Chronotropic incompetence (CI) has typically been assessed using maximal heart rate (MHR) achieved during a graded exercise test (GXT). Wilkoff et al recommended using a chronotropic/metabolic index (WI) consisting of the ratio between predicted maximal heart rate reserve (PMHRR) and metabolic reserve (MR) during submaximal exercise. Using a WI of <0.80 as evidence of CI, Lauer at al reported a prevalence of 14% for men and 12% for women within the Framingham cohort and indicated that the WI was independent of age, resting heart rate and exercise capacity (peak METS at 85% predicted MI-IR). However, the predicted heart rate for a given stage within the WI is based on a predicted (PMHR [220-age]) rather than measured MHR. The purpose of this study was to assess whether the WI, when calculated using MMHR would affect the prevalence of WI <0.80, and to assess whether the WI, when calculated using MIVIHR, is influenced by gender, age, RHR or aerobic capacity as measured by maximal oxygen uptake (V02 max). The sample included 522 self-referred adults (294 women, mean age 43 ± 11 years; 228 men, mean age 46 + 11 years) who completed a GXT test to volitional fatigue using the BSU/Bruce Ramp protocol. Exclusion criteria were use of betablockers, history of myocardial infarction, peak respiratory exchange ratio <1.0, or GXT time <6.0 minutes. WI was assessed at the end of 6th minute of the GXT with a value <0.80 considered evidence of CI. The mean WI from both methods was (PMHR = 1.088 +-0.20 vs MMHR = 1.063 + 0.16 (<.0001), with a correlation of 0.807. The prevalence of WI <0.80 was 8.0% and 4.4% for the PMHR and MMHR methods, respectively, which are considerably lower than the 14% and 12% reported by Lauer et al. Multiple regression. analysis revealed that gender, age, resting heart rate and V02 max were significantly associated with WI when derived using either predicted or measured MHR, (<.0001), however these variables only accounted for 13.6% (PMHR) and 15.6% (MMHR) of the variance in the multiple regression models. In conclusion, these results suggest a rather low prevalence of CI (WI<0.80) in this self-referred, adult population and support the notion that the measure of WI is relatively independent of age, resting heart rate and gender but appears to be directly associated with V02 max. / School of Physical Education
| Identifer | oai:union.ndltd.org:BSU/oai:cardinalscholar.bsu.edu:handle/186864 |
| Date | January 2000 |
| Creators | Howard, Lance M. |
| Contributors | Whaley, Mitchell H. |
| Source Sets | Ball State University |
| Detected Language | English |
| Format | iv, 41 leaves : ill. ; 28 cm. |
| Source | Virtual Press |
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