Final answer:
Junctional tachycardia requires a heart rate over 100 BPM, while the beat frequency from two waves at 300 Hz and 340 Hz is 40 Hz. Cardiac output generally increases with heart rate increases but may plateau or decrease above a certain threshold.
Step-by-step explanation:
The rate of junctional tachycardia rhythms must be greater than 100 BPM. Junctional tachycardia is a type of heart rhythm disorder characterized by a fast heartbeat, originating from the atrioventricular junction. In terms of beat frequency produced by the superposition of two waves, if the frequencies are 300 Hz and 340 Hz, the beat frequency is the difference, which is 40 Hz.
Concerning the cardiac output in healthy young adults, when the heart rate increases above 160 bpm, typically, the cardiac output continues to increase to a certain point, but it may eventually plateau or decrease due to a reduction in the time for ventricular filling and less efficient pumping of the heart.
Outside of tachycardia and arrhythmias, for well-conditioned athletes such as cyclists, a resting heart rate can be quite low, even in the 30-40 beats per minute range, indicating efficient heart function. However, heart rates lower than 50 beats per minute can be indicative of bradycardia, which may lead to decreased blood flow to vital tissues if the rate goes significantly lower.