Blood pressure measurement

Blood pressure measurement

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When measuring your blood pressure in your arm, when you hear the sound to measure the systolic, is that sound NOT the heartbeat?

The sound in question is called the Korotkoff sound:

If the pressure is dropped to a level equal to that of the patient's systolic blood pressure, the first Korotkoff sound will be heard. As the pressure in the cuff is the same as the pressure produced by the heart, some blood will be able to pass through the upper arm when the pressure in the artery rises during systole. This blood flows in spurts as the pressure in the artery rises above the pressure in the cuff and then drops back down beyond the cuffed region, resulting in turbulence that produces an audible sound.

Measuring your blood pressure is the only way to know whether you have high blood pressure. High blood pressure usually has no warning signs or symptoms, and many people do not know they have it.

You can get your blood pressure measured

  • By a health care team member at a doctor&rsquos office.
  • At a pharmacy that has a digital blood pressure measurement machine.
  • With a home blood pressure monitor that you can use yourself.

Take this form pdf icon [PDF &ndash 105 KB] with you on your first blood pressure visit to record important blood pressure-related information.

Plasma is the tissue fluid of blood , It represents 54 % of the blood volume , It contains 90 % water , 1 % inorganic salts such as Ca ++ , Na + , Cl − and ( HCO3 ) − , 7% proteins as albumin , globulin and fibrinogen , 2 % other components as the absorbed food ( sugars and amino acids ) , hormones , enzymes , antibodies and wastes ( urea ) .

RBCs – Red blood cells ( Erythrocytes )

They are the most abundant blood cells , they are nearly about 4 : 5 million cell/mm³ in males , 4 : 4.5 million cell/mm³ in females , Their shape is round corpuscles and biconcave , They produced in the bone marrow of backbone .

Each cell is destroyed after 120 days , They circulate about 172,000 circulations , They are destroyed in the liver , spleen and bone marrow , They are e nucleated cells contain haemoglobin ( protein + iron ) which gives the blood its red colour .


  1. Transporting oxygen from the two lungs to all the body parts , where in the two lungs , the haemoglobin combines with oxygen to form a pale red oxyhaemoglobin ,The oxyhaemoglobin carries the oxygen to the different parts of body , where it leaves the oxygen and changes into haemoglobin .
  2. Transporting CO2 from all the body parts to the two lungs , where the haemoglobin combines with CO2 inside the body cells to form a dark red carbo-aminohaemoglobin , Carbo-aminohaemoglobin carries CO2 to the two lungs , where it leaves CO2 and changes into haemoglobin .

WBCs – White blood cells ( Leucocytes )

The number of white blood cells is 7000 cell/mm³ , this number increases during diseases , Their s hape is colourless and nucleated with many shapes , They are formed in the bone marrow , spleen and lymphatic system , some of their kinds live for 13 – 20 days .

Functions : They are produced in many types , each type with a specific function , but the main function is the protection of body against the infectious diseases thro ugh the following :

They circulate continuously in the blood vessels , attack the foreign particles , destroy and engulf them , Some of them produce antibodies .

Blood platelets

The number of blood platelets is 250 , 000 platelet /mm³ , Their s hape is non-cellular and very small in size , Their size is one fourth of the RBCs , They are produced from the bone marrow , They live for about 10 days , They play a role in blood clot after the injury .

Blood clot

Blood clot occurs when a blood vessel is cut , The i mportance of clotting : Blood forms a clot to prevent the bleeding before it leads to shock followed by death .

Factors of coagulation ( clotting ) of blood :

  1. Exposure of blood to air .
  2. Friction of blood with rough surfaces as destroyed cells & tissues .
Mechanism of blood clotting

In case of the presence of blood clotting factors , the steps are shown as the following :

The blood platelets together with the destroyed cells from a protein calle d thromboplastin .

Platelets + Destroyed cellsThromboplastin in presence of ( clotting factors in blood )

In the presence o f calcium ions ( Ca ++ ) and blood clotting factors in the plasma , thromboplastin activates the conversion of prothrombin into thrombin .

ProthrombinThrombin ( Active enzyme ) , in the presence of Thromboplastin , Ca ++ , clotting factors

Where Prothrombin is a protein that is secreted in the liver with the help of vitamin K and is passed directly into the blood .

Thrombin catalyzes the conversion of fibrinogen ( soluble protein in plasma ) into fibrin ( insoluble protein )

Fibrinogen ( Soluble protein )Fibrin ( Insoluble protein ) in the presence of Thrombin

Fibrin precipitates as a network of microscopic interlacing fibers where the blood cells are aggregated , forming a clot which blocks the cut in the damaged blood vessels .

Reasons of the non-clotting of blood inside the blood vessels
  1. Blood runs in a normal fashion inside the blood vessels without slowing down .
  2. Platelets a lso slide easily and smoothly inside the blood vessels in order not to be broken .
  3. The presence of heparin ( it is secreted by the liver ) which prevents the conversion of prothrombin into active thrombin .
Functions of blood

Transportation : It transports the digested food substances , waste nitrogenous compounds , hormones and some enzymes ( active or inactive ) through the plasma , I t transports O2 and CO2 through RBCs .

Controlling : It controls the processes of metabolism , It keeps the body temperature at 37° C , It regulates the internal environment ( homeostasis ) such as osmotic potential , amount of water and pH in the tissues .

Protection : It protects the body against the microbes and pathogenic organisms through the immunity involving the lymphatic system ( WBCs ) , It protects the blood itself against the bleeding by the formation of blood clot .

Blood Pressure

The blood is a viscous liquid which circulates within the arteries and veins smoothly by the process of heartbeats , but to pass within the microscopic blood capillaries , it needs pressure .

The maximum blood pressure is measured as the ventricles contract and the largest blood pressure is measured in the arteries nearer to the heart .

The minimum blood pressure is measured as the ventricles relax and the blood pressure in the venules i s very low ( about 10 mm Hg ) , This pressure is not sufficient to move the blood back to the heart , So , the returning of blood to the heart depends on :

  • The skeletal muscles near the veins : when these muscles contract , they put a pressure on the collapsible walls of veins and the blood contained in these vessels .
  • Valves of veins : that prevent the backward flow of blood .
Measurement of blood pressure

The blood pressure is measured by means of mercuric instruments sphygmomanometers , There readings consist of two numbers :

  • Maximum : measured during the ventricular contraction which represents the maximum blood pressure .
  • Minimum : measured during the ventricular relaxation which represents the minimum blood pressure .

Example : 120/80 mm Hg is the normal value of blood pressure in youth , so , the number of 120 mm Hg represents the ventricular contraction ( cystolic ) and 80 mm Hg represents the ventricular relaxation ( diastolic ) .


Structure : a mercuric tube and a scale board .

Idea of working : blood pressure can be measured according to the elevation of mercury level inside the tube and it is represented by a number on the scale board .

Method of measurement

The values of blood pressure are determined by listening to the heartbeats , and also between one beat and another , as the following :

on hearing the sound of heartbeat , the doctor can determine the maximum value of blood pressure , referring to the ventricles contraction ( cystolic ) .

When the sound disappears , the doctor can determine the minimum value of blood pressure , referring to the ventricles relaxation ( diastolic ) .

The blood pressure increases gradually by aging and it must be under medical control to avoid its harmful effects , There are some digital instruments to measure the blood pressure , but they are not accurate as the mercuric instruments .

The blood pressure in creases in arteries gradually by aging , leading to the increase of resistance against the passage of blood through them .

Measurement of Blood Pressure in Humans: A Scientific Statement From the American Heart Association

The accurate measurement of blood pressure (BP) is essential for the diagnosis and management of hypertension. This article provides an updated American Heart Association scientific statement on BP measurement in humans. In the office setting, many oscillometric devices have been validated that allow accurate BP measurement while reducing human errors associated with the auscultatory approach. Fully automated oscillometric devices capable of taking multiple readings even without an observer being present may provide a more accurate measurement of BP than auscultation. Studies have shown substantial differences in BP when measured outside versus in the office setting. Ambulatory BP monitoring is considered the reference standard for out-of-office BP assessment, with home BP monitoring being an alternative when ambulatory BP monitoring is not available or tolerated. Compared with their counterparts with sustained normotension (ie, nonhypertensive BP levels in and outside the office setting), it is unclear whether adults with white-coat hypertension (ie, hypertensive BP levels in the office but not outside the office) have increased cardiovascular disease risk, whereas those with masked hypertension (ie, hypertensive BP levels outside the office but not in the office) are at substantially increased risk. In addition, high nighttime BP on ambulatory BP monitoring is associated with increased cardiovascular disease risk. Both oscillometric and auscultatory methods are considered acceptable for measuring BP in children and adolescents. Regardless of the method used to measure BP, initial and ongoing training of technicians and healthcare providers and the use of validated and calibrated devices are critical for obtaining accurate BP measurements.

Keywords: AHA Scientific Statements blood pressure hypertension monitoring, ambulatory.

Measuring arterial blood pressure in humans: Auscultatory and automatic measurement techniques for human biological field studies

Department of Healthcare Policy and Research, Division of Biostatistics and Epidemiology, and Department of Medicine, Division of Nephrology and Hypertension, Weill Cornell Medical College, New York, NY 10065

Department of Anthropology and Decker School of Nursing, Binghamton University, Binghamton, New York 13902

Correspondence Gary D. James, Department of Anthropology, Binghamton University, Binghamton, New York, 13902. Email: [email protected] Search for more papers by this author

Department of Healthcare Policy and Research, Division of Biostatistics and Epidemiology, and Department of Medicine, Division of Nephrology and Hypertension, Weill Cornell Medical College, New York, NY 10065


Human biologists have been examining arterial blood pressure since they began studying the effects of the environment and culture on the health of diverse populations. The Korotkoff auscultatory technique with a trained observer and aneroid sphygmomanometer is the method of choice for blood pressure measurement in many bioanthropological field contexts. Korotkoff sounds (the first and fifth phases) are the preferred determinants of systolic and diastolic pressure, even in infants, children, pregnant women, and the elderly. Training of observers, positioning of individuals, and selection of cuff size are all essential for obtaining standardized measurements. Automatic electronic devices are increasingly being used for blood pressure measurement in human biological studies. The automatic monitors often use the oscillometric method for measuring pressure, but must be validated before use. The emergence of automatic ambulatory blood pressure monitors has opened another avenue of research on blood pressure in human biology, where allostasis and circadian responses to environmental change and real life behavioral challenges can be defined and evaluated, largely because there is now the ability to make multiple measurements over time and in varying contexts. Stand-alone automatic monitors can also be substituted for manual auscultated readings in field contexts, although in studies where participants measure their own pressure, education about how the devices work and protocol specifics are necessary. Finally, computer-driven plethysmographic devices that measure pressure in the finger are available to evaluate short-term reactivity to specific challenges.

How should different blood pressure measurement techniques be used?

Which measures of blood pressure are clinically important?

There are potentially three major measures of blood pressure that could contribute to the adverse effects of hypertension. The first is the average or “true” level, the second is the diurnal variation, and the third the short-term variability.

Average clinic blood pressure

Presently, epidemiologic and clinical data are available only for the average level of blood pressure. In clinical practice, a patient’s blood pressure is typically characterized by a single value of the systolic and diastolic pressures, to denote the average level. Such readings are normally taken in a clinic setting, but there is extensive evidence that in hypertensive patients, clinic pressures are consistently higher than the average 24-hour pressures recorded with ambulatory monitors. 70 This overestimation by clinic readings of the true pressure at high levels of pressure and underestimation at low levels has been referred to as the regression dilution bias and means that the slope of the line relating blood pressure and cardiovascular morbidity should be steeper for the true blood pressure than for the clinic pressure. 71

Diurnal variation in blood pressure

There is a pronounced diurnal rhythm of blood pressure, with a decrease of 10 to 20 mm Hg during sleep and a prompt increase on waking and rising in the morning. The highest blood pressures are usually seen between 6 AM and noon, which is also the time at which the prevalence of many cardiovascular morbid events tends to be highest. 46 The pattern of blood pressure during the day is to a large extent dependent on the pattern of activity, with pressures tending to be higher during the hours of work and lower while at home. 11 In hypertensive patients, the diurnal blood pressure profile is reset at a higher level of pressure, with preservation of the normal pattern in the majority. The short-term blood pressure variability is increased when expressed in absolute terms (mm Hg), but the percentage changes are no different. Thus, hypertension can be regarded as a disturbance of the set point or tonic level of blood pressure with normal short-term regulation. Antihypertensive treatment reverses these changes, again by resetting the set point toward normal, with little effect on short-term variability. The normal diurnal rhythm of blood pressure is disturbed in some hypertensive individuals, with loss of the normal nocturnal fall of pressure. This has been observed in a variety of conditions, including malignant hypertension, chronic renal failure, several types of secondary hypertension, pre-eclampsia, and conditions associated with autonomic neuropathy. 71 There is ample evidence linking elevated nighttime blood pressure to increased cardiovascular morbidity and mortality compared to daytime blood pressure. In the Ohasamma population-based study, a 5% reduction in night time BP resulted in up to 20% higher risk of cardiovascular mortality 56 . Similarly, a 9 mm Hg increase in nighttime diastolic BP was associated a 25% increased risk of congestive heart failure among elderly Swedish men. 28 In the Sys-Eur trial, 83 a large placebo-controlled study of the effects on cardiovascular morbidity of treating systolic hypertension of the elderly with a calcium channel blocker, a substudy of 808 patients used ambulatory blood pressure monitoring. Staessen et al found that nighttime blood pressure was a better predictor of cardiovascular morbidity and mortality than daytime blood pressure. 83 Although these findings are not sufficiently well established to be applied to routine clinical practice, the clinical significance of nocturnal hypertension and nondipping status cannot be ignored for long, given the potential beneficial effect of the treatment of nocturnal hypertension on cardiovascular disease risk reduction in hypertensive patients. 10

Blood pressure variability

Information on the clinical significance of blood pressure variability has accumulated over the past decade with recent data suggesting that increased ambulatory blood pressure variability is associated with the development of early carotid arteriosclerosis, 78 and a high rate of cardiovascular morbidity. 31 More recently, in a prospective ambulatory blood pressure study of initially untreated sample of 2649 hypertensive patients, Vedecchia and colleagues compared the independent prognostic value of daytime and nighttime blood pressure variability for cardiovascular events. They found elevated nighttime systolic blood pressure to be an independent predictor of cardiac events. 89 Similarly, among elderly patients in the Syst-Eur trial, increased nighttime systolic blood pressure variability on admission to the Syst-Eur trial was an independent risk factor for stroke during the trial among those in the placebo arm of the trial. (refs Systolic blood pressure variability as a risk factor for stroke and cardiovascular mortality in the elderly hypertensive population. 75

The combined use of clinic, home, and ambulatory monitoring

The measurement of clinic blood pressure, either by use of automated devices or conventional sphygmomanometry, will continue to be the principal method of clinical evaluation. A cardinal rule is that the closer the blood pressure is to the threshold level at which treatment will be started, the more readings should be taken over more visits, before treatment decision is made. In patients who have persistently elevated clinic pressure and evidence of blood pressure–related target organ damage, it is usually unnecessary to supplement the clinic readings with other types of measurement before reaching a therapeutic decision. When an elevated blood pressure is the only detectable abnormality, however, the possibility that the clinic pressure may overestimate the true pressure should be considered. This can be done either by self-monitoring or by ambulatory monitoring. A schema for the use of the different procedures for measuring blood pressure when evaluating a newly diagnosed hypertensive patient is shown in Fig. 8 . If self-monitoring is chosen and reveals pressures comparable to the clinic value, treatment may be appropriate but if the home readings are much lower than the clinic readings, it does not rule out the possibility that the blood pressure may be elevated at work. This is the advantage of ambulatory monitoring, which gives the best estimate of the full range of blood pressure experienced during everyday life.

Schema for combining different measures of blood pressure in the evaluation of patients with suspected hypertension.

Simultaneous measurements of blood pressures in right and left brachial arteries

The most recent guidelines do not mention which arm to use to measure blood pressure or interarm blood pressure differences. In 357 women and 171 men, mean age 79 +/- 10 years, 2 geriatricians simultaneously measured brachial artery blood pressure (BABP) with the patient in the sitting position. All blood pressure measurements were performed using the same 2 machines, which were calibrated and marked 1 and 2. The machines and cuffs were transferred to the opposite arm for a repeat measurement in all patients and the results of the 2 blood pressures averaged. Patients with conditions that may cause a disparity in blood pressure between the right and left arms were not included in this study. The right systolic BABP was >/= 10 mm Hg higher than the left systolic BABP in 35 of 528 patients (7%), and the left systolic BABP was >/= 10 mm Hg higher than the right systolic BABP in 35 of 528 patients (7%) (P = not significant). The right diastolic BABP was >/= 10 mm Hg higher than the left diastolic BABP in 16 of 528 patients (3%), and the left diastolic BABP was >/= 10 mm Hg higher than the right diastolic BABP in 12 of 528 patients (2%) (P = not significant). There was no significant difference in prevalence of hypertension, atherosclerotic vascular disease, diabetes mellitus, or hypercholesterolemia in patients with or without a >/= 10-mm Hg difference in right and left systolic BABP and in right and left diastolic BABP. Interarm differences of >/=10 mm Hg in systolic BABP were found in 14% of elderly patients and of >/= 10 mm Hg in diastolic BABP in 5% of elderly patients. The higher blood pressure should be used for the diagnosis of hypertension, and the blood pressure in that arm used for all follow-up blood pressure-evaluating therapy.

Related Biology Terms

  • Diastole – The relaxed condition of the heart, being the opposite phase in the cardiac cycle.
  • Electrical Systole – The nerve impulse signaling the heart muscles to contract.
  • Mechanical Systole – The actual contraction of the muscle fibers of heart tissue.
  • Sinoatrial Node – The nerve-embedded region of the right atrium which starts systole by causing the initial nerve impulse.

1. Which of the following must follow the systole phase of the cardiac cycle in order for the heart to pump blood?
A. Cells must resupply on glucose
B. The muscles of the heart must relax
C. The valves between atria and ventricles must close

2. In the hagfish, the cardiac cycle is not organized rhythmically, as it is in higher animals. Does the hagfish heart, which consists of one atrium and one ventricle, go through the phase of systole?
A. Yes
B. No
C. Only when the atrium and ventricle contract at the same time

How Does a Blood Pressure Gauge Work?

Your heart is an amazing pump. It works reliably for decades, and it safely pumps blood -- one of the trickiest liquids around. In the same way, your blood vessels are pipes. They take the output from the pump and distribute it throughout the body. A blood pressure gauge is simply a way to measure the performance of the pump and the pipes.

There are two numbers in a blood pressure reading: systolic and diastolic. For example, a typical reading might be 120/80. When the doctor puts the cuff around your arm and pumps it up, what he/she is doing is cutting off the blood flow with the pressure exerted by the cuff. As the pressure in the cuff is released, blood starts flowing again and the doctor can hear the flow in the stethoscope. The number at which blood starts flowing (120) is the measure of the maximum output pressure of the heart (systolic reading). The doctor continues releasing the pressure on the cuff and listens until there is no sound. That number (80) indicates the pressure in the system when the heart is relaxed (diastolic reading).

If the numbers are too high, it means that the heart is having to work too hard because of restrictions in the pipes. Certain hormones, like adrenaline (which is released when you are under stress) cause certain blood vessels to constrict, and this raises your blood pressure -- if you are under constant stress, your blood pressure goes up, and it means that your heart has to work too hard. Other things that can increase the blood pressure include deposits in the pipes and a loss of elasticity as the blood vessels age.

High blood pressure can cause the heart to fail (from working too hard), or it can cause kidney failure (from too much pressure).

Blood pressure measurement - Biology

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