Healthy Heart and Lungs - Week 04 - PBL Case 01 PDF

HEALTHY HEART AND LUNGS – WEEK 04 – PBL CASE 01: HENRY MCRAE Summary: 81 Y/O retired fisherman with HBP, using outdated prescription drugs. Is a smoker. Upon inspection was found to have weak femoral and absent distal peripheral pulses in the right leg. Has elevated blood pressures that varies slig...

HEALTHY HEART AND LUNGS – WEEK 04 – PBL CASE 01: HENRY MCRAE Summary: 81 Y/O retired fisherman with HBP, using outdated prescription drugs. Is a smoker. Upon inspection was found to have weak femoral and absent distal peripheral pulses in the right leg. Has elevated blood pressures that varies slightly on either side. Terms and conditions Bendroflumethiazide: A thiazide diuretic used to treat hypertension Atenolol: A beta-blocker used to treat hypertension and arrhythmias. L.O.1 – Normal maintenance and control of BP Blood pressure It is the force exerted by blood on a blood vessel wall. The pressure differences in the vascular system is what enables blood to flow throughout the body. The blood pressure is reflective of 2 factors; - Compliance of elastic arteries close to the heart (extent to which they can stretch) - Volume forced into them at any time Blood pressure varies along the vasculature as well as depending on if it is systemic or pulmonary circulation. Arterial blood pressure It is measured as the systolic pressure/diastolic pressure. It is around 120/80 mmHg in a healthy adult. - Systolic pressure: Pressure generated during ventricular contraction - Diastolic pressure: Pressure during cardiac relaxation When the ventricles contract, blood is forced into the arteries, causing them to stretch as they as elastic. When the ventricles relax, the pressure is maintained by the elastic recoil of the arteries. The systolic pressure often increases with age due to the loss of elasticity of the arterial walls. Pulse pressure: Systolic pressure – Diastolic pressure. It represents the force generated by the heart each time it contracts. Mean arterial pressure (MAP) = diastolic BP + {1/3 *(systolic BP – diastolic BP)} It is not the value between the SBP and DBP as diastole lasts longer than systole. Venous pressure Despite the presence of large lumens and valves, the venous pressure alone is insufficient to promote an adequate flow of blood back towards the heart. It is aided by; - The respiratory pump: Pressure changes created during breathing suck blood towards the heart by squeezing local veins. During inhalation, abdominal pressure increases, squeezing the local veins. At the same time, the pressure in the chest decreases, allowing thoracic veins to expand and speed the entry of blood to the RA. - The muscular pump: Contraction of skeletal muscles moves blood towards the heart - Sympathetic vasoconstriction - Gravity Factors influencing BP  Blood volume (volaemia) - If there is a greater volume of fluid in the blood, the pressure increases. It is usually regulated by the kidneys Cardiac output - It is the amount of blood pumped by a ventricle per minute - It is calculated by SV*HR - Stroke volume is affected by the preload (EDV), contractility and the afterload (Pressure that the ventricles must overcome to eject blood. It is essentially the back pressure that arterial blood exerts on the aortic and pulmonary valves) Peripheral resistance - Is affected by the blood viscosity, length of the blood vessel - Haematocrit is the percentage of RBC in the total blood volume. As the haematocrit increases, the viscosity of blood increases. This increases the resistance encountered by it, increasing the BP - Controlled by:  Local factors: metabolic needs  Sympathetic reflexes (e.g. temperature regulation)  Hormones: renin/angiotensin/aldosterone axis; nitric oxide, adenosine, etc…  Myogenic autoregulation (stretch)  Elasticity of blood vessels - A healthy elastic artery expands, absorbing the shock of systolic pressure. The elastic recoil of the vessel then maintains the continued flow of blood during diastole. - When an individual has arteriosclerosis, arteries become calcified and rigid, so they can't expand when the pulse wave of systolic pressure passes through them. Thus the walls of the artery experience higher pressures and become weaker and weaker. CONTROLLING BLOOD PRESSURE Short term control of BP Baroreceptors Changes in the blood pressure is noted by the baroreceptors. These can be found in the carotid sinus and the aortic arch. There are also low-pressure baroreceptors in the walls of the vena cavae and the right atrium. They respond to the degree of stretch caused by the blood. The cardiovascular centre forms part of the ANS. It is found in the medulla oblongata. It has 3 distinct components; - The cardio accelerator centre: Stimulates cardiac function by regulating heart rate and stroke volume via sympathetic stimulation from the cardiac accelerator nerve. - The cardio inhibitor centre: Slows cardiac function by decreasing the heart rate and stroke volume via parasympathetic stimulation from the vagus nerve. - The vasomotor centre: Controls the vessel tone/ the contraction of the smooth muscle in the tunica media. Changes in diameter affect the peripheral resistance, pressure and flow, which in turn affect cardiac output When the blood pressure increases, the baroreceptors are stretched more tightly. They initiate action potentials at a higher rate, sending impulses to the cardiovascular centre in the medulla oblongata. The impulses trigger the parasympathetic response. The cardiac centre reduces the cardiac function by decreasing the heart rate and stroke volume, via parasympathetic stimulation from the vagus nerve. Natriuretic peptides Natriuretic peptides (NPs) are peptide hormones that are synthesized by the heart, brain and other organs. The release of these peptides by the heart is stimulated by atrial and ventricular distension, as well as by neurohumoral stimuli, usually in response to heart failure. The main physiological actions of natriuretic peptides is to reduce arterial pressure by decreasing blood volume and systemic vascular resistance. Anti-diuretic hormone The release of Anti diuretic hormone (ADH) from the OVLT of the hypothalamus in response to thirst or an increased plasma osmolarity (concentration) ADH increases the permeability of the collecting duct to water by inserting aquaporin channels (AQP2) into the apical membrane It also stimulates Na+ reabsorption from the thick ascending limb of the loop of Henle, increasing the reabsorption of water, increasing the plasma volume and reducing the osmolarity. Other neural mechanisms of controlling BP Chemoreceptors; - As the blood pressure changes, the Po2 levels change in the blood and this is detected by the peripheral chemoreceptors. - It can cause either a vagal or sympathetic response to the cardiovascular control. Cushing response - Blood flow to the brain is controlled by the Cerebral Perfusion Pressure (CPP). This is the Mean Arterial Pressure – Intracranial pressure. - To perfuse the brain MAP>ICP - If MAP