Ventilatory Efficiency during Exercise in Healthy Subjects

• Published in: American journal of respiratory and critical care medicine Vol. 166; no. 11; pp. 1443 - 1448
• Main Authors: Sun, Xing-Guo, Hansen, James E, Garatachea, Nuria, Storer, Thomas W, Wasserman, Karlman
• Format: Journal Article
• Language: English
• Published: New York, NY Am Thoracic Soc 01.12.2002; American Lung Association
• Subjects: Adult; Aged; Aging - physiology; Biological and medical sciences; Carbon Dioxide; Exercise - physiology; Female; Humans; Investigative techniques of respiratory function; Investigative techniques, diagnostic techniques (general aspects); Male; Medical sciences; Middle Aged; Oxygen Consumption; Reference Values; Respiration; Respiratory Dead Space; Respiratory Physiological Phenomena; Sex Characteristics; Tidal Volume; Physical exercise; Human; Evaluation; Ventilatory response; Healthy subject; Efficiency; Carbon dioxide; Non invasive method; Expiration; Ventilation; Ratio
• ISSN: 1073-449X; 1535-4970
• DOI: 10.1164/rccm.2202033

When evaluating dyspnea in patients with heart or lung disease it is useful to measure the quantity of ventilation needed to eliminate metabolically produced CO2 (i.e., the ventilatory efficiency). Mathematically, the relationship between ventilation (VE) and CO2 output is determined by the arterial CO2 pressure and the physiologic dead space-tidal volume ratio. We decided to determine how age, sex, size, fitness, and the type of ergometer influenced ventilatory efficiency in normal subjects. Three methods were compared for expressing this relationship: (1) the VE versus CO2 output slope below the ventilatory compensation point, commonly used by cardiologists for estimating the severity of heart failure; (2) the VE/CO2 output ratio at the anaerobic threshold, commonly used by pulmonologists; and (3) the lowest VE/CO2 output ratio during exercise, the latter parameter not previously reported. We studied 474 healthy adults, between 17 and 78 years of age during incremental cycle and treadmill cardiopulmonary exercise tests at three test sites, correcting the total VE for the equipment dead space. The lowest VE/CO2 output ratio was insignificantly different from the ratio at the anaerobic threshold, less variable than that for the slope relationship, and unaffected by the site, ergometer, and gas exchange measurement systems. The regression equation for the lowest VE/CO2 output ratio was 27.94 + 0.108 x age + (0.97 = F, 0.0 = M) - 0.0376 x height, where age is in years and height is in centimeters. We conclude that the lowest VE/CO2 output ratio is the preferred noninvasive method to estimate ventilatory inefficiency.