Broncomotor ToneThe investigation now turns towards the many anecdotal complaints of lung problems following ETS surgery. Patients complain of being “short of breath”, and of worsening asthma.
The lungs have ANS innervation, both SNS and PSNS. The effect of an increase in sympathetic tone is to dilate the bronchial tubes, increasing lung volume. Parasympathetic increase has the opposite effect, constricting the airways. This constriction/dilation helps bring air in and out of the lungs, and is known as “bronchomotor tone”. Sympathetic innervation of the bronchi is from about T1 to T5, so ETS surgery will partially denerve them.
Schematic of ANS Lung Innervation
Prediction: Thoracic sympathectomy will reduce bronchomotor tone.
Empirical Status: Confirmed.
Prediction: Thoracic sympathectomy will diminish lung volume.
Empirical Status: Confirmed.
A group of surgeons in Spain conducted a study to measure the long-term pulmonary effects of ETS. Patients blew into a spirometer, which measures the strength of breathing and the capacity of the lungs. 3 months after surgery, significant reductions in strength (-5.1%) and capacity (-5.2%) were observed. After one year, the test was repeated. The strength had continued to go down, now measuring 11.2% lower than before surgery (-11.2%). The authors claim that lung capacity “had started recovering”, although they do not give any numbers. Nor do they speculate as to whether this partially recovered lung volume might be due to compensatory parasympathetic withdrawal, or a supersensitivity to catecholamines, or regrowth of sympathetic nerve. (see Gonzales et al. 2005)
The study concludes that “thoracic sympathectomy generates a mild, although significant, impairment of the bronchomotor tone, with no clinical consequences. These results suggest that the sympathetic nervous system is involved in pulmonary bronchomotor tone”. (Gonzales et al. 2005)
The language in this study is curious, characterizing the long-term impairment as “significant”, yet claiming this has “no clinical consequences”. While noting the significant and persistent reductions in their measurements, the surgeons state that their patients “remained asymptomatic”. It is not clear what possible symptoms were being considered. It is clear that anecdotal complaints of lung-related problems abound in the oral histories.
A 2003 review of literature stated that “pulmonary functional abnormalities, which could not be attributed to the operative trauma and consisted in a certain loss of lung volume, were observed after upper [thoracic] sympathectomy”. (Hashmonai 2003; see also Molho et al. 1980)
Carbon Dioxide Transfer
The 2005 Spanish study confirmed earlier empirical reports of diminished lung volume resulting from thoracic sympathectomy. (see Noppen et al. 1997). Noppen also measured a reduced ability of the lung membranes to transfer carbon monoxide and carbon dioxide out of the blood; a reduction beyond what would be expected merely from the loss of lung volume. This led the authors to suggest that the SNS may modulate the permeability of the tiny blood vessels in the lungs.
Prediction: Thoracic sympathectomy will reduce CO2 transfer.