HNES 465 Chapter 9

Three major functions of the ventilatory system

• supply O₂ required in metabolism

• Eliminate CO₂ produced in metabolism

• Regulate hydrogen ion concentration [H⁺] to maintain acid-base balance

What does the ventilatory system do?

meets the body’s needs to maintain efficient gas exchange

What are the components of the ventilatory system?

• nose and mouth

• trachea

• bronchi

• bronchioles

• alveoli

inspiration

diaphragm contracts and moves downward, the air in the lungs expands, pressure differential between lungs and ambient air sucks air in through the nose to inflate lungs

Expiration

predominantly passive process, air moves out of the lungs from recoil, sternum and ribs swing down

Tidal volume (TV)

air moved during inspiratory or expiratory phase of breathing cycle; between 0.4 to 1.0 L of air per breath

Inspiratory reserve volume (IRV)

2.5 to 3.5 L above TV; serves as inhalation reserve

Expiratory Reserve Volume (ERV)

after normal exhalation, additional volume exhaled; 1.0 to 1.5 L for men, 10 to 20% lower for women

Forced vital capacity (FVC)

total air volume moved in 1-breath from full inspiration to max expiration; varies with body size and body position when measuring

Residual lung volume (RLV)

following max exhalation, air volume that cannot be exhaled; 1.2 to 1.6 L for men, 1.0 to 1.2 L for women

What are the dynamic measures of pulmonary ventilation

max air volume expired (FVC)

speed of moving a volume of air

FEV_1.0

percentage of FVC expelled in 1 second

FEV_1.0/FVC

reflects expiratory power and overall resistance to air movement in lungs; averages ~85%

Maximum voluntary ventilation

rapid, deep breathing for 15 sec extrapolated to volume for 1 min; ranges between 140 to 180 L*min^-1 for men, 80 to 120 L*min^-1 for women

Gas concentration

amount of gas in a given volume determined by product of gas partial pressure and solubility

Gas pressure

force exerted by gas molecules against surfaces they encounter

Partial pressure

percentage concentration x total pressure of gas mixture

Ambient air

PO₂ = 159 mmHg; PCO₂ = 0 mmHg; PN₂ = 600 mmHg

Tracheal Air

PO₂ = 149 mmHg; PCO₂ stays the same

Alveolar Air

PO₂ = 103 mmHg; PCO₂ = 39 mmHg

Henry’s Law

amount of gas dissolved in fluid depends on:

pressure differential between gas above fluid and dissolved in it

solubility of gas in fluid

Three factors account for dilution of O₂ in inspired air as it passes into alveolar chambers

water vapor saturates relatively dry inspired air

O₂ continually leave alveolar air

CO₂ continually enters alveolar air

Blood transports oxygen in two ways

physical solution

combined with Hb

physical solution

dissolved in fluid portion of blood; establishes PO₂ of blood and tissue fluids

combined with Hb

in loose combination with iron-protein Hb molecule in RBC; increases blood’s oxygen-carrying capacity 65 to 70 times above normal

Men: each 100 mL of blood contains approximately 15 to 16 g Hb

Women: 5-10% less; 14 g per 100 mL of blood

Minute Ventilation (V_E)

Breathing rate x Tidal volume

Functional residual capacity

volume in lungs after tidal expiration

Percentage saturation of Hb

(Total O₂ combined with Hb / Hb O₂ - carrying capacity) x 100

myoglobin

iron protein within skeletal and cardiac muscle that carries oxygen to mitochondrion

Increases in acidity and temperature cause oxyhemoglobin dissociation curve to shift _________________ to reflect enhanced unloading

downward and to the right

Blood transports CO₂ to lungs in three ways

physical solution in plasma (7-10%)

loose combination with Hb (20%)

combined with water as bicarbonate (70%)

chemoreceptors

structures that stimulate ventilation in response to increased CO₂, temperature, acidity, decrease in O₂ and BP, and probable decline in circulating K⁺ ions

What provides the most important respiratory stimulus at rest?

CO₂ pressure in arterial plasma

cortical influence

neural outflow from regions of motor cortex during PA and cortical activation in anticipation of PA stimulate respiratory neurons in medulla

peripheral influence

sensory input from joints, tendons, muscles adjust ventilation during PA

Phase I ventilation

When PA begins, neurogenic stimuli from cerebral cortex and active limbs cause initial breathing increase

Phase II ventilation

central command input plus medullary control neurons and peripheral stimuli from chemoreceptors and mechanoreceptors contribute to control minute ventilation, gradually increasing to a steady level

Phase III ventilation

“fine tuning” of ventilation through peripheral sensory feedback mechanism

Ventilatory equivalent for oxygen (V_E/VO₂)

ratio of minute ventilation to VO₂

remains relatively constant during steady-rate PA

ventilatory equivalent for carbon dioxide (V_E/VCO₂)

ratio of minute ventilation to O₂ produced

remains constant during steady-rate PA because pulmonary ventilation eliminates CO₂ produced during cellular respiration

Despite variations in ventilatory equivalents among healthy people, complete aeration of blood takes place because of 2 factors:

alveolar PO₂ and PCO₂ remain at near-resting value

transit time for blood flowing through pulmonary capillaries proceeds slowly enough to allow complete gas exchange

Tvent

point at which PV increases disproportionately with VO₂ during graded activity

Tvent formula

Lactate + NaHCO₃ → Na lactate + H₂CO₃ → H₂O + CO₂

anaerobic threshold

the abrupt increase in Tvent caused by nonmetabolic CO₂ production from lactate buffering

Onset of blood lactate accumulation (OBLA)

sharp upswing in pulmonary ventilation related to VO₂ during incremental activity

occurs between 55 to 65% VO_2max in healthy untrained subjects and often equals > 80% VO_2max in highly trained endurance athletes

OBLA point increases with aerobic training without accompanying increase in VO_2max

Two factors influence endurance performance

VO_2max

max level for steady-rate activity (OBLA)

Two factors determine energy requirements of breathing

compliance of lungs and thorax

resistance of airways to smooth airflow

What buffers provide rapid first line of defense in acid-base regulation?

bicarbonate, phosphate, and protein chemical

what contributes to pH regulation through changes in alveolar ventilation that rapidly alter free H⁺ concentration in extracellular fluids

lungs

what acts as the body’s final defense by secreting H⁺ into urine and reabsorbing bicarbonate

renal tubules