Income, location, and the demand for health care from public, nonprofit, and for-profit hospitals.

Although, empirically, for-profit hospitals serve few poor and indigent patients, they may be able to shift capital more quickly than hospitals of other ownership types, thereby spatially avoiding poor patients. However, in a market with a relatively high proportion of for-profit hospitals, spatial avoidance of poor patients is not possible because spatial competition will exist in non-poor areas. The study examines hospital choice for maternity care in a market with many for-profits using a gravity model or conditional logit. The analysis shows that poor and Medicaid populations choose for-profit hospitals overall. Income, along with distance, is an important factor in hospital choice.

Acute pulmonary edema complicating diagnostic laparoscopy preceded by thoracotomy.

We report the case of a patient with pelvic endometriosis and recurrent spontaneous pneumothoraces who had thoracotomy and diagnostic laparoscopy, with subsequent acute pulmonary edema. Potential causes are discussed. After a thorough literature search, we believe this to be the first case in which thoracotomy has been combined with diagnostic laparoscopy.

Physician demand for leisure: implications for cesarean section rates.

Logistic regression models test whether physician demand for leisure affects both total and unplanned cesarean section rates, after controlling for relevant clinical variables. Although nature distributes births and associated problems uniformly, time-dependent dummy variables related to leisure are significant predictors of both total and unplanned c-sections.

Social and environmental factors in lung cancer mortality in post-war Poland.

Poland and other Eastern European countries have undergone heavy industrial development with marked increases in air pollution and occupational exposure in the nearly 50 years since World War II. These countries have also experienced substantial increases in chronic disease mortality in the past three decades. While it is tempting to assume a direct association between these phenomena, more detailed analyses are called for. Poland offers a potentially rich opportunity for comparing geographical patterns of disease incidence and of industrial change. In this paper we 1) elucidate the prospects for attributing lung cancer mortality to industrial emissions in Poland, using an ecological approach based on the hitherto unaddressed geographic differences, and accounting for regional differences in cigarette consumption; 2) propose explanatory hypotheses for the observed geographic heterogeneity of lung cancer; 3) begin systematic testing of the widely accepted but not well-scrutinized notion that pollution in Poland is a major contributor to declining life expectancy. Regions with the highest fraction of cancer that cannot be explained by smoking appear to be highly urbanized, have high population exposure to occupational carcinogens, experience the highest rates of alcoholism and crime, and are associated with the post- World War II population resettlement. Although the analysis does not rule out pollution as a significant contributor to lung cancer mortality, it indicates that other factors such as occupational exposures and various social factors are of at least comparable importance.(ABSTRACT TRUNCATED AT 250 WORDS)

Guidelines for overseas eye surgery expeditions using short-term volunteers. Surgical Eye Expeditions international.

Many developing countries face the overwhelming problem of addressing preventable and curable blindness. United States-based ophthalmologists can make important contributions in this regard by volunteering to teach and deliver eye care overseas. However, there are a number of potential risks and difficulties. Surgical Eye Expeditions (SEE) International has developed a logistical outline and planning checklist designed to minimize or avoid such problems. Critical components include a firm timetable, advanced planning, advance contact with a local ophthalmologist or organization, and a thorough understanding of the importance of adapting to the needs of other cultures. With a little planning, the average philanthropic ophthalmologist can make major contributions to individuals and communities in developing nations.

Muscle strengthening in a post-polio subject through a high-resistance weight-training program.

A 48-year-old woman started experiencing increased muscle weakness and fatigue at age 44, 40 years after the onset of acute poliomyelitis. The acute poliomyelitis resulted in severely weak lower limb muscles and as a result, she had used crutches for more than 40 years. Computer-aided force transducer systems were used to determine isometric muscle strength. Both quadriceps and left ankle dorsiflexors were severely weak and could not generate any measurable force. Isometric muscle strength of her right ankle dorsiflexors was 77 Newtons (N) (approximately 1/3 normal); isometric muscle strength of right elbow flexors (171N) and left elbow flexors (160N) were within normal range, although she complained of weakening based on her inability to climb two stairs at a time with crutches as she was used to. She underwent high-resistance weight training of her right ankle dorsiflexors and left elbow flexors for one year. Weight training was three times per week, five sets of ten repetitions per session; total duration of muscle contraction (excluding rest periods) was two and one half minutes per session, 30 minutes per month. Muscle strength (N) was remeasured after four, eight, and 12 months. Muscle strength of right ankle dorsiflexors increased by 61%, whereas that of the left elbow flexors increased by 32% after one year of weight training. She also expressed a subjective feeling of increased muscle strength. High-resistance, short duration muscle strengthening exercise programs should therefore be given a serious consideration in the rehabilitation management of moderately weak muscles of post-polio subjects.

Exposure to tetrachloroethylene via contaminated drinking water pipes in Massachusetts: a predictive model.

A computer model was developed to estimate exposure to tetrachloroethylene leaching from drinking-water pipes in Massachusetts between 1968 and 1979. The model was to be used for an epidemiologic study of cancer in five communities in Massachusetts. This model assigned a relative cumulative exposure score to each individual participant in the study, based on the geometry, size, age, and water flow through the water pipe that supplied a particular household and on the individual's duration of residence in that household. The results of modeling showed a wide range of exposure levels among the study participants. The epidemiologic study is described in the accompanying paper by Aschengrau et al.

Pharmacokinetics of the dermal route of exposure to volatile organic chemicals in water: a computer simulation model.

A kinetic model of dermal absorption of nonpolar organic nonelectrolytes in dilute aqueous solutions is described. The model uses systems dynamics STELLA software and is designed for a Macintosh computer. The model assumes the outer stratum corneum layer of skin to be the rate-determining barrier to dermal absorption and assumes that both stratum corneum and viable epidermal layers have storage capacity for lipophilic solutes. The model predicts between 30 and 94% of experimental results with humans under the same conditions. The degree of departure between experimental and theoretical results is inversely related to the solute's octanol/water partition coefficient, which is consistent with the most recently hypothesized mechanisms of transport of molecules across the dermal barrier. The model has potentially useful applications for risk assessment if used within its defined limits.

Myotonic dystrophy: quantification of muscle weakness and myotonia and the effect of amitriptyline and exercise.

The purpose of this study was to quantify the degree of muscle weakness and myotonia in 12 patients with myotonic dystrophy (MD), and to quantitatively determine the effects of a four- to six-month therapeutic trial of amitriptyline. Patients had exercised with weights for one or more years. Some had shown initial improvement in muscle strength, but had reached a plateau; others had not improved when the study began. Muscle weakness was quantified by comparing the five-second maximum voluntary contraction (MVC) in newtons (N) per kg (body weight) of 12 patients and 20 healthy subjects. Knee extensor, elbow flexor, and first dorsal interosseous (FDI) muscles were compared. Myotonia was quantified by measuring relaxation times (RTs) at the end of the five-second MVC produced by FDI, as the time taken for the MVC to decrease by 50% and 75% (referred to as 1/2 and 3/4RT). The results were as follows: (1) the mean muscle strength of each of the three muscles of the patients was significantly (p less than .001) reduced compared with healthy subjects; and (2) 1/2 and 3/4RT means of the patients (vs healthy subjects) were significantly prolonged (p less than .01). Eight of the patients participated in a therapeutic trial of amitriptyline. Therapeutic effects were quantified by measuring muscle strength, 1/2 and 3/4RT, and percent change in evoked muscle action potential (MAP) from the FDI muscle after a ten-second MVC, to determine change in excitability. Mean muscle strength of FDI improved from .27 to .33N/kg, (p less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased muscular fatigue in patients with neurogenic muscle weakness: quantification and pathophysiology.

The strength of maximum voluntary contraction (MVC) and muscular fatigue measured from ankle dorsiflexors and knee extensors of 15 patients with neurogenic muscle weakness was compared with those of 20 healthy subjects. Muscle weakness, defined as the failure to generate the expected force, was determined by two methods: (1) manual muscle testing and (2) measurement of MVC using a force transducer. Muscle strength was then quantified as the MVC in Newtons (N)/kg body weight. The percent decrease in both MVC (the Fatigue Index [FI]), and rectified-integrated electromyogram (RIEMG) at the end of 60sec of sustained MVC were computed. There were three main findings. (1) Muscle strength was significantly (p less than 0.001) reduced in both muscles of the patient group: in ankle dorsiflexors, means = 1.62 +/- 0.7N/kg vs 4.8 +/- 0.5N/kg; in knee extensors, means = 3.2 +/- 1.8N/kg vs 7.8 +/- 1.5N/kg. (2) Fatigue was significantly greater (p less than 0.01) in the patient group: for ankle dorsiflexors, means = 50 +/- 15% vs 34 +/- 13%; and for knee extensors, means = 62 +/- 17% vs 46 +/- 15%. There was a negative correlation between muscle strength and FI of only the knee extensors of the patients (r = -0.88, p less than 0.001). (3) The mean decline in RIEMG of the two muscles combined was also significantly greater (p less than 0.001) in the patient group (means = 48 +/- 16% vs 2 +/- 11%).(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of normal portal venous blood flow by Doppler ultrasound.

The volume flow rate of blood in the portal vein was measured using a duplex ultrasound system. The many errors inherent in the duplex method were assessed with particular reference to the portal vein and appropriate correction factors were obtained by in vitro calibration. The effect of posture on flow was investigated by examining 45 healthy volunteers in three different positions; standing, supine and tilted head down at 20 degrees from the horizontal. The mean volume blood flow in the supine position was 864 (188)ml/min (mean 1SD). When standing, the mean volume blood flow was significantly reduced by 26% to 662 (169)ml/min. There was, however, no significant difference between flow when supine and when tilted head down at 20 degrees from the horizontal.

Muscle strengthening through electric stimulation combined with low-resistance weights in patients with neuromuscular disorders.

Ten patients with gradually progressive neuromuscular disorders underwent (1) unilateral electric stimulation of anterior tibialis muscles and (2) unilateral stimulation of quadriceps femoris muscles, in combination with voluntary knee extension against ankle weights. After electric stimulation two hours/day, five days/week for two to 14 months, the mean maximum force (muscle strength) of knee extension increased significantly (p less than 0.005), by 108% +/- 56%. The contralateral nonexercised knee extensors also showed some increase in muscle strength. Electric stimulation of ankle dorsiflexors was ineffective; the maximum force of ankle dorsiflexion increased by only 11% +/- 27% (p greater than 0.3). In general, severely weak muscles (less than 10% normal strength) did not improve with either stimulation program. Electric neuromuscular stimulation combined with low-resistance weights can significantly increase muscle strength in patients with neuromuscular disorders if disease progression is gradual and initial muscle strength is greater than 15% normal.

Muscle strengthening through high-resistance weight training in patients with neuromuscular disorders.

The effects of weight training on muscle performance were quantified by measuring (1) maximum force (muscle strength), (2) force-time integral--area under force-time plot during 60 seconds of sustained maximum force (work done), and (3) fatigue index--percentage reduction in maximum force. Subjects included 16 patients with gradually progressive neuromuscular disorders. The muscle strength of these patients ranged from 2% to 75% normal before the program. For patients with markedly to moderately weak muscles, maximum force increased by 80% +/- 48%, force-time integral increased by 132% +/- 93%, and mean fatigue index was significantly reduced from 53% +/- 18% to 34% +/- 7.7% during the study period. Severely weak muscles (less than 10% normal strength) generally did not improve. High-resistance weight training can significantly increase muscle performance of patients with neuromuscular disease if disease progression is slow and initial muscle strength is greater than 15% normal.

Effects of fatiguing exercise on high-energy phosphates, force, and EMG: evidence for three phases of recovery.

Experiments were designed to evaluate the relative contribution of impulse propagation failure, high-energy phosphate depletion, lowered pH, and impaired excitation-contraction coupling to human muscle fatigue and recovery. 31P nuclear magnetic resonance spectroscopy measurements were made on adductor pollicis muscle, together with simultaneous measurements of M-wave, force, and rectified integrated EMG (RIEMG). During fatigue, maximum voluntary contraction force (MVC) fell by 90%, pH fell from 7.1 to 6.4, and phosphocreatine was almost totally depleted. Neuromuscular efficiency (NME = force/RIEMG) was reduced to 40% of control at the end of the fatiguing contraction, and the M wave was reduced in amplitude and prolonged in duration. Following exercise, the M wave returned to normal within 4 minutes. pH, high-energy phosphates, and MVC recovered within 20 minutes. By contrast, neuromuscular efficiency did not recover within 60 minutes. These findings indicate three different components of fatigue. The first is reflected by the altered M wave and indicates impaired muscle membrane excitation and impulse propagation. The second, associated with reduced MVC, correlates with the metabolic state of the muscle (PCr and pH). The third, indicated by reduced NME, is independent of changes in high-energy phosphates and pH and is probably due to impaired excitation-contraction coupling.

Chemical Health Effects Assessment Methodology for airborne contaminants.

Chemical Health Effects Assessment Methodology (CHEM) is a new procedure for assessing hazardous properties of airborne toxic contaminants. CHEM evaluates substances for four major health effect categories: carcinogenicity, mutagenicity, reproductive/developmental toxicity, and toxic effects other than the first three. Three elements are considered in the assessment: weight of evidence, potency, and severity of effect. This approach produces a profile of toxic properties of chemicals which preserves their unique multidimensional character and highlights data gaps.

Quantitative correlation between plasma pyridostigmine levels and neuromuscular function in myasthenia gravis.

In 10 patients with myasthenia gravis, we studied the relationship between plasma pyridostigmine levels and five measures of neuromuscular function (NMF) following single oral doses of 60 to 120 mg. The NMF measures were percent decrement of the evoked muscle compound potential, maximum force, force-time integral, vital capacity, and outstretched-arm time. The combined mean improvement was most significant 2 hours after pyridostigmine ingestion and coincided with the peak plasma pyridostigmine levels in eight patients. In seven patients, there was a positive correlation between plasma pyridostigmine levels and the mean percent improvement.

A methodology for assessing mutagenic hazards of chemicals.

A comprehensive framework for identifying substances which represent a potential threat to public health due to mutagenicity and for relative ranking of their hazards has been developed. The methodology is designed to evaluate a range of genotoxic endpoints of potential significance to humans and is not merely a substitute for, or an adjunct to, the carcinogenicity assessment. A range of endpoints in both somatic and germ cells is considered. The biological test systems utilized here include humans and other mammals, bacteria, Drosophila, yeasts, molds, and plants. Bioassays conducted in vivo and in vitro, with and without metabolic activation, are included. Seventy-five different assays are considered, of which 73 are currently included in the Gene-Tox database. The tests are grouped into three categories on the basis of significance to humans, as well as sensitivity, specificity, validity, and reliability. Seven in vivo mammalian tests comprise Group I. The remaining 68 tests are divided between Groups II and III, in a decreasing order of significance and confidence in the tests. Tests with virtually identical endpoints and organisms are listed together. The system accomplishes two tasks: 1) organizes the data from short-term tests on chemicals, and 2) classifies chemicals into one of five hazard categories, designated by letters A to E, on the basis of that information. Classification into hazard categories depends on the overall strength of evidence that an agent may cause mutations in humans. Generally, score for each chemical is a function of the number and combination of results in each of the three groups of tests. Specifically, it is derived by weighing several variables: the number and type of endpoints measured, the number and type of species represented, the significance of positive and non-positive results, the relevance of specific tests for predicting effects in humans, the group classification (I, II or III) of each test result and the overall pattern presented. Assessment of data for one hundred chemicals shows a good representation of scores from A to E, with category E most commonly represented, followed by D and C.