Moment estimation for chemically reacting systems by extended Kalman filtering.

In stochastic models of chemically reacting systems that contain bimolecular reactions, the dynamics of the moments of order up to n of the species populations do not form a closed system, in the sense that their time-derivatives depend on moments of order n + 1. To close the dynamics, the moments of order n + 1 are generally approximated by nonlinear functions of the lower order moments. If the molecule counts of some of the species have a high probability of becoming zero, such approximations may lead to imprecise results and stochastic simulation is the only viable alternative for system analysis. Stochastic simulation can produce exact realizations of chemically reacting systems, but tends to become computationally expensive, especially for stiff systems that involve reactions at different time scales. Further, in some systems, important stochastic events can be very rare and many simulations are necessary to obtain accurate estimates. The computational cost of stochastic simulation can then be prohibitively large. In this paper, we propose a novel method for estimating the moments of chemically reacting systems. The method is based on closing the moment dynamics by replacing the moments of order n + 1 by estimates calculated from a small number of stochastic simulation runs. The resulting stochastic system is then used in an extended Kalman filter, where estimates of the moments of order up to n, obtained from the same simulation, serve as outputs of the system. While the initial motivation for the method was improving over the performance of stochastic simulation and moment closure methods, we also demonstrate that it can be used in an experimental setting to estimate moments of species that cannot be measured directly from time course measurements of the moments of other species.

Recovery from vegetative state of six months' duration associated with Sinemet (levodopa/carbidopa).

Certain pharmacologic interventions may improve outcome for brain injury in animals and humans. Medications affecting the dopaminergic pathway appear to be important. We present the case of a 24-year-old man with traumatic brain injury who remained unresponsive to commands and unchanged for six months despite periodic aggressive therapy. Within days of beginning Sinemet (levodopa/carbidopa), the patient became conversant and responsive. The reported low likelihood of spontaneous recovery of cognition in patients who are vegetative for six months suggests that Sinemet was responsible for this patient's recovery. In this case, the relatively small risk of side effects from Sinemet was greatly outweighed by the change in functional outcome.

Determinants of vocational disability in patients with low back pain.

Eighty-seven unemployed subjects with low back pain were recruited from an orthopedic back pain clinic and were given a battery of physical and psychologic tests. Subjects were contacted six months later to determine their current compensation status and whether they had returned to work. Age, length of time out of work, how much they had lifted in their previous job, the number of weeks they had been compensated, current activity levels, leg pain, and various psychologic factors significantly differentiated those who worked from those who did not. Physical examination findings and testing of the ability to lift were not significantly related to return to work. It is suggested that demographic, job-related, and psychologic factors should be emphasized, rather than only physical capacity, in the evaluation of vocational potential and the assessment of disability in patients with low back pain.

The right to know: giving the patient his medical record.

Each patient admitted to the 16-bed Rehabilitation Medicine Service at Medical Center Hospital of Vermont since October 1972 has received a carbon copy of his full Admission and Discharge notes, containing the complete problem list, and for each problem the relevant data, the Assessment and the Plans. The objectives were to improve patient education; to improve the patient's chances to contribute to the planning of his care; and to increase the staff's accountability to the patient. Over a period of seven months, we evaluated the effect of this maneuver for 125 consecutive patients by means of (1) a report on the patient's reactions, completed by a nurse after she reviewed the record with the patient; (2) a report by the physician stating whether he had expurgated the record for patient use, and recording his observations of patient and family reaction; (3) a questionnaire mailed to patients after discharge. Results indicated that patients were generally comfortable about reading the record, found it educational and appreciated the trust implied. No substantial difficulties arose. Few records were expurgated. The staff has accepted this style as crucial to an appropriate sharing of responsibility between themselves and the patients. We conclude that giving the patient his record is a safe and inexpensive aid to the rehabilitation process, and is probably mandated by the changing relationships between professionals and their clients, and by the patient's need to negotiate his own health care in an increasingly complex and mobile society.