Emilio Agostoni

Tonic vagal influences on inspiratory duration

The tidal volume (VT), inspiratory (Ti) and expiratory (Te) durations were determined in anesthetized rabbits, cats and dogs under normal conditions, during continuous positive or negative pressure breathing. Elastic loads up to complete occlusion of the airways were applied in order to determine the VT-Ti and Te-Ti relationships. The larger the end-expiratory lung volume the steeper the VT-Ti relationship, the smaller the increase of Ti and the greater the increase of Te produced by the load. Hence, the larger the end-expiratory lung volume the steeper the Te-Ti relationship. In vagotomized animals airways occlusion did not affect Ti and Te. Ti of occluded breaths in vagotomized animals was longer than that of occluded breaths in intact animals, whereas Te was similar at the resting volume of the respiratory system (FRC), shorter above FRC and longer below FRC. These results show that both phasic and tonic vagal discharges determine Ti and Te.

The effect of the abdomen on the vertical gradient of pleural surface pressure

Abstract The effect of the abdomen on the vertical gradient of pleural surface pressure in the horizontal postures has been quantitated by determining the topography of pleural surface pressure after evisceration. In supine, prone and lateral rabbits the overall vertical gradient of transpulmonary pressure after evisceration decreased 2–3 times, and more than the lung density. In prone rabbits suspended from the vertebral column the overall vertical gradient after evisceration decreased while the lung density increased. The lines relating lung height to pleural surface pressure after evisceration became similar in all the horizontal postures. In the head-up rabbits and dogs the overall vertical gradient of transpulmonary pressure was about twice the lung density. These results indicate that the vertical gradient of transpulmonary pressure does not depend essentially upon the lung density and that, in the horizontal postures, it is markedly affected by the vertical gradient of abdominal pressure.

MECHANICAL COUPLING AND LIQUID EXCHANGES IN THE PLEURAL SPACE

The pleural space provides the mechanical coupling between lung and chest wall: two views about this coupling are reported and discussed. Information on volume, composition, thickness, and pressure of the pleural liquid under physiologic conditions in a few species is provided. The Starling pressures of the parietal pleura filtering liquid into pleural space, and those of the visceral pleura absorbing liquid from the space are considered along with the permeability of the mesothelium. Information on the lymphatic drainage through the parietal pleura and on the solute-coupled liquid absorption from the pleural space under physiologic conditions and with various kinds of hydrothorax are provided.

The Fetal Lung, A Source of Amniotic Fluid

Summary Fluid production by fetal lung of guinea pigs and goats has been demonstrated through cannulation of the fetal trachea in the last part of the pregnancy. This fluid is probably produced by an ultrafiltration process because its physico-chemical features in the last third of pregnancy are very similar to those of the interstitial fluid. It is suggested that the fetal lung is an important source of amniotic fluid during this period of fetal life.

Topography of the pleural surface pressure in rabbits and dogs

Abstract A method has been developed that enables the transpulmonary pressure to be measured directly over most of the costal region of animals without introduction of any device into the pleural space. Pleural surface pressure was atmospheric in the lowermost part of the lung of rabbits and dogs in the lateral, supine and prone postures, it was subatmospheric over the rest, and at all levels in the head-up posture, it was positive in the dependent part in the head-down posture. For a given species and posture pleural surface pressure was uniquely related to the percentage of the lung maximal height and no systematic differences were found at a given height. In all points investigated pleural surface pressure was higher than pleural liquid pressure. While pleural liquid pressure at the top of the lung decreases proportionally to the lung height, pleural surface pressure at the top changes less, not only because the overall vertical gradient of transpulmonary pressure is smaller than that of pleural liquid, but also because it decreases with the increase of the size.

Continuous recording of pleural surface pressure at various sites

Abstract A method has been developed that enables continuous recording of pleural surface pressure in dogs without producing a pneumothorax. The end-expiratory values agree with those obtained with the counterpressure technique. The tidal changes are not systematically different at various sites. As with the counterpressure technique, we found that the vertical gradient of transpulmonary pressure disappears when the respiratory system is passively expanded and that a cranio-caudal gradient of transpulmonary pressure is produced in the supine posture when the abdominal pressure is lowered. The kinetics of pleural pressure during spontaneous breathing in some cases differed among sites and among dogs. During inspiratory efforts the kinetics tended to become similar. During artificial ventilation small differences in kinetics occurred. Cardiac oscillations were recorded in the 3rd, 4th and 5th intercostal spaces, seldom in the 6th.

Thickness and pressure of the pleural liquid in some mammals

Abstract The thickness of the pleural liquid in the superior part of the chest of dogs, rabbits, rats and mice in the lateral position was about equal to that in the inferior part, as previously shown in cats. The average value of pleural liquid thickness, except in the regions at the bending of the lobar edges, was about 10 μ in dogs and mice, as previously found in cats, 15 μ in rats, 27 μ in rabbits. The average end-expiratory pressure of the pleural liquid in the most dependent part was −2 cm H2O in dogs, −1.5 in cats, −1.2 in rats, −0.9 in rabbits. In spite of the fact that this pressure is only slightly subatmospheric, it is lower than the pressure determined by the recoil of the most dependent part of the lung, which has been shown to be nil in the lateral position. The vertical pressure gradient of the pleural liquid in dogs, cats, rabbits and rats in the lateral position was about 1 cm H2O/cm. Hense, at least for these species, the larger the chest the lower the pleural liquid pressure in the upper part.

Solute-coupled liquid absorption from the pleural space

The occurrence of a solute-coupled absorption of liquid from the pleural space was studied by measuring in anesthetized rabbits the volume of liquid of the right pleural space 1 h after injecting into it 2 ml of Ringer solution or of Ringer with an inhibitor of a Na(+)-Cl- coupled transport or of the Na+/K+ pump. Volume collected after Ringer was 1.56 +/- 0.08 ml. Initial volume being 2.2 ml, net absorption rate was 0.64 ml/h. Volume collected after disulfonic stilbene (0.1 mM) or bumetanide (0.1 mM) was 2.01 +/- 0.06 and 2.01 +/- 0.05 ml, respectively; net absorption rate was reduced to 0.19 ml/h. This suggests the occurrence of Na(+)-Cl- coupled transports. Volume collected after ouabain (0.5 mM) was 2.08 +/- 0.08 ml; net absorption rate was reduced to 0.12 ml/h. This suggests the occurrence of the Na+/K+ pump. The marked reduction in the hydrothorax absorption produced by the inhibitors shows the occurrence of a solute-coupled liquid absorption from the pleural space. Liquid absorbed through the visceral pleura by the solute-coupled transport should be removed by the Starling forces of pulmonary capillaries. Solute-coupled absorption of liquid through the parietal pleura should oppose the filtration caused by the Starling forces.

Comparative features of the transpulmonary pressure

Pleural surface pressure, overall recoil of the isolated lung, lung height and abdominal pressure have been measured in rats, rabbits, small and large dogs, and rams at FRC in the lateral posture. Transpulmonary pressure (Pl) at top was 2.5, 3.6 and 5.7 cm H2O in rats, rabbits and small dogs, respectively; in the other groups of dogs and in rams it was nearly equal to small dogs. The overall recoil of the lung increased from 1.5 to 2.8 cm H2O from rats to rams. The overall vertical gradient of Pl decreased from 0.88 to 0.24 cm H2O/cm from rats to rams. The progressive increase of the zero level of abdominal pressure from small dogs to rams and the small increase with size of ΔPl between top and bottom in eviscerated animals support the view that the respiratory system is designed so as to keep within narrow limits Pl, both at top and bottom, over a wide range of size and that the lung weight contributes little to the vertical gradient of Pl.

Electrolyte transport across the pleura of rabbits

The amounts of Na+ and Cl- in the right pleural space of anesthetized rabbits were determined 10 and 60 min after a 2 ml hydrothorax with the following solutions: Ringer, Ringer with an inhibitor of the Na(+)-Cl- coupled transport or of the Na+/K+ pump, Ringer with gluconate instead of Cl- or with methylglucamine instead of Na+. During the 10-60 min period: (a) with Ringer Na+ and Cl- decreased (P less than 0.01) along with an iso-osmotic liquid absorption, (b) with disulfonic-stilbene (0.1 mM), amiloride (0.7 mM), acetazolamide (0.1 mM), or ouabain (0.5 mM) Na+ did not change and Cl- decreased less (P less than 0.01) than with Ringer. With gluconate-Ringer or methylglucamine-Ringer the liquid flow reversed: in the former case Cl- and, to a smaller extent, Na+ increased (P less than 0.01); in the latter only Na+ increased (P less than 0.01). These findings suggest: (1) the occurrence of a Na+/H+ and Cl-/HCO3- double exchange on the serosal side and of a Na+/K+ pump on the interstitial side of the pleural mesothelium; (2) a slow efflux from the pleural space of gluconate or methylglucamine relative to the corresponding influx of Cl- or Na+, respectively; this drags liquid into the space by osmotic gradient.