Chapter 12 Pulmonary Structure and Function Exercise Physiology: Energy,

Transcription

Chapter 12
Pulmonary Structure and Function
Copyright © 2007 Lippincott Williams & Wilkins.
McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance, Sixth Edition
Anatomy of Ventilation
• Pulmonary ventilation
– Process of air moving in and out of lungs
• Anatomy
– Trachea
– Bronchi
– Bronchioles
– Alveoli
The Lungs
• Provide a large surface area (50 − 100 m2)
• Highly vascularized to allow for gas
exchange
The Alveoli
• The lungs contain 600 million
membranous sacs called alveoli.
• Characteristics of alveoli
– Elastic
– Thin walled
• Very small blood–gas barrier
The Alveoli
• Pores of Kohn allow for even dispersion of
surfactant.
• Surfactant decreases surface tension.
• Pores also allow for gas interchange
between alveoli.
Mechanics of Ventilation
• Conducting zone (anatomic dead space)
– Trachea
– Bronchioles
• Respiratory zone
– Respiratory bronchioles
– Alveolar ducts
– Alveoli
Fick’s Law
• Explains gas exchange through the alveolar
membranes
• Gas diffuses through a tissue at a rate
proportional to surface area and inversely
proportional to its thickness.
Inspiration
• During inspiration
– Diaphragm contracts and flattens
– Chest cavity elongates and enlarges and air
expands in lungs
– Intrapulmonic pressure decreases
– Air is sucked in through nose and mouth
Expiration
• During rest and light exercise, expiration is
predominantly passive.
– Stretched lung tissue recoils
– Inspiratory muscles relax
– Air moves to atmosphere
• During strenuous exercise
– Internal intercostals and abdominal
muscles assist
Surfactant
• Resistance to expansion of the lungs increases
during inspiration due to surface tension on alveoli.
• Surfactant _ a lipoprotein mix of phospholipids,
proteins, and Ca2+ produced by alveolar epithelial
cells _ mixes with fluid around alveoli.
• Surfactant disrupts and lowers surface tension.
Lung Volumes & Capacities
• Are measured using a spirometer
• Lung volumes vary with
– Age
– Size (mainly stature)
– Gender
Static Lung Volumes
•
•
•
•
TV: Tidal volume: 0.4 − 1.0 L air/breath
IRV: Inspiratory reserve volume: 2.5 − 3.5 L
ERV: Expiratory reserve volume: 1.0 − 1.5 L
IRV and ERV decrease during exercise as
TV increases
• FVC: Forced vital capacity: 3 − 5 L
Residual Lung Volume
• RLV averages 0.8 − 1.4 L
• RLV increases with age as lung elasticity
decreases.
Total Lung Capacity
RLV + FVC = TLC
Dynamic Lung Volumes
• Dynamic ventilation depends upon
– Maximal FVC of lungs
– Velocity of flow
• Velocity of flow is influenced by lung
compliance.
FEV-to-FVC Ratio
• FEV1/FVC indicates pulmonary airflow
capacity.
• Healthy people average ~ 85% of FVC in
1 second.
• Obstructive diseases result in significant
lower FEV1/FVC.
Maximum Voluntary Ventilation
• MVV evaluates ventilatory capacity with
rapid and deep breathing for 15 seconds.
– MVV = 15 second volume × 4
• MVV in healthy individuals averages 25%
> ventilation than occurs during max
exercise.
Exercise Implications
• Gender Differences in Static and Dynamic
Lung Functional Measures
– Women have smaller lung function measures
than men.
– Highly fit women must work harder to maintain
adequate alveolar-to-arterial O2 exchange.
Lung Function, Aerobic Fitness, and
Exercise Performance
• Little relationship exists among diverse
lung volumes and capacities and exercise
performance.
• Maximum exercise is not limited by
ventilation.
Pulmonary Ventilation
• Volume of air moved into or out of total
respiratory tract each minute
• Air volume that ventilates only alveolar
chambers each minute
Minute Ventilation
• Minute ventilation
– Volume of air breathed each minute VE
• Minute ventilation increases dramatically
during exercise.
– Values up to 200 L · min-1 have been reported.
– Average person ~ 100 L · min-1
• Despite huge VE, TVs rarely exceed 60% VC.
Alveolar Ventilation
• Anatomic dead space
– Averages 150 − 200 mL
• Only ~ 350 mL of the 500 mL TV enters
alveoli.
Dead Space vs. Tidal Volume
• Anatomic dead space increases as TV
increases.
• Despite the increase in dead space,
increases in TV result in more effective
alveolar ventilation.
Ventilation−Perfusion Ratio
• Ratio of alveolar ventilation to pulmonary blood
flow
• V/Q during light exercise ~ 0.8
• V/Q during strenuous exercise may increase up to
5.0.
Physiologic Dead Space
• Occurs when there is either
1. Inadequate ventilation
2. Inadequate blood flow
Rate vs. Depth
• During exercise, both rate and depth of
breathing increase.
• Initially, larger increases in depth occur.
• Followed by increases in rate and depth
Hyperventilation
• An increase in pulmonary ventilation that
exceeds O2 needs of metabolism
• Hyperventilation decreases PCO2.
Dyspnea
• Subjective distress in breathing
• During exercise, respiratory muscles may
fatigue, resulting in shallow, ineffective
breathing and increased dyspnea.
Valsalva Maneuver
• Closing the glottis following a full
inspiration while maximally activating the
expiratory muscles
• Causes increase in intrathoracic pressure
• Helps stabilize chest during lifting
Physiologic Consequences of
Valsalva Maneuver
• An acute drop in BP may result from a
prolonged Valsalva maneuver.
– Decreased venous return
– Decreased flow to brain
• Dizziness or fainting result
Respiratory Tract During
Cold-Weather Exercise
• Cold ambient air is warmed as it passes
through the conducting zone.
• Moisture is lost if the air is cold and dry.
• Contributes to
– Dehydration
– Dry mouth
– Irritation of respiratory passages
Postexercise Coughing
• Related to water loss and the drying of the
throat

Chapter 12 Pulmonary Structure and Function Exercise Physiology: Energy,

Transcription

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