Exercise-induced asthma

Exercise-induced bronchoconstriction: celebrating 50 years

This article examines in detail the history of more than half a century of investigations into elucidating the causation of exercise-induced bronchoconstriction. Despite earnest attempts by many researchers from many countries, answers to some pivotal questions await the next generation of investigators into exercise-induced bronchoconstriction.

Dichotomous airway response to exercise in asthmatic patients

The extent and location of airway narrowing in asthmatic subjects are usually inferred from measurements of maximal expiratory flow rates and airway resistance. In the present study, we used the acoustic reflection technique to measure the airway cross-sectional area in 14 asthmatic subjects and 8 normal controls before and following treadmill exercise tests. In normal subjects, exercise caused no significant change in FEV1 and bronchial area, but did cause a significant increase in the intrathoracic tracheal area from 2.0 +/- 0.7 cm2 to 3.1 +/- 0.7 cm2 (p less than 0.002). In the asthmatics, exercise was followed by a 37 +/- 15% reduction in forced expiratory volume in 1 s(FEV1), and a 36% decrease in bronchial area from 8.5 +/- 2.8 cm2 to 5.4 +/- 1.1 cm2 (p less than 0.001); however, extra- and intrathoracic tracheal areas increased significantly. These findings provide direct and quantitative evidence that the bronchi are the main site of airway narrowing in exercise-induced asthma, and draw attention to the phenomenon of tracheal dilatation that occurs concomitant with bronchoconstriction in asthmatic patients.

Physical Activity and the Asthmatic

In brief: Recent studies suggest that avoiding exercise is unwarranted and detrimental for asthmatics. Although exercise provokes bronchospasm in most asthmatics, the severity of exercise-induced asthma can be reduced by several factors: control of exercise duration; less intense, intermittent exercise; warm-ups; warmer, humid inspired air; aerobic fitness; and drugs. Regular vigorous activity increases fitness, enhances tolerance to attacks, and provides more social and psychological independence. The recent development of protective medications has made such activity possible for many asthmatics. Preexercise cromolyn sodium and beta adrenergic agonists are recommended for blocking or reversing attacks.

Protective effects of repeated short sprints in exercise-induced asthma

Many asthmatic patients demonstrate bronchial lability with a six-minute period of exercise, which is characterised by an initial bronchodilatation followed by bronchoconstriction. This early bronchodilatation response has been further analysed by investigation of the effects of repeated 30-second sprints before and after a six-minute run. It was found that these repeated short sprints did not induce bronchoconstriction, resulted in less bronchoconstriction after a subsequent six-minute run, and caused bronchodilatation if exercise-induced bronchoconstriction was present. It is postulated that this effect may be related to an increase in circulating catecholamines or altered vagal-sympathetic balance.

Breathing dry or humid air and exercise-induced asthma during swimming

Recent studies have shown the relevance of air humidity to the provocation of bronchoconstriction by running. The present study was undertaken to ascertain whether the humid air breathed during swimming could explain the protective effect of swimming on the asthmatic. Nine asthmatic children 9--15 years old swam while inspiring dry (15--35% R.H.) or humid (80--90% R.H.) air administered in a random order, a week separating the two sessions. The exercise challenge was an 8-min tethered swim at a metabolic rate (VO2) of 29 ml.kg-1.min-1, minute ventilation (VE) of 34 L.min-1, and a heart rate (HR) of 161 beats.min-1. Ambient air and water temperature were 28 +/- 2 degrees C and 27 +/- 2 degrees C, respectively. Pulmonary functions were tested pre and post swimming. Exercise VE, VO2 and HR were similar under the two conditions. No reduction in any of the pulmonary functions (FVC,FEV1.0,MMEFR,MBC) was found after 5 and 10 minutes following the swimming exercise in either of the conditions. In contrast, a treadmill run of similar metabolic and ventilatory intensity induced bronchoconstriction when room air was dried to 25--30% R.H. It is suggested that, unlike running, swimming is of low asthmogenicity even when inspired air is dried to 25--30% at neutral temperatures.

Arterial pH, airway caliber and response to acetylcholine and catecholamines in vivo

Direct assessment of tracheal circumference, which permits evaluation of constriction and dilatation in vivo, was made continuously in intact, pentobarbital-anesthetized, spontaneously breathing dogs. Immediate response to induction of hypercapnia included tracheal constriction and cessation of normal, vagus-dependent rhythmicity of airway tone. The characteristic constrictor response to acetylcholine was exaggerated significantly during hypercapnic acidosis and returned to normal when arterial pH, but not CSF pH, was corrected by NaHCO3 infusion. Epinephrine produced significant tracheal dilatation (infrequently followed by constriction) and isoproterenol produced only dilatation at normal pH. The catecholamine-induced dilatation was decreased significantly during hypercapnic acidosis, but improved after NaHCO3 infusion. Responses to acetylcholine and epinephrine were the the same as control during alkalemia, whereas the response to isoproterenol was unexplainedly diminished. Thus alkalemia may inhibit the action of isoproterenol; acidemia enhances parasympathomimetic constriction and reduces sympathomimetic dilatation; and correction of arterial pH returns these responses to normal, even if hypercapnia and CSF acidosis persist.

A critical assessment of the roles of circulating hydrogen ion and lactate in the production of exercise-induced asthma

To evaluate the roles of circulating hydrogen ion and lactate in the production of exercise-induced asthma, two experiments were performed. In the first, we exercised six asthmatic subjects to exhaustion on a bicycle ergometer while recording arterial pH at periodic intervals. Multiple aspects of pulmonary mechanics were measured before and after the work load. After recovery, the identical procedures were repeated, but sufficient quantities of sodium bicarbonate were infused to keep the pH at the pre-exercise level. In both experiments, statistically identical attacks of asthma were induced. To study the effect of lactate, five subjects were exercised on several occasions in order to determine the lowest level of work, and hence arterial lactate, that was reproducibly associated with an acute asthma attack. When this was known, sufficient quantities of sodium lactate were infused into the resting subjects so as to equal or exceed the amount produced with exercise. Pulmonary mechanics were not altered with this intervention. These findings demonstrate that lactic acidemia is not the cause of exercise-induced asthma.

The effect of Sch 1000 and disodium cromoglycate on exercise-induced asthma

The effect of disodium cromoglycate and Sch 1000 on exercise-induced asthma was studied in nine patients. The exercise stimulus consisted of either treadmill running or jogging; spirometric measurements were made before and at intervals after exercise. In six patients, disodium cromoglycate and Sch 1000 were both effective in preventing exercise-induced asthma. In two patients, Sch 1000 was effective, while disodium cromoglycate gave no protection. In the remaining patient, disodium cromoglycate was more effective than Sch 1000. The findings of this study suggest that the mechanism of exercise-induced asthma may be multifactorial, and the relative importance of each factor may vary in different patients.

Bronchoconstriction induced by repeated forced vital capacity manoeuvres

An asthmatic atopic patient who developed bronchoconstriction during repeated forced vital capacity manoeuvres and after exercise is reported. Since increases in total airway and upper segment resistances and drop in FEV1 and Vmax 50 were induced, it is considered that bronchoconstriction involved most of the airways. Partial prevention of this effect could be demonstrated after inhalation of an adrenergic bronchidilator or disodium cromoglycate. Atropine completely prevented the flow response but did not alter the total airway resistance increase. Bronchoconstriction is interpreted as partially related to mast cell disruption and cholinergically mediated stimuli.

Exercise-induced asthma

A review of exercise-induced asthma is presented which describes work that has been carried out by the authors and by other investigators over recent years. The effect of exericse on lung function in asthmatic and normal subjects is compared. The influence of the type and severity of exercise on the response of the asthmatic is noted and the importance this has for interpretation of results. The effects of various drugs on exercise-induced asthma are considered in some detail. The clinical implications of the results of exercise tests in asthmatics, their relatives, and other subjects are considered in terms of the diagnosis and prognosis of asthma and its mode of inheritance. It is concluded that there is as yet no explantation for the mechanism of exercise-induced asthma, but it is a tool of potentially great value for research into the physiology and treatment of clinical asthma.

Metabolic and ventilatory changes in asthmatic patients during and after exercise

Five asthmatic patients aged 25-30 years were studied during and after 6-8 minutes of steady exercise on both a bicycle ergometer and a treadmill. For each patient the duration of work, oxygen consumption, minute ventilation, and heart rate were similar in each form of exercise.

During exercise all patients had an increase in peak expiratory flow rate. The blood lactate level was higher during bicycle exercise but arterial Pco₂ and pH fell to similar levels during both forms of exercise. There was a rise in arterial oxygen tension in four of the patients during exercise; in one subject arterial oxygen tension fell.

Bronchoconstriction was greater following treadmill exercise in all subjects and was associated with an increase in ventilation/perfusion inequality, as shown by arterial hypoxaemia, an increase in alveolar-arterial oxygen tension gradients, and an increase in physiological dead space. In one subject whose PEFR fell to 25% of the predicted value Co₂ retention occurred. These changes are similar to those found in other forms of acute asthma.

In one subject, during both forms of exercise the mixed expired Pco₂ was observed to be higher than the arterial Pco₂, thus giving a negative value for physiological dead space. This observation is discussed.

Significance of effect of beta blockade on ventilatory function in normal and asthmatic subjects

The lability index was examined in 45 normal subjects between 17 and 45 years and also in six patients with asthma, five with a history of asthma in childhood but no clinical attacks, and three with hay fever. The measurements were repeated after β blockade with propranolol. Fifteen per cent of the normal subjects exhibited a degree of lability after propranolol which has been previously found only in asthma. It is suggested that a constrictor mechanism exists in normal subjects on exercise but that β receptor activity protects them from bronchiolar constriction; post-exercise bronchoconstriction in the asthmatic may be explained in terms of this mechanism. It is also suggested that a proportion of `normal' subjects are potentially more labile than the remainder of the population and that it is these who may develop clinical asthma if they also happen to be atopic subjects.

Exercise-induced airways constriction

Airway conductance was measured in a body plethysmograph at different lung volumes before and after graded exercise. In 14 out of 19 patients, mostly asthmatics, airway conductance fell significantly after exercise. These subjects also showed other signs of an increased bronchial reactivity to different stimuli, including forced breathing, hyperventilation, and cold air, but they had no exogenous allergy. The exercise-induced bronchoconstriction could be blocked by atropine in six of the nine patients tested. Exercise-induced bronchoconstriction in patients with clinical and physiological evidence of increased airway reactivity thus seems to be primarily mediated via a vagal reflex, probably from hyperresponsive airway mechanoreceptors reacting to increased ventilatory flow or lung distension. No relation was found between PaCO₂ or pH and the severity of airways constriction. Cromoglycic acid failed to block the exercise reaction in five of the six hyperreactive patients tested. In addition to or following the vagal reflex a disturbed relation between beta and alpha receptors in bronchial muscles or a release of humoral spasmogens may contribute to the progression of post-exercise airways constriction.

Metabolic changes preceding exercise-induced bronchoconstriction

Five asthmatics aged 25-30 were studied during bicycle ergometer and treadmill exercise. Metabolic and ventilatory changes during exercise were compared with the degree of bronchoconstriction which followed exercise. In all patients bronchoconstriction was greater after treadmill exercise. Contrary to previous suggestions, exercise-induced bronchoconstriction did not seem to be caused by lactic acidosis, increase in minute ventilation, acidaemia, hypocapnia, or change in arterial Po(2)

Specificity of exercise in exercise-induced asthma

Ventilatory function after three types of exercise-running, cycling, and swimming-was studied in 10 control subjects and 40 asthmatic patients. All performed eight minutes of submaximal aerobic exercise during each of the programmes, which were conducted in a randomly selected order. Biotelemetric monitoring of heart rates was used to equate the intensity of the exertion undertaken during the three systems of exercise. No control subject showed any significant variation in ventilatory capacity after exercise, and the responses after the three forms of exercise did not differ.In asthmatics exercise-induced asthma was observed after 72.5% of running tests, 65% of cycling tests, and 35% of swimming tests. In addition, those patients who developed exercise-induced asthma after swimming were noted to have significantly smaller falls in FEV(1) levels than were recorded after running and cycling. These results were statistically significant (P <0.01).The unexplained aetiology of increased airways resistance after exercise in asthmatics is discussed. This study indicates that swimming should be recommended in preference to running or cycling as an exercise programme for adults and children with asthma.

Comparison of bronchoconstriction induced by cycling and running

Bicycle ergometer, treadmill, and free range running exercise have been used to induce bronchoconstriction in 10 asthmatic subjects who were relatively well and free from symptoms at the time of study. Comparisons have been made with normal subjects under similar laboratory conditions. Bronchoconstriction was measured by peak expiratory flow rate before, during, and after each test. Ventilation, pulse rate, and gas exchange were also measured. The work involved in the different types of exercise was matched to produce similar ventilation and pulse rates for any one subject.

Exercise-induced bronchoconstriction was significantly less on the bicycle ergometer than on running (treadmill or free range). The normal subjects showed less than one quarter the bronchial lability of the asthmatic subjects in any one test. All subjects had lower respiratory exchange ratios during running compared with cycling and this appeared to correlate with the bronchial lability in the asthmatics, who also had rather higher pulse rates during running. Running involves a proportion of high-efficiency negative work which might partly account for the observed differences.

Exercise asthma and disodium cromoglycate

Exercise-induced asthma (defined as a fall in PEF of at least 25% of the pre-exercise value) was studied in adult patients with uncomplicated asthma. This was found to occur in 22 out of 52 patients. Pre-exercise inhalation of disodium cromoglycate reduced the mean fall in PEF after maximal exercise from 50% of the pre-exercise value to 23% (open assessment in 11 cases). After submaximal exercise for eight minutes the reduction was from 18% to 10% (double-blind crossover study in 28 cases). It is concluded that disodium cromoglycate partly inhibits the increase of airways resistance after exercise in asthmatic patients.