Bernard Segal

Unilateral Loss of Peripheral Vestibular Function in Patients: Degree of Compensation and Factors Causing Decompensation

Unilateral surgical ablation of peripheral vestibular function has been suggested for the treatment of a number of diseases that involve vestibular dysfunction. The postoperative distressing symptoms usually subside with time, whereupon the patient is said to have clinically compensated. However, even in well-compensated patients, the initial symptoms may reappear—under certain conditions that are briefly discussed (decompensation)—and, in addition, vestibular gaze stabilization deficits, (apparently permanent) appear whenever moderately rapid head movements are imposed. Thus, surgical ablation of unilateral peripheral vestibular function should not be considered “a treatment of choice,” and should be performed in only carefully selected cases.

The electromagnetic environment due to portable sources in a typical hospital room

In order to characterize the electromagnetic environment, due to portable sources, inside a typical Montreal area hospital room, fields were measured in the 148-174 MHz, 425-480 MHz and 825-850 MHz ranges over a period of 24 hours. Call durations in each frequency range remained below 8 seconds 50% of the time, while field levels were 63 dB/spl mu/V/m (1.4 V/m) or lower, 50% of the time. Similar field monitoring in high traffic areas, such as emergency, for longer periods of time, should enable the characterization of call profiles, thereby leading to improved susceptibility testing of medical equipment.

The measured and predicted electromagnetic environment at urban hospitals

The need for electromagnetic compatibility (EMC) is crucial in health care environments, since electromagnetic interference (EMI) effects on critical care medical equipment may be life-threatening. Field strength measurements, made inside and outside five Montreal hospitals at frequencies between 30-1000 MHz, were compared to fields predicted using line-of-sight, and hybrid methods. Although measured fields generally remained below 3 V/m, EMI still caused medical equipment malfunctions at the five hospitals. The line-of-sight prediction method provided a worst-case estimate of the electromagnetic environmental hazard, predicting outside fields to within 20 dB of those measured. The hybrid method predicted fields to within 10 dB.

Measurement of indoor propagation at 850 MHz and 1.9 GHz in hospital corridors

The fields at 850 MHz and 1.9 GHz were measured in five hospital corridors. The field strength tended to decline with distance at a free-space rate within about 2 m of the source, but at a slower rate when further away. Fields at 1.9 GHz declined more slowly than 850-MHz fields. The implications for hospital EMC management are discussed.

Ray optical simulation of indoor corridor propagation at 850 and 1900 MHz

In indoor propagation, the decline in field strength with distance has been modeled as inversely proportional to r/sup n/, where n is found empirically. In this paper, the field strength in a 50 m hospital corridor is computed by geometrical optics. The computed field strength is well represented as declining as 1/r at close distances and as 1/r/sup n/ farther away, with n chosen to minimize the error between the computed field and the r/sup n/ approximate model. Values of n are found for four wall constructions, at 850 and 1900 MHz.

Hospital emergency room electromagnetic environment

The electromagnetic environment of the emergency room of an urban hospital was estimated, characterizing electric fields over a 4.4-day period. Measured fields did not exceed 1 V/m over the 0.1-1 GHz range, but exhibited substantial day-night variation. Such temporal variation was characterized with respect to intensity and frequency of emissions. The observed field level variation implied a substantial temporal variation of electromagnetic-interference-malfunction risk to medical equipment. This risk tended to be highest during the daytime, early evening and weekends.

Specifying zones for cellular telephone operation in hospital hallways

Critical-care medical equipment can malfunction if exposed to radio-frequency (RF) fields greater than the equipments immunity. For newly purchased equipment, such immunity levels are at least 3 V/m. Since fields near a 600-mW, 850-MHz cell phone can greatly exceed this immunity level, hospitals often restrict locations where cell phone usage is permitted, some even banning cellphone usage throughout the hospital. To clarify whether such restriction is appropriate, this paper employs geometrical optics to investigate field strengths in a patient room due to cell phone usage in an adjacent hallway. Cellular-usage zones are maximized when wall construction employs both shielding and absorber elements. Criteria are suggested for specifying zones where cellphone usage should be restricted.

Evaluation of free-space propagation in hospital corridors

It has been proposed that increased usage of wireless communication (e.g. portable radio-frequency (RF) sources; wireless local area networks) should reduce health care costs and improve clinical-care efficiency. However, such increased usage must take place without increasing the risk of electromagnetic interference (EMI) to medical devices. Recommendations for electromagnetic compatibility (EMC) in health care environments have been described [e.g., ref 1]. Central to such recommendations is the requirement to manage RF sources and susceptible medical devices so that their interaction is minimized. It is usually proposed that this be done by specifying a Minimal Separation between RF sources of given power and medical devices of given immunity, assuming that free-space propagation is approximately valid. Alternately, it has been proposed that Zones be specified where approved RF sources and approved medical devices can operate. The latter approach would be required in areas where free-space propagation is invalid. We describe a preliminary study that assesses the validity of free-space propagation in hospital corridors, in order to evaluate whether minimal separations predicted by free-space propagation might safely permit EMC within corridors of a typical urban hospital.

Volumetric 1.9-GHz fields in a hospital corridor: electromagnetic compatibility implications

The current draft of the next medical-equipment EMC standard, IEC 60601-1-2, will recommend usage of free-space minimal separations (between RF sources of given power and medical devices of given immunity) to minimize EMI malfunction of medical equipment. We have previously reported that such separations were useful in most hospital corridors, but such reports were based on mid-corridor measurements. We now describe preliminary three-dimensional 1.9-GHz extensions of these reports. We found that mid-corridor path loss was less than that at corridor walls. Path loss near floors was much less then that at higher locations. Because medical devices are rarely placed on the floor, our previously reported minimum-separation recommendations are still likely to apply at most corridor locations.

Indoor propagation of wireless LAN signals in a hospital and electromagnetic compatibilty implications

The rapid growth of wireless communication associated with usage of cellular phones, PDAs, pagers and other wireless devices has been phenomenal. Yet such growth has not occurred within healthcare, in part due to concerns about electromagnetic interference (EMI) potentially causing malfunction of life-critical medical equipment. Interference with critical-care medical equipment can threaten patient safety [1, 2, 3], and as a result many hospitals have banned cellular telephones, and other wireless sources.