Yong-Yu Zhang

Lung Function and Exercise Gas Exchange in Chronic Heart Failure

BACKGROUND The ventilatory response to exercise in patients with chronic heart failure (HF) is greater than normal for a given metabolic rate. The objective of the present study was to determine the mechanism(s) for the high ventilatory output in patients with chronic HF. METHODS AND RESULTS Centers in Germany, Italy, Japan, and the United States participated in this study. Each center contributed studies on patients and normal subjects of similar age and sex. One hundred thirty patients with chronic HF and 52 healthy subjects participated. Spirometric and breath-by-breath gas exchange measurements were made during rest and increasing cycle exercise. Arterial blood was sampled for measurement of pH, PaCO2, PaO2, and lactate during exercise in 85 patients. Resting forced expiratory volume in 1 second (FEV1) and vital capacity (VC) were proportionately reduced at all levels of impairment. Patients with more severe HF had greater tachypnea and a smaller tidal volume (VT) at a given exercise expired volume per unit time (VE). This was associated with an expiratory flow pattern characteristic of lung restriction. VE and VCO2 as a function of VO2 were increased during exercise in HF patients. The increases were greater the lower the peak VO2 per kilogram of body weight. The ratio of VD (physiological dead space) to VT and the difference between arterial and end tidal PCO2 at peak VO2 also increased inversely with peak VO2/kg. In contrast, the difference between alveolar and arterial PO2 and PaCO2 were both normal, on average, at peak VO2 regardless of the level of impairment. The more severe the exercise limitation, the higher the lactate and the lower the HCO3- at a given VO2, although pH was tightly regulated. CONCLUSIONS The increase in VE in chronic HF patients is caused by an increase in VD/VT due to high ventilation/perfusion mismatching, an increase in VCO2 relative to VO2 resulting from HCO3- buffering of lactic acid, and a decrease in PaCO2 due to tight regulation of arterial pH. With regard to the excessive VE in HF patients, the increases in VD/VT and VCO2 relative to VO2 are more important as the patient becomes more exercise limited. Regional hypoperfusion but not hypoventilation typifies lung gas exchange in HF. This and other mechanisms might account for the restrictive changes leading to exercise tachypnea in HF patients.

Effect of exercise testing protocol on parameters of aerobic function

Four different patterns of increasing work rate (ramp and 1-min, 2-min, and 3-min steps) to maximum tolerance were studied in eight normal male subjects during cycle ergometer exercise testing to determine the effect of the work rate protocol on the parameters of aerobic function. The overall rate of work rate increase was kept constant. Measurements included VO2max, anaerobic threshold (AT), and the O2 uptake increase with respect to work rate increase (delta VO2/delta WR). VO2, VCO2, VE, respiratory exchange ratio (R), PETCO2, and PETO2 were calculated breath-by-breath. No significant difference was found in VO2max, AT, AT/VO2max, and delta VO2/delta WR among the four work rate protocols. Other measurements such as total work, maximal work rate, VCO2, VE, R, HR, O2 pulse, and the VO2 at which VE increases disproportionately to VCO2 (ventilatory compensation point) were also similar among the four protocols. Both the ramp and 1-min step work rate tests had no step pattern in either VO2 or VCO2, and the step pattern for the 2-min and 3-min step tests was attenuated or disappeared at work rates above AT. We conclude that the parameters of aerobic function, and other physiological responses at maximum work rate, were independent of the pattern of work rate increase, provided that the overall rate of work rate increase was the same.

A Four-Minute Submaximal Constant Work Rate Exercise Test to Assess Cardiovascular Functional Class in Chronic Heart Failure

To develop a submaximal constant work rate exercise test able to grade cardiovascular dysfunction in patients with chronic heart failure, 80 patients and 59 control subjects performed a symptom-limited incremental exercise test and a constant work rate exercise test at a fixed work rate (50 W for 4 minutes). The time constant of VO2 at the start of constant work rate exercise and time for gas exchange ratio (respiratory exchange ratio) to equal 1 were independent predictors of cardiovascular functional class and correctly classified the functional class in 89 +/- 9% and 83 +/- 11% of patients, respectively.

A method for estimating bicarbonate buffering of lactic acid during constant work rate exercise

AbstractA method to estimate the CO2 derived from buffering lactic acid by HCO3− during constant work rate exercise is described. It utilizes the simultaneous continuous measurement of O2 uptake (

O2 Uptake Kinetics in Response to Exercise: A Measure of Tissue Anaerobiosis in Heart Failure

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The role of fitness on VO2 and VCO2 kinetics in response to proportional step increases in work rate

O2) and CO2 output (

Lung function and exercise gas exchange in chronic heart failure [2] (multiple letters)

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