Hemodynamics and Blood Flow Control in Pathophysiology

PATHOPHYSIOLOGY Dr.Wasfi Dhahir Abid Ali Department of medical sciences College of Nursing University of Basrah

HEMODYNAMICS ALTERED BLOOD FLOW & BLOOD PRESSURE

Control of Flow Blood flow throughout the periphery is controlled by central mechanisms that are mediated by the Autonomic nervous system 1- The venous and thoracic pumps 2- Intrinsic auto regulatory mechanisms. Lymphatic flow is controlled by 1-Increasing interstitial fluid colloid osmotic 2- pressure The stimulation of the contractile fibers (often called lymphatic pumps) as they are stretched.

Extrinsic Mechanisms The autonomic nervous system provides the primary extrinsic control of blood flow through the sympathetic nervous system (SNS). The vasomotor center responds to direct stimulation and to afferent stimuli of both an excitatory and an inhibitory nature. Arteries have the most smooth muscle, they are most affected by SNS stimulation. The release of norepinephrine, the SNS postganglionic neurotransmitter, results in arterial vasoconstriction. Epinephrine, released by the adrenal medulla produce vasodilation

Extrinsic Mechanisms Blood flow through the venous system into the right side of the heart is maintained by the pressure gradient from the veins and by the venous and thoracic pumps. The thoracic pump acts to increase venous return to the heart as intrathoracic pressure changes with breathing Contraction of the skeletal muscles bordering the veins compresses them, forcing the valves open and propelling venous blood back toward the heart.

Intrinsic Mechanisms Autoregulation refers to the ability of blood vessels within organs to maintain a relatively constant blood flow, regardless of changes in arterial pressure. Vascular smooth muscle is stretched, it contracts. Therefore, as arterial pressure rises and arterial walls stretch, contraction is stimulated, producing vasoconstriction or vasodilation. The tissue pressure produce acute increase in the pressure within the arterial system causes an increase in interstitial volume and pressure and increases resistance and reduces flow

Control of Lymphatic Flow The movement of lymph is expedited by lymphatic pumps. Like veins, lymphatic vessels have valves on their intimal surface that allow forward movement of fluid to join the venous return to the systemic circulation. Compression of lymphatic channels by adjacent skeletal muscles, the smooth muscle of organs, Lymphatic flow is therefore enhanced by increased physical activity, increased blood pressure, or increased respiratory rate. Lymphatic contractions are thought to be the primary factor in lymphatic flow. The rate of contractions increases as the volume of lymph increases.

Mechanism altered blood flow First: Thrombosis Thrombosis cause blood flow slows and becomes turbulent . Second: Inflammation in vein(phlebitis) with clot. Third: Blood vessels obstruction in arteries or veins . Fourth :Embolus(traveling clot) produced by other causes like fat , air ,amniotic fluid ,Infection exudate and Malignant neoplasms Fifth: vassospasm ,sudden construction

Results Mechanism altered blood flow The causes that altered blood flow lead to reduction in blood flow and impairs the ability to transport gasses and nutrient to body tissues resulting in Hypoxia Ischemia venous engorgement and obstruction

Mechanism altered blood flow Inflammation in a vein ( phlebitis) Inflammation with a clot in vein( thrombophlebitis) Reduction in flow that impairs the ability to transport gases and nutrients lead to hypoxia , ischemia , venous engorgement venous obstruction Blood vessels obstruction:involve arteries and veins

Mechanism altered blood flow Embolus : material that formed a clolt within blood stream Embolus leaving left ventricle causes ischemic stroke Embolism in right ventricle cased pulmonary embolism Fat embolus , gases, infectious exudate Vasospasm: sudden constriction of arterial smooth muscle Aneurysms: localized arterial dilatation

Blood pressure Blood pressure (BP) define as the pressure of circulating blood on the walls of blood vessels Blood pressure is one of the vital signs, along with respiratory rate,heart rate , oxygen saturation and body temperature . Normal resting blood pressure in an adult is approximately 120 millimeters of mercury systolic, and 80 millimeters of mercury diastolic, abbreviated "120/80 mmHg.

hypotension& Hypertension Blood pressure that is low due to disease state is called hypotension, and pressure that is consistently high is hypertension. Both have many causes. and may be of sudden onset or of long duration. Long-term hypertension is a risk factor for many diseases, including heart disease ,strok and kidney failure. Long-term hypertension is more common than long term hypotension and often goes undetected because of infrequent monitoring and the absence of symptoms.

Mean arterial pressure The mean arterial pressure (MAP) is the average over a cardiac cycle and is determined by the cardiac output (CO , systemic vascular resistance SVR)and central venous pressure(SVR) MAP = P Diastole + 1 ( P systole - P diastole ) 3

Mean systemic pressure Or mean circulatory filling pressure, (MCFP)) is defined as the mean pressure the circulatory system when the blood has had a chance to redistribute evenly to all vessels and organs. MSP is approximately 7 mm of Hg. It is an indicator of how full the circulatory system is (i.e. the volume of blood in the system compared to the capacity of the system), and is influenced by the volume of circulating blood and the smooth muscle tone in the walls of the venous system determines the capacity of the system that exists in (which

Regulation of blood pressure The endogenous regulation of arterial pressure Baroreceptor reflex : In the high pressure receptors zones detect changes in arterial pressure. These baroreceptors send signals ultimately to the medulla of brain stem , baroreceptors are located in the left and right carttid sinuses and in the aortic arch Renin- angiotensin system (RAS): This system is generally known for its long-term adjustment of arterial pressure. This system allows the kidney to compensate for loss in blood volume or drops in arterial pressure by activating an endogenous vasoconstrictor known as angiotensin II.

Regulation of blood pressure Aldosterone release: This steroid hormone released from the adrenal gland cortex in response to angiotensin II or high potassium levels. Aldosterone stimulates sodium retention and potassium excretion by the kidneys. Since sodium is the main ion that determines the amount of fluid in the blood vessels by osmosis, aldosterone will increase fluid retention, and indirectly, arterial pressure. Baroreceptor in low pressure receptor (mainly in the venae cavae and the pulmonary veins , and in the atria ) result in feedback by regulating the secretion of antidiuretic hormone (ADH/Vasopressin),renin and aldosterone . The resultant increase in blood volume results in an increased cardiac output in turn increasing arterial blood pressure.