Toshiaki Yasuda

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.

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.

Beat-to-beat QT interval variability in children: normal and physiologic data

BACKGROUND QT interval variability provides information on ventricular vulnerability. However, QT interval variability in children has not been adequately evaluated. METHODS One hundred seventy-three consecutive nursing infants and children (male-female, 106:67) up to school age with no intrinsic cardiac disease were included in this study, and they were categorized into 6 age-related groups. The QT variability index (QTVI) was calculated based on an electrocardiogram; and age-specific standard values, sex-specific classification, and a standard growth curve covering 0 to 7 years were constructed. RESULTS The QTVI decreased in an age-dependent manner, reached constant values after school age, and exhibited no sex-specific differences in 6 age-related groups. CONCLUSIONS Based on the age-dependent standardized QTVI values, it is possible to estimate the instability of ventricular repolarization in pediatric patients with better accuracy.

The QT Intervals in Infancy and Time for Infantile ECG Screening for Long QT Syndrome

Background: Electrocardiographic and molecular studies have clarified an association between sudden infant death syndrome (SIDS) and long QT syndrome (LQTS), and few data are available for the QT interval in infancy from birth to 1 year of age. Appropriate time of electrocardiographic screening is not clarified. Medical examinations during infancy are mandatory in Japan.