The Pulmonary System and Exercise

The Pulmonary System

Major Functions of Pulmonary System

l  Supply O2 required in metabolism

 

l  Eliminate CO2 produced in metabolism

 

l     Regulate [H2] to maintain acid-base balance

Mechanics of Ventilation

l   Inspiration (at rest)

–   Diaphragm contracts and moves downward

l  Causing outside air to be pulled into lungs due to pressure differential

–   Degree of filling due to:

l  Magnitude of inspiratory movements

l  Pressure gradient between air inside and air outside lungs

l   Expiration (at rest)

–   Passive process

l  Diaphram relaxes

l  Pressure differential (greater inside than out, so air moves out)

Mechanics of Ventilation

l  Inspiration (during exercise)

–  External intercostals and scaleni muscles pull ribs up and out

 

l  Expiration (during exercise)

–  Internal intercostals and abdominals pull ribs back down and in

Lung Volumes

l  Static – denote dimensional components of lung, i.e. how much air can be moved into or out of lungs without time limitation

 

l  Dynamic – denote power components of lung, i.e. how quickly air can be moved into or out of lung based upon time

Static Lung Volumes

Dynamic Lung Volumes

l   Depend on 2 factors:

–   Volume of air moved

–   Speed of air movement

 

l   Examples of dynamic lung volumes:

–   FEV1 – forced expiratory volume

–   FVC – forced vital capacity

–   FEV1/FVC – helps to indicate lung problems

l  e.g.  An airway obstruction is most likely evident if the FEV1/FVC is less than 70%

–   MVV – maximum voluntary ventilation (usually deep breaths for 15 sec; then multiply by 4 to determine volume in 1 minute)

Pulmonary Ventilation

l   Pulmonary ventilation – movement of air into and out of the body

      pulmonary ventilation = tidal volume* x

                   frequency of breaths per minute

         example: 0.5 L x 12 breath/min = P.V.

                                                                = 6 L/min

 

* Tidal volume – amount of air either inspired or expired in a normal breath

Alveolar Ventilation

l  The portion of minute ventilation that mixes with air in the alveolar chambers

–  Not all air inspired in single breath gets to alveoli (this air is called anatomic dead space)

l Approximates 30% of tidal volume breath

–  Deeper breaths, as in exercise, allows more fresh air to reach the alveoli

Physiologic Dead Space

l   When alveoli don’t function normally, there is poor perfusion of O2 to the body tissues

–   This is usually due to:

l  Underperfusion of O2 to the blood (hemorrhage or blockage of blood vessel)

l  Inadequate movement of fresh air to alveoli (chronic pulmonary disease)

–   Physiologic dead space is negligible in the health lung

l  With lung disease, physiologic dead space can reach 60% or greater

Response of Lung Volumes to Exercise

Disruptions in Breathing Patterns which may affect exercise

l  Dyspnea – shortness of breath or sense of difficulty in breathing during exercise

–  Due to elevated CO2 and [H+] which cause you to breathe faster – from poorly conditioned ventilatory muscles

 

l  Hyperventilation – increased ventilation (fast breathing) causes CO2 to be expired quickly; accompanied by decrease in [H+]

Valsalva Maneuver

Gas Exchange and Exercise

l  Ability to take in needed O2 for exercise is dependent on its concentration in the ambient (outside) air

l Ambient concentrations (normal)

–    20.93% O2
–    0.03% CO2
–    79.04% N2

Gas concentration vs pressure

l   Gas concentration – reflects amount of gas in a given volume (determined by gas partial pressure x solubility)

l   Gas pressure – reflects amount of force exerted by the gas against a surface

–   Partial pressure – amount of pressure exerted by a particular gas on a surface relative to pressures from other gases

l  Partial pressure = [%] x total pressure of gas mixture

Typical partial pressures and volumes (in dry air at sea level)

Movement of Gas in Air and Fluids

l   Movement of gas is based upon Henry’s Law

–   States that amount of gas dissolved in fluid depends on 2 factors

l  Pressure difference between gas in air vs gas dissolved in liquid

l  Solubility of gas in fluid

 

–   Simply stated – a gas of higher concentration will move to an area of lower concentration. The rate that it moves will depend on the ability of the gas to move in the fluid

l  E.g.  O2 moves into blood from alveoli and CO2 moves from blood to alveoli

Gas Transport

O2 Transport in Blood

l  O2 transported in 2 ways:

l In physical solution – dissolved in fluid portion of blood

l Combined with hemoglobin – connects to iron-protein component of red blood cell

–   Has O2 carrying capacity that is 65-70 times higher than dissolving in blood
–   Average hemoglobin in men = 15-16 grams/100 ml blood
–       “                “            “  women = 14 grams/100 ml blood
                                       (this is 5-10% less than men)*
                * contributes to lower aerobic capacity in women

PO2 and Hemoglobin Saturation

The Bohr Effect

l  An increase in acidity of the blood (from an increase in H+ and CO2) will shift the O2 saturation curve downward and to the right

–  Results in faster unloading of O2 to tissues

l In fatigue states- trying to bring in more oxygen due to faster unloading

l In hot environments – Hgb has harder time holding onto oxygen

CO2 Transport in Blood

l  From tissues to lungs, via the blood, CO2 is transported by:

–  In physical solution in plasma (7-10%)

–  In loose combination with Hgb (20%)

–  Combined with water as bicarbonate (70%)

Regulation of Pulmonary Ventilation

 

 

Temperature Effect on Ventilation

l  Increases ventilation via direct stimulation of neurons in the respiratory center

Receptors in lungs Effect on Ventilation

l  As lung tissue expands, stretch receptors become stimulated and begin to inhibit inspiration and stimulate expiration

Proprioceptors Effect on Ventilation

l  Sensors in the muscles send signals to increase breathing

l  Will stimulate more often as exercise intensity increases

Chemical State of Blood Effect

l   An increase in PCO2 will increase ventilation

l   An increase in [H2] will increase ventilation

l   An increase in PO2 will decrease ventilation

l  Inhaling a gas mixture of 80% or greater O2 will reduce minute ventilation by about 20%

l   A decrease in PO2 will stimulate ventilation

l  The point at which ventilation will be stimulated by a low PO2 is known as hypoxic threshold

–   Usually occurs at arterial PO2 between 60-70 mmHg

Peripheral Chemoreceptors Effect on Ventilation

–   Changes in PO2 are picked up by:

l  Aortic bodies

l  Carotid bodies

–   Provide “early warning” system when:

l   PO2 is low

l  PCO2 is high

l  Temperature increases

l  Acidity of blood increases

l  Blood pressure decreases

l  Plasma potassium decreases

 

Motor Cortex Effect on Ventilation

l  Send signals upon anticipation of exercise and beginning of exercise and cause an increase in ventilation

Integrated Ventilation During Exercise

l   Ventilation during exercise is depicted in 3 phases:

–   Neurogenic stimuli from cerebral cortex and exercising limbs cause abrupt increase in breathing at the start of exercise (Phase I)

–   After a short plateau, ventilation increases to a steady state where breathing is consistent (Phase 2)

–   “Fine tuning” of ventilatory controls from the periphery occurs based upon feedback from temperature, CO2, and [H+] (Phase 3)

Relationship of Ventilation to Lactate Accumulation