Category - Part 3
Competition for Intrathoracic Space Reduces Lung Capacity in Patients With Chronic Heart Failure: Population Characteristics
This retrospective analysis utilized data from 44 chronic heart failure patients from the database of the Mayo Clinic Heart Failure Service or the Cardiovascular Health Clinic (a preventive and rehabilitative center) from 2000 to 2004 (Table 1). Inclusion criteria included patients with a history of ischemic or dilated cardiomyopathy, stable heart failure symptoms (> 3 months), duration of heart failure symptoms > 1 year, left ventricular EF < 35%, body mass index (BMI) < 35 kg/m2, and nonsmokers with a smoking history < 10 pack-years. Patients were treated with standard optimized medications for heart failure at the time of the study. An equal number of control participants were recruited via advertisement from the surrounding area and were matched with the heart failure group for age, gender, and height. Control participants had normal cardiac function (EF > 50%) and were without history of hypertension, lung disease, or coronary artery disease. All participants gave written informed consent after being provided a description of study requirements. The study protocol was approved by the Mayo Clinic Institutional Review Board; all procedures followed institutional and Health Insurance Portability and Accountability Act guidelines.
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Competition for Intrathoracic Space Reduces Lung Capacity in Patients With Chronic Heart Failure
Chronic heart failure is a progressive disease resulting in severe morbidity and mortality. Interestingly, certain resting measures of cardiac function (ie, ejection fraction [EF]) correlate poorly with exercise tolerance, and thus it is clear that chronic heart failure becomes a systemic disorder, influencing a number of organ systems that may contribute to activity intolerance. Because the pulmonary system lies in series with the heart, accepts nearly all of the cardiac output, and is exposed to similar intratho-racic pressure changes, it would be expected that changes in cardiac structure and function may have adverse consequences on the pulmonary system. Most studies suggest mild-to-moderate changes in the pulmonary system with chronic heart failure, including both restrictive and obstructive changes as well as a reduction in lung diffusing capacity. Causes for changes in lung function remain unclear but have been thought to be related to respiratory muscle weakness, chronic pulmonary hypertension, and changes in lung fluid balance. Another possible contributor to the changes in pulmonary function relates to the progressive cardiac enlargement within a closed thoracic cavity. Such changes in cardiac volume would result in primarily restrictive lung changes manifested as reductions in total lung volume as well as vital capacity.” review
Influence of Two Different Interfaces for Noninvasive Ventilation Compared to Invasive Ventilation on the Mechanical Properties and Performance of a Respiratory System: PTPs
During PS, the time course of Paw differed not only during the trigger phase but also later during pressurization (Fig 4). A rapid increase of Paw occurred after the trigger delay during NIV-FM and invasive ventilation, whereas this increase in Paw occurred more slowly during NIV-H. Consequently, PTP was slightly lower during the first 250 ms of inspiration with a helmet compared to NIV-FM and invasive ventilation, but not during the complete inspiration.
Interestingly, not only PTPtot but also PTPtrigger and PTPpeep were significantly influenced by the level of PS (p < 0.001) [Fig 5]. Mean PTPtrigger values averaged over all PS settings were significantly lower in NIV-H (mean, — 77 ± 41 cm H2O X s) than NIV-FM (mean, — 239 ± 54 cm H2O X s) or invasive ventilation (mean — 215 ± 15 cm H2O X s) [p < 0.001], and a similar pattern was observed for PTPpeep resulting in a significant difference for all PS settings in the post hoc analysis. However, there was no significant difference of average PTPtot values among NIV-H (mean, 8,744 ± 5,594 cm H2O X s), NIV-FM (mean, 7,161 ± 5,584 cm H2O X s) or invasive ventilation (mean, 9,902 ± 6,659 cm H2O X s), although significant differences between NIV-FM and invasive ventilation were observed at higher PS levels (Fig 5).
Prospective Study of the Diagnostic Accuracy of the Simplify D-dimer Assay for Pulmonary Embolism in Emergency Department Patients: Conclusion
However, this may not occur in real practice. For example, in the present study, although the Canadian score < 2 produced a pretest probability of 2.9%, the actual measured posttest probability of PE was 1.2% (95% CI, 0.8 to 2.0%). In our population, the < 1.0% posttest probability objective was met only when a negative Simplify D-dimer result occurred when the physician’s unstructured pretest probability estimate was < 15%, which yielded a population with only a 2.7% prevalence of PE. With this combination, the actual measured posttest probability of PE was 0.7% (95% CI, 0.3 to 1.4%). We emphasize that these results are from one ED that appears to test for PE at a very low threshold.
Several factors could limit the external validity of this study. The upper limit of the 95% CI for the 0.7% post-test probability for PE after an unstructured estimate of PE < 15% plus a negative Simplify D-dimer result was 1.4%. Patients deemed low risk by clinicians were drawn from a cohort of urban ED patients with an overall 4.7% prevalence of PE. Researchers in Europe have found the prevalence of PE to be > 20% in patients referred from the ED; however, we submit that the threshold at which clinicians decide to order a d-dimer assay to rule out PE in the ED has decreased remarkably in the past 10 years, and continues to drop in the United States and also in Canada.” further
Prospective Study of the Diagnostic Accuracy of the Simplify D-dimer Assay for Pulmonary Embolism in Emergency Department Patients: Discussion
Figure 3 shows the plot of the likelihood ratio as a function of prevalence (R2 = 0.006 with t test on slope yielding p = 0.85; power to detect a significant correlation of 29%). The Pearson correlation coefficient observed for the plot of sensitivity vs prevalence yielded R2 = 0.20, with p = 0.27 from the t test on the slope; the plot of specificity vs prevalence yielded R2 = 0.38 with p = 0.10, and power of 36% (plots not shown). These regression analyses suggest the absence of a significant spectrum bias for either the pretest probability estimate or the underlying prevalence of PE on the diagnostic accuracy of the d-dimer assay. These computations do not address the possibility of spectrum effect, and the power to detect a significant relationship was small for each regression. This large, single-center study measured the diagnostic accuracy of a rapid, point-of-care, qualitative d-dimer assay in the ED setting. In a cohort of 2,302 patients, we found a moderate sensitivity of 80.5% and a relatively high specificity of 72.5%, leading to a negative likelihood ratio of 0.27. review
Prospective Study of the Diagnostic Accuracy of the Simplify D-dimer Assay for Pulmonary Embolism in Emergency Department Patients: Results
The d-dimer assay was performed on 2,302 patients enrolled from October 1, 2001, until June 30, 2004. Clinical characteristics of the study population are shown in Table 1. PE was diagnosed in 108 patients (4.7%; 95% CI, 3.6 to 5.6%). Figure 1 shows the flow diagram of diagnostic imaging relevant to PE. One thousand two hundred sixty-two patients with negative d-dimer results had no imaging performed, so the results of 90-day follow-up served as the criterion standard.
The distributions of pretest probability estimates from the unstructured approach, the Canadian score, and the Charlotte criteria are shown in Figure 2, which demonstrates that patients categorized as low risk for PE, either by the unstructured method < 15%, or by the Canadian score < 2, had a very low observed frequency of PE, at 2.7% (95% CI, 1.9 to 3.6%) and 2.9% (95% CI, 2.2 to 3.9%), respectively. When the Charlotte rule was negative, the frequency of PE was 3.9% (95% CI, 3.1 To 4.8%). read only
Prospective Study of the Diagnostic Accuracy of the Simplify D-dimer Assay for Pulmonary Embolism in Emergency Department Patients: Criterion Standard
Imaging was performed according to a flow diagram posted in the ED. The primary pulmonary vascular imaging study was CT angiography of the chest and venography of the legs, performed and interpreted as we have previously described. Patients who were allergic to iodinated contrast or had a serum creatinine measurement > 1.5 mg/dL underwent ventilation-perfusion scintillation lung scanning, interpreted by board-certified radiologists with specialty training in nuclear medicine in accordance with Prospective Investigation of Pulmonary Embolism Diagnosis study criteria. Lower-extremity venous ultrasound was ordered at the discretion of the attending emergency physician. Radiologists who interpreted images were unaware of the of the d-dimer result. Patients with negative d-dimer results did not necessarily undergo pulmonary vascular imaging. For all patients, the criterion standard was the result of 90-day follow-up, using a structured combination of telephone and medical record follow-up as we have previously described.