Mechanisms underlying CO2 retention during flow-resistive loading in patients with chronic obstructive pulmonary disease.

Abstract

A B S T R A C T The present study examined the respiratory responses involved in the maintenance of eucapnea during acute airway obstruction in 12 patients with chronic obstructive disease (COPD) and 3 agematched normal subjects. Acute airway obstruction was produced by application of external flow-resistive loads (2.5 to 30 cm H20/liter per s) throughout inspiration and expiration while subjects breathed 100% 02. Application of loads of increasing severity caused progressive increases in Pco2 in the patients, but the magnitude of the increase in Pco2 varied substantially between subjects. On a resistance of 10 cm H2O/liter per s, the highest load that could be tolerated by all COPD patients, the increase in Pco2 ranged from 1 to 11 mm Hg, while none of the normal subjects retained CO2. Based on the magnitude of the increase in Pco2 the patients could be divided into two groups: seven subjects whose Pco2 increased by <3 mm Hg (group I) and five subjects whose Pco2 increased by >6 mm Hg (group II). Base-line ventilation and the pattern of breathing were similar in the two groups. During loading group I subjects maintained or increased tidal volume while all group II patients decreased tidal volume (VT). The smaller tidal volume in group II subjects was mainly the result of their shorter inspiratory time as the changes in mean inspiratory flow were similar in the two groups. The magnitude of CO2 retention during loading was inversely related to the magnitude of the change in VT (r = -0.91) and inspiratory time (T,) (r = -0.87) but only weakly related to the change in ventilation (r = -0.53). The changes in PCO2, VT, and T, during loading correlated with the subjects' maximum static

Respiratory Muscle Function in Chronic Obstructive Pulmonary Disease

“…10 On the other hand, a study assessing the effect of inspiratory and expiratory loading on COPD patients demonstrated that some patients could compensate for added loads, whereas other patients developed a fall in V T and a rise in PaCO 2 . 118 Comparison of these two groups revealed no difference in airflow limitation, but a significantly lower PI max in the group that was unable to compensate for the added loads. 118 Various measurements have been used to evaluate impending versus overt respiratory muscle fatigue.…”

“…118 Comparison of these two groups revealed no difference in airflow limitation, but a significantly lower PI max in the group that was unable to compensate for the added loads. 118 Various measurements have been used to evaluate impending versus overt respiratory muscle fatigue. Impending fatigue implies that overt fatigue is likely to develop if no change is made in the demands on the respiratory muscles.…”

Extracorporeal Carbon Dioxide Removal for the Exacerbation of Chronic Hypercapnic Respiratory Diseases

“…Acute exacerbations of COPD (aeCOPD) constitute a significant cause of morbidity and mortality among these patients. Patients with moderate to severe acute exacerbations develop alveolar hyperinflation that may lead to increased work of breathing, muscle fatigue, and hypercapnia, creating a vicious loop refractory to medical treatment [25][26][27]. The standard respiratory support in this setting in order to break this cycle is noninvasive ventilation (NIV).…”

The Application of a New Tool for Evaluation of Lung Function in COPD

“…The increase in very high VȦ/Q̇ or physiological dead space is associated with elevated levels of arterial carbon dioxide [66]. Rapid shallow breathing may also be a contributor to high VȦ/Q̇ [67,68]. If ALPE is to be used in patients suffering from COPD, description of high VȦ/Q̇ must be included.…”