Effects of paralysis with pancuronium on chest wall statics in awake humans.

The influence of tonic inspiratory muscle activity on the relaxation characteristics of the chest wall, rib cage (RC), and abdominal wall (ABW) has been investigated in four highly trained subjects. Chest wall shape and volume were estimated with magnetometers. Pleural pressure (Pes) and abdominal pressure were measured with esophageal and gastric balloons, respectively. Subjects were seated reclining 30 degrees from upright, and respiratory muscle weakness was produced by pancuronium bromide until RC inspiratory capacity was decreased to 60% of control. Only minor changes were observed for Konno-Mead relaxation characteristics (RC vs. ABW) between control and paralysis. Similarly, although RC relaxation curves (RC vs. Pes) during paralysis were significantly different from control (P less than 0.05), the changes were small and not consistent. The differences between paralysis-induced changes in resting end-expiratory position of the chest wall and helium-dilution functional residual capacity (FRC) suggested changes in volume of blood within the chest wall. We conclude that 1) although tonic inspiratory activity of chest wall muscles exists, it does not significantly affect the chest wall relaxation characteristics in trained subjects; 2) submaximal paralysis produced by pancuronium bromide is likely to modify either spinal attitude or the distribution of blood between extremities and the thorax; these effects may account for the changes in FRC in other studies.

Effect of halothane on bronchial calibre of anaesthetised cattle.

A computer-aided forced oscillation technique was used to examine the effects of halothane on bronchial calibre in three adult cows after anaesthesia had been induced with xylazine and thiopentone. The administration of halothane failed to produce bronchodilatation, possibly owing to low resting bronchomotor tone in the animals. However, an increase in expiratory reserve volume, associated with a small fall in airway resistance, was observed, suggesting that changes in elastic recoil may make a significant contribution to changes in airway resistance during anaesthesia. The results also emphasise the importance of relating airway resistance to lung volume.

Effects of morphine and pancuronium on lung volume and oxygenation in premature infants with hyaline membrane disease.

To determine the effect of analgesia and paralysis on lung volume and oxygenation in premature infants supported by mechanical ventilation because of hyaline membrane disease, functional residual capacity (FRC), and arterial/alveolar oxygen tension ratio were measured in nine premature infants with hyaline membrane disease before and after the administration of morphine sulfate and pancuronium bromide. Without a change of positive end-expiratory pressure, ventilator rate and peak inspiratory pressure were increased before the first set of measurements to minimize the contribution of the infants' own respiratory effort to total ventilation. These ventilator settings were then held constant (except fraction of inspired oxygen) before and after the administration of the drugs. The FRC was measured with a multiple-breath N2 washout technique by means of whole-body plethysmography to measure airway flow. The FRC and the ratio of arterial to alveolar oxygen tension decreased in seven of nine patients after treatment with morphine and pancuronium. The decrease in FRC for all patients was significant (2.4 +/- 2.9 ml/kg; p < 0.05), and a significant correlation was demonstrated between the change in the arterial/alveolar oxygen tension ratio and the change in FRC (r = 0.82; p < 0.01). Gestational age, birth weight, postnatal age, severity of lung disease, and time after the administration of morphine and pancuronium were not significantly correlated with the change in FRC. We believe that a decrease in oxygenation caused by alveolar derecruitment occurred even though the ventilator settings had been increased before the first set of measurements. The decrease in FRC in these infants, who are thought to have alveolar instability because of surfactant deficiency, may have resulted from the loss of expiratory braking mechanisms. We conclude that analgesia and paralysis should be used with caution under these circumstances.

Effects of neuromuscular blockade on respiratory mechanics in conscious man.

The effect of submaximal neuromuscular blockade (SMNB) on lung and chest wall mechanics was studied in six normal, awake subjects infused with pancuronium. Measurements of static lung volumes, specific airway conductance (sGaw), maximum expiratory and inspiratory flow-volume (MEFV, MIFV) curves, and static pressure-volume (PV) curves of the lung and of the relaxed chest wall were obtained after lung recoil pressure (Pst(L)) at full inflation had been reduced to 60 +/- 10% of control. Inspiratory capacity was decreased, but residual volume was not increased. Inspiratory PV curve of the lung was not modified, and the observed decrease in expiratory compliance and the slight increase in Pst(L) during deflation were compatible with the altered lung volume history. SMNB did not modify sGaw nor the relationship between Pst(L) and MEF; by contrast it markedly reduced MIF rates. Finally, SMNB transposed the chest wall PV curve to higher levels on the pressure axis (it decreased the outward pull of the chest wall) without greatly affecting its slope, and thereby it reduced the resting level of the respiratory system. We conclude that 1) muscle weakness per se does not affect the eleastic properties of the lungs and airways, and 2) involuntary respiratory muscle activity influences the elastic recoil of the chest wall. We believe this muscle activity originates from muscle spindles, and lies essentially in the inspiratory portion of the intercostal musculature.

Paralysis of ventilated newborn babies does not influence resistance of the total respiratory system.

Paralysis with pancuronium bromide is used in newborn infants to facilitate ventilatory support during respiratory failure. Changes in lung mechanics have been attributed to paralysis. The aim of this study was to examine whether or not paralysis per se has an influence on the passive respiratory mechanics, resistance (Rrs) and compliance (Crs) of the respiratory system in newborn infants. In 30 infants with acute respiratory failure, Rrs was measured during paralysis with pancuronium bromide and after stopping pancuronium bromide (group A). Rrs was also measured in an additional 10 ventilated infants in a reversed fashion (group B): Rrs was measured first in nonparalysed infants and then they were paralysed, mainly for diagnostic procedures, and the Rrs measurement repeated. As Rrs is highly dependent on lung volume, several parameters, that depend directly on lung volume were recorded: inspiratory oxygen fraction (FI,O2), arterial oxygen tension/alveolar oxygen tension (a/A) ratio and volume above functional residual capacity (FRC). In group A, the Rrs was not different during (0.236+/-0.09 cmH2O x s x mL(-1)) and after (0.237+/-0.07 cmH2O x s x mL(-1)) paralysis. Also, in group B, Rrs did not change (0.207+/-0.046 versus 0.221+/-0.046 cm x s x mL(-1) without versus with pancuronium bromide). FI,O2, a/A ratio and volume above FRC remained constant during paralysis. These data demonstrate that paralysis does not influence the resistance of the total respiratory system in ventilated term and preterm infants when measured at comparable lung volumes.

Functional residual capacity, thoracoabdominal dimensions, and central blood volume during general anesthesia with muscle paralysis and mechanical ventilation.

Functional residual capacity (FRC), rib cage and abdominal dimensions (rc-ab), central blood volume (CBV), and extra vascular lung water (EVLW) were measured in six lung-healthy subjects awake and during halothane anesthesia, muscle paralysis, and mechanical ventilation. FRC was assessed by multiple breath nitrogen washout, rc-ab dimensions by computerized tomography, and CBV and EVLW by a double-indicator dilution technique (thermo-dye). During anesthesia, FRC decreased by 0.5 1 (17%). The cross-sectional chest area was reduced by 12-20 cm2, causing an approximate reduction in thoracic volume by 0.3 1. Concomitantly, the diaphragm was moved cranially by an average of 1.9 cm, diminishing the thoracic volume a further 0.5 1. The abdominal cross-sectional area did not alter significantly, despite the shift of the diaphragm. CBV decreased by 0.3 1. EVLW did not change significantly. It is concluded that the thoracic volume is reduced during halothane anesthesia, muscle paralysis, and mechanical ventilation as a result of cranial shift of the diaphragm and reduction in transverse area. The decrease in thoracic volume is accompanied by a reduction in FRC and a displacement of blood from the thorax to the abdomen, the transverse area of the latter thus being maintained despite the shift of the diaphragm.