Patients suffering from chronic obstructive pulmonary diseases, frequently exhibit expiratory airflow limitation. We propose a mathematical model describing the mechanical behavior of the ventilated respiratory system. This model has to simulate applied positive end-expiratory pressure effects during expiration, a process used by clinicians to improve airflow. The proposed model consists of a nonlinear two-compartment system. One of the compartments represents the collapsible airways and mimics its dynamic compression, the other represents the lung and chest wall compartment. For all clinical conditions (...) tested, the mathematical model simulates the removal of expiratory airflow limitation at PEEP lower than 70–80% of intrinsic end-expiratory pressure, i.e. the end-expiratory alveolar pressure without PEEP. It also shows the presence of an optimal PEEP. The optimal PEEP contributes to decrease PAet from 7.4 ± 0.9 to 5.4 ± 0.9 hPa. This simplistic mathematical model gives a plausible explanation of the expiratory airflow limitation removal with PEEP and a rationale to the practice of PEEP application to airflow limited patients. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:26. IN DEFENSE OF SECTION V: A REPLY TO PROFESSOR YOLTON Professor Yolton's article is especially valuable for its opening paragraphs on the writing done in the eighteenth century on the physiological basis of cognition. These provide a much-needed background to Hume's own remarks on the nature of perceptions.. It is both correct and helpful, I think, to understand any philosopher as a man of his own century. Professor (...) Yolton offers this article, in part at least, to differ with my interpretation given in "The Location, Extension, Shape, and Size of Hume's Perceptions." It seems to me, however, that this opening part of his article serves instead to lend support to mine. I have not said, by the way, that Hume believes that ideas are "brain impressions," since Hume has not used that phrase himself. Instead, I have merely provided evidence that Hume believes some perceptions have location, extension, shape and size; and I have pointed out an inconsistency that arises in this connection. Professor Yolton warns against taking Hume to intend, in saying that an idea represents its impression, that the idea is an image of the impression. I find, however, that Hume does assert that ideas are images: Those perceptions, which enter with most force and violence, we may name impressions.... By ideas I mean the faint images of these in thinking and reasoning.... (Tl) Again, in explaining memory: For what is the memory but a faculty, by which we raise up the images of paet perceptions? And as an image necessarily resembles its object.... (T260) At the end of his Part I, Professor Yolton concludes: (1) Hume never mentions the brain and the physiological processes. It is the mind or the soul which considers, conceives, imagines, remembers, thinks It seems to me not at all clear that Hume distinguishes soul 27. or mind from the brain, for he says: Bodily pains and pleasures...arise Originally in the soul, or in the body, whichever you please to call it.... (T276) And Hume certainly does describe the brain and its physiological processes on T60-61 and T185, as Professor Yolton himself later recognizes explicitly on his pages 12 and 16. An ambiguity arises regarding 'representation', Professor Yolton concludes, because Hume is writing in two languages in his account of ideas as representations : The difficulties of interpretation arise from Hume's application of quantitative terms to ideas - size, parts, divisibility. We have to balance this quantitative language of ideas by Hume's ascription of logical properties to ideas - truth, contradiction, possibility. When he speaks of ideas 'representing' things, to which language does 'representation' belong: to the quantitative or to the logical language? (6) I gather that Professor Yolton finds some sort of incompatibility between the "quantitative" characteristics of ideas and their "logical" ones; yet he offers no explanation why he finds them incompatible. More to the point, of course, is whether Hume himself regarded them as incompatible. I find he does not. Rather, it appears that it is the "quantitative" aspects of some ideas that permit them to be adequate representations, having the same "logical" properties as do objects. On T28 Hume has concluded that some ideas are very small: This however is certain, that we can form ideas, which shall be no greater than the smallest atom of the animal spirits of an insect a thousand times less than a mite.... Then on the following page he makes use of this conclusion to argue that ideas have the same "logical" properties as the objects they represent: Wherever ideas are adequate representations of objects, the relations, contradictions and 28. agreements of the ideas are all applicable to the objects ; and this we may in general observe to be the foundation of all human knowledge. But our ideas are adequate representations of the most minute parts of extension; and thro' whatever divisions and subdivisions we may suppose these parts to be arriv'd at, they can never become inferior to some ideas, which we form. The plain consequence is, that whatever appca rn impossible and contradictory upon the comparison of these ideas, must be really impossible and contradictory, without any farther excuse or evasion. (T29), Thus I... (shrink)