Biomedical subjects

A Pedotti

Publications and source records attributed to A Pedotti.

At least 55 records · Page 3Linked to original sources

PubMed2001

Baroreflex effectiveness index: an additional measure of baroreflex control of heart rate in daily life.

In healthy subjects, progressive beat-to-beat increases or decreases in systolic blood pressure (SBP) ramps are not always accompanied by baroreflex-driven lengthening or shortening in pulse interval (PI) ramps, respectively. This phenomenon has been quantified by a new index, the baroreflex effectiveness index (BEI), defined as the ratio between the number of SBP ramps followed by the respective reflex PI ramps and the total number of SBP ramps observed in a given time window. Specificity of BEI was shown in eight cats by a -89% reduction of BEI after sinoaortic denervation. In 14 healthy humans, the 24-h average BEI value was 0.21, with a marked day-night modulation ( approximately 0.25 day, approximately 0.15 night) in counterphase with modulation of baroreflex sensitivity (BRS). Our analysis indicates that 1) in normal subjects, arterial baroreflex can induce beat-by-beat PI changes in response to only 21% of all SBP ramps, possibly because of central inhibitory influences or of interferences at sinus node level by nonbaroreflex mechanisms and 2) BEI provides information on the baroreflex function that is complementary to BRS.

Adult↗

PubMed2001

Static and dynamic postural control in long-term microgravity: evidence of a dual adaptation.

The adaptation of dynamic movement-posture coordination during forward trunk bending was investigated in long-term weightlessness. Three-dimensional movement analysis was carried out in two astronauts during a 4-mo microgravity exposure. The principal component analysis was applied to joint-angle kinematics for the assessment of angular synergies. The anteroposterior center of mass (CM) displacement accompanying trunk flexion was also quantified. The results reveal that subjects kept typically terrestrial strategies of movement-posture coordination. The temporary disruption of joint-angular synergies observed at subjects' first in-flight session was promptly recovered when repetitive sessions in flight were analyzed. The CM anteroposterior shift was consistently <3-4 cm, suggesting that subjects could dynamically control the CM position throughout the whole flight. This is in contrast to the observed profound microgravity-induced disruption of the quasi-static body orientation and initial CM positioning. Although this study was based on only two subjects, evidence is provided that static and dynamic postural control might be under two separate mechanisms, adapting with their specific time course to the constraints of microgravity.

Adaptation, Physiological↗

PubMed2001

[Opto-electronic techniques and 3D body surface reconstruction for the control of patient positioning in the radiotherapy of breast cancer].

PURPOSE: In radiotherapy clinical practice, the currently existing gap between the high degree of accuracy in treatment planning and, the possibility of conforming the high-energy radiation beams on the one hand, and the uncertain set-up of each irradiation session on the other is a decisive factor for optimizing radiation treatment. Indeed there is wide experimental evidence that the current methods used for patient alignment and immobilization do not guarantee the necessary precision in delivering therapy with respect to the specifications of the treatment plan. The main reason for this is the lack of control systems that may be applied systematically to provide quantitative real-time feedback on the quality of patient repositioning and immobility during radiation emission. MATERIAL AND METHODS: Opto-electronic techniques and body surface registration methods were sygergisically used for the automatic three-dimensional verification and correction of patient position at the therapy unit. The method is based on radiotherapy applications of real-time opto-electronic human motion analysis using passive markers to control patient repositioning and to acquire and describe body surfaces in three dimensions. The quantitative detection of the localization error relies on the real-time detection of the position of an hybrid set of control points, namely physical passive markers and laser light markers, and their immediate comparison with a reference data set. The data set consists of the reference positions of the passive markers and a three-dimensional model of the body surface. The method was experimentally tested at the Radiotherapy Division of the European Institute of Oncology to control the repositioning of a phantom and of a volunteer, with reference to the clinical realignment procedure applied for breast cancer radiotherapy. RESULTS: The results confirm that the technique represents a valuable method to detect and automatically correct localization errors in the irradiation set-up. The use of the information provided by the laser markers allows one to reduce the potential inaccuracies in the manual relocation of the passive markers on the subject's skin and guarantees that position control is based on a redundant set of data describing the three-dimensional localization and configuration of the irradiated body surface portion. The experimental results show that the initial displacements of the controlled body area were systematically reduced to median values below 1 millimeter and 1.2 millimeters for the phantom and the volunteer, respectively. CONCLUSIONS: The synergistic use of opto-electronic technologies and stereophotogrammetric techniques associated to surface registration methods proved to provide an accurate description of the spatial transformation between the reference position and the actual position of the controlled body area. This allowed us to define an effective procedure to correct the patients position and recover the quality of the irradiation set-up, in agreement with the clinical requirements. The reported results confirm that the dynamic sensing of the body surface by opto-electronic technologies is a particularly promising technique that allows to systematically achieve swift and accurate patient alignment, thus ensuring that the treatment plan specifications are reproduced in the reality of each irradiation session.

Algorithms↗

PubMed2001

[Optoelectronic plethysmography: a new tool in respiratory medicine].

Opto-electronic plethysmography (OEP) is a new noninvasive technique, recently introduced, which is highly accurate in the measurement of total chest wall volume variations, allowing partitioning of the complex shape of the chest wall into different functional compartments. It can measure breathing patterns and, if combined with pressure measurements, can be used to study statics, dynamics and energetics of the respiratory system. OEP does not require connection to the patient and can be used without a subject-specific calibration. All these features and the results obtained in several studies make the OEP not only a reliable system for basic physiological and pathophysiological research studies, but also an attractive tool to be used in clinics.

Electronics, Medical↗

PubMed2000

Real-time opto-electronic verification of patient position in breast cancer radiotherapy.

OBJECTIVE: The clinical application of an opto-electronic system for real-time three-dimensional (3D) control of patient position in breast cancer radiotherapy is described. The specific features of the motion analysis technology (shape recognition of passive markers) are detailed, and the outcomes of its clinical use for quantitative position control and immobility verification of the thoracic irradiation field during breast cancer treatment are reported. MATERIALS AND METHODS: The position control system is based on the ELITEtrade mark opto-electronic motion analyzer, which provides in real time the 3D coordinates of a set of passive markers (plastic hemispheres 3 mm in diameter) previously placed on selected landmarks on the patient's skin. The system-dedicated hardware performs marker recognition by means of 2D correlation of shape with a predefined marker modeling mask. This feature ensures a high accuracy, even with small marker dimensions, and successful analysis in a noisy environment (due to room light, reflexes, etc.). The patient repositioning control was based on a comparison between the current positions of the markers and a corresponding reference configuration. The resulting marker displacements were graphically displayed in real time for immediate control. This information was not provided to the operator as a repositioning tool. Instead, the kinematic data was stored for subsequent off-line analysis aimed at quantifying the different factors contributing to patient mis-positioning (initial repositioning errors, patient's breathing, and random movements) when conventional means for patient alignment (laser centering) and immobilization (casting techniques) are used. RESULTS: Clinical application of the system revealed median 3D localization errors for the directly controlled anatomical landmarks of around 4.5 mm. This value is proposed to represent the intrinsic accuracy of conventional laser-centering techniques in breast cancer radiotherapy, including the effects of patient body deformations. When the positional inaccuracies introduced by patients' respiration were also considered, the extent of the resulting 3D mis-positioning of the control points increased to median values of up to 8 mm. CONCLUSIONS: The reported clinical trial confirms the significant role that real-time opto-electronic motion analysis based on passive markers can have in augmenting the accuracy of patient repositioning and immobility verification in the radiotherapy of a non-rigid body area while also accounting for physiological movements. Evaluation of the data collected during each irradiation session for five patients provided valuable information concerning the optimization of the efficacy of traditional methods for patient centering and immobilization.

Breast Neoplasms↗

PubMed2000

Real-time three-dimensional motion analysis for patient positioning verification.

BACKGROUND AND PURPOSE: This paper describes the technology and methods involved in a system for automatically checking the position of patients at radiotherapy units. This is proposed for improving the accuracy in the irradiation geometrical set-up, which is a crucial factor in radiotherapy quality control. MATERIALS AND METHODS: The system is based on real-time opto-electronics and close-range photogrammetry and detects multiple passive markers placed on selected patient skin landmarks. Patient alignment and position monitoring is carried out by comparing the current three-dimensional positions of the markers with those of an initial reference position acquired during the simulation procedure and/or the first irradiation session. The system was used to measure the accuracy of conventional laser centering techniques for patient repositioning. Inaccuracies due to breathing and random movements were also taken into account. Professional technicians were asked to reposition three volunteer subjects carefully using a traditional laser centering procedure. RESULTS: The results revealed significant repositioning errors even in highly controlled conditions, affecting particularly body areas relatively far from the skin reference points used for laser alignment. CONCLUSIONS: The outcome of the experimental application of this technology confirms its potential as a tool for patient repositioning and automatic detection of any errors caused by breathing or other unpredictable movements. The real-time feedback on the patient's position given by the system provides operators with appropriate visual indices and allows them to take suitable countermeasures in case of significant failures. In addition, the use of the system output for automatic position control is envisaged.

Artifacts↗

PubMed2000

Quantitative analysis of neutral body posture in prolonged microgravity.

The experiment was performed during a 6-month space flight and focused on the quantitative three-dimensional description of the Neutral Body Posture (NBP) and of subjects' spine anthropometry in Erect Posture (EP). The NBP joint angles' configuration is described along the long-term microgravity exposure and compared with respect to previous in-flight collected data. Observed spinal length modification during EP in-flight is related to on-ground investigations focused on circadian anthropometrical fluctuations. The flattening of the spinal lumbar lordosis and thoracic kyphosis is also described. Even though only two subjects were studied, this analysis points out the maturity of the opto-electronic technology for the quantitative analysis of posture in microgravity and confirms the need of enriching the anthropometrical database of human postures in weightlessness for the design optimization of permanently inhabited space modules.

Adult↗

PubMed2000

Paraplegic adaptation to assisted-walking: energy expenditure during wheelchair versus orthosis use.

STUDY DESIGN: To study the energy cost of locomotion during ambulation with different orthoses (HIP Guidance Orthosis Orlau Parawalker (PW), n=4; Reciprocating Gait Orthosis (RGO), n=6; RGO + FNS, n=4). OBJECTIVES: Since high energy costs of locomotion have been proposed as a major reason for early rejection of orthotic use, our aims were (a) to evaluate the impact of functional neuromuscular stimulation (FNS) on energy expenditure during orthosis-assisted ambulation; (b) to study whether energy expenditure data can predict the poor long-term patients' compliance and (c) to assess selection criteria for the assignment of the different types of orthosis. SETTING: The study was completed at the Center of Sports Medicine and Center of Bioengineering, don C. Gnocchi Foundation, IRCCS, Milan, Italy. METHODS: The HR/VO2 relationship and the energy cost of locomotion (C) were studied in 14 patients (lesion level C7-T11) during wheelchair (WHCH) use at various speeds and during locomotion with different orthotic devices. Patients' short- and long-term compliance were assessed by questionnaires evaluating duration of and problems related to orthotic use. RESULTS: (a) In patients using RGO + FNS the slope difference of HR/VO2 curves (deltaslHR/VO2) between WHCH and orthosis was significantly lower than in other groups (-3 beats l(-1) in RGO + FNS vs 43 and 52 beats l(-1) in RGO and PW, respectively); (b) neither C, nor VO2 peak, or deltaslHR/VO2 correlated with orthosis duration of use; (c) in the RGO + FNS group, C was lower at maximal walking speed, which linearly correlated with maximal WHCH speed. CONCLUSION: (a) Electrical stimulation seems to improve locomotion, as a consequence of hemodynamic effects, but does not decrease energy expenditure, which remains high; (b) the poor long-term compliance to orthosis use cannot be predicted by the energy expenditure parameters; (c) the subjects who can reach high speeds by WHCH seem to be the most appropriate for RGO + FNS locomotion.

Adaptation, Physiological↗

PubMed2000

Equilibrium and movement control strategies in trans-tibial amputees.

This study was aimed at identifying changes in equilibrium and movement control strategies in trans-tibial amputees (TTA) related to both the biomechanical changes and the loss of afferent inflow. The coordinations between equilibrium and movement were studied in traumatical TTA and in controls during transition from bipedal to monopodal stance. TTA failed to perform the task in a high percentage of trials both when the sound and the prosthetic limb were supporting. Significant differences were also found between TTA and controls in the duration of the weight transfer phase, in the length of the initial centre of pressure (CP) displacement and in the electromyographic (EMG) patterns. Despite adaptive posturomotor control strategies, transition from bipedal to monopodal stance remains a difficult task to perform for TTA, both when the supporting limb is the affected one and when the sound one is. The results of this study are discussed with respect to the rehabilitation programme and the prosthesis design for transtibial amputees.

Adult↗

PubMed2000

Perspectives on MEMS in bioengineering: a novel capacitive position microsensor.

We describe a novel capacitive position sensor using micromachining to achieve high sensitivity and large range of motion. These sensors require a new theoretical framework to describe and optimize their performance. Employing a complete description of the electrical fields, the sensor should deviate from the standard geometries used for capacitive sensors. By this optimization, the sensor gains a twofold increase in sensitivity. Results on a PC board 10x model imply that the micromachined sensor should achieve a sensitivity of less than 10 nm over 500-micron range of travel. Some bioengineering applications are addressed, including positioning of micromirrors for laser surgery and dose control for implantable drug delivery systems.

Drug Delivery Systems↗

PubMed2000

The relationship between electrical stimulus and joint torque: a dynamic model.

The knowledge of the behavior of electrically activated muscles is an important requisite for the development of functional electrical stimulation (FES) systems to restore mobility to persons with paralysis. The aim of this work was to develop a model capable of relating electrical parameters to dynamic joint torque for FES applications. The knee extensor muscles, stimulated using surface electrodes, were used for the experimental preparation. Both healthy subjects and people with paraplegia were tested. The dynamics of the lower limb were represented by a nonlinear second order model, which took account of the gravitational and inertial characteristics of the anatomical segments as well as the damping and stiffness properties of the knee joint. The viscous-elastic parameters of the system were identified experimentally through free pendular movements of the leg. Leg movements induced by quadriceps stimulation were acquired too, using a motion analysis system. Results showed that, for the considered experimental conditions, a simple one-pole transfer function is able to model the relationship between stimulus pulsewidth (PW) and active muscle torque. The time constant of the pole was found to depend on the stimulus pattern (ramp or step) while gain was directly dependent on stimulation frequency.

Bias↗

PubMed2000

Optoelectronic plethysmography in intensive care patients.

We used optoelectronic plethysmography to study 11 normal subjects during quiet and deep breathing, six sedated and paralyzed patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS) receiving continuous positive pressure ventilation (CPPV) (positive end-expiratory pressure [PEEP] = 10 cm H(2)O, tidal volume [VT] = 300, 600, 900 ml), and seven ALI/ARDS patients receiving pressure support ventilation (PSV) (PEEP 10 cm H(2)O, pressure support = 5, 10, 15, 25 cm H(2)O). The volumes measured using optoelectronic plethysmography were compared with measurements taken using spirometry and pneumotachography. The three methods were highly correlated. The discrepancies found were 1.7 +/- 5.9%, -1.6 +/- 5.4%, and 4.9 +/- 6.4% when comparing optoelectronic plethysmography with spirometry, optoelectronic plethysmography with pneumotachography, and spirometry with pneumotachography, respectively. Accuracy of the compartmentalization procedure (upper thorax, lower thorax, and abdomen) was assessed by calculating compartmental volume changes during isovolume maneuvers. The discrepancy from the ideal zero line was -2.1 +/- 48.3 ml. Abdominal contribution to inspired volume was greater for normal subjects than for PSV patients (63 +/- 11% versus 43 +/- 14%, p < 0.001). It decreased with VT for normal subjects (48.5 +/- 15%, p < 0.05), whereas it increased for CPPV patients (61 +/- 10%, p < 0.05). No significant distribution differences were found between 5 and 25 cm H(2)O PSV. We conclude that optoelectronic plethysmography is a feasible technique able to provide unique data on the distribution of chest wall volume changes in intensive care patients.

Adult↗

PubMed1999

Arm raising in humans under loaded vs. unloaded and bipedal vs. unipedal conditions.

The aim of the present experiment was to study the central organization of equilibrium control during arm raising in the frontal plane. Nine adult subjects (five seniors and four young adults) were asked to raise their right arm to a horizontal position in the frontal plane in two support conditions (bipedal vs. unipedal) and two load conditions (unloaded vs. a 3.5-kg load added on the moving hand). No instructions were given concerning the movement speed. The movements were performed at about half the maximum speed achievable under reaction time conditions. The final lateral center of mass (CM) position 1 s after the movement offset, and the time course of the CM shift during the movement were studied in the four experimental conditions, using a CM compensation index. The electromyographic (EMG) pattern of the main muscles involved in the movement performance and in the postural control were studied in three out of nine subjects during movements performed at two velocities (at the preferred speed and as fast as possible). The results indicate that (1) the CM shift remains minimized in the frontal plane during the time course of the arm movement and during the final stabilization of the arm regardless of the stance and load conditions; (2) the time course of the CM compensation index remains stable during the first 400 ms after the movement onset, decreasing late in the movement and increasing again at the end of the stabilization stage. A modelisation suggests that the time course is the result of the interaction of two controls: a first one, putative feedforward, starting early and decreasing with time and a second one, putative feedback, starting late in the movement and increasing with time; (3) both early and late index values are influenced by the support and load conditions, the highest index values being observed during unipedal stance and load conditions; (4) activation of quadratus lomborum (QL) contralateral to the raising arm is time locked with the deltoidus activation of the raising arm in both fast and slow movements: this contralateral QL activation corresponds to an anticipatory postural adjustment (APA) aimed at minimizing the CM shift.

Adult↗

PubMed1999

Long-term adaptation of postural control in microgravity.

Orbital microgravity represents a unique environment, which allows the isolation of variables assumed to be involved in the mechanism of body positioning in space. In this context, the alignment of the trunk axis along allocentric references and the positioning of the body center of mass inside the supporting base compete for the role of the primary-controlled variable when assuming erect posture. This paper reports the quantitative evaluation of the postural strategies exhibited by two subjects with feet fixed to the floor of the space module along a 4-month period of exposure to microgravity. With respect to previous findings in parabolic flights and short term space missions, the analysis focused on long-term process of sensorimotor adaptation to weightlessness. Results show that while trunk-axis orientation is preserved and used as a stable postural frame of reference, the positioning of the body center of mass appears to be significantly biased backward and turns out to be involved in a long-term process of adaptation throughout the entire flight towards the re-emergence of a typically terrestrial postural regulation compatible with equilibrium.

Adult↗

PubMed1999

Methodological and technological implications of quantitative human movement analysis in long term space flights.

In the frame of the 179-days EUROMIR '95 space mission, two in-flight experiments foresaw the analysis of three-dimensional human movements in microgravity. For this aim, a space qualified opto-electronic motion analyser based on passive markers was installed onboard the MIR Space Station. The paper describes the experimental procedures designed in order to face technical and operational limitations imposed by the critical environment of the orbital module. The reliability of the performed analysis is discussed, focusing two related aspects: accuracy in three-dimensional marker localisation and data comparability among different experimental sessions. The effect of the critical experimental set-up and of TV cameras optical distortions is evaluated on in-flight acquired data, by performing an analysis on Euclidean distance conservation on rigid bodies. An optimisation method for the recovering of a unique reference frame throughout the whole mission is described. Results highlight the potentiality that opto-electronics and close-range photogrammetry have for automatic motion analysis onboard orbital modules. The discussion of the obtained results provides general suggestions for the implementation of experimental human movement analysis in critical environments, based on the suitable trade-off between external constraints and achievable analysis reliability.

Algorithms↗

PubMed1998

Electromyographic signals during gait: criteria for envelope filtering and number of strides.

The use of linear envelopes to represent the electromyographic (EMG) measurements obtained during locomotion has become common practice. Guidelines for designing envelope filters and specifying the minimum number of strides needed to produce valid EMG profiles have been developed. Electromyograms from eight major muscles of the lower leg are measured from five normal young adults during self-selected slow, free and fast walking speeds. 30 strides per task are measured. The 'ideal' EMG profile is defined from the ensemble average of the rectified EMG signal. An error measure is defined and used as a criterion to assess the appropriateness of various cut-off frequencies for envelope filters and the number of strides required for establishing a good EMG profile. It is found that between six and ten strides are needed to form a representative profile, and an envelope filter with a minimum cut-off frequency of approximately 9 Hz is necessary.

Adult↗

PubMed1998

Functionally oriented and clinically feasible quantitative gait analysis method.

A protocol for clinical gait analysis is described, and data from 30 normal adult female subjects are presented. Extensive application to pathologic subjects has proven to be feasible and sufficiently accurate. The method is based on a particular location and attachment of retro-reflective markers on the body and on a particular arrangement of four TV cameras. A motion analyser measures the 3D coordinates of each marker. A modelling approach, based on individual anthropometric measurements, and a functional approach, based on kinematical considerations, are used to estimate the location of hip, knee, and ankle joint centers and the orientation of the flexion-extension axis of the knee. 3D relative and absolute movements of pelvis and lower limbs are obtained and shown to be consistent with functional anatomy.

Adult↗

PubMed1998

Implementation and application of real-time motion analysis based on passive markers.

A method for real-time motion analysis based on passive markers is presented. An opto-electronic automatic motion analyser was used as hardware platform and the real-time operation was based on the interfacing between two levels of the system architecture. True real-time acquisition, processing and representation of two-dimensional and three-dimensional kinematics data were implemented through a newly conceived data acquisition procedure and high speed optimisation of the kinematics data processing. The method allows one to operate the motion analysis system in real-time; even when the data elaboration unit is required to perform other processing functions, the only consequence is a decrease in system sampling rate. The maximum number of processed and plotted markers in three dimensions at the highest system sampling rate (100 Hz) turned out to be suitable for the implementation of analytical and visual kinematics biofeedback. An example of the achievable level of complexity in terms of marker disposition model and graphic representation is reported by describing a demonstration of the real-time representation of human face movements. A clinical application of the method for patient position definition and control at radiotherapy units is presented.

Biomechanical Phenomena↗