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At least 19 recordsLinked to original sources
PubMed1996

Measurement of respiratory parameters by using inspired oxygen sinusoidal forcing signals.

A companion paper (C. E. W. Hahn. J. Appl. Physiol 81: 985-997, 1996) described a continuous-flow gas-exchange mathematical model, which predicted that forced inspired oxygen sinusoids could be used to measure respiratory parameters rapidly, in place of the inert gas argon. We therefore made simultaneous measurements of dead space volume (VD) and alveolar volume (VA) in an animal model, using argon and oxygen inspired gas concentration sinusoid forcing signals, and then compared the results. Our data confirmed the model prediction that the attenuations of the oxygen and argon sinusoid perturbations are identical in the alveolar gas space, even though there is a net uptake of oxygen by the body. Our results show that the calculated values of VD and VA, obtained by using inspired oxygen forcing signals, were independent of both the mean fractional inspired oxygen concentration (FIO2; range 0.18-0.80% vol/vol) and the oxygen forcing signal amplitude (range +/- 2-6% vol/vol). In these studies, oxygen forcing signals, with forcing periods between 1 and 2 min, were able to measure controlled changes in instrument dead space to within 16 ml and also measure positive end-expiratory pressure-induced changes in VA. Under hyperoxic conditions, intravascular oxygen sensors confirmed that the sinusoidal PO2 signal passed into the arterial blood but not into the mixed-venous blood. However, the sinusoid perturbation PO2 signal did pass into the mixed-venous blood when the mean FIO2 was mildly hypoxic (FIO2 = 0.18% vol/vol). These data show that oxygen can be used instead of argon to measure airways dead space and VA.

Animals↗
PubMed2000

An IBM PC-based system for the assessment of cardio-respiratory function using oscillating inert gas forcing signals.

OBJECTIVE: An IBM PC-based real-time data acquisition, monitoring and analysis system was developed for the assessment of cardio-respiratory function, i.e. airway dead space, alveolar volume and pulmonary blood flow, using oscillating inert inspired gas forcing signals. METHODS: The forcing gas mixture was generated by an in-house sinusoid gas delivery unit. The system interfaced with a mass spectrometer and an airway flow transducer, and performed real-time tracking of the breath-by-breath end-inspired, end-expired and mixed-expired concentrations. It calculated the cardiorespiratory parameters using two, i.e. continuous and tidal, in-house mathematical models of the lungs. The system's performance was evaluated using a mechanical bench lung, laboratory subjects and awake adults breathing spontaneously. Its predictive accuracy was compared with the measured volumes of the bench lung; single breath CO2 test for airway dead space and N2 washout for alveolar volume in laboratory subjects and awake adults; and thermal dilution technique for pulmonary blood flow in laboratory subjects. RESULTS: Close agreements were found between the true and predicted airway dead space, i.e. mean differences of -12.39%, 14.47% and -17.49%, respectively, and that of alveolar volume, i.e. -8.03%, -3.62% and 7.22%, respectively, in the bench lung, laboratory subject and awake adult studies; and that of pulmonary blood flow (-23.81%) in the laboratory subjects using the continuous lung model. Even closer agreements were observed for airway dead space (-5.8%) and alveolar volume (-4.01%) of the bench lung and for pulmonary blood flow (-8.47%) in the laboratory subjects using the tidal lung model. CONCLUSIONS: A system was developed to deliver, monitor and analyse on-line, and in real-time, output data from the sinusoid forcing technique. The technique was administered using the system in various subjects, and produced favourable predictions.

Adult↗
PubMedDate not supplied

[Amplitude-time and phase characteristics of pulse signal force transducer in multizone pulse diagnosis].

The paper provides numerical calculations of module-argument relationship of the transducing function of a pulse signal force transducer in the multiarea pulse diagnostic device to the parameters of the oscillation system. It is shown that free oscillations of the low-frequency oscillation system at 300 pi rad/c or more may yield allowable phase and amplitude-time distortions of signal A transduction, with real values of damping of a low-frequency part of the oscillation system, the noninformity of amplitude-time characteristics is no more than 30% in the working frequency range of the force transducer.

Diagnosis, Computer-Assisted↗
PubMed1994

Assessment of cardiorespiratory function using oscillating inert gas forcing signals.

A theoretical model (Hahn et al. J. Appl. Physiol. 75: 1863-1876, 1993) predicts that the amplitudes of the argon and nitrous oxide inspired, end-expired, and mixed expired sinusoids at forcing periods in the range of 2-3 min (frequency 0.3-0.5 min-1) can be used directly to measure airway dead space, lung alveolar volume, and pulmonary blood flow. We tested the ability of this procedure to measure these parameters continuously by feeding monosinusoidal argon and nitrous oxide forcing signals (6 +/- 4% vol/vol) into the inspired airstream of nine anesthetized ventilated dogs. Close agreement was found between single-breath and sinusoid airway dead space measurements (mean difference 15 +/- 6%, 95% confidence limit), N2 washout and sinusoid alveolar volume (mean difference 4 +/- 6%, 95% confidence limit), and thermal dilution and sinusoid pulmonary blood flow (mean difference 12 +/- 11%, 95% confidence limit). The application of 1 kPa positive end-expiratory pressure increased airway dead space by 12% and alveolar volume from 0.8 to 1.1 liters but did not alter pulmonary blood flow, as measured by both the sinusoid and comparator techniques. Our findings show that the noninvasive sinusoid technique can be used to measure cardiorespiratory lung function and allows changes in function to be resolved in 2 min.

Animals↗
PubMed1981

Time-constant histograms from the forced expired volume signal.

The forced expired volume signal was analyzed using a parallel compartment model in which each compartment emptied exponentially. With this model the forced expired volume signal was represented by a histogram showing the fraction of the vital capacity as a functional of compartmental time constants. We developed an algorithm to compute this histogram from the volume signal. The algorithm used the least-squares criterion function with both smoothness and nonnegativity constraints. In a stimulation study reasonable histograms were obtained even in the presence of realistic random error. Three dependent forced expired volume signals from 16 subjects were analyzed, and the histograms were reproducible. Most histograms were bimodal with fast time constants of 0.12-0.55 s and slow time constants of 1.3-2.7 s. In all normal subjects and patients with restrictive disease more than 75% of the vital capacity was in the fast time-constant mode. Subjects with obstructive disease had more than 40% of the vital capacity in the slow time-constant mode.

Adult↗
PubMed2002

Inhibition of muscle carbonic anhydrase slows the Ca(2+) transient in rat skeletal muscle fibers.

A countertransport of H(+) is coupled to Ca(2+) transport across the sarcoplasmic reticulum (SR) membrane. We propose that SR carbonic anhydrase (CA) accelerates the CO(2)-HCO reaction so that H(+) ions, which are exchanged for Ca(2+) ions, are produced or buffered in the SR at sufficient rates. Inhibition of this SR-CA is expected to reduce the rate of H(+) fluxes, which then will retard the kinetics of Ca(2+) transport. Fura 2 signals and isometric force were simultaneously recorded in fiber bundles of the soleus (SOL) and extensor digitorum longus (EDL) from rats in the absence and presence of the lipophilic CA inhibitors L-645151, chlorzolamide (CLZ), and ethoxzolamide (ETZ), as well as the hydrophilic inhibitor acetazolamide (ACTZ). Fura 2 and force signals were analyzed for time to peak (TTP), 50% decay time (t(50)), and their amplitudes. L-645151, CLZ, and ETZ significantly increased TTP of fura 2 by 10-25 ms in SOL and by 5-7 ms in EDL and TTP of force by 6-30 ms in both muscles. L-645151 and ETZ significantly prolonged t(50) of fura 2 and force by 20-55 and 40-160 ms, respectively, in SOL and EDL. L-645151, CLZ, and ETZ also increased peak force of single twitches and amplitudes of fura fluorescence ratio (R(340/380)) at an excitation wavelength of 340 to 380 nm. All effects of CA inhibitors on fura 2 and force signals could be reversed. ACTZ did not affect TTP, t(50), and amplitudes of fura 2 signals or force. L-645151, CLZ, and ETZ had no effects on myosin-, Ca(2+)-, and Na(+)-K(+)-ATPase activities, nor did they affect the amplitude and half-width of action potentials. We conclude that inhibition of SR-CA by impairing H(+) countertransport is responsible for deceleration of intracellular Ca(2+) transients and contraction times.

Acetazolamide↗
PubMed1983

Myoelectric signal versus force relationship in different human muscles.

An analytic study was initiated to investigate whether the normalized surface myoelectric signal vs. normalized force relationship varies in different human muscles and whether it is dependent on training level and rate of force production. The data were obtained from experiments that involved the biceps, deltoid, and first dorsal interosseous of three pianists, four long-distance swimmers, three power lifters, and six normal subjects. The elite performers (among the world's best) were chosen because they exhibited varying degrees of fine motor control, endurance training, and power training in different muscles. Approximately 200 isometric linearly force-varying contractions peaking at 80% of the maximal voluntary contraction level were processed. The results indicated that the myoelectric signal-force relationship was primarily determined by the muscle under investigation and was generally independent of the subject group and the force rate. Whereas this relationship was quasilinear for the first dorsal interosseous, it was nonlinear for the biceps and deltoid. Several possible physiological causes of the observed behavior of the myoelectric signal-force relationship are discussed.

Adolescent↗
PubMed2004

Conversion of mechanical force into biochemical signaling.

Physical forces play important roles in regulating cell proliferation, differentiation, and death by activating intracellular signal transduction pathways. How cells sense mechanical stimulation, however, is largely unknown. Most studies focus on cellular membrane proteins such as ion channels, integrins, and receptors for growth factors as mechanosensory units. Here we show that mechanical stretch-induced c-Src protein tyrosine kinase activation is mediated through the actin filament-associated protein (AFAP). Distributed along the actin filaments, AFAP can directly active c-Src through binding to its Src homology 3 and/or 2 domains. Mutations at these specific binding sites on AFAP blocked mechanical stretch-induced c-Src activation. Therefore, mechanical force can be transmitted along the cytoskeleton, and interaction between cytoskeletal associated proteins and enzymes related to signal transduction may convert physical forces into biochemical reactions. Cytoskeleton deformation-induced protein-protein interaction via specific binding sites may represent a novel intracellular mechanism for cells to sense mechanical stimulation.

Animals↗
PubMed2000

Relationship between EMG signals and force in human vastus lateralis muscle using multiple bipolar wire electrodes.

This paper describes the relationship between knee extension force and EMG signals detected by multiple bipolar wire electrodes inserted into the human vastus lateralis muscle under isometric conditions. Six healthy male volunteers participated in this study. Eight pairs of bipolar wire electrodes were inserted into the right vastus lateralis muscle and the EMG data were simultaneously detected and analyzed. The EMG raw data and individual force-IEMG relations were influenced by the location of the electrode inserted into the muscle. The force and IEMG relationship averaged across subjects detected from the eight electrodes, however, showed almost the same linear correlation in spite of different electrode locations. No linear correlation was observed between MdF and the knee extension force. This result suggests that, if all of the muscle fibers participate in the same action at the same time, the averaged normalized IEMG from any places using wire electrodes could reflect the total activities of that muscle even if the muscle is large.

Adult↗
PubMed2001

Averaging of strongly varying signals.

Forces acting at the hip joint during a given activity often vary much between trials and subjects. Large variations are also encountered in many other biomechanical signals. Arithmetic mean curves then lead to falsified results, especially if extreme values occur at very different times. A method was developed for calculating a typical curve from such varying, time dependent signals. All cycle times are first averaged and the signals are then more and more smoothed using Fourier series with decreasing numbers of harmonics. The remaining extrema are analysed to decide whether they are typical for all curves or not. This is done by systematically cutting off a varying number of extrema at the beginning or end of all curves. After this an equal number of extrema remains in all curves. These extrema are then shifted to average positions in time, i.e. the times between consecutive extrema are compressed or expanded, and the standard deviation of all curves is calculated. The combination of cut off extrema which results in the smallest standard deviation is then used further on. The same time distortions are applied to the original curves and their arithmetic mean finally results in the typical signal. This procedure is well suited for averaging hip contact forces and other varying signals as long as their complexity and variation is not extremely large.

Arthroplasty, Replacement, Hip↗
PubMed2007

Dual-trap technique for reduction of low-frequency noise in force measuring optical tweezers.

High-resolution long-time force measurements by optical tweezers are often limited by low-frequency (1/f) noise. A dual-trap technique is presented that can reduce such noise in the force signal. It incorporates a second trap (a reference trap) that probes the noise in the system and it is based upon the assumption that the low-frequency parts of the noise from the two traps are correlated. A subtraction of the low-frequency signal from the reference trap from the signal from the force measuring trap will therefore yield a net signal that is significantly less influenced by noise. It is shown that this dual-trap technique can reduce the noise in the force signal up to 60% depending on detection bandwidth.

Equipment Design↗
PubMed2002

Mechanistics of amoeboid locomotion: signal to forces.

Dictyostelium serves as an ideal model system for studying the molecular and structural properties of the actomyosin and microtubule systems. This organism also has been the vehicle on which the gene-targeting technique was pioneered. Dictyostelium also represents a small number of organisms whose chemotactic ligand-receptor mechanism has been well characterized. This article reviews recent advances in studies of the actin-based cytoskeletal system in Dictyostelium, focusing on the mechanistic aspects of the amoeboid motion. Special emphasis is placed on the recently identified cell-substrate-anchoring structures 'eupodia', and the measurement of single-cell migration forces. The recent advances in signal transduction cascade is also discussed with relevance to the mechanistics in amoeboid locomotion.

Amoeba↗
PubMed1994

Identification of dynamic myoelectric signal-to-force models during isometric lumbar muscle contractions.

A 14-muscle myoelectric signal (MES)-driven muscle force prediction model of the L3-L4 cross section is developed which includes a dynamic MES-force relationship and allows for cocontraction. Model parameters are estimated from MES and moments data recorded during rapid exertions in trunk flexion, extension, lateral bending and axial twist. Nine young healthy males participated in the experimental testing. The model used in the parameter estimation is of the output error type. Consistent and physically feasible parameter estimates were obtained by normalizing the RMS MES to maximum exertion levels and using nonlinear constrained optimization to minimize a cost function consisting of the trace of the output error covariance matrix. Model performance was evaluated by comparing measured and MES-predicted moments over a series of slow and rapid exertions. Moment prediction errors were on the order of 25, 30 and 40% during attempted trunk flexion-extensions, lateral bends and axial twists, respectively. The model and parameter estimation methods developed provide a means to estimate lumbar muscle and spine loads, as well as to empirically investigate the use and effects of cocontraction during physical task performances.

Adult↗
PubMed1998

Effects of mechanical forces on signal transduction and gene expression in endothelial cells.

Fluid shear stress and circumferential stretch play important roles in maintaining the homeostasis of the blood vessel, and they can also be pathophysiological factors in cardiovascular diseases such as atherosclerosis and hypertension. The uses of flow channels and stretch devices as in vitro models have helped to elucidate the mechanisms of signal transduction and gene expression in cultured endothelial cells in response to shear stress, which is a function of blood flow and vascular geometry, or mechanical strain, which is a function of transmural pressure and the mechanical properties and geometry of the vessel. Shear stress has been found to increase the activities of a number of kinases to modulate the phosphorylation of many signaling proteins in endothelial cells, eg, the proteins in focal adhesion sites and the proteins in the mitogen-activated protein kinase pathways. Downstream to such signaling cascades, multiple transcription factors such as AP-1, NF-kappaB, Sp-1, and Egr-1 are activated. The actions of these transcription factors on the corresponding cis-elements result in the induction of genes encoding for vasoactivators, adhesion molecules, monocyte chemoattractants, and growth factors in endothelial cells, thus modulating vascular structure and function. Some of the effects of mechanical strain on endothelial cells are similar to those by shear stress, eg, the signaling pathways and the genes activated, but there are differences, eg, the time course of the responses. Studies on the effects of mechanical forces on signal transduction and gene expression provide insights into the molecular mechanisms by which hemodynamic factors regulate vascular physiology, and pathophysiology.

Animals↗
PubMed2000

Error, stress and the role of neuromotor noise in space oriented behaviour.

In this article both movement errors and successful movements are considered to be the product of varying ratios of muscle force signals and the composite of neuromotor noise in which the force signal is embedded. Based on earlier work we derived four propositions, which together form a theoretical framework for understanding the incidence of error in conditions of time pressure and mental load. These propositions are: (1) motor behaviour is an inherently stochastic and therefore noisy process; (2) biophysical, biomechanical and psychological factors all contribute to the level of neuromotor noise in a movement signal; (3) endpoint variability of movement is related to the signal-to-noise ratio of the forces which drive the moving limb to the target; and (4) optimal signal-to-noise ratios in motor output can be arrived at by adjusting limb stiffness. In an experiment with a graphical aiming task in which subjects made pen movements to targets varying in width and distance, we tested the prediction that time pressure and dual task load would influence error rates and movement noisiness, together resulting in biomechanical adaptations of pen pressure. The latter is seen as a manifestation of a biomechanical filtering strategy to cope with increased neuromotor noise levels. The results confirmed that especially under time pressure error rates and movement noise were enhanced, while pen pressure was higher in both conditions of stress.

Adolescent↗
PubMed2003

The effects of pH change on Ca(++) signaling and force in pregnant human myometrium.

OBJECTIVE: This study was designed to determine the effects of both intracellular and extracellular pH change on contractile activity and intracellular Ca(++) during spontaneous contractions, oxytocin, and depolarization-induced stimulation of human myometrium. STUDY DESIGN: Human myometrial tissue was obtained at elective caesarean delivery at term (37-41 completed weeks of gestation). Longitudinal strips were dissected and loaded with the calcium sensitive indicator Indo-1. Statistical significance was tested with the Student t test. RESULTS: Both intracellular and extracellular acidification significantly reduces or even abolishes phasic activity, whether it arises spontaneously or in the presence of oxytocin. These contractile changes can be accounted for by the changes in intracellular Ca(++). Alkalinization produced the opposite effects. However, baseline or maintained tension changes could not be accounted for by changes in intracellular Ca(++). CONCLUSION: We suggest that the effects on phasic activity are due to the inhibition of L-type calcium entry and that, during maintained or baseline activity, pH-sensitive Ca(++) release, possibly from the sarcoplasmic reticulum occurs; but it is insufficient to overcome the inhibitory effects at the myofilaments. We conclude that alterations of pH significantly affect calcium signaling and force production in the human myometrium and may contribute to dysfunction in labor.

Acids↗
PubMed1988

Analysis of electromyographic signals in human jaw closing muscles at various isometric force levels.

The effect of sustained isometric contraction on surface electromyograph (EMG) and force signals derived from these muscles was examined. Premolar-molar region force was measured with a small unilaterally positioned force transducer. Subjects produced and sustained 25, 50, 75 and 100 per cent isometric force levels, and measurements were made at the beginning and end of these efforts. There was no significant change in the resulting EMG/force ratio at any of the force levels. The EMG signal did exhibit a significant shift in its frequency both as the force level increased and during the sustained effort. Neuromuscular fatigue, when defined as a change in the EMG/force ratio, was not demonstrated even though there was a consistent change in the frequency of the EMG signal.

Adult↗