Therefore MAP=CO x TPR = HR x SV x TPR

Transcription

1 Regulation of MAP Flow = pressure gradient resistance CO = MAP TPR Therefore MAP=CO x TPR = HR x SV x TPR TPR is the total peripheral resistance: this is the combined resistance of all blood vessels (remember the importance of vasodilation and vasoconstriction) This means that MAP is completely determined by HR, SV and TPR

2 Regulation of MAP Short-term regulation seconds to minutes (baroreceptor( reflex) Involves heart and blood vessels Primarily neuronal control Long-term regulation minutes to days Regulation of blood volume Involves kidneys Primarily hormonal control

3 Renin-angiotensin-aldosterone system Most important hormonal system involved in regulating Na +

4 Circulatory Pressures Boron & Boulpaep,, fig 18.3

5 Arterial Pressure Systolic Pressure (120 mmhg) occurs with ventricular contraction Diastolic Pressure (80 mmhg) occurs with ventricular refilling BP thus reported as 120 / 80 (mmhg) Pulse Pressure difference between Sys. P. & Dias. P. 40 mmhg at rest MAP (Mean Arterial Pressure) an average pressure regulated pressure Diastolic MAP + = (Pulse P) 3 Sherwood 6 th Ed., fig 10.7

6 Blood Pressure Measurement: Auscultation Utilises sphygmomanometer Pressure cuff Mercury column Stethoscope Recorded at heart level via Brachial Artery Korotkoff sounds via Turbulent flow, upon Cuff pressure release Sherwood 6 th Ed., fig 10.8

7 Blood Pressure Auscultation Inflate cuff above Systolic pressure Slowly deflate cuff. Blood flows when BP > Cuff pressure Generates Korotkoff sounds. Clear tapping audible via stethoscope. Indicates Systolic Pressure Turbulent flow disappears as cuff deflates & artery diameter increases Diastolic pressure indicated via a constant muffled constant sound Sherwood 6 th Ed., fig 10.8

8 Baroreceptors Specialised nerve endings Respond to stretch of vessel wall; indirect response to changes in BP Location Carotid sinus Aortic Arch Type A fibres (myelinated) Low pressure (30-90 mmhg) Important at rest C fibres (unmyelinated) High pressure ( mmhg) Increasingly active at higher pressures Sherwood 6 th Ed., fig 10.35

9 Central Control of CVS Involves integrated responses from: Medulla, hypothalamus, cerebral cortex, cerebellum Baroreceptor input to NTS in medulla (nucleus tractus solitarius) Output to: Parasympathetic NS (vagus) via nucleus ambiguus Cardiac control (limits HR) Sympathetic NS via rostral ventrolateral medulla Cardiac and blood vessel control ( ( ed contractile strength/tone) Hypothalamus & amygdala in cerebellum Overriding output during stress to raise BP

10 Summary Control of CVS Noble & Co.,, fig & 10.4

11 Extra Inputs to CVS Control Atrial stretch receptors Myelinated vagal afferents sensitive to blood volume Located at junction of great veins and atria Influences endocrine regulation of blood volume via: Hypothalamic ADH renal water retention Renin-Angiotensin-aldosterone system (RAS) renal salt & water retention Atrial Natriuretic Peptide renal salt & water excretion Bainbridge reflex Vena cava stretch receptors neural mediated HR Avoids venous congestion

12 MAP = CO! TPR

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15 Factors Affecting Blood Pressure Age & Sex Blood pressure increases with: High dietary intake of; salt, fat, cholesterol, and alcohol Smoking Obesity & diabetes Stress activity/exercise Hypertension Sys P > 160 mmhg Dias P > 100 mmhg White Coat Treatment Always address above factors Noble & Co.,, fig 10.7

16 Hypertension Primarily arises via ed peripheral flow resistance 5% of cases disturbance of normal physiological function e.g. renal diseases, adrenal diseases (associated with salt & water retention, & blood vol.) 95% of cases essential hypertension Mostly via aspects that affect arteriolar smooth muscle Cumulative effect of genetic, lifestyle & environmental factors

17 Hypertensive Drug Treatments Thiazide diuretics Inhibit Na + /K + /Cl - exchange in distal renal tubule β-blockers Reduce HR & contractility L-type Ca 2+ channel blockers Relaxation of vascular smooth muscle dilation & reduced resistance ACE inhibitors Diuretic actions Inhibit aldosterone formation α-blockers Reduce sympathetic tone Dilate arteriolar smooth muscle