Characteristics of a simple measure of respiratory impedance

The ratio of mouth pressure developed 0.1 sec after occlusion at end-expiration (P0.1) to average inspiratory flow rate (VT/TI) has been proposed as 'effective inspiratory impedance', Imeff. We have studied a simple mathematical model of lung mechanics, consisting of an effective resistance, an effective compliance and a single pressure generator, to learn how Imeff is altered by changes in resistance (R), compliance (C), inspiratory duration (TI), and the degree of curvature of the inspiratory pressure wave form. The degree of curvature was varied between concave with respect to the time axis to convex and included a linear inspiratory muscle pressure function. Assuming a linear pressure function, we obtained an explicit equation for Imeff as a function of R, C, and TI. Using the same model we also studied the classical impedance as a function of R, C and frequency (of a sinusoidal excitation pressure). We found that Imeff was increased by increases in R, increasing degrees of concavity, decreases in C, and by decreases in TI. For this model the classical impedance was about 5 times larger than Imeff. Classical impedance was increased by increases in R, decreases in C, and decreases in excitation frequency. In conclusion, measurements of effective inspiratory impedance need to be interpreted in terms of R, C, TI, and the shape of the inspiratory muscle pressure function.     

Survival rates in NYC in the era of combination ART

BACKGROUND: Since the advent of combined antiretroviral therapy in 1996, substantial decreases in HIV-related morbidity and mortality have been observed in the United States and other developed countries. To assess the effects on overall survival and for specific AIDS-defining illnesses (ADIs), survival among persons with AIDS (PWAs) in New York City (NYC) before and after the introduction of combination therapy was investigated. METHODS: Survival among 79,878 PWAs diagnosed between 1990 and 1998 and reported through March 2001 was estimated. Cumulative survival at 24 months among PWAs was estimated by actuarial methods, and Cox proportional hazards model adjusted for covariates was used to estimate the relative hazard (RH) of death for specific ADIs over time. RESULTS: Overall cumulative survival at 24 months increased from 43% among PWAs diagnosed during 1990-1995 to 76% for those diagnosed 1996-1998. Improving survival for all ADIs was found among PWAs diagnosed after 1995, but changes for immunoblastic lymphoma, primary lymphoma of the brain, and invasive cervical cancer were only moderate and were statistically (p >.05) insignificant. Burkitt lymphoma, immunoblastic lymphoma, invasive cervical cancer, and primary lymphoma of the brain had the highest RH of death among PWAs diagnosed after 1995. CONCLUSIONS: Substantial improvements in survival after 1995 were found for all PWAs but varied by gender, race, risk, socioeconomic status, and specific ADIs. Consistent with other studies, neoplastic ADIs have shown less improvement than other diseases after 1995. The relatively poor outcome of PWAs with neoplastic diseases requires further investigation.     

Acute back pain: A control-group comparison of behavioral vs traditional management methods

Back-pain patients with onset in the preceding 1–10 days and comparable on a back examination were randomly assigned to traditional management (A regimen) and behavioral treatment methods (B regimen). Patients were compared at 6 weeks and 9–12 months on a set of Sick/Well scores derived from patient reported vocational status (V), health-care utilization (HCU), claimed impairment (CI), and pain drawings (D) and on two measures of activity level. No differences were found at 6 weeks, but at 9–12 months, A-group S's were more sick. No A/B differences were found on activity-level measures. Group A S's showed significant increases in claimed impairment from preonset to follow-up, whereas Group B S's had returned at follow-up to preonset levelsA special acknowledgment is made to Darnel Rock, M.S., now of the Department of Psychology, Vanderbilt University, for his major contributions to the organization and analysis of the data of this study.     

Partial deletion of 14q and partial duplication of 14q in sibs: Testicular mosaicism for t(14q;14q) as a common mechanism

The propositus and a subsequently born sister presented with multiple congenital anomalies. Chromosome analyses were performed initially on peripheral blood lymphocytes from the propositus and his parents: the propositus was found to have a deletion of chromosome 14 (q32.11->qter); the parents' chromosomes were normal. When the sister of the propositus was born, she was determined to have a duplication of an equivalent segment of 14qter. Chromosome studies on the parents' fibroblasts demonstrated no structural abnormality or mosaicism. The parents have an older, phenotypically normal, healthy daughter, which supports mosaicism for intragonadal t(14;14)(q32.11;q32.33) in one parent. Chromosome polymorphism comparisons show that the normal number 14 chromosome in the propositus and his sister was inherited from the mother, thus indicating paternal testicular mosaicism. Clinical findings are compared to those of other reported cases of deletion 14q and duplication 14q.     

Quality management of human resources. Providers should begin by focusing on education, performance management, and reward systems

For a quality management transformation to occur, a healthcare organization must focus on education and development, performance management, and recognition and reward systems during the first years of implementation. Education and development are perhaps the most important human resource management functions when implementing quality management principles and processes because behavioral changes will be required at all organizational levels. Specific programs that support an organization's quality management effort will vary but should include the conceptual, cultural, and technical aspects of quality management. The essence of quality management is to always satisfy the customer and to continuously improve the services and products the organization offers. The approach to performance management should therefore rely on customer feedback and satisfaction. An organization committed to quality management should base its performance management approach on customer orientation, process improvement, employee involvement, decision making with data, and continuous improvement. Managers and trustees are being challenged to provide innovative recognition and reward systems that reinforce the values and behaviors consistent with quality management. Such systems must also be aligned with the behaviors and outcomes that support the philosophy, mission, and values of the Catholic healthcare ministry. The following components should be considered for a recognition and reward system: base pay, incentives, benefits, and nonmonetary rewards.     

Intermaxillary fixation is not usually necessary to reduce mandibular fractures

We undertook a retrospective study of all isolated mandibular fractures which had required active management over a 1-year period at the Maxillofacial Unit at Newcastle General Hospital. Patients with single or multiple fractures of the mandible were included in the study, if there were other simultaneous fractures of the facial skeleton, those patients were excluded. All case notes and radiographs were reviewed by a single operator. A total of 202 cases of fractured mandible were identified of which 115 fulfilled the selection criteria of: isolated fracture, no previous facial fracture, treatment by open reduction and internal fixation using titanium osteosynthesis miniplates, and all case notes and radiographs available to study. Sixty-six patients had their fractures reduced manually to obtain anatomical reduction without the use of peroperative intermaxillary fixation (IMF). Forty-nine were treated conventionally using peroperative IMF. The two groups were broadly similar in severity and type of fracture, and the method of reduction seemed to be decided by the operator according to their preference. IMF was not used routinely postoperatively. Overall there were significantly fewer occlusal discrepancies in the early postoperative period in those patients treated by anatomical reduction (6/66 compared with 16/49, P = 0.002) but there was no difference in the final outcome of the occlusion between the two methods of reduction. Avoidance of the use of peroperative IMF is more economical in time and cost, is safer for the operator, and more comfortable for the patient. As this technique produces comparable results in the long term with fewer early complications, we conclude that IMF is not usually necessary to reduce fractures confined to the mandibular bone.     

Regulation of PaCO2 during rest and exercise: A modeling study

A nonlinear mathematical model of the CO₂ control system was used to examine a number of issues concerning the regulation of PaCO₂ during rest and exercise. To gain insight to the regulatory properties of the respiratory system, the open loop gain (G_l) and closed loop sensitivities S_i=ξPaCO₂/ξPiCO₂ and were calculated. Gl indicates the ability of a control system to regulate the controlled variable, PaCO₂ in the model. Si and Sv represent the change in PaCO₂ to unit changes in PiCO₂ and , respectively. Model predications were obtained for rest and various intensities of exercise for the following challenges to the respiratory system: (a) CO₂ inhalation, (b) i.v. CO₂ loading, (c) application of an external dead space, and (d) a shift in the resting operating point. Increasing exercise intensity produced a substantial decrease in Gl and increase in Si consistent with the hypothesis that exercise degrades the ability of the respiratory system to regulate PaCO₂. However, Sv decreased indicating that the respiratory system would actually be better able to regulate PaCO₂ if there were fluctuations in . Thus, Gl does not completely describe the regulatory characteristics of the respiratory control system. It is demonstrated that the regulatory characteristics of the respiratory system as described by Gl, Si, and Sv are complex and depend on the nature of the challenge. Techniques for systematically describing the regulatory properties of the CO₂ control system are described.     

Biological Plasticity in Penguin Heat‐Retention Structures

Insulation and vascular heat‐retention mechanisms allow penguins to forage for a prolonged time in water that is much cooler than core body temperature. Wing‐based heat retention involves a plexus of humeral arteries and veins, which redirect heat to the body core rather than to the wing periphery. The humeral arterial plexus is described here for Eudyptes and Megadyptes, the only extant penguin genera for which wing vascular anatomy had not previously been reported. The erect‐crested (Eudyptes sclateri) and yellow‐eyed (Megadyptes antipodes) penguins both have a plexus of three humeral arteries on the ventral surface of the humerus. The wing vascular system shows little variation between erect‐crested and yellow‐eyed penguins, and is generally conserved across the six extant genera of penguins, with the exception of the humeral arterial plexus. The number of humeral arteries within the plexus demonstrates substantial variation and correlates well with wing surface area. Little penguins (Eudyptula minor) have two humeral arteries and a wing surface area of ～ 75 cm², whereas emperor penguins (Aptenodytes forsteri) have up to 15 humeral arteries and a wing surface area of ～ 203 cm². Further, the number of humeral arteries has a stronger correlation with wing surface area than with sea water temperature. We propose that thermoregulation has placed the humeral arterial plexus under a strong selection pressure, driving penguins with larger wing surface areas to compensate for heat loss by developing additional humeral arteries. Anat Rec, 2012. © 2011 Wiley Periodicals, Inc.     

Understanding APRN Distribution in the United States Using NPI Data

This study examined the 2010 Centers for Medicare and Medicaid Services National Plan and Provider Enumeration System's National Provider Identifier (NPI) data to ascertain their usefulness to determine the distribution of advanced practice registered nurses (APRNs) in rural and urban areas of the United States. This study showed that certified registered nurse anesthetists were more likely to practice in rural areas in states with greater practice autonomy. For nurse practitioners, the findings were similar but were of borderline statistical significance. These findings imply that practice autonomy should be considered as a state-level strategy to encourage rural practice by APRNs.