Impact of breathing pattern on work of breathing in healthy subjects and patients with COPD.

The impact of the respiratory pattern on respiratory muscle workload represents an unresolved controversy and is important for the treatment of patients with respiratory disorders and respiratory muscle failure. We designed this study to investigate the relationship of respiratory pattern and inspiratory workload. We measured esophageal pressure and inspiratory flow and calculated work of breathing, tidal volume and respiratory rate. Ten healthy subjects and 10 COPD patients participated and performed five different breathing patterns starting from respiratory rate 12 and tidal volume 1l or quiet breathing, respectively. They were instructed to increase respiratory rate by 50 and 100% as well as tidal volume by 50 and 100% while maintaining constant minute-ventilation. In healthy subjects Delta VT was the single best parameter to predict Delta WOB (R=0.958, R(2)=0.918, p<0.0001). The relationships of changes in tidal volume, respiratory rate and rapid shallow breathing index to changes in WOB were linear. In the COPD Delta VT was also the single best parameter to predict changes in work of breathing (R=0.777, R(2)=0.604, p<0.0001), however the relation of respiratory rate and rapid shallow breathing index to work of breathing was exponential (e-function) with lower indices generating higher workload. We conclude that rapid shallow breathing might be a strategy to compensate for burdensome respiratory mechanics. In COPD patients however we observed a critical threshold where any further increases in rapid shallow breathing index will be of no further benefit.

Short-term effect of controlled instead of assisted noninvasive ventilation in chronic respiratory failure due to chronic obstructive pulmonary disease.

BACKGROUND: Noninvasive positive-pressure ventilation (NPPV) unloads respiratory muscles. Spontaneous-breathing ventilation modes require patient effort to trigger the ventilator, whereas controlled modes potentially economize on patient triggering effort and thus achieve more complete respiratory muscle rest. Data on controlled NPPV have not been published to date. We hypothesize that controlled ventilation is feasible in patients with hypercapnic chronic obstructive pulmonary disease. METHODS: We measured blood gas values, respiratory muscle strength, spontaneous breathing pattern, and lung function before and after a 3-month period of NPPV in 305 patients (213 male, mean +/- SD age 61.3 +/- 8.6 y). The subjects used a controlled NPPV mode when they could tolerate it. RESULTS: Ninety-one percent of the patients were able to adapt to a controlled NPPV mode. In those patients, daytime P(CO(2)) decreased from 56.7 +/- 7.5 mm Hg to 47.5 +/- 6.6 mm Hg (p < 0.001) and P(O(2)) increased from 49.2 +/- 8.8 mm Hg to 56.2 +/- 8.5 mm Hg (p < 0.001). Their mean maximum inspiratory pressure increased from 42.3 +/- 16.9 cm H(2)O to 48.4 +/- 18.0 cm H(2)O (p < 0.001). Their mean vital capacity increased from 1.89 +/- 0.62 L to 1.99 +/- 0.67 L (p = 0.004). And their spontaneous breathing pattern became less rapid and shallow. CONCLUSIONS: Controlled NPPV is feasible in patients with hypercapnic chronic obstructive pulmonary disease. We observed improved blood gas values, lung function, and inspiratory muscle strength.

Tracheostomy decannulation: implication on respiratory mechanics.

BACKGROUND: Tracheostomy decreases airway resistance and work of breathing. No comprehensive data are available on respiratory mechanics after tracheostomy decannulation. We evaluated respiratory mechanics after decannulation. METHODS: Twenty-five patients with tracheostomy were included. Measurement of arterial blood gases, air-flow, and esophageal pressure during spontaneous breathing were evaluated. RESULTS: Overall arterial blood gas parameters as well as flow and pressure measurements including work of breathing and airway resistance were not affected by the intervention. Inspiratory time fraction increased from 40.0 + or - 0.04 to 43% + or - 0.05% (p = .007). We observed marked individual differences. Postdecannulation change in work of breathing is best predicted by change in airway resistance (R = 0.869, R(2) = 0.755, p < .0001) CONCLUSION: Inspiratory time increased after decannulation, and arterial blood gas levels and respiratory mechanics did not change for the whole cohort. Individual changes in work of breathing are considerable and correlate closely to changes in airway resistance.