Blood pressure refers to the force exerted by the circulating blood on the walls of blood vessels and is one of the essential vital signs. Typically, blood pressure is measured in arteries, which are the blood vessels that carry blood away from the heart. The measurement of arterial pressure is commonly done using a sphygmomanometer, although modern devices no longer use mercury but continue to report values in millimeters of mercury (mmHg).
Arterial pressure is characterized by two key values: systolic and diastolic pressure. Systolic pressure represents the peak pressure in the arteries during the heart's contraction phase, while diastolic pressure is the lowest pressure during the heart's relaxation phase. The average pressure throughout the cardiac cycle is referred to as mean arterial pressure, and the difference between the maximum and minimum pressures is known as pulse pressure.
For instance, a typical blood pressure reading for a resting, healthy adult is 115 mmHg for systolic pressure and 75 mmHg for diastolic pressure, often noted as "one fifteen over seventy-five." It's essential to note that blood pressure can vary naturally from one heartbeat to the next and throughout the day, influenced by factors like stress, nutrition, medications, and health conditions. Hypertension is a term used when blood pressure is abnormally high, whereas hypotension refers to abnormally low blood pressure. Alongside body temperature, blood pressure is one of the most frequently monitored physiological parameters.
Arterial hypertension is not typically an acute issue, but it raises concerns for physicians due to its long-term effects and its role as an indicator of other health problems.
Elevated arterial pressure imposes mechanical stress on the artery walls. Higher pressure levels increase the workload on the heart and contribute to the progression of unhealthy tissue growth (atheroma) within the artery walls. With higher pressure, more stress is present, leading to the advancement of atheroma and the potential thickening and weakening of the heart muscle over time.
Persistent hypertension is a significant risk factor for conditions such as strokes, heart attacks, heart failure, arterial aneurysms, and is the primary cause of chronic renal failure. Even moderately high blood pressure can lead to a shortened life expectancy. In cases of severely high pressure, with mean arterial pressures 50% or more above average, individuals can expect a significantly reduced lifespan unless appropriate treatment is provided.
Previously, much emphasis was placed on diastolic pressure, but it's now recognized that both high systolic pressure and high pulse pressure (the difference between systolic and diastolic pressures) are also risk factors. In some situations, reducing excessively high diastolic pressure may increase risk, potentially due to an increased difference between systolic and diastolic pressures.
Hypotension, or low blood pressure, can be a medical concern if it leads to signs or symptoms like dizziness, fainting, or, in severe cases, shock. The similarity in pronunciation with hypertension can be confusing, but hypotension is a concern only when it results in noticeable symptoms.
When arterial pressure and blood flow decrease significantly, the brain's perfusion (blood supply) can become critically insufficient, causing lightheadedness, dizziness, weakness, or fainting.
Interestingly, individuals with consistently low blood pressure who remain functional tend to experience fewer cardiovascular disease events compared to those with normal blood pressure.
Orthostatic hypotension, or postural hypotension, occurs when a person's arterial pressure drops significantly upon standing from a sitting position. Gravity reduces the return of blood from the body's veins below the heart, resulting in reduced stroke volume and cardiac output. However, the body typically adjusts to this change, with veins constricting and the heart rate increasing to compensate for the effects of gravity, minimizing the risk of dizziness and potential blackouts.
Other potential causes of low blood pressure include sepsis, hemorrhage (blood loss), exposure to toxic substances (including excessive blood pressure medication), and hormonal abnormalities, such as Addison's disease.