Gordon D. Moskowitz

Gaseous Exchange and Acid-Base Balance in Premature Lambs during Liquid Ventilation since Birth

Extract: Nine distressed premature lambs were studied before, during, and after ventilation with fluorocarbon liquid (FC-80). It was found that premature lambs, delivered by cesarean section, could be adequately ventilated with oxygenated liquid for periods up to 3 hr. Using fluarocarbon liquid in conjunction with the described liquid breathing system, it was possible to maintain remarkably good pulmonary gas exchange and acid-base balance during normothermic conditions. In addition, peak intratracheal pressures measured during recovery from liquid ventilation were significantly reduced (P < 0.001) as compared with preliquid ventilation values. This improvement in lung function is in direct contrast to the deterioration in that of the adult animal following liquid ventilation as reported previouslySpeculation: Although an enormous amount of studies remain to be performed, at this time it is appealing to speculate about the possibilities of this therapeutic modality in the preterm human neonate with respiratory distress. We cannot help but think that this method of therapy serves a twofold purpose: (1) maintenance of infants with lungs too stiff to ventilate with gas, and (2) a treatment for reducing surface-active forces in infants with marginal lung stability

The role of impact in the stability of bipedal locomotion

A mathematical model of a simple inverted double-pendulum locomotion system was developed. The stability of the nonlinear model was analysed. Periodic impact of the system with the ground plays a major role in the achievement of stable locomotion. Phase-plane portraits of the generalized coordinates and velocities were utilized to study the behaviour of the system.

PASSIVE AND ACTIVE COMPONENTS OF THE INTERNAL MOMENT DEVELOPED ABOUT THE ANKLE JOINT DURING HUMAN AMBULATION

The internal moment developed about a joint during a functional activity is the result of contraction of muscles and the visco-elastic properties of the joint and its surrounding soft tissues. In this study, the contribution of each one of these mechanisms to the total internal moment developed about the ankle joint during human level walking was assessed. The results indicate that during normal level walking the internal moment about the ankle is mainly due to contraction of muscles surrounding the joint. The contribution of the passive component was found to be negligible. These results, however, were found to be different for the pathological case tested. The results indicated that in a subject with a mild equinus ankle deformity, a substantial portion (21%) of the total internal moment was contributed by the passive resistance of the joint and its surrounding structures.

Bipedal locomotion stabilized by impact and switching: I. Two-and three-dimensional, three-element models

Two mathematical models are developed to study the effect of impact and switching on the stability of bipedal locomotion systems. The stability of the systems is analysed by perturbation method and studying the phase-plane portraits of the generalized coordinates.

The theoretical development of a multichannel time-series myoprocessor for simultaneous limb function detection and muscle force estimation

The theoretical development and simulation of a complete time-series myoprocessor which provides reliable and economical predictions of both the magnitude and direction of limb motion from the spectral content of the surface EMG is discussed. Treating multiple channels of surface EMG as a vector-valued autoregressive process incorporates spatially distributed information which extends the operating range of parallel filtering limb function classifiers and reduces their sensitivity to modeling conditions. Active joint moment is estimated simultaneously from the pooled variance of the prewhitened EMG generated during the classification procedure. Estimation from the prewhitened sequence imposes no additional computational requirements and extends optimal myoprocessor to include multiple channels of serially dependent data. Such a system may be applied to the control of actively powered prostheses or orthoses.<<ETX>>

Pulmonary lavage in preterm lambs.

Summary: Pulmonary function was studied before and after bilateral lung lavage with oxygenated FC-80 fluorocarbon liquid in seven preterm Iambs, 134 days of gestation. Measurements of transpulmonary pressure, air flow, tidal volume, and functional residual capacity (FRC) enabled calculations of lung resistance and compliance, specific compliance, and work of breathing. Immediately postlav-age, arterial oxygen tension (PaO2) decreased significantly (P < 0.05) by 41% from control values. In addition, at 1 hr postlavage, lung compliance significantly decreased (P < 0.01) by 43% from control levels. Lung resistance, FRC, work of breathing, arterial carbon dioxide tension, and pH postlavage were not significantly different from postlavage values. The mean volume of FC-80 remaining in the lungs at 1 hr postlavage was 32% of the instilled volume. These data indicate that lung lavage with a low surface tension liquid has a relatively small effect on lung mechanics of the premature lung.Speculation: Adequate blood gas tensions and pH levels can be maintained both during and after bilateral fluorocarbon lavage with relatively small changes in lung mechanics. Based upon these findings, it is appealing to speculate that bilateral fluorocarbon lavage may be useful as a means of alveolar debridement, particularly in aspiration syndromes of the newborn.

The identification of time series models of lower extremity EMG for the control of prostheses using Box-Jenkins criteria

The Box-Jenkins method of model identification and diagnostic checking was used on the EMG of the posterio-lateral thigh while contraction level, electrode position, and limb function were varied. Models remained exclusively autoregressive (AR) of order typically less than five for isometric contractions ranging from 25 to 50% of the maximum voluntary knee flexions and extensions, and for recording sites located within 30 mm of the original electrode position. Diagnostics performed on the residuals from AR(4) models indicate that a fourth-order model is adequate for myoelectric control applications under many circumstances.<<ETX>>

An Electromechanical Demand Regulated Liquid Breathing System

The process of breathing liquid requires consideration of several problems not typical in gas respiration. These problems stem from the physical properties of liquid such as density, viscosity, and low diffusivity of gases which increase respiratory work. The objective of this study was to develop and study the feasibility of a demand controlled system for providing mechanical assistance and ameliorating respiratory work during liquid breathing.

Bipedal locomotion stabilized by impact and switching: II. Structural stability analysis of a four-element bipedal locomotion model

A nonlinear model for a four-element bipedal locomotion system, which includes the impact of the swinging limb with the ground and the switching of pivot is developed. The structural stability of the nonlinear, discontinuous model is studied.

Comments on "Upper Extremity Limb Function Discrimination Using EMG Signal Analysis" and the Relationship Between Parallel-Fltering and Hypothesis-Testing Limb Function Classifiers

A continuity which is not readily apparent exists between certain limb function classification algorithms based on time series models of the surface EMG for use in the control of prostheses and orthoses. Superficially, the parallel-filtering system proposed by Graupe et al. [1], [2] appears to be arbitrary, inconsistent, and ad hoc in nature, and has been criticized as such [3] . Doerschuk et al. independentty developed a multichannel decision algorithm for limb function descrinination within the framework of classical detection theory using multiple-hypothesis testing [3]. This conimtihication establishes the fundamental equivalence of the two algorithms by showing that the system advocated by Graupe is in actuality a degenerate form of that proposed by Doerschuk when conditions of equal residual variance and a priori probabilities are met. A theoretical basis for Graupes system is presented and its relationship to the multiple hypothesis test of Doerschuk is derived which unifies the contributions of both groups.