Oxygen uptake to work rate relation throughout peak exercise in normal subjects: Relevance for rate adaptive pacemaker programming

The oxygen uptake to work rate ((V) over dotO(2)/WR) relationship observed throughout peak exercise testing is already being applied for rate adaptive pacemaker programming. However, the detailed curve design of (V) over dotO (2)/WR with respect to the anaerobic threshold (AT) has not yet been invest igated. It was the purpose of this study to determine the (V) over dotO(2)/ WR slope below and above the AT in a healthy control group. Seventy-eight h ealthy control subjects (45.9 +/- 17.4 years; 34 women: 49.9 +/- 18.6 years 44 men: 43.6 +/- 26.6 years) were exercised on a treadmill with "breath-by -breath" gas exchange monitoring using the symptom limited "ramping increme ntal treadmill exercise" (RITE) protocol. The slope of the VO2/WR relations hip from rest to peak exercise (r-p), rest to AT (slope A), and AT to peak exercise (slope B) in mt oxygen uptake per watt of external treadmill work was determined by linear regression analysis. [GRAPHICS] The oxygen uptake to work rate relationship throughout peak exercise in the entire study group generated a significant slope change at the AT (31%, P < 0.0001) with a decreasing slope during higher work load intensities. Fema le subjects demonstrated a greater percentage of slope change at AT (43%), as compared to men (22%, P < 0.01). When using the oxygen uptake to work ra te relationship for the programming of the pacemaker's rate response to exe rcise, the significant slope change at the AT should be considered to more appropriately pace during high er work intensities supported by anaerobic m etabolism. Fem ale pacemaker patients should be programmed to generate a st eeper VO2/WR slope below AT with a greater slope change at AT, as compared to men. Abnormally high oxygen uptake to work rate ratios above the AT may be possibly used as an indicator of overpacing.