Ventilation and Respiration

Ventilation & Respiration

• Ventilation refers to the movement of air into and out of the lungs.
• Inhalation brings oxygen into the body.
• Exhalation expels carbon dioxide from the body.

External vs. Internal Respiration

• External respiration involves gas exchange between alveoli and pulmonary capillaries, with oxygen moving in and carbon dioxide moving out.
• Internal respiration involves gas exchange between systemic capillaries and body tissues, with oxygen moving into cells and carbon dioxide moving into the blood.

Pressure Changes

• Atmospheric pressure at sea level is approximately 760 mmHg.
• Intrapulmonary pressure, or the pressure in the alveoli, equalizes with atmospheric pressure.
• Intrapleural pressure is slightly negative, around -4 mmHg at rest, which keeps the lungs inflated.
• Inspiration is driven by an increase in volume, which leads to a decrease in pressure, causing air to flow in (Boyle's Law: P ∝ 1/V).

Muscles in Breathing

• The diaphragm and external intercostals are the primary muscles used for inspiration at rest.
• Expiration at rest is passive and results from lung recoil.
• Inspiration is an active process.
• Expiration is passive at rest but becomes active during exercise.

Compliance

• Lung compliance is defined as the ease with which lungs can expand, represented by the formula C = ΔV/ΔP.
• Normal compliance depends on elasticity and surfactant.
• High compliance indicates that the lungs are easy to inflate but have difficulty recoiling, as seen in emphysema.
• Low compliance indicates that the lungs are hard to inflate, as seen in fibrosis and pneumonia.

Lung Volumes & Capacities

• Tidal Volume (TV) is the volume of a normal breath, approximately 500 mL.
• Vital Capacity (VC) is the sum of TV + IRV + ERV, approximately 4800 mL.
• Total Lung Capacity (TLC) is the sum of VC + RV, approximately 6000 mL.
• Residual Volume (RV) is the amount of air left after maximum exhalation, approximately 1200 mL.

Gas Exchange

• The respiratory membrane is a thin barrier for gas exchange, consisting of the alveolar membrane, capillary membrane, and basement membrane.
• During pulmonary gas exchange, oxygen moves from the alveoli (105 mmHg) into the blood (40 mmHg).
• Carbon dioxide moves from the blood (45 mmHg) into the alveoli (40 mmHg).
• Ventilation-perfusion coupling is the matching of air flow to blood flow in the lungs.

Gas Transport

• Oxygen is transported in the blood with 98.5% bound to hemoglobin and 1.5% dissolved.
• Factors promoting oxygen unloading (right shift) include increased CO₂, increased temperature, increased H⁺ concentration, and increased 2,3-BPG.
• A left shift indicates increased oxygen affinity, such as in fetal hemoglobin, decreased CO₂, and decreased temperature.
• Carbon dioxide is transported in the blood with 70% as bicarbonate, 23% bound to hemoglobin, and 7% dissolved.

Chloride Shift

• The chloride shift involves Cl⁻ entering RBCs as HCO₃⁻ leaves, and this process is reversed in the lungs.

Carbon Monoxide

• Carbon monoxide (CO) is dangerous because it binds to hemoglobin 200 times stronger than oxygen, leading to hypoxia.

Control of Respiration

• Respiratory centers are located in the brainstem, specifically the medulla and pons.
• The Hering-Breuer reflex prevents lung overinflation via stretch receptors.
• It isn't possible to hold breath forever because rising CO₂ levels override voluntary control.
• At high altitude, decreased O₂ leads to increased ventilation, increased RBC production, and increased 2,3-BPG.

Respiratory Chemoreceptors

• Peripheral chemoreceptors are located in the carotid and aortic bodies and monitor O₂, CO₂, and pH.
• Central chemoreceptors are located in the medulla and sense CO₂ via pH changes in the cerebrospinal fluid (CSF).
• Normal arterial pH ranges from 7.35 to 7.45.

Acid-Base Balance

• Normal urine pH ranges from 4.5 to 8.0, with an average of around 6.0.
  • Acidosis involves decreased pH and increased H⁺ concentration.
  • Alkalosis involves increased pH and decreased H⁺ concentration.
• A buffer is a substance that resists pH changes.

Body Buffer Systems

• Chemical buffers act immediately and include bicarbonate, phosphate, and protein buffers.
• Respiratory buffers adjust CO₂ levels via breathing within minutes.
• Renal buffers adjust H⁺/HCO₃⁻ excretion over hours to days.

Acid-Base Disturbances

• Respiratory disturbances involve a CO₂ problem.
  • High CO₂ indicates acidosis.
  • Low CO₂ indicates alkalosis.
• Metabolic disturbances involve an HCO₃⁻ problem.
  • Low HCO₃⁻ indicates acidosis.
  • High HCO₃⁻ indicates alkalosis.

Vomiting and Diarrhea

• Vomiting can lead to metabolic alkalosis.
• Diarrhea can lead to metabolic acidosis.

Thermoregulation

• Normal body temperature is 98.6°F / 37°C.
• Heat loss occurs through conduction, convection, radiation, and evaporation.
• Central thermoreceptors are located in the hypothalamus (core temperature).
• Peripheral thermoreceptors are located in the skin and mucous membranes (external temperature).

Temperature Disturbances

• Moderate hypothermia is indicated by a temperature range of 89.6–95°F, leading to shivering and confusion.
• Profound hypothermia is indicated by a temperature below 89.6°F, leading to no shivering and a slowed heart rate.
• Heat exhaustion symptoms include sweating, weakness, and normal mental status.
• Heat stroke symptoms include a temperature above 104°F, no sweat, confusion, and is considered an emergency.
• Shivering occurs during a fever as the body raises the temperature to a new hypothalamic set point.
• When a fever breaks, the set point drops, leading to sweating to cool down the body.