impedance plethysmography

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Related to impedance plethysmography: Impedance phlebography

im·ped·ance pleth·ys·mog·ra·phy

recording changes in electrical impedance between electrodes placed on opposite sides of a part of the body, as a measure of volume changes in the path of the current.
Synonym(s): dielectrography
Farlex Partner Medical Dictionary © Farlex 2012

impedance plethysmography

Cardiovascular disease A noninvasive method that measures changes in electrical resistance between
2 probes, which indicates changes in the volume of different regions of the body, as may be seen in obstruction to venous outflow. See Deep vein thrombosis.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


Synonym/acronym: Impedance plethysmography, PVR.

Common use

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.

Area of application

Veins, arteries, and lungs.




Plethysmography is a noninvasive diagnostic manometric study used to measure changes in the size of blood vessels by determining volume changes in the blood vessels of the eye, extremities, and neck or to measure gas volume changes in the lungs.

Arterial plethysmography assesses arterial circulation in an upper or lower limb; it is used to diagnose extremity arteriosclerotic disease and to rule out occlusive disease. The test requires a normal extremity for comparison of results. The test is performed by applying a series of three blood pressure cuffs to the extremity. The amplitude of each pulse wave is then recorded.

Venous plethysmography, done with a series of cuffs, measures changes in venous capacity and outflow (volume and rate of outflow); it is used to diagnose a thrombotic condition that causes obstruction of the major veins of the extremity. When the cuffs are applied to an extremity in patients with venous obstruction, no initial increase in leg volume is recorded because the venous volume of the leg cannot dissipate quickly.

Body plethysmography measures the total amount (volume) of air within the thorax, whether or not the air is in ventilatory communication with the lung; the elasticity (compliance) of the lungs; and the resistance to airflow in the respiratory tree. It is used in conjunction with pulmonary stress testing and pulmonary function testing.

Impedance plethysmography is widely used to detect acute deep vein thrombosis (DVT) of the leg, but it can also be used in the arm, abdomen, neck, or thorax. Doppler flow studies now are used to identify DVT, but ultrasound studies are less accurate in examinations below the knee.

This procedure is contraindicated for



    Arterial Plethysmography

  • Confirm suspected acute arterial embolization
  • Detect vascular changes associated with Raynaud’s phenomenon and disease
  • Determine changes in toe or finger pressures when ankle pressures are elevated as a result of arterial calcifications
  • Determine the effect of trauma on the arteries in an extremity
  • Determine peripheral small-artery changes (ischemia) caused by diabetes, and differentiate these changes from neuropathy
  • Evaluate suspected arterial occlusive disease
  • Locate and determine the degree of arterial atherosclerotic obstruction and vessel patency in peripheral atherosclerotic disease, as well as inflammatory changes causing obliteration in the vessels in thromboangiitis obliterans
  • Venous Plethysmography

  • Detect partial or total venous thrombotic obstruction
  • Determine valve competency in conjunction with Doppler ultrasonography in the diagnosis of varicose veins
  • Body Plethysmography

  • Detect acute pulmonary disorders, such as atelectasis
  • Detect or determine the status of chronic obstructive pulmonary disease (COPD), such as emphysema, asthma, or chronic bronchitis
  • Detect or determine the status of restrictive pulmonary disease, such as fibrosis
  • Detect infectious pulmonary diseases, such as pneumonia
  • Determine baseline pulmonary status before pulmonary rehabilitation to determine potential therapeutic benefit
  • Differentiate between obstructive and restrictive pulmonary pathology
  • Impedance Plethysmography

  • Act as a diagnostic screen for patients at risk for DVT
  • Detect and evaluate DVT
  • Evaluate degree of resolution of DVT after treatment
  • Evaluate patients with suspected pulmonary embolism (most pulmonary emboli are complications of DVT in the leg)

Potential diagnosis

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

Abnormal findings related to

  • COPD, restrictive lung disease, lung infection, or atelectasis (body plethysmography)
  • DVT (arterial, venous, or impedance plethysmography)
  • Incompetent valves, thrombosis, or thrombotic obstruction in a major vein in an extremity
  • Small-vessel diabetic changes
  • Vascular disease (Raynaud’s phenomenon)
  • Vascular trauma

Critical findings

  • DVT
  • It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

Interfering factors

    Arterial Plethysmography

  • Factors that may impair the results of the examination

    • Cigarette smoking 2 hr before the study, which causes inaccurate results because the nicotine constricts the arteries.
    • Alcohol consumption.
    • Low cardiac output.
    • Shock.
    • Compression of pelvic veins (tumors or external compression by dressings).
    • Environmental temperatures (hot or cold).
    • Arterial occlusion proximal to the extremity to be examined, which can prevent blood flow to the limb.
  • Venous Plethysmography

  • Factors that may impair the results of the examination

    • Low environmental temperature or cold extremity, which constricts the vessels.
    • High anxiety level or muscletenseness.
    • Venous thrombotic occlusion proximal to the extremity to be examined, which can affect blood flow to the limb.
  • Body Plethysmography

  • Factors that may impair the results of the examination

    • Inability of the patient to follow breathing instructions during the procedure.
  • Impedance Plethysmography

  • Factors that may impair the results of the examination

    • Movement of the extremity during electrical impedance recording, poor electrode contact, or nonlinear electrical output, which can cause false-positive results.
    • Constricting clothing or bandages.

    Nursing Implications and Procedure


    • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
    • Patient Teaching: Inform the patient this procedure can assist in evaluating blood vessel size and lung ventilation.
    • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
    • Obtain a history of the patient’s cardiovascular and pulmonary systems, symptoms, and results of laboratory tests and diagnostic and surgical procedures.
    • Record the date of the last menstrual period and determine the possibility of pregnancy in perimenopausal women.
    • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
    • Review the procedure with the patient. Address concerns about pain related to the procedure and explain to the patient that no discomfort will be experienced during the test. Explain that there may be some discomfort during insertion of the nasoesophageal catheter if compliance testing is done. Inform the patient that the procedure is generally performed in a specialized area or at the bedside by an HCP who specializes in this procedure, with support staff, and usually takes 30 to 60 min.
    • Assess the patient’s ability to comply with directions given for rest, positioning, and activity before and during the procedure.
    • For body plethysmography, record the patient’s weight, height, and gender. Determine whether the patient is claustrophobic.
    • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
    • Instruct the patient to refrain from smoking for 2 hr prior to the procedure.
    • Note that there are no food, fluid, or medication restrictions unless by medical direction.


    • Potential complications: N/A
    • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
    • Ensure the patient has refrained from smoking for 2 hr before the procedure.
    • Instruct the patient to void prior to the procedure and to change into the gown, robe, and foot coverings provided.
    • Obtain and record baseline vital signs.
    • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
    • Have emergency equipment readily available.
    • Instruct the patient to report any unexpected symptoms that occur during the test.
    • Arterial Plethysmography

    • Explain to the patient that cuffs are applied to the extremity to measure and compare blood flow.
    • Place the patient in a semi-Fowler’s position on an examination table or in bed.
    • Ask the patient to notify medical personnel if he or she has unexpected symptoms during the test.
    • Instruct the patient to remain still during the procedure.
    • Apply three blood pressure cuffs to the extremity and attach a pulse volume recorder (plethysmograph), which records the amplitude of each pulse wave.
    • Inflate the cuffs to 65 mm Hg to measure the pulse waves of each cuff. When compared with a normal limb, these measurements determine the presence of arterial occlusive disease.
    • Venous Plethysmography

    • Explain to the patient that cuffs are applied to the extremity to measure and compare blood flow.
    • Place the patient in a semi-Fowler position on an examination table or in bed.
    • Instruct the patient to remain still during the procedure.
    • Apply two blood pressure cuffs to the extremity, one on the proximal part of the extremity (occlusion cuff) and the other on the distal part of the extremity (recorder cuff). Attach a third cuff to the pulse volume recorder.
    • Inflate the recorder cuff to 10 mm Hg, and evaluate the effects of respiration on venous volume: Absence of changes during respirations indicates venous thrombotic occlusion.
    • Inflate the occlusion cuff to 50 mm Hg, and record venous volume on the pulse monitor. Deflate the occlusion cuff after the highest volume is recorded in the recorder cuff. A delay in the return to preocclusion volume indicates venous thrombotic occlusion.
    • Body Plethysmography

    • Place the patient in a sitting position on a chair in the body box. Explain to the patient that the cuffs are applied to the extremities to measure and compare blood flow.
    • Position a nose clip to prevent breathing through the nose, and connect a mouthpiece to a measuring instrument.
    • Ask the patient to breathe through the mouthpiece.
    • Close the door to the box, and record the start time of the procedure. At the beginning of the study, instruct the patient to pant rapidly and shallowly, without allowing the glottis to close.
    • For compliance testing, a double-lumen nasoesophageal catheter is inserted, and the bag is inflated with air. Intraesophageal pressure is recorded during normal breathing.
    • Impedance Plethysmography

    • Explain to the patient that cuffs are applied to the extremity to measure and compare blood flow.
    • Place the patient on his or her back with the leg being tested above the heart level.
    • Flex the patient’s knee slightly, and rotate the hips by shifting weight to the same side as the leg being tested.
    • Apply conductive gel and electrodes to the legs, near the cuffs.
    • Apply a blood pressure cuff to the thigh.
    • Inflate the pressure cuff attached to the thigh temporarily to occlude venous return without interfering with arterial blood flow. Expect the blood volume in the other calf to increase.
    • A tracing of changes in electrical impedance occurring during inflation and for 15 sec after cuff deflation is recorded.
    • With DVT, blood volume increases less than expected because the veins are already at capacity.


    • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
    • Remove conductive gel and electrodes, as applied.
    • Instruct the patient to resume usual activity and diet, as directed by the HCP.
    • Monitor for severe ischemia, ulcers, and pain of the extremity after arterial, venous, or impedance plethysmography, and handle the extremity gently.
    • Monitor respiratory pattern after body plethysmography, and allow the patient time to resume a normal breathing pattern.
    • Monitor vital signs every 15 min until they return to baseline levels.
    • Recognize anxiety related to test results, and be supportive of perceived loss of independent function. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
    • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
    • Depending on the results of this procedure, additional testing may be needed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

    Related Monographs

    • Related tests include α1-AT, angiography pulmonary, anion gap, arterial/alveolar oxygen ratio, AT-III, biopsy lung, blood gases, bronchoscopy, carboxyhemoglobin, cardiolipin antibodies, chest x-ray, chloride sweat, cold agglutinin, CBC, CBC hemoglobin, CBC WBC count and differential, CT angiography, CT thoracic, culture and smear for mycobacteria, culture bacterial sputum, culture viral, cytology sputum, d-dimer, echocardiography, ECG, EMG, ENG, fibrinogen, gram stain, IgE, lactic acid, lung perfusion scan, lung ventilation scan, lupus anticoagulant antibodies, MR angiography, MRI chest, MRI venography, osmolality, phosphorus, plasminogen, pleural fluid analysis, potassium, PET chest, PFT, pulse oximetry, sodium, TB skin test, and US arterial and venous Doppler of the extremities.
    • Refer to the Cardiovascular and Pulmonary systems tables at the end of the book for related tests by body system.
    Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners