A preliminary study of the effect of inhaled nitric oxide on lung mechanics in the standing horse with histamine-induced bronchoconstriction.

This research studied how inhaled nitric oxide affects the lung functions of standing horses after their airways were constricted using histamine. Results suggest nitric oxide can partially dilate small airways in horses that have bronchoconstriction due to histamine.

Objective and Methodology of the Study

• The study explored the role of inhaled nitric oxide on pulmonary mechanics in standing horses affected by histamine-induced bronchoconstriction.
• Researchers ensured the respiratory health of the six normal horses, which was confirmed through historical data, clinical observations, and bronchoalveolar lavage examination.
• The pressures within the chest cavity (intrathoracic pressures) were estimated using distal oesophageal pressures.
• A heated pneumotachograph was implemented to measure respiratory gas flows, which was then used to determine pulmonary mechanic variables. The measurements were taken on a breath by breath basis.
• The bronchoconstriction was intentionally caused by nebulizing a solution containing 0.75% w/v histamine over 5 minutes.

Assessment and Analysis

• Pulmonary function was assessed during 4 periods, first while the horse was breathing normal air before exposure to the histamine. And then at intervals of; 5 minutes post histamine exposure; 10 minutes post histamine while the subject horse was inhaling 5ppm nitric oxide; and 14 minutes post histamine still while the horse breathed normal air.
• Friedman’s nonparametric repeated measure analysis of variance followed by Dunn’s multiple comparisons tests was applied in reviewing the statistical data collected.

Observations and Results

• The effect of nitric oxide on pulmonary mechanics was measured using a criteria: a return of the variable value following nitric oxide administration towards control value and subsequent restoration of the value toward post histamine levels after discontinuation of nitric oxide.
• Observations showed five variables (including dynamic compliance, airway resistance, maximum developed pressure, work of breathing, and peak expiratory flow) had changes as a response to histamine.
• However, amongst these, only dynamic compliance, airway resistance, and maximum developed pressure met the defined criteria, still only the change in dynamic compliance and airway resistance was statistically significant (P < 0.05).
• These findings point towards the conclusion that inhaled nitric oxide can partly dilate small airways that had been constricted by histamine.