Low VA/Q areas: arterial-alveolar N2 difference and multiple inert gas elimination technique

In 16 critically ill patients the arterial-alveolar N2 difference and data from the multiple inert gas elimination technique (MIGET) were compared in the evaluation of the contribution of low alveolar ventilation-perfusion ratio (VA/Q) lung regions (0.005 less than VA/Q less than 0.1) to venous admixture (Qva/QT). The arterial-alveolar N2 difference was determined using a manometric technique for the measurement of the arterial N2 partial pressure (PN2). We adopted a two-compartment model of the lung, one compartment having a VA/Q of approximately 1, the other being open, gas filled, unventilated (VA/Q = 0), and in equilibrium with the mixed venous blood. This theoretical single compartment represents all lung regions responsible for the arterial-alveolar N2 difference. The fractional blood flow to this compartment was calculated using an appropriate mixing equation (Q0/QT). There was a weak but significant relationship between Q0/QT and the perfusion fraction to lung regions with low VA/Q (0.005 less than VA/Q less than 0.1) (r = 0.542, P less than 0.05) and a close relationship between Q0/QT and the perfusion fraction to lung regions with VA/Q ratios less than 0.9 (r = 0.862, P less than 0.001) as obtained from MIGET. The difference Qva/QT-Q0/QT yielded a close estimation of the MIGET right-to-left shunt (Qs/QT) (r = 0.962, P less than 0.001). We conclude that the assessment of the arterial-alveolar N2 difference and Q0/QT does not yield a quantitative estimation of the contribution of pathologically low VA/Q areas to QVa/QT because these parameters reflect an unknown combination of pathological and normal (0.1 less than VA/Q less than 0.9) gas exchange units.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lower body positive pressure vs. dopamine during PEEP in humans

The application of lower body positive pressure (LBPP) of approximately 40 Torr was used to increase cardiac index (CI) in eight patients with acute respiratory failure (ARF) during positive end-expiratory pressure (PEEP) ventilation. The effects of LBPP on hemodynamics and gas exchange were compared with those of dopamine at the same level of CI without blood volume expansion. LBPP increased CI via an increase in stroke index without associated tachycardia, whereas dopamine combined both effects. A positive linear relationship (r = 0.82) was evidenced between CI and right atrial pressure (Pra) during application of LBPP according to the Frank-Starling mechanism, whereas dopamine did not increase Pra. The increase in CI with dopamine was associated with a significant rise in venous admixture (r = 0.84, P less than 0.001), whereas no such effect was observed with LBPP (r = 0.088). Changes in venous admixture were directly related to changes in mixed venous O2 pressure (PVO2) in both situations (r = 0.733, P less than 0.01), but the increase in PVO2 was more pronounced with dopamine than with LBPP (P less than 0.04). We conclude that LBPP can effectively counterbalance peripheral venous blood pooling during PEEP ventilation in humans with ARF and that changes in PVO2 appear as a major determinant of venous admixture in this setting.     

Pulmonary vasoconstrictor response to acute decrease in blood P50

The O2 sensor that triggers hypoxic pulmonary vasoconstriction may be sensitive not only to alveolar hypoxia but also to hypoxia in mixed venous blood. A specific test of the blood contribution would be to lower mixed venous PO2 (PvO2), which can be accomplished by increasing hemoglobin-O2 affinity. When we exchanged transfused rats with cyanate-treated erythrocytes [PO2 at 50% hemoglobin saturation (P50) = 21 Torr] or with Créteil erythrocytes (P50 = 13.1 Torr), we lowered PvO2 from 39 +/- 5 to 25 +/- 4 and to 14 +/- 4 Torr, respectively, without altering arterial blood gases or hemoglobin concentration. Right ventricular systolic pressure increased from 32 +/- 2 to 36 +/- 3 Torr with cyanate erythrocytes and to 44 +/- 5 Torr with Créteil erythrocytes. Cardiac output was unchanged. Control exchange transfusions with normal rat or 2,3-diphosphoglycerate-enriched human erythrocytes had no effect on PvO2 or right ventricular pressure. Alveolar hypoxia plus high O2 affinity blood caused a greater increase in right ventricular systolic pressure than either stimulus alone. We concluded that PvO2 is an important determinant of pulmonary vascular tone in the rat.     

Hemodynamic and metabolic responses of the working heart in relation to the oxygen carrying capacity of the perfusion medium

Hemodynamic and metabolic adaptations of isolated working heart perfused alternatively with normal or low oxygen carrying capacity medium were studied in an experimental model. A step change in arterial oxygen content (1.75 to 15.3 ml O2/100 ml) was followed by a decrease in coronary flow, an increase in aortic flow, external work, myocardial oxygen consumption and efficiency, respectively. Metabolic investigations (steady state values) showed the activities of both glycolysis and the Krebs cycle to increase with the oxygen carrying capacity of the perfusion medium. Within the limits of these aerobic conditions, most of the cardiac changes were reversible. The use of reconstituted blood provides physiological conditions of oxygenation, allows a dynamic equilibrium between oxygen supply and oxygen requirements and maintains a near physiological regulation between cardiac dynamic and metabolic functions. These conclusions stress the importance of optimal O2 carrying capacity of perfusion medium in metabolic studies on isolated working heart.     

Ascorbate and glutathione contents in duckweed, Lemna minor, as biomarkers of the stress generated by copper, folpet and diuron

Glutathione and ascorbate are essential components of the general antioxidative strategy to overcome oxidative stress due to environmental constraints such as pollution. The variation of glutathione and ascorbate contents in duckweed (Lemna minor) was investigated after a 48 h exposure to copper, diuron and folpet under laboratory conditions in order to determine whether changes in their level could serve as suitable and early biomarkers of pollution. One could observe that diuron and folpet caused the glutathione level to increase, its redox status remaining unchanged, while copper led to a depletion of this antioxidant and to an increase in its oxidation rate. When duckweed was contaminated by folpet and the metal, an increase of the ascorbate pool size occurred from concentrations as low as 1 mg l^-1 and 50 μg l^-1 respectively. While the ascorbate pool became more oxidized because of exposure to copper concentrations ≤ 200 μg l^-1, folpet caused an increase in its reduction rate. Diuron was responsible for depletion of ascorbate, the redox status of which remained unchanged. Because it is an adaptation to stress and a defence process, the increase in the antioxidant pool size was proposed as a biomarker of exposure to an unsafe environment. Since depletion of antioxidant and an increase in its oxidation rate weakened cellular defences and indicated a precarious state, they could constitute early indicators of toxicity. So they were proposed as potential biomarkers of toxicity. It was concluded that the antioxidant content in duckweed might serve as a useful biomarker for monitoring water quality.     

Decision Making Environment on Rift Valley Fever in Ferlo (Senegal)

The Rift Valley fever (RVF), which first appeared in Kenya in 1912, is an anthropozoonosis widespread in tropical areas. In Senegal, it is particularly felt in the Ferlo area where a strong presence of ponds shared by humans, cattle and vectors is noted. As part of the studies carried out on the environmental factors which favour its start and propagation, the focus of this paper is put on the decision making process to evaluate the impacts, the interactions and to make RVF monitoring easier. The present paper proposes a model based on data mining techniques and dedicated to trade experts. This model integrates all the involved data and the results of the analyses made on the characteristics of the surrounding ponds. This approach presents some advantage in revealing the relationship between environmental factors and RVF transmission vectors for space–time epidemiology monitoring purpose.