Week 8 PT1

• The respiratory system facilitates gas exchange and responds to metabolic needs during rest and exercise.
• An understanding of the respiratory system involves how gases are exchanged to meet physiological demands.

Course Learning Outcomes

• Sketching and identifying the respiratory system's anatomy and its functions is required.
• Breathing mechanics should be described using correct terminology.
• Pulmonary function volumes should be defined with knowledge of their resting values.
• An understanding of how minute ventilation (VE) changes from rest to maximal exercise, including training effects, is needed.
• Restrictive and obstructive pulmonary disorders must be distinguished.

5 Main Topics

• The following topics are covered:
• Anatomy of the respiratory system
• Mechanics of breathing
• Lung volumes
• Ventilation during incremental exercise
• Respiratory disorders

Anatomy of the Respiratory System

• Consists of:
• Nose
• Pharynx
• Larynx
• Trachea
• Bronchi
• Lungs

Bronchi

• Includes primary, secondary, and tertiary structures.
• Terminal and respiratory bronchioles transition into alveolar ducts and alveoli.

Cartilage and Smooth Muscle

• Supportive cartilage is gradually replaced by smooth muscle as airways branch.

Smooth Muscle

• Constriction or dilation has major effects on resistance of the airway.

Conducting Airways

• Leading inspired air to the alveoli.
• The volume of these airways is the anatomic dead space (VD), around 150 mL.

Alveoli

• Small, thin-walled sacs with capillary beds.
• They are the site of O₂ and CO₂ exchange between air and blood; millions exist in the lungs.

Respiratory membrane

• Separates the air in the alveoli from the blood in the capillaries.
• It is very thin (0.6 micrometers average), which optimizes diffusion.
• The membrane has a large surface area (70 square meters in adults), about the size of one side of a tennis court.

Lungs

• Contain conducting airways, alveoli, blood vessels, and elastic tissue.

Mechanics of Breathing

• Pulmonary ventilation is the movement of air into and out of the lungs.
• Molecules move from high to low pressure areas.
• Boyle's Law states that gas pressure is inversely proportional to its volume.

Air Movement

• Air moves in and out of the lungs due to a pressure difference between pulmonary air and the atmosphere.

Compliance

• Lung compliance defines the volume change in the lung for a given change in alveolar pressure.

Inspiration

• An active process:
• The diaphragm descends, and external intercostal muscles contract.
• This increases the volume of the thoracic cavity.

Pressure

• The pressure in the thoracic cavity decreases by 1-2 mm Hg, thus causing a drop in intra-alveolar pressure.
• A negative pressure as great as -30 mm Hg below atmospheric pressure can happen inside the alveoli.
• Air flows into the lungs through respiratory tubes from the atmosphere, following the pressure gradient

Expiration

• Is generally a passive process at rest:
• The diaphragm and external intercostal muscles relax, reducing the volume of the thoracic cavity
• As a result, the pressure in the thoracic cavity increases above the atmospheric pressure.
• Following the pressure gradient, air exits the lung.

Active Expiration

Occurs during exercise:

• Secondary muscles (abdominal and internal intercostal muscles) become involved.
• Forced expiration can produce intra-alveolar pressure as high as +50 mm Hg above atmospheric pressure.

Mouth Breathing

• During exercise, it tends to replace nasal breathing, offering less resistance to airflow.
• Air passing through the respiratory passages is quickly saturated with water vapor and warmed to 37°C even under cold conditions.

Lung Volumes

• Refer to a lab manual for definitions of these different lung volume types.

Tidal Volume

• Volume of gas inspired or expired with each breath at rest or during activity.
• It equals 500 mL per inspiration or expiration at rest.

Breathing Frequency

• The rate of breaths per minute at 12 - 16.

Minute Ventilation

• Volume of gas either inspired or expired per minute.
• Minute Ventilation equals Tidal Volume multiplied by Breathing Frequency

Minute Ventilation in Resting State

• (VT X FR)
• (.5 L x 12-16 breaths/min)
• 6 - 8 liters/min

Minute Ventilation During Max Exercise

• (VT X FR)
• (3 L x 60 breaths/min)
• 180 liters/min

Expiratory Reserve Volume (ERV)

• Refers to maximal volume that can be exhaled from the end-expiratory position.
• Is approximately 25% of vital capacity (VC) at rest.

Inspiratory Capacity (IC)

• Refers to the maximal volume of gas that can be inspired from the end-expiratory position.
• Approximately 75% of vital capacity (VC) at rest.

Vital Capacity (VC)

• The greatest volume of gas that can be expelled by voluntary effort after maximal inspiration.
• It is the sum of the inspiratory capacity and expiratory reserve volume.

Residual Volume (RV)

• The volume of gas remaining in the lungs after forced expiration.

Functional Residual Capacity (FRC)

• The volume of gas remaining in the lungs at the end of a quiet exhalation.
• Composed of expiratory reserve volume plus residual volume.

Total Lung Capacity

• Vital capacity plus residual volume.

Forced Vital Capacity (FVC) Maneuver

• Instructs the subject to expire as hard and as fast as possible for four seconds.

Forced Expiratory Volume

• Volume of air expired in one second during a forced vital capacity maneuver (FEV1.0).

Alveolar Ventilation (VA)

• The volume of air that reaches the alveoli per minute.
• Important because it is the only air that participates in gas exchange with the blood.
• Anatomic dead space (VD) is subtracted from tidal volume (VD) to obtain VA.
  • VA = (FR) X (VT - VD)
  • = 12 X (500 ml - 150 ml)
  • = 12 X (350 ml)
  • = 4200 ml/min.

Body Position

• Most lung volumes and capacities decrease when a person lies down and increase when standing.
• Abdominal contents push against the diaphragm when laying down which increases intrapulmonary blood volume.

Pulmonary Tests

• Pulmonary function test norms are based on sex, age, and height and must consider population make-up.
• Tests should consider a patient's medical, occupational, and smoking history.

Ventilation During Incremental Exercise

• During exercise, minute ventilation increases linearly with exercise intensity (oxygen consumption).

Ventilation Rate

• Increases until approximately 50-60% of VO2 max. in untrained subjects and 75-80% in endurance athletes.

Ventilatory Threshold

• The point at which minute ventilation increases disproportionately with oxygen consumption during graded exercise.

Respiratory Disorders

• Chronic respiratory dysfunctions are divided into obstructive and restrictive disorders.

Obstructive Disorders

• Due to a blockage or narrowing of the airways causing increased airway resistance
• This makes it more difficult to move air in and out, often due to inflammation and edema - or smooth muscle constriction with secretions.
• Examples include asthma, bronchitis, and emphysema.
• Results in difficulties with moving air rapidly and decreased FEV1.0.
• Also a reduction of FEV1.0/VC ratio which is much less than 80%.
• May result in decreased MBC (maximal breathing capacity).

Restrictive Disorders

• Due to lung tissue damage = loss of elasticity and compliance limiting expansion of the lung
• Examples include pulmonary fibrosis and pneumonia
• -Results in lungs being stiff
• Results in reduced volumes
• May result in reduced FEV1.0 and MBC,
• FEV1.0/VC ratio is frequently 90% or greater.