Fig. 6. Concentration of BNP in patients with pulmonary disease. COPD, chronic obstructive pulmonary disease.
of increase is typically less than that for patients with dyspnea from heart failure (Fig. 6). In a substudy of the Breathing Not Properly Multinational Study (25), among 417 sub-j ects with a history of asthma or chronic obstructive pulmonary disease without prior heart failure, 21% were newly discovered to have heart failure. Only 37% of these new cases were identified by physicians in the ED, whereas a concentration ofBNP >100 pg/mL identified 93%. Additionally, a level of BNP >100 pg/mL has been shown to provide diagnostic information beyond that obtained from individual chest radiographic indicators (26).
Because BNP levels appear to correlate with pulmonary capillary wedge pressure and are helpful in differentiating heart failure from lung disease, measurement of BNP may be of value in differentiating noncardiogenic from cardiogenic pulmonary edema (27). For example, when BNP levels were obtained in 35 patients with acute respiratory distress syndrome (ARDS) and in 42 patients hospitalized for severe dyspnea with the diagnosis of heart failure, the median level of BNP in patients with heart failure (773 pg/mL) was significantly higher than for patients with ARDS (123 pg/mL; p < 0.001). The area under the ROC curve using BNP to differentiate heart failure from ARDS was 0.90 (0.83-0.98; p < 0.001). At a cut point of 360 pg/mL, BNP provided 90% sensitivity, 86% specificity, 89% positive predictive value (PPV), and 94% NPV (accuracy: 88%) for the discrimination of ARDS vs heart failure. Thus, BNP may prove useful as an alternative to invasive hemodynamic monitoring in some settings.
Increased plasma concentrations ofBNP are also present in some patients with large pulmonary emboli and are associated with poor prognosis (28). Similarly, plasma levels of BNP are closely related to the degree of functional impairment of patients with primary pulmonary hypertension and parallel the severity of pulmonary hemodynamic changes (29). It is speculated that serial measurements of BNP may improve the management of these patients.
Like systolic ventricular dysfunction, diastolic (or nonsystolic) dysfunction is also associated with an increased concentration of BNP (30,31). In the Breathing Not Properly
study, BNP levels in patients with diastolic dysfUnction were roughly 50% of the median concentration for patients with systolic dysfUnction (Fig. 7) (32). A number of studies have described the detection of diastolic dysfunction using BNP. For example, Lubien et al. (30) assessed BNP levels in 294 patients referred for echocardiography. Patients found to have evidence of LV diastolic dysfunction (n = 119) had a mean BNP concentration of286 ± 31 pg/mL compared with 33 ± 3 pg/mL in the group without LV dysfunction (n = 175). Patients with restrictive-like filling patterns on echocardiography had the highest levels of BNP (408 ± 66 pg/mL), and patients with symptoms had higher BNP levels in all diastolic filling patterns. The area under the ROC curve for BNP to detect any diastolic dysfunction was 0.92 (0.87-0.95; p < 0.001). A BNP value of 62 pg/mL had a sensitivity of 85%, a specificity of 83%, and an accuracy of 84% for detecting diastolic dysfunction when systolic function was normal. In the future, drug trials for treating patients with diastolic dysfunction may use BNP concentrations as an inclusion criterion as well as an end point for treatment success.
Obesity is a strong risk factor for the development of heart failure (33), yet obesity can interfere with the usual diagnostic approaches, including the physical examination, chest X-ray, and echocardiography (34,35). Thus, BNP has the potential to play an important role as an adjunct to the diagnosis of heart failure in this challenging population. However, interpretation of BNP results in this setting requires special consideration. Mehra et al. (36) were the first to demonstrate that there is a significant inverse relationship between BMI and the plasma concentration of BNP. Mehra's data are supported by similar findings from the Breathing Not Properly Multinational Study (37) (Fig. 8). Notably, only 8-24% of patients with heart failure and a BMI >30 kg/m2 had BNP levels >1000 pg/mL.
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.