Peripheral vascular decoupling in porcine endotoxic shock

Cardiac output measurement from arterial pressure waveforms presumes a defined relationship between the arterial pulse pressure (PP), vascular compliance (C), and resistance (R). Cardiac output estimates degrade if these assumptions are incorrect. We hypothesized that sepsis would differentially alter central and peripheral vasomotor tone, decoupling the usual pressure wave propagation from central to peripheral sites. We assessed arterial input impedance (Z), C, and R from central and peripheral arterial pressures, and aortic blood flow in an anesthetized porcine model (n = 19) of fluid resuscitated endotoxic shock induced by endotoxin infusion (7 μg·kg -1·h -1 increased to 14 and 20 μg·kg -1·h -1 every 10 min and stopped when mean arterial pressure <40 mmHg or Sv O2 < 45%). Aortic, femoral, and radial artery pressures and aortic and radial artery flows were measured. Z was calculated by FFT of flow and pressure data. R and C were derived using a two-element Windkessel model. Arterial PP increased from aortic to femoral and radial sites. During stable endotoxemia with fluid resuscitation, aortic and radial blood flows returned to or exceeded baseline while mean arterial pressure remained similarly decreased at all three sites. However, aortic PP exceeded both femoral and radial arterial PP. Although Z, R, and C derived from aortic and radial pressure and aortic flow were similar during baseline, Z increases and C decreases when derived from aortic pressure whereas Z decreases and C increases when derived from radial pressure, while R decreased similarly with both pressure signals. This central-to-peripheral vascular tone decoupling, as quantified by the difference in calculated Z and C from aortic and radial artery pressure, may explain the decreasing precision of peripheral arterial pressure profile algorithms in assessing cardiac output in septic shock patients and suggests that different algorithms taking this vascular decoupling into account may be necessary to improve their precision in this patient population. © 2011 the American Physiological Society

The impact of task rules on distracter processing: Automatic categorization of irrelevant stimuli

The goal of the study was to investigate whether task rules are automatically applied to irrelevant distracters. In three experiments, subjects categorized target words which were superimposed on distracter pictures. The categorization rule was arbitrary and the distracters were not relevant at any point during the experiment. We found congruency effects for distracters that belonged to the task-relevant categories, but were never presented as target words. Responses were faster when target and distracter belonged to the same category, i.e., were mapped to the same response, than when they were mapped to different responses. Since the distracters were never responded to in the course of the experiment, interference caused by retrieval of S-R episodes cannot explain the results. Instead, we propose that even arbitrary categorization rules are applied to all suitable stimuli, including distracters. Results are taken as evidence that a currently relevant task rule enhances processing of target-related information thereby increasing interference by task related, but currently irrelevant information