Miguel Cadena

Steady State Condition in the Measurement of VO 2 and VCO 2 by Indirect Calorimetry

Resting metabolic rate (RMR) is computed using VO2 and VCO2 short 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, VCO 2 measurement 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 (ples0.1) 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

Isothermic vs thermoneutral hemodiafiltration evaluation by indirect calorimetry

HD and HDF as hemodialytic therapies normally alter patients haemodynamic stability, due to the inflammatory response to extracorporeal blood circuit, producing increment of the core temperature (+1.0 °C). However, such increase in temperature could be controlled by lowering dialysates temperature using two main modalities techniques (isothermic and thermoneural) with different patients thermal balance consequences, not yet well studied. In this work, energy expenditure (EE) was measured by indirect calorimetry in a group of 12 patients waiting kidney transplant. In each patient, EE was assessed (as a power generation) during isothermic and thermoneutral modalities as a manner of cross and prospective study (a) at before therapy, (b) during therapy and (c) at the end of the HDF therapy. Wheraeas, power extraction was measured by a BTM (Blood Temperature Monitor from Fresenius Inc) in order to determine power balance in a thermodynamic model of the extracorporeal circuit. The results showed significant differences in the power balance when EE at during therapy was subtracted from the EE at before therapy. Then, EE increments were 32 Kcal/4-hours during isothermic and 3.6 Kcal/4-hours during thermoneutral HDF sessions (p < 0.05). While, BTM totals power extraction was 91 and 16.1 Kcal/4-hours (p<0.05), respectively. Additionally, it was estimated a 12 % of EE/day increment during HDF-isothermic at during therapy stage compared with none significative EE increment during thermoneutral modality. The statistical evidence confirmed the expected hypothesis that both modalities affect in different manner the patients EE. Also, we conclude there is no satisfactory data interpretation when the thermodynamic model was applied expecting null balance between EE increment and BTM power extraction. Therefore, these findings force to think there is need of different BTM design and measurement setting with ability to follow dynamic patients EE changes with the purpose to achieve a better power balance.

Active metabolic weight estimation using bioimpedance, indirect calorimetry and the clino-ortho maneuver

The resting energy expenditure (REE) and substrate utilization are computed by indirect calorimetry technique (ICT). The REE represents 80-85% of the total energy expenditure (TEE) but only accounts for the 7% of the actual body weight (ABW). The TEE is produced by the organs plus muscles, whereas the REE accounts only for the main organs. An important problem comes up when the REE is computed throughout the fat free mass (FFM) computation or anthropometric measurements because they do not explain the tremendous catabolic variability by ICT when subjects show the same body composition. Therefore, the aim of this work is to develop a method to compute the metabolic active weight (MAW) as a new form that may help to understand the catabolic activity of the body composition. The premise was the clino-ortho maneuver can split the ABW in two parts: one in which the MAW reflects the FFM catabolism while the second part was not considered since there is not energy requirement in it. The experiment design studied 37 young volunteers undergoing the clino-ortho maneuver during fast and postprandial conditions. The results showed REE increments of 21% during phase I (fast), while in phase II (postprandial) only 14% was achieved in ortho-postprandial. Therefore, the computed MAWs were 65.5Kg and 58Kg, respectively, when the ABW average was 70 Kg and the FFM was 50 Kg. One first conclusion was that the 15.5 Kg of the MAW above the FFM could explain a catabolic equivalence which can be exclusively related to the fast-ortho position which can help to classify exclusively the dynamic over activity of the FFM.

Metodología para el Estudio de la Disolución de Cálculos Renales Usando Microscopía de Fuerza Atómica (AFM)

Formation and dissolution of kidney stones is an important medical subject, not completely understood jet. Surgery and lithotripsy techniques, nowadays solutions are still expensive and aggressive with important limitations. The aim of this study is to develop a new methodology to evaluate efficiency of different drugs treatment upon renal stone dissolution process, at nanometric scale. The main idea is to visualize (monitoring) the dissolution processes of the renal stones surface during the different substance treatment, including some commercial medical drugs. AFM as nanotechnology technique was used to monitor dissolution at the nanometric level. Here, in this work, we show how to prepare samples for the AFM study and how to record changes in the surface topography during the stone dissolution. The preliminary results, images obtained by using commercial drug Allopurinol, show significant surface layer alternation (the renal stone destruction), which was characterized in the qualitative and quantitative way, in great details.

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.

Estudio de la Composición Corporal Funcional mediante Bioimpedancia, Calorimetría Indirecta y Variabilidad de la Frecuencia Cardiaca

The aim of this work was to study a new concept, the functional body composition analysis (FBCA), as a new instrumental technique that includes the measurement of fatfree mass (FFM) and fat mass (FM), measurement of the energy expenditure (EE), and the measurement of sympatheticvagal index (SVI), using the clino-orthostatic maneuver. This assuming that the FBCA is able to find differences among populations of men and women, when the body mass index (BMI) is very similar. A comparative study was performed implementing the FBCA in a group of individuals during fasting state. The results showed statistically and significant differences in the increase of EE. The male population increased significantly by 18% GE, and women just 5% without statistical significance.

Técnica de Monitoreo del Contenido de Líquido Pulmonar por Espectroscopia de Impedancia

The aim of lung preservation technique is to maintain the integrity and functionality of the lung, specifically at cellular preservation level until it is grafted. Despite of technique advances the lung accessibility is still shorter than 6 hours. Therefore an easy monitoring technique of water content into the organ plays an important role to improve any method which prevents the edema time generation as an attribute of cellular integrity. Electric impedance is a simple technique used to measure body volume water which can be related with the cellular integrity when the spectroscopy concept is used. This work addresses the hypothesis that lung edema formation is highly correlated with the spectroscopy impedance changes in an organ perfusion model. Pulmonary edema was induced increasing the venous pressure and the perfusion time. Reactance, resistance and hemodynamic parameters were recorder in 13 lung dissected Wistar rats as methodology. Results showed changes in the pulmonary block weight (multiple samples, ANOVA, p<0.05) which were correlated with resistance and reactance changes giving 0.64 and 0.70, respectively (p<0.05, Pearson). In addition, analysis showed significant differences in resistance and reactance with the time of perfusion (16, 30, and 50 min) and venous pressure level from 7 to 10 mmHg (p<0.01, ANOVA)). The conclusion are: (a) experimental evidence leads impedance spectroscopy is a good technique for using as a monitor of the lung edema level, (b) the correlation coefficient weight-reactance changes is better compared with the weight-resistance changes suggesting that reactance is a better parameter to be monitored when water pulmonary changes as a consequence of the edema. However more research should be continued.

Metabolismo y Actividad Autonómica en Hemodiafiltración Controlando la Temperatura del Líquido de Diálisis en Forma Fija y Dinámica

Accumulation of heat is an important problem during hemodiafiltration therapy (HDF), which has the potential to lead patients to hypotension. Control of the dialysate’s temperature can reduce hypotension events probability when one of the different equipment thermodynamic modalities is correctly selected. Isothermal, thermoneutral and fixed temperatures @ 35 or 37 °C are available to increase each patient’s hemodynamic stability but previous studies have not well de-fined Which one is the right? The hypothesis is that monitoring metabolism and autonomic nervous system (ANS) activities can provide information to determine the benefits of each modality. Therefore, the aim of this work was to study stable patients’ populations but only with chronic kidney decease. The methodology was to measure energy expenditure (GE) by indirect calorimetry and ANS activity using heart rate variability (HRV). A group of 10 patients were assessed in an across study using 35°C and then 37°C fixed modality. Other 6 patients underwent isothermal and then normothermal modalities. In both populations equally observational times were defined. T1 before the HDF therapy was initiated, T2 after 90 minutes and T3 at the end of HDF therapy. One way ANOVA stadistical analysis was implemented to observe the 3 time stage changes, accepting differences when p< 0.1 since the study was considered as a pilot. The results showed not significant diastolic pressure drops changes except during 37°C modality (p<0.05). The sympatho-vagal index (ISV) was increased significantly only at 35°C as well as the GE and the most significant temperature increase occurs at 37°C (p<0.05). The conclusion is that ISV and GE appear partially sensitive to the type of modality in use. However more patients should be analyzed to continue with this research.

Structural changes of polysulfone membrane use for hemodialysis in the consecutive regime: nanometric analysis by AFM

Nowadays, the hemodialytic treatment of patients with either acute or chronic renal failure has been improved by promoting biocompatibility in the use of new materials and improve membrane surface characteristics. Low and high flux polysulfone membranes (PM) used in dialysis and ultra filtration have been studied in order to understand the geometry and surface chemistry of the pores at inner (nanometric) and outer (micrometric) membrane parts. The surface changes of polysulfone cartridge membrane (PM) during different number of consecutive reuse trials: after 1st, 10th and 23th times of use. The morphology of the hollow fibers surfaces was studied by means of the atomic force microscopy (AFM) imaging and the surface roughness analysis. The roughness of both inner and outer part of PM surface increases with numbers of reuse trails. Thus, small and medium size pores were wiped out when the number of uses changed from zero to 23 on the outer surface. The pore density decreases. The inner part of membrane shows some nanometric size deformation in forms of new openings and raptures. The AFM analysis show differences in the PM morphology at the nanometric level, not previously revealed, which could be important in the evaluation of the PM.

Negative effects of obesity analyzed through bioimpedance, indirect calorimetry, the sympathovagal index and the orthoclinostatic test

Early analysis of the negative effects of obesity is important to prevent the development of chronic diseases related to this condition. There is a need to monitor these effects through simple instrumentation that measures fat-free mass (FFM) catabolism. Obesity leads to a decrease in the FFM energy expenditure and to an increase in the autonomic nervous system (ANS) activity. Thus, the measurement of FFM dynamic catabolism can provide information regarding the effects of obesity. The hypothesis is that this increased ANS activity produces an increase of energy expenditure of carbohydrates and fats when the subjects are under stress; in this case after an 8-hour fast and while they are undergoing an orthoclinostatic test. A pilot study was conducted on 29 volunteers, 16 women and 13 men. The results show significant statistical differences (p0.1) in fat and carbohydrate utilization during the orthoclinostatic tests: A move from the clinostatic to the orthostatic positions produced the following: Fat metabolism varied from 97.2 to 105.9 gr/day of fat for women and 24.9 to 35.7 gr/day of fat for men; carbohydrate metabolism changed from 38 to 39 gr/day for women and 239 to 277 gr/day for men; FFM averages were 47 Kg for women and 57.6 Kg for men; changes in the sympathovagal index (SVI) averages were 0.4 to 1.8 for women and 0.8 to 2.7 for men. The conclusions show that the methodologys sensitivity is such that gender differences can be used as a model to prove FFM metabolic differences. We believe that further studies will lead to the development of a robust methodology for the early detection of the negative effects of obesity.