Cavitation in medicine.

We generally think of bubbles as benign and harmless and yet they can manifest the most remarkable range of physical effects. Some of those effects are the stuff of our everyday experience as in the tinkling of a brook or the sounds of breaking waves at the beach. But even these mundane effects are examples of the ability of bubbles to gather, focus and radiate energy (acoustic energy in the above examples).

Improvement of acoustic theory of ultrasonic waves in dilute bubbly liquids.

The theory of the acoustics of dilute bubbly liquids is reviewed, and the dispersion relation is modified by including the effect of liquid compressibility on the natural frequency of the bubbles. The modified theory is shown to more accurately predict the trend in measured attenuation of ultrasonic waves. The model limitations associated with such high-frequency waves are discussed.

Statistical equilibrium of bubble oscillations in dilute bubbly flows.

The problem of predicting the moments of the distribution of bubble radius in bubbly flows is considered. The particular case where bubble oscillations occur due to a rapid (impulsive or step change) change in pressure is analyzed, and it is mathematically shown that in this case, inviscid bubble oscillations reach a stationary statistical equilibrium, whereby phase cancellations among bubbles with different sizes lead to time-invariant values of the statistics. It is also shown that at statistical equilibrium, moments of the bubble radius may be computed using the period-averaged bubble radius in place of the instantaneous one.

Isolation of Staphylococcus aureus from the urinary tract: association of isolation with symptomatic urinary tract infection and subsequent staphylococcal bacteremia.

Background: Staphylococcus aureus is frequently isolated from urine samples obtained from long-term care patients. The significance of staphylococcal bacteriuria is uncertain. We hypothesized that S.

Pressure wave propagation in a shaken granular bed.

Pressure waves in a granular material travel through particle contact points and are primarily transmitted by the "force chains" that carry most of the load in a granular medium. However, these force chains tend to be fragile and ephemeral and can be disrupted by very minor perturbations including the waves themselves. External vibration also disrupts the force chains and therefore also changes the wave propagation characteristics.

Pressure wave propagation in a granular bed.

The transmission of pressure waves in granular materials is complicated by the heterogeneity and nonlinearity inherent in these systems. Such waves are propagated through particle contacts primarily along the "force chains" which carry most of the load in granular materials. These fragile and ephemeral chains coupled with irregular particle packing lead to the observed heterogeneity.

Lumped parameter model for computing the minimum pressure during mechanical heart valve closure.

The cavitation inception threshold of mechanical heart valves has been shown to be highly variable. This is in part due to the random distribution of the initial and final conditions that characterize leaflet closure. While numerous hypotheses exist explaining the mechanisms of inception, no consistent scaling laws have been developed to describe this phenomenon due to the complex nature of these dynamic conditions.

Injection of highly supersaturated oxygen solutions without nucleation.

It is possible to inject highly supersaturated aqueous solutions of gas through a small capillary into an aqueous environment without the formation of significant gas bubbles. Such a technique has considerable potential therapeutic value in the treatment, for example, of heart attacks and strokes. The present paper is the second in a series (see Brereton et al.

Pneumonia in long-term care: a prospective case-control study of risk factors and impact on survival.

Background: Pneumonia is a major cause of morbidity and mortality in long-term care facilities. Prior studies of pneumonia have failed to identify risk factors potentially amenable to intervention. Our objectives were to (1) identify modifiable risk factors for the occurrence of pneumonia and (2) determine the long-term impact of pneumonia on survival.

Legionnaires' disease in a newly constructed long-term care facility.

Objectives: To determine whether a newly-constructed long-term care facility would become colonized with Legionella and whether Legionnaires' disease would occur in residents of this new facility.

Design: Prospective environmental surveillance of the hospital's water distribution system for the presence of Legionella pneumophila during construction. Utilization of diagnostic tests for Legionnaires' disease in cases of nosocomial pneumonia.

Vancomycin-resistant Enterococcus faecium in a long-term care facility.

Objective: To describe the epidemiology and natural history of colonization with vancomycin-resistant Enterococcus faecium (VREF) in a long-term care facility.

Design: All patients in whom VREF was isolated were followed prospectively, with rectal swab cultures at 2-week intervals, until discharge, death, or clearance of VREF. Clearance was defined as two consecutive negative cultures.

Multiply antibiotic-resistant gram-negative bacilli in a long-term-care facility: a case-control study of patient risk factors and prior antibiotic use.

Objective: To determine the relation between prior exposure to specific antimicrobials and acquisition of gram-negative bacilli resistant to multiple beta-lactam and aminoglycoside antibiotics among long-term-care patients.

Design: Case-control study. Cases were patients from whom multiply resistant Enterobacteriaceae or Pseudomonas aeruginosa were isolated; controls were patients from whom nonresistant bacteria of the same species were isolated.

Pneumonia in a long-term care facility. A prospective study of outcome.

Background: Pneumonia is a major cause of morbidity and mortality among patients in long-term care facilities.

Objectives: To conduct a prospective study of 108 consecutive patients who acquired pneumonia in a Veterans Affairs facility from January through December 1993, and to identify (1) the short- and long-term outcome of pneumonia, (2) the determinants of outcome, and (3) the frequency of recurrent episodes.

Methods: Patient characteristics, including scores from the Activities of Daily Living (ADL) Index of Katz et al and the Comorbidity Index of Charlson et al, were recorded End points were survival at 14 days and 12 and 24 months, recurrent episodes of pneumonia, and hospitalization for nonpneumonic illness.

Infection with methicillin-resistant Staphylococcus aureus among hospital employees.

Objective: To describe the spectrum of clinical infection caused by methicillin-resistant Staphylococcus aureus (MRSA) in healthcare workers.

Design: Case series.

Setting: Two Veterans Affairs hospitals in which methicillin-resistant S aureus (MRSA) is endemic.

Choosing appropriate criteria for tuberculin positivity and conversion in a long-term care facility.

Objectives: The Centers for Disease Control and Prevention has issued new criteria for conversion of the tuberculin skin test; in persons over 35 years of age, an increase in induration of at least 15 mm is considered indicative of new tuberculous infection. We reviewed our experience in a tuberculosis control program in a long-term care facility to assess the applicability of the new criteria to our patient population.

Design: Retrospective review of seven years of tuberculosis control records and outbreak investigation.

Bacteremia in a long-term-care facility: a five-year prospective study of 163 consecutive episodes.

The clinical features, microbiological characteristics, and outcomes of 163 episodes of bacteremia occurring at a long-term-care facility were evaluated. The rate of nosocomial bacteremia increased from 0.20 to 0.

Use of ciprofloxacin versus use of aminoglycosides for therapy of complicated urinary tract infection: prospective, randomized clinical and pharmacokinetic study.

The efficacy of oral ciprofloxacin was compared with that of parenteral aminoglycoside for therapy of complicated urinary tract infection in a prospective randomized trial. The setting was a chronic-care Veterans Administration facility in which long-term bladder catheterization and resistant bacteria were common. Sixty-five consecutive patients were stratified for presence and type of bladder catheter, the presence of Providencia and Pseudomonas aeruginosa organisms versus other urinary pathogens, and renal dysfunction.

Association with prior fluoroquinolone therapy of widespread ciprofloxacin resistance among gram-negative isolates in a Veterans Affairs medical center.

We performed a case-control study of risk factors for the acquisition of ciprofloxacin-resistant gram-negative isolates in a Veterans Affairs medical center. Sixty-five patients with resistant isolates and 50 control patients were identified. Prior fluoroquinolone use was significantly more frequent among patients with resistant isolates than it was among controls (58 versus 20%; P = 0.

Nonlinear effects in the dynamics of clouds of bubbles.

This paper presents a spectral analysis of the response of a fluid containing bubbles to the motions of a wall oscillating normal to itself. First, a Fourier analysis of the Rayleigh-Plesset equation is used to obtain an approximate solution for the nonlinear effects in the oscillation of a single bubble in an infinite fluid. This is used in the approximate solution of the oscillating wall problem, and the resulting expressions are evaluated numerically in order to examine the nonlinear effects.

Methicillin-resistant staphylococcal colonization and infection in a long-term care facility.

Objective: To determine the natural history of colonization by methicillin-resistant Staphylococcus aureus (MRSA) among patients in a long-term care facility. We specifically sought to determine if MRSA colonization was predictive of subsequent infection.

Design: Cohort study.

Conjunctivitis associated with methicillin-resistant Staphylococcus aureus in a long-term-care facility.

Purpose: To determine the clinical characteristics of conjunctivitis associated with methicillin-resistant Staphylococcus aureus (MRSA) in a long-term-care facility.

Patients And Methods: We followed 20 episodes of MRSA-associated conjunctivitis in 19 patients occurring over a three-year period in a 432-bed long-term-care facility.

Results: The clinical picture was that of a purulent conjunctivitis from which MRSA was isolated on culture.

Occult endemic tuberculosis in a chronic care facility.

During the course of a tuberculosis skin testing program at a chronic care Veterans Administration Medical Center, we uncovered evidence of occult transmission of endemic tuberculosis. Skin test conversion of eight patients (one of whom had unsuspected progressive primary tuberculosis) and two employees was ultimately traced to a patient in whom tuberculosis was first diagnosed at autopsy three years earlier. Identification of employee skin test conversions was a key factor in recognizing and terminating disease transmission.

A prospective study of nosocomial infections in a chronic care facility.

To elucidate the epidemiology of nosocomial infections occurring in nursing homes and chronic care facilities, the authors undertook a prospective study of patients requiring two different levels of nursing care. The overall rate of infection was higher on the intermediate care ward than on the nursing home ward (1.35 versus 0.