RESPIRATORY MOVEMENTS
Respiratory Movements
Overview: Understanding respiratory movements is essential for studying human physiology, specifically the mechanics of breathing and gas exchange.
Structure and Function of the Respiratory System
Lower Respiratory Tract:
Trachea: Conveys air from pharynx to bronchi.
Bronchi: Branching airways in the lungs.
Lungs: Contain alveoli responsible for gas exchange.
Upper Respiratory Tract:
Nose: Passageway for air.
Nasal Cavity: Filters, warms, and moistens air.
Pharynx: Common passage for air and food.
Larynx: Routes air and food, also known as "voice box."
Mechanics of Breathing
Inspiration:
Rib cage expands, lungs stretch, diaphragm moves downwards, causing a decrease in alveolar pressure which draws air into the lungs.
Expiration:
Rib cage contracts, lungs contract, diaphragm moves upwards, increasing alveolar pressure and pushing air out of the lungs.
Gas Laws Relevant to Respiration
Kinetic Theory of Gases:
Pressure is generated by collisions of gas molecules; more collisions equal higher pressure.
Charles' Law:
Volume increases with an increase in temperature (
).
Boyle’s Law:
Pressure is inversely proportional to volume at constant temperature (
).
Gas Exchange and Diffusion
Alveolar Gas Exchange: Involves the exchange of oxygen and carbon dioxide across the alveolar and capillary membranes, influenced by partial pressure gradients (e.g.,
P{AO2} > P{VO2} and
P{ACO2} < P{VCO2} ).Composition During Inhalation:
O2: 21%, CO2: 0.03-0.04%, during Exhalation O2: 14%, CO2: 5%.
Ventilation-Perfusion Ratios
Definition: Ratio of alveolar ventilation (
) to blood flow (
).Normal VA/Q Ratio: Approximately 1, indicating balanced gas exchange.
Shunt:
When ventilation is impaired but perfusion is normal; results in low PAO2 and high PACO2.
Dead Space:
Normal ventilation with impaired perfusion; leads to a high PAO2 and low PACO2.
Ventilation Calculations
Pulmonary Ventilation Rate (PVR):
Formula:
Example: At rest, 12 breaths/min x 0.5 l/breath = 6 l/min.
During exercise, can reach up to 120 l/min.
Practice Questions
Example Problem: Evaluate if an artificial ventilated patient at 20 breaths/min with a tidal volume of 250 ml is receiving adequate alveolar ventilation (normal ~ 4000 ml/min).
Question on Gas Composition: Calculating partial pressure of gases in a mixture of dry air given % composition and atmospheric pressure of 760 mmHg.
Understanding respiratory movements is essential for studying human physiology, specifically the mechanics of breathing and gas exchange.
Structure and Function of the Respiratory System
Lower Respiratory Tract:
Trachea: Conveys air from the pharynx to bronchi, supported by C-shaped cartilage rings that prevent collapse.
Bronchi: Branching airways in the lungs that distribute air to each lung and subdivide into smaller bronchioles.
Lungs: Contain alveoli responsible for gas exchange; surrounded by pleura that reduce friction during respiration.
Upper Respiratory Tract:
Nose: Main passageway for air that also serves to filter incoming particles.
Nasal Cavity: Warms, filters, and moistens air using mucous membranes; includes turbinates that create turbulence for filtration.
Pharynx: Common passage for air and food, divided into nasopharynx, oropharynx, and laryngopharynx.
Larynx: Routes air and food to the appropriate channels and houses the vocal cords, functioning in sound production.
Mechanics of Breathing
Inspiration:
The rib cage expands due to intercostal muscle contractions, the diaphragm contracts and moves downwards, resulting in a decrease in alveolar pressure. This pressure gradient draws air into the lungs, filling the alveoli with fresh oxygen.
Expiration:
The rib cage returns to its resting position, the diaphragm relaxes and moves upwards, increasing alveolar pressure which forces air out of the lungs, primarily through passive recoil and intercostal muscle relaxation.
Gas Laws Relevant to Respiration
Kinetic Theory of Gases:
Gas pressure is generated from the collisions of gas molecules; an increase in molecule collisions correlates with higher pressure.
Charles' Law:
Volume increases with a temperature increase, defined mathematically as ( V \text{ is proportional to } T ).
Boyle’s Law:
At constant temperature, pressure is inversely proportional to volume, expressed as ( P \text{ is proportional to } \frac{1}{V} ).
Gas Exchange and Diffusion
Alveolar Gas Exchange:
Oxygen and carbon dioxide exchange occurs across the alveolar and capillary membranes, driven by partial pressure gradients, such that ( P{AO2} > P{VO2} ) indicates diffusion of oxygen, while ( P{ACO2} < P{VO2} ) indicates diffusion of carbon dioxide.
Composition During Inhalation:
O2: 21%, CO2: 0.03-0.04%
During Exhalation:
O2: 14%, CO2: 5%.
Ventilation-Perfusion Ratios
Definition:
The ratio of alveolar ventilation (( V_A )) to blood flow (( Q )).
Normal VA/Q Ratio:
Approximately 1, indicating efficient gas exchange where ventilation matches perfusion.
Shunt:
Occurs when ventilation is impaired but perfusion remains normal, leading to low oxygen (( PAO2 )) and high carbon dioxide (( PACO2 )).
Dead Space:
Represents normal ventilation with impaired perfusion; results in high oxygen and low carbon dioxide in the blood.
Ventilation Calculations
Pulmonary Ventilation Rate (PVR):
Defined by the formula: ( PVR = \text{Frequency of Respiration} \times \text{Tidal Volume} ).
Example: At rest, 12 breaths/min x 0.5 L/breath = 6 L/min. During exercise, PVR can increase to about 120 L/min.
Practice Questions
Example Problem:
Analyze whether an artificially ventilated patient at 20 breaths/min with a tidal volume of 250 ml is receiving adequate alveolar ventilation (normal ~ 4000 ml/min).
Question on Gas Composition:
How to calculate the partial pressure of gases in a mixture of dry air based on percentage composition and the atmospheric pressure of 760 mmHg.