Dynamic Respiratory Compliance Research Articles

Axon reflex in resiniferatoxin-induced bronchoconstriction of guinea pigs

To study the role of the axon reflex in resiniferatoxin (RTX)-induced bronchoconstriction in vivo, 32 guinea pigs weighing 292 ± 7 g were randomly divided into five groups: Group 1, control ( n = 6); Group 2, chlorisondamine ( n = 6); Group 3, tetrodotoxin (TTX, n = 6); Group 4, local capsaicin application ( n = 6); and Group 5, systemic capsaicin application ( n = 8). Chlorisondamine was used to interrupt ganglionic transmission while TTX was employed to block nerve impulse conduction. In Group 4, capsaicin was locally applied to both cervical vagus nerves 30 min prior to the study whereas capsaicin was given subcutaneously for 5 days starting 9 days before the study in Group 5. Each animal was anesthetized with pentobarbital sodium, cannulated with a tracheal cannula and venous catheter, paralyzed with gallamine triethiodide, and artificially ventilated. All the above animals were treated with atropine (0.2 mg/kg) and phenoxybenzamine (0.5 mg/kg). Resiniferatoxin (2 μg/kg) was injected intravenously to induce airway constriction. Immediately upon injection of RTX (at 1 min), each animal in the control group exhibited decreases in maximal expiratory flow, dynamic respiratory compliance, and total lung capacity, indicating severe bronchoconstriction. Then the airway spasm ameliorated gradully with time. Animals in Group 3 and 4 indicated partial abolishment, while those in Group 5 showed abolishment, of the RTX-induced bronchoconstriction. On the other hand, the animals in Group 2 did not display and significant alteration in the RTX-induced brochospasm. Furthermore, we tested RTX-induced bronchoconstriction in 5 additional animals not pretreated with either atropine or phenoxybenzamine. Compared with the data above, no significant differences in RTX-induced respiratory changes were found. Since it is known that TTX blocks nerve conduction, the data suggest that the TTX-sensitive reflex (the axon reflex) via afferent C-fibers plays a significant role in the RTX-induced bronchoconstriction, which is apparently mediated via tachykinins.

Investigation of the effects of histamine inhalation on the tracheobronchial tree of calves by the forced oscillation technique.

Effects of histamine inhalation were investigated with two different techniques in nine conscious, healthy calves. The oesophageal balloon technique was used to measure the dynamic respiratory compliance (Cdyn) and the pulmonary resistance (RL). The reactance (Xrs) and the resistance (Rrs) of the respiratory system were measured at high frequencies by the forced oscillation technique. These parameters were recorded before and after histamine inhalation. Three histamine dihydrochloride solution concentrations were used (16 mg/ml; 32 mg/ml; 64 mg/ml). Histamine inhalation induced a decrease in Cdyn and Xrs an increase in Rrs, RL and of the resonant frequency and a negative frequency dependence of Rrs. Some of these changes were satisfactorily correlated with the histamine solution concentrations. The resonant frequency was well correlated with Cdyn. It was concluded that histamine inhalation induces a decrease of the calibre of small and large airways and a non-homogeneous behaviour of the pulmonary ventilation in awake calves. The forced oscillation technique can be used to perform an inhalation provocation test in unsedated animals.

Respiratory effects of a patent ductus arteriosus in premature newborn lambs.

We examined the respiratory effects of a patent ductus arteriosus in 29 premature lambs (131-135 days gestational age) after infiltrating the ductal wall with formaldehyde solution (Formalin) and placing a snare around the ductus to regulate its patency. The lambs were given sheep surfactant, paralyzed, and mechanically ventilated at birth. We first compared 8 lambs with open ductus and 13 lambs with closed ductus during the 12 h after birth. Although lambs with open ductus had greater pulmonary blood flow (301 +/- 36 vs. 188 +/- 11 ml.min-1.kg-1, mean +/- SE, at 12 h of age) and mean pulmonary arterial (44 +/- 3 vs. 33 +/- 2 mmHg) and left ventricular end-diastolic (6 +/- 0.6 vs 4 +/- 0.7 mmHg) pressures, we found no differences in dynamic respiratory compliance (Cdyn = 0.55 +/- 0.07 vs. 0.55 +/- 0.03 ml.cmH2O-1.kg-1), midtidal volume resistance (62 +/- 5 X 10(-3) vs. 62 +/- 7 X 10(-3) cmH2O.ml-1.s), or functional residual capacity (FRC = 27 +/- 3 vs. 26 +/- 2 ml.kg-1). Alveolar-arterial PO2 difference was lower in the lambs with open ductus (238 +/- 65 vs. 362 +/- 37 Torr). Next, we challenged eight lambs with two separate saline infusions (50 ml.kg-1 over 3 min), each given with the ductus alternately closed or open. When the ductus was closed, FRC was unchanged, but Cdyn increased by 18% immediately after the infusion. When the ductus was open, FRC decreased by 16% and Cdyn decreased by 12%. We conclude that the premature lamb is surprisingly resistant to changes in respiratory function from ductal patency during the immediate neonatal period.

Effect of positive end-expiratory pressure on dynamic respiratory compliance in neonates.

A simplified method of determining dynamic respiratory compliance (C dyn) in the newborn is described. Studies were performed during mechanical ventilation on 24 infants with respiratory distress syndrome (RDS) and 6 infants without RDS. Cdyn was evaluated at pressure settinghs of 20/0, 25/5 and 30/10 cm H2O. Significant decreases (p < 0.05) in Cdyn were noted with each increase in end-expiratory pressure setting. The values for Cdyn in RDS patients obtained by this method closely approximated previously published data for lung compliance in babies with RDS. This simple and reproducible method may be useful in following the course of illness in infants with RDS.

Model of allergic bronchoconstriction in the guinea pig: I. Characteristics of the system

A model of experimental allergic bronchoconstriction was developed in the guinea pig, in which animals were passively sensitized with homologous antibody and challenged with aerosolized antigen. Responses were quantitated by noninvasive methods, utilizing total respiratory dynamic compliance or a mercury strain-gauge recording of respiration. A dose-response relation was demonstrated with the amount of passive antibody used for sensitization. The optimal latent period for challenge following the administration of passive antibody was found to be 7 days. A single dose of antibody sensitized for one reaction, but two successive responses were elicited by the use of two different antisera. Challenge with radioactive antigen showed that the lungs from sensitized animals contained the same amount of antigen as controls, indicating that most of the antigen was retained nonspecifically in both groups. Tantalum bronchograms viewed continuously on a television monitor displayed the rapid development of bronchoconstriction, which did not advance proximal to the secondary bronchi. Sections prepared for light microscopy from lungs obtained 5 min following challenge exhibited hyperinflation and bronchoconstriction. Pretreatment of sensitized animals with an antihistamine drug produced total inhibition of the reaction, but the histamine content of lungs removed from reacting animals was the same as that of controls, suggesting that experimental allergic asthma was mediated by a small fraction of the lung histamine stores.