Evaluación de aspectos clínicos relacionados con la amputación de miembros inferiores en personas que viven con diabetes mellitus tipo 2 en México / Evaluation of clinical aspects related to lower limb amputation among individuals living with type 2 diabetes mellitus in Mexico

RESUMEN Introducción: La diabetes continúa siendo una de las principales causas de discapacidad y muerte en la población mundial. Alrededor del 25% de las personas con diabetes desarrollarán una úlcera en alguno de sus miembros pélvicos inferiores. Objetivo: El presente estudio evalúa los aspectos clínicos relacionados con la amputación del miembro inferior pélvico en una cohorte de pacientes con diabetes mellitus. Métodos: Estudio retrospectivo, transversal, realizado en colaboración entre el Instituto Mexicano del Seguro Social y la Facultad de Farmacia de la Universidad Autónoma del Estado de Morelos, implicó una revisión de expedientes de pacientes con diabetes mellitus tipo 2 en el Hospital General Regional "Ignacio García Téllez". Se seleccionaron 100 expedientes clínicos y Electrónicos basados en criterios de inclusión, que incluían edad mayor de 18 años, afiliación en el sitio del estudio, evolución de la diabetes de al menos 10 años, tratamiento farmacológico para la diabetes y diagnóstico de pie diabético con curación completa o amputación como resultado. Los análisis estadísticos se realizaron mediante STATA y se obtuvo aprobación ética. Resultados: Los pacientes con un control glucémico óptimo cuantificando sus niveles de glucosa en ayunas (<130 mg/dl) así como sus valores de hemoglobina glicosilada (< 7%) tuvieron una menor frecuencia de amputaciones (p˂0,001; Chi2) en comparación con aquellos pacientes sin un control glucémico adecuado. Conclusión: Se encontró que ser hombre, valores de hemoglobina glucosilada superiores al 7% y valores promedio de glucosa en ayunas superiores a 130 mg/L aumentan la probabilidad de presentar una amputación de extremidad inferior.

ABSTRACT Introduction: Diabetes continues to be a leading cause of disability and death in the world's population. About 25% of people with diabetes will develop an ulcer in one of their lower pelvic limbs. Objective: The present study evaluates the clinical aspects related to lower pelvic limb amputation in a cohort of patients with diabetes mellitus. Lazarte Echegaray Hospital during the period 2017-2020. Methods: Retrospective, cross-sectional study, conducted in collaboration between the Mexican Institute of Social Security and the School of Pharmacy of the Autonomous University of Morelos State, involved a review of records of patients with type 2 diabetes mellitus at the Regional General Hospital "Ignacio García Téllez". One hundred clinical and electronic records were selected based on inclusion criteria, which included age over 18 years, affiliation at the study site, diabetes evolution of at least 10 years, pharmacological treatment for diabetes and diagnosis of diabetic foot with complete healing or amputation as an outcome. Statistical analyses were performed using STATA and ethical approval was obtained. Results: Patients with optimal glycemic control by quantifying their fasting glucose levels (<130 mg/dl) as well as their glycated hemoglobin values (< 7%) had a lower frequency of amputations (p˂0.001; Chi2) compared to those patients without adequate glycemic control. Conclusion: Being male, glycosylated hemoglobin values greater than 7% and mean fasting glucose values greater than 130 mg/L were found to increase the likelihood of having a lower extremity amputation.

Adecuación de los catéteres midline y mini-midline en pacientes con COVID-19 / daptation of midline and mini-midline catheters for patients with COVID-19

Objetivo: analizar el tiempo de permanencia y las principales causas de retirada de los catéteres midline (20 cm) y mini-midline (10 cm) en pacientes hospitalizados, y estudiar las diferencias en pacientes con COVID-19. Método: estudio descriptivo, transversal, retrospectivo realizado con datos de las historias clínicas en el Hospital Universitario Vall d´Hebron (Barcelona, España). Se analizaron catéteres insertados por el Equipo de Enfermería de Infusión y Accesos Venosos (EIAV) en pacientes hospitalizados durante 2020. Resultados: se incluyeron 357 catéteres de 305 pacientes (28,9% tenía COVID-19). Estos últimos presentaron mayor proporción de obesidad (21,6% vs. 9,2%; p= 0,003). La mediana de duración de catéteres insertados fue de 11-12 días, sin diferencias por el tipo de catéter ni por tener COVID-19 (p= 0,88). La principal causa de retirada en ambos grupos fue el fin del tratamiento, siendo mayor en pacientes sin COVID-19 (65,7% vs. 53,1%; p= 0,031), seguida del éxitus en pacientes con COVID-19 (22,9% frente a 8,9%; p= 0,001) y oclusión del catéter en el resto (17,3% vs. 8,33%; p= 0,035). Se dieron n= 4 casos de infección del catéter y n= 31 sospechas, sin diferencias según diagnóstico ni tipo de catéter. El motivo de retirada no varió según el acceso venoso de elección. Conclusiones: no existen diferencias en la duración de los catéteres respecto a su longitud, vena de inserción ni diagnóstico de COVID-19. La venopunción ecoguiada, la técnica estéril y la elección del tipo de catéter por parte de un EIAV parecen disminuir las complicaciones asociadas.(AU)

Objective: to analyse the time of permanence and main causes for removal of midline (20 cm) and mini-midline (10 cm) catheters in hospitalized patients, and to study the differences in patients with COVID-19. Method: a descriptive, cross-sectional, retrospective study conducted with data from clinical records in the Hospital Universitario Vall d´Hebron (Barcelona, Spain). The study included catheters inserted by the Infusion and Vascular Access Nursing (IVAN) Team in patients hospitalized during 2020. Results: the study included 357 catheters in 305 patients (28.9% with COVID-19). The latter presented a higher rate of obesity (21.6% vs. 9.2%; p= 0.003). The median duration of catheters inserted was 11-12 days, without any difference by type of catheter or having COVID-19 (p= 0.88). The main cause for removal in both groups was the end of the treatment, and it was higher in patients without COVID-19 (65.7% vs. 53.1%; p= 0.031), followed by exitus in patients with COVID-19 (22.9% vs. 8.9%; p= 0.001), and catheter occlusion in the rest (17.3% vs. 8.33%; p= 0.035). There were n= 4 cases of catheter infection and n= 31 suspected cases, without difference by diagnosis or type of catheter. There was no variation in the cause for removal according to the venous access selected. Conclusions: there are no differences in terms of duration of catheters according to their length, vein of insertion or COVID-19 diagnosis. Ultrasound-guided venipuncture, sterile technique and selection of type of catheter by a member of the IVAN team seem to reduce the complications associated.(AU)

Incorporación urgente de estudiantes de Enfermería durante la pandemia por COVID-19: análisis de competencias / Emergency incorporation of Nursing students during the COVID-19 pandemic: an analysis of competences

Objetivo: describir el nivel de competencia de los y las estudiantes del Grado en Enfermería contratadas como refuerzo en el Hospital Universitario Vall d’Hebron (Barcelona) durante la primera ola de la pandemia por COVID-19 y determinar su satis-facción con el entorno clínico. Método: estudio descriptivo transversal. Se incluyó a todas las personas contratadas (n= 39) entre febrero y mayo de 2020. Al mes de la incorporación se recogieron variables demográficas académicas, laborables y se midió el nivel de competencia (Cuestionario COM_VAT© de 21 ítems puntuados entre 1: ejecución insuficiente y 4 ejecución autónoma y correcta) y la satisfacción con el entorno clínico (cuestionario diseñado ad hoc de tres dimensiones -orientación, integración con el equipo y adaptación al entorno laboral- evaluadas con 15 ítems puntuados de 1 muy en desacuerdo a 5 muy de acuerdo). Se realizó estadística descriptiva y bivariante. Resultados: participaron las 39 personas. La puntuación global mediana de la evaluación competencial fue de 3,9 sobre 4 pun-tos [RIC 3,7-4]. La competencia de valorar, diagnosticar y abordar situaciones de salud cambiantes obtuvo 3,85 puntos [RIC 3,4-4]. La competencia de ayudar al paciente a cumplir el tratamiento y hacerlo partícipe de 4 [RIC 4-4] y la competencia de contribuir a garantizar la seguridad y el proceso asistencial de 3,8 [RIC 3,6 – 4]. La mediana de satisfacción con el entorno clínico fue de 69 sobre 75 [RIC 63-74] sin diferencias estadísticamente significativas en ella en función del resto de características. Conclusión: las personas participantes mostraron un nivel de competencia que representa una correcta ejecución, pero que puede requerir ayuda ocasional. Reportaron una alta satisfacción con el entorno clínico.(AU)

Objective: to describe the level of competence among Nursing Degree students hired as support at the Hospital Universitario Vall d’Hebron (Barcelona) during the first wave of the COVID-19 pandemic, and to determine their satisfaction with the clinical environment. Method: a descriptive cross-sectional study, including all persons hired (n= 39) between February and March 2020. Demographic, academic and occupational variables were collected at one month of their incorporation, and their level of competence was measured (COM_VAT© questionnaire with 21 items scored from 1: insufficient performance, to 4: autonomous and correct performance), as well as the satisfaction with their clinical environment (questionnaire designed ad hoc with three dimensions: orientation, integration with the team, and adaptation to the work environment, evaluated through 15 items scored from 1: high disagreement, to 5: high agreement). Descriptive and bivariate statistics was used. Results: all 39 persons were included. The overall median score of the evaluation of skills was 3.9 out of 4 scores [IQR 3.7-4]. The competence of assessing, diagnosing and addressing ever-changing health situations obtained a score of 3.85 [IQR 3.4-4]. The competence of helping patients to comply with treatment and getting them involved obtained a 4 [IQR 4-4], and the competence of contributing to guarantee safety and care process obtained 3.8 [IQR 3.6 – 4]. The median satisfaction with the clinical environment was 69 out of 75 [IQR 63-74] without statistically significant differences according to the other characteristics .Conclusion: the participants showed a level of competence ensuring correct performance, but that might require occasional help. They reported high satisfaction with the clinical environment.Keywords:care; coronavirus infections; volunteers; clinical competence; nursing students; job satisfaction; working conditions; cross-sectional studies.(AU)

Perfil de los pacientes hospitalizados en dispositivos asistenciales habilitados durante la pandemia por SARS-CoV-2 / Profile of the patients hospitalized in healthcare resources provided during the SARS-CoV-2 pandemic

OBJETIVO: describir el perfil demográfico, clínico y los indicadores de progresión de los pacientes hospitalizados en dispositivos asistenciales habilitados durante la pandemia por SARS-CoV-2. MÉTODO: estudio observacional retrospectivo. Se incluyeron todos pacientes atendidos en el Pabellón Salud Vall d'Hebron (Barcelona) durante el periodo de su apertura (29 marzo al 18 abril de 2020). Se analizaron variables demográficas, clínicas y de progresión. Se llevó a cabo análisis descriptivo. RESULTADOS: 63 pacientes. El 55,6% (n= 35) era hombre, la media de edad fue de 76,5 (11,88) años. Al ingreso, el 79,3% (n= 50) no presentaba antecedentes de deterioro cognitivo; el 61,9% (n= 39) deambulaba de forma libre o controlada; el 74,6% (n= 47) no presentaba problemas de continencia; el 39,7% (n= 25) fue valorado sin riesgo de lesión por presión. La estancia media (DE) fue de 8,1 (3,8) días. En relación a la presencia de eventos adversos durante su estancia hospitalaria, el 12,7% (n= 8) presentó una lesión por presión, el 6,3% (n= 4) algún episodio de desorientación y fueron declaradas dos caídas. Un 67% (n= 42) tenía el diagnóstico principal de Enfermería de Riesgo de sepsis y el 41,3% (n= 26) precisaron continuidad de cuidados. CONCLUSIONES: el perfil del paciente atendido en estos dispositivos asistenciales correspondió a una persona anciana, sin indicadores de fragilidad evidentes y sin eventos adversos destacables durante su estancia. Las unidades de hospitalización habilitadas durante la pandemia por COVID-19 representan un recurso adecuado y seguro para la atención a los pacientes en situación de emergencia

OBJECTIVE: to describe the demographical and clinical profile and the progression indicators for patients hospitalized in healthcare resources provided during the SARS-COV-2 pandemic. METHOD: an observational retrospective study, which included all patients seen at the Pabellón Salud Vall d'Hebron (Barcelona) during its opening period (March, 29th to April, 18th, 2020). Demographic, clinical and progression variables were analyzed; descriptive analysis was conducted. RESULTS: the study included 63 patients; 55.6% (n= 35) were male, with a mean age of 76.5 (11.88) years. At admission, 79.3% (n= 50) did not present a previous history of cognitive deterioration; 61.9% (n= 39) could walk in a free or controlled way; 74.6% (n= 47) did not present continence issues; 39.7% (n= 25) were evaluated as without risk of pressure injury. The mean stay (SD) was 8.1 (3.8) days. Regarding the presence of adverse events during their hospital stay, 12.7% (n= 8) presented pressure injuries, 6.3% (n= 4) had some disorientation episode, and two falls were reported; while 67% (n= 42) had the primary Nursing diagnosis of Risk of Sepsis, and 41.3% (n= 26) required continuity of care. CONCLUSIONS: the profile of the patient managed in these healthcare resources was an elderly person, without evident frailty indicators, and without any outstanding adverse events during their stay. The hospitalization units provided during the COVID-19 represented an adequate and safe resource for patient care in an emergency situation

Benefit of double-reading cytology smears as a triage strategy among high-risk human papillomavirus-positive women in Mexico.

BACKGROUND: The goal of this study was to determine whether the detection of histologically confirmed cases of cervical high-grade squamous intraepithelial lesions or worse (HSIL+) can be increased by having each liquid-based cytology (LBC) slide read by 2 cytotechnologists as part of routine screening. METHODS: Over 36,212 women aged 30 to 64 years participated in the Forwarding Research for Improved Detection and Access for Cervical Cancer Screening and Triage (FRIDA) Study in Mexico between 2013 and 2016. For each participant, 2 cervical samples were collected at the same clinic visit, one to test for high-risk human papillomavirus (hrHPV) and the other for LBC, which was used to triage those with a hrHPV positive result. LBC slides were evaluated by 7 cytotechnologists, with each slide read independently by 2 blinded cytotechnologists. All women with atypical cells of undetermined significance or a worse result were referred to colposcopy for further evaluation and diagnosis. Three pathologists evaluated the biopsy specimens to confirm the final HSIL+ diagnosis. The HSIL+ detection rates for the single versus double reading were estimated and compared. RESULTS: A total of 3,914 women with a positive hrHPV result were triaged with LBC. The first and second cytology readings resulted in 43 HSIL+ cases detected; the double-reading strategy detected 9 additional HSIL+ cases, resulting in a total of 52 HSIL+ cases. The HSIL+ detection rate increased from 10.99/1000 with a single reading to 13.29/1000 with the double-reading strategy (P = .004). CONCLUSION: A 20.9% increase in HSIL+ cases detected was achieved with a double reading of the LBC slides in this sample of hrHPV-positive women.

The Effect of Trabeculae Carneae on Left Ventricular Diastolic Compliance: Improvement in Compliance With Trabecular Cutting.

The role of trabeculae carneae in modulating left ventricular (LV) diastolic compliance remains unclear. The objective of this study was to determine the contribution of trabeculae carneae to the LV diastolic compliance. LV pressure-volume compliance curves were measured in six human heart explants from patients with LV hypertrophy at baseline and following trabecular cutting. The effect of trabecular cutting was also analyzed with finite-element model (FEM) simulations. Our results demonstrated that LV compliance improved after trabecular cutting (p < 0.001). Finite-element simulations further demonstrated that stiffer trabeculae reduce LV compliance further, and that the presence of trabeculae reduced the wall stress in the apex. In conclusion, we demonstrate that integrity of the LV and trabeculae is important to maintain LV stiffness and loss in trabeculae leads to more LV compliance.

Admittance to detect alterations in left ventricular stroke volume.

BACKGROUND: Implantable cardioverter-defibrillators monitor intracardiac electrograms (EGMs) to discriminate between ventricular and supraventricular tachycardias. The incidence of inappropriate shocks remains high because of misclassification of the tachycardia in an otherwise hemodynamically stable individual. Coupling EGMs with an assessment of left ventricular (LV) stroke volume (SV) could help in gauging hemodynamics during an arrhythmia and reducing inappropriate shocks. OBJECTIVE: The purpose of this study was to use the admittance method to accurately derive LV SV. METHODS: Ultrasonic flow probe and LV endocardial crystals were used in canines (n = 12) as the standard for LV SV. Biventricular pacing leads were inserted to obtain admittance measurements. A tetrapolar, complex impedance measurement was made between the Bi-V leads. The real and imaginary components of impedance were used to discard the myocardial component from the blood component to derive instantaneous blood conductance (Gb). Alterations in SV were measured during right ventricular pacing, dopamine infusion, and inferior vena cava occlusion. RESULTS: Gb tracks steady-state changes in SV more accurately than traditional magnitude (ie, |Y|, without removal of the muscle signal) during right ventricular pacing and dopamine infusion (P = .004). Instantaneous LV volume also was tracked more accurately by Gb than ∣Y∣ in the subset of subjects that underwent inferior vena cava occlusions (n = 5, P = .025). Finite element modeling demonstrates that admittance shifts more sensitivity of the measurement to the LV blood chamber as the mechanism for improvement (see Online Appendix). CONCLUSION: Monitoring LV SV is possible using the admittance method with biventricular pacing leads. The technique could be piggybacked to complement EGMs to determine if arrhythmias are hemodynamically unstable.

Imaging flow dynamics in murine coronary arteries with spectral domain optical Doppler tomography.

Blood flow in murine epicardial and intra-myocardial coronary arteries was measured in vivo with spectral domain optical Doppler tomography (SD-ODT). Videos at frame rates up to 180 fps were collected and processed to extract phase shifts associated with moving erythrocytes in the coronary arteries. Radial averaging centered on the vessel lumen provided spatial smoothing of phase noise in a single cross-sectional frame for instantaneous peak velocity measurement without distortion of the flow profile. Temporal averaging synchronized to the cardiac cycle (i.e., gating) was also performed to reduce phase noise, although resulting in lower flow profiles. The vessel angle with respect to incident imaging beam was measured with three-dimensional raster scans collected from the same region as the high speed cross-sectional scans. The variability in peak phase measurement was 10-15% from cycle to cycle on a single animal but larger for measurements among animals. The inter-subject variability is attributed to factors related to real physiological and anatomical differences, instrumentation variables, and measurement error. The measured peak instantaneous flow velocity in a ~40-µm diameter vessel was 23.5 mm/s (28 kHz Doppler phase shift). In addition to measurement of the flow velocity, we observed several dynamic features of the vessel and surrounding myocardium in the intensity and phase sequences, including asymmetric vessel deformation and rapid flow reversal immediately following maximum flow, in confirmation of known coronary artery flow dynamics. SD-ODT is an optical imaging tool that can provide in vivo measures of structural and functional information on cardiac function in small animals.

A bio-telemetric device for measurement of left ventricular pressure-volume loops using the admittance technique in conscious, ambulatory rats.

This paper presents the design, construction and testing of a device to measure pressure-volume loops in the left ventricle of conscious, ambulatory rats. Pressure is measured with a standard sensor, but volume is derived from data collected from a tetrapolar electrode catheter using a novel admittance technique. There are two main advantages of the admittance technique to measure volume. First, the contribution from the adjacent muscle can be instantaneously removed. Second, the admittance technique incorporates the nonlinear relationship between the electric field generated by the catheter and the blood volume. A low power instrument weighing 27 g was designed, which takes pressure-volume loops every 2 min and runs for 24 h. Pressure-volume data are transmitted wirelessly to a base station. The device was first validated on 13 rats with an acute preparation with 2D echocardiography used to measure true volume. From an accuracy standpoint, the admittance technique is superior to both the conductance technique calibrated with hypertonic saline injections, and calibrated with cuvettes. The device was then tested on six rats with 24 h chronic preparation. Stability of animal preparation and careful calibration are important factors affecting the success of the device.

Left ventricular epicardial admittance measurement for detection of acute LV dilation.

There are two implanted heart failure warning systems incorporated into biventricular pacemakers/automatic implantable cardiac defibrillators and tested in clinical trials: right heart pressures, and lung conductance measurements. However, both warning systems postdate measures of the earliest indicator of impending heart failure: left ventricular (LV) volume. There are currently no proposed implanted technologies that can perform LV blood volume measurements in humans. We propose to solve this problem by incorporating an admittance measurement system onto currently deployed biventricular and automatic implantable cardiac defibrillator leads. This study will demonstrate that an admittance measurement system can detect LV blood conductance from the epicardial position, despite the current generating and sensing electrodes being in constant motion with the heart, and with dynamic removal of the myocardial component of the returning voltage signal. Specifically, in 11 pigs, it will be demonstrated that 1) a physiological LV blood conductance signal can be derived; 2) LV dilation in response to dose-response intravenous neosynephrine can be detected by blood conductance in a similar fashion to the standard of endocardial crystals when admittance is used, but not when only traditional conductance is used; 3) the physiological impact of acute left anterior descending coronary artery occlusion and resultant LV dilation can be detected by blood conductance, before the anticipated secondary rise in right ventricular systolic pressure; and 4) a pleural effusion simulated by placing saline outside the pericardium does not serve as a source of artifact for blood conductance measurements.

Validation of a new micro-manometer pressure sensor for cardiovascular measurements in mice.

Abstract The Scisense (London, ON, Canada) micro-manometer pressure sensor is currently being used by investigators to evaluate cardiovascular physiology in mice, but has not been validated to date. The purpose of the current study is to compare the 1.2 F Scisense pressure sensor to the current gold standard produced by Millar Instruments (Houston, TX) (1.4 F). In vitro comparisons were preformed including temperature drift, frequency response analysis up to 250 Hz, and damping coefficient and natural frequency determined via a pop test. The authors also performed in vivo comparisons including pressure drift, dose-response studies to IV isoproterenol, maximum adrenergic stimulation with IV dobutamine, and simultaneous placement of both micro-manometer pressure sensors in the same intact murine hearts. The authors conclude that both sensors are equivalent, and that the Scisense pressure sensor represents an alternative to the current gold standard, the Millar micro-manometer pressure sensor for in vivo pressure measurements in the mouse.

Dynamic correction for parallel conductance, GP, and gain factor, alpha, in invasive murine left ventricular volume measurements.

The conductance catheter technique could be improved by determining instantaneous parallel conductance (G(P)), which is known to be time varying, and by including a time-varying calibration factor in Baan's equation [alpha(t)]. We have recently proposed solutions to the problems of both time-varying G(P) and time-varying alpha, which we term "admittance" and "Wei's equation," respectively. We validate both our solutions in mice, compared with the currently accepted methods of hypertonic saline (HS) to determine G(P) and Baan's equation calibrated with both stroke volume (SV) and cuvette. We performed simultaneous echocardiography in closed-chest mice (n = 8) as a reference for left ventricular (LV) volume and demonstrate that an off-center position for the miniaturized pressure-volume (PV) catheter in the LV generates end-systolic and diastolic volumes calculated by admittance with less error (P < 0.03) (-2.49 +/- 15.33 microl error) compared with those same parameters calculated by SV calibrated conductance (35.89 +/- 73.22 microl error) and by cuvette calibrated conductance (-7.53 +/- 16.23 microl ES and -29.10 +/- 31.53 microl ED error). To utilize the admittance approach, myocardial permittivity (epsilon(m)) and conductivity (sigma(m)) were calculated in additional mice (n = 7), and those results are used in this calculation. In aortic banded mice (n = 6), increased myocardial permittivity was measured (11,844 +/- 2,700 control, 21,267 +/- 8,005 banded, P < 0.05), demonstrating that muscle properties vary with disease state. Volume error calculated with respect to echo did not significantly change in aortic banded mice (6.74 +/- 13.06 microl, P = not significant). Increased inotropy in response to intravenous dobutamine was detected with greater sensitivity with the admittance technique compared with traditional conductance [4.9 +/- 1.4 to 12.5 +/- 6.6 mmHg/microl Wei's equation (P < 0.05), 3.3 +/- 1.2 to 8.8 +/- 5.1 mmHg/microl using Baan's equation (P = not significant)]. New theory and method for instantaneous G(P) removal, as well as application of Wei's equation, are presented and validated in vivo in mice. We conclude that, for closed-chest mice, admittance (dynamic G(P)) and Wei's equation (dynamic alpha) provide more accurate volumes than traditional conductance, are more sensitive to inotropic changes, eliminate the need for hypertonic saline, and can be accurately extended to aortic banded mice.

Electrical conductivity and permittivity of murine myocardium.

A classic problem in traditional conductance measurement of left ventricular (LV) volume is the separation of the contributions of myocardium from blood. Measurement of both the magnitude and the phase of admittance allow estimation of the time-varying myocardial contribution, which provides a substantial improvement by eliminating the need for hypertonic saline injection. We present in vivo epicardial surface probe measurements of electrical properties in murine myocardium using two different techniques (a digital and an analog approach). These methods exploit the capacitive properties of the myocardium, and both methods yield similar results. The relative permittivity varies from approximately 100,000 at 2 kHz to approximately 5000 at 50 kHz. The electrical conductivity is approximately constant at 0.16 S/m over the same frequency range. These values can be used to estimate and eliminate the time-varying myocardial contribution from the combined signal obtained in LV conductance catheter measurements, thus yielding the blood contribution alone. To study the effects of albumin on the blood conductivity, we also present electrical conductivity estimates of murine blood with and without typical administrations of albumin during the experiment. The blood conductivity is significantly altered (p < 0.0001) by administering albumin (0.941 S/m with albumin, 0.478 S/m without albumin).

Impact of physiological variables and genetic background on myocardial frequency-resistivity relations in the intact beating murine heart.

Conductance measurements for generation of an instantaneous left ventricular (LV) volume signal in the mouse are limited, because the volume signal is a combination of blood and LV muscle, and only the blood signal is desired. We have developed a conductance system that operates at two simultaneous frequencies to identify and remove the myocardial contribution to the instantaneous volume signal. This system is based on the observation that myocardial resistivity varies with frequency, whereas blood resistivity does not. For calculation of LV blood volume with the dual-frequency conductance system in mice, in vivo murine myocardial resistivity was measured and combined with an analytic approach. The goals of the present study were to identify and minimize the sources of error in the measurement of myocardial resistivity to enhance the accuracy of the dual-frequency conductance system. We extended these findings to a gene-altered mouse model to determine the impact of measured myocardial resistivity on the calculation of LV pressure-volume relations. We examined the impact of temperature, timing of the measurement during the cardiac cycle, breeding strain, anisotropy, and intrameasurement and interanimal variability on the measurement of intact murine myocardial resistivity. Applying this knowledge to diabetic and nondiabetic 11- and 20- to 24-wk-old mice, we demonstrated differences in myocardial resistivity at low frequencies, enhancement of LV systolic function at 11 wk and LV dilation at 20-24 wk, and histological and electron-microscopic studies demonstrating greater glycogen deposition in the diabetic mice. This study demonstrated the accurate technique of measuring myocardial resistivity and its impact on the determination of LV pressure-volume relations in gene-altered mice.

Detection of vulnerable plaque in a murine model of atherosclerosis with optical coherence tomography.

OBJECTIVES: The aim of this study was to evaluate the feasibility of optical coherence tomography (OCT) to identify the components of vulnerable plaques in a well-established murine model of human atherosclerosis. BACKGROUND: Although the pathologic features that predict plaque rupture at autopsy are well known, the development of a technology to identify these high risk features in vivo is lacking. OCT uses reflected light to provide histology-like images of plaque with higher resolution than competing imaging modalities. Whether OCT can reliably identify the features of an atherosclerotic plaque that define it as vulnerable-thin fibrous cap, large lipid core, and high percent of lipid in the artery-requires further study. METHODS: OCT images of the atherosclerotic innominate artery segments from the apolipoprotein E knockout (apoE(-/-)) mice were recorded and correlated with histology in both in vivo (n = 7) and well as in ex vivo experiments (n = 12). RESULTS: Excellent correlation between the OCT and histology measurements for fibrous cap thickness, lipid core size, and percentage lipid content was found. The fibrous cap thicknesses examined span those of human fibrous caps known to rupture (< 65 microm). Regions of greatest light reflection in OCT images were observed when calcium hydroxy-apatite was scattered in lipid, less in fibrous tissue, and least in lipid. CONCLUSIONS: These findings suggest that OCT holds promise for the identification of features defining vulnerable plaque including fibrous cap thickness, lipid core size, and the percentage of lipid content.

Evidence of time-varying myocardial contribution by in vivo magnitude and phase measurement in mice.

Cardiac volume can be estimated by a conductance catheter system. Both blood and myocardium are conductive, but only the blood conductance is desired. Therefore, the parallel myocardium contribution should be removed from the total measured conductance. Several methods have been developed to estimate the contribution from myocardium, and they only determine a single steady state value for the parallel contribution. Besides, myocardium was treated as purely resistive or mainly capacitive when estimating the myocardial contribution. We question these assumptions and propose that the myocardium is both resistive and capacitive, and its contribution changes during a single cardiac cycle. In vivo magnitude and phase experiments were performed in mice to confirm this hypothesis.

Enhanced left ventricular systolic function early in type 2 diabetic mice: clinical implications.

It is unclear whether the increase in availability of substrates for energy production in diabetes can lead to enhanced systolic function early in the disease, before the onset of structural changes to the myocardium. To examine this issue, BKS.Cg-m +/+ Lepr db (db/db) mice with type 2 diabetes and wild type controls had left ventricular pressure-volume relationships determined in situ. We demonstrated that the db/db mice, when compared to their wild type controls, generated greater left ventricular pressure and an enhancement of left ventricular systolic function based on enhanced power/EDV, positive dP/dt, preload recruitable stroke work, dP/dt--EDV relationship, and curvilinear end-systolic elastance. This enhancement in systolic function occurred despite the db/db mice having greater body weight, but similar preload (end-diastolic volume) and afterload (effective arterial elastance). We postulate that the previously described enhancement in renal glomerular filtration rate seen early in type 2 diabetes may be in part due to enhanced left ventricular systolic function early in this disease.

Enhancement of contractility with sustained afterload in the intact murine heart: blunting of length-dependent activation.

BACKGROUND: It has been hypothesized that because of its rapid heart rate, the intact murine heart functions near maximal contractility in the basal state. If this hypothesis is correct, then the fast and slow components of myocardial length-dependent activation should be blunted compared with larger mammals. METHODS AND RESULTS: Mice (n=24) were anesthetized, and via an open chest, LV pressure-volume relationships were determined by a dual-frequency conductance catheter system. Baseline pressure-volume relationships were determined during transient occlusion of the inferior vena cava, and repeat measurements were made after 1 (n=10) and 7 (n=21) minutes of sustained aortic occlusion. Control experiments were performed in a subset of mice (n=3). For baseline to 1 minute, an increase in afterload (maximal pressure 95+/-9 to 126+/-7 mm Hg; P<0.001) and effective arterial elastance (5.9+/-3.1 to 9.2+/-3.9 mm Hg/microl; P<0.001) resulted in an increase in end-diastolic volume (31+/-8 to 35+/-9 microL; P<0.001). The result was maintenance of stroke volume (17+/-6 to 15+/-6; P=NS) owing to an increase in contractility (leftward shift in V100 [the volume of end-systolic elastance at 100 mm Hg], 24+/-9 to 16+/-5 microL; P<0.001). No additional augmentation of systolic function was found at 7 minutes. CONCLUSIONS: This study demonstrates that the fast phase of length-dependent activation is intact but not the slow phase, consistent with murine myocardium functioning near maximal contractility in the basal state.