Ventilatory pattern during bronchial histamine challenge in asthmatics

We wanted to investigate whether asthmatic subjects change their ventilatory pattern consistently when forced expiratory volume in one second (FEV1) has declined by at least 20% during bronchial histamine challenge, in order to assess whether respiratory pattern analysis can be used to monitor bronchial obstruction continuously. Histamine challenge was performed twice within a four week period, in eight asthmatic teenagers. Respiratory inductive plethysmography (RIP) was used for respiratory pattern evaluation, whilst the patients breathed on a mouthpiece attached to a pneumo-tachometer (PTM) whilst wearing a noseclip (first histamine challenge), and during natural breathing (second HiCh). End-tidal carbon dioxide tension (PETCO2) was measured on both occasions. During the second histamine challenge, four of the eight patients responded with a 72% (mean) increase in minute ventilation (VE), an 80% increase in mean inspiratory flow (VI), and a 20% decrease in PETCO2. VE and VI were unchanged, or tended to decrease, among the other four patients (ventilatory nonresponders). Neither provocative dose producing a 20% fall in FEV1 (PD20) to histamine nor the magnitude of the fall in FEV1 differed between ventilatory responders and nonresponders. The ventilatory response to inhaled histamine was abolished when breathing through a PTM. Histamine induced bronchospasm is not uniformly reflected in the breathing pattern. Hyperventilation during histamine challenge might be the consequence of vagal airway receptor activation. Respiratory pattern analysis is not a feasible way to monitor bronchial obstruction during histamine challenge.