Heart rate from cardiac cycle duration on graph

Steps:

• Measure the time axis to find the duration of one full cardiac cycle (from start of one atrial systole to the next).
• The graph shows one cycle spanning 0.8 seconds.
• Apply the formula: heart rate (bpm) = 60 seconds / cycle duration in seconds.
• Calculation: 60 / 0.8 = 75 beats per minute.

Why A is correct:

• 75 bpm matches the formula using the graph's 0.8-second cycle duration, standard for left heart pressure tracings.

Why the others are wrong:

• B: 80 bpm implies a 0.75-second cycle, shorter than shown.
• C: 120 bpm implies a 0.5-second cycle, much faster than depicted.
• D: 150 bpm implies a 0.4-second cycle, not matching the graph's timeline.

Final answer: A