Aerosols in Asthma

The effects of bronchodilators on spontaneous ventilation and oxygen consumption in rhesus monkeys

The effects of breathing normal saline, salmeterol, fenoterol, ipratropium bromide, or formoterol, and of i.v. infusion of theophylline on oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), heart and respiratory rates, and end-tidal carbon dioxide tension (P(ET)CO2) have been defined in 10 anesthetized, intubated rhesus monkeys (mean age 7.0 y, weight 10.2 kg). VO2 increased over control by + 17.1% after salmeterol (p < 0.001), +33.3% after fenoterol (p < 0.001), +23.7% after formoterol (p < 0.001), +3.9% after theophylline (p < 0.01), but did not change after ipratropium bromide and normal saline. VE increased by 63.0% after fenoterol (p < 0.001), 49.8% after formoterol (p < 0.001), 31.7% after salmeterol (p < 0.01), and 29.7% after theophylline (p < 0.001), but not after ipratropium bromide or normal saline. Heart rate response was greatest after fenoterol, formoterol, and salmeterol, respectively. P(ET)CO2 dropped dramatically after theophylline (-15.7%, p < 0.001), but not at all with any of the inhaled beta2-adrenoceptor agonists. In seven animals, salbutamol (albuterol) caused an increase in V(E) and VO2 of 50.1% and 45.9%, respectively, whereas in the presence of a beta2-adrenoceptor antagonist [racemic or (+/-)-propranolol (0.1 mg/kg i.v.)], inhaled salbutamol (2.5 mg/mL for 10 min) could not increase V(E) (+6.2%, p > 0.05) and VO2 (+1.6%, p > 0.05). The increase in VO2 and V(E) after administration of beta2-agonists may be partly the result of direct stimulation of the respiratory center and partly a response to increased metabolic rate. The dramatic increase in VO2 and V(E) after salbutamol was suppressed in the presence of propranolol, which is consistent with a beta-receptor-mediated mechanism.

Nonbronchodilator effects of pirbuterol and ipratropium in chronic obstructive pulmonary disease

BACKGROUND

Although both beta-adrenergic agonists and anticholinergic agents are widely used in the treatment of patients with COPD, they influence the pulmonary circulation and ventilation differently. We compared the effects of these two agents on gas exchange and distribution of ventilation in COPD.

METHODS

Pirbuterol and ipratropium bromide were administered by inhalation via a metered-dose inhaler to 12 and 14 patients with COPD, respectively, in a randomized, double-blind fashion. Pulmonary function tests, arterial blood gas levels, heart rate, resting minute ventilation (VE), physiologic dead space volume to total ventilation ratio (VD/Vt) and oxygen consumption (VO2) were measured prior to and then 5, 15, 30, and 60 min after administration of the respective drugs. The changes in these measurements after administration of the two drugs were analyzed and compared with each other.

RESULTS

The pulmonary function test measurements showed similar improvement after administration of both drugs. Heart rate fell in both groups. After administration of pirbuterol, the alveolar-arterial oxygen pressure difference (P[A-a]O2) and VE rose significantly and the rise in FEV1 showed a negative correlation with the fall in PaO2. In contrast, the use of ipratropium bromide did not produce these effects, but resulted in a fall in VO2 and a rise in VD/Vt.

CONCLUSION

Pirbuterol and ipratropium are equally effective bronchodilators in COPD. Pirbuterol results in a significant rise in P(A-a)O2 and resting VE. Ipratropium does not affect these measurements and seems to reduce the oxygen cost of breathing. The results suggest significant differences between the effects of the two agents on gas exchange, ventilation, and VO2 which could be of clinical significance.