Time spent in parenthood status among adults in the United States

Transition rates estimated from the 1987-1988 and 1992-1994 waves of the National Survey of Families and Households imply that a U.S. adult will spend approximately one third of the years from ages 20 to 69 as a parent of a dependent child. I distinguish biological from social parenthood and provide separate estimates by gender and race. White women conform most to the conventional image of a biological parent residing with an own child, whereas African American women spend the most adult years as a parent. On average, white men spend fewer years as parents than African American men, but African American men spend more years as biological parents not residing with any children. Implications of these descriptive findings are discussed.

A comprehensive noise survey of the S-70A-9 Black Hawk helicopter

PURPOSE

This paper reports the results of a comprehensive noise survey of the Sikorsky S-70A-9 Black Hawk helicopter environment and provides an assessment of the hearing protection devices worn by Australian Army personnel exposed to that environment.

METHODS AND RESULTS

At-ear noise levels were measured at 4 positions in the cabin of the Black Hawk under various flight conditions and at 13 positions outside the Black Hawk under various ground running conditions using the Head Acoustic Measurement System (Head, GmbH). The attenuation properties of the hearing protection devices (HPDs) normally worn by aircrew and maintenance crews (the ALPHA helmet and the Roanwell MX-2507 Communications headset) were also assessed. At-ear sound pressure levels that would be experienced by personnel wearing their normal HPDs were determined at the positions they would normally occupy in and around the aircraft.

CONCLUSION

Results indicate that HPDs do not provide adequate hearing protection to meet current hearing conservation regulations which allow a permissible noise exposure of 85 dB(A) for an 8-h day.

Long-term follow-up of bowel management after spinal cord injury

Although neurogenic bowel is a major sequelae of spinal cord injury (SCI), little is known about long-term outcomes of bowel management. The major purposes of this study were to: 1) describe bowel management programs, 2) determine the prevalence of gastrointestinal (GI) complaints, including evacuation problems and GI symptoms, 3) describe the impact of neurogenic bowel on life activities, 4) describe satisfaction with bowel management and, 5) identify the relationship between outcomes and selected injury characteristics. A telephone survey questionnaire was administered to 171 adults with a mean SCI duration of 8.9 years (SD = 8.9) and mean age of 39.5 years (SD = 14.5). The most common bowel program reported was chemical rectal stimulant (39%). The average dietary fiber intake was 6.8 grams (SD = 4.6). The prevalence of total GI complaints was 90% and 76% during the past year and the past month, respectively. Despite the high prevalence of complaints, overall satisfaction was high. Persons with long-term SCI can benefit from continuing assessment by the rehabilitation team, dietary instruction on fiber needs, and dissemination of information on new methods or treatments. Future research needs include prospective studies to assess change over time and to test interventions to improve outcomes.

Potassium and thallium uptake in dog myocardium

We sought to ascertain the rates and mechanisms of uptake of markers for regional myocardial blood flows.

METHODS

The rates of exchange of potassium and thallium across capillary walls and cell membranes in isolated blood-perfused dog hearts were estimated from multiple indicator dilution curves recorded for 131I-albumin, 42K and 201Tl from the coronary sinus outflow following injection into arterial inflow. Analysis involved fitting the observed dilution curves with a model composed of a capillary-interstitial fluid-cell exchange region and nonexchanging larger vessels.

RESULTS

Capillary permeability surface products (PSc) for potassium and thallium were similar, 0.82 +/- 0.33 (mean +/- s.d., n = 19) and 0.87 +/- 0.32 ml min-1 g-1 (n = 24) with a ratio for simultaneous pairs of 1.02 +/- 0.27 (n = 19). For the myocardial cells, PSpc averaged 3.7 +/- 3.1 ml min-1 g-1 (n = 19) for K+ and 9.5 +/- 3.9 (n = 24) for Tl+; the ratio of potassium to thallium averaged 0.40 +/- 0.19 (n = 18), thereby omitting a single high value for potassium. This high cellular influx for thallium is interpreted as due to its passage through ionic channels for both Na+ and K+.

CONCLUSION

The high permeabilities and large volumes of distribution make thallium and potassium among the best ionic deposition markers for regional flow. Their utility for this purpose is compromised by significant capillary barrier limitation retarding uptake; so regional flow is underestimated modestly in high-flow regions particularly.

Managed care. Past, present, and future

Managed care is now the driving force of the emerging health care provision systems in the United States. It has 2 well-recognized features: (1) its payers (business and government) seem to be pleased with it and (2) its customers and employees (patients and providers) are concerned with its health care provisions and financial practices.

Quality of life after stroke

BACKGROUND AND PURPOSE

The purposes of this study were to examine overall and domain-specific quality of life in long-term stroke survivors and to identify variables that predict quality of life after stroke.

METHODS

The study used a cross-sectional, descriptive correlational design. Subjects were 86 stroke survivors who were interviewed 1 to 3 years after stroke. Quality of life was measured with the use of an instrument that assesses satisfaction and importance for four domains (health and functioning, socioeconomic, family, and psychological-spiritual). Independent variables were age, social class, aphasia, functional status, motor impairment, depression, comorbidity, and perceived social support. Multiple regression analysis was used to predict quality of life.

RESULTS

Thirty percent of subjects scored in the depressed range. The mean overall quality of life score was relatively high and was comparable to that of a normative population. Quality of life was highest for the family domain and lowest for health and functioning. Depression, perceived social support, and functional status predicted quality of life (adjusted R2 = .38) and contributed to prediction of domain quality of life. Social support and three additional variables, social class, age, and cardiovascular disease, predicted socioeconomic quality of life.

CONCLUSIONS

The identification of depression, social support, and functional status as predictors of quality of life suggests the need to assist stroke survivors in coping and in maintaining and strengthening their support systems.

Cerebrospinal fluid and nerve conduction abnormalities in HIV positive individuals

We studied whether there was an association between nerve conduction studies (NCS), CSF, and CD4-T lymphocyte parameters in a large cohort of HIV positive individuals. Two hundred and twenty-eight HIV positive individuals underwent motor and sensory nerve conduction studies, CSF evaluation, peripheral CD4-T lymphocyte count, and neurologic evaluation to determine the presence or absence of peripheral neuropathy. We compared NCS of HIV positive subjects with and without abnormal CSF parameters in the entire cohort. We also compared CSF parameters in a subset of CD4-matched patients with and without neuropathy. CSF abnormalities (in excess of laboratory norms) occurred frequently in the entire study group. There was no statistically significant relationship between NCS and CSF parameters. In addition, there was no significant difference in the CSF findings in the group of patients with clinical neuropathy compared to the group without neuropathy. However, there was an association (p < 0.05) between lower CD4 counts and NCS parameters. In general, abnormal CSF findings are not associated with deteriorating peripheral nerve function in HIV infected patients and are just as likely to be found in an HIV positive patient whether or not a peripheral neuropathy is present.

Modeling blood flow heterogeneity

It has been known for some time that regional blood flows within an organ are not uniform. Useful measures of heterogeneity of regional blood flows are the standard deviation and coefficient of variation or relative dispersion of the probability density function (PDF) of regional flows obtained from the regional concentrations of tracers that are deposited in proportion to blood flow. When a mathematical model is used to analyze dilution curves after tracer solute administration, for many solutes it is important to account for flow heterogeneity and the wide range of transit times through multiple pathways in parallel. Failure to do so leads to bias in the estimates of volumes of distribution and membrane conductances. Since in practice the number of paths used should be relatively small, the analysis is sensitive to the choice of the individual elements used to approximate the distribution of flows or transit times. Presented here is a method for modeling heterogeneous flow through an organ using a scheme that covers both the high flow and long transit time extremes of the flow distribution. With this method, numerical experiments are performed to determine the errors made in estimating parameters when flow heterogeneity is ignored, in both the absence and presence of noise. The magnitude of the errors in the estimates depends upon the system parameters, the amount of flow heterogeneity present, and whether the shape of the input function is known. In some cases, some parameters may be estimated to within 10% when heterogeneity is ignored (homogeneous model), but errors of 15-20% may result, even when the level of heterogeneity is modest. In repeated trials in the presence of 5% noise, the mean of the estimates was always closer to the true value with the heterogeneous model than when heterogeneity was ignored, but the distributions of the estimates from the homogeneous and heterogeneous models overlapped for some parameters when outflow dilution curves were analyzed. The separation between the distributions was further reduced when tissue content curves were analyzed. It is concluded that multipath models accounting for flow heterogeneity are a vehicle for assessing the effects of flow heterogeneity under the conditions applicable to specific laboratory protocols, that efforts should be made to assess the actual level of flow heterogeneity in the organ being studied, and that the errors in parameter estimates are generally smaller when the input function is known rather than estimated by deconvolution.

Modeling membrane transport

Many substrates cross cell membranes by processes other than passive diffusion. When the transport is carrier-mediated, e.g., facilitated diffusion, active transport, and exchange diffusion, the carrier modifies the conductance of the membrane and may either increase or decrease the flux of the substrate across the membrane. A common characteristic of all carrier-mediated transport is its saturability, as only a finite amount of carrier is available to bind with the substrate; even the simplest one-site carrier model exhibits saturation. Inclusion of carrier-mediated transport adds additional model parameters that describe the transporter. In addition, the model must account for both labeled (tracer) and unlabeled (mother) substrate, but this introduces no new parameters. There are many possible models for a membrane carrier. The applicability of these models must be examined for the specific substrate of interest. Many experiments aimed at measuring carrier parameters are carried out on isolated cells or cell fragments. Experiments in intact organs (either in vivo and in vitro) are also possible. Of particular note is the "bolus sweep" method described by Rickaby et al. (1981) and Malcorps et al. (1984). The increasing sophistication of experimental procedures, data collection techniques, and computers available to investigators continues to extend the depth to which we can probe biological systems. With this increased sophistication comes increased costs in time and equipment. It behooves us then to extract the maximum amount of information from each experimental procedure. Mathematical models assist in doing so, and sophistication in model analysis should parallel that in other phases of the experiment. Increased realism brings several advantages. Simplification of a model to increase its ease of usage and speed in routine data analysis is a desirable goal, and comparing a simplified model against a more realistic model under the conditions specific to a given experiment is one way to test the simplifying assumptions. Additionally, increased model realism can bring new insight into unknown aspects of the system. All models, no matter how realistic, are always "wrong" in that they are less complex than the real system. Failure of the model to explain observed results forces us to further refine the model and teaches us something more about the system.

A vascular transport operator

A pulse or a sharp front in concentration of a tracer or a substrate in the blood within a vessel becomes dispersed while being transported along a vessel. Cross-stream mixing and pulsations in flow with the heartbeat cause the dispersion to be less than would occur with a parabolic velocity profile (Newtonian flow). These characteristics allow intravascular mass transport to be described well by a simple two-parameter differential operator, which is a one-dimensional representation of the rather complex real situation. The operator consists of two components in series, a pure delay and a fourth-order linear differential operator. The latter is merely two underdamped second-order operators in series, with fixed relationships between the natural frequencies and damping coefficients. The operator is useful because it provides a transport function with skewness and kurtosis suitable to intravascular transport where the mean velocity profile is blunter than in Newtonian parabolic flow. The parameters of the operator are its mean transit time, t, and its relative dispersion, RD, which is the standard deviation of the response impulse divided by t. The operator transport function describes blood transport through the human leg arterial system, where the RD values are approximately 15-20%.

Topical aspirin in chloroform and the relief of pain due to herpes zoster and postherpetic neuralgia

OBJECTIVE

To determine pain patterns and relationships in patients with herpes zoster and postherpetic neuralgia before and after topical application of aspirin dissolved in chloroform applied to the painful skin surface.

DESIGN

A consecutive series of 42 patients examined and treated in a uniform manner and followed up until their pain subsided or this management mode failed.

SETTING

An ambulatory referral private practice.

PATIENTS

All patients had pain due to herpes zoster or postherpetic neuralgia and were referred for management of severe pain. None refused.

INTERVENTION

Topical application of crushed aspirin tablets dissolved in chloroform.

OUTCOME MEASURES

Short-Form McGill Pain Questionnaire.

RESULTS

All patients reported substantially decreased pain promptly after treatment, with maximum relief at 20 to 30 minutes and lasting 2 to 4 hours. Patients gradually decreased the use of aspirin in chloroform as pain abated.

CONCLUSIONS

Topical aspirin dissolved in chloroform is an effective means of reducing pain due to herpes zoster and postherpetic neuralgia in most patients. The locus of pain origin and analgesia induced by topical aspirin is most likely at cutaneous free-nerve ending pain receptors. The mechanism responsible for the analgesic properties of aspirin is probably not the same as that responsible for its anti-inflammatory properties.

Scotopic spectral sensitivity of the optomotor response in the green treefrog Hyla cinerea

Amphibians are unusual among vertebrates in having two spectral classes of rod photoreceptors, unique amphibian "green" rods and typical vertebrate "red" rods. Although amphibians have been the subject of extensive research on visual function, it is not known whether possession of two classes of rods is a general feature of Amphibia, nor is it clear to what behaviors each class of rods contributes. The Hylidae comprise one of the largest families within Amphibia but have been little studied with respect to visual function. Here, we demonstrate the presence of green and red rods in Hyla cinerea by microspectrophotometry and provide evidence for the contribution of green rods to one visually based behavior, the optomotor response. In addition, we discuss the role of green and red rods in visually based behavior in light of apparently conflicting demands resulting from the need to maximize absolute sensitivity, visual acuity, and color sensitivity.

Peripheral nervous system involvement in a large cohort of human immunodeficiency virus-infected individuals

OBJECTIVE

In individuals who were infected with the human immunodeficiency virus (HIV) we determined the prevalence of peripheral neuropathies (PNs) and explored the relationship between immunologic competence and nerve function.

DESIGN

Cohort survey.

SETTING

US Air Force medical center.

PATIENTS

Population based. Seven hundred ninety-eight of 817 HIV-positive personnel identified by US Air Force HIV screening program from 1985 to 1989. Average age of cohort was 29.2 years. The majority were male with early-stage HIV disease.

MAIN OUTCOME MEASURES

Neurologists examined all subjects for symptoms and signs of PN. We grouped patients by CD4 T-lymphocyte count. We further studied 300 HIV-infected volunteers without clinical evidene of PN by nervex

Clean and sterile intermittent catheterization methods in hospitalized patients with spinal cord injury

The purpose of this study was to compare the incidence of urinary infection using clean intermittent catheterization with the incidence of infection using sterile intermittent catheterization in patients hospitalized with spinal cord injury who were not receiving prophylactic antibiotics. Forty-six patients were assigned randomly to a clean (n = 23) or sterile (n = 23) study group. Catheterizations were done at least every six hours. Infection was defined as bacteriuria greater than or equal to 100,000 organisms/mL or greater than or equal to 10,000 organisms per mL with fever of 100 degrees F or greater. Results of urinary dipslides were recorded daily. Twenty-eight subjects (60.9%) converted to greater than or equal to 100,000 organisms per mL. Method of catheterization was neither associated significantly with development of greater than or equal to 100,000 organisms per mL. (X2[1,46] = .36, p = .55) nor with symptomatic infections (X2[1,46] = .15, p = .70). Data support the use of clean intermittent catheterization under the conditions used in this study, including the use of a sterile catheter each day and careful monitoring of infection and technique. Before using this method with other diagnostic groups or in different clinical settings, further investigation is needed.

Persistent pain inhibits contralateral somatosensory cortical activity in humans

To assess cortical activity during pain perception, regional cerebral blood flow (rCBF) studies were done in humans using single photon emission computed tomography (SPECT) with the radiotracer Tc99m-HMPAO and magnetic resonance imaging localization. Normalized SPECT data were analyzed by region of interest and change distribution. Contralateral somatosensory rCBF was decreased when the digits of the hand were immersed in a hot water bath for 3 min which was rated as moderately painful (persistent pain). No decrease was observed when the hand was immersed in tepid water (control). In contrast, cortical rCBF was increased during vibratory and sensorimotor tasks, in the contralateral somatosensory and sensorimotor areas, respectively. These results indicate that pain perception in man is associated with somatosensory cortical inhibition.

Certification, accreditation, and specialization in the 1990s

Subspecialization was one of the inevitable consequences of merging medicine with science in the early years of this century. The differentiation of human endeavors increases exponentially with new knowledge, technology, and services. Our current patterns of accreditation, certification, and graduate medical education are being seriously challenged by new patterns of subspecialization. How realistically and creatively we respond to this challenge will be a key element in preserving the management of these functions primarily within the purview of the profession.

The neurosciences and neurosurgery

Enhancing the time-honored bonds between the neurosciences and neurosurgery is essential. The basic neurosciences are the foundation upon which fundamental scientific training and clinical research depend. Together these form the resource essential to improving the public health. Both now face severe restraints in the support systems available to them, limited degrees of reciprocity, and uncertain human resources. It is critical that the neurosurgical and neuroscience communities renew and enhance their joint commitment and trust so that both can more effectively work together to secure resources appropriate to maintaining the cutting edge on behalf of the public health.

Molecular and particulate depositions for regional myocardial flows in sheep

The deposition of microspheres in small tissue regions is not strictly flow dependent. In comparison with the soluble flow marker 2-iododesmethylimipramine (IDMI), deposition of 16.5-microns microspheres was mildly but systematically biased into high flow regions of rabbit hearts (Bassingthwaighte JB, Malone MA, Moffett T-C, King RB, Little SE, Link JM, Krohn KA. Am J Physiol 1987;253 (Heart Circ Physiol 22):H184-H193). To examine the possibility of bias in larger hearts, a similar study was undertaken in sheep. 141Ce- and 103Ru-labeled 16.5-microns microspheres in one syringe and 125I- and 131I-DMI in another syringe were injected simultaneously into the left atrium of five open-chest sheep while obtaining reference blood samples from the femoral artery. In six other sheep, one microsphere type and one IDMI were used. Hearts were removed 1 minute after injection, cut into approximately 254 pieces averaging 217 mg, and regional deposition densities calculated for each tracer from the isotopic counts. Correlations in the five animals between the two differently labeled IDMIs and between the two microspheres were both greater than or equal to 0.98. In all 11 sheep, scatter plots of microsphere deposition densities versus IDMI densities showed that differences between microspheres and IDMI had substantially more scatter (0.84 less than r less than 0.98) but were not random. Microsphere depositions tended to be lower than IDMI depositions in low flow regions and higher in high flow regions, in accord with the expected bias that at a bifurcation a microsphere is most likely to enter the branch with higher flow. There was less bias ascribable to endomyocardial/epicardial maldistribution. Thus, while microsphere depositions appear to err systematically with respect to flow when the regions of interest are small enough that the diameters of their arterioles are only a few times those of the microspheres, microspheres are, in sheep as in rabbits, adequate for estimating regional flows.

Fractal descriptions for spatial statistics

Measures of spatial statistics have been available for estimating means, calculating or assessing differences, estimating nearest neighbor distances, and such, but have not provided a general approach to describing variances. Because measures of heterogeneity depend upon choosing a particular element size in the domain, estimates of apparent heterogeneity are larger with high-resolution observations than with low-resolution data. Many descriptors might be used to describe the relationships between apparent heterogeneity and the size of the observed spatial elements, but we have found that fractal relationships provide concise and precise descriptions of many types of data over large ranges of element sizes. Perhaps more importantly, the fractal approaches give additional insight, such as measures of spatial correlation, and often suggest ways of approaching the underlying basis of the heterogeneity.