Submaximal oxygen pulse divided by body weight during incremental exercise test

Long-term stability of the oxygen pulse curve during maximal exercise

INTRODUCTION

Exercise oxygen pulse (O₂ pulse), a surrogate for stroke volume and arteriovenous oxygen difference, has emerged as an important variable obtained during cardiopulmonary exercise testing.

OBJECTIVES

We hypothesized that the O₂ pulse curve pattern response to a maximal cycling ramp protocol exhibits a stable linear pattern in subjects reevaluated under the same clinical conditions.

METHODS

We retrospectively studied 100 adults (80 males), mean age at baseline of 59 + 12 years, who performed two cardiopulmonary exercise testings (median interval was 15 months), for clinical and/or exercise prescription reasons. The relative O₂ pulse was calculated by dividing its absolute value by body weight. Subjects were classified into quintiles of relative O₂ pulse. Cardiopulmonary exercise testing results and the O₂ pulse curve pattern, expressed by its slope and intercept, were compared among quintiles of relative O₂ pulse at both cardiopulmonary exercise testings.

RESULTS

After excluding the first minute of CPX (rest-exercise transition), the relative O₂ pulse curve exhibited a linear increase, as demonstrated by high coefficients of determination (R² from 0.75 to 0.90; p < 0.05 for all quintiles). Even though maximum oxygen uptake and relative O₂ pulse were significantly higher in the second cardiopulmonary exercise testing for each quintile of relative O₂ pulse (p < 0.05 for all comparisons), no differences were found when slopes and intercepts were compared between the first and second cardiopulmonary exercise testings (p > 0.05 for all comparisons; except for intercept in the 5th quintile).

CONCLUSION

Excluding the rest-exercise transition, the relative O₂ pulse exhibited a stable linear increase throughout maximal exercise in adults that were retested under same clinical conditions.

The Clinical Utility of Cardiopulmonary Exercise Testing in Suspected or Confirmed Myocardial Ischemia

Heart disease is a major cause of morbidity and mortality in the United States, with coronary artery disease (CAD) representing more than half of all cardiovascular events. Stable patients presenting with symptoms suggestive of CAD are likely to undergo an exercise electrocardiogram (ECG) and/ or imaging study as a first-line diagnostic assessment. A cardiopulmonary exercise test (CPX) is an ECG stress test plus ventilatory gas analysis. Recently, CPX has been used to detect exercise-induced myocardial ischemia (EIMI) suggestive of underlying CAD. Two CPX variables, oxygen pulse (VO2/HR) and the slope of oxygen consumption versus work rate (Δ VO2/ Δ WR), have been identified to be especially indicative of EIMI. Currently, there are a number of diagnostic tests available for the identification of CAD, with the most widely used being stress ECG, stress myocardial perfusion imaging (MPI) and echocardiography, and cardiac catheterization. Exercise ECG, although inexpensive, has a number of well-recognized limitations, including low sensitivity resulting in false-negative results. Stress (exercise or pharmaceutically induced) MPI and catheterization are more accurate but also more invasive and expensive. It appears that CPX may improve the diagnostic accuracy of exercise ECG. This review will address the potential utility of CPX in patients with suspected or confirmed myocardial ischemia.

Oxygen pulse during exercise is related to resting systolic and diastolic left ventricular function in older persons with mild hypertension

BACKGROUND

The mechanisms responsible for impaired cardiovascular hemodynamics during exercise among persons with milder forms of hypertension are not well documented. We examined the relationship of oxygen pulse during exercise, a correlate of stroke volume, with echocardiographic indices of resting left ventricular function to determine whether abnormal contractility and relaxation are related to abnormal cardiovascular dynamics during exercise among such persons.

METHODS

Subjects were 44 men and 55 women ages 55 to 75 years with mild hypertension but who were otherwise healthy. Resting left ventricular systolic and diastolic functions were assessed with 2-dimensional Doppler echocardiography and tissue Doppler imaging. Oxygen pulse (millimeters per beat) at rest and during multistage treadmill testing was derived from measurements of oxygen consumption and heart rate. The slope of oxygen pulse between successive exercise stages was calculated.

RESULTS

After a steep rise in oxygen pulse from rest to stage 1 of exercise, a markedly diminished oxygen pulse slope was seen between subsequent exercise stages. In stepwise regression analysis, the increase in the slope of oxygen pulse from rest to stage 1 was explained by a greater lean body mass (57%, P < .001) and a larger left atrial size (2%, P < .001). After exercise stage 1, the increase in the slope of oxygen pulse was explained by sex (24%, P < .001), higher mitral E/A ratio (6%, P < .001), and higher mitral annular systolic velocity (6%, P < .001).

CONCLUSIONS

These results suggest that a blunted oxygen pulse response to exercise among older persons with milder forms of hypertension may reflect impaired left ventricular stroke volume changes during exercise secondary to subtle abnormalities in both systolic and diastolic left ventricular functions.