respiration dr. zainab h.h dept. of physiology lec.5,6

RESPIRATION

Dr. Zainab H.HDept. of Physiology

Lec.5,6

Pulmonary Function Tests

Assessed by spirometry. Subject breathes into a closed system in

which air is trapped within a bell floating in water.

The bell moves up when the subject exhales and down when the subject inhales.

As the person breathes in & out through a tube connecting the mouth to the spirometer, the bell containing air moves up & down

Pulmonary Function Tests

The bell is attached by a pulley to a pen that writes on paper attached to a rotating drum

A downward pen deflection represents expiration & an upward pen deflection represents inspiration

The recording is known as spirogram

Spirometer

Pulmonary Function Tests

Normal range: Male = 5.7 liters Female = 4.2 liters

500 ml of air are inspired and expired At end of quiet expiration, the lungs still contain

2,200 ml of air

Gas exchange continues during expirationMaintains constant gas content

Pulmonary Function Tests

The spirogram shows 4 lung volumes & 4 lung capacities

Values given are for adult males (70 kg) Normal values of lung volume &

capacities depend on:1. Age2. Sex3. Posture4. height

Lung Volumes

1. Tidal Volume (TV): volume of air inhaled or exhaled with each breath = 0.5 L

2. Inspiratory Reserve Volume (IRV): maximum volume of air that can be inhaled after a normal tidal volume inhalation = 3L

3. Expiratory Reserve Volume (ERV) - the maximum amount of gas that ca be expired during forced breathing in addition to tidal volume = 1.1L

4. Residual Volume (RV) - the volume of gas remaining in the lungs after a maximal expiration = 1.2L that keep the alveoli open.

Lung Volumes

Lung Capacities

1. Inspiratory Capacity (IC) - the maximum amount of gas that can be inspired after a normal tidal expiration IC = TV + IRV = 3.5 L

2. Functional Residual Capacity (FRC) - the amount of gas remaining in the lungs after a normal tidal expiration. FRC = ERV + RV = 2.3L

3. Vital Capacity (VC) - the maximum amount of gas that can be expired after a maximum inspirationVC = IRV + TV + ERV (= IC + ERV)

4. Total Lung Capacity (TLC) - total amount of gas in the lungs after a maximum inspiration

TLC = TV + IRV + ERV + RV (= IC + FRC) or(= VC + RV) = 5.8L

Lung Capacities

Note Volumes and capacities cannot be measured

directly with spirometer are: FRC RV TLC Functional residual capacity is determined

by nitrogen wash-out method or helium dilution method and then residual volume and total lung capacity are calculated.

Maximal Voluntary Ventilation

Also called maximal breathing Capacity

largest volume of gas that can be moved into and out of the lungs in 1 minute by voluntary effort

Equals to 125 – 170 L/min.

Factors Affecting Lung Volumes and Vital

Capacity

1. Body build or physique2. Position of the body3. Strength of respiratory muscles4. Pulmonary compliance

Restrictive and Obstructive Disorders

Restrictive pulmonary/lung diseases Expansion of lungs restricted & compliance of

lungs i.e., Fibrosis Pulmonary edema

Obstructive pulmonary diseases Airflow limitation (resistance is high), i.e.,

Chronic obstructive pulmonary diseases (COPD) Asthma

FEV1 (Forced expiratory volume in 1st second): Volume of forced vital capacity (FVC) exhaled in the first second of expiration

Normal ratio of FEV1/FVC ~ 0.8 or 80%

In obstructive pulmonry diseases, ratio is 70%

Forced Expiratory Volume in 1st second (FEV1)

Maximal inspiration

Maximal expiration

or normal

Which of the following is/are decreased in both restrictive and obstructive lung diseases:

vital capacity, FEV1, FEV1/FVC?

In obstructive airways disease. The increase in intrapleural pressure may act to compress airways proximal to the alveoli further obstruction with no increase in expiratory flow and air-trapping distally.