The nasal fluid is an easily accessible form of airway surface liquid. The objective of this study was to find a technically easy and reproducible method for sampling and analysis of this fluid. In a pilot study, several methods to carry out X-ray microanalysis of sub-microliter droplets were compared. Acceptable results were obtained with several of these methods (pipeting on filter paper or analysis of frozen-hydrated droplets at low temperature). Nasal fluid was collected from the inferior turbinate with a micropipette after occlusion of a nostril for 5-10 minutes. Ion concentrations in nasal fluid from six control subjects were (in mM, mean +/- standard error): sodium (Na) 127 +/- 6, chloride (Cl) 140 +/- 7, potassium (K) 27 +/- 3, and calcium (Ca) 5 +/- 1. This sampling method proved difficult to apply to cystic fibrosis (CF) patients because of the viscous quality of their nasal secretion. Therefore, an alternative method was devised. Sephadex G-25, ion exchange beads were mounted on double-sided tape, which was stuck on a filter paper as support. The filter paper was applied for 10 minutes to the nostril of a subject, and kept loosely in place. During the exposure period, the nasal fluid equilibrates with the beads. After removal of the filter paper with the beads from the nostril, the beads were rinsed with a hydrophobic volatile silicone oil to remove excess nasal fluid, dried, and analyzed. This method of collection is not cumbersome for the subject and gives results similar to those obtained by the direct collection method: Na 142 +/- 28 mM, Cl 150 +/- 36 mM, K 43 +/- 10 mM (mean and standard error of four determinations). Small differences between the filter method and the bead method can be explained by the fact that the filter method measured total nasal fluid, whereas the bead method measures predominantly the fluid component. Subjects suffering from mild respiratory illness or rhinitis had higher values for Na, K, and Cl in their nasal fluid.

The composition of the airway surface liquid, a thin layer of fluid covering the airway wall, has been debated. Two new techniques to determine the ionic composition of the airway surface liquid are presented. In the first technique, pieces of the airway were shock-frozen and analyzed by X-ray microanalysis in the frozen state in the scanning electron microscope. In the second technique, the airway surface liquid was collected with the help of dextran beads that were allowed to absorb the fluid. The beads were collected in silicon oil, cleaned, dried, and analyzed. Airway surface liquid from pig airways was isotonic to lightly hypertonic, whereas airway surface liquid from mouse and rat airways was hypotonic. The ionic composition of airway surface liquid from rodent airways could be changed by pharmacological stimulation of fluid transport. Transgenic mice with cystic fibrosis (CF) had significantly higher Na and Cl concentrations in the airway surface liquid than normal mice. Nasal fluid was also collected from humans. In CF patients, CF heterozygotes, and rhinitis patients, the levels of Na and Cl in the nasal fluid were signifi- cantly higher than in healthy controls. In CF patients K levels were also significantly higher than in healthy controls. The ionic concentrations in fluid collected from patients with primary ciliary dyskinesia (PCD) were not different from normal. Females with CF had significantly higher concentrations of Na, Cl and K in their nasal fluid compared to male patients. The dextran bead technique was also used to determine the ionic composition of the apical fluid in cultures of respiratory epithelial cells from healthy controls and CF patients. In the healthy controls, the fluid was hypotonic. In the CF cell cultures, the apical fluid had a higher Na and Cl concentration than in the controls.

The ionic composition of the airway surface liquid (ASL) is of importance in cystic fibrosis and exercise-induced asthma. However, literature data on the composition of the ASL vary markedly. The aim of the study was to determine the composition of the ASL, using two different methods involving minimal manipulation. In one method, the composition of the ASL was measured by X-ray microanalysis of frozen-hydrated samples. In the second method, small dextran beads were equilibrated with the ASL in a moisture chamber, isolated, dried, and analyzed. Plasma or serum from the same pigs was also analyzed. Both methods showed that the Na and Cl concentrations in the ASL are close to the concentrations of these ions in plasma. X-ray microanalysis of frozen-hydrated ASL showed significantly higher K, P, and S because here the upper layer (containing cell debris and secreted mucus) is sampled, whereas the bead method samples the watery component of the ASL. Ultrastructural analysis of the epithelium at various osmotic values showed evident damage at concentrations of 50 mM or less. These data support the notion that the physiologically important watery component of the pig ASL has an ionic composition close to that of plasma.

The ionic composition of the airway surface liquid (ASL) in healthy individuals and in patients with cystic fibrosis (CF) has been debated. Ion transport properties of the upper airway epithelium are similar to those of the lower airways and it is easier to collect nasal ASL from the nose. ASL was collected with ion exchange beads, and the elemental composition of nasal fluid was determined by X-ray microanalysis in healthy subjects, CF patients, CF heterozygotes, patients with rhinitis, and with primary ciliary dyskinesia (PCD). In healthy subjects, the ionic concentrations were approximately isotonic. In CF patients, CF heterozygotes, rhinitis, and PCD patients, [Na] and [Cl] were significantly higher compared when compared with those in controls. [K] was significantly higher in CF and PCD patients compared with that in controls. Severely affected CF patients had higher ionic concentrations in their nasal ASL than in patients with mild or moderate symptoms. Female CF patients had higher levels of Na, Cl, and K than male patients. As higher salt concentrations in the ASL are also found in other patients with airway diseases involving chronic inflammation, it appears likely that inflammation-induced epithelial damage is important in determining the ionic composition of the ASL.

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