MEASUREMENTS OF INTERFACE PRESSURE BETWEEN BODY SITES AND THE SURFACES OF FOUR SPECIALISED AIR MATTRESSES

SUMMARY Four specialised air mattresses had interface pressure measured under six body sites prone to pressure sores in 10 subjects, supine and sitting. The mattresses were the Clinirest (SSI) and FirstStep (KCI) continuous airflow mattress overlays, and Airwave (Pegasus) and Nimbus (Huntleigh) alternating pressure air mattresses. On the mattress overlays, average supine interface pressures were 2.33 kPa (scapula), 4.15 kPa (elbow), 1.94 kPa (sacrum) and 2.79 kPa (buttock), although they were higher at the occiput (7.97 kPa) and heel (11.7 kPa). The alternating pressure air mattresses had an average minimum interface pressure close to zero for three sites, rising to 4.28 kPa under the heel. Average maximum interface pressures were 8.61 kPa (occiput), 5.21 kPa (scapula), 4.90 (elbow), 4.85 kPa (sacrum), 4.61 kPa (buttock) and 13.2 kPa (heel). No accepted scientific method exists for comparing the two types of mattress. Our data suggest a clinical benefit at the occiput and heel (supine) in using an alternating pressure air mattress and a benefit in using a continuous airflow mattress overlay at other sites.     

New epidemiologic evidence confirming that bias does not explain the aspirin/Reye's syndrome association

To determine the validity of the aspirin/Reye's syndrome association, we developed an epidemiologic investigation to assess the effects of five potential sources of bias. A case-control study incorporated procedures to avoid temporal precedence and susceptibility bias. These included classifying cases as having monophasic or biphasic patterns of illness and matching for severity of symptoms at zero-time. To evaluate the effect of a potential recall bias, an "alternate-condition" control group was enrolled. A medical record review study was conducted to assess the potential for diagnostic bias, and a blanket surveillance of all hospitals in a region was conducted to evaluate reporting bias. Twenty-four case subjects and 48 matched controls were enrolled. Eight-eight percent of case subjects and only 17% of controls had received aspirin prior to the onset of Reye's syndrome (matched odds ratio, 35; 95% confidence interval, 4.2 to 288). Further analyses demonstrated that the association could not be attributed to the five potential sources of bias.     

Synchrony levels during evoked seizure-like bursts in mouse neocortical slices

Slices (n = 45) from the somatosensory cortex of mouse (P8-13) generated spontaneous bursts of activity (0.10 +/- 0.05 Hz) that were recorded extracellularly. Multiunit action potential (AP) activity was integrated and used as an index of population activity. In this experimental model, seizure-like activity (SLA) was evoked with bicuculline (5-10 microM) or N-methyl-d-aspartate (NMDA, 5 microM). SLA was an episode with repetitive bursting at a frequency of 0.50 +/- 0.06 Hz. To evaluate whether SLA was associated with a change in synchrony, we obtained simultaneous intracellular and extracellular recordings (n = 40) and quantified the relationship between individual cells and the surrounding population of neurons. During the SLA there was an increase in population activity and bursting activity was observed in neurons and areas that were previously silent. We defined synchrony as cellular activity that is consistently locked with the population bursts. Signal-averaging techniques were used to determine this component. To quantitatively assess change in synchronous activity at SLA onset, we estimated the entropy of the single cell's spike trains and subdivided this measure into network burst-related information and noise-related entropy. The burst-related information was not significantly altered at the onset of NMDA-evoked SLA and slightly increased when evoked with bicuculline. The signal-to-noise ratio determined from the entropy estimates showed a significant decrease (instead of an expected increase) during SLA. We conclude that the increased population activity during the SLA is attributed to recruitment of neurons rather than to increased synchrony of each of the individual elements.