Technical note: Experimental method to reveal the effect of rotor magnet size and air gap on artificial heart driving motor torque and efficiency

To investigate experimentally the effect of rotor magnet design on artificial heart driving motor performance, seven rotors with different magnet lengths or thicknesses, as well as different peripheral angles, were manufactured and tested in the same motor stator with different rotating speeds. The input power (voltage and current) and output torque were measured and the motor efficiency was computed. The results demonstrated that the reduction of rotor magnet size and the enlargement of the air gap between the rotor magnets and the stator coil core have no significant effect on motor efficiency, but will reduce the torque value on which the motor achieves the highest efficiency; it could be remedied however by increasing the rotating speed, because the torque at the high efficiency point will increase along with the rotating speed. These results may provide a basis for developing small rotor magnets, large air gap and high efficiency motors for driving an artificial heart pump.     

Thermodynamic bases and physiological criteria for the application of heat engines for driving artificial heart ventricles

Conclusion We have considered the thermodynamic bases for the application of heat engines to drive the ventricles of artificial hearts in humans. An analysis of the Carnot, Brighton, Stirling, and Rankine cycles indicated that the Rankine cycle is preferable, specifically in its implementation in the steam piston engine. In this context it is essential that the optimal operating frequency for the motion of the steam engine's piston lies in the range of physiological frequencies for the contraction of the human heart, which allows the application of this engine for driving IAH ventricles without converting frequencies. We have further considered the physiological criteria for the application of heat engines as part of IAH, such as overall size, mass, efficiency, and provision of hemodynamics. It is pointed out that from the perspective of physiological compatibility the steam piston engine is optimal. With this in mind, for the implanting of a complete IAH it is necessary to supply separate drives for the ventricles by utilizing independent piston engines, as achieved in the “Mikron” project. Scientific Research Institute for Transplantology and Artificial Organs, Ministry of Health of the of USSR, Moscow. Translated from Meditsinskaya Tekhnika, No. 4, pp. 8–13, July–August, 1990.     

Noninvasive assessment method to determine the anatomic compatibility of an implantable artificial heart system

To assess the anatomic compatibility of an artificial heart (AH), we attempted to develop a computer environment that would facilitate a reliable simulation of an AH implanted in the human thorax. A three-dimensional thoracic computer model with a ventricle-resected heart was constructed, by using manually extracted contour points of the aorta, pulmonary artery, atria, atrioventricular valves, diaphragm, and thoracic wall from a set of consecutive CT images. Such a model enabled simulation of an AH implantation by orienting the AH model in it. Error evaluation on CT imaging and contour extraction with a Plexiglas cylindrical phantom showed that the diameter of the extracted phantom contour was approximately 2 mm smaller than its original with a standard deviation of <0.5 mm. Errors in contour and surface reconstruction could be reduced to far less than 1 mm under constrained conditions. A study on the influence of breathing revealed that variations in some thoracic dimensions between inspiration and expiration could reach 10 mm. In summary, computer simulation of AH implantation is a worthwhile approach with acceptable accuracy, although further considerations of extreme thoracic situations will be required.     

Theoretical assessment of the effect of flow maldistributions on the mass transfer efficiency of artificial organs

A theoretical formula for assessing numerically the extraction ratio of any lineal transport device, applicable in the presence of any type of parallel flow maldistributions, is presented. Two examples of maldistribution, continuous and discrete, are described and calculations are made of their effect on extraction ratio for two general cases and a range of parameters of interest in haemodialysis. Under favourable circumstances surprisingly large amounts of maldistribution may be tolerated.     

A method of increasing the efficiency of air hypotherms and an apparatus for craniocerebral cooling

Conclusions Raising the efficiency of air hypotherms by increasing the velocity of the cooling current and using a special device for cooling the head coverings has made possible the creation of apparatuses for craniocerebral hypothermy in which air is used in the capacity of coolant. This solves the problem of treating patients with open skull-brain injuries and during the post-operative period of neurosurgery. Moscow. Translated from Meditsinskaya Tekhnika, No. 5, pp. 11–14, September–October, 1969.     

The role of motor learning and cage size in the early enrichment effect in mice

Three experiments with C57BL/10J mice examined the possible roles of cage size and simple motor practice as factors responsible for producing improved performance of animals reared in enriched environments. Neither factor was found sufficient to improve subsequent performance in a food-seeking task. Mice reared in flat environments containing a variety of objects, but designed to prevent any climbing practice, out-performed nonenriched animals on a task requiring extensive climbing activity.     

A method for determining the effect of certain drugs on the motor reaction of animals

Summary A method is described for quantiative determination of the motor reaction of experimental animals to pain stimulation with the aid of a simple apparatus. The latter consists of a wooden wheel, on the axis of which a tachometer is located. A cage with a mouse is mounted over the wheel. The electrode hooks were connected by means of a fine conductor with an induction coil. When electric stimulation is applied, the animal tries to escape and so it turns the wheel of the tachometer. Stimulation with an automatic electrode is conducted according to the chosen scheme, every 2 or 5 sec for one or more minutes. From the number of revolutions for a definite period of time, prior to and after the use of the substance investigated, a conclusion may be drawn on the effect produced.(Presented by Active Member AMN SSSR V. V. Parin) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 54, No. 8, pp. 116–118, August, 1962     

Effect of the underwater torque on the energy cost,drag and efficiency of front crawl swimming

Underwater torque (T′) is defined as the product of the force with which the swimmer's feet tend to sink times the distance between the feet and the centre of volume of the lungs. It has previously been shown that experimental changes ofT′, obtained by securing around the swimmer's waist a plastic tube filled, on different occasions, with air, water or 2-kg lead, were accompanied by changes in the energy cost of swimming per unit of distance (C_S) at any given speed. The aim of this study was to investigate whether the observed increases of C_S withT′ during front crawl swimming were due to an increase of active body drag (D_b), a decrease of drag efficiency (η_d) or both. The effect of experimental changes ofT′ on C_S, D_b and η_d were therefore studied on a group of eight male elite swimmers at two submaximal speeds (1.00 and 1.23 m · s⁻¹). To compare different subjects and different speeds, the individual data for C_S, D_b,η_d andT′ were normalized dividing them by the corresponding individual averages. These were calculated from all individual data (of C_S, D_b, η_d andT′) obtained from that subject at that speed. It was found that, between the two extremes of this study (tube filled with air and with 2-kg lead),T′ increased by 73% and that C_S, D_b and η_d increased linearly withT′. The increase of C_S between the two extremes was intermediate ( ≈ 20%) between that of D_b (≈ 35%) and of η_d ( ≈ 16%). Thus, the actual strategy implemented by the swimmers to counteractT′, was to tolerate a large increase of D_b. This led also to a substantial (albeit smaller) increase of did, the effect of which was to reduce the increase of C_S that would otherwise have occurred.     

Experimental determination of the effect of detector size on profile measurements in narrow photon beams

The aim of this work is to investigate experimentally the detector size effect on narrow beam profile measurements. Polymer gel and magnetic resonance imaging dosimetry was used for this purpose. Profile measurements (Pm(s)) of a 5 mm diameter 6 MV stereotactic beam were performed using polymer gels. Eight measurements of the profile of this narrow beam were performed using correspondingly eight different detector sizes. This was achieved using high spatial resolution (0.25 mm) two-dimensional measurements and eight different signal integration volumes A X A X slice thickness, simulating detectors of different size. "A" ranged from 0.25 to 7.5 mm, representing the detector size. The gel-derived profiles exhibited increased penumbra width with increasing detector size, for sizes >0.5 mm. By extrapolating the gel-derived profiles to zero detector size, the true profile (Pt) of the studied beam was derived. The same polymer gel data were also used to simulate a small-volume ion chamber profile measurement of the same beam, in terms of volume averaging. The comparison between these results and actual corresponding small-volume chamber profile measurements performed in this study, reveal that the penumbra broadening caused by both volume averaging and electron transport alterations (present in actual ion chamber profile measurements) is a lot more intense than that resulted by volume averaging effects alone (present in gel-derived profiles simulating ion chamber profile measurements). Therefore, not only the detector size, but also its composition and tissue equivalency is proved to be an important factor for correct narrow beam profile measurements. Additionally, the convolution kernels related to each detector size and to the air ion chamber were calculated using the corresponding profile measurements (Pm(s)), the gel-derived true profile (Pt), and convolution theory. The response kernels of any desired detector can be derived, allowing the elimination of the errors associated with narrow beam profile measurements.     

Estimation of torque on mechanical heart valves due to magnetic resonance imaging including an estimation of the significance of the Lenz effect using a computational model

Mitral and aortic valve replacement is a procedure which is common in cardiac surgery. Some of these replacement valves are mechanical and contain moving metal parts. Should the patient in whom such a valve has been implanted be involved in magnetic resonance imaging, there is a possible dangerous interaction between the moving metal parts and the static magnetic field due to the Lenz effect. Mathematical models of two relatively common forms of single-leaflet valves have been derived and the magnitude of the torque which opposes the motion of the valve leaflet has been calculated for a valve disc of solid metal. In addition, a differential model of a ring-strengthener valve type has been considered to determine the likely significance of the Lenz effect in the context of the human heart. For common magnetic field strengths at present, i.e. 1 to 2 T, the effect is not particularly significant. However, there is a marked increase in back pressure as static magnetic field strength increases. There are concerns that, since field strengths in the range 3 to 4 T are increasingly being used, the Lenz effect could become significant. At 5 to 10 T the malfunction of the mechanical heart valve could cause the heart to behave as though it is diseased. For unhealthy or old patients this could possibly prove fatal.     

胎儿神经加自体雪旺氏细胞桥接周围神经缺损的实验研究

目的 探讨自体雪旺氏细胞植入胎儿神经后修复周围神经缺损的效果,寻找替代自体神经移植的材料。方法 用Wistar大鼠80只切断左侧大腿坐骨神经,造成15mm缺损,分别用自体神经(A组),液氮冷冻胎儿神经(B组),液氮冷冻胎儿神经加自体雪旺氏细胞粗制品(C组)进行桥接。于术后4、12、24周取桥体、桥体远端坐骨神经,分别行电镜、光镜观察、图像分析和电生理检测,所得数据经单因素方差分析和q检验。结果 A组和C组间有髓纤维数目、无髓纤维数目、复合动作电位峰值恢复率、传导速度恢复率均无显著差异,两组神经再生效果相近,而B组的再生效果则不及A、C两组;B组与A组,B组与C组分别作两两比较,部分指标存在显著差异(P<0.01)。结论 作者认为植入自体雪旺氏细胞的胎儿神经桥接周围神经缺损优于单纯胎儿神经桥接,是一种良好的替代自体神经的桥接物,有进一步研究价值和临床应用前景。     

Effects of warmth on newborn rats' motor activity and oral responsiveness to an artificial nipple.

Temperature is a powerful regulator of the behavior and physiology of newborn altricial animals. The effects of warmth on newborn rats' oral responsiveness to suckling stimuli and spontaneous motor activity in a thermoneutral environment were investigated. Newborn rat pups' oral grasp responses to an artificial nipple and overall motor activity were recorded for 18 min. Near-term pups were delivered by cesarean section so that their 1st experiences with suckling stimuli could be observed. Experimental pups were warmed for 15 s every 2 min; control pups were not warmed. Warmed pups grasped the nipple fewer times than the not-warmed pups. However, oral grasp durations became longer for the warmed pups but not for the not-warmed pups. Warmth increased pups' motor activity but only while the heat was applied. Warmth in a thermoneutral environment may promote longer nipple attachment during newborns' early feeding experiences.     

Combined effect of motor imagery and peripheral nerve electrical stimulation on the motor cortex

Although motor imagery enhances the excitability of the corticospinal tract, there are no peripheral afferent inputs during motor imagery. In contrast, peripheral nerve electrical stimulation (ES) can induce peripheral afferent inputs; thus, a combination of motor imagery and ES may enhance the excitability of the corticospinal tract compared with motor imagery alone. Moreover, the level of stimulation intensity may also be related to the modulation of the excitability of the corticospinal tract during motor imagery. Here, we evaluated whether a combination of motor imagery and peripheral nerve ES influences the excitability of the corticospinal tract and measured the effect of ES intensity on the excitability induced during motor imagery. The imagined task was a movement that involved touching the thumb to the little finger, whereas ES involved simultaneous stimulation of the ulnar and median nerves at the wrist. Two different ES intensities were used, one above the motor threshold and another above the sensory threshold. Further, we evaluated whether actual movement with afferent input induced by ES modulates the excitability of the corticospinal tract as well as motor imagery. We found that a combination of motor imagery and ES enhanced the excitability of the motor cortex in the thenar muscle compared with the other condition. Furthermore, we established that the modulation of the corticospinal tract was related to ES intensity. However, we found that the excitability of the corticospinal tract induced by actual movement was enhanced by peripheral nerve ES above the sensory threshold.     

The effect of hypercapnia on the blood supply to the heart

Summary Experiments were carried out on dogs under morphine-urethane anesthesia. A thermoelectric method was used to study the coronary circulation. Simultaneous records were made of the respiration, blood pressure, and ECG while 3, 5, 7, 10, 15, 20, and 30% CO₂ and oxygen were added to the air breathed. Breathing was maintained for from 30 sec to one hour. It was found that in most cases the change of coronary flow was biphasic: in the first phase it was reduced and in the second increased. For a given CO₂ concentration the extent to which the second phase was manifested depended on the time for which the mixture was breathed, there being no effect for periods for less than three minutes. From the curves of the blood pressure and coronary circulation it could be seen that the coronary vessels were constricted in the first and dilated in the second phase.(Presented by Active Member AMN SSSR V. V. Parin) Translated from Byullenten' Éksperimental'noi Biologii i Meditsiny, Vol. 55, No. 4, pp. 9–14, April, 1963     

Effects of blood and dialyzing solution flow rates on the efficiency of an artificial kidney

Biomedical Engineering -     

The effect of air cavity size in cylindrical ionization chambers on the measurements in high-energy radiotherapy photon beams--an experimental study

The present investigation is a continuation of a previous study on the effect of the diameter of the air cavity in cylindrical ionization chambers on perturbation correction factors. Measurements were made using high-energy radiotherapy photon beams (4, 6 and 15 MV) in a water phantom. Two different pairs of cylindrical ionization chambers were used. The chambers in each pair had identical materials and construction but different air cavity diameters. The same methods were employed as in our previous investigation. The diameter of the air cavity in cylindrical ionization chambers influences the mass ionization (the?measured ionization expressed per unit mass of air in the chamber air cavity) at the depth where the maximum ionization is observed and a normalization at this depth is therefore not correct. The corrections obtained at depths of 50 and 100?mm in the phantom showed that the air cavity diameter in cylindrical ionization chambers has a greater effect on the perturbation effects than the photon beam quality. The corrections found at depths of 50 and 100?mm are smaller than those currently used in dosimetry protocols.     

Influence of removal of invisible fixation on the saccadic and manual gap effect

Saccadic and manual reactions to a peripherally presented target are facilitated by removing a central fixation stimulus shortly before a target onset (the gap effect). The present study examined the effects of removal of a visible and invisible fixation point on the saccadic gap effect and the manual gap effect. Participants were required to fixate a central fixation point and respond to a peripherally presented target as quickly and accurately as possible by making a saccade (Experiment 1) or pressing a corresponding key (Experiment 2). The fixation point was dichoptically presented, and visibility was manipulated by using binocular rivalry and continuous flash suppression technique. In both saccade and key-press tasks, removing the visible fixation strongly quickened the responses. Furthermore, the invisible fixation, which remained on the display but suppressed, significantly delayed the saccadic response. Contrarily, the invisible fixation had no effect on the manual task. These results indicate that partially different processes mediate the saccadic gap effect and the manual gap effect. In particular, unconscious processes might modulate an oculomotor-specific component of the saccadic gap effect, presumably via subcortical mechanisms.