Quick review of both the terms - Heart Rate and Blood Pressure -

The rate at which the heart expands and contracts every minute is measured in terms of Beats Per Minute (BPM) and is used to evaluate a person's general health.

The pressure that the blood exerts on the walls of the arteries while pumped by the heart is termed as 'Blood Pressure' and is expressed as a ratio. Normally, it is 120/80 where the first number represents the pressure at which the heart pumps the blood into the arteries and the second number represents the pressure when the heart is resting.

Low Blood Pressure also known as 'Hypotension' is a condition in which the blood pressure drops below the normal level (below 90/60).

How are Heart Rate and Blood pressure related to each other?

Blood Pressure is usually depends on - Heart Rate, Nervous system (hormones) and the stroke volume.

1) As the heart rate increases, the blood pressure too goes up and it comes down as the heart rate drops.

2) Other things like the nervous system, body temperature, hormones, medications and diseases affect the heart rate and indirectly the blood pressure.

3) The Stroke Volume (the amount of blood pumped by the heart out of the ventricle at each beat) is the same as the amount of blood carried back to the heart by the veins while at rest. When the body is under stress, the nervous system increases the stroke volume by making the heart pump harder.

More on High Heart Rate and Low Blood Pressure -

Hypotension may be caused due to -

1) Conditions causing reduction in blood volume.
2) Reduction in the amount of blood pumped by the heart.
3) Medications.

The first category would include dehydration, moderate or severe bleeding and severe inflammation of body organs as other causes. The causes in the second category can be listed as weakened heart muscle, pericarditis, pulmonary embolism, a slow heart rate (bradycardia) and a high heart rate (tachycardia). The third category includes medications such as calcium channel blockers, beta blockers, digoxin to name a few.

How does a High Heart Rate (tachycardia) cause low blood pressure?

A common example of Tachycardia causing low blood pressure is 'Atrial Fibrillation', a heart disorder where rapid, irregular electrical discharges from the heart muscle cause the ventricles to contract irregularly and rapidly. The ventricles would not have sufficient time to fill maximum blood before each contraction, so there is a decrease in the amount of blood pumped, in spite of high heart rate. Hypotension can also be caused by abnormally high heart rate such as 'Ventricular Tachycardia'.