Effects of noninvasive ventilation on lung hyperinflation in stable hypercapnic COPD

Abstract

Effects of noninvasive ventilation on lung hyperinflation in stable hypercapnic COPD. O. Díaz, P. Bégin, B. Torrealba, E. Jover, C. Lisboa. #ERS Journals Ltd 2002. ABSTRACT: Two previous uncontrolled studies have suggested that noninvasive mechanical ventilation (NIMV) in patients with hypercapnic chronic obstructive pulmonary disease (COPD) improves arterial blood gas tensions by decreasing lung hyperinflation with the consequent reduction in inspiratory loads and changes in ventilatory pattern. The aim of this randomised placebo-controlled study was to determine whether these mechanisms play a pivotal role in the effects of NIMV on arterial blood gases.Thirty-six stable hypercapnic COPD patients were randomly allocated to NIMV or sham NIMV. A 2-week run-in period was followed by a 3-week study period, during which ventilation was applied 3 h?day -1 , 5 days a week. Arterial blood gases, spirometry, lung volumes, and respiratory mechanics were measured before and after application of NIMV.Patients submitted to NIMV showed changes (mean (95% confidence interval)) in daytime arterial carbon dioxide tension (Pa,CO 2 ) and arterial oxygen tension of -1.12 (-1.52--0.73) kPa (-8.4 (-11.4--5.5) mmHg) and 1.14 (0.70-1.50) kPa (8.6 (5.3-11.9) mmHg), respectively. Total lung capacity, functional residual capacity (FRC) and residual volume were found to be reduced by 10 (7-13), 25 (18-31), and 36 (27-45)% of their predicted value, respectively, whereas forced expiratory volume in one second and forced vital capacity increased by 4 (1.5-6.9) and 9 (5-13)% pred, respectively. Tidal volume (VT) increased by 181 (110-252) mL. All of the above changes were significant compared with sham NIMV. Changes in Pa,CO 2 were significantly related to changes in dynamic intrinsic positive end-expiratory pressure, inspiratory lung impedance, VT and FRC.It was concluded that the beneficial effects of noninvasive mechanical ventilation could be explained by a reduction in lung hyperinflation and inspiratory loads.

CPAP Decreases Lung Hyperinflation in Patients With Stable COPD

“…Soares et al did not measure RV, FRC, and TLC. Our results also agree with those of Díaz et al, 8 who found that short-term noninvasive ventilation (bi-level positive airway pressure) significantly reduced RV (from 201 Ϯ 48% of predicted to 165 Ϯ 49% of predicted, P Ͻ .001) and TLC (from 173 Ϯ 36% of predicted to 148 Ϯ 35% of predicted, P Ͻ .001) in stable COPD patients. However, Díaz et al measured lung volumes with the nitrogen-washout method, the accuracy of which depends on all parts of the lung being well ventilated.…”

“…Other studies of CPAP in stable COPD have yielded conflicting results; nevertheless, there is some evidence that CPAP prevents gas-exchange deterioration, improves quality of life, and reduces the need for hospitalization in patients with hypercapnia or nocturnal hypoventilation. 8,19,20 In addition to the favorable findings on CPAP for COPD exacerbation, some studies have found that CPAP either during or between exercise sessions can enhance the benefits of pulmonary rehabilitation. 1,2,21,22 However, the underlying mechanisms of CPAP benefits are not fully understood.…”

“…In patients with stable COPD, the benefits of CPAP may be explained by a reduction in lung hyperinflation. 6,8 Indeed, several investigators have found that applied PEEP can counterbalance auto-PEEP without causing further hyperinflation. 9,10 CPAP and applied PEEP decrease the inspiratory load at any given volume, therefore reducing the increased work-load and improving lung mechanics until a critical PEEP value is reached.…”

Hyperinflation on Chest Radiograph as a Marker of Low Adherence to Positive Airway Pressure Therapy in the Overlap Syndrome

“…For instance, NIV reduces total lung capacity by 10% in stable hypercapnic COPD, possibly from increased cross-sectional areas of the airways, decreased airway resistance, and increased expiratory time, which may facilitate the emptying of diseased lung units. 24,25 In contrast, other studies have shown that CPAP only temporarily decreases hyperinflation in COPD. 26 Similarly, high-resolution computed tomographic studies show that although low CPAP (5 cm H 2 O) may cause regional deflation in some subjects, higher CPAP (10 -15 cm H 2 O) may promote overinflation of already hyperinflated zones.…”

Noninvasive Ventilation in Mustard Airway Diseases

“…27 In our subjects with mustard airway disease, we found that NIV decreased functional residual capacity and residual volume non-significantly after 12 months.…”