Tülin Oruç

Effects of Intravenous and Intracerebroventricular Theophylline on Hypoxic Ventilatory Depression in Anesthetized Cats

Objective: The present study was undertaken to investigate the ventilatory response due to sustained isocapnic moderate hypoxia and the possible role of adenosine in hypoxic depression in anesthetized cats. Materials and Methods: Cats anesthetized with pentothal sodium (30 mg kg–1 i.p.) were divided into two groups: treated (n = 11) and control (n = 15). Respiratory frequency (f), tidal volume (VT), minute volume (v̇E) and systemic arterial blood pressure were recorded during air and 20 min of breathing hypoxic gas mixture (14% O2-86% N2). Isocapnia was maintained by adding fractions of 1% CO2 to the inspired hypoxic gas mixture. The PaO2 and PaCO2 were determined. Results: On hypoxic gas mixture breathing, VT and v̇E values of the control animals increased significantly, at 5 min to 50 ± 6 and 53 ± 6%, respectively, above the prehypoxic air phase value (p < 0.001). After that, the magnitude of increase in VT and v̇E declined gradually. At 20 min of hypoxia, VT and v̇E were less than those in prehypoxic air phase (17 ± 7, 16 ± 7%, respectively). In cats injected with an adenosine antagonist (theophylline 13.6 mg kg–1 i.v.), f, VT and v̇E increased significantly at 5 min of hypoxia (p < 0.001). At 20 min of hypoxia, f, VT and v̇E were 8 ± 2, 30 ± 8, and 39 ± 8%, respectively, higher than corresponding values of the prehypoxic stage. In cats injected with theophylline (0.5 mg kg–1) by cisternal puncture VT and v̇E increased significantly at 5 min of hypoxia. At 20 min of hypoxia, VT and v̇E were 27 ± 7 and 31 ± 8% higher than those in the prehypoxic air phase. Conclusion: The results of this study show that accumulation of adenosine in the brain during hypoxia seems to reduce the response of the central mechanisms to chemoreceptor impulses.

The Reflex Effects on the Respiratory Regulation of the CO2 at the Different Flow Rate and Concentration

Purpose The purpose of this study was to investigate the activation of the respiratory centers during insufflation of the larynx with CO2 at different flow rates and concentrations. Materials and Methods The experiments were carried out in spontaneous air breathing rabbits, anesthetized with thiopental sodium (25 mg kg-1i.v.). The larynx was separated from the oropharyngeal cavity and the trachea. The tidal volume (VT) and respiratory frequency (f min-1) were recorded from the lower tracheal cannula. The respiratory minute volume (VE) was calculated, the action potentials from the right phrenic nerve were recorded and the inspiratory (TI) and expiratory (TE) periods and the mean inspiratory flow rate (VT/TI) were calculated. The larynx was insufflated at flow rates of 500 mL min-1 and 750 mL min-1, with 7 and 12% CO2-Air by means of a respiratory pump. Results Insufflation of the larynx, with both gas mixtures, decreased the f and VT significantly. The TI and TE were found to increase significantly due to the decreasing in f. There was a significant decrease in VT/TI ratio. Following bilateral midcervical vagotomy, on the passing of both gas mixtures, significant decreases were observed in the VT, and the responses of f, TI and TE were abolished. After cutting the superior laryngeal nerve, the responses of the VT to both gas mixtures were abolished. Conclusion In conclusion, the results of this study purpose that the stimulation of the laryngeal mechanoreceptors by the effect of hypercapnia decreases the activation of the respiratory center.