Final answer:
A heart pacemaker is a device that regulates the heartbeat by providing electrical impulses when natural heart rhythms are irregular or too slow. It can adjust the rate of these impulses to match the body's activity level, ensuring adequate blood flow to vital tissues.
Step-by-step explanation:
A heart pacemaker is a medical device implanted in patients with arrhythmias, which are irregular heart rhythms. These devices generate electrical pulses that regulate the heart's rhythm, normally firing at a set rate, which could be adjusted based on the patient's needs. For example, a pacemaker set to fire at 81 times per minute helps maintain an adequate heart rate when the heart's natural pacemaker, the sinoatrial node, does not work correctly. Pacemakers can detect changes in body motion and breathing, which enables them to adjust the heart rate during physical activities appropriately, thereby ensuring sufficient blood and oxygen flow to the body.
When arrhythmias are chronic and the heart follows a junctional rhythm coming from the AV node, a cardiologist can implant a pacemaker to restore the full sinus rhythm. These devices can work both on-demand or continuously, with some even containing built-in defibrillators for additional heart rhythm management. The pacemaker's action is based on an appropriate time constant, ensuring the heart contracts and pumps blood effectively.
With respect to athletes like Miguel Indurain, who have exceptionally low resting heart rates, pacemakers ensure that even when lower-than-normal heart rates occur (a condition called bradycardia), the device can maintain a rate that is sufficient to keep blood flowing to vital tissues. Such a mechanism is critical since heart rates significantly lower than 50 beats per minute can lead to serious health complications.