Closing Capacity and Gas Exchange in Chronic Heart Failure

Closing Capacity and Gas Exchange in Chronic Heart FailureCollins et al reported that the ratio of closing volume (CV) to vital capacity (VC) was increased in patients with chronic heart failure (CHF), and suggested that pulmonary congestion and edema promote peripheral airway closure. This is in line with the study by Hughes and Rosenzweig, who showed that in isolated perfused dog lungs the volume of trapped gas increased with increased lung water and was greater in the more dependent parts of the lung in which interstitial pulmonary edema was most prominent on histologic examination. They postulated that enhanced air trapping was caused by premature peripheral airway closure due to the presence of cuffs of edema fluid in the loose connective tissue around the extraalveolar peripheral airways before there was any significant change in alveolar wall thickness. An increase in the CV/VC ratio, however, can be due to an increase in CV and/or a decrease in VC. read

Clearly, the notion that pulmonary congestion and edema promote peripheral airway closure requires validation by the direct assessment of closing capacity (CC), as follows: CC = residual volume (RV) + CV. Collins et al also reported that in CHF patients CV exceed the expiratory reserve volume (ERV), implying that the opening and closure of the peripheral airway is present during tidal breathing. Furthermore, they suggested that the ensuing maldistribution of ventilation should lead to impaired gas exchange within the lung, but they did not measure blood gas levels.
Accordingly, in seated CHF patients and control subjects we assessed the following: (1) the magnitude of CC; and (2) the presence or absence of flow limitation (FL) and airway closure during tidal breathing. Measurements include spirometry, body plethysmography, blood gases, and control of breathing. The study was carried out in 20 stable ambulatory patients (18 men) with congestive heart failure due to cardiomyopathy (6 after ischemia) without pleural effusions. None had been hospitalized within 20 days preceding the study. None were current smokers, but nine patients were ex-smokers. All patients received therapy with diuretics (carvedilol, 15 patients; digitalis, 9 patients; oral anticoagulant therapy [dicumarol], 7 patients; and dobutamine IV, 1 patient).

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