Breathing Intolerance Index in COPD and Obesity: A Comparative Observational Study

Abstract

Background: The breathing intolerance index, BIT, a noninvasive derivation of the tension-time index of respiratory muscles, has been recently used to evaluate patients with respect to their need for noninvasive ventilation. Comparing the BIT index in different disorders with mild to moderate respiratory impairment, such as COPD and obesity, would be useful in determining differences in threshold for respiratory muscle fatigue amongst cohorts. Objectives: The purpose of this study was to compare control of ventilation and BIT in individuals with obesity, chronic obstructive pulmonary disease (COPD), and control subjects free of cardiorespiratory disorders. Because change in posture can alter respiratory load and control of ventilation, variables were assessed in two postures. Methods: We assessed 142 subjects consisting of 81 with obesity, 42 with COPD, and 19 non-smoking healthy adults. All subjects underwent evaluation of pulmonary function, control of ventilation and BIT index [(Ti/Ttot) × (Vt/FVC)] in seated and supine postures. Findings: BIT index was significantly greater in seated posture in all 3 cohorts due primarily to an increase in Vt in this position. BIT index was similar in value amongst cohorts in both postures, but tended to be higher in patients with obesity and COPD. Conclusion: While BIT index is higher in seated posture, and tends to be higher in patients with obesity and COPD as compared to control subjects, discrimination between cohorts is not found in our study because of small inter-group variations of respiratory function amongst cohorts. Thus, in clinically stable patients whose vital capacities are mild to moderately reduced, the BIT index alone cannot be recommended as a predictive guide for initiating assisted ventilation for respiratory failure. Nevertheless, because it is easy to perform, and is comfortably tolerated by patients, its potential usefulness may be in periodic measurements to monitor its increase as respiratory reserve declines.

Breathing Intolerance Index (BIT) and its Relation to Exercise Data: Noninvasive Assessment of Inspiratory Muscle Endurance during Rest and Exercise in Patients with Chronic Obstructive Pulmonary Disease and Cardiovascular Disorders

“…At rest, the ventilatory pattern (Vt, Ti, Ttot, V' E , Vt/Ti) observed in our COPD and CVD patients was similar to that reported to that by other investigators [4,5,[12][13][14][15][19][20][21][22][23]. Bellemare and Grassino [1] showed that the critical product of Pdi/Pdimax and Ti/Ttot, tension-time index (TTdi) leading to diaphragmatic fatigue was 0.15 during inspiratory resistive loading at normal resting V' E .…”

“…The study of Koga et al [3], however, assessed the BIT index in quietly breathing patients mainly with bronchial asthma and restrictive thoracic/neuromuscular disorders. Baydur and Chen [4] measured BIT in patients with obesity and COPD during resting breathing in seated and supine postures, finding that BIT was significantly greater in seated position in both cohorts due primarily to an increase in Vt in this position. BIT tended to be higher in patients with obesity and COPD as compared to control subjects.…”

Methods and Applications in Respiratory Physiology: Respiratory Mechanics, Drive and Muscle Function in Neuromuscular and Chest Wall Disorders

“…In this analysis, lung volumes replace respiratory muscle pressures so that the ratios comprising BIT can be affected by lung and chest wall mechanics in addition to respiratory muscle strength. Later, Baydur and Chen ( Baydur and Chen, 2013 ) found BIT in patients with obesity (a chest wall disorder) tended to be higher than in healthy controls in contrast to patients with chronic obstructive pulmonary disease.…”

Breathing Intolerance Index and Control of Ventilation, a Non-invasive Method for Evaluating Inspiratory Muscle Endurance at Rest and Exercise, in Patients with Cardiomyopathy: One Year Follow-up

“…Koga and associates [6] applied the BIT index to predict the need for noninvasive ventilation in patients with bronchial asthma and restrictive thoracic/ neuromuscular disorders. Later, Baydur and Chen [7] demonstrated that resting BIT was significantly greater in COPD and obese patients than in control subjects and even higher in seated position in both cohorts primarily due to an increase in Vt in this position.…”