Upload
missreith
View
2.378
Download
0
Tags:
Embed Size (px)
Citation preview
RESPIRATION II
Summary of pulmonary ventilation
Pulmonary ventilation primarily functions to maintain a fairly constant and favorable concentration of oxygen and carbon dioxide in the alveolar chambers during rest and exercise.
Ensures complete gaseous exchange before the blood leaves the lungs for transport throughout the body.
Mechanics of Breathing
Pulmonary Ventilation = movement of air from environment lungs
Process = bulk flowThe movement of molecules along a passageway due to a pressure difference between the two ends of the passageway.
Inspiration
Inspiration = due to the pressure in the lungs (intrapulmonary) being reduced below atmospheric pressure.Any muscle capable of increasing the volume of the chest = inspiratory muscle
Cont’d
When the diagram contracts it forces the abdominal contents downward and forward and the ribs lift outward.Results in a reduction of intrapleuralpressure expansion of the lungsEffect of lung expansion on intrapleuralpressure and airflow
Expiration
Occurs when pressure within the lungs exceeds atmospheric pressureA passive process at rest
MechanismExpiration during exercise
Ms involved – rectus abdominus, internal obliquesContraction ↑ intrapulmonary pressure and expiration
Airway Resistance
At any given rate of airflow into the lungs, the pressure difference that must be developed depends on the resistance of the airways.
Basic flow equation applied:Airflow = P1-P2
ResistanceP1-P2 = pressure difference at the two ends of the airwayResistance is the resistance to flow offered by the airway
Cont’d
Airflow is increased at any time there is an increase in the pressure gradient across the pulmonary system. Factors contributing to airway resistance:
Diameter of airwayCOPD, asthma
3000
2000
1000
FRC
0 -10 -20 -30
Intrapleural pressure (cmH2O)
Volu
me
abov
e FR
C (m
l)
COMPLIANCE = ∆V / ∆P
=1000/5
= 200 ml/cmH2O∆V
∆P
Pulmonary Ventilation
V = volumeV (with dot) = volume per unit of time –usually one minuteSubscribe T,D,A,I,E respectively:
TidalDead spaceAlveolarInspiredExpired
Cont’d
Refers to movement of gas into and out of the lungsAmount of gas ventilation per minute = V = VT x fResting values for 70-kg male:
V = 7.5 L/minVT = 0.5 Lf = 15
Cont’d
Maximal ExerciseV = 120-175 L/min
VT = 3-3.5 Lf = 40-50
Ventilation
Not all the air breathed reaches the alveolar gas compartment. Part of each breath remains in the conducting pathways = VD = ventilation dead spaceThe space that VD occupies = anatomical dead space
Cont’d
The volume of inspired air reaching the respiratory zone – alveolar ventilation = VA
Total Minute Ventilation:V = VA + VD
Distribution of pulmonary ventilation throughout the lung
Pulmonary Volumes and Capacities
SpirometryMeasures inspired and expired gas volumes
Definitions
Tidal Volume (VT) = vol of gas inspired/expired during a normal respiration cycleVital Capacity (VC) = max amt of gas expired after a max inspirationResidual Volume (RV) = vol of gas in the lungs after a max expirationTotal Lung Capacity (TLC) = amt of gas in lungs after max inspiration
VC + RV
Netter Physiology Figure 5.06
reproduced by permission from Netter’s Atlas of Human Physiology, by J.T. Hansen and B.M. Koeppen, Teterboro NJ: Icon Learning Systems,2002
VA vs VE
5100(150x6)600061000Deep Breathing
4200(150x12)600012500Normal Breathing
0(150x40)600040150Shallow Breathing
VA(ml/min)
Dead Space Minute Ventilation
Total VE
(ml/min)
Breathing Rate (breaths/min)
TV(ml)
Dead Space vs Tidal Volume
Effect of tidal volume on dead space
Mechanism
Bottom lineDeeper breathing provides more effective alveolar ventilation than a similar minute ventilation achieved through an increased breathing rate.
Blood Flow to the Lung (Pulmonary Circulation)
Begins at pulmonary artery – receives venous blood from Rt ventricle pulmonary capillaries where gas exchange takes place Oxygenated blood flowing back into Lt atrium via pulmonary vein.
Cont’d
C.O. of Rt vs Lt heart
Blood flow through Rt vs Lt heart
Pressure in Rt vs Lt heartMechanismEffect of increased blood flow
Mechanism
Cont’d
Effect of position on blood flow within lung
Standing
Exercise
Supine
Upside down
Ventilation
Blood flow
Concentration depends on ventilation/blood flow
Ventilation-Perfusion Relationships
Normal gas exchange requires a matching of ventilation to blood flow (perfusion, Q)The alveolus can be adequately ventilated, but if blood flow to the alveolus does not adequately match ventilation, normal gas exchange does not occur.
Cont’d
Ideal ventilation to perfusion ratio (V/Q) = 1 or greateri.e. a one to one matching of ventilation to blood flow optimal gas exchange
V/Q differences throughout the lung
Fig 10-13 text
Cont’dA large V/Q represents a disproportionately high ventilation relative to blood flow poor gas exchangeA V/Q lower then 1 represents a greater blood flow vs ventilation in the region of the lung being consideredA V/Q > 0.5 = adequate to meet gas exchange demands at rest
Physiologic Dead Space
DefinitionMalfunctioning of alveoli:
1. underperfusion of blood2. inadequate ventilation relative to alveolar surface
Factors its increase
Netter Physiology Figure 5.19B
reproduced by permission from Netter’s Atlas of Human Physiology, by J.T. Hansen and B.M. Koeppen, Teterboro NJ: Icon Learning Systems,2002
Perfect Lung
Gas Exchange and Transport
Factors dictating supply of O2 to body
1. Ambient air gas concentration Concentration of atmospheric gases
O2
CO2
N2
2. Ambient air gas pressureBarometric pressure
Value at sea levelEffect of weather and altitude
Diffusion of Gases
Partial PressureDalton’s Law = the total pressure of a gas mixture = the sum of the pressures that each gas would exert independently
Partial Pressure = Percentage concentration x Total pressure of gas mixture
Movement of Gas in Air and Fluids
Henry’s Law
Rate of gas diffusion:1. pressure differential between the gas above the fluid and the gas dissolved in the fluid2. solubility of the gas in the fluid
FICK PRINCIPLEVo2
.
vo2-C
Cao2
Vo2
.Q (.
= Cao2 vo2-C- )
Q.
=Vo2
.
Cao2 vo2-C-
Blood and Circulation
O2 and CO2 in the BloodAcid-base Balance
O2 and CO2 Transport in the Blood
Some O2 and CO2 are transported as dissolved gases in the blood
Majority of O2 - Hb
Majority of CO2 – HCO-3
O2 in Solution
Effect of solubility on PO2 in solutionPAO2
Quantity dissolvedTypical blood volume = 5 L
Total volume of O2 dissolvedAbility to sustain life
Hemoglobin and O2 Transport
99% O2 transported in blood = bound to Hb
O2 carrying capacity of HbHb4 + 4 O2 Hb4O8
OxyhemoglobinDeoxyhemoglobinEffect of PO2 in solution on Hb state
Cont’d
Amt of O2 that can be transported per unit volume of blood is dependent upon [Hb]Normal [Hb]
Gender differences (m=150g; f=130g)When completely saturated with O2, each g of Hb can transport 1.34 ml O2
Hemoglobin
PO2 and Hb Saturation
Cooperative binding = the binding of one molecule to another progressively facilitates the binding of progressive molecules.
Oxyhemoglobin Dissociation Curve
Illustrates the saturation of Hb with O2 at various PO2 values
% saturation = O2 combined with Hb x 100O2 capacity of Hb
100 % saturation
Oxyhemoglobin Dissociation Curve
Combination of O2 + Hb in lungs = loadingRelease of O2 from Hb at tissues = unloadingReversible Reaction:
DeoxyHb + O2 OxyHbFactors affecting reaction direction
1. PO2 in blood2. Affinity of Hb for O2
Cont’d
Effect of high PO2
Effect of low PO2
Effect of ↓ affinity of Hb for O2
High PO2 in lungs high arterial PO2 ↑oxyHb formationLow PO2 in tissues ↓ PO2 in systemic capillaries unloading of O2 to be used by the tissues and increasing deoxyHb
O2 Transport Cascade
PO2 in the Lungs
Actual Hb-O2 saturation at sea levelNote sea-level alveolar PO2 of 100 mmHgEffect of an ↑ alveolar PO2
Effect of PO2 < 60 mmHg on O2-Hb saturation
ImportanceSaturation at PO2 = 60 mmHg
PO2 in Tissues
Resting PO2 in cells
Dissolved O2 from the plasma diffuses across the capillary membrane into cell
Effect on plasma PO2 and cellular PO2
Effect on Hb saturation
Hb saturation at cellular PO2
Resting (a-v)O2 difference
(a-v)O2 Difference
DefinitionResting valuesAmount of O2 bound to Hb
Importance
Effect of exercisePO2 = 2-3 mmHg – effect on O2-Hb
O2 Transport in Muscle
Myoglobin
Location
Composition
Affinity for O2
Myoglobin
Mb + O2 MbO2
Primary function
CO2 Transport in the Blood
CO2 transported in the blood in 3 forms:
1. dissolved CO2 (10%)2. bound to Hb = carbaminohemoglobin (20%)3. HCO-
3 = bicarbonate (70%)
CO2 Transport as BicarbonateCO2 in solution combines with H2O to form carbonic acid
CO2+H2O H2CO3 (enzyme = carbonic anhydrase)
In tissues: CO2+H2O H2CO3 H++HCO-3
As tissue PCO2 ↑, CO2 binds with H2O to form H2CO3 (carbonic acid). H2CO3 dissociates into HCO-
3 + H+. H+ combines with Hb and HCO-3
diffuses out of the RBC and into the plasma.
Control of blood acid-base balance
pH=6.1 + log (HCO-3 / CO2)