PSL301-Lecture 6 Blood Pressure 2022 PDF

PSL301H- Lecture 6: Blood Pressure What is blood pressure and where is it measured? How is blood pressure controlled? Silverthorn 7th ed: 482-488, 492-495 Silverthorn 8th ed: 481-486, 489-494 Pressure Throughout the Systemic Circulation Blood pressure is highest in the arteries and decr...

PSL301H- Lecture 6: Blood Pressure What is blood pressure and where is it measured? How is blood pressure controlled? Silverthorn 7th ed: 482-488, 492-495 Silverthorn 8th ed: 481-486, 489-494 Pressure Throughout the Systemic Circulation Blood pressure is highest in the arteries and decreases continuously as it flows through the circulatory system Figure 15-5 Measuring Arterial Blood Pressure Measuring Arterial Blood Pressure The five “Korotkoff” sounds * 1. the snapping sound first heard at the systolic pressure. Clear tapping, repetitive sounds for at least two consecutive beats is considered the systolic pressure. 2. murmurs heard for most of the area between the systolic and diastolic pressures. 3. loud, crisp tapping sound. 4. Sounds at pressures~10 mmHg above the diastolic, were described as "thumping" and "muting“ * 5. Silence as the cuff pressure drops below the diastolic blood pressure. The disappearance of sound is considered diastolic blood pressure- two points below the last sound heard. Pulse Pulse – pressure wave of circulating blood Monitored at “pressure points” where pulse is easily palpated Blood Pressure “Pulse Pressure” = systolic P – diastolic P For a person who is 120mmHg/80mmHg : what is pulse pressure? Mean arterial pressure (MAP) = diastolic P + 1/3(systolic P – diastolic P) = 2/3 diastolic + 1/3 systolic Using 120/80 ! MAP = Example calculations: Blood Pressure “Pulse Pressure” = systolic P – diastolic P 120/80 : what is pulse pressure? 120-80 =40 mmHg Mean arterial pressure (MAP) = diastolic P + 1/3(systolic P – diastolic P) = 2/3 diastolic + 1/3 systolic Using 120/80 ! MAP = =2/3 (80) + 1/3 (120) =53.333 + 40 = 93.333mmHg Thinking Question: The factor that most affects the pulse pressure is: A. afterload B. stroke volume C. cardiac output D. heart rate Mean Arterial Pressure is the time-average pressure in the arterial “bag” What controls the pressure in the “aortic bag”? Mean arterial pressure is a function of cardiac output and resistance in the arterioles – both regulate aortic blood volume at entry and exit Mean arterial pressure Cardiac output Variable resistance Arterioles Left ventricle Elastic arteries Mean arterial pressure µ cardiac output ´ resistance Figure 15-8 Blood Pressure is needed to drive flow into tissues Local Mediators Control Local Flow Total Resistance Influences Mean Arterial Pressure Review: Resistance Opposes Flow Flow µ DP/R Flow of blood in the systemic circuit is Directly proportional to the pressure gradient Inversely proportional to the resistance to flow Therefore: Total flow (CO) µ Pa- Pv / Total Resistance Review: Arteriolar diameter (resistance) affects flow between venous and artery “bags” Cardiac Output Influences Mean Arterial Pressure Summary Slide: Stroke Volume and Heart Rate Determine Cardiac Output CARDIAC OUTPUT CO = HR x SV is a function of Heart rate Stroke volume determined by determined by Rate of depolarization Force of contraction in in autorhythmic cells ventricular myocardium b1R, Gas, NE/epinephrine, Increased cAMP/PKA is influenced by more I(f) Decreases Increases increases Contractility End-diastolic volume Sympathetic b1R, Gas, Due to innervation and NE/epinephrine which varies with parasympathetic innervation epinephrine Increased cAMP/PKA VGCC, SERCA = SR Ca2+ increases Venous constriction Venous return M2R , Gai, ACh, lowered cAMP/PKA, less I(f) aided by Skeletal muscle Respiratory pump pump Blood distribution Influences Mean Arterial Pressure Review: Arteriolar diameter (resistance) affects flow between venous and artery “bags” Blood Volume Influences Mean Arterial Pressure RAAS controls blood volume and Peripheral Resistance Kidney senses pressure blood lung Adrenal cortex aldosterone Slow response: Aldosterone adrenal cortex reabsorption of salt (Na) and water by kidney renin-angiotensin-aldosterone system Feedback loop - salt intake vs renin secretion Blood Pressure (Fast vs. Slow Control Mechanisms) Stretch and Blood volume KEY baroreceptors Stimulus leads to (aortic arch, Integrating center carotid sinus, Blood Tissue response and other large pressure Systemic response arteries) triggers Fast response pressure Slow response natriuresis Compensation by Compensation cardiovascular by kidneys system " renin- angiotensin Vasodilation Cardiac output Excretion of fluid in urine blood volume Blood pressure to normal Baroreceptor Reflex – Fast response ( within a few heartbeats) Components of the baroreceptor reflex KEY Stimulus Sensory receptor Medullary cardiovascular Integrating center control center Efferent path Effector Change in blood pressure Parasympathetic neurons Carotid and aortic baroreceptors Sympathetic neurons SA node Ventricles Veins Arterioles Figure 15-22 Baroreceptor Reflex – response to increased BP The baroreceptor reflex: the response to increased blood pressure Figure 15-23 Baroreceptor Reflex – response to low BP The baroreceptor reflex: the response to orthostatic hypotension