Closing Capacity and Gas Exchange in Chronic Heart Failure: Lung Volumes

In line with the results of most previous re-ports,’’ our patients exhibited a reduction in TLC and FRC but normal FEV1/FVC ratio. In contrast, Yap et al found a significant reduction in TLC but not in FRC. Their patients, however, were studied just after a period of acute decompensation, which may be associated with the presence of FL and dynamic hyperinflation with the patient in the sitting position. Hart et al found no reduction of either TLC or FRC in 10 CHF patients; half of their patients, however, had CHF due to coronary artery disease. In the present study, only 30% of the patients (6 of 20) had a history of coronary artery disease.

The reduction of FRC (gas), which in our patients averaged 11% of the predicted TLC (Fig 1), was probably mainly due to space competition of gas with solids and/or liquids (eg, cardiomegaly, congestion, or interstitial edema). Assuming an equal elas-tance of the lung and chest wall at FRC, the chest wall volume should have also increased by 11% of the predicted TLC (ie, an amount equal to the reduction of FRC [gas]). However, TLC was reduced more than FRC, namely, 19% of the predicted TLC. This probably reflects the Plmax decrease due to (1) chest wall expansion by an increased volume of the heart and blood, (2) an intrinsic weakness of the inspiratory muscles, and (3) increased elastic lung recoil pressure due to pulmonary congestion, and/or fibrosis. A decrease in the force of skeletal muscles (including inspiratory muscles) has been documented in CHF patients by many authors.” Other functional abnormalities, such as the increased Raw shown in Table 1, probably mainly reflect the reduced thoracic gas volume in CHF patients. Indeed, while the Raw was abnormal, sGaw was within normal limits.
In CHF patients, Collins et al found an increased CV/VC ratio relative to normal control subjects and, in line with the results of previous studies, suggested that pulmonary congestion and edema promote the premature closure of peripheral airways. In our CHF patients, the CV/VC ratio was also significantly increased, but the CV was not abnormal. This implies that the increase in CV/VC ratio was due entirely to decreased VC.

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