Measurement Of Mechanical Power Research Articles

Mechanical power during mechanical ventilation

Mechanical ventilation provides lifesaving support for patients with acute respiratory failure. However, the pressures and volumes required to maintain gas exchange can cause ventilator-induced lung injury. The current approach to mechanical ventilation involves attention to both tidal volume and airway pressures, in particular plateau pressures and driving pressures. The ventilator provides energy to overcome airway resistance and to inflate alveolar structures. This energy delivered to the respiratory system per unit time equals mechanical power. Calculation of mechanical power provides a composite number that integrates pressures, volumes, and respiratory rates. Increased levels of mechanical power have been associated with tissue injury in animal models. In patients, mechanical power can predict outcomes, such as ICU mortality, when used in multivariable analyses. Increases in mechanical power during the initial phase of ventilation have been associated with worse outcomes. Mechanical power calculations can be used in patients on noninvasive ventilation, and measurements of mechanical power have been used to compare ventilator modes. Calculation of mechanical power requires measurement of the area in a hysteresis loop. Alternatively, simplified formulas have been developed to provide this calculation. However, this information is not available on most ventilators. Therefore, clinicians will need to make this calculation. In summary, calculation of mechanical power provides an estimate of the energy requirements for mechanical ventilation based on a composite of factors, including airway resistance, lung elastance, respiratory rate, and tidal volume.
 
 Key words: mechanical ventilation, mechanical power, ventilator-induced lung injury, energy, work

Mechanical Power in Prone Position Intubated Patients with COVID-19-Related ARDS: A Cohort Study.

Respiratory monitoring of mechanical ventilation (MV) is relevant and challenging in COVID-19. Mechanical power (MP) is a novel and promising monitoring tool in acute distress respiratory syndrome (ARDS), representing the amount of energy transferred from the ventilator to the patient. It encompasses several setting parameters and patient-dependent variables that could cause lung injury. MP can therefore be an additional tool in the assessment of these patients. This study aims to evaluate respiratory monitoring through MP and its relationship with mortality in patients with COVID-19-related ARDS (CARDS) under mechanical ventilation (MV) and prone position (PP) strategies. Retrospective, unicentric, and cohort studies. We included patients with CARDS under invasive MV and PP strategies. Information regarding MP, ventilation, and gas exchange was collected at 3 moments: (1) prior to the first PP, (2) during the first PP, and (3) during the last PP. We tested the relationship between MP and VR with in-hospital mortality. We included 91 patients. There was a statistically significant difference in MP measurements between survivors and nonsurvivors only in the last prone position (p < 0.001). This is due to the significant increase in MP measurements in nonsurvivors (difference from the baseline: 3.63 J/min; 95% CI: 0.31 to 6.94), which was not observed in the group that survived (difference from the baseline: 0.02 J/min; 95% CI: -2.66 to 2.70). In multivariate analysis, MP (p=0.009) was associated with hospital death when corrected for confounder variables (SAPS 3 score, mechanical ventilation time, age, and number of prone sessions). MP is an independent predictor of mortality in PP patients with CARDS.

Inorganic phosphate, protons and diprotonated phosphate may contribute to the exacerbated muscle fatigue in older adults

Inorganic phosphate, protons and diprotonated phosphate may contribute to the exacerbated muscle fatigue in older adults

A high-accuracy torque transducer for small-scale wind and hydrokinetic turbine experiments

The design, assembly, use, and analysis of a torque transducer for small-scale wind and hydrokinetic turbines is presented. The new transducer provides a calibration between the torque and electrical current produced by a model turbine that uses a DC motor as a generator. The transducer transfers the torque generated by the turbine’s shaft to a small beam instrumented with a full bridge configuration of strain gauges whose voltage response is calibrated to known torques. The design of the transducer, coupled with specific procedural considerations, yields torque measurements from 5 to 50 mNm and a calibration uncertainty of 1.2%. We believe this is the lowest uncertainty achieved to date for a torque transducer calibration of this type. The primary difference between the presented approach and previous approaches in the literature is that we use a control motor to impart the applied calibration torque as opposed to relying on the fluid flow, which improves both the ease of use and accuracy. The presented calibration allows for an accurate measurement of mechanical power by non-intrusive means. Measurement of mechanical power is preferred over other methods of quantifying turbine power as it makes the fewest assumptions and is most closely related to the fluid dynamics. The detailed calibration procedure is provided, including considerations particular to model turbines not previously discussed, such as the necessity of avoiding hysteresis during the calibration and the fluctuations in voltage characteristic of DC generators.

A Simplified Indirect Technique for the Measurement of Mechanical Power in Three-Phase Asynchronous Motors

Abstract This paper presents an indirect method for measuring the mechanical power produced by three-phase induction motors. The proposed technique is based on the hypothesis that three-phase induction motors are balanced systems that transform electrical power into mechanical one. The measurement of a single phase current is used to estimate the mechanical power generated at the axis. The relationship between electric current and mechanical power is generally non-linear. By expressing the quantities in p.u., this trend is approximated with a second order polynomial. From the analysis of the mechanical power characteristics related to 13 motors we obtained the parameters of the interpolating parabolic curves of motors from 1.1 kW to 75 kW rated power. The proposed technique can be easily adopted in order to monitor the mechanical power of three phase induction motors using only one phase current transducer. Starting from the motor nameplate no experimental measurement or other data are necessary to estimate the mechanical power. This technique can be widely used in low cost multipoint measurement system able to monitor the mechanical power where no other transducer or voltage divider are necessary.

Friction power modeling and measurements in sliding vane rotary compressors

In compressed air systems, mechanical and organic losses account for 15% of compressor energy consumption. In the current research, the energy saving potential achievable through friction power reduction in sliding vane rotary compressors was investigated using experimental and modeling approaches. Tests on a new mid-size industrial compressor operating at different steady conditions (outlet pressure 9, 12.5, 14.5 bar at 1000 and 1500 RPM) assessed the machine performance through measurement of mechanical power and the reconstruction of the pressure-volume diagram. An experimental methodology was also developed to quantify the power lost by friction and its measurement uncertainty using the concept of indicated mean effective pressure. Modeling the compressor blade dynamics allowed a friction power decomposition while an analysis of the hydrodynamic lubrication at the most severe friction location, namely between blade tip and stator wall, additionally provided the oil film thickness evolution along the contact surface. The agreement between modeling and experimental data identified a value for the friction coefficient of 0.065. Design suggestions on existing machines and new design solutions were eventually outlined varying blade mass, revolution speed and compressor aspect ratio. These improved configurations predicted an efficiency increase up to 6%.

Theoretical modeling and experimental investigations for the improvement of the mechanical efficiency in sliding vane rotary compressors

Positive displacement compressors lead the market of compressed air production for industrial applications. Among them, sliding vane rotary compressors represent an energetically virtuous alternative to the current compression technologies. In the present work, the effects of compressor design parameters were investigated through a comprehensive approach that aimed at addressing more efficient machines to promote sliding vane compressors as the key enabling technology in compressed air systems. A comprehensive mathematical model was developed to study the main phenomena occurring in this kind of compressors. The model provides the cell volume evolution over a whole rotation during which filling, compression and discharge processes occur. The first and latter phases are described by the quasi-propagatory approach that represents the inertial, capacitive and resistive features of one-dimensional unsteady flows. The dynamics of the compressor blades led to four different arrangements inside the rotor slots while an analysis of the hydrodynamic lubrication established between blade tip and stator wall focused on the oil film thickness evolution to prevent dry contacts. An extensive experimental campaign on a mid-size industrial compressor allowed the model validation at different outlet pressure levels and revolution speeds using a direct measurement of mechanical power and the reconstruction of the indicator diagram from piezoelectric pressure transducers. The friction coefficient at the contact points between blades with stator and rotor was estimated in 0.065 and further improvements of the mechanical efficiency were eventually addressed considering the roles of compressor aspect ratio, revolution speed, and blade tilt. The first two theoretical optimizations might lead to an increase of the compressor efficiency of 2 and 9 percentage points respectively. On the other hand, acting on the blade tilt would not produce relevant improvements.

The metabolic power requirements of flight and estimations of flight muscle efficiency in the cockatiel (Nymphicus hollandicus)

Little is known about how in vivo muscle efficiency, that is the ratio of mechanical and metabolic power, is affected by changes in locomotory tasks. One of the main problems with determining in vivo muscle efficiency is the large number of muscles generally used to produce mechanical power. Animal flight provides a unique model for determining muscle efficiency because only one muscle, the pectoralis muscle, produces nearly all of the mechanical power required for flight. In order to estimate in vivo flight muscle efficiency, we measured the metabolic cost of flight across a range of flight speeds (6-13 m s(-1)) using masked respirometry in the cockatiel (Nymphicus hollandicus) and compared it with measurements of mechanical power determined in the same wind tunnel. Similar to measurements of the mechanical power-speed relationship, the metabolic power-speed relationship had a U-shape, with a minimum at 10 m s(-1). Although the mechanical and metabolic power-speed relationships had similar minimum power speeds, the metabolic power requirements are not a simple multiple of the mechanical power requirements across a range of flight speeds. The pectoralis muscle efficiency (estimated from mechanical and metabolic power, basal metabolism and an assumed value for the 'postural costs' of flight) increased with flight speed and ranged from 6.9% to 11.2%. However, it is probable that previous estimates of the postural costs of flight have been too low and that the pectoralis muscle efficiency is higher.

1215 足関節の機械的パワー・下肢筋EMG併用計測による陸上短距離用スパイクシューズの評価(OS12-4 スポーツ関連,オーガナイズドセッション:12 人間・生物・植物等に関するエンジニアリングの研究)

1215 足関節の機械的パワー・下肢筋EMG併用計測による陸上短距離用スパイクシューズの評価(OS12-4 スポーツ関連,オーガナイズドセッション:12 人間・生物・植物等に関するエンジニアリングの研究)

B18 足関節の機械的パワー・下肢筋出力併用計測による陸上短距離用スパイクシューズの評価(陸上競技)

The purpose of this study was to evaluate the spike shoes for the sprint race by the parallel measurement of mechanical power of foot joint and the lower limbs muscular strength. To perform this purpose, the system for the parallel measurement of mechanical power of foot joint and the lower limbs muscular strength was developed. Furthermore, the mechanical power of subject's foot joint in wearing the high performance spike, the general competition spike and the running shoes was measured in the conditions of the plantar flexion jump (PFJ ), the counter movement jump (CMJ) and the drop jump (DJ) using the sliding seat. The experiment led us conclusions as follows; the mechanical power of the high performance spike in DJ was the highest of experimental shoes. The increasing ratio from CMJ to DJ of the high performance spike was the highest of these, too. The iEMG in wearing the high performance shoes in DJ was the lowest. The high performance spike could be output the high mechanical power in the phase of the plantar flexion.

Total Anaerobic Work in Trained Cyclists

BACKGROUND: Previous studies have suggested that the total amount of anaerobic work that can be performed during exhausting work bouts is constant for work tasks of 2–5 min duration. These studies were based on constant intensity exercise to fatigue, rather than on time trials (TT) with subjects free to regulate momentary power output. The aim of the present study was to quantify and compare the contribution of the anaerobic energy system in 750, 1500, 2500 and 4000-m cycling TT. METHODS: Well-trained male cyclists (n=10) performed 4 randomly ordered TT. The duration of the TT was short enough so that exercise intensity remained >VO2max throughout the trials. The contributions of the energy systems were calculated from measurements of mechanical power and VO2. Gross efficiency was measured at 150W on the same day, and was assumed to be the same during the TT. RESULTS: The TT of 750, 1500, 2500 and 4000 m were completed in (mean + sd) 57.2 + 1.7, 116.3 + 1.7, 198.5 + 4.9 and 325.3 + 9.4 s, respectively. The total work, attributable to anaerobic sources, accomplished in the four distances was 22.7 + 2.7, 26.9 + 2.4, 29.8 + 4.7 and 33.9 + 7.0 kJ, respectively. Anaerobically attributable work for 750-m was lower (p<0.05) than in all other trial distances; the two middle distances (1500-m and 2500-m) did not differ; and the 4000-m was larger than all other TT distances. CONCLUSIONS: It can be concluded that: 1) The anaerobically attributable work during high intensity TT is dependent on distance, increasing with increasing TT distance; which is contrary to the hypothesis that anaerobic capacity is constant during exhausting exercise bouts of 2–5 min duration, 2) The effect of assuming a constant efficiency based on submaximal trials remains problematic with this technique.

Burning the engine: a time‐marching computation of fat and protein consumption in a 5420‐km non‐stop flight by great knots, Calidris tenuirostris

Samples of great knots (Calidris tenuirostris) were collected in an earlier project, before and after a 5420‐km migration stage from Australia to China (believed to be flown non‐stop) to determine the mass of fat consumed, and also the mass of protein withdrawn from the flight muscles and other organs. The flight was simulated by a “time‐marching” computation, which calculated the fuel energy required, and allowed different hypotheses to be tried for the consumption of protein. The simulation predicted that the great knots would take about 4 days to cover the distance, in agreement with field estimates. Realistic predictions of the consumption of fat and protein were obtained by setting the conversion efficiency to 0.23 and the body drag coefficient to 0.10, withdrawing sufficient protein from the flight muscles to keep the specific work in the myofibrils constant throughout the flight, and taking enough additional protein from other tissues to bring the energy derived from oxidising protein to 5% of the total energy consumed.The same computation was applied to published data on the pre‐migration body composition of bar‐tailed godwits (Limosa lapponica), which are said to migrate over 10 000 km from Alaska to New Zealand. The computed range for a sample killed by collision with an obstruction, while actually departing from Alaska, was sufficient to reach the South Pole. A second sample, shot before departure from New Zealand, would have run out of fat before reaching Alaska, but could easily have reached northern Australia, where these godwits stage on their northbound migration. The higher range estimate for the Alaskan birds was not due to higher fat mass (only 5% difference) but to a higher fat fraction, which they had achieved by reducing the mass of other organs before departure.Some recent observations of high chemical power, observed in wind tunnel experiments, have been interpreted as being due to much lower conversion efficiency than the value of 0.23 assumed here, but this interpretation is flawed. Measurements of mechanical power from another wind tunnel project were also unexpectedly high, suggesting that unsteady flight by wind tunnel birds increases their power requirements, both mechanical and chemical, with no implications for efficiency. The calculated power is for “steady horizontal flight”, meaning that a valid test of predicted power requires birds to be trained to hold a constant position in the test section, while maintaining a steady wingbeat frequency and amplitude. This has not been achieved in recent experiments, and is hard to achieve when using physiological methods, because of the long periods of continuous flight needed. Measurements of mechanical rather than chemical power require shorter flight times, and offer better prospects for reliable power measurements.

Role of mechanical power estimates in the O2 cost of walking in children with cerebral palsy.

It has been established in able-bodied children that traditional biomechanical descriptors of gait such as stride length or stride frequency do not fully account for the differences seen in the energy cost of locomotion noted with age. Hence, measures of total body mechanical power output have been adopted to explain these differences. The aim of this study was to estimate the ability of this mechanical power calculation to explain the variability in the metabolic energy cost of treadmill walking in children with spastic cerebral palsy (CP). Thirteen subjects volunteered for the study. One group consisted of eight (6 male, 2 female) children with CP (age 12.2 +/- 2.7 yr). The second group consisted of five (4 male, 1 female) able-bodied controls (age 13.4 +/- 2.8 yr). The treadmill walking protocol consisted of one 4-min stage at 0% grade, 3 km x h(-1). Infrared markers were placed on 12 anatomical landmarks and data were collected using the OPTOTRAK motion analysis system over a 5-s time period during the last 30 s of the 4-min stage. On-line oxygen consumption VO2 measurements were obtained throughout using the Beckman Horizon Metabolic Cart. Relative VO2 (mL x kg(-1) x min(-1)) was significantly (P < 0.05) different between the two groups (CP: 16.6 +/- 6.5 vs control: 10.2 +/- 1.2). Simple linear regression analysis demonstrated that mechanical power measurements, incorporating transfers of energy between and within adjacent body segments, accounted for 87.2% of the total variability noted in VO2 for the children with CP, compared with only 2.4% in the able-bodied subjects. The results indicate that mechanical power differences explain the majority of the variability noted in VO2 in children with CP at a submaximal walking speed.

Muscle efficiency and elastic storage in the flight motor of Drosophila.

Insects could minimize the high energetic costs of flight in two ways: by employing high-efficiency muscles and by using elastic elements within the thorax to recover energy expended accelerating the wings. However, because muscle efficiency and elastic storage have proven difficult variables to measure, it is not known which of these strategies is actually used. By comparison of mechanical power measurements based on gas exchange with simultaneously measured flight kinematics in Drosophila, a method was developed for determining both the mechanical efficiency and the minimum degree of elastic storage within the flight motor. Muscle efficiency values of 10 percent suggest that insects may minimize energy use in flight by employing an elastic flight motor rather than by using extraordinarily efficient muscles. Further, because of the trade-off between inertial and aerodynamic power throughout the wing stroke, an elastic storage capacity as low as 10 percent may be enough to minimize the energetic costs of flight.

Application of robust control to sustained oscillations in power systems

Transient control of the sustained oscillations that can occur after a major disturbance to a power system is investigated. A control scheme for an n-generator system is first developed using a classical machine model, and then extended to a machine model that includes governor/turbine dynamics. The proposed control strategies are linear and require only local relative angle and velocity measurements for the classical model case, plus the measurement of mechanical power if governor/turbine dynamics are included. Using Lyapunov's direct method, the control is shown to be robust with respect to parameter and load variations, and topology changes in the power system. The overall power system is shown to be exponentially stable in the main so that any oscillation, anywhere in the system, can be damped efficiently. The results are obtained without any linearization of the power system model. Simulation results for the 30-bus New England system demonstrate the effectiveness of the proposed control. >

A system for measurement of mechanical power in stretch — Shortening type exercises

A system for measurement of mechanical power in stretch — Shortening type exercises

A simple method for measurement of mechanical power in jumping.

A simple test for the measurement of mechanical power during a vertical rebound jump series has been devised. The test consists of measuring the flight time with a digital timer (+/- 0.001 s) and counting the number of jumps performed during a certain period of time (e.g., 15-60 s). Formulae for calculation of mechanical power from the measured parameters were derived. The relationship between this mechanical power and a modification of the Wingate test (r = 0.87, n = 12 males) and 60 m dash (r = 0.84, n = 12 males) were very close. The mechanical power in a 60 s jumping test demonstrated higher values (20 W X kgBW-1) than the power in a modified (60 s) Wingate test (7 W X kgBW-1) and a Margaria test (14 W X kgBW-1). The estimated powers demonstrated different values because both bicycle riding and the Margaria test reflect primarily chemo-mechanical conversion during muscle contraction, whereas in the jumping test elastic energy is also utilized. Therefore the new jumping test seems suitable to evaluate the power output of leg extensor muscles during natural motion. Because of its high reproducibility (r = 0.95) and simplicity, the test is suitable for laboratory and field conditions.

Myocardial efficiency in the isolated ventricle of the snail, helix pomatia L.

1. Mechanical power measurements of snail perfused isolated ventricle were made with increasing hydrodynamic pressures of hacmolymph or physiological salines. 2. Microcalorimetry, using the Calvet apparatus, gives the total energy flux: Σ(−ΔH) where H is enthalpy, produced by the isometric beating heart. 3. The value of α = [mechanical power]/[Σ(−ΔH)] is a measurement of myocardial efficiency; it varies from 0·08 to 0·26 in haemolymph or Ringer saline. 4. Efficiency is not affected by lowering PO 2 in haemolymph but is modified by increasing K + or Ca 2+ in isotonic salines.

Measurement of Mechanical Power

IN a lecture on the measurement of mechanical power by Dr. C. V. Drysdale, delivered to the Junior Institution of Engineers, and published in its Journal of August, he points out the urgent demand there is for the accurate measurement of mechanical power under service conditions and how impossible it is to judge the relative merit of various mechanical devices without knowledge of this and the economy of the fuel used. In mercantile shipping, this is fully recognized and has led to great improvements in torsion meters. Many engineers are now studying the performance of aero engines especially at high altitudes, and this involves the making of power measurements, more especially at high altitudes during actual flight. The Royal Aircraft Establishment has now designed and constructed a mechanical power (watt) meter for air-screw testing. Utilizing the principle that a constantly excited generator produces an electromotive force proportional to the speed and that the torque is proportional to the current, it has constructed a mechanical power meter which acts satisfactorily. Alternating current at a frequency of 1,500 is supplied by a small wind-driven alternator on the plane. Records are given which prove that accurate testing of power during flight has been accomplished. Dr. Drysdale states that, of the millions of mechanically propelled vehicles in use, it is probably safe to say that not one per cent of their engines are working with anything like their maximum efficiency. One has only to watch the tuning up of an engine after decarbonization and regrinding of the valves to realize how much it depends upon the almost unaided judgment of the mechanic.

Dynamometers

THE late Mr. Jervis-Smith, a vicar at Taunton until in 1886—he took charge of the Millard engineering laboratory at Oxford, was a very modest and ingenious enthusiast in the experimental study of natural science. He was particularly absorbed in the study of methods of measuring mechanical power. A dynamometer measures the product of force into velocity. The chemical balance illustrates the great accuracy with which we can measure force and there is also great accuracy possible in measuring speed, but the measurement of their product with accuracy is a very different thing. To measure the electrical power given out by or given to a machine is very easy; however large or small the power may be, our measurements may be made accurate to the fourth or even to the fifth,significant figure. It is only in very exceptional cases that the measurement of mechanical power is correct to two significant figures. Dynamometers. By Rev. F. J. Jervis-Smith. Edited and Amplified by Prof. C. V. Boys. Pp. xvi + 267.(London: Constable and Co., Ltd., 1915). Price 14s. net.