This document summarizes key aspects of blood flow and alterations in blood flow. It describes the organization of the circulatory and lymphatic systems, including vessel structure and changes with aging. Principles of blood flow such as pressure, resistance, and Starling's hypothesis are explained. Common mechanisms that can cause altered blood flow are discussed, including obstructions, thrombosis, embolism, vasospasm, and structural alterations. Specific conditions that can affect arterial and venous flow are also summarized.

1. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
CHAPTER 15
ALTERATIONS IN BLOOD FLOW

2. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ORGANIZATION OF THE CIRCULATORY
AND LYMPHATIC SYSTEMS
• Circulatory circuit
• Absorption and delivery of nutrients
• Oxygen uptake and delivery
• Removal of waste products
• Lymphatic circulation
• Specialized system of channels and tissues
• Reabsorbs fluid that leaks from vascular network into
the interstitium and returns it to the general
circulation

3. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ORGANIZATION OF THE CIRCULATORY
AND LYMPHATIC SYSTEMS (CONT.)
• Vessel structure
• Arterioles: primary tissue is smooth muscle
• Venules: connective tissue predominates
• Capillaries: single layer of endothelial cells
• Changes occur with aging

4. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
CHANGES IN THE CIRCULATORY
SYSTEM DUE TO AGING
• Thickening of the basement membrane in
microvasculature
• Narrowed vessel lumen
• Impaired exchange of oxygen, nutrients and metabolic
wastes
• Decreased elastin and increased collagen
• Decreased elasticity of arteries
• Increased fibrosis in media and thickening of intima
• Increased systolic blood pressure and arterial insufficiency

5. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ORGANIZATION OF THE CIRCULATORY
AND LYMPHATIC SYSTEMS
Anatomy of Arteries and Veins
• Three microscopically distinct layers (tunicae)
• Intima: endothelial cells in direct contact with the
blood as it flows through the vessel
• Media: smooth muscle tissue (thickest section in
arteries)
• Adventitia: collagenous connective tissue (thickest
section in veins)

6. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
STRUCTURE OF BLOOD VESSELS

7. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ORGANIZATION OF THE CIRCULATORY
AND LYMPHATIC SYSTEMS
Anatomy of Capillaries
• Single thickness of endothelial cells attached to a
basement membrane
• Spaces between endothelial cells determine the
capillary permeability
• Blood-brain barrier
• Kidney capillary beds

8. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ORGANIZATION OF THE CIRCULATORY
AND LYMPHATIC SYSTEMS (CONT.)
Lymphatic Structure
• Thin walled and resemble veins
• Range in size from capillaries to vessels of
increased diameter
• Intermittent valves that extend into lumen
• Capillary walls contain contractile fibers that
propel lymph along the vessel

9. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
LYMPHATIC NETWORK

10. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW
Blood Flow, Pressure, and Resistance
• Blood flow—movement along a pressure gradient
within the vascular bed
• Pressure—blood moves from areas of higher
pressure (arteries) to an area of lower pressure
(veins); the greater the pressure difference, the
greater the blood flow
• Resistance—Opposing forces that deter blood flow;
as resistance increases, blood flow decreases

11. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)
Blood Flow, Pressure, and Resistance
• Poiseuille’s law represents resistance
• Determinants of resistance
• Vessel length
• Vessel radius
• Blood viscosity
• Ohm’s law represents the variables of driving
pressure and resistance and their effect on blood
flow

12. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)

13. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)
Velocity and Laminar and Turbulent Flow
• Velocity: a measure of the distance traveled in a
given interval of time (centimeters/second)
• Parabolic profile of laminar flow: velocity of the
layers of blood flow within the vessel vary, with
blood in the center moving faster than blood in
outer layers

14. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)

15. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)
Velocity and Laminar and Turbulent Flow
• Turbulent flow is an interruption in the forward
current of blood flow by crosswise flow
• Turbulent flow may manifest as:
• Bruit
• Thrill
• Thrombus formation

16. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)
Wall Tension and Compliance
• Law of Laplace represents the relationship between
distending pressure and wall tension
• An increase in radius or distending pressure results in
increased wall tension

17. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)

18. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)
Dynamics in the Microcirculation:
Capillaries and Lymphatics
• Exchange of gases and nutrients
• Dependent on pressure gradient between the
capillary and the interstitium through balance of:
• Capillary hydrostatic pressure
• Interstitial fluid colloid osmotic pressure
• Plasma colloid osmotic pressure
• Interstitial fluid pressure

19. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)
Dynamics in the Microcirculation:
Capillaries and Lymphatics
• Starling’s hypothesis: net filtration is equal to the
combined forces fostering filtration minus the
combined forces opposing filtration
• Capillary fluid pressure and plasma colloid osmotic
pressure are most clinically relevant

20. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)

21. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
PRINCIPLES OF FLOW (CONT.)
Dynamics in the Microcirculation:
Capillaries and Lymphatics
• Changes in capillary permeability that allows
plasma proteins to leak out can result in edema
• Impairment of lymphatic flow allowing fluid to
collect in the interstitium is referred to as
lymphedema

22. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
CONTROL OF FLOW
• Blood flow controlled by central mechanisms
mediated by:
• Autonomic nervous system
• Venous and thoracic pumps
• Intrinsic autoregulatory mechanisms
• Lymphatic flow controlled by:
• Increasing interstitial fluid colloid osmotic pressure
• Stimulation of contractile fibers (lymphatic pumps)

23. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
CONTROL OF FLOW (CONT.)
Control of Blood Flow
• Extrinsic mechanisms
• Sympathetic nervous system (SNS)—medulla–vasomotor
center: responds to direct stimulation and to
excitatory/inhibitory afferent stimuli
• Smooth muscle in vessels is innervated by adrenergic fibers
from the SNS

24. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
CONTROL OF FLOW (CONT.)
Extrinsic Mechanisms
• Release of norepinephrine results in vasoconstriction
via α1 receptors
• Release of epinephrine results in vasodilation via β2-
adrenergic receptors
• Venous system flow controlled by pressure gradient
from veins and venous and thoracic pumps

25. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
CONTROL OF FLOW (CONT.)
Intrinsic Mechanisms
• Autoregulation is the ability of blood vessels within
organs to maintain a relatively constant blood flow
regardless of changes in arterial pressure
• High BP leads to stretch that results in constriction of
arterioles and precapillary sphincters
• Low BP results in vessel dilation

26. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
CONTROL OF FLOW (CONT.)
Control of Lymphatic Flow
• Movement of lymph is enhanced by:
• Lymphatic pumps
• Compression of lymphatic channels (ambulation)
• Intrathoracic pressure changes (deep breathing)
• Lymphatic contractions (increased BP)

27. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
GENERAL MECHANISMS THAT
CAUSE ALTERED FLOW
• Reduction in flow impairs ability to transport
gases and nutrients to body tissues resulting
in:
• Hypoxia
• Ischemia
• Venous engorgement
• Venous obstruction

28. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
GENERAL MECHANISMS THAT
CAUSE ALTERED FLOW (CONT.)
Blood Vessels: Obstructions
• May involve arterial or venous system
• Obstruction results in reduced flow beyond the
obstruction (downstream) and increased pressure
before the obstruction (upstream)
• In the arterial system obstruction manifests as distal
ischemia, in the venous system obstruction
manifests as edema

29. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
GENERAL MECHANISMS THAT
CAUSE ALTERED FLOW (CONT.)
Thrombosis
• Thrombus is a stationary blood clot formed within a
vessel or a chamber of the heart
• Arterial thrombosis results in ischemia
• Venous thrombosis results in edema
• Prophylactic interventions include oral/parenteral
anticoagulant therapy, or drugs that block platelet
activation/aggregation
• Once a thrombus has formed, anticoagulant
therapy is initiated to prevent clot enlargement

30. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
GENERAL MECHANISMS THAT
CAUSE ALTERED FLOW (CONT.)
Embolus
• Material that forms a clot within the bloodstream
• Embolus leaving L ventricle = ischemic stroke
• Embolus leaving R ventricle = pulmonary embolus
• Treatment may involve anticoagulant therapy,
embolectomy (for thromboemboli) or a filter in the
inferior vena cava (Greenfield filter)

31. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
GENERAL MECHANISMS THAT
CAUSE ALTERED FLOW (CONT.)
Vasospasm
• Sudden constriction of arterial smooth muscles
resulting in obstruction of flow
• May be mediated by hormonal changes, food
additives, or environmental factors
• Manifestations include:
• Prinzmetal angina
• Hemorrhagic stroke
• Migraine headaches

32. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
GENERAL MECHANISMS THAT
CAUSE ALTERED FLOW (CONT.)
Inflammation
• Can increase risk of thrombotic process
• Vasculitis—inflammation of the intima of an
artery
• Phlebitis—inflammation of the lining of a vein
• Arteritis—inflammatory process of
autoimmune origin in arteries

33. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
GENERAL MECHANISMS THAT
CAUSE ALTERED FLOW (CONT.)
Mechanical Compression
• External forces to the vascular system may result in
partial or complete obstruction
• May be caused by:
• Trauma
• Tight casts, dressings, or stockings
• Compartment syndrome

34. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
GENERAL MECHANISMS THAT
CAUSE ALTERED FLOW (CONT.)
Blood Vessels: Structural Alterations
• Types of structural alterations
• Valvular incompetence
• Arteriosclerosis/atherosclerosis
• Aneurysms
• Arteriovenous fistulas

35. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
GENERAL MECHANISMS THAT
CAUSE ALTERED FLOW (CONT.)
Lymphatic Vessels
• Changes in capillary or interstitial oncotic pressure
increase filtration into tissues resulting in edema
• Lymphedema results from impairment in the
circulation of lymph

36. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN ARTERIAL FLOW
Alterations in arterial flow result from:
• Obstruction
• Arteriosclerosis/atherosclerosis
• Inflammation
• Vasospasm
• Thrombi/emboli
• Acute occlusion
• Mechanical alterations
• Arteriovenous fistulas
• Aneurysms

37. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN ARTERIAL FLOW
(CONT.)
Arteriosclerosis/Atherosclerosis
• Includes three pathologic processes:
• Mönckeberg sclerosis
• Arteriolar sclerosis
• Atherosclerosis
• Underlying pathologic condition leading to
hypertension, cardiac and renal disease, peripheral
arterial disease, and stroke
• Identification and interventions directed toward
modifiable risk factor reduction

38. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN ARTERIAL FLOW
(CONT.)
Thromboangiitis Obliterans (Buerger
Disease)
• Rare inflammatory condition affecting small and
medium-size arteries and veins of upper and lower
extremities resulting in varying degrees of
obstruction
• Treatment entails smoking cessation (if applicable)
and use of prostaglandins

39. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN ARTERIAL FLOW
(CONT.)
Raynaud Syndrome
• Extreme vasoconstriction producing cessation of
flow to fingers and toes
• Intrinsic structural factors, extrinsic neuroregulation,
and locally produced mediators are involved
• Treatment directed toward enhancing circulation
through biofeedback, relaxation, calcium-channel
blockers, sympatholytic drugs, and prostaglandins

40. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN ARTERIAL FLOW
(CONT.)
Aneurysms
• Localized arterial dilations
• Classified as true or false aneurysms
• Frequently found in cerebral circulation and
thoracic and abdominal aorta
• Dissecting aortic aneurysms are a medical
emergency and treated medically and/or surgically

41. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
CLASSIFICATION OF ANEURYSMS

42. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN ARTERIAL FLOW
Acute Arterial Occlusion
• Absence of arterial circulation—emergency
• May result from thrombi/emboli or
mechanical compression
• Classic signs and symptoms (6 Ps)
• Pallor
• Paresthesia
• Paralysis
• Pain
• Polar
• Pulseless

43. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN VENOUS FLOW
• Incompetent valves (obesity, pregnancy, right heart
failure, prolonged standing) producing varicose
veins, chronic venous insufficiency, and obstruction
by deep vein thrombosis
• Accompanied by edema, venous stasis ulcers, and
pain
• Deep vein thrombosis can be life threatening

44. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN VENOUS FLOW
(CONT.)
Valvular Incompetence
• Overstretching of the valves owing to excessive
venous pressures resulting in backflow of blood
• Results in:
• Venous insufficiency
• Varicose veins
• Treatment is directed toward smoking cessation
and regular exercise

45. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN VENOUS FLOW
(CONT.)
Varicose Veins
• Impaired venous return results in increased capillary
pressure causing edema, and superficial, darkened,
raised, and tortuous veins
• Greater saphenous vein most commonly affected
• Treatment directed toward increasing venous flow
and reducing venous pressure; sclerotherapy and
surgical interventions may be used for severe cases

46. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN VENOUS FLOW
(CONT.)
Chronic Venous Insufficiency
• Results when valvular incompetence involves the
deep veins
• Venous stasis ulcers are typically present
• Venous ulcers treated with compression therapy
and infection control

47. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN VENOUS FLOW
(CONT.)
Deep Vein Thrombosis
• Most frequently due to thrombus in a deep vein of
the lower extremity
• May be asymptomatic
• Treated aggressively with anticoagulation therapy
• Previous DVT is a risk factor for further
hypercoagulation

48. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN LYMPHATIC FLOW
Lymphedema
• Occurs when normal flow is obstructed or altered in
some fashion
• Primary lymphedema due to congenital anomaly or
dysfunction of the lymphatic system
• Secondary lymphedema associated with a disease
process or iatrogenic

49. Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.
ALTERATIONS IN LYMPHATIC
FLOW (CONT.)
Lymphedema
• Typically affects extremities
• Interventions are medical (external compression
therapy and exercise) and surgical (resection of
subcutaneous fatty tissue)