Helium Dilution Method: To measure FRC, RV & TLC FRC: Volume of air that remains in lung at the...

Helium Dilution Method: To measure FRC, RV & TLC

• FRC: Volume of air that remains in lung at the end of normal expiration. Helpful for lung function.

• Significance: Changes in some types of pulmonary diseases. Helps in diagnosis.

• Limitation: Spirometer cannot measure it directly as the air in the residual volume of the lungs, cannot be expired into the spirometer. This RV is nearly ½ FRC.

• So, spirometer is used in an indirect manner to measure FRC, by means of HELIUM DILUTION METHOD.

Helium Dilution Method:PROCEDURE:• A Spirometer of known volume is

filled with air mixed with helium at a known conc.

• Before breathing from the spirometer, the person expires normally.

• At the end of tidal expiration, remaining volume in the lungs = FRC.

• At this point subject immediately begins to breathe from the spirometer gases of spirometer mix with gases of the lungs.

Helium Dilution Method:

• helium becomes diluted by FRC gases & volume of FRC can be calculated from the degree of dilution of helium, using the formula:

•

• Ci He = initial conc. of helium in spirometer. • Cf He = final conc. of helium in spirometer. • Vi Spir = initial volume of spirometer.

Measurement of RV & TLC:

• Calculation of RV:– FRC – ERV = RV– ERV is measured from normal spirometry.

• Calculation of TLC:– FRC + IC = TLC– IC is measured from normal spirometry.

DEAD SPACE: Anatomical & Physiological function & Protective Reflexes:

DEAD SPACE:

Definition:• It is the portion of

inspired air that does not take part in gaseous exchange with pulmonary capillary blood.

• Its extent is from nose up to terminal bronchiole.

• Value: It is equal to 150 ml.

• VT = 500 ml– 350 ml alveoli– 150 ml remains in conducting airways (up to

terminal bronchioles)= Dead space

• TYPES OF DEAD SPACE– Anatomical Dead Space– Physiological Dead Space

• Anatomical Dead Space= Consists of conducting airways, i-e., 150 ml.

Anatomic Dead Space

Low Blood Flow

Physiologic Dead Space

Definitions of Dead Space

Copyright © 2006 by Elsevier, Inc.

Alveolar dead space:

• Consists of non-functional or partially functional alveoli because of lack of perfusion.

• The inspired air which goes to non-functional alveoli is of no benefit & no exchange takes place in result WASTAGE VENTILATION.

• Whenever there is alveolar dead space, it is wastage ventilation.

• Physiological dead space = Anatomical dead space + Alveolar dead space

• Normally there is no Alveolar dead space, so Anatomical dead space = physiological dead space / total / functional dead space.

• When alveolar dead space is present physiological dead space increases and is greater than anatomical dead space.

• When we expire out, first 150 ml is expired out from the dead space

& then 350 ml from ventilation area is expired.

ADVANTAGE OF DEAD SPACE?

• Conditioning of inspired air which includes warming & humidification & filteration.

Effect of Tracheostomy on dead space!

• There is exclusion of dead space no conditioning of inhaled air complications.

Measurement • Anatomical dead space is

measured by Nitrogen washout Method.

• Subject is asked to have a deep breath of pure oxygen.

• Then asked to expire in nitrogen meter & measure the nitrogen content of expired air.

Record of changes in nitrogen conc. in expired air after singe previous inspiration of pure oxygen

Measurement

Measurement• Physiological dead space is measured by Bohr’s Method.

• Formula: VD = VT (PaCO2 – PeCO2) ------------------------• PaCO2• = 500 (42 – 28) ------------ = 150 ml 42 VD = Dead space, VT = Tidal volume, Pa = partial pressure of alveoli, Pe = partial pressure of expired air

Dead space slightly increases:• With Age (in old age elasticity of alveoli is less fully

functional alveoli are less physiological dead space increases).

• In males (anatomical dead space is more)

• On Standing

• During deep inspiration (in young men) due to expansion of airway containing no alveoli.

• When a person breathes from a long tube (during anesthesia or artificial respiration).

Dead space slightly decreases:

• On tracheostomy (breathing through a hole made surgically in trachea).

• Anatomical dead space may fall to 110 ml during expiration, as expiration is accompanied by constriction of airways.

Functions of LUNG:

1. Respiratory functions: – Exchange of gases in lungs.

2. Non-Respiratory functions

Non-Respiratory functions of lungs:

1) SYNTHETIC FUNCTION:Synthesis of:• Surfactant• Heparin• Histamine• Serotonin• PGs• Conversion of Angiotensin I Angiotensin II

– In endothelial cells of lung capillaries, there is enzyme ACE (Angiotensin Converting Enzyme) for it.

Non-Respiratory functions of lungs:

2) REMOVAL OF SOME SUBSTANCES INCLUDING AMINES:

• APUD cells (Amine Precursor uptake and Decarboxylation Cells) in lungs remove histamine, serotonin (amines).

Non-Respiratory functions of lungs:

3) LUNGS HAVE blood FILTERING FUNCTION:

Small blood clots are filtered out when blood flows through lungs.

Non-Respiratory functions of lungs:

4) RESERVOIR FUNCTION:• In blood vessels of lungs, 450 – 600 ml blood is

stored.• It can be expelled in general circulation, if

required.• This blood can serve to maintain left

ventricular stroke volume for a few beats, even if right ventricular output may fall to zero.

Non-Respiratory functions of lungs:

5) ACID BASE BALANCE:

• lungs hypoventilate to compensate for metabolic alkalosis.

• lungs hyperventilate to compensate for metabolic acidosis.

Non-Respiratory functions of lungs:

6) TEMPERATURE REGULATION:

• From surface of airways, there is insensible perspiration heat loss.

Non-Respiratory functions of lungs:

7) WATER BALANCE OF THE BODY:

• By insensible perspiration from surface of airways.

Non-Respiratory functions of lungs:

8) ROUTE OF DRUG ADMINISTRATION:

Respiratory system is a route of administering drugs like:

• Anesthesia• Other drugs (inhalers)

Non-Respiratory functions of lungs:

• 9) INVOLVED IN PHONATION:

• Spoken speech has 3 processes:– 1) Phonation: it is sound production in voice box / larynx

by vocal cord vibration. Expired air sets the vocal cords into vibration.

– 2) Articulation– 3) Resonance

Non-Respiratory functions of lungs:

10) METABOLIC & ENDOCRINE FUNCTION:a. Lungs synthesize certain Prostaglandins, e.g., PGE2.b. Histamine, heparin & Kallikrein are also produced in

lungs.c. Release of excessive amounts of histamine & several

other chemical mediators from mast cells in antigen-antibody reactions is the basis of pulmonary allergic disorders, like bronchial asthma, as these chemicals narrow the airways by:– constricting bronchiolar smooth muscle & – producing mucosal edema.

Non-Respiratory functions of lungs:

d. Partial inactivation of certain circulating compounds like:

• Bradykinin (a vasodilator) is inactivated by Angiotensin II

• Nor-epinephrine• Acetylcholine• Fibrin clots

Non-Respiratory functions of lungs:

f. In certain lung diseases like Tuberculosis & Lung Abscess, lung cancer There is abnormal

secretion of hormones like vasopressin (ADH) & ACTH.

Non-Respiratory functions of lungs:

11) DEFENCE FUNCTION:• Mucus: Produced by goblet cells & bronchial

glands.• mucus layer can trap small particles entering

the bronchial tree.• Mucus has lysozyme & antibodies (IgA) with

antibacterial activity.• Ciliary epithelium is an important defence

mechanism.

Non-Respiratory functions of lungs:

• Lungs contain lymphocytes & plasma cells which antibodies.

• Pulmonary alveolar macrophages act as scavengers (against silica, asbestos, cigarette smoke).

Non-Respiratory functions of lungs:

12) MISCELLANEOUS FUNCTIONS:

• Alternate inspiration & expiration help in venous return

• Lungs make surfactant keeps the alveoli expanded.