Edgardo D'Angelo

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.

Local alveolar size and transpulmonary pressure in situ and in isolated lungs

Abstract Local volume to surface ratio (V/S) of in situ subpleural and inner alveoli was determined on planes parallel and normal to the lung surface of rabbits under various conditions under which the topo- graphy of transpulmonary pressure (P tp ) over the costal region had been previously determined (supine, head-up, normal, eviscerated, at FRC, with changed alveolar or abdominal pressure; supine eviscerated with tungsten beads in the airways). The shape of subpleural and inner alveoli was similar both in situ and in isolated lobes. The local V/S and P tp values fitted the V/S-P tp relationship in isolated lobes. Only in the uppermost alveoli of head-up rabbits at FRC and in the ventral ones of rabbits with tungsten beads in the airways the values of V/S in the direction normal to the lung surface differed from those in the directions parallel to the surface. This deformation was consistent with the departure of the V/S and P tp values measured in the direction normal to the surface, from the V/S-P tp relationship of isolated lobes.

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.

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.

Stress-strain relationships during uniform and nona uniform expansion of isolated lungs

Stress-strain relationships in various directions were determined on isolated rabbit and cat lungs both during unrestrained and restrained expansion, the latter approximating the condition of cylindrical deformation. Under this condition the distortion due to the weight supported at the lung surface was also studied. Experimental data did not fit the equilibrium equations for a continuum solid, except for relatively small distortions of lung parenchyma. On the contrary, over the full range of lung distortions they fitted a model made up by a three-dimensional network of interconnected springs. While distortions produced even at relatively low lung volumes caused substantial changes of surface pressure distribution, the distorting effects of the weight were negligible under this respect. These results support the conclusion that pleural surface pressure distribution in rabbits, cats and dogs is mainly due to the lung distortion caused by the mismatching between lung and chest wall inherent shapes, while that caused by the lung weight plays only a minor role.

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.

The thickness of the pleural liquid

Abstract Cat chests were quick-frozen and cores drilled out. These were cut and observed through a reflex light microscope in a special cryostat. Since the pleural liquid reflects less light than the surrounding tissues it appears as a dark band. The thickness of the pleural liquid at FRC is 5–10μ both in the superior and dependent parts. When the lung volume is 3 times that at FRC the thickness is halved. If 5 ml of saline are introduced into the superior part of the pleural space its thickness increases only in the dependent part. The finding of an equal thickness in the superior and dependent parts of the normal cat agrees with previous findings showing that pleural liquid pressure is more subatmospheric than pleural surface pressure because other forces besides the lung recoil oppose reduction of pleural liquid below a certain limit. If pleural liquid and pleural surface pressure were the same, the thickness of the pleural liquid in the dependent part would be markedly greater than in the superior part, but this was observed only when the volume of pleural liquid was increased.

Decay rate of inspiratory muscle pressure during expiration in man.

Decay rate of inspiratory muscle pressure (PmusI) was studied in 4 subjects during post-inspiratory period of zero flow (TEz) occurring under discontinuous inspiratory elastic load (DIL). End-inspiratory pressure (PmuseI) was increased by dead spaces or exercises. Decay rate was related to PmuseI by a power function with exponent greater than 1. It was not directly affected by concomitant changes of PCO2. It did not increase when an expiratory resistive load was added, i.e. when braking action of inspiratory muscles was no longer required. Time course of PmusI during TEz was more straight than exponential. Relative decay rate increased with PmuseI and with decrease of inspiratory or expiratory time. Experiments with resistive loads suggest that relative rate is mainly related to timing factors. During voluntary inspiratory efforts with closed airways, relative decay rate was not related to PmuseI, while decay rate increased linearly with PmuseI.

The effect of limb movements on the regulation of depth and rate of breathing

In anesthetized dogs and rabbits passive or active limb movements (1) shifted to the left the relationship between tidal volume (Vt) and inspiratory time (Ti), (2) lowered the relationship between expiratory time (Te) and Ti and decreased its slope, and (3) increased the output to the inspiratory muscles (Vt/Ti). These effects increased with increasing the frequency of movements. Similar effects were obtained after vagotomy. When the stimulus was started during expiration. Te was shorted in spite of the previous unaffected Ti, Arterial PCO2 during exercise was similar (active movements) or below (passive movements) control value. Since other chemical and physical humoral factors do not seem involved, the whole increase of ventilation should be produced by neurogenic stimuli. The time course of Te, Ti and VT/Ti at the onset and at the offset of limb movements indicates an abrupt and a slow component in the neurogenic drive. A single contraction of the limb during expiration of inspiration affected the timing and the VT/Ti of 3-8 breaths.