Litter and dead wood dynamics in ponderosa pine forests along a 160-year chronosequence

Disturbances such as fire play a key role in controlling ecosystem structure. In fire-prone forests, organic detritus comprises a large pool of carbon and can control the frequency and intensity of fire. The ponderosa pine forests of the Colorado Front Range, USA, where fire has been suppressed for a century, provide an ideal system for studying the long-term dynamics of detrital pools. Our objectives were (1) to quantify the long-term temporal dynamics of detrital pools; and (2) to determine to what extent present stand structure, topography, and soils constrain these dynamics. We collected data on downed dead wood, litter, duff (partially decomposed litter on the forest floor), stand structure, topographic position, and soils for 31 sites along a 160-year chronosequence. We developed a compartment model and parameterized it to describe the temporal trends in the detrital pools. We then developed four sets of statistical models, quantifying the hypothesized relationship between pool size and (1) stand structure, (2) topography, (3) soils variables, and (4) time since fire. We contrasted how much support each hypothesis had in the data using Akaike's Information Criterion (AIC). Time since fire explained 39-80% of the variability in dead wood of different size classes. Pool size increased to a peak as material killed by the fire fell, then decomposed rapidly to a minimum (61-85 years after fire for the different pools). It then increased, presumably as new detritus was produced by the regenerating stand. Litter was most strongly related to canopy cover (r2 = 77%), suggesting that litter fall, rather than decomposition, controls its dynamics. The temporal dynamics of duff were the hardest to predict. Detrital pool sizes were more strongly related to time since fire than to environmental variables. Woody debris peak-to-minimum time was 46-67 years, overlapping the range of historical fire return intervals (1 to > 100 years). Fires may therefore have burned under a wide range of fuel conditions, supporting the hypothesis that this region's fire regime was mixed severity.

Assessment of aortic regurgitation by transesophageal color Doppler imaging of the vena contracta: validation against an intraoperative aortic flow probe

OBJECTIVES

This study was performed to validate the accuracy of color flow vena contracta (VC) measurements of aortic regurgitation (AR) severity by comparing them to simultaneous intraoperative flow probe measurements of regurgitant fraction (RgF) and regurgitant volume (RgV).

BACKGROUND

Color Doppler imaging of the vena contracta has emerged as a simple and reliable measure of the severity of valvular regurgitation. This study evaluated the accuracy of VC imaging of AR by transesophageal echocardiography (TEE).

METHODS

A transit-time flow probe was placed on the ascending aorta during cardiac surgery in 24 patients with AR. The flow probe was used to measure RgF and RgV simultaneously during VC imaging by TEE. Flow probe and VC imaging were interpreted separately and in blinded fashion.

RESULTS

A good correlation was found between VC width and RgF (r = 0.85) and RgV (r = 0.79). All six patients with VC width >6 mm had a RgF >0.50. All 18 patients with VC width <5 mm had a RgF <0.50. Vena contracta area also correlated well with both RgF (r = 0.81) and RgV (r = 0.84). All six patients with VC area >7.5 mm2 had a RgF >0.50, and all 18 patients with a VC area <7.5 mm2 had a RgF <0.50. In a subset of nine patients who underwent afterload manipulation to increase diastolic blood pressure, RgV increased significantly (34 +/- 26 ml to 41 +/- 27 ml, p = 0.042) while VC width remained unchanged (5.4 +/- 2.8 mm to 5.4 +/- 2.8 mm, p = 0.41).

CONCLUSIONS

Vena contracta imaging by TEE color flow mapping is an accurate marker of AR severity. Vena contracta width and VC area correlate well with RgF and RgV obtained by intraoperative flow probe. Vena contracta width appears to be less afterload-dependent than RgV.

Detection of myocardial perfusion defects by contrast echocardiography in the setting of acute myocardial ischemia with residual antegrade flow

Although myocardial contrast echocardiography accurately demarcates area at risk during total coronary occlusion, the ability of MCE to delineate area at risk in the presence of residual antegrade flow is unknown. We hypothesized that perfusion defects in myocardial segments supplied by severe coronary stenoses with residual antegrade flow could be detected by MCE using intravenous FS069. We studied 13 open-chest dogs using an intravenous injection of FS069 during intermittent harmonic imaging. Images were collected at baseline, during acute ischemia with residual antegrade flow, physiologic hyperemia (release of stenosis), and total coronary occlusion. Regional myocardial blood flow was assessed using colored microspheres. MCE risk area during acute ischemia with residual antegrade flow and total occlusion was planimetered and compared with pathologic risk area (area unstained by monastral blue). Background-subtracted peak videointensity in the risk area was assessed for all flow states. Regional myocardial blood flow confirmed expected flow states, being significantly greater during physiologic hyperemia (4.16 +/- 1.22 ml/min/g) than at baseline (0.71 +/- 0.19 ml/min/g) and significantly diminished during coronary stenosis with residual antegrade flow (0.20 +/- 0.16 ml/min/g) and total occlusion (0.09 +/- 0.06 ml/min/g; p < 0.0001). Myocardial risk area by MCE during coronary stenosis with residual antegrade flow correlated well with pathologic risk area determined by monastral blue staining (r = 0.86). Peak videointensity during coronary stenosis (111 +/- 27) was significantly less than at baseline (157 +/- 50) but greater than during total occlusion (81 +/- 34; p < 0.0001). In conclusion, intravenous FS069 in conjunction with intermittent harmonic imaging delineates area at risk in ischemic myocardium supplied by a coronary stenoses with residual antegrade flow. The presence of a perfusion defect on MCE does not necessarily imply that the coronary artery is totally occluded.

Comparison of vena contracta width by multiplane transesophageal echocardiography with quantitative Doppler assessment of mitral regurgitation

Mitral regurgitation (MR) severity is routinely assessed by Doppler color flow mapping, which is subject to technical and hemodynamic variables. Vena contracta width may be less influenced by hemodynamic variables and has previously been shown to correlate with angiographic estimates of MR severity. This study was performed to compare mitral vena contracta width by multiplane transesophageal echocardiography (TEE) with simultaneous quantitative Doppler echocardiography in 35 patients with MR. The vena contracta width was measured at the narrowest portion of the MR jet as it emerged through the coaptation of the leaflets; it was identified in 97% of the patients. Vena contracta width correlated well with regurgitant volume (R2 = 0.81) and regurgitant orifice area (R2 = 0.81) by quantitative Doppler technique. A vena contracta width > or = 0.5 cm always predicted a regurgitant volume >60 ml and an effective regurgitant orifice area > or = 0.4 cm2 in all patients. A vena contracta width < or = 0.3 cm always predicted a regurgitant volume <45 ml and a regurgitant orifice area < or = 0.35 cm2. Thus, vena contracta width by multiplane TEE correlates well with mitral regurgitant volume and regurgitant orifice area by quantitative Doppler echocardiography and provides a simple method for the identification of patients with severe MR.

Safety and efficacy of QW7437, a new fluorocarbon-based echocardiographic contrast agent

The aim of this study was to evaluate the safety and efficacy of QW7437, a new fluorocarbon-based transpulmonary myocardial echocardiographic contrast agent. QW7437 is an anionically charged 2% dodecafluoropentane emulsion molecule, similar to EchoGen, a contrast agent previously shown to be efficacious in providing myocardial opacification by means of venous injection. This new agent has theoretical potential to provide greater safety and efficacy as a result of (1) reduced adherence to the negatively charged vascular endothelium and (2) reduced microbubble coalescence. Myocardial contrast echocardiography was performed in 10 dogs to evaluate the safety and efficacy of this agent. QW7437 (0.05 ml/kg) was injected as an intravenous bolus during intermittent harmonic epicardial imaging. Hemodynamic variables including heart rate, blood pressure, pulmonary artery pressure, pulmonary capillary wedge pressure, cardiac output, and arterial blood gases were determined at baseline and serially after contrast administration. Left ventricular fractional area shortening the regional myocardial blood flow at rest and during hyperemia (adenosine 140 micrograms/kg/min) were measured before and after contrast echocardiography. QW7437 provided dense myocardial opacification which persisted for more than 2 minutes in all subjects. This prolonged contrast effect did not result in significant changes in any hemodynamic variables, left ventricular function, or myocardial blood flow. Future studies should address the potential of this agent for human use.

Does digoxin provide additional hemodynamic and autonomic benefit at higher doses in patients with mild to moderate heart failure and normal sinus rhythm?

OBJECTIVES

This study sought to examine the hemodynamic and autonomic dose response to digoxin.

BACKGROUND

Previous studies have demonstrated an increase in contractility and heart rate variability with digitalis preparations. However, little is known about the dose-response to digoxin, which has a narrow therapeutic window.

METHODS

Nineteen patients with moderate heart failure and a left ventricular ejection fraction < 0.45 were studied hemodynamically using echocardiography and blood pressure at baseline and after 2 weeks of low dose (0.125 mg daily) and 2 weeks of moderate dose digoxin (0.25 mg daily). Loading conditions were altered with nitroprusside at each study. Autonomic function was studied by assessing heart rate variability on 24-h Holter monitoring and plasma norepinephrine levels during supine rest.

RESULTS

Low dose digoxin provided a significant increase in ventricular performance, but no further increase was seen with the moderate dose. Low dose digoxin reduced heart rate and increased heart rate variability. Moderate dose digoxin produced no additional increase in heart rate variability or reduction in sympathetic activity, as manifested by heart rate, plasma norepinephrine or low frequency/high frequency power ratio. In addition, we did not find that either low or moderate dose digoxin increased parasympathetic activity.

CONCLUSIONS

We conclude that moderate dose digoxin provides no additional hemodynamic or autonomic benefit for patients with mild to moderate heart failure over low dose digoxin. Because higher doses of digoxin may predispose to arrhythmogenesis, lower dose digoxin should be considered in patients with mild to moderate heart failure.

Assessment of mitral regurgitation severity by Doppler color flow mapping of the vena contracta

BACKGROUND

Although Doppler color flow mapping is widely used to assess the severity of mitral regurgitation (MR), a simple, accurate, and quantitative marker of MR by color flow mapping remains elusive. We hypothesized that vena contracta width by color flow mapping would accurately predict the severity of MR.

METHODS AND RESULTS

We studied 80 patients with MR. Vena contracta width was measured in multiple views with zoom mode and nonstandard angulation to optimize its visualization. Flow volumes across the left ventricular outflow tract and mitral annulus were calculated by pulsed-Doppler technique to determine regurgitant volume. Effective regurgitant orifice area was calculated by dividing the regurgitant volume by the continuous-wave Doppler velocity-time integral of the MR jet. The cause of MR was ischemia in 24, dilated cardiomyopathy in 34 mitral valve prolapse in 12, endocarditis in 2, rheumatic disease in 2, mitral annular calcification in 1, and uncertain in 5. Regurgitant volumes ranged from 2 to 191 mL. Regurgitant orifice area ranged from 0.01 to 1.47 cm2. Single-plane vena contracta width from the parasternal long-axis view correlated well with regurgitant volume (r = .85, SEE = 20 mL) and regurgitant orifice area (r = .86, SEE = 0.15 cm2). Biplane vena contracta width from apical views correlated well with regurgitant volume (r = .85, SEE = 19 mL) and regurgitant orifice area (r = .88, SEE = 0.14 cm2). A biplane vena contracta width > or = 0.5 cm was always associated with a regurgitant volume > 60 mL and a regurgitant orifice area > 0.4 cm2. A biplane vena contracta width < or = 0.3 cm predicted a regurgitant volume < 60 mL and a regurgitant orifice area < 0.4 cm2 in 24 of 29 patients. No other parameter, including jet area, left atrial size, pulmonary flow reversal, or semiquantitative MR grade, correlated significantly with regurgitant volume or regurgitant orifice area in a multivariate analysis.

CONCLUSIONS

Our results demonstrate that careful color flow mapping of the vena contracta of the MR jet provides a simple quantitative assessment of MR that correlates well with quantitative Doppler techniques.

An analysis of dilemmas posed by prehospital DNR orders

This article briefly recounts the development of the prehospital do-not-resuscitate (DNR) order and indicates certain situations, such as a choking episode or a suicide attempt, in which the presence of a DNR order may provoke a moral dilemma for the emergency medical technician as to whether or not the patient should be treated. An ethical analysis of this question is performed and concludes that resuscitative treatment is ethical and mandatory.

Time course of improvement in left ventricular function, mass and geometry in patients with congestive heart failure treated with beta-adrenergic blockade

OBJECTIVES

We examined the time course of ventricular functional improvement in patients with dilated cardiomyopathy who received beta-blockade and the long-term effects of beta-blockade on ventricular mass and geometry in these patients.

BACKGROUND

Previous studies have shown that beta-adrenergic blocking agents when administered long term improve ventricular function in patients with heart failure. However, the time course of improvement in ventricular function and the long-term effects of beta-blockade on ventricular mass and geometry are not known.

METHODS

Twenty-six men with dilated cardiomyopathy underwent serial echocardiography on days 0 and 1 and months 1 and 3 of either metoprolol (n = 16) or standard therapy (n = 10). At 3 months all patients on standard therapy were crossed over to metoprolol, and late echocardiograms were obtained after 18 +/- 5 (mean +/- SD) months of metoprolol therapy. All echocardiograms were read in blinded manner.

RESULTS

Patients treated with metoprolol had an initial decline (day 1 vs. day 0) in ventricular function (increase in end-systolic volume and decrease in ejection fraction). Ventricular function improved between months 1 and 3 (p = 0.013, metoprolol vs. standard therapy). Left ventricular mass regressed at 18 months (333 +/- 85 to 275 +/- 53 g, p = 0.011) but not at 3 months. Left ventricular shape became less spherical and assumed a more normal elliptical shape by 18 months (major/minor axis ratio 1.5 +/- 0.2 to 1.7 +/- 0.2, p = 0.0001).

CONCLUSIONS

Patients with heart failure treated with metoprolol do not demonstrate an improvement in systolic performance until after 1 month of therapy and may have a mild reduction in function initially. Long-term therapy with metoprolol results in a reversal of maladaptive remodeling with reduction in left ventricular volumes, regression of left ventricular mass and improved ventricular geometry by 18 months.

Transperineal palladium 103 prostate brachytherapy: analysis of morbidity and seed migration

OBJECTIVES

To evaluate the early morbidity of palladium 103 (103Pd) prostate brachytherapy.

METHODS

Thirty-two patients with Stage A or B prostate carcinoma were implanted transperineally with 103Pd using transrectal ultrasound and fluoroscopy between May 1990 and December 1992. Patients were subsequently followed to evaluate for morbidity and possibility of migration of the implanted seeds into the lungs.

RESULTS

The median follow-up time was 20 months (range, 2 to 45 months). The major acute toxicity of the procedure, dysuria, was seen in 88% of the patients. Although this was generally grade 1 or 2 and transient, grade 3 or 4 toxicity occurred in 18% of patients. Mild rectal symptoms (transient diarrhea, rectal bleeding) occurred in 19% of patients. Sexual functions could not be evaluated. Seven of the 3213 total seeds implanted (0.2%) were found to have migrated to the lung in 6 of 30 (20%) patients having a postoperative chest radiograph. This did not cause any clinical problems.

CONCLUSIONS

103Pd prostate brachytherapy is generally associated with only mild or moderate urinary and rectal symptoms, and the incidence of severe complications is low. Further follow-up is required to evaluate the efficacy.

Chicxulub Multiring Impact Basin: Size and Other Characteristics Derived from Gravity Analysis

The buried Chicxulub impact structure in Mexico, which is linked to the Cretaceous- Tertiary (K-T) boundary layer, may be significantly larger than previously suspected. Reprocessed gravity data over Northern Yucatan reveal three major rings and parts of a fourth ring, spaced similarly to those observed at multiring impact basins on other planets. The outer ring, probably corresponding to the basin's topographic rim, is almost 300 kilometers in diameter, indicating that Chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago.

Should public health respect autonomy?

This paper suggests that public health, due to its community orientation, may be ignoring certain ethical principles--namely the rights of individuals and communities to self-determination. The expectation of individual rights as a member of a community is reviewed and the additional right of a community for self-determination is proposed. The influences on ethical evaluations by the legal and economic environments are suggested, using US examples. The conclusion argues that as the focus of health-care delivery changes, it will become more important to consider these questions of group ethics.