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Reed Humphrey

Publications and source records attributed to Reed Humphrey.

8 recordsLinked to original sources
PubMed2003

Prognostic ability of VE/VCO2 slope calculations using different exercise test time intervals in subjects with heart failure.

BACKGROUND: The minute ventilation-carbon dioxide production (VE/VCO2) slope, obtained during exercise testing, possesses prognostic value in heart failure (HF). The VE-VCO2 relationship is generally linear thereby hypothetically producing similar slope values regardless of the exercise-test time interval used for calculation. DESIGN: This study assesses the ability of the VE/VCO2 slope, calculated at different time intervals throughout a progressive exercise test, to predict 1-year cardiac-related hospitalization and mortality in subjects with HF. METHODS: Seventy-two subjects underwent symptom-limited exercise testing with ventilatory expired gas analysis. Mean age and left ventricular ejection fraction for 44 male and 28 female subjects were 51.2 years (+/-13.0) and 27.0% (+/-12.3) respectively. The VE/VCO2 slope was calculated from time 0 to 25, 50, 75 and 100% of exercise time and subsequently used to create five randomly selected VE/VCO2 slope categories. RESULTS: (The intraclass correlation coefficient found calculation of the VE/VCO2 slope, when divided into quartiles, to be a reliable measure (alpha=0.94, P<0.0001). Univariate Cox regression analysis revealed all VE/VCO2 slope categories (25-100% and random selections) were significant predictors of cardiac-related hospitalization and mortality over a 1-year period. Multivariate Cox regression analysis revealed all VE/VCO2 slope categories outperformed peak oxygen consumption (VO2) in predicting hospitalization and mortality at 1 year. CONCLUSIONS: Although the different classification schemes were not identical, these results suggest VE/VCO2 slope maintains prognostic significance regardless of exercise-test time interval. Calculation of VE/VCO2 slope may therefore still be valuable in subjects putting forth a sub-maximal effort while effort-dependent measures, such as peak VO2, are not.

Adult↗
PubMed2002

Comparison of ventilatory expired gas parameters used to predict hospitalization in patients with heart failure.

BACKGROUND: Several ventilatory expired gas measures obtained during exercise testing demonstrate prognostic value in the heart failure (HF) population. Comparison of prognostic efficacy between pertinent measures is sparse. METHODS: The ability of various expressions of peak oxygen consumption (VO2), the relationship between minute ventilation (VE) and carbon dioxide production (VCO2), and the partial pressure of end-tidal carbon dioxide (P(ET)CO2) were assessed to determine which measure(s) best predicted cardiac-related hospitalization over a 1-year period in subjects diagnosed with HF. RESULTS: Univariate Cox regression analysis found that several expressions of peak VO 2, VE-VCO2 relationship, and P(ET)CO2 were significant predictors of hospitalization. Multivariate Cox regression analysis revealed that the VE/VCO2 slope significantly predicted hospitalization (chi2 = 29.1, P <.00001). Peak VO 2 and P(ET)CO2 did not provide additional predictive value. CONCLUSIONS: The prognostic superiority of the VE/VCO2 slope over peak VO2 may be a result of the latter measure's partial dependence on subject effort and skeletal muscle function.

Adult↗
PubMed2002

Comparison of oxygen uptake on-kinetic calculations in heart failure.

PURPOSE: The analysis of oxygen (O(2)) uptake on-kinetics during steady-rate is gaining interest in the heart failure (HF) population. The rate change in O(2) at the initiation of exercise can be assessed via nonlinear regression time constant (TC) or an algebraic equation (mean response time [MRT]). These calculations are presumed to be interchangeable, but research supporting this claim is limited. This investigation compares and contrasts two of the more commonly used O(2) uptake on-kinetic calculations. METHOD: Twenty-eight subjects diagnosed with compensated HF and 19 age, sex, and activity-matched controls underwent a symptom-limited exercise test and a steady-rate exercise session (6 min). Peak O(2) uptake, O(2) uptake at ventilatory threshold, the O(2) uptake TC (TC), and the O(2) uptake mean response time (MRT) were calculated for each subject. RESULTS: O(2) uptake on-kinetics was significantly faster for the control group ( < 0.05) regardless of calculation method. There was a significant difference between the O(2) uptake TC and MRT for the HF group. All O(2) uptake on-kinetic calculations were significantly correlated with aerobic capacity. CONCLUSIONS: O(2) uptake TC and MRT values may not be interchangeable in the HF population. All O(2) uptake on-kinetic calculations did produce a significant difference between experimental and control groups and correlated with indicators of aerobic capacity. The 10-s O(2) uptake on-kinetic calculations may be preferable secondary to expired gas fluctuations associated with breath-by-breath measures. Further work is, however, needed to determine which averaged O(2) uptake on-kinetic expression is optimal given the significant difference between TC and MRT. A mechanism for this difference may be the oscillatory ventilatory expired gas pattern demonstrated by some patients with HF.

Adult↗
PubMedDate not supplied

Relationship between the Minnesota Living With Heart Failure Questionnaire and key ventilatory expired gas measures during exercise testing in patients with heart failure.

PURPOSE: This study assessed the relationship between the Minnesota Living With Heart Failure Questionnaire (MLWHFQ) and key ventilatory expired gas measures during a symptom-limited exercise test in the heart failure (HF) population. Specifically, is there evidence to indicate that perceived quality of life (QOL) influences exercise performance independent of physiologic function in the HF population? METHODS: Thirty-one subjects (21 male/10 female), diagnosed with compensated HF, underwent exercise testing and completed the MLWHFQ. Mean age and left ventricular ejection fraction were 52.8 years and 27.2%, respectively. Partial correlation, controlling for age and sex, assessed the relationship between MLWHFQ (overall and subscores) and key ventilatory expired gas measures. Intraclass correlation coefficient (ICC) analysis was used to determine reliability of the MLWHFQ. RESULTS: MLWHQ overall score (mean = 38.9, median = 36.0), physical subscore (mean = 14.8, median = 16.0), and psychosocial/symptomatology subscore (mean = 24.1, median = 19.0), were significantly correlated (P < or =.05) with peak oxygen consumption (VO2). The relationship between MLWHFQ and the minute ventilation-carbon dioxide production (VE/VCO2) slope was, however, not significant. ICC analysis revealed high reliability (0.95) for the MLWHFQ. CONCLUSIONS: The MLWHFQ demonstrates a significant relationship with peak VO2, a measure whose validity is dependent upon subject effort. VE/VCO2 slope, which is independent of subject effort and therefore potentially a better predictor of true physiologic function, does not appear to have a relationship with perceived QOL. These findings have implications for how the MLWHFQ is assessed, related to an exercise test, and used during clinical practice.

Adult↗
PubMedDate not supplied

Predicting peak oxygen consumption during a conservative ramping protocol: implications for the heart failure population.

PURPOSE: A significant discrepancy between measured oxygen consumption (VO(2)) (via ventilatory expired gas analysis) and estimated VO(2) (via the imposed workload) frequently is reported in the heart failure (HF) population during symptom-limited exercise testing. The purpose of this investigation was to examine the difference between measured and estimated VO(2) (VO(2) discrepancy) during a highly conservative ramping protocol. METHODS: For this study, 28 subjects with compensated HF (20 men and 8 women; age, 51.1 +/- 14.6 years) and 19 healthy control subjects (age-, gender-, and activity-matched to an HF subgroup) underwent symptom-limited exercise testing (treadmill) with ventilatory expired gas analysis. RESULTS: Peak estimated and measured VO(2) values were significantly higher in the age-, gender-, and activity-matched control group than in the HF group, but the change in measured VO(2) per change in estimated VO(2) (Deltameasured/Deltaestimated VO(2) slope) and the VO(2) discrepancy did not reach statistical significance. Peak estimated VO(2) was a significant predictor of peak measured VO(2) in the overall HF group (R2 = 0.90; P <.001). CONCLUSIONS: Although estimated VO(2) is not considered a replacement for measured VO(2), these results indicate that a highly conservative exercise protocol may allow for a more accurate prediction of peak measured VO(2) via the estimated oxygen cost for a given workload in patients with compensated HF.

Adult↗