Hypercapnic ventilation response in patients with lung disease: improved accuracy by correcting for ventilation ability.

The hypercapnic ventilation response (HCVR) is positively correlated with forced expired volume in 1 s (FEV1). Therefore, subjects of small stature or patients with lung disease have low values for HCVR. However, indexing the HCVR for the subject's predicted maximal voluntary ventilation (MVV) results in a corrected HCVR (CHCVR) which is not dependent on FEV1 in normal subjects [Respiration 1993;60:197-202]. We hypothesized that the CHCVR would also be useful in assessing chemosensitivity in patients with poor lung function. To obtain the predicted MVV, we used the linear regression for FEV1 vs. measured MVV obtained from 411 patients with a wide range of FEV1 values (MVV = 31.2 x FEV1 + 11.8, r = 0.90, p < 0.001). We compared HCVR and CHCVR to the occlusion pressure response to hypercapnia (OPRH) in 34 patients with chronic obstructive pulmonary disease (COPD) and in 19 patients with low FEV1 due to small stature. All patients had been referred for assessment of possible sleep apnea. The results for the two groups of patients were similar. For the COPD patients, the HCVR had high values for sensitivity (86%) and negative predictive value (94%), but specificity, positive predictive value and accuracy were low (59, 35 and 65%, respectively). In contrast, CHCVR had high values for all the foregoing (86, 96, 100, 100 and 97%, respectively). Our results suggest that the CHCVR is useful in assessing chemosensitivity in patients who are ventilation-limited.