Bronchomotor tone

Responses to activation of the parasympathetic system. Parasympathetic nerves regulate processes connected with energy assimilation (food intake, digestion, absorption) and storage. These processes operate when the body is at rest, allowing a decreased tidal volume (increased bronchomotor tone) and decreased cardiac activity. Secretion of saliva and intestinal fluids promotes the digestion of foodstuffs transport of intestinal contents is speeded up because of enhanced peristaltic activity and lowered tone of sphincteric muscles. To empty the urinary bladder (micturition), wall tension is increased by detrusor activation with a concurrent relaxation of sphincter tonus. 

Hulks, G., Warren, P.M. and Douglas, N.J. (1993). The effect of inhaled nitric acid on bronchomotor tone in the normal human airway. Am. Rev. Respir. Dis. 147, A287. 

Respiratory Barbiturates are respiratory depressants. Induction doses of thiopental decrease minute ventilation and tidal volume with a smaller and inconsistent decrease in respiratory rate reflex responses to hypercarbia and hypoxia are diminished by anesthetic barbiturates at higher doses or in the presence of other respiratory depressants such as opiates, apnea can result. With the exception of uncommon anaphylactoid reactions, these drugs have little effect on bronchomotor tone and can be used safely in asthmatics. 

It is also likely that changes common in CB and CBA are due to different pathophysiologic mechanisms. It is known that the inflammatory cell infiltrate in the mucosa is different in CB as opposed to CBA. The hypersecretion of mucus and vagal bronchomotor tone seen in both CB and CBA may also have different mechanisms. The little that is known about the basic pathophysiologic mechanisms at the human level is often soft data because the specific pathologic process of the subjects studied was not clearly identified. Often these mechanisms are proposed from studies of normal humans or arbitrary animal models. The transference of facts obtained by these methods to the interpretation of the pathophysiology of specific disease states should be undertaken cautiously. 

Anticholinergic agents may represent the first true broncho-dilators for the CB patients. Ipratropium by inhalation has been demonstrated to provide 5-6 hours of bronchodilation in CB as was similarly seen earlier with atropine (13). The mechanism of action is thought to be a blocking of the vagal efferent discharge which is responsible for the increased bronchomotor tone of the bronchial smooth muscle in CB as well as in CBA. Parenteral or inhaled atropine appears to have the deleterious effect of drying bronchial secretions and has not been useful for protracted therapy, whereas inhaled ipratropium does not appear to have this unwanted effect. 

As discussed previously (Sec. II.B), bronchial smooth muscle tone is under autonomic control. Cold air and stimulation of receptors by irritants such as cigarette smoke, dust particles, and sulfur dioxide can also cause increased tone and hence bronchoconstriction (229). Bronchomotor tone is also modulated by vagal stretch reflexes and varies inversely with lung volume. Paradoxically, the rise in bronchomotor tone and/or increase in FRC during an attack of asthma may partially reverse the reduction in airway caliber that occurs in this condition, making assessment of response to therapy complex. Similarly, bronchodilators have been shown to cause paradoxical reductions in airflow and desaturation in some infants with history of wheeze, a phenomenon that has been attributed at least partially to changes in airway wall compliance (230-232). 

Butorphanol increases cardiac work and can cause pulmonary hypertension. At super-therapeutic doses, it can incite dysphoria. Other CNS effects include depression of spontaneous respiratory activity and cough, stimulation of the emetic center, miosis, and sedation. Effects possibly mediated by non-CNS mechanisms include alteration in cardiovascular resistance and capacitance, bronchomotor tone, gastrointestinal secretory and motor activity, and bladder sphincter activity. Butorphanol metabolites have minor analgesic activity [2,3]. 

In addition to these classic responses, activation of sensory nerves can cause an increase in bronchial blood flow (8), bronchomotor tone (1), mueous secretion (9-12), and ciliary beat frequency (13), and possibly an increase of transepithelial fluid transport (14,15). In concert, these effects on the components of the mucociliary transport system are likely to cause an increase in mucoeiliary... 

Gross NJ, Skorodin CE. Cholinergic bronchomotor tone in COPD, estimation of its amount in comparison with that in normal subjects. Chest 1989 96 856-870. 

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