Effects of resistive breathing on exercise capacity and diaphragm functionin patients with ischaemic heart disease

Background: Muscle weakness has been suggested to result from the deconditi oning that accompanies decreased activity levels in chronic cardiopulmonary diseases. The benefits of standard exercise programmes on exercise capacit y and muscular strength in disease and health are well documented and exerc ise capacity is a significant predictor of survival in patients with chroni c heart failure (CHF). Selective respiratory muscle training has been shown to improve exercise tolerance in CHF and such observations have been cited to support the suggestion that respiratory muscle weakness contributes to a reduced exercise capacity (despite biopsies showing the metabolic profile of a well trained muscle). Aims: This study aimed to determine the effects of selective inspiratory muscle training on patients with chronic coronary artery disease to establish if an improved exercise capacity can be obtain ed in patients that are not limited in their daily activities. Methods: Nin e male patients performed three exercise tests (with respiratory and diaphr am function assessed before the third test) then undertook a 4-week program me of inspiratory muscle training. Exercise tolerance, respiratory and diap hragmatic function were re-assessed after training. Results: Exercise capac ity improved from 812 +/- 42 to 864 +/- 49 s, P < 0.05, and velocity of dia phragm shortening increased (during quiet breathing from 12.8 +/- 1.6 to 19 .4 +/- 1.1 mm s(-1), P < 0.005, and sniffing from 71.9 +/- 9.4 to 110.0 +/- 12.3 mm s(-1), P < 0.005). In addition, five from nine patients were stopp ed by breathlessness before training; whereas only one patient was stopped by breathlessness after training. Conclusion: The major findings in this st udy were that a non-intensive 4-week training programme of resistive breath ing in patients with chronic coronary artery disease led to an increase in exercise capacity and a decrease in dyspnoea when assessed by symptom limit ed exercise testing. These changes were associated with significant increas es in the velocity of diaphragmatic excursions during quiet breathing and s niffing. Patients that exhibited small diaphragmatic excursions during quie t breathing were most likely to improve their exercise capacity after the t raining programme. However, the inspiratory muscle-training programme was n ot associated with any significant changes in respiratory mechanics when pe ak flow rate, forced expiratory volume and forced vital capacity were measu red. The resistive breathing programme used here resulted in a significant increase in the velocity of diaphragm movement during quiet breathing and s niffing. In other skeletal muscles, speed of contraction can be determined by the relative proportion of fibre types and muscle length (Jones, Round, Skeletal Muscle in Health and Disease. Manchester: University Press, 1990). The intensity of the training programme used here, however, is unlikely to significantly alter muscle morphology or biochemistry. Short-term training studies have shown that there can be increases in strength and velocity of shortening that do not relate to changes in muscle biochemistry or morphol ogy. These changes are attributed to the neural adaptations that occur earl y in training (Northridge et al., Br. Heart J. 1990; 64: 313-316). Independ ent of the mechanisms involved, this small, uncontrolled study suggests tha t inspiratory muscle training may improve exercise capacity, diaphragm func tion and symptoms of breathlessness in patients with chronic coronary arter y disease even in the absence of heart failure. (C) 1999 European Society o f Cardiology. All rights reserved.