Studying the Effect of Temperature on the Tensile Strength of an Intravascular Catheter Using a Degradation Model / Estudiando el Efecto de la Temperatura en la Resistencia Tensil de un Catéter Intravascular Usando un Modelo de Degradación

ABSTRACT The accelerated aging process is incorporated into the design and development of intravascular catheters to assess their reliability assuring that this medical device is safe and effective for the intended use during their shelf life. The accelerated aging process is based on a common approach that assumes that the rate of aging increases by a factor of 2^(∆T/10), where ∆T is the temperature increment. However, with the life data obtained from this empirical method is difficult to do inferences about reliability. This paper presents an accelerated destructive degradation test using thermal stress to obtain degradation data directly relates reliability to critical performance characteristic, which is the tensile strength in the intravascular catheter tip considered as a critical concern in patients' safety. The degradation data model is given by a stochastic Wiener process with the drift parameter being represented as Arrhenius function. The parameters of the Wiener process and Arrhenius function are estimated using maximum likelihood; these parameters are used to estimate the first-passage time (time to failure) distribution when the intravascular catheters degradation path reaches a tensile strength critical value in each thermal stress level. Based on this, a complete product reliability assessment is performed and presented.

RESUMEN El proceso de envejecimiento acelerado es incorporado en el diseño y desarrollo de catéteres intravasculares para evaluar su confiabilidad y asegurar que el dispositivo medico es seguro y efectivo para su uso durante su vida de estante. Este proceso está basado en un enfoque que asume que la tasa de envejecimiento se incrementa por un factor de 2^(∆T/10), en donde ∆T es el incremento de temperatura. Sin embargo, con los datos de vida obtenidos de este método empírico resulta complicado realizar inferencias sobre la confiabilidad del dispositivo. Este articulo presenta una prueba de degradación acelerada destructiva que considera un estrés termal para obtener datos de degradación que se relaciona directamente la confiabilidad con la resistencia tensil de la punta de un catéter intravascular y que es considerada como una característica critica para la seguridad de los pacientes. El modelo de degradación esta dado por un proceso estocástico Wiener, con el parámetro de deriva representado la relación de Arrhenius. Los parámetros del proceso Wiener y la relación de Arrhenius son estimados mediante máxima verosimilitud; estos parámetros son usados para estimar la distribución de primer paso, la cual se caracteriza cuando la resistencia de un catéter alcanza el nivel crítico de resistencia en cada nivel de estrés. Considerando esto, se lleva a cabo y se presenta una evaluación de confiabilidad completa del producto.

Estimación de la edad de Swietenia macrophylla (Meliaceae) a partir del diámetro normal en poblaciones del sureste mexicano

Introducción: Swietenia macrophylla King ("caoba") es la especie arbórea de mayor importancia comercial en el sureste mexicano y utilizada como guía en el manejo forestal, por lo que conocer su edad y tasas de crecimiento es fundamental para la sostenibilidad de los aprovechamientos maderables. Objetivos: Estimar laedad (E t ) a partir del método del 'tiempo de paso' (Tp) y calcular las tasas de crecimiento absoluto (TCA) y relativo (TCR) para Swietenia macrophylla en Quintana Roo, México. Métodos: Se ajustaron ecuaciones para calcular TCA y TCR con remediciones periódicas durante 15 años del diámetro normal (d) en 403 árboles de S. macrophylla en Felipe Carrillo Puerto, Quintana Roo, México; también, se determinaron el Tp y la E t para el cálculo del incremento corriente anual (ICA) e incremento medio anual (IMA), y definir así los turnos comercial y técnico. Resultados: La máxima TCR se alcanzó a los 28 cm de d (0.015 cm año-1) (aplicación de aclareos), mientras que la mayor TCA (0.69 cm año-1) y menor Tp (3.5 años) a los 55 cm de d (turno comercial). El máximo ICA al considerar la E t fue de 1.43 cm en la categoría diamétrica de 50 cm, con un IMA de 0.67 cm año-1 a una edad de 75 años, mientras que el turno técnico (ICA = IMA) se alcanzó a los 96 años (incrementos de 0.78 cm año-1). Conclusiones: A través de mediciones periódicas del diámetro normal en S. macrophylla es posible obtener su edad, además los resultados pueden ser utilizados para elaborar programas de manejo y ejecutar prácticas silvícolas que propicien el incremento diamétrico en Quintana Roo.

Introduction: Swietenia macrophylla King (Mahogany) is the most commercially important tree species in Southeastern of Mexico and is used as a guide in forest management. Therefore, knowing its age and growth rates is essential for the sustainability of timber harvest. Objective: Estimate the age (Et) from the 'step time' (Tp) method and calculate the absolute (TCA) and relative (TCR) growth rates for Swietenia macrophylla in Quintana Roo, Mexico. Methods: Equations were adjusted to calculate TCA and TCR with periodic re-measured for 15 years of the normal diameter (d) in 403 S. macrophylla trees in Felipe Carrillo Puerto, Quintana Roo, Mexico. Tp and Et were determined for the calculation of the annual current increase (ICA) and average annual increase (IMA), to define the commercial and technical shifts. Results: The maximum TCR was reached at 28 cm of d (0.015 cm year-1) (thinning application), whereas the highest TCA (0.69 cm year-1) and lower Tp (3.5 years) at 55 cm of d (commercial shift). The maximum ICA when considering Et was 1.43 cm in the 50 cm of diametric category with an IMA of 0.67 cm year-1 at an age of 75 years, while the technical shift (ICA = IMA) was reached at 96 years (increments of 0.78 cm year-1). Conclusions: Through periodic measurements of the normal diameter in S. macrophylla it is possible to obtain its age, these results also can be used to elaborate management programs and apply silvicultural practices that propitiate the diametric increase in Quintana Roo.

Changes in Hematologic and Physiologic Values Before and After Hot Water Bathing in Healthy Men / 日本温泉気候物理医学会雑誌

To clarify the effects of full bathing at 42°C for 10min, we measured hematologic (white blood cells, red blood cells, hemoglobin, hematocrit, platelets, whole blood passage time) and physiologic (body weight, blood pressure, pulse rate) values of 10 healthy men aged 28 to 37 years. Data were collected before, immediately after, and 60min after bathing, and values were compared using a one-factor ANOVA.<br>No significant changes in hemotologic values were found among the three measurement timepoints. Regarding physiologic values, no significant changes in body weight and systolic blood pressure were found among the three measurement time-points. However, diastolic blood pressure decreased after bathing (53.0±9.8mmHg) compared with that before bathing (76.2±10.3mmHg), then increased again 60min after bathing (71.1±10.6mmHg) compared with that immediately after bathing. Furthermore, pulse rate increased significantly after bathing (101.3±10.3bpm) compared with that before bathing (69.0±5.9bpm), and then decreased significantly 60min after bathing (69.8±7.0bpm) compared with that immediately after bathing.<br>Our results indicate that hot water bathing does not influence hematologic values, body weight, or systolic blood pressure in healthy men. Although diastolic blood pressure and pulse rate changed significantly after bathing, they returned to baseline values 60min after bathing. The changes in hematologic and physiologic values may be explained by the maintenance of the body's homeostasis.

The Clinical Significance of Venous Filling Time through Panretinal Photocoagulation in Proliferative Diabetic Retinopathy

PURPOSE: To verify the clinical correlation between retinopathy progression and the change of venous filling time (VFT), measured before and after panretinal photocoagulation (PRP), in proliferative diabetic retinopathy (PDR) patients. METHODS: We conducted this study on 32 patients (32 eyes) who received PRP for PDR. These patients were subdivided into two groups in accordance with the clinical course of PRP: the stabilized group in which retinal neovascularization was regressed and the progressed group in which retinal neovascularization was continued and a complication, such as vitreous hemorrhage or tractional retinal detachment, was developed within 12 months of laser treatment. Arteriovenous passage time (AVP) and VFT were measured by video fluorescein angiogram (FAG) using scanning laser ophthalmoscope (SLO) before and after PRP. VFT values were assigned by measuring by the time duration from start of venous lamina flow to the fullness of fluorescence on the vascular arch. RESULTS: In the stabilized group, AVP was decreased by 0.20+/-0.89sec and VFT was decreased by 0.30+/-1.69 sec through PRP. In the progressed group, AVP was increased in 0.12+/-1.22 sec and VFT was increased by 0.99+/-1.60 sec through PRP. In both groups, the VFT changes were significant (P=0.04) but the AVP changes were not (P=0.34). CONCLUSIONS: VFT was significantly decreased in the stabilized group and significantly increased in the progressed group after PRP. Accordingly, we suggest that VFT changes after PRP can be utilized as a prognostic indicator for evaluating clinical course of diabetic retinopathy after performing PRP and for monitoring the clinical effect of PRP.

Scanning Laser Ophthalmoscopic Examination on Circulation in Primary Open Angle Glaucoma

To investigate the retinal hemodynamics in chronic primary open angle glaucoma (POAG), high-quality video fluorescein angiograms using a scanning laser ophthalmoscope(SL0 101, Rodenstock, Munich, Germany) were obtained from 22 eyes of 16 patients with POAG and 14 eyes of 14 healthy subjects. From these angiograms, the arm to retinal time (ART), arteriovenous passage time (AvFT), venous fulling time(VFT) and arteriovenous fulling time (AvFT) were quantified. And these parameters of retinal circulation of the group of patients with POAG were compared with those of the age-matched group of healthy subjects. There were no significant differences in the ART between two groups (p=0.09). But significant prolongations of the AvPT, VFT and AvFT of the group of patients with POAG(2.5 +/- 1.1, 8.4 +/- 1.8 and 10.9 +/- 2. sec, respectively) were observed compared to the values (1.8 +/- 0.7, 6.4 +/- 2.2 and 8.1 +/- 2. 4 sec, respectively) obtained among the healthy subjects (p=0.04, p=0.007 and p=0.0008, respectively). These results indicate that a significant retinal microcirculatory deficit exists in the eyes of POAG, and the VFT and AvFT may be good indices of retinal microcirculatory deficit in the eyes of POAG.

Study on Retinal Circulation by Scanning Laser Ophthalmoscope I. Evaluation of Retinal Circulation Times in Non-proliferative Diabetic Retinopathy

The scanning laser ophthalmoscope was used to measure arm-retinal time(ART) and arteriovenous passage time(AVP) in 27 non-proliferative diabetic retinopathic eyes(NPDR eyes) and 22 normal controls. The ART in NPDR eyes(12.10 +/- 4.21 sec) was similar to that in normal eyes(12.79 +/- 3.59 sec). The AVPs measured from each quadrant were significantly longer in all quadrants in the NPDR eyes (2.41 +/- 0.85 sec in superior temporal quadrant (ST), 2.29 +/- 0.63 sec in inferior temporal one(IT) , 2.41+/-0.88 see in superior nasal one (SN), and 2.30 +/- 0.72 sec in inferior nasal one(IN)) than in normal eyes(1.73 +/- 0.61 sec in ST, 1.81 +/- 0.75 sec in IT, 1.83 +/- 0.58 sec in SN, and 1.83 +/- 0.58 sec in IN). This results suggest that retinal blood flow and its velocity are reduced in NPDR.