Influence of heart rate and age on Q-Korotkoff sound intervals.

The Korotkoff sound appearance time (QK intervals) was measured in 224 normal subjects of both sexes between the age of 6 and 79 years. The sex difference was not obvious except for the diastolic values of the intervals (QKd) in the sixth decade. Although the QK intervals remained almost unchanged between the third and the fifth decade, both the systolic (QKs) and the diastolic values were significantly smaller in the young subjects under the age of 20. On the other hand, QKs was significantly decreased and QKd and the difference between the systolic and diastolic values (QKs-d) were significantly increased in the elderly subjects. The short QK interval in the young subjects was considered to be mainly attributable to the short preejection period, while the increased pulse wave velocity was postulated to be the main responsible factor for the shortening of QKd in the elderly subjects. A statistically significant negative correlation was demonstrated between QKd and the heart rate in both sexes, while QKs and QKs-d were not significantly correlated with the heart rate.