Pulmonary Ventilation

Dr.Niranjan Murthy H.L Assistant Prof of Physiology SSMC, Tumkur

Behaviour of gases 1. Kinetic theory of gases 2. Boyle’s law- Pressure and volume are inversely related at a given temperature 3. Charles’s law- volume of a gas is inversely related to temperature at a given pressure 4. Avogadro's law- equal volume of different gases at a given temperature & pressure have same number of molecules

Boyle’s law

5. Ideal gas law- PV=nRT 6. Dalton’s law- Px=P.Fx 7. Henry’s law- volume of gas dissolved in a liquid is proportional to it’s partial pressure Cx=K.Px 8. Graham’s law- Rate of diffusion of a gas is inversely proportional to square root of it’s density

Ventilation • Process of moving O2 from atmosphere into alveoli and removing CO2 from alveoli into atmosphere • Tidal volume- volume of air moved in or out of lungs with each breath at rest. It is normally 500ml in young adults. It includes alveolar gas and dead space gas

Lung volumes and capacities Spirometry- in 1846, Hutchison used it for the first time in London on sailors, pugilists giants and dwarfs

Spirogram

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Tidal volume- amount of air breathed in or out in a single resting respiratory cycle. 500ml 2. Expiratory reserve volume- maximum amount of air that can expired after the end of tidal expiration. 1100ml 3. Inspiratory reserve volume- maximum amount of air that can be inspired at the end of tidal inspiration. 3000ml 4. Residual volume- amount of air left behind in the lungs at the end of maximal expiration. 1200ml

5. Inspiratory capacity- tidal volume + inspiratory reserve volume. 3500ml 6. Functional residual capacity- expiratory reserve volume + residual volume. 2300ml 7. Vital capacity- IRV+TV+ERV. 4600ml 8. Total lung capacity- VC+RV. 5800ml

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Vital capacity gives useful information about strength of muscles of respiration • Factors affecting VC: 3. Physiological (i) Age (ii) Sex (iii) posture (iv) strength of respiratory muscles 8. Pathological (i) VC decreases in restrictive lung diseases, pleural effusion, pulmonary edema (ii) VC decreases in ascites

Measurement of FRC 1. Helium dilution methodC1xV1=C2(V1+V2) C1.V1=C2.V1+C2.V2 C2.V2=C1.V1-C2.V1 V2=V1(C1-C2)/C2 2. Nitrogen exhalation method

Helium dilution method

N2 exhalation method

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Significance of FRC- it acts as a buffer and prevent rapid changes in alveolar air by maintaining residual volume • Factors affecting FRC3. COPD 4. Old age 5. Atelectasis

Flow of air in lungs Bulk flow- air moves by bulk flow or convection in conducting zone Diffusion- as the flow rate comes almost to stagnation, the movement of air in respiratory zone occurs by diffusion

Total Vs. Alveolar ventilation Tidal volume- 500ml Respiratory rate- 12 to 16/min Total ventilation= TV x RR= 6000ml/min Dead space= 150ml Alveolar ventilation= 350x12= 4200ml/min

Measurement of alveolar ventilation VT=VD+VA

VT= tidal volume

n.VT=n.VD+n.VA

VD=dead space volume

n.VE=n.VD+n.VA

VA=alveolar volume n=respiratory rate

1. Simple approximation- dead space volume is approximately equal to the weight of subject in pounds

2. CO2 estimation method There is no CO2 in dead space at the end of inspiration So, VCO2 = VA.FA CO2 VA = VCO2 / FA CO2 where VCO2 is volume of CO2 expired per unit time and FACO2 is fractional concentration of CO2 in alveolar gas VCO2 is estimated by collecting expired air and analyzing it for CO2 FA CO2 is estimated by a rapid CO2 analyzer in the mouthpiece

PACO2 = FACO2.K PaCO2 ά PACO2 VA = (VCO2/ PaCO2).K

Dead space 1.    

Anatomic dead space Conducting zone of airways 150ml Depends on size & posture of subject and volume of inspiration Estimation by Fowler’s method

Fowler’s method

Sampling of gases

2. Physiological dead space  Alveoli not involved in air exchange + conducting zone  Estimated by Bohr’s method

Bohr’s method All expired CO2 comes from alveoli VT.FECO2 = VA.FACO2 VT.FECO2 = (VT-VD).FACO2 VT.FECO2 = VT.FACO2-VD.FACO2 VD/VT = (FACO2-FECO2)/FACO2 VD/VT = (PaCO2-PECO2)/PaCO2 Normal VD/VT is 0.2-0.35 It is increased in old age, emphysema, bronchiectasis & pulmonary embolism and reduced in exercise.

Variations in dead space 1. physiological(i) sex (ii) age (iii) height 5. pathological(i) emphysema (ii) bronchiectasis (iii) pulmonary embolism

Analysis of respiratory gases • Chemical absorption methods(ii) Haldane’s method (iii) Scholander’s method • Physical methods(v) Respiratory mass spectrometer (vi) Infrared analyzers (vii) Radiation emission (viii)Paramagnetic analyzers (ix) Gas chromatography (x) Thermal conductivity analyzers

Non-respiratory functions of the lung 1.Functions of respiratory passages 1. Filtration (i) hairs of nostrils (ii) turbulent precipitation (iii) gravitational precipitation (iv) PAM 2. Cough reflex 3. Sneeze reflex 4. Warming inspired air 5. Humidification of inspired air 6. Phonation

2. Functions of pulmonary circulation 1. Reservoir for left ventricle 2. Filter- small clots, fat cells, gas bubbles, detached cancer cells, debris from stored blood 3. Fluid exchange and drug absorption

3. Metabolic & endocrine functions 1. 2. 3. 4. 5.

Surfactant Prostaglandins Histamine Kallikrein Substances removed from bloodprostaglandins, bradykinin, serotonin, nor-epinephrine, acetylcholine 6. Substances activated in lungsangiotensin