Lung volume ,capacities and mechanics of respiation

Dr.Sivaramakrishnan

Introduction

Respiration includes two parts External respiration Internal respiration

External & Internal Respiration

External Respiration The movement of gases into & out of

body Gas transfer from lungs to tissues of

body Maintain body & cellular

homeostasis

Internal Respiration Intracellular oxygen metabolism Cellular transformation ATP generation O2 utilization

Goals of Respiration

Primary Goals Of The Respiration System

Distribute air & blood flow for gas exchange

Provide oxygen to cells in body tissues

Remove carbon dioxide from body Maintain constant homeostasis for

metabolic needs

Functions of Respiration

Respiration divided into four functional events:

1.Mechanics of pulmonary ventilation2.Diffusion of O2 & CO2 between alveoli

and blood3.Transport of O2 & CO2 to and from

tissues4.Regulation of ventilation & respiration

Physiological Lung Structure

Lung weighs 1.5% of body weight Alveolar tissue is 60% of lung weight

Alveoli have very large surface area 70 m2 internal surface area

Short diffusion pathway for gases Permits rapid & efficient gas exchange into blood 1.5 µm between air & alveolar capillary RBC Blood volume in lung (10% of total blood

volume)

Air passages

After passing through the nasal passages and pharynx, where it is warmed and takes up water vapor, the inspired air passes down the trachea and through the bronchioles, respiratory bronchioles, and alveolar ducts to the alveoli

Branching pattern

Total airway cross section area

Alveoli

The alveoli are surrounded by pulmonary capillaries.

In most areas, air and blood are separated only by the alveolar epithelium and the capillary endothelium, so they are about 0.5 mcm apart

300 million alveoli in humans, and the total area of the alveolar walls in contact with capillaries in both lungs is about 70 m2.

Type I cells are flat cells with large cytoplasmic extensions and are the primary lining cells.

Type II cells (granular pneumocytes) are thicker and contain numerous lamellar inclusion bodies. These cells secrete surfactant

Also helps in alveolar repair

Anatomic Dead Space Dead Space = ventilated

but not perfused The portion of tidal

volume fresh air which does not go directly to the terminal respiratory units (30%)

The conducting airways do not participate in O2 & CO2 exchange

Dead space roughly 2 ml/kg ideal body weight or weight in pounds

Anatomical differs from physiological dead space also described as wasted ventilation

Wasted Ventilation

The concept of physiologic dead space (VPD) describes a deviation from ideal ventilation relative to blood flow

Wasted ventilation includes anatomical dead space plus any portion of alveolar ventilation that does not exchange O2 or CO2 with pulmonary blood flow (alveolar dead space)

Ventilation/blood flow (V/Q) mismatch where blood flow blocked ( clot or emboli)

Wasted ventilation = VPD = VD + VAD

Wasted Ventilation

Bronchi and innervation

The trachea and bronchi have cartilage in their walls.

Lined by a ciliated epithelium that contains mucous and serous glands.

Cilia are present as far as the respiratory bronchioles, but glands are absent from the epithelium of the bronchioles and terminal bronchioles

Bronchioles and term bronchioles do not have but contain more smooth muscle

Abundant muscarinic receptors, and cholinergic

discharge causes bronchoconstriction.

There are β2-adrenergic receptors in the bronchial epithelium and smooth muscle.

The β2 receptors mediate bronchodilation. They increase bronchial secretion while α1 adrenergic receptors inhibit secretion

Noncholinergic, non-adrenergic innervation of the bronchioles that produces bronchodilation, and there is evidence that VIP is the mediator responsible for the dilation.

Pulmonary circulation

Almost all the blood in the body passes via the pulmonary artery to the pulmonary capillary bed, where it is oxygenated and returned to the left atrium via the pulmonary vein

The separate and much smaller bronchial arteries come from systemic arteries. They form capillaries, which drain into bronchial veins or anastomose with pulmonary capillaries or veins

The bronchial veins drain into the azygos vein. The bronchial circulation nourishes the bronchi and pleura. Lymphatic channels are more abundant in the lungs than in any other organ

Tidal volume is the amount of air that moves into the lungs with each inspiration and expiration

Inspiratory reserve volume is the air inspired with a maximal inspiratory effort in excess of the tidal volume

The volume expelled by an active expiratory effort after tidal expiration is the expiratory reserve volume

The air left in the lungs after a maximal expiratory effort is the residual volume

Vital capacity is defined as the amount of air moved in out of the lungs with max inspiration and expiration

Total lung capacity is the volume of gas occupying the lungs after maximum inhalation

Functional residual capacity is the amount of air left in the lungs after tidal expiration• Remember: A

capacity is always a sum of certain lung volumes

• TLC = IRV + TV + ERV + RV

• VC = IRV+ TV + ERV

• FRC = ERV + RV• IC = TV + IRV

Spirometry

REMEMBER: Spirometry cannot measure Residual Volume (RV) thus Functional Residual Capacity (FRC) and Total Lung Capacity (TLC) cannot be determined using spirometry alone.

Chest wall

Chest wall compliance is a major determinant of FRC

FRC reached at a point where outward thoracic cage recoiling counterbalances inward lung recoiling

Measured FRC in infants is higher than expected

Increased chest wall compliance is a distinct disadvantage

Poorly equipped to sustain large workloads

Easily fatigable thereby limiting their ability to maintain ventilation in lung disease

In poor compliance conditions, there is greater retraction of chest wall leading to more loss of FRC

Obstructive lung diseases produce greater chest recoil and reduced FRC

PEEP beneficial in these conditions

Respiratory Mechanics

Multiple factors required to alter lung volumes

Respiratory muscles generate force to inflate & deflate the lungs

Tissue elastance & resistance impedes ventilation

Distribution of air movement within the lung, resistance within the airway

Overcoming surface tension within alveoli

The Breathing Cycle

Airflow requires a pressure gradient Air flow from higher to lower

pressures During inspiration alveolar pressure

is sub-atmospheric allowing airflow into lungs

Higher pressure in alveoli during expiration than atmosphere allows airflow out of lung

Changes in alveolar pressure are generated by changes in pleural pressure

Elastance Property of a substance to oppose

deformation or stretching Calculated as change in pressure / change

in volume Elastic recoil is a property that enables it

to return to its original state after it is no longer subjected to pressure

Compliance Is the reciprocal of elastance Refers to distensibility

Resistance Amount of pressure required to generate

flow of gas across the airways Poiseuille’s law – R = 8 Lη/Πr⁴

Newborns and young infants have inherently smaller airways

Prone to marked increase in airway resistance from inflamed tissues and secretions.

In diseases in which airway resistance is increased, flow often becomes turbulent.

Re =2rvd/η Turbulance in airflow is most likely if

Re number exceeds 2000 Neonates and young infants are

predominantly nose breathers and, therefore, even a minimal amount of nasal obstruction is poorly tolerated.

Inspiration

Active Phase Of Breathing Cycle

Motor impulses from brainstem activate muscle contraction

Phrenic nerve (C 3,4,5) transmits motor stimulation to diaphragm

Intercostal nerves (T 1-11) send signals to the external intercostal muscles

Thoracic cavity expands to lower pressure in pleural space surrounding the lungs

Pressure in alveolar ducts & alveoli decreases

Lungs expand passively as pleural pressure falls(-2.5mmHg to -6mmHg)

Fresh air flows through conducting airways into terminal air spaces until pressures are equalized

The act of inhaling is negative-pressure ventilation

Muscles of Inspiration: Diaphragm

Most Important Muscle Of Inspiration

Responsible for 75% of inspiratory effort

Thin dome-shaped muscle attached to the lower ribs, xiphoid process, lumbar vertebra

Innervated by Phrenic nerve (Cervical segments 3,4,5)

During contraction of diaphragm Abdominal contents forced downward &

forward causing increase in vertical dimension of chest cavity

Rib margins are lifted & moved outward causing increase in the transverse diameter of thorax

Diaphragm moves down 1cm during normal inspiration

During forced inspiration diaphragm can move down further

Paradoxical movement of diaphragm when paralyzed Upward movement with inspiratory drop of

intrathoracic pressure Occurs when the diaphragm muscle is

denervated

Expiration

The Passive Phase Of Breathing Cycle

Chest muscles & diaphragm relax contraction

Elastic recoil of thorax & lungs return to equilibrium

Pleural & alveolar pressures rise Gas flows passively out of the lung Expiration - active during hyperventilation

& exercise

Movement of Thorax During Breathing Cycle

Movement of Diaphragm

THAT’S ALL FOR TODAY thank you