The American journal of physiology
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Most physiological scientists have restricted understanding of probability as relative frequency in a large collection (for example, of atoms). Most appropriate for the relatively circumscribed problems of the physical sciences, this understanding of probability as a physical property has conveyed the widespread impression that the "proper" statistical "method" can eliminate uncertainty by determining the "correct" frequency or frequency distribution. However, many relatively recent developments in the theory of probability and decision making deny such exalted statistical ability. ⋯ In the subjectivist view, probability and statistics are means of expressing a consistent opinion (a probability) to handle uncertainty but never means to eliminate it. In the physiological sciences the contrast between the two views is critical, because problems dealt with are generally more complex than those of physics, requiring judgments and decisions. We illustrate this in testing the efficacy of penicillin by showing how the physical probability method of "hypothesis testing" may contribute to the erroneous idea that science consists of "verified truths" or "conclusive evidence" and how this impression is avoided in subjectivist probability analysis.
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Comparative Study
Cerebral blood flow and oxygen delivery during hypoxemia and hemodilution: role of arterial oxygen content.
To determine the role of arterial O2 content (CaO2) in the cerebral blood flow (CBF) responses to hypoxemia and hemodilution, CaO2 was progressively reduced from approximately 18 to approximately 6 ml O2/dl in normocapnic, normothermic, pentobarbital-anesthetized rabbits. This was done either by reducing PaO2 (hypoxemia, minimum PaO2 approximately 26 mmHg) or arterial hematocrit (isovolemic hemodilution with hetastarch, minimum hematocrit approximately 14%) while CBF was measured with radioactive microspheres. As CaO2 decreased, CBF increased in both groups but was greater in hypoxemic animals at CaO2 values < or = 9 ml O2/dl. ⋯ By contrast, the small increase in oxygen extraction ratio seen with hypoxemia did not achieve significance. These results suggest that there are different adaptive responses to acute hypoxemia or hemodilution. They also imply that at similar CBF and CaO2 values, tissue O2 availability may be greater during hemodilution than during hypoxemia.
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Comparative Study
Capillary hemodynamics in hemorrhagic shock and reperfusion: in vivo and model analysis.
A computer network model and in vivo measurements of microcirculatory blood flow in skeletal muscle were used to study the mechanisms responsible for low flow in hemorrhagic shock and reperfusion, with focus on the potential importance of capillary diameters and leukocyte rheology. Model flows were determined by the network pressure gradient, systemic hematocrit and leukocrit, leukocyte cytoplasmic viscosity, and vessel dimensions. ⋯ Ringer-lactate (RL) reperfusion only partially restored control LDF flow, whereas a small-volume bolus of hypertonic saline-dextran followed by RL gave complete LDF flow recovery. The model predicted these flows for moderate hemodilution states, with the added insight that low-flow conditions are exacerbated by leukocytes only if they become activated, which is often a complication in ischemia/reperfusion.
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The potential influence of mucosal sensory receptors on the regulation of oral-pharyngeal swallow events was studied in 15 healthy volunteers using simultaneous videoradiography and manometry. We determined the effects of selective pharyngeal and oral plus pharyngeal anesthesia on the following temporal and manometric measures in response to liquid and viscous swallows: regional transit and clearance times; motion of hyoid and larynx; upper esophageal sphincter relaxation, opening, and closure; and pharyngeal contraction wave characteristics. ⋯ Although midpharyngeal and distal pharyngeal contraction amplitudes were not influenced by mucosal anesthesia, midpharyngeal contraction wave duration was reduced significantly by both pharyngeal (P = 0.02) and oral plus pharyngeal anesthesia (P = 0.0005). We conclude that 1) neither elicitation of the pharyngeal swallow response nor temporal regulation among swallow events is dependent on mucosal sensory receptors and 2) duration of the pharyngeal contraction is influenced by sensory input from the oral-pharyngeal mucosa.
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Comparative Study
Pressure-flow analysis of portal vein and hepatic artery interactions in porcine liver.
Interactions between the hepatic arterial and portal venous circulations were investigated in nine intact and eight isolated perfused porcine livers. Pressure-flow (P-Q) relationships were obtained in either the portal vein or hepatic artery with constant baseline or low flow in the other bed and a stable hepatic venous pressure (Phv). The slope was obtained by linear regression analysis of the P-Q relationship, and effective back pressure (Pback) was obtained from the pressure intercept for the portal vein and the measured zero-flow pressure for the hepatic artery. ⋯ Decreasing Qha caused an identical change in Pback of the portal vein (P < 0.05) in the intact and isolated liver preparations. A change in Qpv alters the hepatic arterial resistance upstream from the site of a constant arterial Pback. Changes in total flow through the common sinusoidal compartment appear to alter the Pback of the portal vein via hydraulic mechanisms.