Comparison of BiPAP Nasal Ventilation and Ventilation via Iron Lung in Severe Stable COPD: Conclusions

During the initial setting of BiPAP, most of our patients seemed unable to tolerate an I PAP of more than 10 cm H20. Acclimation and practice seemed also to be important factors during nasal ventilation, frequently mentioned in negative pressure ventilation (NPV).-’ This observation is supported by the study of Strumpf and coworkers in which 7 of 19 patients dropped out due to intolerance of the nasal mask. In our experience during BiPAP ventilation, it usually took naive patients several hours to several days to adapt to higher levels of pressure support. Conversely, patients in acute exacerbation tended to become accustomed to the ventilator more quickly.
In the preliminary report of Ambrosino and coworkers, 2-h use of BiPAP showed marked improvements in ABG, ventilatory pattern (Ve, Vt, RR), and iEMGdi. Twenty-two cm H20 of IPAP was used in their study, whereas only 10 cm H20 of IPAP was used in our study. If we could use higher pressure support longer in patients with more severe disease, the result might be different.
Response to Iron Lung
Our study did not find any significant changes in phase angle, iEMGdi, iEMGst, Vt, RR, Vt/Ti, Sa02, etC02, PR, Pimax, or PEmax after 40-min use of iron lung. This result was similar to that of Belman and coworkers, but contradicted those of Nava et al and Rodenstein et al. In the study of Nava and coworkers, the iEMGdi reduced significantly after 10 min of pneumowrap when the negative pressure was above — 15 cm H20. In the study of Rodenstein and coworkers, a short run (5 min) of a tank ventilator did not reduce iEMGdi, but longer ventilatory support (20 to 60 min) did decrease iEMGdi by 20 percent. They suggested that acclimation and learning effect might play an important role in the initial 5 to 20 min when NPV was used in a naive patient. Conversely, our result did not show any progressive reduction in iEMGdi during 40 min of iron lung ventilation (Fig 6). To answer whether a 40-min period is still too short for patients to adapt to the iron lung, further investigation with longer ventilatory support is needed.
The effect of long-term intermittent NPV has also been studied in patients with severe COPD. The investigation by Zibrak and coworkers observed no clinically significant improvements in pulmonary function, ABG, respiratory muscle strength, or exercise endurance after the use of poncho wrap. The activities of respiratory muscles were not documented in their study during NPV. Eleven of their 20 patients dropped out because of intolerance to the ventilator. This problem was not encountered in our study because patients with orthopnea had been excluded. In addition, the use of the iron lung in our study was believed to be more efficient than other NPV, including poncho wrap, and might have better patients acceptance. Celli and coworkers had similar findings that long-term intermittent pulmowrap together with pulmonary rehabilitation did no better than a rehabilitation program alone in the improvements of FEV,, Pdimax, TTdi, and endurance time. However, one of their patients, who had severe hypercapnea, did improve. Cropp and DiMarco also found that patients with the highest PaC02 tended to benefit most from NPV Because of the relatively small number of patients included in these studies, including ours, a subgroup of patients who had more severe disease and would have responded favorably to the NPV might have been excluded inadvertently leading to the conflicting results from different investigators.
For stable patients with severe COPD using shortterm BiPAP or iron lung, we concluded the following:
(1)    ventilatory pattern (TAA), gas exchange, or respiratory muscle strength was not significantly improved;
(2)    ventilatory drive and activities of respiratory muscles were not significantly suppressed; (3) the suppression of sternocleidomastoid muscle activity during short-term BiPAP ventilatory support correlated significantly with the severity of the disease.