Kenji Nishibata

Oxygen uptake efficiency slope: a new index of cardiorespiratory functional reserve derived from the relation between oxygen uptake and minute ventilation during incremental exercise.

OBJECTIVES We investigated the usefulness of a new variable, oxygen uptake efficiency slope (OUES), as a submaximal measure of cardiorespiratory functional reserve. The OUES is derived from the relation between oxygen uptake (Vo2 [ml/min]) and minute ventilation (VE [liters/min]) during incremental exercise and is determined by VO2 = a log VE + b, where a = OUES, which shows the effectiveness of Vo2. BACKGROUND Maximal oxygen uptake (VO2max) is effort dependent. There is no standard submaximal measurement of cardiorespiratory reserve that provides generally acceptable results. METHODS Exercise tests, following a standard Bruce protocol, were performed on a treadmill by 108 patients with heart disease and 36 normal volunteers. Expired gas was continuously analyzed. The OUES was calculated from data of the first 75%, 90% and 100% of exercise duration. We also determined the following submaximal variables: the ventilatory anaerobic threshold (VAT), the slope of the regression line of the minute ventilation-carbon dioxide production relation (VE-VCO2 slope) and the extrapolated maximal oxygen consumption (EMOC). We analyzed the relation of OUES and other submaximal variables against VO2max and examined the effects of submaximal exercise on OUES. RESULTS The correlation coefficient of the logarithmic curve-fitting model was 0.978 +/- 0.016 (mean +/- SD). The OUES and VO2max had a significant correlation (r = 0.941, p < 0.0001). The correlation between VO2max and OUES was stronger than that between VO2max and VAT, the VE-VCO2 slope or EMOC. The OUES values for 100% and 90% of exercise were not different from each other (at an alpha value of 0.05 and treatment effect of 170, the power of the test [1-beta] was 0.90); OUES for 75% of exercise was slightly lower (3.5%). CONCLUSIONS Our results suggest that OUES may provide an objective, effort-independent estimation of cardiorespiratory functional reserve that is related both to pulmonary dead space and to metabolic acidosis.

Analysis of heart rate variability demonstrates effects of development on vagal modulation of heart rate in healthy children

OBJECTIVES Analysis of heart rate variability (HRV) has been found to be a useful method of assessing cardiovascular autonomic control, but normal values for standard HRV measures in children have not been established. We analyzed HRV in 60 healthy children aged 3 to 15 years to determine normal values and to assess the effects of development on cardiac autonomic control with the use of ambulatory electrocardiographic monitoring. RESULTS The high-frequency (HF) component, an index of cardiac autonomic tone, increased significantly with age from 3 to 6 years (p < 0.01) and decreased with age from 6 to 15 years (p < 0.01), and the magnitude of HF correlated significantly with the R-R intervals. Thus the changes in cardiac autonomic tone could be described as a simple equation using age and heart rate. CONCLUSIONS We present normal values and changes in the cardiac autonomic system during childhood after HRV analysis, which could lead to a better understanding and treatment of cardiac disease in children.

Oxygen uptake efficiency slope as a useful measure of cardiorespiratory functional reserve in adult cardiac patients.

Abstract In this study we aimed to elucidate the validity and usefulness of the oxygen uptake efficiency slope (OUES) in the evaluation of adult cardiac patients. Cardiopulmonary exercise tests were performed on a treadmill by 50 adult patients with chronic heart failure. The OUES was calculated from data for the first 75%, 90%, and 100% of exercise duration. The OUES is derived from the following equation: V˙O2=a× logV˙E+b, where V˙O2 is oxygen uptake (ml/kg/min), V˙E is minute ventilation (l/kg/min), and the constant “a” represents OUES. We also determined the ventilatory anaerobic threshold (VAT). The correlation coefficient of the logarithmic curve-fitting model was [mean (SD)] 0.986 (0.009). The OUES could be used to discriminate effectively between New York Heart Association functional classes (P < 0.001). OUES and maximum V˙O2 were significantly correlated (r=0.78, P < 0.01). Agreement between the OUES values for the first 90%, 75%, and 100% of the exercise was excellent (intraclass correlation coefficient = 0.99). Our results suggest that OUES is applicable to adult cardiac patients as an objective, effort-independent estimation of cardiorespiratory functional reserve.

Role of the oxygen uptake efficiency slope in evaluating exercise tolerance

OBJECTIVE To investigate the interprotocol agreement of oxygen uptake efficiency slope (OUES). METHODS 16 Japanese children and adolescents (10 boys and six girls) underwent two sessions of maximal exercise testing according to the following two treadmill protocols: the standard Bruce protocol and the rapidly increasing staged (RIS) protocol. Maximal oxygen uptake (VO2max), the ventilatory anaerobic threshold (VAT), and the OUES were obtained from the gas analysis data. Agreement between the protocols was tested by means of the Bland-Altman method. RESULTS Interprotocol agreement was excellent for the OUES (limit of agreement, −18% to 17% of the mean value), slightly less good for VO2max (limit of agreement, −20% to 24% of the mean value), and poor for the VAT (limit of agreement, −31% to 31% of the mean value). CONCLUSION These results confirm the clinical usefulness of the OUES as a measure of evaluating exercise tolerance in the paediatric population.

Ventilatory Control during Exercise in Normal Children

We investigated the relation between age and respiratory control during exercise in 80 children aged 6.4-17.6 y (42 male, age, 11.6 ± 3.3 y; body weight, 41.3 ± 14.7 kg; and 38 female, age, 12.6 ± 2.7 y; body weight, 42.5 ± 9.3 kg). Exercise tests were performed on a treadmill after a standard symptom-limited Bruce protocol. Data were analyzed separately for boys and girls. At rest and at peak exercise, the ratio of minute ventilation to carbon dioxide production(˙VE/˙VCO2), the ratio of effective alveolar ventilation to carbon dioxide production(˙VA/˙VCO2), the ratio of pulmonary dead space to tidal volume (Vd/V t), and arterial PCO2 (PaCO2) were not correlated with age. At the exercise intensity of ventilatory anaerobic threshold, the PaCO2 increased, and the ˙VA/˙VCO2 decreased, significantly with age, whereas the Vd/V t was not related to age. Linear regression analysis demonstrated that the slope of the relationship between ˙VE and ˙VCO2(Δ˙VE/Δ˙VCO2) and the slope of the relationship between ˙VA and ˙VCO2(Δ˙VA/Δ˙VCO2) decreased with age. There were no gender differences in the regression slopes and the intercepts of the relationships. Results show that younger children breathe more during exercise to eliminate a given amount of CO2 to keep PaCO2 set point slightly but significantly lower than older children. This age dependence must be considered in investigating ventilatory control during exercise in children.

Comparison of casual blood pressure and twenty-four-hour ambulatory blood pressure in high school students

OBJECTIVE To perform ambulatory blood pressure monitoring (ABPM) in high school students and to compare the 24-hour values with casual blood pressure (BP). METHODS Ambulatory BP monitoring was carried out in 190 high school students, 15 or 16 years of age, with elevated casual BP during the first examination at school for hypertension; 66 had elevated casual BP at both the first and the second examinations (group H1), and 124 students were normotensive at the second examination (group H2). Sixty-two students who were consistently normotensive served as control subjects (group N). Average BPs for the 24-hour period, the awake period (10 AM to 10 PM), and the sleeping period (1 AM to 6 AM) were calculated. RESULTS Average BP for each period was significantly higher in group H1 than in group N. Average BP in group H2 for these periods was intermediate between those of group H1 and of group N. The casual BP had a significant positive correlation with the average BP during the awake period (r = 0.55, p < 0.01 for systolic BP; r = 0.37, p < 0.01 for diastolic BP). In most subjects the casual BP readings were higher than BP during ABPM. CONCLUSIONS Casual BP measurements correlated with 24-hour BP, but they tended to be higher than the measurements obtained during 24-hour ABPM.

Inhalation of Low-Dose Nitric Oxide to Evaluate Pulmonary Vascular Reactivity in Children with Congenital Heart Disease

Abstract. The objective of this study was to investigate the efficacy of low-dose nitric oxide (NO). The study used fifteen consecutive Japanese preoperative patients (7 males and 8 females) with congenital heart disease and pulmonary hyptertension (mean pulmonary arterial pressure >30 mmHg), 6 of these patients had Downs syndrome. Hemodynamic measurements were taken in room air, 100% oxygen, 5 and 40 parts per million NO (NO5 and NO40) by inhalation. The differences between two observations within the same group were determined by the two-tailed paired t-test. A pulmonary vascular resistance (Rp) regression curve was constructed by using linear regression analysis. The percentage change in pulmonary arterial pressure per systemic arterial pressure (Pp/Ps) with NO40 (Pp/Ps-40) exceeded that of Pp/Ps-5 (p < 0.0001). The percentage change for the Rp with NO40 (Rp-40) was larger than that for the Rp-5 (p= 0.0003). The percentage change of Pp/Ps-5 and that with oxygen were similar (p= 0.266). The relationship between Rp-5 and Rp-40 was linear. In conclusion, the effects of NO5 were equivalent to 100% oxygen but less than NO40. NO5 should initially be used to test pulmonary reactivity. If there is no response, patients should still be given NO40.