Resistance to pulmonary blood flow in COPD-A was less (p < 0.001) than that in ILD when FVC was less than 50 percent predicted (PDG = 18 ± 6 mm Hg). There were no significant differences in cardiac output heart rate or systemic arterial pressures among the three groups. Conventional calculation of ohmic resistance to blood flow in the pulmonary circulation yielded estimates of PVR in emphysema and mild-moderate ILD that were mildly elevated (234 ± 132 and 206 ± 89 dyne-sec-cm”, respectively) and not significantly different from each other (p > 0.4). Calculation of ohmic resistance in moderate-severe ILD (714 ± 279 dyne-sec-cm) was significantly greater than that in emphysema (p < 0.001).

We sought the cause of increased pulmonary vascular resistance in patients with COPD-A by examining the relation between PDG and each of the indices of pulmonary function included in Table 1. The data were examined by linear regression analysis to determine which indices of pulmonary function correlated best with PDG (Table 2). Pulmonary diastolic gradient correlated most closely with l/DcoSB which accounted for 76 percent of the total variance in pulmonary vascular resistance. Of the remaining indices, FVC percent predicted and FEV{ percent predicted also were related significantly to PDG, but neither effected a significant reduction in variance which could not be attributed to l/DcoSB. Canadian family pharmacy more Partial correlation analysis indicated that FVC explained only 3 percent and FEVl only 10 percent of the observed variation in the gradient which DcoSB had failed to explain (p > 0.6 and p > 0.3, respectively).

The relationship between pulmonary vascular resistance in emphysema and disruption of the pulmonary microcirculation, as reflected by abnormalities in DcoSB measurement, is illustrated in Figure 2. Similar observations in patients with ILD are included. The PDG increased in both groups in a curvilinear fashion as DcoSB fell. The similarity between emphysema and ILD is especially striking over the range of observations in patients with ILD whose FVC exceeded 50 percent of predicted levels (DcoSB >47 percent predicted). Linear transformation of these PDG-DcoSB relationships (Fig 3) yields an r value of – 0.869 for emphysema (p < 0.001), and r = – 0.839 for ILD (p < 0.001). Calculated ohmic resistance (PVR) in emphysema yields a similar linear relation with 1/ DcoSB (r = – 0.69, p < 0.05). When all values of DcoSB are considered, the slope of the regression of PDG on l/DcoSB in emphysema is lower than in ILD (p < 0.001), but when the evaluation is limited to the range of DcoSB observed in the 24 patients with ILD whose vital capacities exceeded 50 percent of predicted levels, neither the slopes nor the intercepts of the two regressions differ significantly (p > 0.4 and p > 0.5, respectively).

**Table 2 — Correlation of Pulmonary Funtion Measurements With PDG in 12 Patients With Type A COPD**

r | Pi | p2 | |

l/(Dco_{SB}, % pred) |
-0.87 | <0.001 | |

FVC, % pred | -0.56 | <0.05 | >0.6 |

FEV,, % pred | -0.58 | <0.05 | >0.3 |

FEV,/FVC % | -0.30 | NS | |

RV/TLC % | -0.51 | NS | |

TLC, % pred | -0.35 | NS | |

Pa0_{2}, mm Hg |
-0.55 | NS | |

PaCo_{2}, mm Hg |
-0.12 | NS | |

pHa | -0.19 | NS |

*Figure 2. Relation between PDG and microcirculation represented by DcoSB in patients with emphysema and ILD. The PDG increased in both groups in a curvilinear fashion as DcoSB fell (r = – 0.869, p < 0.001 and r = – 0.839, p < 0.001, respectively).*

*Figure 3. Linear transformation of the PDG-DcoSB relationships in emphysema and ILD. When all values of DcoSB are considered, the slope of the regression of PDG on l/DcoSB in emphysema is lower than in ILD (p < 0.001), but when the evaluation is limited to the range of Dco^ oDserved in the 24 patients with ILD whose vital capacities exceeded 50 percent of predicted levels, neither the slopes nor the intercepts of the two regressions differed significantly (p > 0.4 and p > 0.5, respectively).*