Zimmerman M I, Miller A, Brown L K, Bhuptani A, Sloane M F, Teirstein A S
Pulmonary Physiology Laboratory, Mount Sinai School of Medicine, New York.
Chest. 1994 Jul;106(1):131-6. doi: 10.1378/chest.106.1.131.
The physiologic dead space/tidal volume ratio (VD/VT) at rest and during exercise is a sensitive measurement of gas exchange that reflects matching of ventilation to perfusion, but requires an invasive measurement for its calculation. Determining VD/VT noninvasively uses estimations of arterial PCO2 based on the end-tidal PCO2. To further standardize incremental cardiopulmonary exercise testing, we compared actual VD/VT with estimated VD/VT values in 35 patients referred for evaluation of dyspnea. Estimates of VD/VT used the Jones' equation (VD/VT[J]) derived from healthy subjects during steady-state exercise or PETCO2 alone (VD/VT[ET]) to approximate PaCO2. At rest, mean values for VD/VT(J) and actual VD/VT were not different: 0.372 +/- 0.08 vs 0.376 +/- 0.09, p = not significant (NS). Each method identified 61 percent of values > or = to 0.36. In 26 subjects who achieved higher work rates, the mean difference between actual VD/VT and VD/VT(J) increased from 0.009 +/- 0.04 (NS) at low work rate (VO2 = 28.3 percent pred max) to 0.040 +/- 0.06 at high work rate (VO2 = 54.7 percent pred max), p = 0.006. Actual VD/VT identified 18 (69 percent) patients as abnormal vs 13 (50 percent) so identified by VD/VT(J). With exercise, VD/VT(J) was no better than VD/VT(ET). We conclude that during incremental exercise in a patient population, methods for estimating VD/VT progressively underestimate this measurement; and therefore, "normal" estimated VD/VT values may fail to identify underlying pulmonary and/or pulmonary vascular impairment.
静息和运动时的生理死腔/潮气量比值（VD/VT）是气体交换的一项敏感指标，反映了通气与灌注的匹配情况，但计算该比值需要进行有创测量。基于呼气末二氧化碳分压（PETCO2）无创测定VD/VT需对动脉血二氧化碳分压（PaCO2）进行估算。为进一步规范递增式心肺运动试验，我们比较了35例因呼吸困难前来评估的患者的实际VD/VT与估算VD/VT值。VD/VT估算采用了Jones公式（VD/VT[J]），该公式源自健康受试者在稳态运动时的情况，或仅使用PETCO2（VD/VT[ET]）来近似PaCO2。静息时，VD/VT（J）的平均值与实际VD/VT无差异：分别为0.372±0.08和0.376±0.09，p = 无显著性差异（NS）。两种方法识别出的VD/VT≥0.36的值均为61%。在26例达到更高运动负荷的受试者中，实际VD/VT与VD/VT（J）之间的平均差异从低运动负荷（VO2 = 预计最大值的28.3%）时的0.009±0.04（无显著性差异）增加至高运动负荷（VO2 = 预计最大值的54.7%）时的0.040±0.06，p = 0.006。实际VD/VT识别出18例（69%）患者异常，而VD/VT（J）识别出13例（50%）。运动时，VD/VT（J）并不优于VD/VT（ET）。我们得出结论，在递增运动的患者群体中，估算VD/VT的方法会逐渐低估该测量值；因此，“正常”的估算VD/VT值可能无法识别潜在的肺部和/或肺血管损伤。
