HHE Respiratory 2019 | Page 8

TLD uses a radiofrequency ablation catheter to disrupt the pulmonary connections of the vagus nerve with a minimally- invasive technique cholinergic receptors. Intravenous atropine administration would therefore cause systemic disruption of parasympathetic pathways, including those supplied by the pulmonary trunks of the vagus nerve. Both nocturnal and daytime PEF significantly improved after atropine. Whilst the nocturnal fall in PEF was not completely abolished, it was certainly diminished. The proposed mechanism was speculative, but it was suggested that the normal circadian effects of the vagus nerve are exaggerated by hypersensitisation of airway muscarinic receptors by inflammatory mediators. 8 Therefore blocking the actions of the nerve (pharmacologically or physically) could help to limit nocturnal airflow obstruction, a phenomenon which causes symptoms in many asthma patients. History of vagal section TLD is not the first procedure proposed for asthma that involves section of airway nerves. In 1923, the German surgeon Professor Hermann Kümmell reported the first surgical intervention on the nerve supply to the lungs for asthma. 9 He actually performed a unilateral cervical sympathectomy in the belief that some vagal fibres enter the lung via the sympathetic trunk. It was subsequently postulated that the sympathetic trunk is the afferent part of a reflex arc, of which the efferent component is the bronchoconstriction-inducing parasympathetic vagal fibres. 3 Kümmell’s report documented immediate relief of asthma after the surgery. This led to the uptake of similar procedures in other centres. In 1929, Phillips and Scott 8 HHE 2019 | hospitalhealthcare.com published a review of cases of operations to the pulmonary nerves. They found over 300 cases had been performed since 1923, but only 29 had been reported in sufficient detail and had undergone at least 6 months follow-up. Of these, 8 (28%) were ‘cured,’ 5 (17%) were ‘improved,’ and 16 (55%) were ‘unimproved.’ 10 Most of these procedures involved intervention to the sympathetic trunk, with few vagotomy procedures. Vagal section for asthma underwent something of a revival in the 1950s. Blades et al carried out procedures that involved destruction of the pulmonary plexus around the main bronchus, as well as division of the vagus nerve below the level of the recurrent laryngeal nerve. Of the 38 patients treated, 22 saw a resolution or improvement in their asthma, though 7 patients died. 11 Dimitrov-Skokodi et al performed 19 cases of vagotomy and sympathectomy. They reported asthma attacks ceased altogether in ten patients and were reduced in seven. There were also improvements in mucosal oedema, sputum volume and eosinophilia, radiographic ‘emphysema,’ bronchographic bronchospasm and forced vital capacity. 12 Rienhoff and Gay described bilateral pulmonary plexus resection in 11 patients. Results were very similar to Dimitrov- Skokodi’s results, with a reduction in the severity and frequency of asthma attacks, reduced sputum volume, and resolution of radiographic ‘emphysema.’ 13 Given the period these reports were published in, the assessment of outcomes are mostly subjective with little objective physiological data. It was also prior to the onset of randomised controlled trials, with the reports