41 - Rate and rhythm of breathing. Pulmonary and alveolar ventilation. Elastic and nonelastic resistance to breathing. Air flow during breathing. The work of breathing.

sections

rate and rhythm of breathing

pulmonary and alveolar ventilation

compliance of lungs

work of breathing

elastic and non-elastic resistance

rate

• Alveolar ventilation per minute is the total volume of new air entering the alveoli and adjacent gas exchange areas each minute.

• It is equal to the respiratory rate times the amount of new air that enters the areas with each breath.

• Va= Frequency x (VT – VD)

• Va = Volume of alveolar ventilation per minute

• Frequency = frequency of respiration per minute

• VT= Tidal volume- volume of air inspired or expired per inspiration at rest- 500 ml

• VD= physiologic dead space volume

rhythm

• Eupnoea Normal respiration rate.

• Polypnoea- Rapid respiration rate.

• Tachypnoea- Very rapid and superficial respiration.

• Hyperpnoea- Deep and rapid respiration.

• Olygopnoea- Abnormally infrequent respiration.

• Beadypnoea -Abnormally slow respiration.

• Dysonoea- Difficult and laboured breathing.

• Apnea- Termination of breathing

• Asphyxia- suffocation and lack of oxygen in respired air

asphyxia

suffocation and lack of oxygen in respired air

apnea

termination of breathing

Dysonoea

difficult and laboured breathing

beadypnoea

abnormally slow respiration

olygopnoea

abnormally infrequent respiration

hyperpnoea

deep and rapid respiration

tachypnoea

very rapid and superficial respiration

polypnoea

rapid respiration rate

eupnoea

normal respiration rate

pulmonary and alveolar ventilation

• Pulmonary ventilation -inflow and outflow of air between the atmosphere and lung alveoli.

• Lungs can expand and contract in 2 ways.

  • Downward and upward movement of the diaphragm to lengthen or shorten the chest cavity.

  • Elevation and depression of the ribs to increase/decrease anteroposterior diameter of the chest cavity

• The main purpose for pulmonary ventilation is to continually renew the air in the gas exchange areas.

• These areas include the alveoli, alveolar sacs, alveolar ducts, and respiratory bronchioles. The rate at which the new air reaches these areas is called alveolar ventilation.

• Some air inhaled does not reach the gas exchange areas but simply fills the passages where gas exchange does not occur.

• Such as the nose, pharynx, and trachea. This air is called dead space air.

• On expiration, the air in the dead space is expired first, before any air from the alveoli.

• Therefore the dead space is very disadvantageous for removing expiratory gases from the lungs.

compliance of lungs

• change in lung volume per unit change in transpulmonary pressure

• Dependent on:

  • Elastic forces of the lung tissue itself- elastin and collagen fibres

  • Elastic forces caused by surface tension of the fluid that lines the inside walls of the alveoli and other lung spaces.

work of breathing

• Work of breathing = energy needed to inhale or exhale a breathing gas.

• types of work:

  • Elastic work: work required to expand the lungs against the lung and chest elastic forces

  • Resistance work: work required to overcome the viscosity of the lungs and chest wall structures

  • Airway resistance work: work required to overcome airway resistance to movement of air into the lungs

elastic and non-elastic resistance

• Work against elastic resistance:

  • this work is usually generated during inhalation phase - stored as potential energy which is released during exhalation.

• Work against non-elastic resistance

  • pressure difference is required to overcome the frictional resistance to gas flow due to viscosity (major reason for non-elastic resistance)

  • to provide movement of non-elastic components of the airway tissues to make space for pulmonary volume change