Respiratory System Notes

Respiratory System Overview

• Summarize the role of the respiratory system.

• Discuss pulmonary ventilation and its regulation.

• Examine external and internal respiration.

• Summarize oxygen and carbon dioxide transport.

Fun Facts About the Respiratory System

• Approximately 2,400 kilometers of airways.

• 300 to 500 million alveoli, with a total surface area of about 70 square meters.

• Lungs weigh roughly one kilo.

• Lungs are the only organ that can float on water.

Key Functions of the Respiratory System

• Gas exchange: intake of oxygen and removal of carbon dioxide.

• Regulation of blood pH.

• Sense of smell receptors.

• Filters inspired air and produces vocal sounds.

• Excretion of water and heat.

Types of Respiration

• Pulmonary ventilation: air moves into and out of the lungs.

• External respiration: oxygen from lungs to blood, carbon dioxide from blood to lungs.

• Internal respiration: oxygen from blood to cells, carbon dioxide from cells to blood.

• Cellular respiration: oxygen used to create energy, carbon dioxide is produced as waste.

Pulmonary Ventilation

• Movement of air into and out of the lungs.

• Inhalation: diaphragm contracts, lungs expand, air moves in.

• Exhalation: diaphragm relaxes, lungs recoil, air is forced out.

• V \propto \frac{\Delta P}{R}, airflow (V) depends on pressure gradient ($\Delta P$) and resistance (R).

Pressure Changes

• Before inspiration: atmospheric pressure and chest cavity pressure are roughly equal (760 mmHg).

• Inspiration: lung expansion decreases pressure, air flows in.

• Expiration: lung recoil increases pressure, air flows out.

• Pressure gradient drives airflow.

Partial Pressures

• Partial pressure of oxygen in the atmosphere: 159 mmHg.

• Partial pressure of oxygen in the alveoli: 105 mmHg.

• Oxygenated blood: partial pressure of oxygen about 100 mmHg.

• Systemic tissue: partial pressure of oxygen about 40 mmHg.

• Pressure gradient drives oxygen delivery to tissues.

Pulmonary Ventilation Quantification

• VE = TV \times f, pulmonary ventilation (VE) is the product of tidal volume (TV) and frequency (f).

• Resting pulmonary ventilation: roughly 6 liters per minute.

• Alveolar ventilation: considers respiratory dead space where no gas exchange occurs.

Lung Volumes and Capacities

• TLC (Total Lung Capacity): greatest amount of air in the lungs.

• TV (Tidal Volume): air inspired or expired in a normal breath.

• VC (Vital Capacity): greatest amount of air exhaled after maximal inhalation.

• RV (Residual Volume): air left in lungs after maximal exhalation.

• ERV (Expiratory Reserve Volume): greatest amount of air expired after a normal breath.

• IRV (Inspiratory Reserve Volume): greatest amount of air inspired after a normal inspiration.

• FRC (Functional Residual Capacity): air left in lungs after normal expiration.

Spirometry

• Measures lung volumes.

Regulation of Pulmonary Ventilation

• Medulla oblongata: houses inspiratory and expiratory centers.

• Pons: contains pneumotaxic and apneustic centers.

• Inspiratory center: stimulates diaphragm and intercostals (inspiration).

Respiratory Cycle at Rest

• Inspiration: 2 seconds. Nerves stimulate diaphragm and intercostals.

• Expiration: 3 seconds. Nerve impulse is interrupted, muscles relax.

Centers Within the Pons

• Pneumotaxic center: interrupts inspiratory center.

• Apneustic center: stimulates inspiratory center to maintain breathing rhythm.

Other Influences on Respiration

• Emotional or psychological factors.

• Cerebral cortex and hypothalamus.

• Systemic receptors (irritants, stretch).

• Mechanoreceptors (minor role during exercise).

• Chemoreceptors (sensitive to changes in P{a}CO2).

Chemoreceptors

• An increase of 5 mmHg in carbon dioxide triggers about a 68\%% increase in pulmonary ventilation.

• Regulation:

  • Normal partial pressure of oxygen is around 98 mmHg, little change in ventilation until very low.

  • A 5 mmHg increase in carbon dioxide significantly increases ventilation.

Key Respiratory Variables

• VA: Alveolar ventilation.

• PaO2: Partial pressure of oxygen in arterial blood.

• PvO2: Partial pressure of oxygen in venous blood.

• PaCO2: Partial pressure of carbon dioxide in arterial blood.

• PvCO2: Partial pressure of carbon dioxide in venous blood.

• a-vO2 difference: Arterial-venous oxygen difference.

• SvO2\%: Percent saturation of venous blood with oxygen.

• SaO2\%: Percent saturation of arterial blood with oxygen.

• PACO2: Partial pressure of carbon dioxide in alveoli.

External Respiration

• Gas exchange from alveoli to pulmonary capillaries, driven by pressure gradient.

• Carbon dioxide moves from 45 mmHg (pulmonary artery) to 40 mmHg (alveoli).

• Oxygen moves from 40 mmHg (arterial end) to 104 mmHg (alveoli).

Internal Respiration

• Oxygen offloading and carbon dioxide loading at the tissue level, driven by pressure gradients.

• Arterial oxygen partial pressure: 95 mmHg.

• Muscle tissue oxygen partial pressure: 40 mmHg.

• Arterial carbon dioxide partial pressure: 40 mmHg.

• Resting tissue carbon dioxide partial pressure: 45 mmHg.

Factors Influencing Respiration

• Primary: Pressure gradients.

• External respiration: Surface area and thickness of respiratory membrane, ventilation rate, oxygen-hemoglobin affinity.

• Internal respiration: Metabolic activity, blood flow, oxygen and carbon dioxide binding to hemoglobin.

Oxygen Transport

• Hemoglobin: protein in red blood cells with four heme groups that bind oxygen.

• 97 to 98.5% of oxygen transported via hemoglobin, the rest dissolved in plasma.

Oxygen Dissociation Curve

• Describes the relationship between the partial pressure of oxygen in the blood and oxygen saturation.

• Cooperative binding: Hemoglobin's affinity for oxygen increases as more oxygen molecules bind to it.

Affinity

• Higher affinity in oxygen-rich environments (lungs).

• Lower affinity in oxygen-depleted environments (working muscles).

• Shifts in temperature and pH can shift the curve left or right.

Haldane Effect

• The influence of oxygen on the binding of carbon dioxide to hemoglobin. When hemoglobin binds with oxygen, it is more inclined to release carbon dioxide. Where oxygen levels are lower, hemoglobin's affinity for carbon dioxide increases.

Bohr Effect

• The effect of blood acidity on the binding and release of oxygen by hemoglobin. In more acidic blood, hemoglobin's affinity for oxygen decreases, causing it to release more oxygen. Where blood is more alkaline, hemoglobin's affinity for oxygen increases.

Respiratory Responses to Exercise

• Short term, light to moderate aerobic exercise. Focus on pulmonary ventilation, external respiration, and internal respiration.

• Long term moderate to heavy submaximal aerobic exercise.

• Incremental to maximum aerobic exercise.

Transition from Rest to Exercise

• Initial rapid increase in minute ventilation.

• Minor blip in partial pressure of carbon dioxide.

• Small dip in partial pressure of oxygen.

Short Term Light to Moderate Aerobic Exercise - Pulmonary Ventilation

• Small increase in tidal volume.

• Slight decrease in dead space.

• Relatively steep increase in frequency.

• Relatively steep increase in minute ventilation.

Short Term Light to Moderate Aerobic Exercise - External Respiration

• Relatively sharp increase in alveolar ventilation.

• No change in the partial pressure of oxygen.

• No change in the difference in partial pressure.

• No change in saturation of oxygen. (less than 1%).

Short Term Light to Moderate Aerobic Exercise - Internal Respiration

• Steady. Little Change.

• Partial pressure of oxygen at the arterial level, again, we see it about a 95, 96 millimercury, very little change.

• Partial pressure of carbon dioxide in arterial.

• aVO2 difference increases with plateau.

Oxygen Extraction

Increased for metabolic activity.
Increase oxygen gradient, slight uptick in carbon dioxide, slight decrease in pH, increase in temperature.
Shift oxygen hemoglobin dissociation curve to the right.

Long Term Moderate to Heavy Exercise – Pulmonary Ventilation

• Steeper increase rise increase in tidal volume, over time slight dip.

• After approximately 20 to 30 minutes a need to account for increased workload causes increased frequency (breaths per minute).

• This leads to significate positive rise in minute ventilation.

• Significant increase in minute ventilation despite no change in workload is called ventilatory drift, from increase in core temperature and lactate production.

Long Term Moderate to Heavy Exercise – External Respiration

Alveolar ventilation mirrors the response from minute ventilation positive dirft.
Little change occurs. Slight change in partial of oxygen in alveolar with a similar response through time.
This indicated increase oxygen demond and potential mismatch between ventilation and perfusion.
Increase in oxygen uptake.

Long Term Moderate to Heavy Exercise – Internal Respiration

Increase in oxygen uptake, results in increase CO2 produced, we transport more CO2 back to the lung.
The venous system also has increase and carbon dioxide, and stabilize.
AVO2 drift mirrors ventilation again. With minimal change to the oxygen venous.

Incremental to Maximum Exercise

• Linear increases in tidal volume to the point of near maximal.
  Continuous increase with frequency. Steady positive increase occurs.
  Then we reach to different thresholds.
  When at near limit the respiratory frequence limits the increases in Tidal volume decreasing the amount you can breath.

Ventilatory Thresholds

At VT1 or lower intensity level can perform lipid metabolism. VT2 is the higher threshold we can go and more hyperventilations occur and rhythmic occurs.
With this again ventilation mimics VT1 and VT2.
Near max we see oxygen rise in alveoli, with no change at the arteries, leading to increase in the alveolar partial pressure difference.