Skip to content

Human Physiology · Cardiovascular system

Haemodynamics and Blood Pressure

Blood pressure is the force that drives blood through the vessels, and it is the vital sign you will measure most often. This page explains what sets it, how to measure it properly, how exercise changes it, and why exercise is one of the best treatments for high blood pressure.

12Sections
5Figures
4Tables
10Questions

Part 3 · Cardiovascular System · Chapter 13 of 47

Learning objectives

By the end of this page you should be able to:

  • Relate flow, pressure and resistance, and explain why vessel radius dominates resistance.
  • Describe how pressure changes along the circulation and the role of the arterioles.
  • Define systolic, diastolic, pulse and mean arterial pressure and calculate MAP.
  • Measure blood pressure correctly and classify the result.
  • Describe blood pressure responses to dynamic and resistance exercise.
  • Summarise the evidence for exercise as a treatment for high blood pressure.

Why it matters

You will take blood pressure before, during and after exercise in many patients. You need to know whether a reading is normal, whether a rise during exercise is expected, and when it is a reason to stop.

High blood pressure is also one of the commonest conditions in adults, and exercise lowers it. Prescribing the right exercise is part of a physiotherapist’s job.

Flow, pressure and resistance

Blood flows from high pressure to low. The flow through any vessel or organ equals the pressure difference across it divided by its resistance. Applied to the whole circulation, this gives a central equation: mean arterial pressure equals cardiac output multiplied by total peripheral resistance.

Two equations to remember

Flow = pressure difference ÷ resistance. Mean arterial pressure ≈ cardiac output × total peripheral resistance.

Resistance depends on the length of the vessel, the viscosity of the blood and, above all, the radius. In smooth flow, resistance is proportional to length and viscosity divided by the fourth power of the radius. This is Poiseuille’s relationship.

Figure 1 · Why radius matters so much

Effect of vessel radius on resistance to flow Three vessels of decreasing radius with bars showing resistance. Reducing the radius to 0.8 increases resistance about 2.4 times; halving it increases resistance 16 times. Radius 1resistance × 1Radius 0.8resistance × 2.4Radius 0.5resistance × 16Resistance rises with the fourth power of the narrowing: halve the radius, resistance rises 16-fold.
Poiseuille’s relationship. Resistance depends on vessel length and blood viscosity, but above all on radius to the fourth power.

Because of the fourth power, small changes in arteriolar diameter produce large changes in resistance and flow. That is how the body redirects blood to working muscle and holds blood pressure steady.

Pressure along the circulation

Figure 2 · Pressure along the systemic circulation

Blood pressure from the aorta to the venae cavae Pressure oscillates between about 120 and 80 millimetres of mercury in the aorta and large arteries, then falls steeply in the arterioles, where pulsation disappears. It falls from about 35 to 15 across the capillaries and approaches zero in the great veins. AortaLarge arteriesArteriolesCapillariesVenules and veinsVenae cavae04080120largest pressure drop:the resistance vesselsPressure (mmHg)
Arterioles set the resistance. The biggest fall in pressure happens across them, so small changes in their diameter change blood pressure and flow distribution. Schematic.
VesselMain roleTypical pressure
Aorta and large arteriesElastic reservoir; smooth out pulsatile ejectionabout 120/80 mmHg
ArteriolesResistance vessels; control flow and blood pressureLarge fall, pulsation lost
CapillariesExchange (Chapter 4)about 35 falling to 15 mmHg
VeinsCapacitance; hold most of the blood volumeLow; a few mmHg near the heart

Elastic arteries stretch during ejection and recoil during diastole, which keeps blood flowing between beats. With age they stiffen, so systolic pressure rises and pulse pressure widens.

Laminar and turbulent flow

Normally blood flows in smooth layers, fastest in the centre. Narrowing, high speed or low viscosity can make flow turbulent. Turbulence is noisy, which is why a narrowed artery may produce a bruit, and why you hear Korotkoff sounds when measuring blood pressure.

Describing blood pressure

TermMeaningExample for 120/80 mmHg
Systolic pressure (SBP)Peak pressure during ejection120
Diastolic pressure (DBP)Lowest pressure before the next beat80
Pulse pressureSBP − DBP40
Mean arterial pressure (MAP)Average driving pressure; about DBP + one third of pulse pressureabout 93

Measuring blood pressure

Figure 3 · Measuring blood pressure

Cuff pressure falling through arterial pressure during auscultatory measurement An arterial pressure wave oscillates between 80 and 120 millimetres of mercury. A straight line of cuff pressure falls from 150 to 60. Tapping Korotkoff sounds begin when cuff pressure falls below the systolic peak and stop when it falls below diastolic pressure. Cuff pressure (deflating)Sounds start = systolic (about 120)Sounds stop = diastolic (about 80)Korotkoff sounds heard with the stethoscope6080100120140
Sounds are turbulence. Blood spurts through the partly compressed artery only while cuff pressure lies between systolic and diastolic pressure. Deflate at about 2 mmHg per second.

Seat the patient with back supported, feet flat and arm supported at heart level, after about five minutes’ rest. Use a cuff whose bladder suits the arm size. Inflate above the expected systolic pressure, then deflate at about 2 mmHg per second while listening over the brachial artery.

A cuff that is too small, an unsupported arm or recent talking all raise the reading. Guidelines recommend averaging two or more readings on two or more occasions before labelling someone hypertensive [3].

Category (2017 ACC/AHA) [3]SystolicDiastolic
Normalunder 120andunder 80
Elevated120–129andunder 80
Stage 1 hypertension130–139or80–89
Stage 2 hypertension140 or moreor90 or more

Other guidelines, including European ones, still use 140/90 mmHg as the threshold for hypertension. Use the classification your service follows, and record readings accurately.

Short-term and long-term control

Moment to moment, the baroreceptor reflex adjusts heart rate and vessel tone to hold pressure steady (Chapter 1). Over days and weeks, the kidneys control blood pressure by adjusting salt and water balance and blood volume, under hormonal control. These are covered in the cardiovascular control and renal chapters.

Blood pressure during exercise

Figure 4 · Blood pressure during exercise

Blood pressure at rest, in moderate dynamic exercise and in heavy resistance exercise Paired bars. At rest about 120 over 80. During brisk dynamic exercise systolic pressure rises to around 160 while diastolic stays near 80. During a heavy double-leg press, mean peak pressures reached about 320 over 250. Rest120 systolic80 diastolicBrisk walking or cycling160 systolic78 diastolicHeavy double-leg press [2]320 systolic250 diastolicDynamic exercise: systolic rises, diastolic changes little. Heavy lifting with breath-holding: both soar.
Type of exercise changes the pressure load. The heavy-lifting values are group means from experienced bodybuilders lifting to failure [2]; the dynamic values are typical, not measured here.

During dynamic exercise such as walking, cycling or swimming, cardiac output rises and working muscles dilate. Systolic pressure rises with intensity while diastolic pressure changes little.

Heavy resistance exercise is different. MacDougall and colleagues measured pressure directly in the arteries of experienced bodybuilders. During double-leg presses to failure, mean peak pressures reached about 320/250 mmHg, and over 480/350 in one subject [2]. Muscle compressing vessels, a strong pressor reflex and the Valsalva manoeuvre all contributed [2].

Practical skill · avoiding the Valsalva response

Teach patients to breathe out during the effort phase of each lift and never to hold their breath. Use moderate loads and avoid taking sets to failure in patients with heart disease, uncontrolled hypertension, recent eye or brain surgery, or aneurysm. These precautions follow from the pressures measured during heavy straining [2].

Exercise as treatment for high blood pressure

Edwards and colleagues pooled 270 randomised trials with 15,827 participants. Every form of exercise training studied lowered resting blood pressure [1].

Figure 5 · Exercise lowers resting blood pressure

Mean reductions in resting blood pressure by exercise training mode Paired bars of mean reductions in resting systolic and diastolic pressure: isometric training 8.24 and 4.00, combined 6.04 and 2.54, dynamic resistance 4.55 and 3.04, aerobic 4.49 and 2.53, high-intensity interval 4.08 and 2.50 millimetres of mercury. Isometric−8.24−4.00Combined−6.04−2.54Dynamic resistance−4.55−3.04Aerobic−4.49−2.53High-intensity interval−4.08−2.50Systolic (mmHg)Diastolic (mmHg)
Every mode helps; isometric training ranked highest. Pooled results from 270 randomised trials and 15,827 participants [1].

Isometric training, such as wall squats or handgrip holds, produced the largest average falls and ranked highest overall. Combined aerobic and resistance training ranked next [1]. Falls of 4–8 mmHg are comparable to those produced by a single blood pressure drug.

This does not mean isometric exercise replaces other training. Aerobic exercise brings other cardiovascular benefits. The practical message is that a mix of exercise types, including some isometric work, is a reasonable prescription.

Clinical relevance for the physiotherapist

  • Screening. Measure resting blood pressure before starting an exercise programme, using correct technique [3].
  • Prescription. Exercise lowers resting blood pressure; include isometric and dynamic work where appropriate [1].
  • Safety during lifting. Avoid breath-holding and heavy sets to failure in at-risk patients [2].
  • Older adults. Stiffer arteries raise systolic and pulse pressure; postural drops are also commoner.
  • Medications. Antihypertensives may cause dizziness after exercise or on standing; cool down gradually.

Assessment and application

SituationWhat to do
Resting BP well above the patient’s usual levelRecheck after rest; follow local thresholds before exercising
Systolic fails to rise, or falls, as exercise intensity increasesStop; this can indicate poor cardiac reserve
Very large rise in systolic pressure during exerciseReduce intensity; follow local stop criteria
Dizziness after exerciseCool down gradually; check postural blood pressure

Common mistakes

  • Using the wrong cuff size or an unsupported arm.
  • Calculating MAP as the simple average of systolic and diastolic.
  • Forgetting that resistance depends on radius to the fourth power.
  • Allowing patients to hold their breath during lifting [2].
  • Assuming only aerobic exercise lowers blood pressure [1].

Exam preparation

Long answer

Define arterial blood pressure. Describe the factors that determine it and the methods used to measure it.

  • Definitions: SBP, DBP, pulse pressure, MAP.
  • MAP = cardiac output × total peripheral resistance; Poiseuille and the role of arterioles (Figures 1 and 2).
  • Measurement: auscultatory method and Korotkoff sounds (Figure 3); classification [3].
  • Short-term and long-term regulation in outline.
  • Exercise responses and training effects [1, 2].

Short notes

  • Poiseuille’s law.
  • Korotkoff sounds.
  • Blood pressure response to resistance exercise [2].
  • Exercise in the management of hypertension [1].

Viva and practical

  • “Why are arterioles called resistance vessels?” — the largest pressure drop occurs across them.
  • “Which exercise mode most lowers resting blood pressure?” — isometric training ranked highest [1].
  • “Why avoid breath-holding during lifting?” — it adds to extreme pressure rises [2].
  • OSCE: measure and classify blood pressure using correct technique [3].

Current evidence

Exam and traditional teaching

Aerobic exercise is taught as the exercise for hypertension, and resistance or isometric exercise is often discouraged.

What the evidence adds

Across 270 trials, all exercise modes lowered resting pressure, and isometric training produced the largest average falls [1].

The danger in resistance exercise lies mainly in heavy loads taken to failure with breath-holding, not in resistance training itself [2].

What the student should understand

Measure carefully, prescribe a mix of exercise types, and teach patients to breathe through effort.

Check yourself

10 questions on this page. Tap one to see the answer and the reasoning.

Q1. Mean arterial pressure is approximately equal to:
  1. (A) Systolic + diastolic
  2. (B) Diastolic + one third of pulse pressure
  3. (C) Systolic − diastolic
  4. (D) Twice diastolic

Answer: (B) MAP ≈ DBP + (SBP − DBP)/3; for 120/80, about 93 mmHg. Guidelines classify pressure from systolic and diastolic readings [3].

Q2. If the radius of a vessel halves, its resistance rises about:
  1. (A) 2-fold
  2. (B) 4-fold
  3. (C) 16-fold
  4. (D) No change

Answer: (C) Resistance varies with the fourth power of radius, which is why arterioles control blood pressure; exercise training acts partly through vessel function [1].

Q3. The largest drop in pressure in the systemic circulation occurs across the:
  1. (A) Aorta
  2. (B) Arterioles
  3. (C) Veins
  4. (D) Venae cavae

Answer: (B) Arterioles are the main resistance vessels, the site where training-related changes in resistance lower pressure [1].

Q4. In the 2017 ACC/AHA guideline, a blood pressure of 134/84 mmHg is classified as:
  1. (A) Normal
  2. (B) Elevated
  3. (C) Stage 1 hypertension
  4. (D) Stage 2 hypertension

Answer: (C) Stage 1 is 130–139 systolic or 80–89 diastolic [3].

Q5. When measuring blood pressure by auscultation, systolic pressure is read when:
  1. (A) Sounds disappear
  2. (B) Korotkoff sounds first appear
  3. (C) The cuff is fully inflated
  4. (D) The radial pulse is strongest

Answer: (B) The first sounds mark systolic pressure; guideline methods specify technique [3].

Q6. During heavy double-leg presses to failure, MacDougall and colleagues recorded mean peak pressures of about:
  1. (A) 140/90 mmHg
  2. (B) 200/100 mmHg
  3. (C) 320/250 mmHg
  4. (D) 100/60 mmHg

Answer: (C) Mean peaks reached about 320/250 mmHg, partly from the Valsalva manoeuvre [2].

Q7. Part of the extreme pressure rise in heavy lifting is due to:
  1. (A) Sleep
  2. (B) The Valsalva manoeuvre (straining against a closed glottis)
  3. (C) Lying supine
  4. (D) Low heart rate

Answer: (B) Raised intrathoracic pressure during straining contributed to the rise [2].

Q8. In a large network meta-analysis, which training mode produced the largest mean fall in resting systolic pressure?
  1. (A) Aerobic
  2. (B) Isometric
  3. (C) High-intensity interval
  4. (D) None

Answer: (B) Isometric training reduced systolic pressure by about 8.24 mmHg and ranked highest [1].

Q9. The same meta-analysis found that aerobic training lowered resting blood pressure by about:
  1. (A) 0/0 mmHg
  2. (B) 4.5/2.5 mmHg
  3. (C) 20/10 mmHg
  4. (D) 50/25 mmHg

Answer: (B) Aerobic training reduced pressure by about 4.49/2.53 mmHg [1].

Q10. During moderate dynamic exercise such as brisk walking, diastolic pressure usually:
  1. (A) Rises steeply
  2. (B) Changes little
  3. (C) Falls to zero
  4. (D) Doubles

Answer: (B) Muscle vasodilation offsets the rise in output, unlike heavy straining, where both pressures soar [2].

Quick review

Key takeaways

  • Flow = pressure difference ÷ resistance; MAP ≈ cardiac output × peripheral resistance.
  • Resistance ∝ length × viscosity ÷ radius⁴; arterioles control it.
  • MAP ≈ DBP + one third of pulse pressure.
  • Measure with correct cuff and posture; 2017 ACC/AHA stage 1 = 130–139 or 80–89 [3].
  • Heavy lifting to failure can push pressure above 300/250 mmHg; avoid breath-holding [2].
  • Exercise training lowers resting BP; isometric training most [1].

Further reading

SourceWhy it earns its place
Levick JR — An Introduction to Cardiovascular PhysiologyHaemodynamics explained clearly
Edwards JJ et al. — BJSM, 2023The largest analysis of exercise and blood pressure [1]
Whelton PK et al. — Hypertension, 2017Measurement and classification guidance [3]
MacDougall JD et al. — J Appl Physiol, 1985Direct measurements during heavy lifting [2]

References

  1. Edwards JJ, Deenmamode AHP, Griffiths M, Arnold O, Cooper NJ, Wiles JD, O’Driscoll JM. Exercise training and resting blood pressure: a large-scale pairwise and network meta-analysis of randomised controlled trials. British Journal of Sports Medicine. 2023;57(20):1317–1326. doi:10.1136/bjsports-2022-106503 PMID 37491419 Network meta-analysis
  2. MacDougall JD, Tuxen D, Sale DG, Moroz JR, Sutton JR. Arterial blood pressure response to heavy resistance exercise. Journal of Applied Physiology. 1985 Mar;58(3):785–790. doi:10.1152/jappl.1985.58.3.785 PMID 3980383 Experimental study
  3. Whelton PK, Carey RM, Aronow WS, et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline for the prevention, detection, evaluation, and management of high blood pressure in adults. Hypertension. 2017;71(6):e13–e115. doi:10.1161/HYP.0000000000000065 PMID 29133356 Guideline

Related topics

Reviewed by the Physiotherapist India Team. · Human Physiology contents