Toward consistent definitions for preload and afterload.

Significant differences exist among textbook definitions for the terms preload and afterload, leading to confusion and frustration among students and faculty alike. Many faculty also chose to use in their teaching simple terms such as "end-diastolic volume" or "aortic pressure" as common-usage approximations of preload and afterload, respectively, but these are only partial representations of these important concepts. Straightforward definitions both of preload and afterload that are concise yet still comprehensive can be developed using the Law of LaPlace to describe the relationships among chamber pressure, chamber radius, and wall thickness. Within this context, the term "preload" can be defined as all of the factors that contribute to passive ventricular wall stress (or tension) at the end of diastole, and the term "afterload" can be defined as all of the factors that contribute to total myocardial wall stress (or tension) during systolic ejection. The inclusion of "wall stress" in both definitions helps the student appreciate both the complexities of cardiac pathophysiology and the rationale for therapeutic intervention.

Race/ethnicity and OMB Directive 15: implications for state public health practice.

OBJECTIVES: This study assessed the impact of the Office of Management and Budget's (OMB's) 1997 revised standards for the collection of race and ethnicity data on state health departments, using the Massachusetts Department of Public Health (MDPH) as the primary example, and we make recommendations for states' implementation of these standards. METHODS: After analyzing the revised OMB standards, existing MDPH data sets were assessed for the impact of the revised standards on data collection, tabulation, analysis, and reporting for state health departments. RESULTS: The revised OMB standards will have an impact on the MDPH and other state health departments. Similarities and differences exist between federal and state health agencies regarding the purpose of data collection, tabulation, analysis, and reporting. These similarities and differences will affect state implementation of the revised OMB standards. CONCLUSIONS: States need to plan for the implementation of the revised OMB standards and to understand the impact of this revision on the collecting and reporting of public health data. The revised OMB standards will introduce added complexities to the collection and analysis of race and ethnicity data, but they will also produce a more nuanced understanding of the relationship of race and ethnicity to the health of the American people.

A visual aid for teaching ventilation-perfusion relationships.

To help students understand the concept of the ventilation-perfusion ratio (VA/Q) and the effects that VA/Q mismatching has on pulmonary gas exchange, a "sliding rectangles" visual aid was developed to teach VA/Q relationships. Adjacent rectangles representing "ventilation" and "perfusion" are slid past one another so that portions of the ventilation and perfusion rectangles are not touching, illustrating the concepts of dead-space ventilation (VD) and shunt flow (QS). The portion of the ventilation bar representing VD is further subdivided into anatomical and alveolar VD and used to show the effects of alveolar dead space on the PO2 (PAO2) and PCO2 of alveolar air (PACO2); movement away from the "ideal" point). Similarly, the portion of the perfusion bar representing QS is used to define anatomical and physiological shunts and the effect of shunts on the PO2 (PaO2) and PCO2 of arterial blood (PaCO2). The genesis of the PAO2-PaO2 (A-a) PO2 difference as well as the effects of VA/Q mismatching and diffusion abnormalities can all be discussed with this visual aid. This approach has greatly assisted some students in mastering this traditionally difficult area of respiratory physiology.

The amo operon in marine, ammonia-oxidizing gamma-proteobacteria.

While there is an extensive database of genes encoding ammonia monooxygenase (amo) found in the ammonia-oxidizing beta-proteobacteria, few amo sequences are available representing the gamma-proteobacteria. We sequenced the complete amo operon (amoCAB) for Nitrosococcus oceani (ATCC 19707), a marine, autotrophic, ammonia-oxidizing bacterium belonging to the gamma-subdivision of the proteobacteria. An additional autotrophic, ammonia-oxidizing bacterium isolated from a marine environment (strain C-113) was identified as belonging to the Nitrosococcus genus by 16S rDNA analysis and its amo operon was sequenced. This is the first report of a full-length sequence for the amo operon from a gamma-subdivision autotrophic ammonia-oxidizing bacterium. The N. oceani and C-113 amo genes were 88-90% identical to each other, 49-53% identical to the pmo genes encoding the related particulate methane monooxygenase of Methylococcus capsulatus (Bath), and 39-42% identical to the amo genes of the beta-subdivision autotrophic ammonia-oxidizing bacteria. In both Nitrosococcus strains, the amo operon was found as a single copy and contained three genes, amoC, amoA, amoB, with intergenic spacer regions between amoC and amoA (286 bp) and between amoA and amoB (65 bp). We conclude that the amo genes will allow for a finer scale phylogenetic differentiation than 16S rDNA within the gamma-subdivision AOB.

Effects of position of chest drainage tube on volume drained and pressure.

BACKGROUND: The nursing practice of avoiding dependent loops in the tubing of chest drainage systems because such loops may impede drainage and alter the intrapleural pressure is not research based. OBJECTIVES: To determine if the volume of fluid drained and pressure vary when the chest drainage tubing is straight, coiled, has a dependent loop, or has a dependent loop that is periodically lifted and drained. METHODS: A repeated-measures design was used. For each tubing position, 500 mL of fluid was infused into the pleural space of 8 adult pigs during 45 minutes. The volume of fluid drained and the pressure at 2 locations within the drainage tubing were measured for 1 hour. RESULTS: After 60 minutes, significantly less fluid (least significant difference test, P = .03) was drained with the dependent-loop tubing position (65 mL) than with the other 3 positions. However, the amount of fluid drained was not significantly different among the lift and drain (250 mL), coiled (301 mL), or straight (337 mL) tubing positions. Throughout the entire study, pressure at the connection between the chest tube and the drainage tube was significantly higher (least significant difference test, P = .003) for the dependent loop with and without periodic lifting and draining. CONCLUSIONS: Straight and coiled tube positions are optimal for draining fluid from the pleural space. If a dependent loop cannot be avoided, lifting and draining it every 15 minutes will maintain adequate drainage.

Multiple copies of ammonia monooxygenase (amo) operons have evolved under biased AT/GC mutational pressure in ammonia-oxidizing autotrophic bacteria.

The recent availability of complete sequences of ammonia monooxygenase (16 amoA, 5 amoB and 5 amoC gene sequences) and particulate methane monooxygenase (2 pmoA, pmoB and pmoC gene sequences each) genes allowed for a detailed analysis of their relatedness. Nucleotide sequence analysis was performed in order to identify the origins of the nearly identical operon copies within a given nitrosofier/methanotroph strain. Our data suggest that amo-homologous gene evolution has occurred in individual strains (orthology) under biased AT/GC pressure rather than by horizontal transfer. The multiple operon copies within individual strains are the result of operon duplication (paralogy). While the near identity of the multiple operon copies makes it impossible to determine whether paralogous gene expansion occurred in the last common ancestor of ammonia oxidizers or after speciation took place, we conclude that the duplication events were not recent events. We propose that the elimination of third basepair degeneracy between copies within one organism is implemented by a rectification mechanism resulting in concerted evolution.

Transcription of the amoC, amoA and amoB genes in Nitrosomonas europaea and Nitrosospira sp. NpAV.

Nitrifying bacteria such as Nitrosomonas europaea and Nitrosospira sp. NpAV use ammonia monooxygenase (AMO) for oxidation of their primary growth substrate, ammonia. Two polypeptides of AMO are coded for by contiguous genes, amoA and amoB, which are preceded by a third gene, amoC. The amoCAB clusters are present in multiple copies in nitrifying bacteria of the beta subdivision. These bacteria also have one amoC copy that is not adjacent to a copy of amoAB. The seven known amoC genes in different nitrifiers code for similar polypeptides (> 68%). Reverse transcriptase-polymerase chain reactions and Northern blots indicated that amoC from the amoCAB cluster is contained on a transcript with amoAB. Two other transcripts were detected with amo probes and may be a product of processing of the amoCAB mRNA or independent transcripts.

A gene encoding a membrane protein exists upstream of the amoA/amoB genes in ammonia oxidizing bacteria: a third member of the amo operon?

The gene cluster encoding ammonia monooxygenase (AMO) in the chemolithotrophic soil bacterium Nitrosospira sp. NpAV was found to contain a third open reading frame, termed amoC, upstream of the genes amoA and amoB that encode the subunits of AMO. The amoC gene and its flanking regions were isolated and sequenced from a 4.4 kb EcoRI fragment that contains one of three copies of the ammonia monooxygenase gene cluster. The presence of this gene upstream of the other two amoA gene copies in Nitrosospira NpAV as well as upstream of amoA genes in the genomes of other ammonia oxidizing nitrifiers (strains in the genera Nitrosomonas, Nitrosopira, Nitrosolobus and Nitrosovibrio) was confirmed using genomic DNA, oligodeoxyribonucleotide primers and the PCR. The amoC gene in Nitrosospira sp. NpAV encodes a 270 amino acid polypeptide of approximately 36 kDa. Topological analysis of the predicted primary structure revealed 6 membrane spanning domains. The amoC gene was expressed in recombinant Escherichia coli from its indigenous promoter.

Positioning of chest tubes: effects on pressure and drainage.

BACKGROUND: Maintaining a chest drainage tube in a position that is free of dependent loops, as is commonly recommended, can be very difficult. Is there a beneficial effect on the patient's outcome when the drainage tubing is free of dependent loops? OBJECTIVE: The purpose of this study was to determine, under controlled laboratory conditions, (1) what are the differences in drainage with tubing in straight, coiled, or dependent-loop (with and without periodic lifting) positions and (2) what are the differences in pressure with each of the four tubing conditions? METHODS: In laboratory simulations, pressure and drainage were observed in a chest tube drainage system that was connected to a glass bottle simulating the lung. Pressure and drainage were measured for 1 hour with the drainage tubing placed in straight, coiled, and dependent-loop positions. For the periodic lifting condition, the dependent loop was lifted and drained every 15 minutes. RESULTS: We found no differences in pressure or drainage between straight and coiled positions of the drainage tubing. However, with the dependent-loop position, pressure at the "lung" side increased from about -18 cm H2O to as high as +8 cm H2O. Drainage dropped to zero without tube lifting. When the tube was lifted and drained every 15 minutes, there was no difference in drainage with the tubing in the straight or coiled positions. CONCLUSION: Findings support recommendations to maintain tubing free of dependent loops by placing tubing in straight or coiled positions. Frequently lifting and draining a dependent loop will provide the same total drainage amount as maintaining the tubing in a straight or coiled position, but pressures may be altered sufficiently within the tube to exceed recommended levels.

A comparison of methods for dealing with troublesome examination questions.

This study compared two methods for identifying troublesome examination questions: a postexam student "challenge committee" process and a "question citation" procedure allowing students to identify troublesome questions during an exam. Challenged and cited questions on eight examinations given to second-year medical students were compared with respect to the percentage of correct responses (%CR) and the discrimination index (DI). Challenged questions had a significantly lower mean value for %CR (53.2 +/- 22.5, n = 74) than unchallenged questions (84.7 +/- 15.4, n = 428) but the two groups did not differ with respect to DI. For cited questions, the number of citations was correlated with %CR (r = -0.5480, p < 0.001) but not with DI. The group of questions that received three or more citations (n = 145) included 67.6% of all challenged questions and 78.3% of challenges that eventually led to a change in an answer key. A simple citation procedure completed during an exam could replace a complicated, post-exam challenge committee process and achieve the same goal of identifying troublesome questions.

The gene encoding ammonia monooxygenase subunit A exists in three nearly identical copies in Nitrosospira sp. NpAV.

The gene encoding ammonia monooxygenase subunit A (AmoA) was found in three copies of the genome of the chemolithotrophic soil bacterium, Nitrosospira sp. NpAV. The open reading frame and flanking regions of the three copies were isolated from digested size fractionated genomic DNA using oligodeoxyribonucleotide primers and polymerase chain reaction. The three gene copies of amoA were sequenced and the sequences compared to each other. The open reading frames and the upstream and downstream flanking regions were nearly identical in the three copies. All three copies were expressed in recombinant Escherichia coli strains from the indigenous promoter producing a product of approximately 30 kDa. All amoA copies encode 274 amino acid polypeptides which have similarity to the ammonia monooxygenase acetylene-binding protein from Nitrosomonas europaea.

Sequence of an ammonia monooxygenase subunit A-encoding gene from Nitrosospira sp. NpAV.

One of three gene copies encoding ammonia monooxygenase subunit A (AmoA) and flanking sequences was isolated from genomic DNA of the chemolithotrophic soil bacterium Nitrosospira sp. NpAV using oligodeoxyribonucleotide primers and the polymerase chain reaction (PCR). The gene (amoA) encodes a 274-amino-acid polypeptide which has similarity to the ammonia monooxygenase acetylene-binding protein from Nitrosomonas europaea.

Refining chest tube management: analysis of the state of practice.

Critical care nurses routinely care for patients who require chest tube management. To obtain the best patient outcome, critical care nurses develop standards of practice from research derived recommendations. Although there are several studies recommending chest tube management practices, there is limited research in some areas of chest tube management. The authors analyze the body of research and recommend clinical practice changes and timely research projects on chest tube management.

A tissue pressure model for palpatory perception of the cranial rhythmic impulse.

A tissue pressure model was developed to provide a possible physiologic basis for the manifestation of the cranial rhythmic impulse (CRI). The model assumes that the sensation described as the CRI is related to activation of slowly adapting cutaneous mechanoreceptors by tissue pressures of both the examiner and the subject, and that the sources of change in these tissue pressures are the combined respiratory and cardiovascular rhythms of both examiner and subject. The model generates rhythmic impulses with patterns similar to those reported for the CRI. Also, a significant correlation was found between frequencies calculated from the model and published values for CRI obtained by palpation. These comparisons suggest that the CRI may arise in soft tissues and represents a complex interaction of at least four different physiologic rhythms.

Metabolic status of bacteria and fungi in the rhizosphere of ponderosa pine seedlings.

We determined the quantity and metabolic status of bacteria and fungi in rhizosphere and nonrhizosphere soil from microcosms containing ponderosa pine seedlings. Rhizosphere soil was sampled adjacent to coarse, fine, or young roots. The biovolume and metabolic status of bacterial and fungal cells was determined microscopically and converted to total and active biomass values. Cells were considered active if they possessed the ability to reduce the artificial electron acceptor 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride (INT) to visible intracellular deposits of INT formazan. A colorimetric assay of INT formazan production was also used to assess dehydrogenase activity. INT-active microorganisms made up 44 to 55% of the microbial biomass in the soils studied. The proportion of fungal biomass that exhibited INT-reducing activity (40 to 50%) was higher than previous estimates of the active proportion of soil fungi determined by using fluorescein diacetate. Comparison between soils from different root zones revealed that the highest total and INT-active fungal biomass was adjacent to fine mycorrhizal roots, whereas the highest total and active bacterial biomass was adjacent to the young growing root tips. These observations suggest that fungi are enhanced adjacent to the fine roots compared with the nonrhizosphere soil, whereas bacteria are more responsive than fungi to labile carbon inputs in the young root zone. Colorimetric dehydrogenase assays detected gross differences between bulk and rhizosphere soil activity but were unable to detect more subtle differences due to root types. Determination of total and INT-active biomass has increased our understanding of the role of spatial compartmentalization of bacteria and fungi in rhizosphere carbon flow.

The effect of macrocytosis on rat erythrocyte deformability during recovery from phenylhydrazine-induced anemia.

To investigate the role of red blood cell (RBC) geometry in determining the filterability of stress-induced macrocytes, measurements of RBC volume, diameter, and passage time through 3 micron and 5 micron filters were made on RBCs from control rats and from phenylhydrazine-treated rats during a 28-day recovery period following the peak hemolytic response to the anemia induced by phenylhydrazine (PHZ). Mean cell volumes (MCV) were calculated from volume distribution curves; RBC diameters were obtained from peripheral blood smears; surface area (SA) and mean cylindrical diameter (MCD) were calculated using a biconcave erythrocyte model. At the time of the peak macroreticulocyte response to PHZ, MCD and MCV were significantly increased compared to controls (3.07 vs 2.57 microns, and 102.1 vs 59.7 cubic microns, respectively), the ratio SA/MCV was significantly reduced (1.405 vs 1.670), and RBC filterability through both 3 and 5 micron cylindrical pores was significantly reduced. During the 28-day recovery period, MCV, MCD, SA/MCV, and filterability all returned toward the control values, MCD was inversely correlated with filterability through both 3 micron (r = -0.861, p less than .01) and 5 micron (r = -0.767, p less than .01) pores, and MCD fell below 3.6 microns in 97.5% of the animals despite the persistence of large macrocytic subpopulations. These results emphasize the correlation between RBC geometry and filterability, and demonstrate that macrocytes with favorable geometry can persist in the circulation for extended periods without remodeling or reduction in size.

Decreased deformability of erythrocytes from smokers.

The deformability of erythrocytes from smoking and non-smoking human subjects was examined by filtration through 3-mu pores and capillary viscometry of cell suspensions. In both cases, small but significant differences were found between the two groups that are consistent with a reduction in the surface area-to-volume ratio and/or a diminished membrane flexibility in erythrocyte from smokers. Additional evidence suggests that these findings represent a chronic rather than an acute effect of smoking on erythrocyte deformability.