Effects of varying the threshold of alarm systems and workload on human performance.

The purpose of this research was to investigate the effects of varying the threshold of alarm systems and workload on human response to alarm signals and performance on a complex task. A receiver operating characteristic (ROC) curve was selected to reflect the sensitivity of the alarm system. The threshold of the alarm system was manipulated by changing the value of beta along the ROC curve. A total of 84 students participated in experiment 1 and 48 students participated in experiment 2. Participants performed a compensatory-tracking, a resource management and a monitoring task. As expected, results showed that participants responded significantly faster to true alarm signals when they were using the system with the highest threshold under low-workload conditions. Results also indicated that changing the threshold of the alarm system had a significant effect on overall performance and this effect was greater under high-workload conditions. However, contrary to expectations, the highest level of performance was achieved by setting the threshold at a low level. Results from both experiments revealed that the advantage of faster alarm reaction time as a result of increasing the system's threshold was lost because of its increased probability of missed events.

Pleural fluid characteristics in hantavirus pulmonary syndrome.

Hantavirus pulmonary syndrome (HPS), is a rodent-borne, acute, often fulminant cardiorespiratory illness. Noncardiogenic pulmonary edema is prominent in HPS as is cardiac dysfunction. Pleural effusions are commonly noted in patients with HPS and have been thought to be exudative. This report describes the prevalence and characteristics of pleural effusions by an assessment of chest radiographs for the presence of pleural fluid and reviews all pleural fluid specimens obtained from patients with HPS. Of 23 patients treated at the University of New Mexico Hospital for HPS, 22 had evidence of pleural fluid while 4 had sampling of their pleural fluid. Two samples met criteria for an exudate by pleural fluid protein to serum protein ratio of more than 0.5; one was clearly a transudate and the other had inconsistent characteristics. The two exudative samples were obtained 7 days after admission, while the other 2 were obtained within 1 day of admission. Pleural fluid cultures were sterile, and the total of nucleated cells was less than 170/mm3, and predominately mononuclear. A hypothesis may be formulated that the pleural fluid in HPS is initially transudative, consistent with the observed cardiopulmonary dysfunction. However, following aggressive resuscitative efforts and as the acute illness resolves, fluid shifts occur as cardiac function normalizes; the pleural fluid may take on characteristics of an exudate.

Sputum induction compared with bronchoalveolar lavage by Ballard catheter to diagnose Pneumocystis carinii pneumonia.

Specimens from sputum induction (SI) are often of insufficient volume or have poor diagnostic yield for the diagnosis of Pneumocystis carinii pneumonia (PCP). The Ballard catheter for bronchoalveolar lavage (BAL) is a disposable BAL device which is passed transnasally into the airway and wedged by sensation. Thirty consecutive episodes (21 inpatient and 9 outpatient) in 28 patients positive for HIV (15 with AIDS) were studied with SI and BAL at a tertiary-care university hospital. Six SIs yielded no specimen, and six were judged inadequate for investigation by the laboratory. The BAL return averaged 53 ml (range, 10 to 77 ml), and all specimens were excellent quality based on microscopy. Of the 10 patients (33 percent) who were PCP-positive on BAL, only 2 (6.9 percent) were detected by SI (McNemar p = 0.0078). Of 12 patients in whom SI was unobtainable or inadequate, 6 were positive for PCP on BAL. Two adequate specimens from SI were negative, but BAL specimens were positive for PCP. No patients had specimens that were positive for PCP on SI who had negative BAL specimens. The adequacy of the specimen and the PCP diagnosis with BAL were statistically superior to SI (McNemar p = 0.007). The Ballard BAL catheter allows easy transnasal access to the airway and safe BAL, with a statistically significant superior yield of specimens when compared to SI.