When a person is infected with the influenza virus, a noticeable drop in blood pressure, known as hypotension, can occur as the body struggles against the illness. Blood pressure is the force exerted by circulating blood against the walls of the body’s arteries, and a drop indicates that this force is too low to maintain proper circulation. This common symptom of the flu is caused by a combination of physical fluid loss and a widespread immune system response. The body’s reaction to the virus creates two distinct physiological changes that directly reduce the pressure within the circulatory system.
Dehydration and Fluid Loss
The most direct and easily understood cause of lowered blood pressure during the flu is a reduction in the total volume of circulating blood. The flu often triggers symptoms that rapidly deplete the body’s fluid reserves, directly impacting the volume needed to maintain arterial pressure. A high fever, which is a common flu symptom, causes the body to lose water through excessive sweating as it attempts to regulate its temperature.
This fluid loss is compounded by other symptoms such as vomiting and diarrhea, which are sometimes associated with influenza. Each of these physical processes results in a direct loss of water and electrolytes like sodium and potassium. When the body loses too much fluid, the absolute volume of blood decreases, a state called hypovolemia.
Less blood volume means there is less fluid pushing against the artery walls, resulting in a measurable drop in blood pressure. Furthermore, the loss of electrolytes impairs the body’s ability to retain the remaining fluid. This worsens the overall state of dehydration and contributes to the sustained low pressure.
Systemic Inflammation and Vessel Dilation
Beyond simple fluid loss, the body’s deep immune response to the influenza virus triggers a complex chemical reaction that actively lowers blood pressure. When the immune system detects the virus, it releases a cascade of pro-inflammatory signaling molecules called cytokines into the bloodstream. Specific cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukins (IL-6 and IL-1β), are significantly elevated during an influenza infection.
These chemical messengers circulate throughout the body and target the endothelial cells that line the inside of blood vessels. The cytokines stimulate the production of vasodilatory mediators, including nitric oxide and bradykinin, which act to relax the smooth muscle in the vessel walls. This relaxation causes widespread vasodilation, meaning the arteries and arterioles widen significantly.
Vasodilation effectively increases the total capacity of the circulatory system without adding any more blood volume. When the system’s “hoses” suddenly widen, the same amount of fluid can no longer fill the space, causing the pressure to fall dramatically. The change in vessel size, driven by the inflammatory response, is a major contributing factor to the low blood pressure experienced during the flu.
Managing Hypotension and When to Seek Help
For mild hypotension associated with the flu, management primarily focuses on reversing the factors that cause the pressure drop. Increasing fluid intake is the most effective self-care measure, aiming to restore the lost blood volume. Consuming fluids that contain electrolytes, such as oral rehydration solutions or broths, is better than plain water because it helps the body absorb and retain the necessary water and minerals.
When moving from a lying or sitting position, it is advisable to do so slowly. A sudden change in posture can lead to a temporary, more pronounced drop in pressure known as orthostatic hypotension. This temporary drop can cause lightheadedness or dizziness, increasing the risk of falls. Proper rest also allows the body to conserve energy and manage the systemic inflammatory response more effectively.
However, certain warning signs indicate that hypotension has become severe and requires immediate medical attention. Prompt medical evaluation is necessary if any of these symptoms appear:
- Persistent dizziness
- Confusion or an inability to wake up
- Trouble breathing
- Chest pain or a severe lack of urine output