1.
How does lobeline injected intravenously produce a cough?
Raj, H, Bakshi, GS, Tiwari, RR, Anand, A, Paintal, AS
Respiratory physiology & neurobiology. 2005;(1):79-90
Abstract
In order to examine, whether the lobeline-induced cough is a true reflex or a voluntary effort to get rid of its irritating sensations in the upper respiratory tract, we systematically studied the cough response to lobeline, of subjects who were unable to make conscious discriminations i.e. were either comatose (n=4) or anaesthetized (n=5). 8 microg/kg lobeline injected into the right atrium of one and 29 microg/kg intravenously (i.v.) into another evenly and spontaneously breathing comatose subject produced a cough after 4s and 12s, respectively. Cough was repeatable and showed a dose response relationship i.e., its latency decreasing and its duration/intensity increasing with the dose. In a third subject, capable only of weak spontaneous respiration, a relatively high dose injected into the right atrium (44 microg/kg) generated a pronounced cough-like respiratory movement superimposed on the artificial ventilation and also during the apnoea after disconnecting the pump. No respiratory response was evoked in a fourth subject who had no evidence of brainstem reflexes. In five normals, cough was elicited with a mean dose of 35+/-5 microg/kg i.v. (latency 14+/-2 s; duration 10+/-3 s). After thiopental anaesthesia, injecting 41+/-7 microg/kg produced a cough within 13+/-2 s that lasted for 12+/-2 s. It may be noted that neither the later dose nor the latency or duration of cough that it produced were significantly different from the pre anaesthesia values (P>0.05). These two sets of results show unequivocally that the lobeline-induced cough is evoked reflexly; its magnitude in the conscious state could vary by subjective influences. We discuss the likelihood of its origin from juxtapulmonary capillary receptors.
2.
Induced sputum derives from the central airways: confirmation using a radiolabeled aerosol bolus delivery technique.
Alexis, NE, Hu, SC, Zeman, K, Alter, T, Bennett, WD
American journal of respiratory and critical care medicine. 2001;(10 Pt 1):1964-70
Abstract
Indirect evidence suggests that induced sputum derives from the surfaces of the bronchial airways. To confirm this experimentally, we employed a radiolabeled aerosol bolus delivery technique that preferentially deposits aerosol in the central airways in humans. We hypothesized that there would be significantly more radioactivity recovered in an induced sputum sample, and greater airways clearance of radiolabeled particles, immediately after a central versus peripheral airways deposition. Ten healthy volunteers underwent radiolabeled aerosol deposition ((99m)Tc sulfur colloid particles) to the central and peripheral airways on separate occasions followed immediately by induced sputum or no sputum (control), while seated in front of a gamma camera. Radioactivity was measured in the selected sputum sample, processed cell pellet, and supernatant fraction. Significantly more radioactivity was present in all portions of the sputum sample after central versus peripheral airways deposition (i.e., selected sample: 15,607 counts +/- 2,985 versus 943 counts +/- 298, p = 0.001). Clearance from the whole lung was significantly greater 40 min after central versus peripheral airways deposition (48 +/- 3% versus 5 +/- 1%, p = 0.0001). Compared with control, induced sputum greatly enhanced clearance after central deposition (48 +/- 3% versus 11 +/- 6%, p = 0.0001), but not after peripheral deposition (5 +/- 1% versus 3 +/- 0.8%). These results provide direct evidence that induced sputum derives from the central airways with little or no contribution from the peripheral airways.
3.
Inhaled isotonic alkaline versus saline solution and radioaerosol clearance in chronic cough.
Haidl, P, Schönhofer, B, Siemon, K, Köhler, D
The European respiratory journal. 2000;(6):1102-8
Abstract
The aim of the present study was to test the influence of inhaled isotonic Ems salt (brine from the spa of Bad Ems, Germany) compared to isotonic saline on radioaerosol clearance (RC) in patients with chronic cough. Ems salt is an alkaline solution (pH 8.0-9.0) containing largely bicarbonate ions rather than the chloride ions present in isotonic saline (pH 6.4). RC was assessed with a radioaerosol technique using technetium-99m albumin in supine patients. After a 30-min baseline measurement of RC according to a single blind and randomized design, patients inhaled Ems salt (n=22, 20-77 yrs) or isotonic saline (n=21, 34-72 yrs) via a jet nebulizer (Pari Boy) for 10 min and were scanned for an additional 30 min. There was no difference between the two groups before intervention in terms of deposition pattern, lung function and baseline RC rate. After inhalation of Ems salt, the RC rate (1/tau) improved significantly from 0.15+/-0.14 (mean+/-SD) to 0.53+/-0.70 L.h(-1) (p<0.005); no change was found after isotonic saline (0.13+/-0.13 to 0.08+/-0.09 L.h(-1), NS). Voluntary coughs performed after 60 min had no effect on the RC rate. However, in the Ems salt group, significantly more patients reported an inhalation induced cough. Compared to the Ems salt patients, who did not cough during and after inhalation, the RC rate in the cough group was enhanced significantly (0.10+/-0.12 versus 0.73+/-0.83, p=0.017), this effect being seen more frequently in females (p=0.003). It is concluded that Ems salt improves radioaerosol clearance significantly in patients with chronic cough. The underlying mechanism, regarding whether induced cough, increased water content in the mucus or enhanced ciliary beat frequency is the leading cause of Ems salt action, remains unclear.