Chinese J Physiol
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Previous studies in anesthetized humans positioned in the left lateral decubitus (LLD) posture have shown that unilateral positive end-expiratory pressure (PEEP) to the dependent lung produce a more even ventilation distribution and improves gas exchange. Unilateral PEEP to the dependent lung may offer special advantages during LLD surgery by reducing the alveolar-to-arterial oxygen pressure difference {(A-a)PO2 or venous admixture} in patients with thoracic trauma or unilateral lung injury. We measured the effects of unilateral PEEP on regional distribution of blood flow (Q) and ventilation (V(A)) using fluorescent microspheres in pentobarbital anesthetized and air ventilation dogs in left lateral decubitus posture with synchronous lung inflation. ⋯ Bilateral PEEP disproportionately increased FRC in the right lung but again produced no significant changes in venous admixture or V(A)/Q distribution. We conclude that the reduced dependent lung blood flow observed without PEEP occurs secondary to a reduction in lung volume. When tidal volume is maintained, unilateral PEEP increases dependent lung volume with little effect of perfusion distribution maintaining gas exchange.
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The effect of left lung atelectasis on the regional distribution of blood flow (Q), ventilation (V(A)) and gas exchange on the right lung ventilated with 100% O2 was studied in anesthetized dogs in the lateral decubitus posture. Q and V(A) were measured in 1.7 ml lung volume pieces using injected and aerosolized fluorescent microspheres, respectively. Hypoxic pulmonary vasoconstriction (HPV) in the atelectatic lung shifted flow to the ventilated lung. ⋯ Left lung atelectasis caused a compensatory increase in the ventilated lung FRC that was smaller in the right (RLD) than left (LLD) lateral posture, the effect of lung compression by the atelectatic lung and mediastinal contents in the RLD posture. The O2 deficit measured by (A-a)DO2 increased with left lung atelectasis and was exacerbated in the LLD posture by 10 cm H2O PEEP, a result of increased shunt caused by a shift in Q from the ventilated to the atelectatic lung. The PEEP-induced O2 deficit was eliminated with inversion to the RLD posture.
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Using an in vitro primary cell culture model in which cortical neurons undergo a gradual and delayed neuronal death after a brief (5 min) challenge with glutamate receptor agonist N-methyl-D-aspartate (NMDA, 300 microM), the neuroprotective effects of various nitric oxide synthases (NOS) inhibitors were compared with that of the NMDA receptor antagonist dizocilpine maleate (MK-801). Our rat cortical cultures consisted of approximately 80-96% neurons and 5-20% astroglia as determined by immunocytochemical staining with antibodies against glial fibrillary acidic protein (GFAP) or neuron specific enolase (NSE). The delayed type of NMDA-induced neurotoxicity was examined by the morphological estimate of cell injury and was further confirmed by the activity of lactate dehydrogenase (LDH) in the extracellular fluid measured 24 hrs after the 5-min NMDA exposure. ⋯ Thus the results indicate that a brief NMDA exposure leads to delayed neuronal damage with concomitant increase in NO production in cortical neuronal cultures. We suggest that the NO may originate primarily from nNOS. The neuroprotective effects of NOS inhibitors are weaker than that of MK-801.
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This study investigated the roles of hippocampal N-methyl-D-aspartate (NMDA) receptors and alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate (AMPA) receptors in acquisition, consolidation and retrieval processes of spatial memory. Male Wistar rats with indwelling cannulae in the dorsal hippocampus received 4 training trials on the Morris water maze for consecutively 6 days. Rats received infusion of the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP5) or the AMPA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) into the hippocampus under one of the three schedules: 5 min prior to each daily training session, immediately after each daily training session or 5 min prior to the final testing trial. ⋯ Pretraining intra-hippocampal infusion of 1.0 micrograms CNQX also impaired acquisition, but posttraining infusion of CNQX at 1.0 or 2.0 micrograms had no effect. However, pretest infusion of 1.0 micrograms CNQX markedly impaired retrieval of the already-formed spatial memory. These findings taken together suggest that acquisition in a spatial task involves hippocampal NMDA and AMPA receptors, consolidation of spatial memory involves NMDA receptors and retrieving such memory involves AMPA receptors.
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The present study was designed to determine whether arterial pressure or blood flow contributes to the reduction in tissue bleeding (TB) during sodium nitroprusside (SNP) induced hypotension. We performed the experiment in dogs with sinus denervation and vagotomy to minimize reflex intervention. The Group 1 of Series I experiment consisted of 6 dogs with the measurements of systemic arterial pressure (SAP) and femoral arterial flow (Q). ⋯ The amount of TB at this condition was greatly increased to 48.6 +/- 2.9 ml/20 min (P less than 0.001). The results indicate that SNP decreases SAP, hindlimb Q, vascular resistance and TB in dogs with baroreceptor denervation. The data obtained from the studies of the constant Q perfusion with and without SNP suggest that the major determinant of tissue bleeding is blood pressure instead of blood flow.