Relative Phase Duration Research Articles

Agreement and consistency of five different clinical gait analysis systems in the assessment of spatiotemporal gait parameters

BackgroundMeasuring gait function has become an essential tool in the assessment of mobility in aging populations for both, clinicians and researchers. A variety of systems exist that assess gait parameters such as gait cycle time, gait speed or duration of relative gait phases. Due to different measurement principles such as inertial or pressure sensors, accurate detection of spatiotemporal events may vary between systems. Research questionTo compare the absolute agreement and consistency in spatiotemporal gait parameters among five different clinical gait analysis systems using different sensor technologies. MethodsWe compared two devices using inertial sensors (GaitUp & Mobility Lab), two devices using pressure sensor systems (GAITRite & Zebris) as well as one optical system (OptoGait). Twelve older adults walked at self-selected speed through a walkway integrating all of the above systems. Basic spatiotemporal parameters (gait cycle time, cadence, gait speed and stride length) as well as measures of relative phase (stance phase, swing phase, double stance phase, single limb support) were extracted from all systems. We used Intraclass Correlation Coefficients as measures of agreement and consistency. ResultsHigh agreement and consistency between all systems was found for basic spatiotemporal parameters, whereas parameters of relative phase showed poorer agreement and consistency. Overground measurement (GAITRite & OptoGait) showed generally higher agreement with each other as compared to inertial sensor-based systems. SignificanceOur results indicate that accurate detection of both, the heel-strike and toe-off event are crucial for reliable results. Systematic errors in the detection of one or both events may only have a small impact on basic spatiotemporal outcomes as errors remain consistent from step to step. Relative phase parameters on the other hand may be affected to a much larger extent as these differences lead to a systematic increase or reduction of relative phase durations.

Effects of central apneas on sympathovagal balance and hemodynamics at night: impact of underlying systolic heart failure

BackgroundIncreased sympathetic drive is the key determinant of systolic heart failure progression, being associated with worse functional status, arrhythmias, and increased mortality. Central sleep apnea is highly prevalent in systolic heart failure, and its effects on sympathovagal balance (SVB) and hemodynamics might depend on relative phase duration and background pathophysiology.ObjectiveThis study compared the effects of central apneas in patients with and without systolic heart failure on SVB and hemodynamics during sleep.MethodsDuring polysomnography, measures of SVB (heart rate and diastolic blood pressure variability) were non-invasively recorded and analyzed along with baroreceptor reflex sensitivity and hemodynamic parameters (stroke volume index, cardiac index, total peripheral resistance index). Data analysis focused on stable non-rapid eye movement N2 sleep, comparing normal breathing with central sleep apnea in subjects with and without systolic heart failure.ResultsTen patients were enrolled per group. In heart failure patients, central apneas had neutral effects on SVB (all p > 0.05 for the high, low, and very low frequency components of heart rate and diastolic blood pressure variability). Patients without heart failure showed an increase in very low and low frequency components of diastolic blood pressure variability in response to central apneas (63 ± 18 vs. 39 ± 9%; p = 0.001, 43 ± 12 vs. 31 ± 15%; p = 0.002). In all patients, central apneas had neutral hemodynamic effects when analyzed over a period of 10 min, but had significant acute hemodynamic effects.ConclusionEffects of central apneas on SVB during sleep depend on underlying systolic heart failure, with neutral effects in heart failure and increased sympathetic drive in idiopathic central apneas.

The effect of unilateral lingual nerve injury on the kinematics of mastication in pigs

ObjectiveThis study evaluates the effect of unilateral lingual sensory loss on the spatial and temporal dynamics of jaw movements during pig chewing. DesignX-ray Reconstruction of Moving Morphology (XROMM) was used to reconstruct the 3-dimensional jaw movements of 6 pigs during chewing before and after complete unilateral lingual nerve transection. The effect of the transection were evaluated at the temporal and spatial level using Multiple Analysis of Variance. Temporal variables include gape cycle and phase durations, and the corresponding relative phase durations. Spatial variables include the amplitude of jaw opening, jaw yaw, and mandibular retraction-protraction. ResultsThe temporal and spatial dynamics of jaw movements did not differ when chewing ipsilateral versus contralateral to the transection. When compared to pre-transection data, 4 of the 6 animals showed significant changes in temporal characteristics of the gape cycle following the transection, irrespective of chewing side, but the specific response to the lesion was highly dependent on the animal. On the other hand, in affected individuals the amplitude of jaw movements was altered similarly in all 3 dimensions: jaw opening and protraction-retraction increased whereas jaw yaw decreased. ConclusionThe variable impact of this injury in this animal model suggests that individuals use different compensatory strategies to adjust or maintain the temporal dynamics of the gape cycle. Because the amplitude of jaw movements are more adversely affected than their timing, results suggest that maintaining the tongue-jaw coordination is critical and this can come at the expense of bolus handling and masticatory performance.

Inertial sensing of the motion speed effect on the sit-to-walk activity

The STW execution at motion speed faster than normal most possibly enhances the risk for balance loss due to the increase in body segment accelerations. The purpose of the study was to use inertial sensing to examine the effect of motion speed on the STW segmental kinematics and its temporal events. Eighteen young men (20.7 ± 2.0 years) performed STW trials at preferred (PS) and fast (FS) motion speed. Data were collected with Xsens inertial sensors positioned at the trunk, thigh, shank, and foot segments. The maximum segmental values of angular displacement, angular velocity and linear acceleration, the duration of total STW (ttotal), the absolute and relative (% ttotal) phase duration (Flexion, Transition, Extension, Walking) and, the absolute and relative time taken to reach each maximum value were determined. In FS, ttotal and the absolute phase duration (except for Transition), were all significantly shorter (p = 0.000). The relative phase duration was not altered (p > 0.05), except for the Extension shortening (p = 0.001). The maximum angular displacement was altered only for the thigh (decreased, p = 0.038) and shank (increased, p = 0.004). Maximum angular velocities and linear accelerations were all significantly increased (p = 0.000 for all). The absolute time to reach the maximum values shortened in FS (p ≤ 0.05), while, the relative times were not altered (p > 0.05), except for the delayed trunk maximum angular displacement (p = 0.039). Inertial sensing appears to identify the motion speed effect on STW segmental kinematics and their temporal events in healthy young men. The results of the study may contribute improving the preventive or rehabilitation interventions in persons with impaired postural control.

Changes in force production and stroke parameters of trained able-bodied and unilateral arm-amputee female swimmers during a 30 s tethered front-crawl swim

This study examined changes in the propulsive force and stroke parameters of arm-amputee and able-bodied swimmers during tethered swimming. Eighteen well-trained female swimmers (nine unilateral arm amputees and nine able-bodied) were videotaped performing maximal-effort 30 s front-crawl swims, while attached to a load cell mounted on a pool wall. Tether force, stroke rate, stroke phase durations and inter-arm angle were quantified. The able-bodied group produced significantly higher mean and maximum tether forces than the amputee group. The mean of the intra-cyclic force peaks was very similar for both groups. Mean and maximum tether force had significant negative associations with 100 m swim time, for both groups. Both groups exhibited a similar fatigue index (relative decrease in tether force) during the test, but the amputees had a significantly greater stroke rate decline. A significant positive association between stroke rate decline and fatigue index was obtained for the able-bodied group only. Inter-arm angle and relative phase durations did not change significantly during the test for either group, except the recovery phase duration of the arm amputees, which decreased significantly. This study’s results can contribute to the development of a more evidence-based classification system for swimmers with a disability.

Control of oscillation periods and phase durations in half-center central pattern generators: a comparative mechanistic analysis

Central pattern generators (CPGs) consisting of interacting groups of neurons drive a variety of repetitive, rhythmic behaviors in invertebrates and vertebrates, such as arise in locomotion, respiration, mastication, scratching, and so on. These CPGs are able to generate rhythmic activity in the absence of afferent feedback or rhythmic inputs. However, functionally relevant CPGs must adaptively respond to changing demands, manifested as changes in oscillation period or in relative phase durations in response to variations in non-patterned inputs or drives. Although many half-center CPG models, composed of symmetric units linked by reciprocal inhibition yet varying in their intrinsic cellular properties, have been proposed, the precise oscillatory mechanisms operating in most biological CPGs remain unknown. Using numerical simulations and phase-plane analysis, we comparatively investigated how the intrinsic cellular features incorporated in different CPG models, such as subthreshold activation based on a slowly inactivating persistent sodium current, adaptation based on slowly activating calcium-dependent potassium current, or post-inhibitory rebound excitation, can contribute to the control of oscillation period and phase durations in response to changes in excitatory external drive to one or both half-centers. Our analysis shows that both the sensitivity of oscillation period to alterations of excitatory drive and the degree to which the duration of each phase can be separately controlled depend strongly on the intrinsic cellular mechanisms involved in rhythm generation and phase transitions. In particular, the CPG formed from units incorporating a slowly inactivating persistent sodium current shows the greatest range of oscillation periods and the greatest degree of independence in phase duration control by asymmetric inputs. These results are explained based on geometric analysis of the phase plane structures corresponding to the dynamics for each CPG type, which in particular helps pinpoint the roles of escape and release from synaptic inhibition in the effects we find.

Cross‐Country Skiing

The purpose was to study the adaptation to speed in the temporal patterns of the movement cycle and determine any differences in velocity, cycle rate and cycle length at the maximum speed level in the different classical style and freestyle cross‐country skiing techniques. Eight skilled male cross‐country skiers were filmed with a digital video camera in the sagittal plane while skiing on a flat cross‐country ski track. The skiers performed three classical style techniques the diagonal stride, kick double poling and the double poling technique and four freestyle techniques paddle dance (gear 2), double dance (gear 3), single dance (gear 4) and combiskate (gear 5) at four different self‐selected speed levels slow, medium, fast and their maximum. Cycle duration, cycle rate, cycle length, and relative and absolute cycle phase duration of the different techniques at the different speed levels were analysed by means of a video analysis system. The cycle rate in all tested classical and freestyle techniques was found to increase significantly (p < .01) with speed from slow to maximum. Simultaneously, there was a significant decrease in the absolute phase durations of all the investigated skiing techniques. A minor, not significant, change in cycle length, and the significant increase in cycle rate with speed showed that the classical and freestyle cross‐country skiing styles are dependent, to a large extent, on an increase in cycle rate for speed adaptation. A striking finding was the constant relative phase duration with speed, which indicates a simplified neural control of the speed adaptation in both cross‐country skiing styles. For the practitioner, the knowledge about the importance of increasing cycle frequency rather than cycle length in the speed adaptation can be used to optimise a rapid increase in speed. The knowledge about the decrease in absolute phase duration, especially the thrust phase duration, points to the need for strength and technique training to enable force production at a high cycle rate and skiing speed. The knowledge that the relative phase duration stays constant with speed may be used to simplify the learning of the different cross‐country skiing techniques.

Role of differential cell proliferation in the tail bud in aberrant mouse neurulation

In the mouse mutant curly tail, the phenotypes spina bifida and curled tail result from a delay in closure of the posterior neuropore (PNP). At the developmental stage when this delay can first be recognized, the caudal region of the embryo demonstrates a transiently enhanced curvature of the body axis which likely inhibits elevation, convergence, and fusion of the neural folds. The enhanced curvature is thought to be the result of a decreased proliferation in the ventrally located gut endoderm and notochord, together with a normal proliferation of the overlying neuroepithelium of the PNP. However, the proliferation defect and the enhanced curvature were originally demonstrated at the same developmental stage, while it is expected that reduced proliferation should precede enhanced curvature and delayed PNP closure. The caudal region originates from the tail bud and we therefore propose that the enhanced curvature is induced by a disturbed dorso-ventral proliferation pattern in the tail bud. Using flow cytometry, proliferation patterns were determined separately for the dorsal and ventral halves of the tail bud of curly tail and of control embryos as well as of recombinant embryos having the curly tail phenotype with a genetic background which is matched to the BALB/c control strain. In general, it appeared that about half of the cell cycle duration in tail bud cells was occupied by S phase, about 40% by G0/G1 and the rest by G2/M. For the control embryos, no dorso-ventral differences in relative phase duration were demonstrated. However, curly tail and recombinant embryos at the 21–25 somite stage, prior to the onset of enhanced curvature, exhibited ventrally a higher proportion of G0/G1 phase cells than dorsally, and a complementary relationship for S phase cells. We interpret these observations as indicating a prolonged G1 phase at the ventral side of the tail bud, resulting in a prolongation of the cell cycle and thus a decreased proliferation. In 26–30 somite stage embryos, prior to the normalization of curvature in curly tail embryos, the dorso-ventral proliferation balance was re-established. We conclude that a reduced proliferation in the ventral part of the tail bud of the curly tail embryo precedes both the onset of enhanced curvature and the previously observed reduction in proliferation of the hindgut and notochord, and is a likely candidate for an early event in the pathogenetic sequence leading to the curly tail phenotype. Dev. Dyn. 1998;211:382-389. © 1998 Wiley-Liss, Inc.

Role of differential cell proliferation in the tail bud in aberrant mouse neurulation.

In the mouse mutant curly tail, the phenotypes spina bifida and curled tail result from a delay in closure of the posterior neuropore (PNP). At the developmental stage when this delay can first be recognized, the caudal region of the embryo demonstrates a transiently enhanced curvature of the body axis which likely inhibits elevation, convergence, and fusion of the neural folds. The enhanced curvature is thought to be the result of a decreased proliferation in the ventrally located gut endoderm and notochord, together with a normal proliferation of the overlying neuroepithelium of the PNP. However, the proliferation defect and the enhanced curvature were originally demonstrated at the same developmental stage, while it is expected that reduced proliferation should precede enhanced curvature and delayed PNP closure. The caudal region originates from the tail bud and we therefore propose that the enhanced curvature is induced by a disturbed dorso-ventral proliferation pattern in the tail bud. Using flow cytometry, proliferation patterns were determined separately for the dorsal and ventral halves of the tail bud of curly tail and of control embryos as well as of recombinant embryos having the curly tail phenotype with a genetic background which is matched to the BALB/c control strain. In general, it appeared that about half of the cell cycle duration in tail bud cells was occupied by S phase, about 40% by G0/G1 and the rest by G2/M. For the control embryos, no dorso-ventral differences in relative phase duration were demonstrated. However, curly tail and recombinant embryos at the 21-25 somite stage, prior to the onset of enhanced curvature, exhibited ventrally a higher proportion of G0/G1 phase cells than dorsally, and a complementary relationship for S phase cells. We interpret these observations as indicating a prolonged G1 phase at the ventral side of the tail bud, resulting in a prolongation of the cell cycle and thus a decreased proliferation. In 26-30 somite stage embryos, prior to the normalization of curvature in curly tail embryos, the dorso-ventral proliferation balance was re-established. We conclude that a reduced proliferation in the ventral part of the tail bud of the curly tail embryo precedes both the onset of enhanced curvature and the previously observed reduction in proliferation of the hindgut and notochord, and is a likely candidate for an early event in the pathogenetic sequence leading to the curly tail phenotype.

Prolongation of G1 phase in cultured glioma cells by cis-dichlorodiammineplatinum (II) (CDDP): analysis using bromodeoxyuridine (BrdU)-Hoechst technique.

The cytokinetic response of three murine (AC) and human (GB-1 and GB-2) glioma cell lines to cisdichlorodiammineplatinum (II) (CDDP) was investigated by flow cytometry. Using the 5-bromodeoxyuridine (BrdU)-Hoechst technique, percentages of cultured glioma cells in the various phases of the cell cycle, and relative phase duration were calculated. This technique proved to be a rapid and easily performed method to characterize phase length and transition rate for the complete cell cycle. In the presence of CDDP IC10 (a concentration in which 10% inhibition of cell growth be induced as compared to controls), perturbations of the cell cycle in AC and GB-1 cells included G2 delay or block, decreased transit velocity from G1 to S phase, and prolongation of G1 phase. The mean cell cycle time increased 1.4 times in AC and 1.6 times in GB-1 as compared to controls. In CDDP IC 50-treated GB-2 cells, the mean cell cycle time was prolonged three times longer than control: however, duration of each phase could not be calculated because of significant perturbation of cell cycle. These results suggest that CDDP influences glioma cells at the G1/S boundary and in the G2 phase, resulting in prolongation of the G1 phase and, to a minor degree, in block of the G2 phase.

CELL CYCLE CHARACTERISTICS OF SYNCHRONIZED AND ASYNCHRONOUS POPULATIONS OF HUMAN CELLS AND EFFECT OF COOLING OF SELECTED MITOTIC CELLS

The method of synchronizing cells by means of mitotic selection has been adapted to the human line NHIK 3025. Increase in cell number as a function of time in asynchronous and synchronous populations was studied as well as mitotic index as a function of time after selection of synchronized populations. Phase durations of the cell cycle of synchronous populations were determined by 3H-thymidine incorporation and scintillation counting. The relative phase durations of exponentially growing asynchronous populations were determined by mathematical analysis of DNA-histograms recorded by flow cytofluorimetry. Both the generation time and the various phase durations of the cell cycle were found to be the same in asynchronous and synchronous populations. It was found that NHIK 3025 cells are damaged by cooling to 4 and 0 degrees C so that cooling of selected cells in order to increase the yield would reduce the quality of the synchronized populations.

The application of age distribution theory in the analysis of cytofluorimetric DNA histogram data.

Age distribution theory has been employed in a model to analyse a variety of histograms of the DNA content of single cells in samples from experimental tumours growing in tissue culture. The method has produced satisfactory correspondence with the experimental data in which there was a wide variation in the proportions of cells in the intermitotic phases, and generally good agreement between the 3H-thymidine labelling index and the computed proportion in S phase. The model has the capacity to analyse data from populations which contain a proportion of non-cycling cells. However, it is concluded that reliable results for the growth fraction and also for the relative durations of the intermitotic phase times cannot be obtained for the data reported here from the DNA histograms alone. To obtain reliable estimates of the growth fraction the relative durations of the phase time must be known, and conversely, reliable estimates of the relative phase durations can only be obtained if the growth fraction is known.