Document Detail


Estimated vs actual values for dead space/tidal volume ratios during incremental exercise in patients evaluated for dyspnea.
MedLine Citation:
PMID:  8020259     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
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.
Authors:
M I Zimmerman; A Miller; L K Brown; A Bhuptani; M F Sloane; A S Teirstein
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Chest     Volume:  106     ISSN:  0012-3692     ISO Abbreviation:  Chest     Publication Date:  1994 Jul 
Date Detail:
Created Date:  1994-08-02     Completed Date:  1994-08-02     Revised Date:  2004-11-17    
Medline Journal Info:
Nlm Unique ID:  0231335     Medline TA:  Chest     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  131-6     Citation Subset:  AIM; IM    
Affiliation:
Pulmonary Physiology Laboratory, Mount Sinai School of Medicine, New York.
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MeSH Terms
Descriptor/Qualifier:
Adult
Aged
Dyspnea / diagnosis,  etiology,  physiopathology*
Exercise Test*
Female
Humans
Male
Middle Aged
Pulmonary Diffusing Capacity
Respiratory Dead Space*
Tidal Volume*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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