3.2.7 PVR

Formula for PVR:

$\text{Pulmonary Ventilation Rate (PVR)} = \text{Tidal Volume (TV)} \times \text{Ventilation Rate (VR)}$

1. Tidal Volume (TV):

• The volume of air inhaled or exhaled in a single breath during normal breathing.
• Typical value: 0.5 dm³ (500 cm³) in a healthy adult.

2. Ventilation Rate (VR):

• The number of breaths taken per minute.
• Typical value: 12–20 breaths per minute in a resting adult.

Key Factors Affecting PVR:

1. Exercise:

• Tidal volume increases to bring in more oxygen and remove more carbon dioxide.
• Ventilation rate also increases, leading to a higher PVR.

2. Health Conditions:

• Respiratory diseases like asthma or chronic obstructive pulmonary disease (COPD) can reduce PVR by limiting air flow or lung capacity.
• Lung infections (e.g., pneumonia) or scarring (e.g., pulmonary fibrosis) can also impair ventilation.

3. Age:

• Lung capacity generally decreases with age, potentially reducing PVR.

Example Calculation:

If the tidal volume is 0.5 dm³ and the ventilation rate is 15 breaths per minute:

$$\text{PVR} = 0.5 \, \text{dm³} \times 15 \, \text{breaths/minute} = 7.5 \, \text{dm³/minute}$$

The pulmonary ventilation rate in this case is 7.5 dm³/minute.

Importance of PVR:

1. Oxygen Delivery:

• A higher PVR ensures that enough oxygen reaches the alveoli to meet metabolic demands.

2. Carbon Dioxide Removal:

• Maintains a low carbon dioxide concentration in the blood, preventing acidosis.

3. Indicator of Respiratory Health:

• Changes in PVR can indicate problems like lung disease or the effects of physical fitness on lung efficiency.

Adaptations for Increased PVR:

1. During Exercise:

• Both tidal volume and ventilation rate increase to supply more oxygen and remove carbon dioxide.

2. In High Altitudes:

• Ventilation rate increases to compensate for the lower oxygen concentration in the air.

Key Points to Remember:

• Tidal Volume: Volume of air per breath.
• Ventilation Rate: Number of breaths per minute.
• PVR: Total air moved in and out of the lungs per minute, calculated using the formula:

$$\text{PVR} = \text{Tidal Volume (TV)} \times \text{Ventilation Rate (VR)}$$