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)