Tibor Asztalos

Changes in respiratory mechanics during cardiac surgery

We investigated the role of cardiopulmonary bypass (CPB) in compromised lung function associated with cardiac surgery. Low-frequency respiratory impedance (Zrs) was measured in patients undergoing cardiac surgery with (n = 30; CPB group) or without (n = 29; off-pump coronary artery bypass [OPCAB] group) CPB. Another group of CPB patients received dopamine (DA) (n = 12; CPB-DA group). Extravascular lung water was determined in five CPB subjects. Zrs was measured before skin incision and after chest closure. Airway resistance and inertance and tissue damping and elastance were determined from Zrs data. Airway resistance increased in the CPB group (74.9% ± 20.8%;P < 0.05), whereas it did not change in the OPCAB group (11.8% ± 7.9%; not significant) and even decreased in the CPB-DA patients (−40.6% ± 9.2%;P < 0.05). Tissue damping increased in the CPB and OPCAB groups, whereas it remained constant in the CPB-DA patients. Significant increases in elastance were observed in all groups. There was no difference in extravascular lung water before and after CPB, suggesting that edema did not develop. These results indicate a significant and heterogeneous airway narrowing during CPB, which was counteracted by the administration of DA. The mild deterioration in tissue mechanics, reflecting partial closure of the airways, may be a consequence of the anesthesia itself.

Respiratory consequences of red sludge dust inhalation in rats

The environmental disaster following flooding by red sludge in the Ajka region in Hungary poses a serious public health threat with particular concern regarding the potentially adverse respiratory effects of the inhalation of red sludge dust (RSD). The respiratory consequences of the inhalation of RSD obtained from field samples were investigated in rats. Rats were either exposed to RSD at a high concentration (2 weeks, 8h/day), or kept in room air. After the exposures, the airway resistance (R(aw)) and the respiratory tissues mechanics were measured under baseline condition, and following methacholine (MCh) challenges with the aim of establishing airway hyper-responsiveness (AH). Histopathology was performed to assess lung morphologic alterations. The physical properties and the chemical composition of the RSD were also characterized. The size distribution, chemical composition and topology of the RSD particles applied in our experiments were similar to those observed at the site of the disaster. The inhalation of RSD did not alter the basal respiratory mechanics, whereas it led to greater MCh-induced responses in R(aw), demonstrating the progression of mild AH. Histopathological investigations revealed fine, granular particles in the alveolar macrophages, as evidence that RSD had reached the lower respiratory tract and induced mild inflammation around the alveoli and the pulmonary vasculature. The mild respiratory symptoms that developed following short-term exposure of healthy individuals to high concentrations of airborne RSD do not appear to pose a greater respiratory hazard than the inhalation of urban dust at a comparable concentration.

Components of respiratory resistance monitored in mechanically ventilated patients

The interrupter technique is commonly adopted to monitor respiratory resistance (Rrs,int) during mechanical ventilation; however, Rrs,int is often interpreted as an index of airway resistance (Raw). This study compared the values of Rrs,int provided by a Siemens 940 Lung Mechanics Monitor with total respiratory impedance (Zrs) parameters in 39 patients with normal spirometric parameters, who were undergoing elective coronary bypass surgery. Zrs was determined at the airway opening with pseudorandom oscillations of 0.2–6 Hz at end inspiration. Raw and tissue resistance (Rti) were derived from the Zrs data by model fitting; Rti and total resistance (Rrs,osc=Raw+Rti) were calculated at the actual respirator frequencies. Lower airway resistance (Rawl) was estimated by measuring tracheal pressure. Although good agreement was obtained between Rrs,osc and Rrs,int, with a ratio of 1.07±0.19 (mean±sd), they correlated poorly (r2=0.36). Rti and the equipment component of Raw accounted for most of Rrs,osc (39.8±11.9 and 43.0±6.9%, respectively), whereas only a small portion belonged to Rawl (17.2±6.3%). It is concluded that respiratory resistance may become very insensitive to changes in lower airway resistance and therefore, inappropriate for following alterations in airway tone during mechanical ventilation, especially in patients with relatively normal respiratory mechanics, where the tissue and equipment resistances represent the vast majority of the total resistance.

Endothelin-1-induced airway and parenchymal mechanical responses in guinea-pigs: the roles of ETA and ETB receptors

Endothelin-1 (ET-1) has been shown to have a constrictor effect on the airways and parenchyma; however, the roles of the ETA and ETB receptors in the ET-1-induced changes in the airway and tissue compartments have not been fully explored. Low-frequency pulmonary impedance (ZL) was measured in anaesthetized, paralysed, open-chest guinea-pigs. ZL spectra were fitted by a model to estimate airway resistance (Raw) and inertance (Iaw), and coefficients of tissue damping (G) and elastance (H), and hysteresivity (eta = G/H). Two successive doses of ET-1 (0.05 and 0.2 nmol x kg(-1)) each evoked significant dose-related increases in Raw, G, H and eta. Pretreatment with 20 nmol x kg(-1) BQ-610 (a highly selective ETA receptor antagonist) resulted in a significantly decreased elevation only in H after the lower dose of ET-1. However, all parameters changed significantly less on the administration of ET-1 after pretreatment with 80 nmol-kg(-1) BQ-610, with 20 nmol x kg(-1) ETR-P1/fl (a novel ETA receptor antagonist) or with 20 nmol x kg(-1) IRL 1038 (an ETB receptor antagonist). The results of the separate assessments of the airway and tissue mechanics demonstrate that endothelin-1 induces airway and parenchymal constriction via stimulation of both receptor types in both compartments.

Volume increments and crackle sounds during lung reinflation

Lung sounds and central airway flow were recorded during the slow reinflation of isolated dog lung lobes. The flow transients coincided with crackles or their bursts, which were rare and powerful before the mass recruitment of airspaces, but became more frequent and attenuated as the reopenings moved towards the periphery.