Mild dehydration: a risk factor of broncho-pulmonary disorders?

Several expert committees recommend a high fluid intake in patients with chronic bronchitis and asthma. Is there a relationship between fluid intake or hydration status and broncho-pulmonary disorders like bronchitis and asthma? First, basic physiologic mechanisms like regulation of lung fluid balance and water transport at pulmonary surfaces were analyzed, in order to characterize the role of local hydration status in lung and airways. Second, making use of the computer-based literature searches (PubMed), evidence for a role of hydration status in complex physiological and pathophysiological conditions of lungs and airways like perinatal lung adaptation (PLA) (in prematures), mucociliary clearance(MC) and asthma was categorized. The movement of fluid between the airspaces, interstitium, and vascular compartments in the lungs plays an important physiological role in the maintenance of hydration and protection of the lung epithelium and significantly contributes to a proper airway clearance. PLA is characterized by a rapid change from fluid secretion to fluid absorption in the distal respiratory tract, with the literature data confirming a critical role of the epithelial sodium channel. Only few studies have investigated the effect of different fluid input regimens on PLA in prematures. MC relies on the interaction between epithelial water fluxes, mucus secretions, and ciliary activity. Whereas animal data show that drying of the airway epithelium decreases MC, few clinical studies investigating the effect of local or systemic hydration on MC have led to ambiguous results. Asthma (A) is characterized by chronic airway inflammation and episodic airway obstruction. Data in animals and humans indicate an association between exercise-induced-A and conditioning (humidity and heat exchange) of inspired air. However, epidemiological studies (children and adults), investigating the role of fluid (and salt) input in the etiology of the disease as well as studies analyzing different markers of hydration status during asthmatic attacks have so far led to conflicting results. Some expert groups recommend sufficient hydration as a complementary A-therapy. Analysis of basic physiological mechanisms in lungs and airways clearly demonstrates a critical role for water transport and local hydration status. In broncho-pulmonary diseases, however, analysis of the complex pathophysiological mechanisms is difficult. Thus, we still need more studies to confirm or refute mild dehydration or hypohydration as a risk factor of broncho-pulmonary disorders.