Ventilation and Patterns in Respiratory Therapy

Ventilatory Patterns

• Normal ventilatory pattern involves Tidal Volume (VT), Ventilator Rate (RR), and Inspiratory to Expiratory Ratio (I:E).
• VT refers to the volume of air exchanged in one quiet breath, ranging from 7-9 mL/kg.
• Typical RR is approximately 15 breaths per minute, with a normal range of 12-20 bpm.
• The I:E ratio is commonly set at 1:2.

Alveolar Ventilation vs. Dead Space Ventilation

• Alveolar ventilation includes the inspired air that effectively reaches the alveoli for gas exchange.
• Dead space ventilation represents air that doesn't reach the alveoli and can be categorized into:
  • Anatomic dead space: volume in conducting airways, approximately 1 mL/lb (or 2.2 mL/kg), totaling around 150 mL.
  • Alveolar dead space: ventilated but not perfused alveoli.
  • Physiologic dead space: total of anatomic and alveolar dead space.

Anatomic Dead Space

• The gas volume within the conducting airways constitutes anatomic dead space.
• Alveolar ventilation (VA) calculation formula: VA = (VT - VD) x breaths/min.
• Example calculation:
  • VT = 450 mL, VD = 150 mL, RR = 12 bpm, results in VA of 3.6 L.
• Breathing pattern, including depth and rate, can influence total alveolar ventilation.

Intrapleural Pressure and Regional Ventilation

• In an upright position, intrapleural pressure (Ppl) is around -7 to -10 cm H2O at the apices and -2 to -3 cm H2O at the bases.
• Upper-region alveoli have higher expansion but lower compliance compared to base regions.
• There is increased blood flow and pressure at base alveoli due to gravity, enhancing support and ventilation effectiveness in lower lung regions.

Effects of Resistance (Raw) and Compliance (CL) on Ventilatory Patterns

• In a normal state: RR of 15 bpm with VT of 500 mL.
• Decrease in compliance (CL) results in increased RR and decreased VT.
• Increase in resistance (Raw) leads to decreased RR and increased VT.
• Changes in ventilatory patterns are based on minimum work requirements, rather than efficiency.

Specific Ventilatory Patterns

• Apnea: complete absence of spontaneous ventilation.
• Eupnea: normal, spontaneous breathing.
• Biot's breathing: characterized by rapid, deep inspirations followed by 10-30 seconds of apnea, often associated with conditions like meningitis.

Ventilatory Patterns

• Normal Ventilatory Pattern includes Tidal Volume (VT), Ventilator Rate (RR), and Inspiratory to Expiratory Ratio (I:E).
• Tidal Volume (VT) is the volume of air per breath: 7-9 mL/kg.
• Respiratory Rate (RR) averages around 15 breaths per minute (12-20 bpm).
• Inspiratory to Expiratory Ratio (I:E) is typically 1:2.

Alveolar Ventilation vs. Dead Space Ventilation

• Alveolar Ventilation consists of inspired air that participates in gas exchange.
• Dead Space Ventilation refers to inspired gases that do not reach the alveoli, categorized into:
  • Anatomic Dead Space: Volume of gas in conducting airways; normal value is 1 mL/lb (about 2.2 mL/kg) with an average of ~150 mL.
  • Alveolar Dead Space: Ventilated alveoli that lack pulmonary blood flow.
  • Physiologic Dead Space: Combined value of anatomic and alveolar dead space.

Anatomic Dead Space

• Calculation of Alveolar Ventilation (VA): VA = (VT - VD) x breaths/min.
• Example calculation:
  • If VT = 450 mL, VD = 150 mL, RR = 12 bpm, then VA = 3.6 L.
• Factors affecting total VA include depth and rate of breathing.

Intrapleural Pressure and Regional Ventilation

• In an upright position, intrapleural pressure (Ppl) varies:
  • At the apices: -7 to –10 cm H2O, resulting in expanded alveoli.
  • At the bases: -2 to –3 cm H2O, leading to more blood flow and support due to gravity.
• Ventilation is more effective in lower lung regions due to better compliance at the bases.

Effects of Raw and Compliance (CL) on Ventilatory Patterns

• Normal Ventilatory Pattern: RR at 15 bpm with a VT of 500 mL.
• Decreased compliance (CL) results in:
  • Increased respiratory rate (RR).
  • Decreased tidal volume (VT).
• Increased resistance to airflow (Raw) results in:
  • Decreased RR.
  • Increased VT.
• Changes in ventilatory patterns aim to minimize work rather than optimize efficiency.

Specific Ventilatory Patterns

• Apnea: Complete absence of spontaneous ventilation.
• Eupnea: Normal, spontaneous breathing.
• Biot’s Breathing: Characterized by rapid deep inspirations followed by 10-30 seconds of apnea, often associated with conditions like meningitis.