Pulmonary Ventilation and Pulmonary circulation

Pulmonary Ventilation and Pulmonary circulation

1. PULMONARY VENTILATION AND PULMONARY CIRCULATION Dr. Sanjeev Shrivastava 05/01/2019 09:00 AM to 10.00 AM

2. Pulmonary ventilation Alveolar ventilation Dead space types of dead space measurement of dead space Ventilation Perfusion ratio Effect of gravity on ventilation perfusion ratio Pulmonary circulation Bronchial circulation Functions of pulmonary circulation

3. Pulmonary ventilation Volume of air that enters lungs each minute. Product of TV and RR. = 500x 12 =6 L/min Range = 5 L to 10 L/min

4. The rate of alveolar ventilation Alveolar ventilation per minute is the total volume of new air entering the alveoli and other adjacent gas exchange areas each minute. Va = Respiratory rate X ( Vt – Vd ) = Respiratory rate X ( Vtidal volume – Vdead space) = 12 X (500 – 150) = 4200ml

5. Effect of rate & tidal volume on ALVEOLAR VENTILATION V T R V E V A ml/min ml/min 20 3 6000 no alveolar ventilation 500 12 6000 4200 normal ventilation 1000 6 6000 5100 excess ventilation V A = ( V T - V D ) RR = ( 500 - 150 ) x 12 = 4200ml Fixed V E & V D

6. Dead space volume of air in airways that can not exchange gases with blood . Occupies the conducting zone. typical value about 150 ml or 1 ml per pound body weight . Ratio of dead space volume to tidal volume in normal health is 25% - 30%.

7. DEA D S P AC E V D 7 Physiological Dead space (volume) sum of anatomical and alveolar dead space Anatomical Dead Space (volume) volume of air in airways that can not exchange gases with blood - typical value about 150 ml or 1 ml per pound body weight. Alveolar Dead Space (volume) volume of alveoli that are ventilated but do not receive a blood flow and thus no gas exchange. Small in normal lung but can be very large in some pulmonary diseases.

8. Measurement of anatomical dead space 1- Single breath oxygen technique/Single breath N2 washout method- calculate the anatomical dead space area A x VE VD= ---------------------------- Area A + Area B

9. Measurement of physiological dead space Bohr’s equation - by determining CO2 conc in expired and alveolar gas. Based on the fact that inspired air contains negligible CO2. All the CO2 in expired air is derived from the functional alveoli. VD= ( PaCO2 – P E CO2) x VE PaCO 2

10. Pulmonary Circulation

11. Three Types of circulations Pulmonary artery - Pulmonary trunk divides into Rt n Lt pulmonary arteries. Bronchial artery (2 left 1 Right) - Two left and one right -From descending thorasic aorta -Contributes to a physiological shunt -1 to 2 % of COP. Lymphatic circulation – present in walls of terminal bronchioles n in all supportive tissue. Perticulate matter entering the alveoli during inspiration is removed by lymphatics. Remove the plasma proteins leaking from capilarries and help to prevent the pulmonary oedema .

12. Pulmonary Arterial Circulation

13. General Characters Thin walled , distensible , large compliance Low pressure , low resistance , high capacitance system Pul capillaries are larger and have more anastamosis Helps in gas exchange Serves as a filter Metabolic functuions Serves as a blood reservoir

14. Comparison of the Pulmonary & Systemic Circulation PULMONARY CIRCULATION LOW PRESSURE - because it only needs to pump blood to the top of the lungs. - if it is HI pressure, then following Starling forces, the fluid would flood the lungs. LOW RESISTANCE - only 1/10 th of the resistance of the systemic circ. - arterioles have less smooth muscle, veins are wider & shorter & pulmonary vessel walls are thinner. HIGH COMPLIANCE - accommodates 5 L of blood (same as the systemic circulation) - Accommodates shifts of blood more quickly e.g. when a person shifts from a standing to a lying position SYSTEMIC CIRCULATION HIGH PRESSURE - B/c it needs to send blood to the brain even when standing & to the tip of en elevated fingertip. HIGH RESISTANCE - because of increased smooth muscle in the arterioles & the metarterioles . LOW COMPLIANCE - because of resistance offered by the arterioles and the metarterioles .

15. Advantages of Pulmonary Circulation being a Low Resistance system: Accommodates more blood as a person shifts from the standing to the lying position. High compliance allows the vessel to dilate in response to modest increase in Pulmonary arterial pressure. Pulse pressure in the pulmonary circulation is rather low.

16. Pressures in pulmonary system Pressure Pulmonary system Systemic vasculature Ventricular pressure RV- 25 (systolic) LV- 120 systolic Pulmonary artery 25 sys 8 diastolic 120 sys 80 dias MAP 15 mm/hg 100 Pulse pressure 17 40 atrial pressure LA – 5 RA - 0 Pressure gradient Pp= MAP- MVP = 15-5 =10 100

17. Pulmonary Capillary Pressure Mean value is 10 mmHg Is less than colloid osmotic pressure 25mmHg So a net suction force of 15mmHg is keeping the alveoli dry However if hydrostatic pressure raises more than 25mmHg then pulmonary edema ensures e.g. exercise, high altitude, left heart failure. Layer of fluid increases the distance b/w blood and gases in alveoli. This reduces rate of gas exchange in lungs

18. Pulmonary Blood Flow Vessels contain 600 ml of blood at rest (200-900) D ecreases in standing and haemorrhage according to posture and pathological conditions Act as a reservoir Increase in lying position, mitral stenosis MR n Lt heart failure.

19. Pulmonary Capillary Wedge Pressure Is measured to give the LAP Direct measurement of LAP is difficult So indirect measurement is done LAP corresponds to PCWP Measures by swans gans catheter Catheter is wedged in the tip of the small branch of pulmonary artery Stops flow of blood in that

20. Swans Gans Catheter

21. Regional Distribution Of Pulmonary Blood Pulmonary bld flow same as the CO or LV output Effect of gravity :- in supine position MAP is same all over the lungs so uniform perfusion Gravity changes the hydrostatic pressure Zero reference plane is at the level of RA which is at the middle of the lung in the region of hilum. Which is approximately at the middle of the lung or hilum

22. At Standing Position In a 30cm height lung In the middle pressure is 15mmHg In the apex its 11 mmHg less ie 4mmHg In the base its 26mmHg

23. Perfusion Zones Of Lungs Depends upon three pressure PA - alveolar pressure Pa – pulmonary arterial pressure Pv – pulmonary venous pressure Divided into three zones in erect posture – 1, 2, 3

24. The Zones of the Lung and the Difference in Regional Blood Flow

25. ZONES OF THE LUNGS

26. Zone 1 Area of zero perfusion Does not exist in normal lungs Occurs when Pul arterial pressure becomes less than alveolar pressure Pulmonary capillaries become collapsed Flow becomes zero Ex- pulmonary embolism , shock , obstructive lung diseases ,

27. Zone 2 Region of intermittent blood flow This occurs during systole when the pul arterial pressure raises more than PA In normal lungs this zone occurs from apex to hilum of the lungs Systolic Pa pressure is 25 mmHg and diastolic is 8 mmHg

28. Zone 3 This zone has continues high blood flow Here pa is greater than PA during the entire cardiac cycle this region occurs in from the middle zone of lungs to bottom

29. Effect of exercise Blood flow increases 4- 7 times Near base its 2-3 times In apex its 8 times So whole lungs becomes zone 3 Possible because of two reasons Recruitment Distensibility Ability of lungs to accommodate large blood serve two purpose Reduces R t heart work and prevents pulmonary edema

30. Pulmonary Capillary Dynamics Pulmonary transit time 4sec Net filtration pressure Net outward forces :- Interstitial oncotic pressure = 14mmHg Intersttial hydrostatic pressure = -8 Capillary hydroststic pressure = 7 Total = 29mmHg Net inward pressure:- Plasma oncotic pressure = 28mmHg NFP = 29-28= 1

31. Functions of pulmo . Circulation Gas exchange Reservoir of L t ventricle. Filters for removal of emboli n other particles from blood. Removal of fluid from alveoli. Absorption of drugs. Synthesis of ACE.

32. Regulation Neural regulation is not very effective - Effrent Sympathatic – Vasoconstrictor when stimulated *Baroreceptor stimulation- reflex dilation. *Chemoreceptor stimulation-vasoconstriction. Baroreceptors- tunica adventitia of pulmo trunk-bradycardia n hyotentn Volume receptors-at the junc of pulmo vain n LA-tachycardia n diuresis J receptors-Adjacent 2 pulmo capi .-Reflex tachypnea n decrease in ms tone . sti by microemboli Chemical control is major regulatory mechanism

33. Chemical Regulation Local hypoxia – Produce vasoconstriction. - divert pulmo bld flow from the alveolithat are poorly ventilated to better ventilated regions. Hypercapnia n acidosis- vasoconstriction. Just opposite to the systemic circulation Chr. Hypoxia – Pulmonary hypertension result I Rt venti hypertrophy.

34. The overall V/Q = 0.8 [ ven =4 lpm , per=5 lpm ] Ranges between 0.3 and 3.0 Upper zone –nondependent area has higher ≥ 1 Lowe zone – dependent area has lower ≤ 1 VP ratio indicates overall respiratory functional status of lung V/Q = 0 means ,no ventilation-called SHUNT V/Q = ∞ means ,no perfusion – called DEAD SPACE Ventilation Perfusion ratio V A /Q

35. Ventilation pattern - V A Pleural pressure [Ppl] increased towards lower zone Constricted alveoli in lower zones & distended alveoli in upper zones More compliant alveoli towards lower zone Ventilation: distributed more towards lower zone

36. Ventilation Perfusion ratio V A /Q Ventilation & Perfusion both are distributed more towards lower zone. Ventilation[V A ] less increased t0wards l0wer zone than Perfusion[Q] Perfusion more increased towards Lower zone than Ventilation Ventilation Perfusion ratio V A /Q: Less towards lower zone V A /Q V A Q

37. Ventilation Perfusion ratio V A /Q Ventilation & Perfusion both are distributed more towards lower zone. Ventilation[V A ] less increased t0wards l0wer zone than Perfusion[Q] Perfusion more increased towards Lower zone than Ventilation Ventilation Perfusion ratio V A /Q: Less towards lower zone V A /Q V A Q

38. Means – Wasted perfusion Shunt – 1. Absolute Shunt : Anatomical shunts – V/Q = 0 2. Relative shunt : under ventilated lungs –V/Q ≤ 1 Shunt estimated as Venous Admixture Venous Admixture expressed as a fraction of total cardiac output Qs/Qt Qs = CcO2-CaO2 Qt CcO2-CvO2 Normal shunt- Physiologic shunt < 5% Q V V/Q<1 SHUNT

39. PULMONARY EDEMA Definition: It is a condition in which fluid accumulates in the lungs. OR It is the effusion of fluid into the alveoli and the interstitial spaces of the lungs. Underlying Cause: Any factor that causes the Pulmonary Interstitial fluid pressure to rise from the negative range into the positive range will cause rapid filling of the pulmonary interstitial spaces & alveoli with large amounts of free fluid.

40. CAUSES OF PULMONARY EDEMA: Left-sided heart failure or mitral valve disease (Most common). Damage to the pulmonary capillary membrane caused by infections. e.g. pneumonia, inhalation of poisonous gases as chlorine or sulfur dioxide. This causes the leakage of the plasma proteins & fluids into the pulmonary interstitial spaces & alveoli that raises the Pulmonary Interstitial pressure. Safety Factor in Pulmonary edema: The plasma capillary pressure must rise from the normal value of 7 mmHg to above 28 mmHg (plasma colloid osmotic pressure) for edema to occur. So there is a safety factor of 21 mmHg.

41. Signs & Symptoms of Pulmonary edema: Difficulty breathing Coughing up blood (pink, frothy sputum) Anxiety Excessive sweating and pallor Inability to lie down due to breathlessness Signs of left ventricular failure like peripheral edema & raised JVP. Respiratory failure Death

42. Treatment: Symptomatic treatment High-flow oxygen therapy. Diuretics to improve preload and afterload & aid in improving the cardiac function.

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