To the Editors:
In their recent publication in the European Respiratory Journal, Sartori et al. 1 explain the difference between their results and previous studies by arguing that in other studies “no particular care was taken to locate the electrode in the inferior turbinate”, without contacting the investigators who performed the measurements that they criticise. This argument is not acceptable for us. We can assure them that we paid very careful attention to the placement of the nasal electrode as we are well aware that potentials vary considerably in magnitude in different regions of the nose 2, 3. The fact that the magnitude of measured potentials is comparable among all studies at high altitude rules out a significant effect of the site of recording and disproves the argument by Sartori et al. 1.
We would like to make further observations on the discrepant results which are summarised in table 1⇓. In a study by Mairbäurl et al. 5, performed in 1999 in freezing temperatures and strong winds, subjects reported dryness of the nasal epithelium. This was not a problem in a second study performed in 2003 6 when weather conditions were warm and nasal dryness was prevented with aerosolised isotonic saline. This manoeuvre entirely prevented the hyperpolarisation of total nasal potential difference. Mason et al. 4 and Sartori et al. 1 did not observe a problem with nasal dryness, although the subjects in Mason et al. 4 bathed their nostrils with isotonic saline twice daily. These variations indicate the problems and difficulty of interpretation of nasal potential difference measurements. Mairbäurl et al. 5 found no statistically significant change in the amiloride-sensitive change in the nasal potential difference (NPΔamil) in high-altitude pulmonary oedema (HAPE)-susceptible subjects; only a nonsignificant trend was reported, whereas, in another study by Mairbäurl et al. 6, significantly decreased NPΔamil in HAPE was seen, again pointing to possible effects of nasal dryness. This argument is strengthened by the increase seen in the chloride-sensitive change in the nasal potential difference (NPΔCl) reported by both Mairbäurl et al. 5 and Mason et al. 4. Increased NPΔCl is compatible with increased nasal secretion. This possibility was not addressed in the study by Sartori et al. 1.
In summary, these results indicate that the potential across the nasal epithelium might very well be affected by climatic conditions 7 to which the nose is exposed but to which the alveolar epithelium is not 1, 4. Due to this, particular caution must be exercised when extrapolating data obtained at the nasal epithelium to make claims about changes occurring at the level of the alveolar epithelium.
- © ERS Journals Ltd