Ineffectiveness of Intravenous β₂-Agonists on Improving Exercise Tolerance in Patients with Reversible Chronic Airway Obstruction

Abstract

The effects on exercise tolerance after acute administration of β₂-agonists were investigated in 11 patients with partly reversible chronic airway obstruction after 400 μg of salbutamol (S) given intravenously (i.v.) and after 400 μg i.v. of a new selective β₂-agonist, broxaterol (B), by a cardiopulmonary incremental exercise test. At rest, while VE increased in respect to basal conditions (C) after S (from 13.3 ± 2.2 to 14.4 ± 2.8 l/min;p < 0.05) and after B (from 13.6 ± 3.1 to 15.5 ± 3.61/min; p < 0.05), VO₂, VCO₂ and VO₂/HR showed no substantial variations. A small, not significant reduction of PaO₂ was observed both after S (from 82.7 ± 11.7 to 79.1 ± 16.7 mm Hg) and B (from 81.6 ± 10.5 to 78.0 ± 11.0 mm Hg). The maximum workload increased neither after S (from 67.5 ± 39.1 to 66.6 ± 37.0 W) nor after B (from 65.7 ± 39.3 to 60.0 ± 35.8 W). At peak of exercise, VO₂, VCO₂ and VO₂/HR did not change after S and B as compared with C, whereas VE remained higher after both β₂-agonists throughout the effort. VO₂ at ventilatory anaerobic threshold (AT) was significantly greater either after S (from 744 ± 378 to 815 ± 302 ml/min; p < 0.05) and after B (from 756 ± 290 to 842 ± 292 ml/min; p < 0.05). The PaO₂ increase shown by these patients during effort was greater after β₂-agonists administration, ΔPaO₂ from rest to peak of exercise amounting to 14.9 ± 14.3 vs. 7.8 ± 8.2 mm Hg after Sand to 17.8 ± 15.1 vs. 8.8 ± 10.9 mm Hg after B, in respect to relative baseline (p < 0.05). We conclude that β₂-agonists, when given acutely, do not improve exercise tolerance in patients with reversible chronic airflow obstruction, although these drugs can induce a small increment of ventilatory AT. In addition, arterial blood gases do not deteriorate at rest and are better preserved during exercise after β₂-agonists.

Effects of β2-adrenergic stimulation on exercise capacity in normal subjects

“…This result is in keeping with previous reports (McKenzie et al 1983;Violante et al 1989;Malerba et al 1996;Carlsen et al 1997), and conWrmed in the present study with the highest possible tolerated dose given intravenously. It thus appears that 2 agonist-induced increases in stroke volume, indirectly suggested by increased pulse pressures and O 2 pulse in the present experiments, related to positive inotropic eVects and increased venous return (Hopkins et al 1996), cannot contribute to an improved aerobic exercise capacity through and increased O 2 delivery to the exercising muscles.…”

“…2-Adrenergic stimulant drugs used for the treatment of asthma are generally thought to enhance exercise performance, even though the evidence of it has been reported variably depending on doses, modes of administration and study designs (Malerba et al 1996;Carlsen et al 1997;van Baak et al 2000;Goubault et al 2001;Kindermann 2007;Le Panse et al 2007;Decorte et al 2008;Arlettaz et al 2009). …”

Doping and Respiratory System

“…On the contrary some experiments failed in demonstrating that inhalation of salbutamol or salmeterol can improve the performances of healthy or asthmatic athletes [36-37-38] at therapeutic doses. Other experiments also showed that intravenously salbutamol could not improve exercise tolerance in asthmatic athletes [39]. Conversely asthma has a very high prevalence in athletes: from 3.7% up to 22.8% in the systemic review of Helenius I and Haahtela T [40].…”