ANESTHESIOLOGY PHYSIOLOGY Pulmonary

1
ANESTHESIOLOGY PHYSIOLOGY Pulmonary Bronchial
Circulations

• Scott Stevens D.O.
• Gannon University
• School of Graduate Nursing

2
Pulmonary Circulation
3
Pressures of the Pulmonary System

• Blood flow varies throughout lung as result of
  low vascular pressures, gravity distensible
  pulmonary vessels
• Right ventricle ejection fraction of blood is
  distributed into lungs equals LV cardiac output
• Pulmonary blood pressure lower because the
  resistance to flow in pulmonary system is one
  tenth of systemic circulation
• Pulmonary artery is thin walled (1/3 thickness of
  aorta) and very compliant

4
Pulmonary Hemodynamics
5
(No Transcript)
6
Pulmonary Artery Pressure Waveform Curve
7
The Pulmonary Circulatory SystemPhysiologic
Anatomy

• Pulmonary Vessels Divided Into Alveolar
  Extra-alveolar
• Alveolar vessels are closely related to acini
• Alveolocapillary network involved in gas exchange
• Alveolar vessels directly affected by alveolar
  pressure
• High positive pressure during lung expansion
  collapses alveolar vessels
• Alveolar capillaries can be compressed so that
  they contain no blood
• Extra-alveolar vessels are the arteries veins
  which convey blood to-and-from the respiratory
  units
• Larger vessels with thicker walls and
  substructure connective tissue
• These vessels not directly affected by pressures
  in the lung
• Compression during positive pressure does not
  occur
• Surrounding lung tissue pulls these vessels open
  during lung volume increases
• Bronchial vessels oxygenated blood from
  systemic circulation, 1-2 of cardiac output,
  empty into left atrium

8
(No Transcript)
9
Pulmonary Blood Flow RegulationCapillary
Resistance

• Alveolar vessels provide longitudinal resistance
  to flow
• Alveolar vessel network dimensions
  distensibility resist pulmonary blood flow
• Network dimensions are not regulated by autonomic
  or hormone control
• Alveolar capillary walls contribute 40 of total
  resistance
• Alveolar arterioles contribute 50 of resistance
  (In the body - arterioles are major resistance
  vessels 75 total systemic circulation
  resistance)
• Resistance of Capillary vessels dependant on lung
  conditions
• Reduced resistance at low lung volumes
• Reduced resistance at high blood flow rates
• Greater resistance at lower blood pressures or
  less vascular distending pressures
• Passive Regulation of blood flow through
  capillaries occurs in response to changes in
  cardiac output
• Increases in blood flow accommodated by
  recruitment distention
• Prevent rise in pulmonary driving pressure with
  increase in blood flow

10
(No Transcript)
11
(No Transcript)
12
Pulmonary Vessel Pressures
Pulmonary artery wedge pressure approximates the
left atrial pressure, usually 2-3 mmHg higher
13
The Pulmonary Capillaries

• Extensive network within alveolar walls
• 70-80 of alveolar surface area covered by
  capillary bed
• Total capillary surface area almost equals
  alveolar surface area
• Functional capillary volume
• Capillary volume increases by opening closed
  segments (recruitment)
• 70 ml (1 ml/kg body weight) normal volume at rest
• 200 ml at maximal anatomical volume

14
Alveolocapillary Network

• Continuous network over several alveoli
• Average distance RBC travels through network is
  600 to 800 µm
• Capillary network blood volume equal to RV stroke
  volume
• RBC remain in network for one cardiac cycle (0.75
  sec)
• RBC require less than 0.25 seconds for gas
  exchange equilibrium

15
(No Transcript)
16
Pulmonary Circulation Volume

• Total blood volume from main pulmonary artery to
  left atrium is 500 ml
• Lung is 40-50 blood by weight
• This volume fraction gt than any other organ
• Equal distribution of blood between artery vein
• Capacitance reservoir for the left atrium-
  pulmonary vasculature acts as a reservoir and can
  alter its volume from 50 to 200 of resting
  volume
• Prevents changes in blood return to right
  ventricle from affecting left ventricular
  diastolic filling pressures over 2-3 cardiac
  cycles

17
Pulmonary Capillary Volume

• Approximately equal to Stoke Volume of Right
  ventricle
• Red Blood Cell remain in pulmonary capillary for
  0.75 seconds
• Capillary bed contains 70 ml of blood at rest
• Maximum volume 200 ml during exercise

18
Capillary Volume Changes

• Distension
• Internal vessel pressures raise open capillary
  beds
• Elevated left atrial pressure distends capillary
  beds (mitral regurgitation, LV failure)
• Leads to lung congestion ultimately heart
  failure
• Mechanism seen at high vascular pressures

• Recruitment
• Process of increasing capillary volume by opening
  closed vessels
• Increased CO raises pulmonary vascular pressures,
  BUT decreases pulmonary vascular resistance
• Occurs during periods of stress increased
  tissue oxygen demand
• Chief mechanism for fall in PVR

19
Capillary Volume During Exercise

• Strenuous exercise increases cardiac output
  significantly
• Increased CO raises pulmonary arterial pressure
• More alveolar wall capillaries are recruited
• Capillary volume doubles to give time for
  adequate gas exchange during increased blood flow

20
Pulmonary Blood Flow Altered by Breathing

• Inspiration
• Greater subatmospheric pleural pressure
• Pleural pressure more negative than -5 mm H2O
• Pressure gradient for blood flow into thorax is
  increased
• RV receives greater blood volume in diastole
• Increase of venous blood return into thorax
• LV ejects less blood secondary to increased
  pressure gradient between LV systemic pressures

• Expiration
• Lower pleural pressure gradient
• Pleural pressure less negative than -5 mm H2O
• More positive thoracic pressure decreases venous
  blood return
• Decreased pressure gradient prevents venous blood
  return to RV
• Less RV ejection pressure
• The reduced gradient between LV systemic
  arteries allows increased stroke volumes

21
Lung Volumes PVR

• Changes in lung volumes during breathing alter
  PVR
• PVR minimal when lung volume close to FRC
• PVR increased with higher lower lung volumes
• Extra-alveolar vessels dilate during inspiration
• Radial traction exerted on these distributing
  arteries veins increase diameter and reduce
  flow resistance
• These vessels receive increased blood volume as
  higher alveolar pressure compresses alveolar
  vessels
• Alveolar vessels compress during inspiration
• Capillary resistance increase during elevated
  alveolar pressures
• Pulmonary capillaries are vessels of major
  vascular resistance

22
(No Transcript)
23
Effects of Mechanical Ventilation

• Alveolar pressure artificially increased by
  mechanical positive pressure ventilation
• Mechanical ventilation increases amount of ZONE 2
  lung volume relative to pulmonary venous pressure
• The rise in alveolar pressure increases
  resistance to blood flow in ZONE 2
• Positive-pressure ventilation can decrease
  Cardiac Output or increase V/Q imbalance

24
The Bronchial Circulation

• Circulation of oxygenated blood from the aorta
  returning to nourish following lung structures
• Conducting airways to terminal bronchioles
• Parenchyma supporting structures
• Pleura Interlobar septal tissues
  Pulmonary arteries veins
• Bronchial blood flows at systemic pressures and
  is 1-2 of cardiac output
• 50 of Bronchial blood circulation returns to
  right atrium via azygos vein
• The rest of the bronchial blood exits lung by
  small anastomoses with pulmonary veins
  contributing to normal venous admixture
  (right-to-left shunt)

25
The Pulmonary Lymphatic System

• Critical to keep alveoli free of fluid moving
  from capillaries
• Hydrostatic starling forces tend to move fluid
  out at 20 ml/hr
• Numerous lymphatics drain fluid from interstium
• Alveolar edema interferes with pulmonary gas
  exchange
• Interstitium kept at a slight negative pressure

Interstitium
26
Slight neg. press.
LYMPHATICS
27
Pulmonary Blood FlowMeasurement Techniques

• Fick Principle
• One method of determining CO, bloodflow through
  lungs/min
• Oxygen consumption/min oxygen uptake by blood
  in lungs/min (Vo2 at rest is 300ml/min.)
• Measurement of arterial mixed venous blood and
  determination of O2 consumption
• CO O2 consumption (Vo2)/ arteriovenous o2
  difference
• Indicator Dilution Principle
• Dye injected into venous circulation
• Diluted concentration measured on arterial side
• Thermodilution technique also commonly used to
  measure CO

28
Gravity Circulation

• Gravity effects on systemic blood pressure
• Degree of pressure change from level of the heart
• Pressure gradient of 0.74 mm Hg/cm
• Postural dependent relationship with gravity
• In supine person arterial pressure higher in
  feet than head
• Effects of gravity on pulmonary circulation
• Greater alterations in flow occur because
  pulmonary circulation pressures much lower
• Distribution of blood flow in the lung affected
  by gravity
• Changes in pulmonary arterial pressure affect
  distribution of blood flow over the height of the
  lung

29
Blood Flow at Different Lung Levels
EXERCISE INCREASES BLOOD FLOW TO LUNGS 4 TO 7
FOLD, CONVERTS ENTIRE LUNG TO ZONE 3 PATTERN OF
FLOW
30
Hydrostatic Pressure

• The pressure effect gravity has on a column of
  fluid
• Hydrostatic pressure alters the potential energy
  of the fluid column
• The right atrium level middle of lung are
  considered zero reference points
• Supine or prone position ? hydrostatic pressures
  minimized
• Gravity affects the perfusion of blood in the
  different zones of the lung
• Lung base receives greater portion of RV ejection
  fraction than apex of lung
• Hydrostatic pressure cause distension
  recruitment of pulmonary capillaries in base of
  lung

31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
Functional Zones of Blood Flow

• Blood flow distribution over the height of lung
  is divided into three functional zones
• Blood flow depends on pressures in pulmonary
  vessels relative to alveolar pressure
• Pressures dependant on
• Hydrostatic pressure
• Gravity
• Transmural compressive pressure
• Lung volume

35
Lung Perfusion Zones

• The Perfusion Zones Of The Lung Depend On The
  Relationship Between
• Alveoli And Blood Pressure In Pulmonary Arteries
  Veins
• Zone 1 region does not receive blood flow
• Alveolar pressure gt Regional pulmonary blood
  pressure (PA gt Pa)
• Pulmonary capillaries are collapsed by higher PA
• Zone 2 occurs where blood flow driving force is
  arterial-Alveolar pressure gradient
• Pa gt PA gt PV
• Intermittent blood flow
• Water fall effect downstream venous pressure
  changes do not alter blood flow
• Zone 3 conditions exists in lung base because of
  effect of gravity
• Hydrostatic gravity pressures cause distention
  recruitment of pulmonary capillaries
• Pa gt PV gt PA
• Distension recruitment decrease resistance to
  blood flow (increased flow in zone3)
• Zone 4 is an abnormal condition of reduced blood
  flow
• High pulmonary venous pressures (e.g., LV failure
  or mitral stenosis)
• Pulmonary edema creating fluid accumulation
  vascular cuffing
• Increased vascular resistance reduced local
  blood flow

36
Perfusion Distribution in the Lung

• Gravity affects the regional distribution of
  blood flow in the different lung zones
• Transmural distending pressure of vessels at
  bottom of lung gt apex
• Blood vessels are more distended in base
• Decreased resistance to flow in base
• Greater blood flow in lower lung
• Alveoli pressure affects blood flow
• Higher alveoli pressures in apex of lung than
  capillary pressures
• Decreased perfusion in apex
• Pulmonary arterial, venous alveolar pressure
  differences create lung zones

37
Factors Altering Zone 1 Perfusion

• Expand Zone 1
• Decreased Pulmonary artery pressure
• Shock, hypovolemia
• Increased Alveolar pressure
• Positive end-expiratory pressure (PEEP)
• Occlusion of blood vessels
• Pulmonary embolism

• Reduce Zone 1
• Increased pulmonary artery pressure
• Infusion of fluid or blood
• Reduced hydrostatic effect
• Change patient position
• Standing to supine

38
Factors Altering Pulmonary Blood Flow
39
Pressure-Flow Curves

• Pulmonary-Hemodynamic Curve
• Assessment of driving pressures across the
  pulmonary vasculature as CO varies
• Increased PA pressures w/ increased CO (exercise)
• PVR is the change in pressure over cardiac output
• PVR Slope of line from point of origin to point
  on curve
• Hypoxia raises resistance over entire curve

40
Pulmonary Vascular Resistance

• Active Regulation of Blood Flow
• Active regulation occurs by altering vascular
  smooth muscle tone in pulmonary vessels
  (arterioles)
• The pulmonary capillary smooth muscle alters PVR
• Vasomotor tone of pulmonary vessels is affected
  by many factors

41
Regulation of Pulmonary FlowVasculature
Innervation

• Motor innervation from the sympathetic branch of
  Autonomic Nervous System
• Increase in sympathetic outflow causes stiffening
  of the pulmonary vessel walls (vasoconstriction)
• Very little evidence of active external
  regulation
• Sensory innervation found adventitia is
  stimulated by vascular pressure changes (Stretch)
  chemical substances
• Most active regulation of pulmonary vessels is
  mediated by local metabolic influences

42
Pulmonary Vascular Resistance Factors Affecting
Vasomotor Tone

• Vasoconstrictors
• Reduced PAO2
• Increased PCO2
• Thromboxane A2
• a-adrenergic catecholamines
• Histamine
• Angiotensin
• Prostaglandins
• Neuropeptides
• Leukotrienes
• Serotonin
• Endothelin
• Norepinephrine

• Vasodilators
• Increased PAO2
• Prostacyclin
• Nitric oxide
• ß-adrenergic catecholamines
• Acetylcholine
• Bradykinin
• Dopamine
• Isoproterenol

43
Pulmonary Blood FlowLocal Vasoconstrictor

• Thromboxane A2 Potent Vasoconstrictor
• Product of cell membrane arachidonic acid
  metabolism
• Constrictor of pulmonary arterial venous smooth
  muscle
• Produced during acute lung tissue damage by
  macrophage, leukocytes endothelial cells
• Effect localized to injured region because
  half-time of thromboxane inactivation is only
  seconds

44
Pulmonary Blood FlowPotent Vasodilator

• Prostacyclin (Prostaglandin I2)
• Potent vasodilator inhibitor of platelet
  activation
• Produced by endothelial cells
• Product of arachidonic acid metabolism

45
Pulmonary Blood FlowEpithelial Vasodilator

• Nitric Oxide (NO)
• Potent endothelium-derived endogenous vasodilator
• Strictly localized effect to vascular site of
  production
• Formed from L-arginine leads to smooth muscle
  relaxation through synthesis of cyclic GMP
• NO activates guanylyl cyclase and increases cGMP
• How Nitroglycerin (NTG) and Sodium Nitroprusside
  (SNP) work
• Clinical use of NO for selective pulmonary
  vasodilatation delivered by inhalation technique
• NO is very toxic at high concentrations
• NO diffuses into circulating blood to immediately
  irreversibly binds to heme iron in hemoglobin
• NO binds to hemoglobin 200,000 times gt oxygen

46
Pulmonary Blood FlowEffect of Alveolar Oxygen
Tension

• Partial pressure of Oxygen (PAO2) in alveoli -
  critical factor governing pulmonary circulation
• PO2 in alveoli more important than oxygen tension
  in mixed venous blood
• Oxygen diffusing into pulmonary arteriole walls
  causes smooth muscle dilation
• As alveolar oxygen tension decreases
  surrounding arterioles constrict
• Low alveolar PO2 causes increase in local
  vascular resistance
• Blood flow shifted to areas of lung with higher
  PO2
• These small changes in local resistance do not
  effect overall PVR (provided lt 20 of lung volume
  involved
• Global reduction in alveolar oxygen tension
  increases total PVR by constriction of arterioles
  small arteries

47
Alveolar Hypoxia Vasoconstriction

• Alveolar hypoxia produces hypoxic pulmonary
  vasoconstriction (HPV)
• Localized response of pulmonary arterioles
• Caused by hypoxia and enhanced by hypercapnia
  acidosis
• Contraction of smooth muscle in small arterioles
  in hypoxic region
• Opposite reaction than systemic circulation to
  hypoxia
• HPV is an important mechanism of balancing V/Q
  ratio
• Shift of flow to better ventilated pulmonary
  regions
• Results from decreased formation release of
  Nitric Oxide by pulmonary endothelium in hypoxic
  region

48
(No Transcript)
49
Pulmonary Hypertension

• Increased resistance to blood flow in the lung
• High pulmonary vascular resistance (PVR) elevated
  pulmonary artery pressures
• Generalized alveolar hypoxia increases total
  pulmonary resistance
• Hypoventilation
• Low inspired PO2
• Increased PCO2
• Pain
• Histamine release
• High altitudes
• Pulmonary Hypertension causes increased work for
  the right ventricle
• Right ventricular hypertrophy
• Tricuspid regurgitation
• Right heart failure (cor pulmonale)

50
Pulmonary Hypertension

• Serious pulmonary vascular condition
• Small muscular pulmonary arteries narrow
• Pulmonary arterial pressure increases
• Right ventricle pressures rise to compensate
  until occurrence of RV failure
• Lung Transplant is only effective treatment

51
Distribution of Ventilation

• Normal lung is not uniformly ventilated in
  standing lung
• The tidal volume is unevenly distributed
  throughout lung
• Most of volume changes occur at more compliant
  base of lung
• Linear reduction in regional tidal volume from
  base to apex
• Variation in airway resistance, compliance
  hydrostatic effects cause nonuniform regional
  local (acini) ventilation
• Regional nonuniform ventilation
• Gravity causes hydrostatic interpleural pressure
  gradient
• Regional lung volume changes vary because
  transpulmonary pressures are influenced by
  interpleural pressure gradient
• Differences in transpulmonary pressure affect
  lung compliance
• Local nonuniform ventilation is caused by
  variable airway resistance localized
  differences in compliance of lung
• Healthy lungs have essentially equal time
  constants in all acini
• Acini ventilation not as effected by hydrostatic
  pressure changes

52
Regional Ventilation Distribution

• Nonuniform ventilation caused by effects gravity
  on the parenchyma of lung
• Gravity pulls down on lung
• Alveoli are more expanded at top than at base of
  lung
• Alveolar volume parallels lung compliance curve
• Lower portion of lung tends to be ventilated gt
  apex of lung
• the end expiratory volume (FRC) is less at base
• Compliance of base of lung gt top of lung
• More movement of air into out of alveoli at
  base of lung

53
Local Ventilation Distribution

• Ventilation is not evenly distributed throughout
  the lung
• Airway Resistance Lung compliance differences
  among terminal respiratory units vary dependant
  on alveolar time constant
• Time constant establishes rate of acinar volume
  change
• A longer time constant means slower ventilation
  of lung unit
• Increased resistance and/or decreased compliance
  indicates longer alveolar filling time
• Decreased compliance (stiff lung) reduces lung
  volume changes

54
V/Q Alveoli Gas Composition
55
(No Transcript)
56
Matching Ventilation to Perfusion

• V/Q distribution regulated to maintain systemic
  oxygen partial pressure range between 85 to 100
  mmHg
• Distribution of V/Q ratios among the terminal
  respiratory units not uniform even in normal lung
• A diseased lungs V/Q ratios may be very
  nonuniform
• Alveolar-arterial (A-a) PO2 differences express
  the unequal match of V/Q ratio
• Normal (A-a) PO2 differences are 10 to 15 mmHg
• Larger (A-a) PO2 gradients indicate intrinsic
  pulmonary disease ? shunting
• Hypoxemia with normal (A-a) PO2 gradient
  indicates hypoventilation
• Mismatched V/Q ratio most common cause of
  inefficient O2 CO2 exchange
• Wasted ventilation venous admixture are both
  causes of abnormal (A-a) PO2 differences

LOWER LUNG
UPPER LUNG
57
Right-to-Left Heart Shunt Pulmonary Venous
Admixture

• Shunt perfused but not ventilated
• A portion of Cardiac Output (CO) flowing through
  pulmonary circulation does not participate in gas
  exchange
• A fraction of blood flow bypasses the lung to
  enter the systemic arteries without becoming
  oxygenated leading to venous admixtures
• Reduction of systemic arterial oxygen tension
  concentration
• Reduce efficiency of gas exchange
• Small shunts are normal because some venous blood
  bypasses the lung to enter left heart
• True anatomical shunts
• Bronchopulmonary venous anastomoses
• Intracardiac thebesian veins
• Mediastinal veins
• Pleural veins
• Venous admixture is the blood flow equivalent of
  wasted ventilation

58
Right-to-Left Venous Admixture
59
Left-to-Right Heart Shunt Pulmonary Venous
Recirculation

• A portion of CO returns to right heart without
  flowing through the body
• This type of shunt does not affect systemic
  arterial oxygen tension
• The oxygen tension in right heart increased
• Location of increased oxygen concentration
  indicates site of L-to-R shunt
• Amount of change in PO2 allows estimate of shunt

60
THATS ALL FOR TODAY