When the body begins fighting an illness, the heart often beats faster than usual. This fluctuation is usually a normal physiological response, signaling that the immune system is actively engaged in defense. Understanding the difference between a typical response to sickness and a potentially dangerous change is important. Monitoring your heart rate provides insight into how your body is coping with the stress of an infection or virus.
What is a Normal Resting Heart Rate?
A resting heart rate (RHR) provides the baseline measurement against which any changes during an illness should be compared. For most healthy adults, a normal RHR falls within a range of 60 to 100 beats per minute (BPM) while the body is calm and at rest. Factors like age, fitness level, and medications influence this rate; athletes may have an RHR as low as 40-50 BPM. Knowing your personal baseline is helpful.
You can easily measure your pulse manually by locating the radial artery on the wrist or the carotid artery on the neck. Place your index and middle fingers on the underside of the wrist or in the soft groove on the side of the neck. Count the number of beats that occur over a 30-second period. Multiplying this count by two provides your heart rate in beats per minute.
The Body’s Stress Response: Why Heart Rate Rises During Illness
An elevated heart rate during sickness is primarily a sign of increased metabolic demand as the body works to fight an infection. This process is complex, involving several interconnected biological systems that drive the heart to pump blood faster. The elevation is a necessary mechanism to ensure that the body’s defenses and energy sources are delivered where they are needed most.
Fever is one of the most common causes of an accelerated heart rate, showing a direct correlation between body temperature and pulse. For every one degree Celsius (or 1.8 degrees Fahrenheit) rise in body temperature, the heart rate typically increases by about 10 BPM. This is the heart working harder to circulate blood, which helps regulate temperature and distribute heat throughout the body.
Furthermore, the body’s inflammatory response to a virus or bacterial infection stimulates the heart. As the immune system activates, it releases chemical messengers called cytokines into the bloodstream. These substances increase the overall metabolic rate, demanding more oxygen and nutrients. The heart must then increase its output to deliver immune cells and oxygen to the infection sites and meet this heightened energy requirement.
Dehydration is another frequent contributor to a faster pulse when a person is ill, especially if they are experiencing vomiting, diarrhea, or low fluid intake. When the body loses fluids, the total volume of blood decreases. The heart must compensate for this reduced volume by beating faster to maintain adequate blood pressure and circulate the remaining blood effectively to the organs.
Recognizing When Heart Rate Changes Signal Danger
While an elevated heart rate is generally an expected response to illness, certain thresholds and accompanying symptoms indicate the need for medical attention. The number itself is less important than the context and the presence of other physical distress signals. Knowing these signs can help differentiate a normal sick response from a serious complication.
A persistent resting heart rate consistently above 100 BPM, known as tachycardia, warrants medical evaluation, particularly if it remains high even after a fever has broken. A rate that stays above 120 to 130 BPM, even at rest, should be cause for serious concern. This level of sustained elevation may signal a more severe systemic infection or an underlying cardiac issue that the illness has unmasked.
Conversely, a heart rate that is unusually slow, known as bradycardia, can also be a warning sign when a person is sick. For a non-athlete, a heart rate below 50 BPM should be noted. This slow rate, combined with illness, may indicate certain infections, medication side effects, or a problem with the heart’s electrical system.
The most concerning sign is when a change in heart rate is accompanied by severe physical symptoms that suggest the body is not receiving enough oxygenated blood. These symptoms require urgent care:
- Chest pain or discomfort.
- Severe shortness of breath.
- Feeling dizzy or lightheaded to the point of fainting.
- Confusion or any alteration in mental status.
If you experience noticeable heart palpitations, such as a fluttering, pounding, or irregular heartbeat, along with these severe symptoms, seek emergency medical help right away. Monitoring your pulse rate is a simple self-care tool, but it should always be paired with attention to these physical warning signs.