Pulmonary Vascular Resistance in Emphysema: Discussion

In a carefully selected population of patients with emphysema (type A COPD), we observed a mild increase in resistance to pulmonary blood flow that correlated poorly with the severity of airflow obstruction. In none of the patients was vascular resistance sufficiently elevated to produce resting pulmonary hypertension. Statistical evaluation indicated that DcoSB, employed as a marker of extent of the pulmonary microcirculation, was the major determinant of the level of pulmonary vascular resistance in this population. Indeed, none of the other indices of lung function that we examined effected a significant reduction in variance of resistance independent of DcoSB. Comparison of these findings with those reported previously in a population of patients with ILD, where resistance to blood flow is widely accepted as stemming from anatomic restriction of the bed, demonstrated a striking similarity in the pulmonary vascular resistance/DcoSB relationship in the two groups. Disruption of the pulmonary microcirculation appears to be responsible for mildly increased pulmonary vascular resistance in patients with COPD-A when hemody-namically significant disturbances in respiratory gas exchange are not present.
Our procedure for patient selection contributed critically to the clarity of the relationships between abnormal pulmonary hemodynamics and disturbed lung function. The inclusionary criteria of Nash et al permitted identification of the study population on purely clinical grounds. http://birthcontroltab.com more The selections were subsequently confirmed by observed disturbances in lung function. We excluded factors that are not intrinsic features of uncomplicated COPD-A (the hypervolemia of obesity, reversible airflow obstruction, respiratory muscle weakness, intercurrent infection) and might affect the pulmonary circulation or the level of lung function, thereby obscuring the relationships under study.
We had hoped to secure a patient population with the widest possible spectrum of compromised lung function. The observed ranges of FEV/FVC and RV/ TLC from 41 to 63 percent and 30 to 65 percent, respectively, suggest that we approximated this goal. Nevertheless, we had anticipated inclusion of subjects with even more severely disturbed lung mechanics. Review of our patient logs and pulmonary functions tests over the period of study recruitment indicated that potential subjects with lower FEV/FVC ratios had not been considered because of either respiratory muscle weakness, inadequate inspiratory efforts during testing, or because intensity of dyspnea precluded use of a mouthpiece to measure minute ventilation. These patients also tended to manifest more severe derangements of gas exchange (hypoxemia and hypercarbia).

This entry was posted in Emphysema and tagged airflow obstruction, emphysema, pulmonary function, pulmonary vascular resistance, resistance pulmonary blood.