(VIII.) blood pressure in man (IX.) Non-invasive methods of blood pressure measurement Physiology - practicals Arterial blood pressure curve SBP Systolic blood pressure area above MAP area under MAP DBP Diastolic blood pressure MAP Mean arterial pressure inter-beat interval Mean arterial pressure (MAP) : mean value of blood pressure in the inter-beat interval (IBI) •area under MAP = area above MAP •aproximation: MAP» DBP + 1/3 pulse pressure (PP); PP = SBP – DBP) • PP pulse pressure Blood pressure (BP): pressure on vascular wall (continual variable) Definition: SBP - maximum of BP in the inter-beat interval DBP – minimum of BP in the inter-beat interval Attention: Values of SBP and DBP varies in different parts of cardiovascular system MAP is a function of cardiac output and total peripheral resistance •SBP is given mainly by CO •DBP is given mainly by TPR Mean arterial pressure (MAP) Total peripheral resistance (TPR) Heart rate (HR) Stroke volume (SV) = * * Cardiac output (CO) •Short-term – neural control, mainly baroreflex •Medium-term – hormonal regulation, renin-angiotensin-aldosteron system (RAAS) • •Long-term – hormonal regulation of blood volume Blood pressure regulation Short-term BP control: Baroreflex Autonomic nervous system: sympathetic nerves ( BP, HR, SV a TPR) X parasympathetic nerves (¯BP, HR, SV a TPR) Baroreflex: regulation of BP via changes of HR and TPR baroreceptors – sinus caroticus + aorticus afferentation: n. vagus, n. glosopharyngeus •Cardiac branch of baroreflex: efferentation: n. vagus - SA node sympathetic efferentation: change of HR and cardiac contractility ↑BP →↓HR and vice versa •Peripheral branch of baroreflex: efferentation: sympathetic vascular innervation ↑BP →↓TPR and vice versa (vasoconstriction, venoconstriction) Short-term influences •blood volume - influence to SV (bleeding, dehydration) •external pressure to the vessels - intrathoracal a intraabdominal pressure (cough, defecation, childbirth, artificial ventilation) •position – orthostasis: higher DBP (TPR) a lower STK (¯venous return® ¯heart filling ® Starling principle® ¯cardiac contraction ® ¯SV) •CNS – emotions, mental stress,… •physical load – BP changes depend on intensity, duration and type of exercise •heat (¯ TPR), cold ( TPR) •alcohol, medicaments,… Long-term influences •age (the fastest changes during childhood and adolescence) •sex (men: higher BP) Blood pressure changes Methods of the arterial blood pressure measurement 24-hour blood pressure monitoring Photoplethysmografic (volume-clamp method, Peňáz) Palpatory (sphygmomanometer) Auscultatory (sphygmomanometer, stethoscope) Oscillometric In practicals: Another approaches: Laminar / turbulent flow, Korotkoff sounds 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: viskosity of blood (higher in anemia) S1 < S2 a v1≈ v2 → Re1 < Re2 → turbulent flow laminar flow Re < 2000 turbulent flow Re > 3000 r1 r2 cuff a. brachialis laminar flow turbulent flow Re1 Re2 v1 v2 closely behind narrowing of the artery: 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 Principles of blood pressure measurement 24-hour blood pressure monitoring BP decrease during night: 10 - 15% 8 9 11 10 12 13 14 16 15 17 18 19 21 20 22 23 24 2 1 3 4 5 7 6 120 140 100 80 60 [mmHg] SBP DBP Heart rate waking sleeping Blood pressure hours •Patient is sitting for a few minutes before the measurement. •Only validated apparatus must be used. •Perform at least two measurements in the course of 1–2 minutes. •Use cuff of standard size (12–13 cm width and 35 cm length); however smaller and bigger cuffs must be available for patients with smaller or bigger size of arm, respectively. •Cuff must be always at the level of heart of examined person. •Pressure in the cuff must be decreased slowly: 2mmHg/s. During BP measurement following rules must be observed methods 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 STK a DTK oscillometric •exact estimation of MAP •automatic, fast •BP can be measured by layman, cheap (home measurement) •DBP/SBP is calculated (dependence on model, influence on shape of pulse wave) •SBP/DBP from different IBI •false values during arrhytmias MAP, sometimes SBP (it depends on 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-thysmographic (Peňáz) •continual BP record •possibility of beat-to beat SBP/DBP calculation (BP variability analysis) •measuring on the finger, brachial BP recalculating •expensive device continual BP record Diagnosis of hypertension •isolated systolic hypertension: SBP> 140 and DBP <90 •high normal BP – annual monitoring recomended •home measurement to exclude white coat hypertension •hypertension is diagnosed when: •average BP from 4 – 5 examinations is > 140/90 •BP during a home measurement repeatedly > 135/80 •mean BP from 24-hour monitoring is > 130/80 Changes of blood pressure during exercise •increase of BP depends on the type, intensity and duration of the load •sympathetic activation: changes in the cardiovascular system serve to satisfy metabolic needs of working muscle •impact of exercise on blood pressure •increased cardiac output ® ↑SBP •Redistribution of blood in the body - metabolic vasodilation in muscle (muscle increases blood flow), vasoconstriction in the GIT, skin and kidneys ® maintaining or slight change in DBP (depending on the extent of the TPR decrease) • •vasoconstriction in the skin is temporary, since thermoregulatory mechanisms dominate •DBP increases during isometric muscle work (eg. weightlifting) •after exercise: decrease of BP on the initial or a slightly lower value, the blood flow in the muscle remains elevated until recovery •Recovery interval is determined by the parasympathetic tone (can be increased training)