Comparison of BiPAP Nasal Ventilation and Ventilation via Iron Lung in Severe Stable COPD: Materials and Methods
Respiratory muscle fatigue may contribute to exercise limitation and respiratory failure in patients with severe chronic obstructive pulmonary disease (COPD). Conventional mechanical ventilation has been successful in supporting ventilation and resting the respiratory muscles when severe respiratory muscle fatigue or failure occurs, but severe complications may ensue from repeated and long-term endotracheal intubation.
Noninvasive ventilators such as the iron lung, pneumowrap, or positive pressure ventilation via a nasal or face mask can spare the complications of artificial airways. These ventilators have successfully improved the alveolar ventilation in patients with neuromuscular diseases or thoracic deformities. However, their efficacy in patients with severe COPD remains controversial.” Strumpf and coworkers found that longterm nocturnal nasal ventilation had no obvious effect on gas exchange, respiratory muscle strength, exercise endurance, or dyspnea rating in COPD patients. Nava and coworkers showed that negative pressure ventilation could induce respiratory muscle rest in similar patient groups. However, Belman and coworkers demonstrated that positive ventilation was much more effective than negative pressure ventilation in reducing diaphragmatic activity. According to our experience in BiPAP ventilation, COPD patients in acute exacerbation tended to get used to the ventilator more quickly than those in stable condition. Therefore, we hypothesize that the effects of noninvasive ventilators are correlated with the disease severity.
Using a randomized crossover design, this study aims to assess and compare the short-term effects of noninvasive ventilators on respiratory muscle activity, respiratory drive, respiratory muscle strength, gas exchange, and thoracoabdominal asynchrony (TAA) in patients with severe COPD.
Eleven male patients were included in the study. All had a previously documented diagnosis of COPD and met the following criteria: (1) FEV, below 1.1 L; (2) being stable for at least 1 week; and (3) the ability to tolerate the supine position for at least 2 h. The study protocols were approved by the ethical research committee of our hospital. All the patients gave their informed consent prior to the study. All patients underwent flow-volume examination (Sensormedics 2450, Anaheim, Calif) and arterial blood gas (ABG) analysis on room air (Radiometer ABL 3, Copenhagen, Denmark) before the study. Maximum inspiratory pressure (Pimax) and maximum expiratory pressure (PEmax) of mouth were also measured using a mouthpiece with a small airleak that was connected to a differential aneroid pressure transducer (Coulbourn T41-05, Lehigh Valley, Pa).