Gijsbertus Jacob Verkerke

Exercise and Fatigue

Physical exercise affects the equilibrium of the internal environment. During exercise the contracting muscles generate force or power and heat. So physical exercise is in fact a form of mechanical energy. This generated energy will deplete the energy stocks within the body. During exercise, metabolites and heat are generated, which affect the steady state of the internal environment. Depending on the form of exercise, sooner or later sensations of fatigue and exhaustion will occur. The physiological role of these sensations is protection of the exercising subject from the deleterious effects of exercise. Because of these sensations the subject will adapt his or her exercise strategy. The relationship between physical exercise and fatigue has been the scope of interest of many researchers for more than a century and is very complex.The exercise intensity, exercise endurance time and type of exercise are all variables that cause different effects within the body systems, which in turn create different types of sensation within the subject’s mind during the exercise.Physical exercise affects the biochemical equilibrium within the exercising muscle cells. Among others, inorganic phosphate, protons, lactate and free Mg2+ accumulate within these cells. They directly affect the mechanical machinery of the muscle cell. Furthermore, they negatively affect the different muscle cell organelles that are involved in the transmission of neuronal signals.The muscle metabolites produced and the generated heat of muscle contraction are released into the internal environment, putting stress on its steady state. The tremendous increase in muscle metabolism compared with rest conditions induces an immense increase in muscle blood supply, causing an increase in the blood circulatory system and gas exchange. Nutrients have to be supplied to the exercising muscle, emptying the energy stocks elsewhere in body. Furthermore, the contracting muscle fibres release cytokines, which in their turn create many effects in other organs, including the brain. All these different mechanisms sooner or later create sensations of fatigue and exhaustion in the mind of the exercising subject. The final effect is a reduction or complete cessation of the exercise.Many diseases speed up the depletion of the energy stocks within the body. So diseases amplify the effect of energy stock depletion that accompanies exercise. In addition, many diseases produce a change of mind-set before exercise. These changes of mind-set can create sensations of fatigue and exercise-avoiding behaviour at the onset of an exercise. One might consider these sensations during disease as a feed-forward mechanism to protect the subject from an excessive depletion of their energy stocks, to enhance the survival of the individual during disease.

Exergaming for balance training of elderly: state of the art and future developments

Fall injuries are responsible for physical dysfunction, significant disability, and loss of independence among elderly. Poor postural control is one of the major risk factors for falling but can be trained in fall prevention programs. These however suffer from low therapy adherence, particularly if prevention is the goal. To provide a fun and motivating training environment for elderly, exercise games, or exergames, have been studied as balance training tools in the past years. The present paper reviews the effects of exergame training programs on postural control of elderly reported so far. Additionally we aim to provide an in-depth discussion of technologies and outcome measures utilized in exergame studies. Thirteen papers were included in the analysis. Most of the reviewed studies reported positive results with respect to improvements in balance ability after a training period, yet few reached significant levels. Outcome measures for quantification of postural control are under continuous dispute and no gold standard is present. Clinical measures used in the studies reviewed are well validated yet only give a global indication of balance ability. Instrumented measures were unable to detect small changes in balance ability as they are mainly based on calculating summary statistics, thereby ignoring the time-varying structure of the signals. Both methods only allow for measuring balance after the exergame intervention program. Current developments in sensor technology allow for accurate registration of movements and rapid analysis of signals. We propose to quantify the time-varying structure of postural control during gameplay using low-cost sensor systems. Continuous monitoring of balance ability leaves the user unaware of the measurements and allows for generating user-specific exergame training programs and feedback, both during one game and in timeframes of weeks or months. This approach is unique and unlocks the as of yet untapped potential of exergames as balance training tools for community dwelling elderly.

Comparative anatomical dimensions of the complete human and porcine spine

New spinal implants and surgical procedures are often tested pre-clinically on human cadaver spines. However, the availability of fresh frozen human cadaver material is very limited and alternative animal spines are more easily available in all desired age groups, and have more uniform geometrical and biomechanical properties. The porcine spine is said to be the most representative model for the human spine but a complete anatomical comparison is lacking. The goal of this descriptive study was to compare the anatomical dimensions of the cervical, thoracic, and lumbar vertebrae of the human and porcine spine in order to determine whether the porcine spine can be a representative model for the human spine. CT scans were made of 6 human and 6 porcine spines, and 16 anatomical dimensions were measured per individual vertebrae. Comparisons were made for the absolute values of the dimensions, for the patterns of the dimensions within four spinal regions, and normalised values of the dimensions within each individual vertebra. Similarities were found in vertebral body height, shape of the end-plates, shape of the spinal canal, and pedicle size. Furthermore, regional trends were comparable for all dimensions, except for spinal canal depth and spinous processus angle. The size of the end-plates increased more caudally in the human spine. Relating the dimensions to the size of the vertebral body, similarities were found in the size of the spinal canal, the transverse processus length, and size of the pedicles. Taking scaling differences into account, it is believed that the porcine spine can be a representative anatomical model for the human spine in specific research questions.

Comparison of velocity profiles for different flow chamber designs used in studies of microbial adhesion to surfaces

ABSTRACT Flow chambers are commonly used to study microbial adhesion to surfaces under environmentally relevant hydrodynamic conditions. The parallel plate flow chamber (PPFC) is the most common design, and mass transport occurs through slow convective diffusion. In this study, we analyzed four different PPFCs to determine whether the expected hydrodynamic conditions, which control both mass transport and detachment forces, are actually achieved. Furthermore, the different PPFCs were critically evaluated based on the size of the area where the velocity profile was established and constant with a range of flow rates, indicating that valid observations could be made. Velocity profiles in the different chambers were calculated by using a numerical simulation model based on the finite element method and were found to coincide with the profiles measured by particle image velocimetry. Environmentally relevant shear rates between 0 and 10,000 s−1 could be measured over a sizeable proportion of the substratum surface for only two of the four PPFCs. Two models appeared to be flawed in the design of their inlets and outlets and allowed development of a stable velocity profile only for shear rates up to 0.5 and 500 s−1. For these PPFCs the inlet and outlet were curved, and the modeled shear rates deviated from the calculated shear rates by up to 75%. We concluded that PPFCs used for studies of microbial adhesion to surfaces should be designed so that their inlets and outlets are in line with the flow channel. Alternatively, the channel length should be increased to allow a greater length for the establishment of the desired hydrodynamic conditions.

In vitro biomechanical characteristics of the spine: a comparison between human and porcine spinal segments.

Study Design. An in vitro study on human and porcine multilevel spinal segments. Objective. To compare human and porcine thoracolumbar spinal segments with respect to their biomechanical characteristics and the effects of creep, recovery, and removal of ligaments and posterior parts on the biomechanical characteristics. Summary of Background Data. Availability of human cadaver spines for in vitro testing of new spinal implants and surgical procedures is limited. Therefore, it is important to search for animal models with representative biomechanical characteristics. Methods. A total of 6 human and 6 porcine cadaver spines were dissected in multilevel spinal segments. Pure moments were applied to each segment in flexion/extension, lateral bending, and axial rotation. Creep tests were performed for 30 minutes in 4 creep directions, followed by cyclic tests, a recovery period of 30 minutes, and a series of cyclic tests after removal of ligaments and posterior parts. The range of motion, neutral zone (NZ), and neutral zone stiffness (NZStiff) were calculated from the acquired load-displacement data and results were compared between human and porcine segments. Results. The porcine segments generally had significantly higher absolute values for range of motion and NZ and significantly lower absolute values for NZStiff than the human segments in all directions. The effects of creep and recovery were quite similar in the higher and midthoracic regions of the spine. The influence of removal of ligaments was the same in human and porcine segments. After removal of posterior parts, the lower thoracic porcine spine behaved quite similar to the lumbar human spine. Conclusion. This study showed that the porcine spine can be a good biomechanical model for the human spine in specific situations. The question if the porcine spine can be used to predict the behavior of a human spine depends mainly on the application and the research question.

Animal models for tracheal research.

Tracheal research covers two main areas of interest: tracheal reconstruction and tracheal fixation. Tracheal reconstructions are aimed at rearranging or replacing parts of the tracheal tissue using implantation and transplantation techniques. The indications for tracheal reconstruction are numerous: obstructing tracheal tumors, trauma, post-intubation tissue reactions, etc. Although in the past years much progress has been made, none of the new developed techniques have resulted in clinical application at large scale. Tissue engineering is believed to be the technique to provide a solution for reconstruction of tracheal defects. Although developing functional tracheal tissue from different cultured cell types is still a challenge. Tracheal fixation research is relatively new in the field and concentrates on solving fixation-related problems for laryngectomized patients. In prosthetic voice rehabilitation tracheo-esophageal silicon rubber speech valves and tracheostoma valves are used. This is often accompanied by many complications. The animal models used for tracheal research vary widely and in most publications proper scientific arguments for animal selection are never mentioned. It showed that the choice on animal models is a multi-factorial process in which non-scientific arguments tend to play a key role. The aim of this study is to provide biomaterials scientists with information about tracheal research and the animal models used.

Glottal flow through a two-mass model: Comparison of Navier–Stokes solutions with simplified models

A new numerical model of the vocal folds is presented based on the well-known two-mass models of the vocal folds. The two-mass model is coupled to a model of glottal airflow based on the incompressible Navier-Stokes equations. Glottal waves are produced using different initial glottal gaps and different subglottal pressures. Fundamental frequency, glottal peak flow, and closed phase of the glottal waves have been compared with values known from the literature. The phonation threshold pressure was determined for different initial glottal gaps. The phonation threshold pressure obtained using the flow model with Navier-Stokes equations corresponds better to values determined in normal phonation than the phonation threshold pressure obtained using the flow model based on the Bernoulli equation. Using the Navier-Stokes equations, an increase of the subglottal pressure causes the fundamental frequency and the glottal peak flow to increase, whereas the fundamental frequency in the Bernoulli-based model does not change with increasing pressure.

Suitability of Kinect for measuring whole body movement patterns during exergaming

Exergames provide a challenging opportunity for home-based training and evaluation of postural control in the elderly population, but affordable sensor technology and algorithms for assessment of whole body movement patterns in the home environment are yet to be developed. The aim of the present study was to evaluate the use of Kinect, a commonly available video game sensor, for capturing and analyzing whole body movement patterns. Healthy adults (n=20) played a weight shifting exergame under five different conditions with varying amplitudes and speed of sway movement, while 3D positions of ten body segments were recorded in the frontal plane using Kinect and a Vicon 3D camera system. Principal Component Analysis (PCA) was used to extract and compare movement patterns and the variance in individual body segment positions explained by these patterns. Using the identified patterns, balance outcome measures based on spatiotemporal sway characteristics were computed. The results showed that both Vicon and Kinect capture >90% variance of all body segment movements within three PCs. Kinect-derived movement patterns were found to explain variance in trunk movements accurately, yet explained variance in hand and foot segments was underestimated and overestimated respectively by as much as 30%. Differences between both systems with respect to balance outcome measures range 0.3-64.3%. The results imply that Kinect provides the unique possibility of quantifying balance ability while performing complex tasks in an exergame environment.

Medical technology assessment: The use of the analytic hierarchy process as a tool for multidisciplinary evaluation of medical devices

Most types of medical technology assessment are performed only after the technology has been developed. Consequently, they have only minor effects on changes in clinical practice. Our study introduces a new method of constructive medical technology assessment that can change the development and diffusion of a medical device to improve its later clinical effectiveness. The method, based on Saatys Analytic Hierarchy Process, quantitatively supports discussions between various parties involved in technological development and diffusion. We applied this method in comparing a new blood pump with two competitors based on technical, medical and social requirements. These discussions changed the evaluators’ perspectives, reduced diasagreements, and ended in a reliable evaluation of the pumps performance. On the basis of these results, adaptations were derived which improved the design and diffusion of the blood pump. This application shows the adequate potential of our method to steer technological development and diffusion of artificial organs.

In vitro and in vivo microbial adhesion and growth on argon plasma-treated silicone rubber voice prostheses

Patients who undergo a total laryngectomy usually receive a silicone rubber voice prosthesis for voice rehabilitation. Unfortunately, biofilm formation on the esophageal side of voice prostheses limits their lifetime to 3–4 mon on average. The effects of repeated argon plasma treatment of medical grade, hydrophobic silicone rubber on in vitro adhesion and growth of bacteria and yeasts isolated from voice prostheses, as well as in vivo biofilm formation are presented here. In vitro experiments demonstrated that initial microbial adhesion over a 4 h time span to plasma-treated, hydrophilized, silicone rubber was generally less than on original, hydrophobic silicone rubber, both in the absence and presence of a salivary conditioning film on the biomaterial. Growth studies over a time period of 14 d at 37°C in a modified Robbins device, showed that fewer Candida cells adhered on plasma-treated, hydrophilized silicone rubber as compared to on original, hydrophobic silicone rubber. For the in vivo evaluation of biofilm formation on plasma-treated silicone rubber voice prostheses, seven laryngectomized patients received a partly hydrophilized “Groningen Button” voice prosthesis for a planned evaluation period of 4 wk. After removal of the voice prostheses, the border between the hydrophilized and the original, hydrophobic side of the prostheses was clearly visible. However, biofilm formation was, unexpectedly, less on the original, hydrophobic sides, although the microbial compositions of the biofilms on both sides were not significantly different. Summarizing, this study demonstrates that in vitro microbial adhesion and growth on silicone rubber can be reduced by plasma treatment, but in vivo biofilm formation on silicone rubber voice prostheses is oppositely enhanced by hydrophilizing the silicone rubber surface. Nevertheless, from the results of this study the important conclusion can be drawn that in vivo biofilm formation on voice prostheses is controlled by the hydrophobicity of the biomaterials surface used.