Plethysmography

Plethysmography is a topic covered in the Davis's Lab & Diagnostic Tests.

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Synonym/Acronym:
Impedance plethysmography, PVR.

Rationale
To measure changes in blood vessel size or changes in gas volume in the lungs to assist in diagnosing diseases such as deep vein thrombosis (DVT), chronic obstructive pulmonary disease (COPD), and some peripheral vascular disorders.

Patient Preparation
There are no food, fluid, or medication restrictions unless by medical direction. Instruct the patient to refrain from smoking for 2 hr prior to the procedure.

Normal Findings

  • Arterial plethysmography:
    • Normal arterial pulse waves: Steep upslope, more gradual downslope with narrow pointed peaks
    • Normal pressure: Less than 20 mm Hg systolic difference between the lower and upper extremities; toe pressure greater than or equal to 80% of ankle pressure and finger pressure greater than or equal to 80% of wrist pressure
  • Venous plethysmography:
    • Normal venous blood flow in the extremities
    • Venous filling times greater than 20 sec
  • Body plethysmography:
    • Thoracic gas volume: 2,400 mL
    • Compliance: 0.2 L/cm H2O
    • Airway resistance: 0.6 to 2.5 cm H2O/L per sec
  • Impedance plethysmography:
    • Sharp rise in volume with temporary occlusion
    • Rapid venous outflow with release of the occlusion

Critical Findings and Potential Interventions

  • DVT

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

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