From the Research
The compliance of the respiratory system is 100 ml/cmH2O. When two compliant structures are arranged in series, as the lung and chest wall are in the respiratory system, their total compliance can be calculated using the formula 1/Ctotal = 1/C1 + 1/C2. In this case, 1/Ctotal = 1/200 + 1/200 = 2/200 = 1/100, which gives us a respiratory system compliance of 100 ml/cmH2O. This means that for every 1 cmH2O increase in pressure, the respiratory system volume will increase by 100 ml. The lower compliance of the combined system compared to its individual components reflects the mechanical constraints that the chest wall and lungs place on each other during breathing. This concept is important in understanding respiratory mechanics, especially when assessing patients with respiratory disorders or those on mechanical ventilation 1.
Key Points
- The formula to calculate total compliance is 1/Ctotal = 1/C1 + 1/C2
- The compliance of the lung and chest wall are 200 ml/cmH2O each
- The total compliance of the respiratory system is 100 ml/cmH2O
- Understanding respiratory mechanics is crucial in assessing patients with respiratory disorders
Clinical Implications
The calculation of respiratory system compliance is essential in clinical practice, particularly in mechanically ventilated patients. A study published in the Journal of Clinical Monitoring and Computing 1 highlights the importance of measuring respiratory system compliance during pressure support ventilation. Although the study does not directly address the calculation of compliance, it emphasizes the need for accurate assessment of respiratory mechanics in critically ill patients. In the context of the provided question, the calculation of respiratory system compliance using the formula 1/Ctotal = 1/C1 + 1/C2 provides a straightforward answer, which is supported by the principles of respiratory physiology. However, it is essential to consider the clinical context and the potential limitations of this calculation in real-life scenarios. For instance, factors such as airway resistance, lung recruitment, and chest wall mechanics can influence the actual compliance of the respiratory system 2, 3. Therefore, clinicians should always consider these factors when interpreting the results of compliance calculations and making decisions about patient care.