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Normal Levels of Static Compliance

Lung compliance is a measurement of the relationship between changes in lung volume and lung pressure. Compliance is calculated according to a formula; lower levels of compliance make it harder for a person to breathe normally. Static compliance describes lung compliance when no air is coming in.

  1. Calculating Lung Compliance

    • When you breathe in, your lungs expand in volume and increase in pressure; when you breathe out, your lungs decrease in volume and pressure. Lung compliance is a way to measure the relationship between volume and pressure. To calculate lung compliance, doctors divide the change in lung volume by the change in lung pressure. For example, if the volume change is equal to 500 ml and the pressure change is equal to 2 cm of H2O, then the lung compliance is stated as 250 ml per cm of H2O.

    Static and Dynamic Compliance

    • Doctors can measure for two types of lung compliance. Dynamic compliance is the measurement taken immediately after the lung is expanded, when the pressure is at its highest. If the lung is left in an expanded state, the pressure will drop by about 20 or 30 percent in approximately one minute. The compliance measured in this condition is the static compliance. In all case, the dynamic compliance figure is higher than the static compliance figure.

    Normal Ranges

    • According to the "Bedside Critical Care Manual" by Edward D. Chan, a patient who is simply breathing naturally should display a static compliance level of less than 90 ml per centimeter of H2O. In a patient who is intubated but does not have lung disease, the normal range of static compliance is between 50 to 70 ml per centimeter of H2O. Normal ranges for static compliance are determined by collecting results from groups of healthy test subjects.

    Factors That Can Affect Static Compliance

    • Static compliance can be decreased by certain medical conditions, including fibrosis and pulmonary hypertension or congestion. Alveolar atelectasis is another factor that can decrease static lung compliance. Static compliance can be increased both by asthma and by the normal effects of growing older. Pulmonary emphysema has the effect of increasing static compliance while simultaneously decreasing dynamic compliance. When calculating whether a patient's static compliance is within normal ranges, doctors must consider whether any of these conditions may be present.

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