Inhaled Water and Salt Suppress Respiratory Droplet Generation and COVID-19 Incidence and Death on US Coastlines

Abstract

Dry air alters salt and water balance in the upper airways and increases the risks of COVID-19 among other respiratory diseases. We explored whether such upper airway variations in salt and water balance might alter respiratory droplet generation and potentially contribute to observed impacts of airway hydration on respiratory disease. In a randomized 4-arm study of 21 healthy human subjects we found that the breathing of humid air, the wearing of cotton masks, and the delivery of (sodium, calcium, and magnesium chloride) salt droplets sized to deposit in the nose, trachea, and main bronchi similarly reduce the exhalation of respiratory droplets by approximately 50% ([Formula: see text] ¡ 0.05) within 10 minutes following hydration. Respiratory droplet generation returns to relatively high baseline levels within 60–90 minutes on return to dry air in all cases other than on exposure to divalent (calcium and magnesium) salts, where suppression continues for 4–5 hours. We also found via a preliminary ecological regression analysis of COVID-19 cases in the United States between January 2020 and March 2021 that exposure to elevated airborne salt on (Gulf and Pacific) US coastlines appears to suppress by approximately 25%–30% ([Formula: see text] ¡ 0.05) COVID-19 incidence and deaths per capita relative to inland counties — accounting for ten potential confounding environmental, physiological, and behavioral variables including humidity. We conclude that the hydration of the upper airways by exposure to humidity, the wearing of masks, or the breathing of airborne salts that deposit in the upper airways diminish respiratory droplet generation and may reduce the risks of COVID-19 incidence and symptoms.

Aerosol particle emission increases exponentially above moderate exercise intensity resulting in superemission during maximal exercise

“…Explaining this unexpected increase of the concentration of aerosol particles during exercise is a challenge for future studies. Possible factors include changes in the velocity and type (i.e., turbulent versus laminar) of gas flow, changes of the composition of the liquids that line the airways, and changes in the hydration status of the airways ( 20 , 21 ). Thus, besides exercise intensity, the airway dehydration that was potentially caused by the endurance exercise and higher ventilation rates could have contributed to the increased aerosol particle emission.…”

“…A further limitation is that possible changes of the hydration status of the subjects were not assessed, as the hydration status can affect aerosol particle emission ( 20 , 21 ). Subjects were allowed to drink water ad libitum in the 3 h before the test to avoid pretest dehydration.…”

“…The number of aerosol particles emitted by a person per unit of time varies and increases when that person talks, coughs, sings ( 14 , 15 ), or is physically active ( 16 – 20 ). It has also been shown that the number of emitted aerosol particles is influenced by the airway hydration status ( 20 , 21 ). Dehydration of the airways can be caused by exercise and increased ventilation and both could lead to a higher number of emitted aerosol particles.…”

COVID-19 symptoms are reduced by targeted hydration of the nose, larynx and trachea

“…The breathing of dry air has recently been observed to amplify upper-airway respiratory droplet generation 41 on normal tidal breathing. Hydration of the upper airways by the breathing of humid air, the wearing of a face mask, or the direct delivery of isotonic or hypertonic saline droplets targeted to the posterior of the nose, larynx and trachea 42 with mean droplet sizes around 8-12 μm reduces respiratory droplet generation to similar degrees and durations 41 . Beyond the consequences of hydration on glottal aperture and laryngeal-jet features-hydration of the larynx increases glottal aperture and reduces phonation threshold pressure 43 , the fluid mechanical basis of laryngeal hydration protocols for singers 43 -hydration alters respiratory droplet formation by volume expansion of the airway lining fluid.…”

A longitudinal study on the effects of hygro‐thermal conditions and indoor air pollutants on building‐related symptoms in office buildings

“…At the same temperature but higher humidity around 50%, transmission efficiency was significantly reduced 34 . Recent studies on COVID‐19 in humans revealed that hydration of the upper airways diminishes respiratory droplet generation and may reduce the risks of respiratory infectious disease incidence and symptoms 35,36 . Thus, those combined host and environment effects due to low humidity might be causative for respiratory infectious diseases in the low humidity season.…”