Summary of pulmonaryventilation 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 flow The 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 intrapleural pressure expansion of the lungs Effect of lung expansion on intrapleural pressure and airflow
Expiration Occurs when pressure within the lungs exceeds atmospheric pressure A passive process at rest Mechanism Expiration during exercise Ms involved – rectus abdominus, internal obliques Contraction ↑ 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 Resistance P1-P2 = pressure difference at the two ends of the airway Resistance 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 airway COPD, asthma
Pulmonary Ventilation V = volume V (with dot) = volume per unit of time – usually one minute Subscribe T,D,A,I,E respectively: Tidal Dead space Alveolar Inspired Expired
Cont’d Refers to movement of gas into and out of the lungs Amount of gas ventilation per minute = V = VT x f Resting values for 70-kg male: V = 7.5 L/min VT = 0.5 L f = 15
Cont’d Maximal Exercise V = 120-175 L/min VT = 3-3.5 L f = 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 space The 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 andCapacities Spirometry Measures inspired and expired gas volumes
Definitions Tidal Volume (VT) = vol of gas inspired/expired during a normal respiration cycle Vital Capacity (VC) = max amt of gas expired after a max inspiration Residual Volume (RV) = vol of gas in the lungs after a max expiration Total 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 TV Breathing Total VE Dead VA (ml) Rate Space (ml/min) (breaths/min) (ml/min) Minute VentilationShallow 150 40 6000 (150x40) 0BreathingNormal 500 12 6000 (150x12) 4200BreathingDeep 1000 6 6000 (150x6) 5100Breathing
Dead Space vs Tidal Volume Effect of tidal volume on dead space Mechanism Bottom line Deeper 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 heart Mechanism Effect of increased blood flow Mechanism
Cont’d Effect of position on blood flow within lung Standing Exercise Supine Upside down
Ventilation Concentration depends on ventilation/blood flowBlood flow
Ventilation-PerfusionRelationships 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 greater i.e. a one to one matching of ventilation to blood flow optimal gas exchange V/Q differences throughout the lung
Cont’d A large V/Q represents a disproportionately high ventilation relative to blood flow poor gas exchange A V/Q lower then 1 represents a greater blood flow vs ventilation in the region of the lung being considered A V/Q > 0.5 = adequate to meet gas exchange demands at rest
Physiologic Dead Space Definition Malfunctioning of alveoli: 1. underperfusion of blood 2. 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
Factors dictating supply of O2 to body 1. Ambient air gas concentration Concentration of atmospheric gases O2 CO2 N2 2. Ambient air gas pressure Barometric pressure Value at sea level Effect of weather and altitude
Diffusion of Gases Partial Pressure Dalton’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 fluid 2. solubility of the gas in the fluid
. Vo2FICK PRINCIPLE - C vo 2 Ca o 2 . . - Vo2 = Q ( Ca o - C vo ) 2 2 . . Vo2 Q = - Ca o - C vo 2 2
Blood and CirculationO2 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 solution PAO2 Quantity dissolved Typical blood volume = 5 L Total volume of O2 dissolved Ability to sustain life
Hemoglobin and O2 Transport 99% O2 transported in blood = bound to Hb O2 carrying capacity of Hb Hb4 + 4 O2 Hb4O8 Oxyhemoglobin Deoxyhemoglobin Effect 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
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 100 O2 capacity of Hb 100 % saturation
Oxyhemoglobin Dissociation Curve Combination of O2 + Hb in lungs = loading Release of O2 from Hb at tissues = unloading Reversible Reaction: DeoxyHb + O2 OxyHb Factors affecting reaction direction 1. PO2 in blood 2. 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 formation Low PO2 in tissues ↓ PO2 in systemic capillaries unloading of O2 to be used by the tissues and increasing deoxyHb
PO2 in the Lungs Actual Hb-O2 saturation at sea level Note sea-level alveolar PO2 of 100 mmHg Effect of an ↑ alveolar PO2 Effect of PO2 < 60 mmHg on O2-Hb saturation Importance Saturation 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 Definition Resting values Amount of O2 bound to Hb Importance Effect of exercise PO2 = 2-3 mmHg – effect on O2-Hb
O2 Transport in Muscle Myoglobin Location Composition Affinity for O2
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 toform carbonic acidCO2+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 balancepH=6.1 + log (HCO-3 / CO2)