RESPIRATORY PHYSIOLOGY

MODERATOR:DR.KALYAN RAM

PRESENTOR:DR.KAMALA

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• Function of the respiratory system is to provide an adequate supply of oxygen to the tissues and to regulate the carbon dioxide , so as to maintain a normal acid base balance.

• 3 principle factors are concerned in their function. 1. Ventilation, 2. Diffusion, 3. Pulmonary blood flow.

• In order to reach the lungs air has to pass through series of air passages such as nose[or mouth],pharynx ,larynx, trachea, bronchi and bronchioles.•Between trachea and alveoli air passage divides 23 times , conducting

zone constitutes first 16 divisions ,the next 7 divisions involves areas like respiratory bronchioles, alveolar ducts and alveolar sacs , where gas exchange occurs.•Upper respiratory tract :nasal and oral cavities , pharynx and larynx Lower respiratory tract :from trachea to alveoli

CONTROL OF BREATHING

.• There are nerve cells in the brain stem which under normal circumstances generate the rhythm of breathing.

• Voluntary control system in cerebral cortex.• Automatic control system in brain stem.• Inspiratory center lies in the dorsal part of medulla.• Expiratory center is situated ventral part on each side of

medulla.• Pneumotoxic center in the upper pons , it transmits impulses

to the inspiratory area limiting inspiration tending to produce faster respiratory rate.

• Apneustic center lies in the lower pons over riding by pneumotoxic center.

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• Chemical control : • central H+ chemo receptor

Peripheral chemo receptors : carotid & aortic bodies

TRANSPORT OF GASES IN BLOOD

OXYGEN :• In alveolar air , the tension of oxygen is 110 mm Hg ,

whereas it is only 40 mm Hg in the venous blood entering the pulmonary capillaries.

• This pressure gradient is sufficient to induce oxygen to pass rapidly ACROSS the alveolar membrane. On reaching the blood stream , the oxygen becomes dissolved in plasma before finally uniting with hemoglobin for its carriage to tissues.

• Simple solution of oxygen in the plasma : only a very small portion of oxygen carried in the arterial blood – 0.3ml per 100 ml of blood at a PaO2 of 100 mm of Hg- is physically dissolved in plasma.

OXYGEN FLUX

• Amount of oxygen leaving the left ventricle per minute in arterial blood has been termed the OXYGEN FLUX.

OXYGEN DISSOCIATION CURVE

*It is nothing but the binding ability of Hb with oxygen at different partial pressure of oxygen ( po2 )

it can be measured by a graphic representation known as ODC.

* It is sigmoidal in shape .

NORMAL ODC :

• When PH of blood = 7.4• Paco2 = 40mmhg• Temp = 37*c• 2,3 DpG = 15micro/ mol / gr of Hb• Hb - normal variety• Shift to left or right mainly depends on BOHR effect • BOHR EFFECT : PH & H*• Binding of oxygen to Hb decreases with increasing h* concentration (

lower ph ) or when the Hb is exposed to increased partial pressure of co2 ( pco2) this phenomenon is known as BHOR.

• It is due to change in the binding affinity of oxygen to Hb. Bohr effect causes a shift in oxygen dissociation curve to the right.

ODC: SHIFT TO RIGHT• Fall in blood PH.• Acidosis . • Increased CO2• Increased H+ • Hyperthermia• Increased conc. Of 2,3 DPG.• Decrease the affinity of hemoglobin, higher PO2 is required for

hemoglobin to bind a given amount of oxygen , therefore CO2 enters the blood from tissues & helps unloading of oxygen. This phenomenon is called BOHR EFFECT.

• Decrease in O2 affinity of hemoglobin when PH of blood falls,loading of CO2 to blood causes unloading of oxygen. This phenomenon seen at tissue level.

ODC : SHIFT TO LEFT

• affinity of Hb to combine with oxygen increases , causing less release of O2 to the tissue.

• Alkalosis, • Hypothermia,• Decreased 2,3 DPG levels,• CO,• Myoglobin,• HbF,• Storage blood.• In ACD blood there is a rapid fall of in conc of 2,3DPG in the

red cells & dissociation curve shift to left.• Use of CPD as the anticoagulant in stored blood delay the fall

in 2,3 DPG for about 10 days, at which time DPG levels are normal in CPD blood,but ACD reduced to 30% of normal.

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• Most of the oxygen is used in the mitochondria and if the level of PO2 here falls below 1-2 mm Hg,the so called pasteur point then aerobic metabolism stops.

• The PO2 drops in stages from 158mm Hg in dry air to the low levels in mitochondria.

• The O2 cascade shows these changes :• Alveolar PO2 in fit young adult is about 100mm Hg.• The drop from inspired to alveolar PO2 depends mainly on

alveolar ventillation & oxygen consumption.• The 1st drop due to humidification as so that fully saturated air

at 37 degrees.• Difference between lveolar PO2 and arterial PO2 often referred

to as the A-a gradiet.• PO2 falls frequently from arterial to veonus end of capillaries.

CLASSIFICATION OF HYPOXIA

• 1. Hypoxic Hypoxia,• 2. Anaemic Hypoxia, • 3. Stagnant Hypoxia,• 4. Histotoxic Hypoxia,• 5. Low p50.

CO2 TRANSPORT

CO2 TRANSPORT• The tissues produce CO2 & this is given upto blood circulating through

capillaries,it rapidly enters the plasma and RBC.• Venous PCO2 is 46mm of Hg to reduce 40 mm of Hg in alveolus.• Pressure gradient is 6mm of Hg.• 100ml of arterial blood contains 48ml of CO2.• CO2 distributed in the blood in following manner:• 1. solution in plasma(5%) – CO2 physical form & H2CO3.• 2. as carbonate : carbonic acid formed by carbonic anhydrase in the red

cell.• Carbon dioxide diffuses into the red cell where the presence of carbonic

anhydrase,it combines with water to form carbonic acid which dissociates into hydrogen ions & bicarbonate ions.the bicarbonate diffuses out of red cell into plasma and so that ionic equilibrium is maintained, chloride ions diffuse in opposite direction from plasma into red cell,this is called chloride shift or HAMBURGER EFFECT.

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Inspiration/inhalation

Expiration/exhalation

Respiratory pressures

Lung capacities

• Expiratory capacity:maximum volume of air that can be expired after normal tidal inspiration.[TV+ERV],it is about 1700ml.

• Inspiratory capacity:Maximum volume of air that can be inspired after normal tidal expiration.[TV+IRV],It is 3500ml.

• Functional residual capacity:volume of air in the lungs after normal expiration[ERV+RV],2400ML.

• Total lung capacity:TV+IRV+ERV+RV,5900ml.• Vital capacity:maximum volume of air breathed out after

maximum inspiration[IRV+TV+ERV]

• Compliance increased in:Emphysema during an asthma attack ageing

VENTILATION –PERFUSION

• The normal pulmonary blood flow is same as right ventricular output i.e about 5L/min.

• Alveolar perfusion is not uniform ,in erect posture basal alveoli are much better perfused than apical alveoli.

• The PO2 and PCO2 of well perfused basal alveoli becomes equal to that of pulmonary arteryi.e low po2 and high pco2.

• Alveolar air composition of poorly perfused apical alveoli approximates more to that of inspired air i.e high po2 and low pco2.

VENTILATION PERFUSION RATIO[V/Q]

• Considering cardiac output 5 lit and alveolar ventilation 4.2lit/min,the perfusion ratio is 0.8

• Due to gravity apical alveoli are both under ventilated and under perfused,while basal alveoli are over perfused and over ventilated.

• Gravity affects perfusion more than ventilation,so v/q is maximum at apex[3],at base [0.6]

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