Respiratory Part1b
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Transcript of Respiratory Part1b
RESPIRATORY PHYSIOLOGY
PART Ib
Overview
Mechanics of breathing refers to the factors that participate
in moving of the lungs and of the chest wall along the respiratory cycle
Breathing
Breathing, or pulmonary ventilation, consists of two phases Inspiration – air flows into the lungs Expiration – gases exit the lungs
Pulmonary Ventilation
A mechanical process that depends on volume changes in the thoracic cavity
Volume changes → pressure changes
→ flow of gases to equalize pressure
Pressure Relationships in the Thoracic Cavity
Respiratory pressure is always described in relation to atmospheric pressure Respiratory pressure of 0 = atmospheric P (-) “ “ of -4 = 756 mmHg (+) “ “ of +4 = 764 mmHg
Pulmonary Pressures
Atmospheric pressure = Patm
Intrapulmonary pressure = Palv
Intrapleural pressure = Pip
Transpulmonary pressure
Atmospheric Pressure
760 mm Hg at sea level decreases as altitude increases increases under water Other lung pressures given
relative to atmospheric (set Patm = 0 mm Hg)
Intra-alveolar Pressure(intrapulmonary pressure)
pressure within the alveoli varies with phase of respiration
During inspiration = negative (less than atmospheric)
During expiration = positive (more than atmospheric)
but it always equalizes with atmospheric P Difference between Palv and Patm
drives ventilation
Alveolar pressure
During inspiration: –1cm of H2O (this slight negative pressure is enough to move about 0.5 liter of air into the lungs in the first 2 second of inspiration)
During expiration: it rises to about +1cm of H2O (this forces 0.5 liter of inspired air out of the lungs during the 2 to 3 seconds of expiration
Intrapleural Pressure
Pressure inside pleural cavityAlways negative under normal conditionsAlways less than Palv
Varies with phase of respirationvaries between -5 and -7.5 cmH2O
(inspiration to expiration)At rest, -4 mm Hg
Intrapleural Pressure Negative pressure due to :
opposing forces of the lungs trying to collapse
chest wall trying to expand
Intrapleural pressure
Always ~ 4 mmHg less than pressure in alveoli
Any condition that equalizes the intrapleural pressure to the intrapulmonary (atm P) Pressure causes immediate lung collapse
Collapse of the lungs If the pleural space communicates with the
atmosphere, i.e. pleural P = atmospheric P the lung will collapse
Causes: Puncture of the parietal pleura
Sucking chest wound Erosion of visceral pleura Also if a major airway is blocked, the air trapped
distal to the block will be absorbed by the blood and that segment of the lung will collapse
Pleura and negative pressure
Pneumothorax: lung collapse due to air entering in the pleural cavity
(not to be confused with atelectasis alveoli collapse)
Transpulmonary Pressure
Transpulmonary pressure = Palv – Pip
Distending pressure across the lung wall Keeps the lungs from collapsing peaks at the end of inspiration Increase in transpulmonary pressure:
Increase distending pressure across lungsLungs (alveoli) expand, increasing volume
Pressure Relationships
Intrapulmonary pressure and intrapleural pressure fluctuate with the phases of breathing
Intrapulmonary pressure always eventually equalizes itself with atmospheric pressure
Intrapleural pressure is always less than intrapulmonary pressure and atmospheric pressure
Pressure Relationships
Figure 22.12
Diagram of Diaphragm
Boyle’s Law
Boyle’s law – the relationship between the pressure and volume of gases As volume of a chamber increases,
pressure of the gas within it decreases As volume of a chamber decreases,
pressure of the gas within it increases
Boyle’s Law
Volume of gas is inversely proportional to pressure (if temperature constant)
Volume = Constant
Pressure
P1V1 = P2V2
Boyle’s Law P1V1 = P2V2 Volume of gas is inversely proportional to pressure (if temperature constant)
Volume = Constant Pressure
Boyle’s Law P1V1 = P2V2 Volume of gas is inversely proportional to pressure (if temperature constant)
Volume = Constant Pressure
CHARLES’ LAW
If pressure is constant, the volume of a gas and its temperature vary proportionately, or V≈T
GENERAL GAS LAW
At constant temperature, an increase in thoracic volume leads to a decrease in pleural pressure
Driving Force for Air Flow
Airflow driven by the pressure difference between atmosphere (barometric pressure) and inside the lungs (alveolar pressure).
760 mmHg
Pressure gradient drives flowAir moves from high to low pressure
Air moves in and out of lungs by bulk flow
Inspiration: pressure in lungs less than atmosphere
Expiration: pressure in lungs greater than atmosphere
Muscles of Inspiration
Diaphragm forces abdominal contents down & forward
External intercostals lift ribs up and outwards during quiet breathing diaphragm works alone during exercise, accessory muscles called into
play
Muscles of Expiration
Expiration during quiet breathing is passive due to elastic recoil of chest cavity
Decrease in lung size force air out of lungs During exercise and voluntary
hyperventilation, rectus abdominus, transverse abdominus: push
diaphragm up internal intercostals: pull ribs downwards
PRESSURE CHANGES AND AIRFLOW Flow of air into and out of the lungs is
governed by two physical principles:
1. Changes in volume result in changes in pressure
*** Boyle’s law
> muscles of respiration change thoracic volume and therefore pressure within the thoracic cavity
2. Air flows from areas of higher to lower pressure
BREATHING CYCLE
AT REST ( before inspiration)
A. alveolar pressure equals atmospheric pressure
B. intrapleural pressure is NEGATIVE
C. lung volume is at FRC
INSPIRATION
EXPIRATION
Normal Breathing Cycle
Normal Breathing Cycle
INSPIRATION Inspiratory muscles contract (diaphragm descends;
rib cage rises)↓
Thoracic cavity volume increases↓
Lungs stretched; intrapulmonary volume increases↓
Intrapulmonary pressure drops ( to -1mmHg)↓
Air flows into the lungs down its pressure gradient until intrapulmonary pressure is 0 (equal to atmospheric
pressure)
EXPIRATION Inspiratory muscles relax (diaphragm rises; rib cage
descends due to recoil of costal cartilages)↓
Thoracic cavity volume decreases↓
Elastic lungs recoil passively ; intrapulmonary volume decreases
↓Intrapulmonary pressure rises ( to +1mmHg)
↓Air flows out of lungs down its pressure gradient until
intrapulmonary pressure is 0
Physiology of respiration
In the intact lung as the thoracic cage expands the pleural and the
alveolar pressures decrease below atmospheric pressure forcing
airflow to the lung, increasing the lung volumes
QUESTIONS?
Thank you