Defining new aims for BME programs in Latin America: the case of UAM-Iztapalapa.

The need for upkeep and management of medical technology has fostered the creation of a large number of under graduate programs in the field of biomedical Engineering. In Latin America alone, there are over 85 programs dedicated to this. This contrasts with programs in other regions where most of the undergraduates continue on to pursue graduate degrees or work as research and development engineers in the biomedical industry. In this work we analyze the situation regarding curricular design in the 48 BME programs in Mexico and compare this to suggestions and classifications of programs according to needs and possibilities. We then focus on a particular institution, Universidad Autónoma Metropolitana and due to its characteristics and performance we propose that it should redefine its aims from the undergraduate program on, in order to not only generate research but also to provide a nurturing environment for a budding biomedical industry in Mexico.

Tiempo de pinzamiento del cordón umbilical y complicaciones neonatales, un estudio prospectivo / Time of cord clamping and neonatal complications, a prospective study

OBJETIVO: Evaluar los efectos del pinzamiento precoz o tardío del cordón umbilical en recién nacidos a término y su correlación con los niveles de hemoglobina, hematocrito, ferritina y ciertas complicaciones neonatales. PACIENTES Y MÉTODOS: Estudio prospectivo en recién nacidos sanos, a término, nacidos por parto eutócico o distócico en nuestro hospital, entre mayo del 2009 y mayo del 2010. Se asignó a los pacientes según el tiempo de pinzamiento: grupo 1 (< 60 s), grupo 2 (1 a <2 min) y grupo 3 (2 a 3 min). Se realizaron análisis al momento del nacimiento y a las 48 h de vida, valorando los niveles de hemoglobina, hematocrito, ferritina y bilirrubina. Se evalúo el riesgo de aparición de policitemia, síndrome distrés respiratorio, fototerapia o ingreso en la Unidad de Cuidados Intensivos neonatal y el tiempo de estancia hospitalaria. RESULTADOS: Se incluyó a 242 pacientes: grupo 1 (g1=80), grupo 2 (g2=31) y grupo 3 (g3=131). Los antecedentes maternos y las características neonatales fueron similares en todas las categorías. El primer análisis demostró diferencias significativas en los niveles de ferritina de aquellos recién nacidos con pinzamiento más tardío (g1: 111 mg/dl, g2: 125 mg/dl, g3: 173 mg/dl; p < 0,01). En el segundo análisis los valores de hemoglobina (g1: 17,3 g/dl, g2: 18,9 g/dl, g3: 19,2 g/dl; p < 0,01), hematocrito (g1: 53,4%, g2: 58%, g3: 59%; p < 0,01) y ferritina (g1: 254 mg/dl, g2: 254,7 mg/dl, g3: 313 mg/dl; p = 0,008), fueron estadísticamente mayores en este mismo grupo. Al evaluar las complicaciones, observamos un aumento significativo en el número de casos de policitemia asintomática en el grupo 3. CONCLUSIONES: El pinzamiento tardío del cordón umbilical se asocia a un aumento en los niveles de hemoglobina, hematocrito y ferritina a las 48 h de vida y en el número de casos de policitemia asintomática

OBJECTIVE: To assess the effects of early or late clamping of the umbilical cord in term newborns, assessing the levels of hemoglobin, hematocrit, and ferritin, and their correlation with some of the complications. PATIENTS AND METHODS: A prospective study of healthy newborns at term or born by dystotic or eutocic delivery in our hospital between May 2009 until May 2010. Patients were assigned according to the time of clamping, group 1 (< 60 seconds), group 2 (1 to < 2 minutes), and group 3 (2 to 3 minutes). Laboratory tests were performed at birth and at 48hours of life, assessing the levels of hemoglobin, hematocrit, ferritin, and bilirubin. The risk of polycythemia, respiratory distress syndrome, neonatal phototherapy or admission to the Intensive Care Unit and the hospital stay, were evaluated. RESULTS: A total of 242 patients were included: group 1 (g1 = 80), group 2 (g2 = 31) y group 3 (g3=131). The background maternal and neonatal characteristics were similar in all sets. The first test showed significant differences in ferritin levels in those infants with delayed clamping (g1: 111 mg/dl, g2: 125 mg/dl, g3: 173 mg/dl; p < 0.01). In the second analysis the values of hemoglobin (g1: 17.3 g/dl, g2: 18.9 g/dl, g3: 19.2 g/dl; p < 0.01), hematocrit (g1: 53.4%, g2: 58%, g3: 59%; p < 0.01) and ferritin (g1: 254 mg/dl, g2: 254.7 mg/dl, g3: 313 mg/dl; p = 0.008) were statistically higher in this group. As regards complications, a significant increase was observed in the number of cases of polycythemia symptoms in group 3. CONCLUSIONS: The late cord clamping is associated with an increase in hematocrit, hemoglobin and ferritin at 48hours of life, as well as an increased risk of polycythemia present with symptoms

[Time of cord clamping and neonatal complications, a prospective study]. / Tiempo de pinzamiento del cordón umbilical y complicaciones neonatales, un estudio prospectivo.

OBJECTIVE: To assess the effects of early or late clamping of the umbilical cord in term newborns, assessing the levels of hemoglobin, hematocrit, and ferritin, and their correlation with some of the complications. PATIENTS AND METHODS: A prospective study of healthy newborns at term or born by dystotic or eutocic delivery in our hospital between May 2009 until May 2010. Patients were assigned according to the time of clamping, group 1 (<60 seconds), group 2 (1 to<2 minutes), and group 3 (2 to 3 minutes). Laboratory tests were performed at birth and at 48 hours of life, assessing the levels of hemoglobin, hematocrit, ferritin, and bilirubin. The risk of polycythemia, respiratory distress syndrome, neonatal phototherapy or admission to the Intensive Care Unit and the hospital stay, were evaluated. RESULTS: A total of 242 patients were included: group 1 (g1=80), group 2 (g2=31) y group 3 (g3=131). The background maternal and neonatal characteristics were similar in all sets. The first test showed significant differences in ferritin levels in those infants with delayed clamping (g1: 111 mg/dl, g2: 125 mg/dl, g3: 173 mg/dl; p<0.01). In the second analysis the values of hemoglobin (g1: 17.3 g/dl, g2: 18.9 g/dl, g3: 19.2 g/dl; p<0.01), hematocrit (g1: 53.4%, g2: 58%, g3: 59%; p<0.01) and ferritin (g1: 254 mg/dl, g2: 254.7 mg/dl, g3: 313 mg/dl; p = 0.008) were statistically higher in this group. As regards complications, a significant increase was observed in the number of cases of polycythemia symptoms in group 3. CONCLUSIONS: The late cord clamping is associated with an increase in hematocrit, hemoglobin and ferritin at 48 hours of life, as well as an increased risk of polycythemia present with symptoms.

Lung water assessment in isolated lung perfusion model via reactance monitoring.

The aim of this work was to build up a new monitoring technique for the lung preservation. The medical aside problem is to measure the integrity and functionality of the lung tissue, specifically at cellular preservation level in order to improve the survival time until it is grafted. The Impedance monitoring technique for diagnosis edema development is the key in this new technique. The hypothesis was that lung edema formation is highly correlated with the reactance changes so that a rat lung perfusion model was considered as a good model to produce edema in vitro. To prove that pulmonary edema can be induced increasing the venous pressure and the perfusion time, the reactance and hemodynamic parameters were recorder in 16 pulmonary blocks of Wistar rats as methodology. Results showed statistical changes in each pulmonary block weight as a consequence to apply 7.5 ± 1.2 and 10.2 ± 1.7 mmHg venous pressure (multiple samples, Anova, p<0.05). These edema weights were correlated with the reactance changes giving 0.6 (p<0.05, Pearson). Also, data analysis showed significant differences in reactance with the time of perfusion at 16, 30, and 50 min when venous pressure level were intermittent switched from 7.5 to 10.2 mmHg. The conclusion was this preliminary evidence sustains that reactance measurement is a good technique for monitoring the lung edema level in rats. However, more research should be continuing in bigger animal models in order to prove the validity and application of this monitoring technique in human lungs.

The predictive value of gastric reactance for postoperative morbidity and mortality in cardiac surgery patients.

No useful method to directly monitor the level of end organ tissue injury is currently available clinically. Gastric reactance has been proposed to measure changes in a tissue structure caused by ischemia. The purpose of this study was to assess whether gastric reactance is a reliable, clinically relevant predictor of complications and a potentially useful tool to assess hypoperfusion in cardiovascular surgery patients. The value of gastric reactance measurements, standard hemodynamic and regional perfusion variables, and scores to predict postoperative complications were compared in 55 higher risk cardiovascular surgery patients with cardiopulmonary bypass. Low frequency gastric reactance, X(L), had a significant predictive value of postoperative persistent shock requiring more than 48 h of vasopressors and associated complications, before, during and after surgery (p < 0.05). Results suggest that reactance is an earlier predictor of patients at risk than all other variables tested. Patients with a high reactance (X(L) > 26) before surgery had a significantly higher incidence of complications, higher mortality and more days in the ICU than patients with a low reactance (X(L) < 13). X(L) was found to be a reliable and clinically relevant measurement. These results justify further clinical research to explore how this information may be used to improve patient management.

Trileaflet valve hydrodynamic resistance assessment.

Valve hydrodynamic performance is usually assessed by effective orifice area, transvalvular resistance, regurgitation and blood damage effect. Some studies suggest effects in effective orifice area due to cardiovascular resistance, compliance and angle position of the valve. We suppose that silicone rubber valves under study have a good performance under different cardiovascular resistance conditions. Two in vitro experiments were made to test this hypothesis under constant and pulsatile flow rate. Transvalvular gradient pressure, transvalvular resistance, Gorling effective orifice area, effective orifice area in the ascending aorta and Reynolds numbers were estimated in both flow rates. Results suggest that cardiovascular resistance has no significant effect for this kind of valves, however resistance effect is observed in pumping pressure. Small transvalvular resistance and transvalvular pressure gradients were found. Gorlin effective orifice areas greater than 0.3 cm(2) have not viscosity effect. P-value 0.001 was found between Gorlin effective orifice area under constant and pulsatile flow rate.

Metabolic variability analysis using a mixing chamber-breath by breath based indirect calorimeter and the clino-ortho maneuver.

This work proposes the clino-ortho maneuver to analyze the metabolic energy expenditure variability by Indirect Calorimetry (IC). This analysis uses a hybrid calorimeter which includes simultaneously the mixing-chamber (MC) and the breath by breath (BbB) IC techniques. VO2 and VCO2 short-term variability was characterized as metabolic variability in the MC technique by intra-group standard deviation averages. When the BbB technique was used the metabolic variability characterization was done by VO2 and VCO2 discrete time series power spectrum analysis in the 0-0.5 Hz band. Thus a statistical population of 17 young healthy volunteers was studied using a clino-ortho maneuver with 30-30 minutes in each position after 8 hours of fasting. The results showed an energy expenditure change of 40% in Kcal/day (p<0.01). The metabolic variability was partially significant using the MC technique while BbB total power spectrum changed from 35 to 60 for the VO2 and from 24 to 37 for the VCO2 (ml/bth)(2), (p<0.05) in the region from 0 to 0.04 Hz. It was concluded that using this new measurement technique and the clino-ortho maneuver metabolic variability information not yet studied was revealed.

Gastric impedance spectroscopy in elective cardiovascular surgery patients.

Impedance spectroscopy has been proposed as a method of monitoring mucosal injury due to hypoperfusion and ischemia in critically ill patients. The present study characterizes human gastric impedance spectral changes under gastric hypoperfusion in patients undergoing cardiovascular surgery, and evaluates spectral differences between patients with no evidence of gastric ischemia and complications, and patients who developed ischemia and complications. Cole and Kun parameters were calculated over time to characterize changes as tissue injury progresses. Gastric ischemia was determined by air tonometry. Impedance spectroscopy spectra were obtained from 63 cardiovascular surgery patients. The recorded spectra were classified into three groups: group 1 for patients without ischemia or complications, group 2 for patients with a short period of ischemia (less than 2 h) and group 3 for patients with more than 4 h of gastric ischemia and complications. Two distinct dispersion regions of the spectra centered at about 316 Hz and 215 kHz become clearer as tissue damage develops. The average spectrum in group 3 shows a significant difference in tissue impedance at all frequencies relative to group 1. The parameters obtained for human gastric tissue show significant changes that occur at different times and at different frequencies as ischemia progresses, and could be correlated with patient outcome. This confirms our hypothesis that hypoperfusion and ischemia cause evident changes in the impedance spectra of the gastric wall. Therefore, this technology may be a useful prognostic and diagnostic monitoring tool.

A simple model implementation to measure breath by breath the VO2 and VCO2 by the indirect calorimetry technique.

This paper proposes a discrete random time series modeling for the VO2 and VCO2 measurement in the indirect calorimetry technique (ICT). Mathematical equations are developed in order to establish clear differences between the breath-by-breath and mixing chamber measurement based calorimeters. This simple model offers not only a physiological ICT definition approach but also defines the idea of VO2 and VCO2 short-term variability information for research. The preliminary results show a new physiological information when a computer oriented algorithm model implementation was applied to a data acquisition system in order to obtain the power spectrum analysis from a typical observation subject submitted to the clino-ortho maneuver.

Hydrodynamic effects of the partial opening of a trileaflet valve.

Manufacturing process of medical grade silicon rubber trileaflet valves for VADs could propitiate important leaflet thickness variations which could result in partial opening of the valve and affect its hydrodynamic performance. The leaflets of a total of 10 valves were measured to assess its thickness variability. Two experiments were performed to asses the impact of the leaflets thickness variation under hypothetical situations. The first experiment was divided into three hypothetical cases. In each case either none, one or two leaflets of different valves were mechanically blocked, resembling possible critical working circumstances. The second experiment was intended to know how the variation on the leaflets thickness affects the hydrodynamic performance of the valves. The results demonstrated a significant variation on the leaflets thickness was found. As for the first experiment, a small variation on the hydrodynamic performance was found above 4 L/min flow rates and a slightly higher energy loss was found in one of the cases. As for the second experiment, the results showed that the variation of the leaflet thickness does not affect the general hydrodynamic performance of the valves. No relationship between the thickness variability and the hydrostatic performance of the valves was found.

Structural performance and hydrodynamic resistance of a new silicone auricular cannula tip.

Development of a new generation pneumatic of Ventricular Assist Device (VAD) required the design of cannulae to improve its optimal performance. In this case, a relevant restrictive design parameter was the material of the cannulae. Silicone was the best choice in a hemocompatible focus, but this is a material with very low stiffness. If the material is flexible, the most important parameter that affects either the structural performance or the hydrodynamic resistance is the amount of side holes on the cannulae tip, known as the effective drainage area. In order to obtain an estimation of the structural performance and of the hydrodynamic resistance, a study based on two independent analysis is needed: the structural and the in vitro drop pressure analysis. Structural analyses based on computer simulations were made in order to estimate the bending behavior of four silicone prototypes of cannulae tips. On the other hand, experiments under hydrostatic conditions were made to test and compare the pressure loss and flow rate relationship. A cannula tip with six side holes showed good hydrostatic performance, having almost the same as the one with nine side holes. Plus, it presented and a satisfactory structural behavior. This study assisted the design process of an auricular silicone cannula, recommending the use of cannulae with six side holes for a specific VAD.

Experimental and Computer-Based Performance Analysis of Two Elastomer VAD Valve Designs.

The development of a new generation pneumatic Ventricular Assist Device (VAD) required the design of valves for the optimization of its performance. Experiments and computer-based simulations under hydrostatic conditions were analyzed in order to test and compare two low-cost elastomer valve designs. The trileaflet valve design showed a superior hydrostatic performance, having almost a ratio of 1:2 hydraulic resistance than the bileaflet valve design in agreement with both, the experimental and the simulation evidences. This study will address the use of a trileaflet valve designs in the future VAD redesign.

Steady State Condition in the Measurement of VO2and VCO2by Indirect Calorimetry.

Resting Metabolic Rate (RMR) is computed using VO2and VCO2short time 15-minute window measurement with Indirect Calorimetry (IC) instruments designed with mixing chamber. Steady state condition using a 10% variation coefficient criteria is the main objective to achieve metabolic long time prediction reliability. This study address how susceptible is the steady state VO2, VCO2measurement condition to the clino-orthostatic physiological maneuver. 30 young healthy subjects were analyzed. Only 18 passed the 10% variation coefficient inclusive criteria. They were exposed to 10 minutes clino-stage and 10 minutes orthostage. The hypothesis tests show not statistical significance (p< 0.1) in the average and variance analysis. It is concluded that the steady state is not influenced by the patient position IC test, probably because IC mixing chamber instruments are insensitive to detect a mayor physiological dynamics changes that can modify the steady state definition.

Hemodynamic performance in-vivo of a new ventricular assist device.

Nowadays, circulatory support has become a common practice in medicine and a standard in the treatments of Cardio Vascular Disease (CVD). A new Pneumatic Ventricular Assist Device (VAD) has been developed in México City. This paper shows the first results of acute in-vivo trials, intended to verify the new system for providing physiological flows and pressures. Two VADs were implanted to as right (RVAD), left (LVAD) support in a 65 kg pig. The support time was 20 minutes with RVAD, 20 minutes with LVAD and 20 minutes with Biventricular (BiVAD). The VAD proved its capability to maintain physiological parameters during the support time. We are satisfied with the results of this trial, and we believe this study will ascertain the first step on the next phase of invivo trials.

Gastric Impedance Spectroscopy in Cardiovascular Surgery Patients vs. Healthy Volunteers.

Impedance spectroscopy has been proposed as a method of monitoring mucosal injury due to hypoperfusion and ischemia in the critically ill. The present study evaluates spectral differences in elective cardiovascular surgery patients compared with the impedance spectra of the gastric mucosa in healthy adults. An impedance spectroscopy probe and nasogastric tube (ISP/NGT) was placed into the stomach of 77 heart surgery and 21 healthy volunteers. The recorded impedance spectra were classified into 3 groups: group 1 for healthy volunteers; group 2 for patients with neither ischemia nor complications; and group 3 for patients with ischemia and complications during the first 3 days in the recovery unit. There were statistical differences in resistance (p<0.001) and reactance (p<0.001) among the 3 groups. The results show that impedance spectra are distinct and significantly different in patients with probable ischemic mucosal injury compared to healthy subjects, and therefore this technology may be a useful prognostic and diagnostic monitoring tool.

Supplemental systemic oxygen support using an intestinal intraluminal membrane oxygenator.

An intraluminal membrane oxygenator (IMO) prototype was surgically inserted in the ileum and evaluated as a method of supporting systemic oxygenation in an acutely hypoxemic porcine model. Animals were assigned randomly to the test (n = 12) or the control (n = 8) groups, which underwent identical protocols with the exception of the O2 flow in the IMO device, which was shut off in the control group. In each case, hypoxia was induced by a reduction in the inspired oxygen fraction (FiO2) to 0.14. A highly significant improvement (p < 0.005) in arterial and venous O2 content and lower arteriovenous O2 difference (p < 0.05), cardiac output, and hemoglobin (p < 0.005) were found in the test group during hypoxia. The results show that it is possible to meet a physiologically significant portion of the body's O2 demands via the intestine during respiratory hypoxia and suggests that similar devices may be of significant potential value as a supplemental oxygenation device in cases of respiratory distress.

Validation of tonometric measurement of gut intramural pH during endotoxemia and mesenteric occlusion in pigs.

Tonometry is a minimally invasive method for estimating gastrointestinal intramural pH (pHi). Tissue pH is calculated by using the Henderson-Hasselbalch equation and measurements of arterial [HCO-3] and CO2 tension (PCO3) of saline contained in a Silastic balloon within the lumen of the gut. The validity of the method rests on two key assumptions: 1) PCO2 in saline in the tonometer balloon is similar to tissue PCO2 and 2) tissue and arterial [HCO-3] are similar. To validate this method, ileal pHi measured directly with a microelectrode was compared with pHi estimated tonometrically in four groups of anesthetized pigs. Group I (n = 4) were controls. In group II (n = 4), intestinal tissue acidosis was induced by total occlusion of the superior mesenteric artery (SMA). In group III (n = 5), acidosis was induced by partial occlusion of the SMA. In group IV (n = 4), tissue acidosis was induced by endotoxemia. Agreement was excellent between direct and tonometric measurements in groups I and IV and less good in groups II and III. Weighted mean correlation coefficients (rw) for the two measurement methods were 0.743 and 0.9447 in groups II and IV, respectively. Correlation coefficients for the individual animals in group III were more variable than the other groups and ranged from 0.547 to 0.990. The tonometric method for measuring GI pHi is invalid under conditions of zero flow and leads to error under conditions of low flow. However, the method is reliable in the setting of tissue acidosis induced by endotoxemia.