![]() ![]() Health Care Economics, Insurance, Payment.Clinical Implications of Basic Neuroscience.Challenges in Clinical Electrocardiography.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. With exercise, VD/VT(J) was no better than VD/VT(ET). Actual VD/VT identified 18 (69 percent) patients as abnormal vs 13 (50 percent) so identified by VD/VT(J). 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. Each method identified 61 percent of values > or = to 0.36. 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). ![]() Estimates of VD/VT used the Jones' equation (VD/VT) derived from healthy subjects during steady-state exercise or PETCO2 alone (VD/VT) to approximate PaCO2. ![]() 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. Determining VD/VT noninvasively uses estimations of arterial PCO2 based on the end-tidal PCO2. 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. ![]()
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