Apical Clearance Research Articles

Effects of sustained exercise on pulmonary clearance of aerosolized 99mTc-DTPA.

The effects of intensive prolonged exercise on the pulmonary clearance rate of aerosolized 99mTc-labeled diethylenetriaminepentaacetate (99mTc-DTPA) and pulmonary mechanics were studied in seven healthy nonsmoking volunteers. 99mTc-DTPA clearance and pulmonary mechanics (lung volumes and compliance) were assessed before and after 75 min of constant-load exercise performed on a treadmill, corresponding to 75% of maximal O2 uptake. Because both clearance measurements were made in similar conditions of pulmonary blood flow, respiratory rate, and tidal volume, changes in clearance rate can be assumed to represent changes of alveolar epithelial permeability. After exercise, total, apical, and basal clearance were significantly increased (P less than 0.01, 0.05, and 0.05, respectively) and the increases in total clearance and tidal volume observed during exercise were significantly correlated (P less than 0.05). In contrast, no significant change was found in pulmonary mechanics. These results show that prolonged intensive exercise induces an increase in epithelial permeability, which appears to be related to the mechanical effects of sustained increased ventilation. Because no change was evidenced in pulmonary volumes or in lung elasticity, our results suggest that this increase may result from alteration of the intercellular tight junctions rather than from a surfactant deficiency.

The design of the back surface ofgas permeable lenses

The introduction of gas permeable contact lenses into general practice has opened up a new era for practitioners, and the advantages over hard PMMA and soft lenses are well documented. For many new patients it will be quite possible to fit the standard hard lens designs which are favoured by the individual practitioner. However, for those wearers who subsequently suffer from flare, lens instability or lid irritation it is necessary to consider lenses with larger back central optic diameters and/or overall size and less edge lift. Similarly the soft lens wearer who is having to be refitted with a hard type lens will prefer immediate flare free stable vision which is not always immediately available with the standard hard lens constructions. In order to fulfil these requirements there have been several new designs offered for gas permeable lenses. To date these have received a mixed reception from practitioners and it is the purpose of this paper to compare these designs with the familiar PMMA constructions and offer new constructions which practitioners may find useful as an adjunct to those already available. Historically the initial interest with gas permeables goes back to CAB, but the lack of stability of lathe cutting reduced the effectivity of the material and forced us to consider moulded lenses such as the Hartflex from Wohlk. The edge lift of these lenses is, however, as little as 0.045mm, to 0.06ram,' and when fitted in the standard British fashion would lead to a very tight lens although giving often an amazing amount of tear interchange. Satisfaction is only really obtained utilizing a flatter than 'K' approach or by adding a flat edge curve about 0.5mm wide and blended into the lens periphery. The second lens introduced, the Menicon 02 works in a similar fashion. The lens like the Hartflex has a very reduced edge lift, varying from 0.06mm on steeper radii. These figures the manufacturers will not vary. Fitting this lens with apical clearance gives absolutely no edge lift, but fitted 0.15mm flatter than 'K' as suggested by the manufacturers means again we depart from conventional methods of fitting. At the same time as these lenses were introduced to Great Britain a similar investigation was being undertaken by Williams in the USA 2. He designed for the Syntex Corporation two series of lenses made from Polycon. The first set of lenses (Table 1) had an overall size of 9.50mm with a BCOD of 8.40ram, and an axial edge lift of about 0.12mm. No mention was

Report on 600 cases of micro-corneal lenses fitted with apical clearance.

Report on 600 cases of micro-corneal lenses fitted with apical clearance.