Effect of aerosolized histamine on occlusion pressure and ventilation in humans

Cooperation between mast cells and neurons is essential for antigen-mediated bronchoconstriction

Mast cells are important sentinels guarding the interface between the environment and the body: a breach in the integrity of this interface can lead to the release of a plethora of mediators that engage the foreign agent, recruit leukocytes, and initiate adaptive physiological changes in the organism. While these capabilities make mast cells critical players in immune defense, it also makes them important contributors to the pathogenesis of diseases such as asthma. Mast cell mediators induce dramatic changes in smooth muscle physiology, and the expression of receptors for these factors by smooth muscle suggests that they act directly to initiate constriction. Contrary to this view, we show herein that mast cell-mediated bronchoconstriction is observed only in animals with intact innervation of the lung and that serotonin release alone is required for this action. While ablation of sensory neurons does not limit bronchoconstriction, constriction after Ag challenge is absent in mice in which the cholinergic pathways are compromised. Linking mast cell function to the cholinergic system likely provides an important means of modulating the function of these resident immune cells to physiology of the lung, but may also provide a safeguard against life-threatening anaphylaxis during mast cell degranulation.

Breathing pattern variability during bronchial histamine and methacholine challenges in asthmatics

Breathing pattern variability was determined in 10 asthmatic adolescents during repeated bronchial histamine and methacholine challenges (HiCh/MeCh). The purpose was to provide information on ventilatory control in asthmatics by comparing the variability of the various breathing pattern parameters at rest and during induced bronchial obstruction. Changes in variability during bronchial obstruction might be explained by either anxiety effects causing increased variability or by the minimization of the work of breathing causing decreased variability. Ventilation was monitored by respiratory inductive plethysmography in order to minimize the effects on the spontaneous pattern of breathing. Breath-to-breath and day-to-day variability were determined concerning respiratory frequency (fR), inspiratory tidal volume (VTI), inspiratory ventilation (V'I), inspiratory time to total cycle time ratio (TI/TTOT), mean inspiratory flow (VTI/TI, an index of ventilatory drive), rib cage fraction of VTI (VRC/VTI), and maximum compartmental amplitude to VTI ratio (MCA/VTI; an index of rib cage and abdominal phasing). No difference in any parameter was found regarding breath-to-breath coefficient of variation (CV = SD/mean) between recordings at baseline, after saline inhalation and after threshold dose of the provocative agents, i.e. > 20% fall in FEV1. Variability was less for MCA/VTI and VRC/VTI (mean CV 1.3 and 7.7%, respectively) than for TI/TTOT, fR, VTI/TI, VTI, and V'I (14.2, 15.8, 20.9, 22.2 and 21.1%, respectively) (P < 0.01). Likewise, the day-to-day variability did not differ in any parameter between recordings at baseline, after saline inhalation and after threshold dose. The variability was less for MCA/VTI (0.7%) than for TI/TTOT, VRC/VTI, V'I, VTI/TI, fR and VTI (7.1, 12.1, 12.8, 14.2, 13.0 and 15.4%) (P < 0.05). Furthermore, TI/TTOT was less variable than VTI (P < 0.05). Thus, the ventilatory pattern was quite reproducible on a day-to-day basis, despite considerable breath-to-breath variability. Ventilatory drive and tidal volumes were more variable than the rib cage and abdominal phasing, the respiratory timing and the rib cage fraction of tidal volume. The lack of difference in variability between rest and induced bronchial obstruction indicates that other factors than anxiety or minimization of the work of breathing are important for the control of respiration in asthmatics during bronchial challenge.

Hyperventilation during bronchial challenges in asthmatics: reproducibility and assessment of contributing factors

Among asthmatics, the ventilatory response is heterogeneous during bronchial challenge. This study aimed to investigate the reproducibility of the response and to assess possible causes for hyperventilation. Repeated bronchial histamine and methacholine challenges (HiCh/MeCh) were performed in 10 asthmatic adolescents. Ventilation was monitored by respiratory inductive plethysmography (RIP), in order to minimally affect the spontaneous breathing pattern. FEV1 and the volume of trapped gas (measured as the volume of air mobilized by five maximal breaths after a multiple breath nitrogen washout to 2% N2), were used to assess mainly central and peripheral airways obstruction, respectively. When FEV1 had decreased by at least 20%, mean inspiratory flow (VTI/TI) increased by 21% and minute ventilation (V'I) by 21% and 23% during HiCh and MeCh, respectively (both P < 0.05). No correlation was found between the magnitude of the ventilatory response and either: the degree of FEV1 decline, the increase in gas trapping, SaO2 decline or the increase in dyspnoea score. Histamine challenge after beta 2-agonist pre-treatment was associated with increased ventilatory drive in one patient despite the absence of bronchial obstruction, indicating that histamine might directly stimulate afferent airway nerves which cause hyperventilation. The intra-individual variability of the ventilatory response (increase in V'I and VTI/TI) was more than 100% of the mean ventilatory response, while the variability of the bronchomotor response was about 25% of the mean bronchomotor response. Thus, during induced bronchial obstruction in asthmatics, the occurrence of hyperventilation and its intensity are not related to either the degree of central or peripheral airways obstruction, or to the degree of dyspnoea. The reproducibility of the ventilatory response is poor. The ventilatory response appears to be the result of a complex interaction between several afferent stimuli and central ventilatory control.

Preventive effects of beclomethasone on histamine-induced changes in breathing pattern in asthma

Bronchial mucosa inflammation is a hallmark of asthma. Epithelial damage due to inflammatory process may contribute to induce a pattern of rapid and shallow breathing (RSB). Probably due to its effects on inflammatory process, beclomethasone dipropionate (BDP) decreases bronchial hypersensitivity (BH), as assessed in terms of histamine concentration causing a 20 percent FEV1 decrease from saline solution (PC20FEV1); however, no data are available on the effect of BDP on RSB. We studied 32 asymptomatic asthmatic subjects with a severe to moderate levels of BH (PC20FEV1 0.01 to 1.7 mg/ml). After they were randomly assigned to one month of either BDP (2 mg daily, 17 patients) or placebo (15 patients), they inhaled progressively doubling concentrations of histamine phosphate by tidal breathing method. With histamine in seven BDP-treated and in five placebo-treated patients, decrease in FEV1 > or = 20 percent from saline solution was paralleled by a significant decrease in tidal volume (VT), inspiratory time (Ti), and expiratory time (Te), and increase in respiratory frequency (RF). In the remaining patients, histamine failed to change the breathing pattern. In the seven RSB patients, BDP resulted in a smaller VT decrease (p < 0.02) and a smaller RF increase (p < 0.02) with histamine. The five RSB placebo-treated patients were then given one month BDP (2 mg daily): inhaled BDP, but not placebo, resulted both in a significant increase in PC20FEV1 and modulation in histamine-induced changes in breathing pattern. We conclude that high doses of BDP seem to be able to modulate histamine-induced RSB, an effect that might be linked to reversal of airway inflammation.

Pulmonary gas exchange during histamine-induced bronchoconstriction in asthmatic subjects

Bronchial provocation for testing airway hyperreactivity is now well-established. However, the effects of histamine-induced bronchoconstriction on pulmonary gas exchange in man have not been systematically studied. We empirically noted marked decreases in PaO2 in some asthmatic subjects following induced bronchoconstriction. Nine subjects with mild, stable asthma were studied, each on two separate days. The first determined the dose of inhaled histamine necessary to decrease FEV1 by 20 percent and the relationship to lung volume and to pulmonary resistance by the interrupter technique (Rint). On the second day arterial blood gases, ventilation, Rint, and the anatomic (VDan) and physiologic (VDphys) dead spaces were measured simultaneously. There was a significant (p less than 0.05), profound fall in PaO2 (mean, -21.8 mm Hg) and in P(A-a)O2 (mean +14.7 mm Hg) within 5 min after bronchoconstriction, associated with a significant (p less than 0.05) increase in respiratory frequency (mean +5.1 min-1); and decrease in tidal volume (mean, -0.3 L). The ratio VDphys/VT increased significantly (p less than 0.05; mean change, +0.08) even though VDan and VDphys did not. Bronchoconstriction induced the broadening of ventilation (V)/perfusion (Q) ratios, with, most likely, an increase in areas of high V/Q. Histamine-induced bronchoconstriction in mild asthma results in a marked fall in PaO2 due to induced V/Q inequality. Therefore, histamine airway challenge should be used with caution in patients with any preexisting hypoxemia.

Effect of inhaled histamine on occlusion pressure and breathing pattern in asthmatic patients

In animals, histamine inhalation is known to increase either respiratory frequency or respiratory drive by stimulation of airway vagal sensitive endings. However, it is not well known whether these changes are concomitant in man. In order to elucidate this point, we carried out the present investigation in thirty-five asthmatic patients who underwent bronchial provocation test by progressively doubling the dose of inhaled histamine. Bronchial reactivity to histamine allowed two populations of patients to be defined: group I with moderate and group II with mild, increased reactivity. In the twenty-three group I patients, neuromuscular inspiratory drive, assessed by mouth occlusion pressure (P0.1), was found to be significantly increased while no significant changes in breathing pattern were noted. In the twelve group II patients histamine did not modify P0.1 or breathing pattern. However, we were able to separate in group I a sub-group of ten patients, as with atopic asthma, in which histamine-induced increase in P0.1 was paralleled by rapid and shallow breathing (RSB). Changes in P0.1 and breathing pattern did not depend on baseline airway calibre. In group I, after bronchoconstriction had been reversed by inhaling a beta 2-agonist bronchodilator agent (fenoterol), P0.1 decreased significantly and RSB was found to be reversed; however, these changes were not interrelated. We concluded that: in asthmatics, histamine-induced increase in P0.1 is not necessarily paralleled by, nor related with, change in breathing pattern and in atopics a 'sensitization' of vagal receptors could account for the concomitance of enhanced P0.1 with RSB.

Ventilatory response to bronchospasm induced by methylcholine and histamine in man

In 9 normal subjects, we compared mouth occlusion pressure (P0.1) and breathing pattern in bronchospasm of the same magnitude induced by inhalation of acetyl-beta-methylcholine (M) and histamine phosphate (H). The measurements were performed on two different days, in a single blind randomized crossover design, under basal conditions first, then after control inhalation of isotonic buffered saline and finally after inhalation of M or H. For a same mean decrease in FEV1 (+/- SD) by 22.2% (+/- 7.2) after M and 22.3% (+/- 9.4) after H (P less than 0.001), the increases in P0.1 were similar (P less than 0.01 for both drugs) and were correlated to the magnitude of the bronchospasm (r = 0.775, P less than 0.01 for M; r = 0.692, P less than 0.05 for H). However, the minute ventilation and breathing pattern parameters did not differ from each other and from basal or control conditions. Thus, although we can assume that both drugs have different effects on vagal airway receptors, they induce the same respiratory response. We conclude that only receptors indirectly stimulated via airway smooth muscle contraction contribute to the mediation of drive and breathing pattern in drug induced bronchospasm in humans.