Why does an increased heart rate mean increased blood pressure?

Question

Say a person starts exercising. If their cardiac volume remains the same but their heart rate increases so that the overall result is an increase in cardiac output, will their blood pressure increase during the exercise ? If it does, why ?

Answer 1

In good approximation, the arterial blood pressure P_A depends with

P_A = P_V + R x dv/dt,

on central venous pressure P_V, total peripheral resistance R (also referred to as TPR or PVR) and cardiac output dv/dt (aka CO) – the usually cited equation MAP = CO * PVR is an over-simplification. Since cardiac output is defined with

dv/dt = R_H * V_S

as a result of heart rate (R_H) and stroke volume (V_S) the blood pressure should increase if heart rate increases.

However, in reality, the conditions are more complex. In exercise body temperature increases, which leads (via the thermoregulatory system) to vasodilation, so that the total peripheral resistance R decreases, which is able to reduce the blood pressure again.

Decreasing P_V in exercise should occur on a very slow time-scale and only be relevant in long-time endurance training.

Concentrations of some hormones change in exercise. Levels of some stress hormones (catecholamines) rise and therefore increase cardiac output, but their action on peripheral resistance is heterogeneous. It goes up, if alpha receptors are stimulated, but decreases after stimulation of beta receptors. Similar to (and partly mediated by) beta adrenergic action classic thyroid hormones (e.g. T4, T3 and 3,5-T2) increase heart rate but decrease total peripheral resistance. It depends on the type of exercise if thyroid hormones rise or drop. They are increased in short-term or endurance exercise (representing type 2 allostasis) but decrease in exhausting exercise (leading to type 1 allostasis).

In summary, it depends on many factors, if blood pressure increases during exercise. In ergometry the blood pressure usually slightly rises.

References

1: GREENE BA. Cardiac output and total peripheral resistance in anesthesiology; clinical applications. J Am Med Assoc. 1958 Mar 1;166(9):1003-10. PMID 13502096. https://www.ncbi.nlm.nih.gov/pubmed/13502096 https://doi.org/10.1001/jama.1958.02990090011003

2: Mayet J, Hughes A. Cardiac and vascular pathophysiology in hypertension. Heart. 2003 Sep;89(9):1104-9. PMID 12923045. https://www.ncbi.nlm.nih.gov/pubmed/12923045/ https://doi.org/10.1136/heart.89.9.1104

3: Silva AS, Zanesco A. Physical exercise, β-adrenergic receptors, and vascular response. Jornal Vascular Brasileiro. 2010 9(2). https://doi.org/10.1590/S1677-54492010000200007

4: Chatzitomaris A, Hoermann R, Midgley JE, Hering S, Urban A, Dietrich B, Abood A, Klein HH, Dietrich JW. Thyroid Allostasis-Adaptive Responses of Thyrotropic Feedback Control to Conditions of Strain, Stress, and Developmental Programming. Front Endocrinol (Lausanne). 2017 Jul 20;8:163. doi: 10.3389/fendo.2017.00163.. PMID 28775711. https://www.ncbi.nlm.nih.gov/pubmed/28775711 https://doi.org/10.3389/fendo.2017.00163

Answer 2

By cardiac volume I assume your talking about Stroke Volume, that is, the volume of blood pumped from the left ventricle per beat.

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Blood pressure will probably increase.

Stroke Volume depends on contractility, duration of contraction, preload (end-diastolic volume) and afterload.

Exercise usually increases the preload (due to an increased venous return caused by muscle contractions) and contractility (due to sympathetic effects).

So, to maintain a constant Stroke Volume, and cancel out the preload and contractility increments, you need to either:

• reduce the duration of contraction (by raising the heart rate beyond 120bpm/ 140bpm, for instance) or
• increase the Afterload (by increasing the Total Peripheral Resistance, for instance).

Since blood pressure is positively affected by both cardiac output and Total Peripheral Resistance, unless the Heart Rate gets really high, blood pressure should increase.

Answer 3

This portion of the text in Robbins Pathology will answer the question;

Blood pressure is a function of cardiac output and peripheral vascular resistance, both of which are influenced by multiple genetic and environmental factors.

Cardiac output is a function of stroke volume and heartrate. The most important determinant of stroke volumeis the filling pressure, which is regulated throughsodium homeostasis and its effect on blood volume.Heart rate and myocardial contractility (a second factoraffecting stroke volume) are both regulated by the α-and β-adrenergic systems (in addition to their effects onvascular tone).

Therefore, increasing the heart rate will lead to an increase in the mean arterial blood pressure.

Answer 4

Let me give a answer that is more intuitive, without considering other factors. Blood is pumped by your heart to arteries then to capillaries then to veins then back to heart. It is easy to transfer fluids through big tubes like arteries, but is is hard to "squeeze" fluid through capillaries since there is a lot of resistance.

So when the heart pump once, the heart move some blood from vein to artery then stop. The pumped blood are all stored in the arteries because they can't get through the capillaries immediately which make your arteries enlarge and the pressure in arteries get higher and you get the systolic blood pressure. At the same time, the pressure in vein become lower since some blood is pumped away. As the blood stored in the arteries getting drained through capillaries to veins, the pressure in the arteries get lower and lower----until your heart pump again. This is why your blood pressure will be higher if your heart pump more frequently---if the heart rate is slower, the blood pressure in the arteries will drop to a lower value before the heart pump for the next time.

The heart need to pump blood again and again to keep the blood pressure in arteries higher than veins, it is this blood pressure difference that squeeze blood from arteries through capillaries to veins. The higher the difference, the faster blood get transferred from arteries to veins which bring oxygen etc faster to everywhere in your body to satisfy the need during exercise.