DEPENDENCE OF QT INTERVAL ON THE HEART-RATE DURING ALTERATIONS OF PULMONARY VENTILATION IN YOUNG HEALTHY-SUBJECTS

In 77 young healthy volunteers of both sexes the dependence of the QT interval of ECG on the heart rate was investigated during normal venti lation (control) and after 1, 2, 3, 4 min of voluntary hyperventilatio n, after 6 min of hypoxic-hypercapnic ventilation (through an enlarged dead space) and during the Valsalva manoeuvre. The absolute coefficie nts (a) of the regression lines QT = a + b. HR were significantly diff erent in all groups. The slopes of regression lines (b) were significa ntly different in all groups with the exception of 4 min hyperventilat ion. Our results indicate that short-term alterations of pulmonary ven tilation may change not only the duration of the QT interval but also its dependence on the heart rate. Voluntary hyperventilation lasting 1 -2 min and the Valsalva manoeuvre decrease the rate dependence of the QT interval and this change may cause its prolongation at higher heart rates.