Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 1 Blood pressure Preclinical practice 13. 5. 2024 Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 2 Blood pressure ̶Blood pressure (BP): pressure of blood on the vessel wall (arterial BP – part of the energy of systole converted into lateral pressure on the vascular wall) Forces related to the vessel wall. Arrows in red represent forces exerted by the blood flow on the endothelial layer: pressure forces normal to the interior of the vessel (P) and the shear stress of the flow, in the flow direction (S). Arrows in black represent forces that, though influenced by the blood flow, may have a different origin: longitudinal forces (L) and circumferential stresses (R C ). Figure based on Jacobsen et al. (2009) with permission of Elsevier B. V. given by a position vector X) to the current state B f (at time t) is the result of a local growth step defined by the tensor G and an elastic process A. The local growth transformation originates conceptually a virtual discontinuous stress-free configuration V, which, through the elastic process A, leads finally to the stressed continuous current configuration B f (see Figure 2): Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 3 Arterial blood pressure curve ̶Pulse wave ̶arises when the blood is expelled from the left ventricle into the circulation during the systolic phase ̶ ̶Mean arterial pressure (MAP): mean value of blood pressure in the inter-beat interval (IBI) – integral of the BP curve; area above MAP = area below MAP aproximation: MAP = DBP + 1/3 PP (PP = SBP – DBP) ̶ ̶Definition: ̶SBP (systolic BP) maximum of BP in the inter-beat interval ̶DBP (diastolic BP) minimum of BP in the inter-beat interval ̶ ̶ SBP DBP MAP Inter-beat interval PP pulse pressure Dicrotic notch Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 4 Pulse wave velocity (PWV) ̶The pulse wave propagation rate (PWV) is measurable, around 4 m/s in the aorta. ̶Beware, the actual speed of blood flow is significantly lower, it is around 80-100 cm/s in the aorta ̶The peripheral pulse wave velocity is 10-20 m/s (depending on the site of measurement) ̶Measureable by inderect method: Sphygmography with ECG ̶ A B T1 T2 d PWV= d/ (T2-T1) A B Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 5 Blood pressure ̶a function of cardiac output (CO) and total peripheral resistance ̶SBP is determined mainly by CO ̶DBP is determined mainly by TPR ̶ Blood pressure = Cardiac output (CO) * Total peripheral resistence (TPR) CO = Heart rate (HR) * Stroke volume (SV) Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 6 Total peripheral resistence ̶consist of resistence from all vessels ̶the narrower tube (↓ diameter) → the ↑ pressure needs to be exerted to maintain the flow ̶determined by the Hagen-Poiseuille law for tube resistance ̶ Relationship among Vessels in the Systemic Circuit Adobe Systems Cardiac cycle ̶Isovolumic contraction (IVC): ̶Contraction of ventricular myocardium leads to an increase in intraventricular pressure ̶Ejection (E): ̶Intraventricular pressure overcomes diastolic pressure in big arteries, semilunar valves open, and blood flows to the arteries ̶Isovolumic relaxation (IVR): ̶Semilunar valves close, rapid decrease in intraventricular pressure even below pressure values in atria, AV valves open ̶Inflow (I): ̶Inflow phase (ventricular diastole), atrial systole https://upload.wikimedia.org/wikipedia/commons/thumb/3/38/2027_Phases_of_the_Cardiac_Cycle.jpg/370p x-2027_Phases_of_the_Cardiac_Cycle.jpg 7 Department of Physiology, Faculty of Medicine, Masaryk University Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 8 P-V diagram (Left ventricle) 10 80 100 120 50 120 SBP DBP ESV EDV P [mmHg] V [ml] IVR IVC E I Systole = IVC + E IVC = 0.06 s E = 0.21 s Diastole = IVR + I IVR = 0.07 s I = 0.49 s Normal RV systolic pressure is 20–30 mmHg and normal diastolic pressure is 3–7 mmHg (Table 2). LV – 130-9 Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 9 P-V diagram Normal RV systolic pressure is 20–30 mmHg and normal diastolic pressure is 3–7 mmHg (Table 2). LV – 130-9 Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 10 Arterial blood pressure ̶stable blood flow thanks to aortic compliance ̶the aorta expands and holds the ejected blood volume (change of kinetic energy into elastic) and during diastole, it contracts and moves the blood further into the bloodstream (change of elastic energy to kinetic) ̶ ̶ Aortic pulse pressure Normal RV systolic pressure is 20–30 mmHg and normal diastolic pressure is 3–7 mmHg (Table 2). LV – 130-9 Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 11 Blood pressure in veins ̶low pressure system ̶peripherial pressure in veins is usually between 8 and 10 mmHg ̶central vein pressure is aproximately 0–6 mmHg ̶ ̶ Normal RV systolic pressure is 20–30 mmHg and normal diastolic pressure is 3–7 mmHg (Table 2). LV – 130-9 Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 12 Blood pressure in veins Normal RV systolic pressure is 20–30 mmHg and normal diastolic pressure is 3–7 mmHg (Table 2). LV – 130-9 Adobe Systems C:\Users\user\Desktop\výuka\učení fyziologie\Boron - Medical Physiology\Pages\Images\IV. The Cardiovascular System\Chap 18_Arteries and Veins\S23283-018-f003a.jpg C:\Users\user\Desktop\výuka\učení fyziologie\Boron - Medical Physiology\Pages\Images\IV. The Cardiovascular System\Chap 18_Arteries and Veins\S23283-018-f003b.jpg Large circle Small circle Boron and Boulpaep, Medical physiology 13 Department of Physiology, Faculty of Medicine, Masaryk University Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 14 Blood pressure regulation ̶Short-term – neural control – mainly by baroreflex – chemical substancis ̶Middle-term – hormonal regulation - renin-angiotensin-aldosterone system (RAAS) ̶Long-term – hormonal regulation of blood volume Adobe Systems 15 Short-term BP control – baroreflex image https://www.ncbi.nlm.nih.gov/books/NBK538509/ Adobe Systems 16 BP control – substances ̶vasoconstrictors ̶ATP, epinephrine, norepinephrine, antidiuretic hormone, and angiotensin II ̶ ̶vasodilators ̶epinephrine, atrial natriuretic peptide, histamin, arginine (→NO), and lactic acid (metabolic reaction) Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 17 Blood pressure changes ̶Short-term influences ̶blood volume – influence on cardiac output (bleeding, dehydration) ̶external pressure to the vessels – intrathoracic and intraabdominal pressure (cough, defecation, childbirth, artificial ventilation) ̶position – orthostasis/clinostasis: redistribution of blood due to gravity ̶CNS – emotions, mental stress, … ̶physical exercise – BP changes depend on intensity, duration and type of exercise ̶heat (↓ TPR), cold (↑ TPR) ̶alcohol, drugs,… ̶Long-term influences ̶age (the fastest changes during childhood and adolescence, in adults slow increase in SBP) ̶sex (men have higher BP) ̶genetic background Adobe Systems 18 ̶ Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 19 Methods of the arterial BP measurement ̶Invasive ̶arterial catether perioperativeCPD.com Invasive arterial blood pressure measurement Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 20 Methods of the arterial BP measurement ̶Invasive ̶arterial catether ̶ ̶Non-invasive ̶Auscultatory (sphygmomanometer, stethoscope) Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 21 Methods of the arterial BP measurement ̶Invasive ̶arterial catether ̶ ̶Non-invasive ̶Auscultatory (sphygmomanometer, stethoscope) ̶Oscillometric ̶ Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 22 Methods of the arterial BP measurement ̶Invasive ̶arterial catether ̶ ̶Non-invasive ̶Auscultatory (sphygmomanometer, stethoscope) ̶Oscillometric ̶ ̶Photoplethysmographic/Peňáz/volume-clamp method Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 23 Methods of the arterial BP measurement ̶Invasive ̶arterial catether ̶ ̶Non-invasive ̶Auscultatory (sphygmomanometer, stethoscope) ̶Oscillometric ̶ ̶Photoplethysmographic/Peňáz/volume-clamp method Adobe Systems 24 Basic principle: Laminar / turbulent flow (Korotkoff sounds in auscultatory method; oscillation in oscilometric method). Reynolds number Re: predicts the transition from laminar to turbulent of flow v: velocity of blood flow S: area of vascular lumen (p.r2) r: density of blood h: viscosity of blood (lower in anemia) laminar flow Re < 2000 turbulent flow Re > 3000 r1 r2 cuff a. brachialis laminar flow turbulent flow Re1 Re2 v1 v2 Department of Physiology, Faculty of Medicine, Masaryk University Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 25 Principles of BP measurement Korotkoff sound (auscultatory method) Continually measured BP Pressure in the cuff Pressure oscillations in the cuff (oscillometric method) SBP DBP SBP MAP DBP Blood flow in the artery Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 26 Photoplethysmographic/Peňáz/volume-clamp method ̶Peňáz method - it is based on clamping the volume of finger arteries by fast changes of pressure in a special cuff equipped with a photoelectric plethysmograph to measure the vascular volume ̶ ̶Photopletysmography - an optical method for measuring the amount of light that is absorbed or reflected by blood vessels in living tissue. The amount of light absorbed or reflected in photoplethysmography depends on the amount of blood in the optical path. Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 27 Assesmemt of BP varaibility ̶Very short term – from continous BP measurement ̶Neurohormonal factors (baroreflex, sympathetic activation) ̶Nitric oxide, renin‐angiotensin‐aldosterone system ̶Enviromental, behavioral, and emotional factors ̶Short tem (within 24-h) ̶Neurohormonal factors (baroreflex, sympathetic activation) ̶Environmental, behavioral, and emotional ̶Circadian rhythm https://www.ahajournals.org/doi/full/10.1161/JAHA.122.029297 Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 28 Assesmemt of BP varaibility ̶Medium term (day to day) ̶drugs ̶vascular factors (endothelial damage, arterial compliance) ̶age ̶Long tern (visit to visit) ̶drugs ̶seasonal changes ̶vascular factors (endothilial damage, arteriál compliance) ̶age Adobe Systems method advantages disadvantages measured value auscultatory •exact estimation of SBP/DBP •easy, it doesn´t require electricity •subjective, experience is necessary •SBP/DBP from different IBI SBP and DBP oscillometry •exact estimation of MAP •automatic, fast •BP can be measured by layman, cheap (home measurement) •DBP/SBP is calculated (dependence on model, influenced by a shape of pulse wave) •SBP/DBP from different IBI •false values during arrhythmia MAP, sometimes SBP (it depends on a device) 24-hour BP monitoring •BP record from whole day •diagnosis of white-coat hypertension •disruptive influence of measuring (during sleeping) •SBP/DBP from different IBI BP is measured each 15–60 min photople-thysmography (Peňáz) •continual BP record •possibility of beat-to beat SBP/DBP calculation (BP variability analysis) •measurement on a finger, brachial BP is calculated •expensive device continual BP record Adobe Systems Department of Physiology, Faculty of Medicine, Masaryk University 30 Rules for BP measurement ̶Environment: pleasant room temperature, quiet surroundings ̶Position: the patient sits with his back leaning backwards, both legs are on the floor, forearm rests on a surface ̶Reasonable cuff size, correct positioning at heart level ̶The measurement happens at rest and starts after 5 – 10 minutes of sitting down ̶Measurement by auscultatory method ̶Inflate the cuff to a pressure 30 mmHg higher than the pressure at which the radial pulse disappeared ̶The pressure reduction rate in the cuff is 2 – 3 mmHg/s ̶The pressure value is determined with 2 mmHg accuracy ̶The BP should be measured 3 times at least five minutes apart and the final BP value is a mean value of the last two measurements Adobe Systems Diagnosis of hypertension ̶Isolated systolic hypertension: SBP> 140 and DBP <90 mmHg ̶High normal BP – annual monitoring recommended ̶Home measurement to exclude white coat hypertension ̶Hypertension is diagnosed when: ̶average BP from 4–5 examinations is > 140/90 mmHg ̶BP during a home measurement repeatedly > 135/80 mmHg ̶mean BP from 24-hour monitoring is > 130/80 mmHg