Changes in breathing and ventilatory muscle recruitment patterns induced by lung volume reduction surgery.

Abstract

Patients with chronic obstructive pulmonary disease have abnormal breathing and ventilatory muscle recruitment patterns at rest and during exercise, and these alterations may contribute to the limited exercise capacity seen in this disease. Lung volume reduction surgery (LVRS), a recently described treatment for emphysema, is reported to improve exercise performance. We studied the breathing and ventilatory muscle recruitment (VMR) patterns in eight patients with severe chronic obstructive lung disease (median FEV1 = 0.79 L, range 0.46 to 1.13 L) by measuring esophageal and gastric pressure measurements as well as tidal volumes (VT), respiratory rates (f), inspiratory (TI) and expiratory (TE) times, and watts at rest and during maximal exercise, before and 3 mo after lung volume reduction surgery. Maximal exercise capacity increased a median of 49% (median increase 17 watts, range 6 to 44 watts, p < 0.05) and maximal minute ventilation (VEmax) increased by a median of 22% (median increase 6.5 L/min, range 3 to 25 L/min, p < 0.05). At isowatt exercise after surgery, VT increased 0.31 L (range 0.07 to 0.69 L) and f decreased four breaths/min (range +0.5 to -15 breaths/min). Dyspnea scores as measured by a visual analog scale (VAS) decreased significantly at rest and at peak exercise after surgery. End-expiratory esophageal (Pes) and gastric (Pga) pressures at rest and at isowatt exercise decreased. A rightward shift in the slope of the Pes versus Pga plot was also observed suggesting increased use of the diaphragm after surgery. Our data indicate that LVRS improves the mechanics of breathing both at rest and during exercise.

Physiological basis of improvement after lung volume reduction surgery for severe emphysema: where are we?

“…The latter finding possibly reflects a paradoxical movement of the abdomen during the respiratory cycle, but it is more probable that abdominal muscles relax during inspiration after being extensively recruited during expiration. This is supported by the high values of end-expiratory gastric pressure in these two studies [51,61]. After surgery, there was a decrease in pleural pressure swings, essentially owing to a decrease in end-expiratory positive oesophageal pressure whereas the abdominal pressure returned to a more normal pattern, showing an increase during the inspiratory phase [51,61] and demonstrating either a greater recruitment of the diaphragm after surgery or a lesser expiratory recruitment of the abdominal muscles.…”

“…Nevertheless, it obviously contributes to the decrease in work of breathing through a lower burden on the inspiratory muscles. It also leads to a decrease in the end-expiratory pleural pressure, as demonstrated in some studies [51,61,67].…”

“…This is an important determinant of intrinsic PEEP in such patients [29]. As end-expiratory gastric pressure was shown to decrease after LVRS in one study [61], probably signalling a derecruitment of abdominal muscles during expiration, improvement in dynamic lung mechanics is not likely to be the only determinant of decreased intrinsic PEEP after LVRS.…”

“…Besides FEV1, more specific indices of airflow obstruction have been reported less frequently. Three groups reported improved FEV1/VC ratios, using stapling techniques and with most patients operated on bilaterally [52,61,62]. Others found a lack of significant improvement in FEV1/VC [4,48,53,59].…”

“…Using plots of oesophageal versus gastric pressure during tidal breathing, it has been demonstrated that, before surgery, severe emphysematous patients show large inspiratory decreases in oesophageal pressure during inspiration [51,61] whereas the end-inspiratory gastric pressure does not change [61] or is even reduced compared to the end-expiratory value [51] (fig. 3a).…”