A non invasive estimate of dead space ventilation from exercise measurements.
BACKGROUND
During exercise, heart failure patients (HF) show an out-of-proportion ventilation increase, which in patients with COPD is blunted. When HF and COPD coexist, the ventilatory response to exercise is unpredictable.


OBJECTIVE
We evaluated a human model of respiratory impairment in 10 COPD-free HF patients and in 10 healthy subjects, tested with a progressive workload exercise with different added dead space. We hypothesized that increased serial dead space upshifts the VE vs. VCO2 relationship and that the VE-axis intercept might be an index of dead space ventilation.


METHODS
All participants performed a cardiopulmonary exercise test with 0, 250 and 500 mL of additional dead space. Since DS does not contribute to gas exchange, ventilation relative to dead space is ventilation at VCO2 = 0, i.e. VE-axis intercept. We compared dead space volume, estimated dividing VE-axis intercept by the intercept on respiratory rate axis of the respiratory rate vs. VCO2 relationship with standard method measured DS.


RESULTS
In HF, adding dead space increased VE-axis intercept (+0 mL = 4.98±1.63 L; +250 mL = 9.69±2.91 L; +500 mL = 13.26±3.18 L; p<0.001) and upshifted the VE vs.VCO2 relationship, with a minor slope rise (+0 mL = 27±4 L; +250 = 28±5; +500 = 29±4; p<0.05). In healthy, adding dead space increased VE-axis intercept (+0 mL = 4.9±1.4 L; +250 = 9.3±2.4; +500 = 13.1±3.04; p<0.001) without slope changes. Measured and estimated dead space volumes were similar both in HF and healthy subjects.


CONCLUSIONS
VE-axis intercept is related to dead space ventilation and dead space volume can be non-invasively estimated.
SDN Foundation, Institute of Diagnostic and Nuclear Development, Naples, Italy.
Paola
P
Gargiulo
Centro Cardiologico Monzino, IRCCS, Milan, Italy.
Anna
A
Apostolo
Department of Advanced Biomedical Sciences, Division of Cardiology, "Federico II" University, Naples, Italy.
Pasquale
P
Perrone-Filardi
Department of Cardiovascular and Respiratory Sciences, "La Sapienza" University, Rome, Italy.
Susanna
S
Sciomer
Department of Public Health and Infectious Diseases, Division of Pulmonary Research, "La Sapienza" University, Rome, Italy.
Paolo
P
Palange
Centro Cardiologico Monzino, IRCCS, Milan, Italy ; Department of Clinical Sciences and Community Health, Cardiovascular Section, University of Milan, Milan, Italy ; Department of Medicine, Division of Pulmonary and Critical Care Medicine, University of Washington, Seattle, Washington, United States of America.
Piergiuseppe
P
Agostoni
D002245:Carbon Dioxide / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D005260:Female; D064368:Healthy Volunteers; D006333:Heart Failure / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012119:Respiration; D014691:Ventilation / Q000379:methods
D002245:Carbon Dioxide