respiratory physiology

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  • 1. Ventilation
    Diffusion
    Ventilation-perfusion Relationships
    Gas Transport by the Blood
    Respiratory Physiology

2. Lung Volumes
3. LUNG VOLUMES AND CAPACITIESRemember: Capacities are always the summation of volumes.TIDAL VOLUME (TV): Volume inspired or expired with each normalbreath.INSPIRATORY RESERVE VOLUME (IRV): Maximum volume that can be inspired over the inspiration of a tidal volume/normal breath. Used during exercise/exertion.EXPIRATRY RESERVE VOLUME (ERV): Maximal volume that can be expired after the expiration of a tidal volume/normal breath.RESIDUAL VOLUME (RV): Volume that remains in the lungs after a maximal expiration. CANNOT be measured by spirometry.INSPIRATORY CAPACITY ( IC): Volume of maximal inspiration:IRV + TVFUNCTIONAL RESIDUAL CAPACITY (FRC): Volume of gas remaining in lung after normal expiration, cannot be measured by spirometry because it includes residual volume:ERV + RVVITAL CAPACITY (VC): Volume of maximal inspiration and expiration:IRV + TV + ERV = IC + ERVTOTAL LUNG CAPACITY (TLC): The volume of the lung after maximal inspiration. The sum of all four lung volumes, cannot be measured by spirometry because it includes residual volume:IRV+ TV + ERV + RV = IC + FRCDEAD SPACE: Volume of the respiratory apparatus that does not participate in gas exchange, approximately 300 ml in normal lungs. --ANATOMIC DEAD SPACE: Volume of the conducting airways, approximately 150 ml --PHYSIOLOGIC DEAD SPACE: The volume of the lung that does not participate in gas exchange. In normal lungs, is equal to the anatomic dead space (150 ml). May be greater in lung disease.FORCED EXPIRATORY VOLUME in 1 SECOND (FEV1): The volume of air that can be expired in 1 second after a maximal inspiration. Is normally 80% of the forced vital capacity, expressed as FEV1/FVC. In restrictive lung disease both FEV1 and FVC decrease , thus the ratio remains greater than or equal to 0.8. In obstructive lung disease, FEV1 is reduced more than the FVC, thus the FEV1/FVC ratio is less than 0.8.
4. Ventilation
5. Ventilation
PaCO2 ventilatory status
Ventilation
PaCO2
Ventilation
PaCO2
6. Ventilation
Minute ventilation (VE) = Tidal volume (VT) x RR
= (VD + VA) RR
VT (RR) = VD(RR) + VA(RR)
VA(RR)= VT (RR) - VD(RR)
Alveolar ventilation = (tidal volume VD ) RR
7. VA= RR ( VT VD )
8. Ventilation
Anatomic dead space - volume of the conducting airways (150 ml)
Physiologic dead space - volume of gas that does not eliminate CO2
9. Diffusion
Vgas = A . D . (P1 P2 )
T
Ficks Law
The rate of diffusion of a gas through a tissue slice:
proportional to the area, partial pressure difference, solubility of the gas in the tissue
inversely proportional to the thickness and the square root of the molecular weight
10. Uptake of carbon monoxide, nitrous oxide, and O2 along the pulmonary capillary
11. Diffusion of Oxygen Across the Blood-Gas Barrier:
12. Measurement of Diffusing Capacity
Carbon Monoxide
Gas of choice
Diffusion-limited
Ficks Law
Vgas = A . D . (P1 P2 )
T
13. Measurement of Diffusing Capacity
Vgas = DL (P1 P2 )
DL Diffusing capacity of the lung (area, thickness, and diffusion properties
DL CO =VCO/P1-P2
DL CO =VCO /PA co
NV DL CO =25ml/min/mmHg (increases 2-3x during exercise
14. Ventilation-Perfusion Relationships
PO2of air: 20.93%
Barometric pressure at sea level: 760mmHg
Water vapor pressure of moist inspired air: 47mmHg
PO2 of inspired air = (.2093) X (760 - 47)=149 mm Hg
15. Ventilation-Perfusion Relationships
Scheme of the O2 partial pressures from air to tissues
16. 5 Causes of Hypoxemia
Hypoventilation
Diffusion abnormality
Shunt
Ventilation-perfusion inequality
Decreased inspired oxygen
17. Hypoventilation
18. Hypoventilation
Causes:
Drugs (morphine and barbiturates)
Damage to chest wall or paralysis of respiratory muscles
High resistance to breathing (underwater)
19. Hypoventilation
Increases the PCO2
Decreases the PO2 unless additional O2 is inspired
Hypoxemia is easy to reverse by adding O2
20. 5 Causes of Hypoxemia
Hypoventilation
Diffusion abnormality
Shunt
Ventilation-perfusion inequality
Decreased inspired oxygen
21. Shunt
Refers to blood that enters the arterial system without going through ventilated areas of lung
Bronchial artery collected by pulmonary veins
Coronary venous blood draining through thebesian veins
AV fistula
Hypoxemia responds poorly to added inspired O2
When 100% O2 is inspired, the arterial PO2 does not rise to the expected level- a useful diagnostic test
22. VQ Mismatch/Inequality
O2 = 150 mmHg
CO2 = 0
23. Regional Gas Exchange in the Lung
24. Gas Transport by the Blood
Oxygen is carried in the blood in 2 forms:
Dissolved O2
Amount dissolved is proportional to the partial pressure (Henrys Law)
0.003 ml O2 in 100ml blood/mmHg of PO2
N Arterial blood w/ PO2 of 100mmHg has 0.3ml O2/IL blood
Combined with hemoglobin
25. O2 + Hb HbO2 (oxyhemoglobin)
O2 capacity - maximum amount of 02 that can be combined with Hb
O2 saturation - percentage of the available binding sites that have O2 attached,
O2 combined w/ Hbx 100
O2 capacity
O2 saturation of arterial blood with PO2 100mmHg is 97.5%
26. O2 Dissociation Curve
27. Carbon Dioxide
Carried in the blood in 3 forms:
Dissolved
As bicarbonate
As carbamino compounds
28. Scheme of the uptake of CO2 and liberation of O2 in systemic capillaries
Chloride shift
29. Some of the H+ ions liberated are bound to reduced hemoglobin (better proton acceptor)
H+ + HbO2 H+. Hb + 02
Reduced Hb in the peripheral blood helps unload CO2
Haldane effect:deoxygenation of blood increases itsability to carry CO2, mop up H+ ions, and form carbamino-Hb
30. CO2 Dissociation Curve
31. Acid-base Status
HCO3 (Metabolic)
pH= (6.1) + log--------
PaCO2 (Respiratory)
HCO3
--------- = pH
PaCO2
32. 32
iHCO3
------ = iipH
PaCO2
HCO3
------ = iipH
hPaCO2
Metabolic Acidosis
Respiratory Acidosis
hHCO3
------ = hhpH
PaCO2
HCO3
------ = hhpH
iPaCO2
Metabolic Alkalosis
Respiratory Alkalosis
33. 33
hHCO3
------ = hhpH
iPaCO2
Combined
Respiratory & Metabolic
Alkalosis
iHCO3
------ = iipH
hPaCO2
Combined
Respiratory & Metabolic
Acidosis
34. 34
iHCO3
------ = iipH
PaCO2
iHCO3
------ = ipH
iPaCO2
iHCO3
------ = N pH
iPaCO2
Compensated
Uncompensated
Partly Compensated
Metabolic Acidosis
35. Thank YOU!