Continuous tracheal gas insufflation during partial liquid ventilation in juvenile rabbits with acute lung injury.

To examine the hypothesis that combined treatment with tracheal gas insufflation (TGI) and partial liquid ventilation (PLV) may improve pulmonary outcome relative to either treatment alone in acute lung injury (ALI), saline lavage lung injury was induced in 24 anesthetized, ventilated juvenile rabbits that were then randomly assigned to receive (n = 6/group) 1) conventional mechanical ventilation (CMV) alone, 2) continuous TGI at 0.5 l/min, 3) PLV with perfluorochemical liquid, and 4) combined TGI and PLV (TGI + PLV), and subsequently ventilated with minimized pressures and tidal volume (Vt) to keep arterial Po(2) (Pa(O(2))) >100 Torr and arterial Pco(2) (Pa(CO(2))) at 45-60 Torr for 4 h. Gas exchange, lung mechanics, myeloperoxidase, IL-8, and histomorphometry [including expansion index (EI)] were assessed. The CMV group showed no improvement in lung mechanics and gas exchange; all treated groups had significant increases in compliance, Pa(O(2)), ventilation efficacy index (VEI), and EI, and decreases in PaCO(2), oxygenation index, physiological dead space-to-Vt ratio (Vd/Vt), myeloperoxidase, and IL-8, relative to the CMV group. TGI resulted in lower peak inspiratory pressure, Vt, Vd/Vt, and greater VEI vs. PLV group; PLV resulted in greater compliance, Pa(O(2)), and EI vs. TGI. TGI + PLV resulted in decreased peak inspiratory pressure, Vt, Vd/Vt, and increased VEI compared with TGI, improved compliance and EI compared with PLV, and a further increase in Pa(O(2)) and oxygenation index and a decrease in PaCO(2) vs. either treatment alone. These results indicate that combined treatment of TGI and PLV results in improved pulmonary outcome than either treatment alone in this animal model of ALI.     

Distal tubule bicarbonate reabsorption during rebound metabolic alkalosis.

Rebound metabolic alkalosis is a transient alkalemia that is seen during recovery from NH4Cl-induced metabolic acidosis. The persistent elevation of plasma bicarbonate concentration is the result of continuing excretion of net acid by the kidney. Bicarbonate transport by inner medullary collecting ducts has been reported by others to proceed normally (i.e., bicarbonate reabsorption continues in this segment) during rebound metabolic alkalosis. No other segmental responses have been evaluated. Since the surface distal tubule of the rat is known to both reabsorb and secrete bicarbonate in vivo, it was of interest to determine the response of this segment. Our results show that the distal tubule microperfused in vivo during rebound metabolic alkalosis continues to reabsorb significant amounts of bicarbonate, despite the presence of systemic alkalemia that we have previously shown to be associated with distal tubule bicarbonate secretion.     

The vestibular cortical projection during spinal decompensation

The removal of spinal afferents in rabbits submitted to unilateral lesion of the labyrinth and fully compensated greatly modified the field potentials as well as the single unit responses recorded from the cortical vestibular area during stimulation of the intact eighth nerve. In particular, an increase of contralateral and a decrease of ipsilateral potentials were observed. These asymmetrical responses indicate that the influence of the spinal cord in compensating the effects of unilateral lesion of the labyrinth is directed to balance not only the electrical activity of the brain-stem structures, but also that of the cerebral cortex. It appears, therefore, that spinal signals intervene not only in the compensation of vestibulospinal and vestibulo-oculomotor functions but also of cortical functions, such as that related to vestibular sensation.     

Estimation of tracheal sound intensity during forced expiration

The tracheal sounds during forced expiration were studied using the mathematical model of forced expiration. It has been shown that separated flow in the region of dynamic constriction of the trachea during forced expiration may cause the generation of tracheal sounds.     

The projection patterns of the ventral horn to the hind limb during development.

Horseradish peroxidase is injected into specified regions of the hind limb bud of Xenopus laevis tadpoles at serial stages of development. Ventral horn cells projecting to the injection sites become labelled by the retrograde axonal transport of the enzyme. By mapping the labelled cells the developing pattern of projection of the ventral horn to the hind limb is charted. The earliest patterns of projection suggest that the first motor axons to invade the limb grow to the mesenchyme nearest to their point of entry. Thereafter, however, the projection patterns begin to resemble the adult patterns and indicate that subsequently invading axons are guided to limb regions related to the location of their cell bodies in the ventral horn. Further abrupt changes of the projection patterns leading to the final adult patterns are seen at the time of onset of ventral horn cell degeneration and just prior to the onset of limb movements.     

Distal protection devices during percutaneous coronary and carotid interventions

Distal embolization of particulate matter complicates percutaneous coronary and peripheral interventions more often than had been recognized until recently. A number of distal protection devices are under development. The PercuSurge GuardWire™ is a balloon occlusion thrombectomy device approved by the United States Food and Drug Administration for saphenous vein graft intervention. A number of filter devices utilize an expandable filter mounted on the angioplasty guidewire to facilitate entrapment of particles and safe removal. The Parodi Anti-Emboli System™ is an example of a catheter occlusion device that establishes protection by reversing blood flow in the target vessel.     

Gas-blood PCO2 gradients during avian gas exchange.

The avian respiratory system is a crosscurrent gas exchange system. One of the aspects of this type of gas exchange system is that end-expired PCO2 is greater than arterial PCO2, the highest possible value being equal to mixed venous PCO2. We made steady-state measurements of arterial, mixed venous, and end-expired PCO2 in anesthetized, spontaneously breathing chickens during inhalation of room air or 4-8% CO2. We found end-expired PCO2 to be higher than both arterial and mixed venous PCO2, the sign of the differences being such as to oppose passive diffusion. The observation that end-expired PCO2 was higher than arterial PCO2 can be explained on the basis of crosscurrent gas exchange. However, the observation that end-expired PCO2 exceeded mixed venous PCO2 must be accounted for by some other mechanism. The positive end-expired to mixed venous PCO2 gradients can be explained if it is postulated that the charged membrane mechanism suggested by Gurtner et al. (Respiration Physiol. 7: 173-187, 1969) is present in the avian lung.     

Regulation of cell migration during tracheal development in Drosophila melanogaster

Most of the knowledge concerning the intracellular mechanisms involved in cell locomotion have been obtained from in vitro studies of cells in culture. Many of the concepts derived from these studies have been partially confirmed in in vivo systems but numerous questions regarding the developmental control of cell migration remain to be addressed. Tracheal morphogenesis in Drosophila melanogaster embryos represents an in vivo model system to study the genetic control of cell migration. We review what is known about tracheal development and regulation of tracheal cell migration. We try to link these in vivo studies and the movement of cells over two dimensional substrates and elaborate on important questions which remain to be addressed in the future.     

Ontogeny of tracheal dimensions and gas exchange capacities in the grasshopper, Schistocerca americana

How does body size affect the structure and gas exchange capacities of insect tracheae? Do insects become more oxygen-limited as they grow? We addressed these questions by measuring the dimensions of two transverse tracheae within the abdomen of American locusts of different ages, and evaluating the potential for diffusion or convection to provide adequate gas exchange. The grasshopper abdomen has longitudinal tracheae that run along the midgut, heart, nerve cord, and lateral body wall. Transverse tracheae run from each spiracle to the longitudinal tracheae. Dorsal air sacs attach near each spiracle. In both transverse tracheae studied, diffusive capacities increased more slowly than metabolic rates with age, and calculated oxygen gradients necessary to supply oxygen by diffusion increased exponentially with age. However, surgical studies demonstrated that transport of gas through these transverse tracheae occurred by convection, at least in adults. Convective capacities paralleled metabolic rates with age, and the calculated pressure gradients required to sustain oxygen consumption rates by convection were independent of age. Thus, in growing grasshoppers, tracheal capacities matched tissue oxygen needs. Our morphological and physiological data together suggest that use of convection allows older grasshoppers to overcome potential limitations on size imposed by diffusion through tracheal systems.     

Active and passive components in the length-dependent stiffness of tracheal smooth muscle during isotonic shortening.

Contraction of smooth muscle tissue involves interactions between active and passive structures within the cells and in the extracellular matrix. This study focused on a defined mechanical behavior (shortening-dependent stiffness) of canine tracheal smooth muscle tissues to evaluate active and passive contributions to tissue behavior. Two approaches were used. In one, mechanical measurements were made over a range of temperatures to identify those functions whose temperature sensitivity (Q(10)) identified them as either active or passive. Isotonic shortening velocity and rate of isometric force development had high Q(10) values (2.54 and 2.13, respectively); isometric stiffness showed Q(10) values near unity. The shape of the curve relating stiffness to isotonic shortening lengths was unchanged by temperature. In the other approach, muscle contractility was reduced by applying a sudden shortening step during the rise of isometric tension. Control contractions began with the muscle at the stepped length so that properties were measured over comparable length ranges. Under isometric conditions, redeveloped isometric force was reduced, but the ratio between force and stiffness did not change. Under isotonic conditions beginning during force redevelopment at the stepped length, initial shortening velocity and the extent of shortening were reduced, whereas the rate of relaxation was increased. The shape of the curve relating stiffness to isotonic shortening lengths was unchanged, despite the step-induced changes in muscle contractility. Both sets of findings were analyzed in the context of a quasi-structural model describing the shortening-dependent stiffness of lightly loaded tracheal muscle strips.     

Distal pressure-flow relations during in vivo distal microperfusion in the rat

Distal convoluted tubule reabsorptive fluxes for various substances have been measured using the technique of in vivo microperfusion with quantitative sampling of the perfusate after it traverses a known length of tubule. It is unclear, a priori, whether physiologic pressures can be maintained under these sampling conditions. The present experiments were designed to monitor these pressure changes continuously by means of a microtransducer. We have found that over the range of 10-20 nL/min, during repeat sampling, the rise in pressure is 0.11 mmHg X nL-1 X min-1 (1 mmHg = 133.322 Pa) a value which is similar to 0.15 mmHg X nL-1 X min-1 obtained without sampling. This small rise in pressure over the microperfusion range supports the view that this technique does not introduce unphysiologic pressure effects. The present study also provides for the first time directly measured in vivo distal tubule pressure values over a wide flow range without changing whole kidney urine flow.     

Protein Patterns and Synthetic Profiles during Distal Regeneration in Hydra oligactis

Protein patterns and synthetic profiles were examined during distal regeneration in Hydraoligactis . Electrophoretic and radioactive tracer analyses revealed qualitative changes in the general protein profile during regeneration, with a heightened period of protein synthesis between 27–30 hr of regeneration, immediately preceding emergence of the first pair of tentacles. Following this, an increase in collagen-rich mesogleal protein secretion was observed coincident with tentacle initiation. Inhibition of collagen secretion with the proline analog L-azetidine-2-carboxylic acid (LACA) inhibited tentacle formation, and resulted in the development of unique "hypostome buds" at the distal regeneration surface. At the cellular level LACA did not inhibit the nerve cell differentiation that normally precedes tentacle growth, although some predicted decline in cnidocyte production was noted. It is proposed that mesogleal collagen secretion and structural organization may play a major role in the mechanical aspects of Hydra tentacle morphogenesis.