Block 3 Objective 2b

Identify relationships and general principles about gas exchange as it relates to the respiratory system.
- The mechanical movement of air into and out of the airways in a cycle fashion
- Alveolar ventilation-ventilation of alveoli that are being perfused and adequate gas exchange is taking place
- Dead Space Ventilation-volume of gas that is ventilated, but not physiologically effective (Anotomic, Alveolar, and Physiologic)
Anatomic Dead Space
- The volume of air contained in the pulmonary conducting system that is not involved in gas exchange
- Rule of Thumb-1ml/lb body weight
- Abbreviated as VDanat
Alveolar Dead Space
- The ventilation of an alveoli that is not being perfused (the passing of blood or fluid through a vascular bed) via the pulmonary capillary bed therefore has no gas exchange
- If significant it indicates a pulmonary pathological disease
- Abbreviated VDalv
Physiologic Dead Space
- The portion of inhaled air that does not take part in pulmonary gas exchange
- Combination of anatomic and alveolar dead space
- Abbreviated VDphy
Clinical Terms Associated with Ventilation
- Normal Ventilation-the amount of minute ventilation (also referred to as respiratory rate or tidal volume) to provide adequate alveolar ventilation and fulfill the body's gas exchange needs
- Hypoventilation-the state of impaired breathing where the alveoli are inadequately ventilated to fulfill the body's gas exchange needs
- Hyperventilation-an over-aeration of the alveoli beyond gas exchange needs (may be voluntary or involuntary)
Volumes and Capacities
- Vital Capacity (VC)-the amount of air that is maximally exhaled after a maximal inhalation
- Residual Volume (RV)-the amount of air remaining in the lungs at the end of a maximal exhalation
- Total Lung Capacity (TLC)-the amount of air remaining in the lungs after a maximal inhalation
- Functional Residual Capacity (FRC)-the amount of air remaining in the lungs at the end of a normal resting exhalation
- Refers to the molecular gas exchange of oxygen and carbon dioxide
- External Respiration-exchange of gases between the alveoli and the pulmonary capillaries
- Internal Respiration-the exchange of gases between systemic capillaries and tissue cells
Pulmonary Blood Volume
- The volume of blood between the beginning of the pulmonary artery and the end of the pulmonary veins
About 900 to 1000ml (healthy adult)
- 30% (p) arteries
- 10% (p) capillaries
- 60% (p) veins
Pulmonary Capillary Blood Volume
- The volume of blood in the capillary bed at any given moment
- Contains about 100ml at any given time (healthy adult)
- At rest, complete oxidation of the RBC takes 0.75 seconds
- During exercise oxidation of the RBC takes 0.35 seconds
- About 95% of the diffusion of O2 takes place before the blood has passed halfway along the pulmonary capillaries
Pulmonary Blood Flow
- 100ml/sec
Effected by gravity
- Supine or Prone-close to uniform blood flow
- Erect Position-non uniform blood flow
Pulmonary Vessels
- In general are shorter, thinner, and more distensible and contain less smooth muscle than systemic blood vessels
- Hold a larger volume in relation to their systemic counterparts, due to the smaller amount of muscle tissue
Pulmonary Artery Pressures
- Systolic-25mmHg
- Diastolic-8mmHg
- Reflect right ventricular systolic pressures
- Hypoxia is a potent constrictor