(Exam 3) Pt. 5 Ventilatory and Blood-Gas Responses to Exercise Acid-Base

Ventilatory changes during exercise:

• Ventilation increases as exercise intensity [….]

•   Ventilation increases […]after beginning of exercise

• Compared to HR and VO2 peak; ventilation and VO2 start out linear and we see a spike, b/c eventually has a flexion point because of intensity. (Ventilatory threshold)

• increases

• rapidly

Ventilatory changes during constant-load moderate intensity exercise:

• When exercise is constant there is […].

• The figure implies intensity is […]

• Partial pressure of O2 and CO2 is constant; does not change.

• What changes is the amount of time we […]

•   VE increases […] at the onset of exercise followed by slower rise to steady state

•   Arterial PO2 and PCO2 are unchanged indicating excellent homeostatic control

• no threshold

• constant

• breathe

• rapidly

Changes in ventilation, blood gases, and pH during incremental exercise:

• Ventilatory threshold does not always happen at 60%.

• In untrained 50-60% and in trained individuals […]

• In elite runners when the person reaches 100% it actually 90-95%; we see drastic drop in the PO2.

•   Key points:

  • Linear increase in VE up to ~50-75% VO2 followed by exponential […] in VE (ventilatory threshold)

  •    Note differences in arterial PO2 between untrained individual versus elite trained distance runner

    • Possible causes of [….] due: short RBC transit time due to high cardiac output

• The idea is that high intensity cardiac output in athlete is very high

  • That time, specifically RBC spent on pulmonary capillaries are not enough.

  •   As a result, oxygen molecules diffuse from the alveoli compartment to the blood.

  • RBC don’t fully load with oxygen which leads to lower arterial PO2

  • This is possible and not 100% proven.

• 70-80%

• increase

• exercise-induced hypoxemia

Sex differences exist in work of breathing during exercise:

• Before maturation, boys have higher risk of asthma than girls

  •   men have […] airway and lungs

  •    women have […] airway

  •   smaller diameter […] the resistance

  • Smaller airways results in higher resistance to airflow and limitations to maximal ventilatory capacity during very heavy and severe exercise.

    •   true for airflow and blood flow.

•  When matched for […], women have smaller airways than men

• Increased airway resistance in women results in [….] work of breathing during exercise.

• larger

• smaller

• greater

• body weight

• greater

Control of ventilation at rest:

Inspiration:

• The neural pacemaker is […].

  •   Aim to […] ventilation to the metabolic rate.

• Respiratory control center is in the […]

• Output from the […] regulates motor neurons in the spinal cord that control respiratory muscles.

• Primary neural pacemaker responsible for inspiration is the preBotzinger complex (located in medulla oblongata)

• preBotizinger complex

• increase

• medullar oblongata

• respiratory control center

Control of ventilation at rest:

Expiration:

• The neural pacemaker is […]

• Function:

  •   Increases […]to help match breathing to metabolic demand

• Retrotrapezoid nucleus/ parafacial responsible for inspiration is the preBotzinger complex (located in medulla oblongata) controls active expiration.

• Input to the respiratory control center from both humoral chemoreceptors and neural sources (higher brain centers and afferent pathways) for example, muscle mechanoreceptors and chemoreceptors.

• RTN/pFRG

• ventilation

Control of ventilation at rest:

•   Pontine respiratory center:

  •   We have classes of neurons that communicate with neural pacemaker of the […] and […] muscles groups to find breathing and regulate rate and hierarchy.

  • [….] by coordinating signals between the brainstem respiratory centers.

• inspiratory and expiratory

• fine-tune breathing rhythm

Input to respiratory control center:

Humoral chemoreceptors:

• Specialized neurons that can respond to changes in the […]environment

  • Two types:

    •   […] chemoreceptors:

      • Located in the medulla 

      • Sensitive to PCO2 and H+ concentration on cerebrospinal fluid

    •   […] chemoreceptors:

      • Aortic and carotid bodies

      • Sensitive to PO2, PCO2, H+, and K+ in blood.

• internal

• Central

• Peripheral

Input to respiratory control center:

• Neural input:

•   Comes from […] receptors.

•   Has two receptors

•   Muscle [….]:

  •   Muscle spindles, Golgi tendon organs, joint pressure receptors

•    Muscle [….]:

  •   Sensitive to K+ and H+ concentration

• motor cortex and skeletal muscle

• mechanoreceptors

• chemoreceptors

Training reduces the ventilatory response to exercise:

• Endurance promotes decreasing ventilation degree moderate to high intensity exercise.

• Ventilation is […] during exercise following endurance training

  • Exercise ventilation is 20-30% lower at same submaximal work rate

• Plausible mechanisms

  • Changes in aerobic capacity of locomotor muscles

    • Result in less production of […]

    • Less afferent feedback from muscle to stimulate breathing

• lower

• H+

Endurance training does not change lung structure:

• Training does not […] lung structure

• Normal lungs exceed demand for […]

  • Therefore, training-induced adaptation is not required for the lung to maintain […] during exercise

• alter

• gas exchange 

• blood-gas homeostasis

Does the pulmonary system limit exercise performance?

•    […] intensity exercise

  • Pulmonary system does not limit exercise tolerance

• […] intensity exercise

  •   Pulmonary ventilation/gas exchange is NOT a limitation in healthy individuals at sea level at most exercise intensities

    • […] does occur during high intensity exercise (95- 100% VO2 max) and therefore, can limit [….] capacity during prolonged high intensity exercise

• Low-to-moderate

• High

• Respiratory muscle fatigue

• ventilatory

Acids and bases:

[…]

o   Any atom that is missing electrons or has gained electrons (atom with an electric charge)

• Ion

Acids and bases:

[….]

o   Can release hydrogen ions

o   Molecules that can liberate hydrogen ions (H+ )

o   Acids increase the H+ concentration in a solution (decreases pH)

• Acid

Acids and bases:

[…]

o   Can combine with hydrogen ions

o   Molecule capable of combining with (H+ )

o   Bases decrease the H+ concentration in a solution (increases pH)

• base

[…]

-          The concentration of H+ in a solution is expressed in pH units on a 0 to 14 scale.

-          pH solutions 7 are basic.

• pH scale

Hydrogen ion production during exercise:

•   High intensity leads to […] in hydrogen atoms

•   High-intensity exercise decreases muscle and blood pH

•    Contributors:

  •   Production of […]

    • CO2 + H2O «——» H+ + HCO3 –

  •   Production of lactate during high-intensity exercise coincides with acidosis

  •    ATP breakdown during muscle contraction:

    • Results in release of […]

    •   ATP + H2O «——» ADP + HPO4 - + H+

• increase

• carbon dioxide

• H+

Sport and exercise-induced disturbances in acid-base balance:

• Sports that involve high intensity: (high-intensity exercise lasting > 45 seconds produces large amount of H+.

  • Have higher risk of […]

  •    Why is this bad

    • Acidosis increases […]

    • Hydrogen binds to the troponin that impedes troponin and calcium resulting in no muscle contraction

    •   When we increase concentration of hydrogen then pH goes down and it affects enzymatic activity

•    Acidosis can impair exercise performance

  •   Contributes to […]

  • Increasing blood buffering capacity may improve performance in some events.

• acidosis

• hydrogen atoms

• muscle fatigue

Acid-base buffer systems:

•    Acid-base balance maintained by […]

  •    by releasing H+ when pH is high

  • Accept H+ ions when pH is low

•   […]

  •    Proteins, phosphate groups, and Bicarbonate

•     […]:

  •   Bicarbonate, hemoglobin, and blood proteins.

• buffers

• Intracellular buffers

• Extracellular buffers

Intracellular buffers:

• First line of defense against pH challenges

•  In skeletal muscle

• Regulates pH by recruiting or employing chemicals that can […] hydrogen ions or by recruiting hydrogen ion transporters.

  • Four major classes in the cytosol of muscle

•    Recruits these chemicals to remove ions

•   Bicarbonate

•    Phosphates

•    Cellular proteins

•    Histidine –dipeptides (primarily carnosine)

  •   Muscle pH is also regulated by H+ transporter

  • [...]

    •   Exchanges one sodium ion for one hydrogen ion

    •   Brings into the muscle one sodium ion and removes one hydrogen ion from the muscle into the interstitial space.

  •    […]

    • Co-transports, lactate and hydrogen from inside the muscle to the interstitial space.

• remove

• Sodium-hydrogen exchanger (NHE)

• Monocarboxylate Transporter (MCT)

Influence of muscle fiber type and exercise training on intracellular buffering capacity:

• Muscle buffering capacity is fiber-type specific:

  •    [….] buffering capacity is greater in Type 2 fibers compared to Type 1

    • Because we are including type 2 fibers mostly during high intensity exercises.

  •   This adaptation is advantageous in performances that rely on […] type fiber recruitment

  • Exercise training has been shown to increase intracellular content of […]

• Intracellular

• fast

• carnosine and MCTs

Extracellular buffers:

•   Most important is […] buffering system

•   3 principal buffering systems

  •    Proteins, hemoglobin, bicarbonate

  • Bases can combine with […]

  •   Bicarbonate will combine with hydrogen ion

  •    It will form […] acid; […] acid will split into water and CO2

  •    Water will then be absorbed into […] or […] (gas)

  •     CO2 leaves the body when we breathe out.

• bicarbonate

• hydrogen

• carbonic

• body or evaporate

Diets low in acids can increase plasma pH but do not improve performance during very heavy or severe exercise

• Supplementation with sodium bicarbonate (baking soda)

  •    Increase times to […]

  •    Although large doses before an exercise session can lead to nausea and vomiting and can promote alkalosis.

•   Supplementation with […]

  • Promotes […]

    • It is an antioxidant

    • Precursor to carnosine synthesis

    • Carnosine serves as an intracellular buffer and can […] time to exhaustion during high-intensity exercise (events lasting 1 to 4 minutes)

    •   Only known side effect is paresthesia (tingling of skin)

• exhaustion

• beta-alanine

• carnosine

• increase

Regulation of acid-base balance via the kidneys:

• Kidneys are important in […]

  • Kidneys do not play a key role in acid-base balance during […]

•   Kidneys contribute to acid-base balance (at rest) by regulating […] concentration in blood

  •    When blood pH […], bicarbonate excretion is reduced

  • When blood pH […], bicarbonate excretion is increased

• long-term acid-base balance

• exercise

• bicarbonate

• decreases

• increases

Regulation of acid-base balance during exercise:

• […] depends on

  • \ Exercise intensity

  •    Amount of muscle mass involved

  •   Duration of exercise

•    […] pH

  •   Declines with increasing intensity of exercise

• […] pH

  •   Declines with increasing intensity of exercise – muscle pH is lower than blood pH

    • Muscle is the site of H+ production and has lower buffering capacity.

• H+ production

• Blood

• Muscle