False-positive results obtained with the Alexon ProSpecT Cryptosporidium enzyme immunoassay.

Cryptosporidium is known to cause diarrhea in immunocompromised patients and is also associated with outbreaks of disease due to food-borne and waterborne parasites. Traditional procedures, involving iodine staining of wet mounts of stool sediments and trichrome staining, lack the sensitivity to detect Cryptosporidium. Special staining procedures, such as the modified acid-fast and safranin stains, are generally employed. Less labor-intensive antigen detection assays have simplified detection; however, careful attention to local epidemiology is important because false-positive tests occur. Here, we report two incidents involving 62 false-positive results obtained with the Alexon ProSpecT Cryptosporidium enzyme immunoassay, which were deemed false-positive based on negative results obtained from extensive microscopic examinations.

A dynamic analysis of cardiovascular regulation using sinusoidal acceleration in dogs.

Control of cardiovascular function during time-dependent pooling of blood in the upper and lower body was studied in intact dogs (n = 5) and in dogs in which hearts had been surgically denervated (n = 5). The animal was positioned horizontally on a platform mounted on the arm of a centrifuge; rotation of the platform at one of nine rates with a period ranging from 3.3 min to 4 s exposed the subject to a sinusoidally varying force (+/- 2 g) that periodically translocated blood from the chest to the lower quarters and back again. The resulting oscillatory changes in arterial blood pressure (BP), cardiac output, stroke volume, heart rate (HR), and peripheral resistance (PR) were analyzed using a fast Fourier transform. Normal dogs were superior to cardiac-denervated dogs in minimizing arterial BP fluctuations, especially in the midfrequency range (i.e., approximately 0.032 Hz); after pharmacological alpha-, beta-, and muscarinic-receptor blockade, the BP oscillations were similar in the two groups. The unblocked denervated dogs regulated BP poorly primarily because of their inability to 1) make appropriately timed changes in HR and 2) minimize inappropriate oscillations in SV. Both groups of dogs in the unblocked state showed large appropriately timed PR fluctuations at the lower frequencies, which minimized BP oscillations; these became less optimally timed as acceleration frequency increased, thereby potentiating the natural disposition for BP to oscillate at the acceleration frequency. Afferent information from cardiac receptors did not appear to be essential for controlling this aspect of vascular function.

Cardiovascular regulation in canines during low-frequency acceleration.

Integrated, reflex, cardiovascular regulation in unanesthetized (tranquilized), chronically-instrumented dogs was studied using sinusoidal whole-body spinal-axis acceleration (+/- 2 Gz) at frequencies below 0.25 Hz. The participation of neurally mediated cardiac and vascular control mechanisms was examined by comparing the responses of the same animal in a normal (reflexive) state and ina pharmacologically blockaded (nonreflexive) state. Integrated neural mechanisms were found to be the most effective in minimizing acceleration-induced, arterial pressure disturbances for frequencies below 0.012 Hz; became progressively out of phase with the disturbances between 0.012 and 0.052 Hz, resulting in decreased effectiveness; and failed to significantly participate in the regulatory process for frequencies between 0.052 and 0.25 Hz, where "protection" was provided by the hydraulic and intrinsic biomechanical characteristics of the circulatory system. An analysis of the relative contribution of peripheral vascular and cardiac mechanisms indicated that 1) neurally mediated, systemic vascular responses were largest for frequency; 2) heart rate oscillations were large for frequencies below 0.052 Hz (corner frequency) and then decreased rapidly with increasing frequency; and 3) neurally mediated stroke volume oscillations were the largest for the lowest frequencies and decreased with increasing frequency.