), mefenamic acid (20.7), indomethacin (19.0), meclofenamate sodium (9.60), sulindac (7.20), fenoprofen calcium (3.70), tolmetin (1.30), zomepirac sodium (0.70), and piroxicam (0.44). Significant linear correlations were found between mouse ED50 values and the various recommended human analgesic or anti-inflammatory dosages. Thus, analgesic ED50 values (mg/kg p.o.) in mice (X) may be used to predict human dosages (Y) of NSAIDs according to the equation Y = 8.26X + 535, where Y is the projected human daily dosage (mg).