Sigmoidal equation for lung and chest wall volume-pressure curves in acute respiratory failure

To assess incidence and magnitude of the “lower inflection point” of the chest wall, the sigmoidal equation was used in 36 consecutive patients intubated and mechanically ventilated with acute lung injury (ALI). They were 21 primary and 5 secondary ALI, 6 unilateral pneumonia, and 4 cardiogenic pulmonary edema. The lower inflection point was estimated as the point of maximal compliance increase. The low constant flow inflation method and esophageal pressure were used to partition the volume-pressure curves into their chest wall and lung components on zero end-expiratory pressure. The sigmoidal equation had an excellent fit with coefficients of determination >0.90 in all instances. The point of maximal compliance increase of the chest wall ranged from 0 to 8.3 cmH2O (median 1 cmH2O) with no difference between ALI groups. The chest wall significantly contributed to the lower inflection point of the respiratory system in eight patients only. The occurrence of a significant contribution of the chest wall to the lower inflection point of the respiratory system is lower than anticipated. The sigmoidal equation is able to determine precisely the point of the maximal compliance increase of lung and chest wall.

Effects of hypoxia and histamine infusion on lung blood volume

Using an isolated perfused cat lung preparation we examined the effects of hypoxia and histamine infusion on the lung blood volume. Total lung blood volume was determined from the indocyanine green transit time and the ether bolus technique was used to estimate arterial and venous volumes during forward and retrograde perfusion, respectively. Changes in lung total fluid content were determined from changes in the blood volume of the perfusion system. Hypoxia increased perfusion pressure and decreased total fluid and blood volume. Histamine infusion also increased perfusion pressure and decreased blood volume. However, histamine increased total fluid volume, indicating an increase in vascular permeability. Hypoxia decreased arterial and venous volumes, and histamine decreased venous volume. The slopes of the arterial and venous volume/pressure curves were not altered by hypoxia or histamine.

Influence of starvation on the lung: effect on glucose and palmitate utilization

The relative utilization of [U-14C]glucose and [1–14C]palmitate was examined in lung slices of male Long Evans hooded rats fed ad libitum and starved for 72 h. Food deprivation (72-h fast) significantly decreased [U-14C]flucose oxidation and incorporation into lung lipids. Glucose incorporation into phospholipid-fatty acid (53%) was, in proportion, more markedly reduced than into phospholipid-gluceride glycerol (33%), suggesting that glucose was being conserved for the formation of alpha-glycerol phosphate. (1–14C) palmitate utilization following fasting showed a significant 40% increase in oxidation, and a significant 16% increase in phospholipids, indicating preferential utilization of fatty acids over glucose. Phospholipid fatty acid composition, surface tension measurements and volume-pressure curves were not affected by fasting. Khe data indicate that glucose and palmitate metabolism are interrelated, and that the relative utilization of these substrates is changed to maintain essential lung lipids during an altered physiologic state.

Static features of the passive rib cage and abdomen-diaphragm

The static relation between lung volume and rib cage circumference has been determined over the vital capacity range, during relaxation and activity of the respiratory muscles with open airway. At small volume the circumference is larger during relaxation; the reverse occurs at large volume. During relaxation at full expiration the cross section of the rib cage becomes more elliptical and in some subjects also greater. Hence the shape of the chest wall during muscular activity is different from that during relaxation. Because of this change of chest wall shape the outward recoil of the passive rib cage at full expiration, in the seven subjects examined, is higher than that given by the conventional volume-pressure curve during relaxation. The volume displacements of the rib cage and of the abdomen-diaphragm have been calculated and the volume-pressure curves of the passive rib cage and abdomen-diaphragm have been constructed, taking into account the changes of the chest wall shape occurring during relaxation. change of chest wall shape during relaxation; relation between lung volume and rib cage circumference during relaxation; relation between pleural pressure and rib cage circumference during relaxation; recoil of the passive rib cage; pressure exerted by the expiratory muscles at full expiration; volume-pressure curve of the passive rib cage; volume-pressure curve of the passive abdomen-diaphragm Submitted on September 14, 1964