Heamolysis during in vitro CO2 removal from human blood using a membrane lung

Haemolysis of human blood has been examined in vitro as a function of pH in the range 7.2–8.0. The hydrogen ion concentration of freshly donated blood from 11 donors was manipulated in 42 experiments, entirely by altering the carbon dioxide fraction of air with which the blood was equilibrated using a membrane lung. In contrast to the known alkalaemic haemolysis which occurs in canine blood, we observed no correlation between plasma haemoglobin concentrations and blood pH. We conclude that alkalaemic haemolysis is unlikely to complicate the clinical application of extracorporeal carbon dioxide removal in the management of acute respiratory failure.     

Cerebral blood flow during orthostasis: role of arterial CO2

Reductions in end-tidal Pco(2) (Pet(CO(2))) during upright posture have been suggested to be the result of hyperventilation and the cause of decreases in cerebral blood flow (CBF). The goal of this study was to determine whether decreases in Pet(CO(2)) reflected decreases in arterial Pco(2) (Pa(CO(2))) and their relation to increases in alveolar ventilation (Va) and decreases in CBF. Fifteen healthy subjects (10 women and 5 men) were subjected to a 10-min head-up tilt (HUT) protocol. Pa(CO(2)), Va, and cerebral flow velocity (CFV) in the middle and anterior cerebral arteries were examined. In 12 subjects who completed the protocol, reductions in Pet(CO(2)) and Pa(CO(2)) (-1.7 +/- 0.5 and -1.1 +/- 0.4 mmHg, P < 0.05) during minute 1 of HUT were associated with a significant increase in Va (+0.7 +/- 0.3 l/min, P < 0.05). However, further decreases in Pa(CO(2)) (-0.5 +/- 0.5 mmHg, P < 0.05), from minute 1 to the last minute of HUT, occurred even though Va did not change significantly (-0.2 +/- 0.3 l/min, P = not significant). Similarly, CFV in the middle and anterior cerebral arteries decreased (-7 +/- 2 and -8 +/- 2%, P < 0.05) from minute 1 to the last minute of HUT, despite minimal changes in Pa(CO(2)). These data suggest that decreases in Pet(CO(2)) and Pa(CO(2)) during upright posture are not solely due to increased Va but could be due to ventilation-perfusion mismatch or a redistribution of CO(2) stores. Furthermore, the reduction in Pa(CO(2)) did not fully explain the decrease in CFV throughout HUT. These data suggest that factors in addition to a reduction in Pa(CO(2)) play a role in the CBF response to orthostatic stress.     

CO2 angiography: measuring blood flow with injected gas bubbles]

The use of CO2 gas as a contrast medium for visualizing blood vessels has been considerably facilitated by the development of a gas metering device for mechanical injection of CO2. The present paper describes the possibility of using CO2 not only for visualizing blood vessel morphology, but also for the diagnostic evaluation of the haemodynamics within the vessels. For this reason in vitro experiments with an artery simulation model were undertaken to examine the behaviour of injected gas bubbles. The information thus obtained was then translated to animal experiments.     

Cochlear blood flow during stepwise bleeding and CO2 inhalation in the anaesthetized dog and cat

Normal blood flow values, autoregulatory tendency and CO2 sensitivity of the cochlear blood vessels were studied in acute experiments in anesthetized, artificially ventilated dogs and cats. Cochlear blood flow was measured with the hydrogen-gas clearance technique using 100 mu platinum electrodes implanted into the perilymphatic space. Normal mean cochlear blood flow at normal systemic blood pressure and arterial pH values was found to be 30 +/- 7 ml . 100 g-1 . min-1 in the dog, and 16 +/- 5 ml . 100 g-1 . min-1 in the cat. There was no evidence of the existence of an autoregulatory mechanism of cochlear blood flow during stepwise bleeding in the dog. Blood flow seemed to follow passively the changes of arterial pressure. Cochlear blood flow increased by 79% on 5% CO2 inhalation in the cat, as a result of decreased vascular resistance. The relationship between arterial pCO2 values and cochlear blood flow proved to be exponential.     

Genetic diversity and gene flow in collapsed and healthy abalone fisheries

Overexploitation of marine species invariably results in population decline but can also have indirect effects on ecological processes such as larval dispersal and recruitment that ultimately affect genetic diversity and population resilience. We compared microsatellite DNA variation among depleted and healthy populations of the black-lip abalone Haliotis rubra from Tasmania, Australia, to determine if over-fishing had affected genetic diversity. We also used genetic data to assess whether variation in the scale and frequency of larval dispersal was linked to greater population decline in some regions than in others, and if larval dispersal was sufficient to facilitate natural recovery of depleted populations. Surprisingly, allelic diversity was higher in depleted populations than in healthy populations ( P <  0.05). Significant subdivision across hundreds of metres among our sampling sites ( F _ST = 0.026, P  < 0.01), coupled with assignment tests, indicated that larval dispersal is restricted in all regions studied, and that abalone populations across Tasmania are largely self-recruiting. Low levels of larval exchange appear to occur at the meso-scale (7–20 km), but age estimates based on shell size indicated that successful migration of larvae between any two sites may happen only once every few years. We suggest that genetic diversity may be higher in depleted populations due to the higher relative ratio of migrant to self-recruiting larvae. In addition, we expect that recovery of depleted abalone populations will be reliant on sources of larvae at the meso-scale (tens of km), but that natural recovery is only likely to occur on a timescale unacceptable to fishers and resource managers.     

Interrelationship of static mechanical factors and anatomical structure in lung evolution

Summary The inflation curves in 8 reptilian and in 2 avian lungs are sigmoid in comparison with the complex curve in the rat. Compliance is greatest in the lungs of those reptiles possessing well developed, membranous lung regions, and is similar to the extremely high compliance of avian air sacs. The body-weight standardized compliance of mammalian lungs is 1 to 2 orders of magnitude lower than that in reptilian lungs or in avian air sacs. Comparison of breathing pattern, elastic work of breathing and ventilatory rate indicates that a low-work strategy predominates in reptiles and in birds, which are obligatory rib breathers. Mammals can sustain a work rate per unit ventilation rate some 10 times greater than that of other groups because of efficient diaphragm breathing. The evolutionary implications of static mechanics for lung structure are discussed.Supported by grants Du 50/3 and 50/4 from the Deutsche Forschungsgemeinschaft     

Diversity and temperature indirectly reduce CO2 concentrations in experimental freshwater communities

Oecologia - Biodiversity loss and climate warming are occurring in concert, with potentially profound impacts on ecosystem functioning. We currently know very little about the combined effects of...