respiratory

Pulmonary System

Essentials of Exercise Physiology

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Respiration External respiration: ventilation and exchange of

gasses in the lungs (pulmonary function). Internal respiration: ventilation and exchange of

gasses in the tissues (pulmonary function).

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Functions of Respiratory SystemPrimary purpose of

respiratory system is:Provide means of oxygen

exchange between external environment and body

Provide a means of carbon dioxide exchange between the body and the external environment

Exchange occurs as result:Ventilation: mechanicalDiffusion: random movement

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Functions of Respiratory System

Respiratory system also helps regulate acid-base balance in body, especially during exercise.

Cl- + H+ + NaHCO3

NaCl + H2CO3

CO2 + H2O

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Acid - Base Balance

Acids - molecules which can liberate hydrogen ions

Bases - molecules which can accept hydrogen ions

Buffer - resists changes in pH by either accepting hydrogen ions or liberating them depending upon local conditions

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Structure Pulmonary System

Right and left lungs enclosed by membranes called pleura

Visceral pleura adheres to outer surface of lungs

Parietal pleura adheres to thoracic wall and diaphragm

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Intrapleural Space

Contains fluid which lubricates pleura

Creates a low pressure area– pressure is below

atmospheric during inspiration, allowing the lungs to inflate

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Functional Zones of Air Passages

Conducting zone– passageways leading to respiratory zone– area where no gas exchange occurs– nasal cavity, pharynx, larynx, trachea, bronchioles

Respiratory zone– where gas exchange actually occurs– alveoli

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Roles of Conducting Zone

Warms air Mucus traps small particles Cilia sweep particles upwards Macrophages engulf foreign particles

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Roles of Respiratory Zone

Provides large surface area for gas exchange– 600 million alveoli– Total surface area is 60 – 80 square meters or

about size of half a tennis court Provides a very thin barrier for gas exchange

– 2 cell layers thick

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Alveoli

Type II alveolar cells secrete pulmonary surfactant– form a monomolecular layer over alveolar

surfaces– surfactant stabilizes alveolar volume by

reducing surface tension created by moisture

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Mechanics of Ventilation

Change in thoracic cavity volume produces corresponding change in lung volume

Increase in lung volume results in decrease in lung pressure (Boyle’s law)

Differences in pressure pulls air into the lungs– pressure within the lungs becomes less than the

atmospheric pressure– bulk flow (from high pressure to low pressure)

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Muscles of Inspiration

Diaphragm– contracts, flattens, & moves downward up to 10 cm– enlarges & elongates chest cavity, expands volume– during quiet breathing diaphragm works alone

External intercostals, pectoralis minor, sternocleidomastoid & scaleni– lift ribs up and outwards– during exercise, accessory muscles called into play

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Muscles of Inspiration

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Muscles of Expiration

Expiration during quiet breathing is passive due to elastic recoil of chest cavity

Decrease in lung volume forces air out of lungs

During exercise and voluntary hyperventilation, – rectus abdominus, transverse abdominus: push

diaphragm up– internal intercostals: pull ribs downwards

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Total Lung Capacity Tidal volume (VT)

– amount either inspired or expired during normal ventilation

Inspiratory reserve volume– maximal volume inspired after a normal inspiration

Expiratory reserve volume– volume expired after a normal expiration

During exercise VT increases largely from IRV. Residual volume

– volume remaining in lungs after maximal expiration

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Lung Capacities Total lung capacity

– volume within lung after a maximal inspiration Inspiratory capacity

– maximal volume inspired from the end of tidal expiration

Functional residual capacity– volume in lungs after normal expiration

Vital capacity– maximal volume expired after maximal inspiration

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Dynamic Lung Volumes

Depend on volume and speed of air movement; more useful in diagnosing lung disease.

FEV: Forced Expiratory Volume. Volume that can be forcefully expired after maximal inspiration within given time, usually 1 sec.

MVV: Maximal Voluntary Ventilation. Volume of air that can be ventilated by maximal effort in one minute. Breathe maximally for 12 (or 15) seconds and total volume recorded, multiplied by five (or 4).

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Minute Ventilation Volume of gas ventilated in one minute

– equal to tidal volume times frequency– Rest in 70 kg man, 6.0 L/min = 0.5 L x 12– Maximal exercise, 120-175 L/m = 3-3.5 x 40-50– increases as oxygen consumption increases– closely associated with CO2 production

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Anatomical vs Physiological Dead Space

Anatomical dead space– areas of conducting zone not designed for

diffusion of gases– VT = VA + VD

– At rest, VT = 500 ml = 350 ml + 150 ml

Physiological dead space – areas of lung and pulmonary capillary bed which

are unable to perform gas exchange as designed

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Anatomic Dead Space

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Physiologic Dead Space Optimal diffusion requires matching of ventilation to

perfusion: 1 ventilated alveoli/ 1 blood perfused alveoli Ventilation (V) / perfusion (Q) is not equal across the

lung Top of lung is poorly perfused

– V / Q = 3.3 at top of lung Bottom of lung has more perfusion than ventilation

– V / Q = .63 at bottom of lung V / Q values above .5 are generally adequate

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Minute Ventilation in Exercise

Adjustments in breathing rate and depth maintain alveolar ventilation as exercise.

Trained athletes maintain alveolar ventilation by increasing VT and minimal increase rate.

Deeper breathing causes a greater percentage of incoming “fresh” VT to enter alveoli.

Increasing VT in exercise results from encroaching primarily on IRV or ERV?

VT plateaus at about 60% vital capacity.

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Disruptions in Normal Breathing

Dyspnea shortness of breath or subjective distress in breathing.

Hyperventilation ≠ Hyperpnea

Valsalva maneuver: forced exhalation against closed glottis. What happens to blood pressure?

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Gas Exchange

Fick’s Law Diffusion occurs at a rate which is

proportional to differences in partial pressure and the surface area available and is inversely proportional to the thickness of the membrane.

Diffusion rate = (P1 - P2) area thickness