Blood Pressure

The function of the heart is to circulate blood around the body. The heart comprises of four chambers:

• Right Atrium
• Left Atrium
• Right Ventricle
• Left Ventricle

Functionally the heart comprises of two pumps:

• The right atrium receives blood from the body (de-oxygenated blood) and the right ventricle pumps it into the lungs for aeration (removal of carbon dioxide and to add oxygen).
• The left atrium receives the oxygenated blood from the lungs and the left ventricle pumps it around the body.

Blood Pressure

Blood pressure represents the force (pressure) exerted by blood against the arterial walls during a cardiac cycle (heart beat) which consists of heart muscle contraction (systole) and heart muscle relaxation (diastole).

Systolic blood pressure, the higher of the two pressure measurements, occurs as the heart muscles contract pumping blood into the aorta. Heart muscles then relax allowing the heart to refill with blood and the lowest pressure reached represents the diastolic blood pressure.

Normal systolic blood pressure in an adult varies between 110 and 140 mm Hg, and diastolic pressure varies between 60 and 90 mm Hg.

Blood Pressure Classification

The following table is the British Hypertension Society classification of blood pressure levels. (Note: "mm Hg" means millimeters of mercury)

Resting Heart Rate

The resting heart rate for the average person is between 70 and 90 beats per minute (bpm). The term tachycardia is applied to a rapid heart rate (over 100 bpm) and the term bradycardia indicates a slow heart rate (less than 50 bpm). Endurance athletes may have a resting heart rate of less than 50 bpm.

Cardiac Output

This is the amount of blood pumped from your heart and is calculated by multiplying heart rate by stroke volume (the amount of blood ejected by the heart in each beat). An endurance athlete will have a lower resting heart rate and a larger stroke volume than a non-athlete. The cardiac output for an endurance athlete is approx. 35 litres while that for the non-athlete is 22 litres.

Starling's Law of the Heart

Starling's law of the heart states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart. A paper by Solaro (2007) [3] examines the mecahnism of Starling's Law.

Blood Pressure daily variations

Research by Millar-Craig et al. (1978) [1] found that blood pressure was lowest at 3-am and began to rise again during the early hours of the morning before waking.

Classification of the Hypertensive Disorders of Pregnancy

Higgins et al. (2001) [2] defines the clasifications as:

• Chronic hypertension - hypertension (>140 mm Hg systolic or >90 mm Hg diastolic) that is present and observable before pregnancy or that is diagnosed before the 20th week of gestation
• Pre-eclampsia-eclampsia - usually occurs after 20 weeks of gestation
• Pre-eclampsia superimposed upon chronic hypertension - with hypertension and no proteinuria early in pregnancy <20 weeks, new-onset proteinuria (urinary excretion of 0.3 g Protein or greater in a 24-hour specimen)
• Gestational hypertension - blood pressure elevation detected for the first time after mid pregnancy, without proteinuria

Referenced Material

1. MILLAR-CRAIG, M.W. and BISHOP, C.N. and RAFTERY, E.B (1978) Circadian Variation of Blood-Pressure. The Lancet, 311 (8068), p. 795-797
2. HIGGINS, J.R. and SWIET, M. (2001), Blood-pressure measurement and classification in pregnancy. The Lancet, 357 (9250), p. 131-135
3. SOLARO, R. J. (2007) Mechanisms of the Frank-Starling Law of the Heart: The Beat Goes On, Biophys J., 93 (12), p. 4095–4096

Page Reference

The reference for this page is:

• MACKENZIE, B. (2001) Blood Pressure [WWW] Available from: http://www.brianmac.co.uk/bloodp.htm [Accessed

Associated Pages

The following Sports Coach pages should be read in conjunction with this page:

• Articles on Physiology
• Maximum Heart Rate
• VO2 max