BlueCross and BlueShield of Montana Medical Policy/Codes
Chapter: Medicine: Tests
Current Effective Date: August 27, 2013
Original Effective Date: August 27, 2013
Publish Date: May 27, 2013

Plethysmography is the measurement and recording (by one of several methods) of variations in the size of an organ, body part, or limb reflecting the circulation of blood to that body area. 

Body plethysmography may be used for measurement of residual volume, functional residual capacity and total lung capacity.  The patient sits inside an airtight box, inhales or exhales to a particular volume (usually functional residual capacity [FRC]), and then a shutter drops across their breathing tube.  The subject makes respiratory effort against the closed shutter causing their chest volume to expand and decompressing the air in their lungs.  The increase in chest volume slightly reduces the box volume (the non-person volume of the box) and thus slightly increases the pressure in the box.  A calculation is made to determine the original volume of gas present in the lungs when the shutter was closed. Body plethysmography may be appropriate for patients who have air spaces within the lungs that do not communicate with the bronchial tree.  In these individuals, gas dilution methods of measurement would give an erroneously low volume reading. 

Body composition analysis (i.e., BOD POD Body Composition Tracking System) measures whole body mass and volume, which are then used to estimate whole body density. The patient sits in a fiberglass cabin while computerized pressure sensors determine the amount of air displaced by their bodies. Once whole body density is measured, the relative proportions of body fat and lean body mass can be calculated using population specific equations which relate body density to body fat and lean tissue masses.

Another test frequently billed as total body plethysmography is Body Composition Analyzer/Scales (Tanita).  A person's height, age, and gender are entered and the patient steps on the scales.  Within seconds, weight, body mass index and body fat percentages are displayed.  If more in-depth results are desired such as hydration levels, fat free mass, basal metabolism rate, a separate software package is available.  This type of analysis is not true plethysmography.

In vivo (in the living body, referring to a process or reaction occurring therein) body composition analysis involves prediction of total body water, extracellular water and intracellular water using the bioelectrical impedance system.

Photoplethysmography uses a light emitting diode to measure blood volume and pressure changes, based on absorption and reflection of light through the skin.  Inductance plethysmography employs sensors that are able to measure changes in a cross-sectional area of the patient, for example to measure air in the lungs or gas in the abdomen.  Capacitance plethysmography is usually done on the arm or leg to detect venous flow obstruction.  The blood volume and pressure are calculated based on the ability of the body to hold an electrical charge.  Mechanical plethysmography devices measure the amount of air or water that is displaced, which determines blood volume changes.  Electrical plethysmography devices have replaced most mechanical devices.


Prior authorization is recommended. To authorize, call Blue Cross and Blue Shield of Montana (BCBSMT) Customer Service at 1-800-447-7828 or fax your request to the Medical Review Department at 406-441-4624. A retrospective review is performed if services are not prior authorized.

Medically Necessary

BCBSMT may consider body plethysmographic determination of thoracic gas volume (VTG), airways resistance (Raw), and specific airways conductance (sGaw) medically necessary as an adjunct to complete pulmonary function testing for any of the following indications:

  • Measurement of lung volumes to distinguish between restrictive and obstructive processes; or
  • Evaluation of obstructive lung diseases, such as bullous emphysema and cystic fibrosis, which may produce artifactually low results if measured by helium (He) dilution or nitrogen (N2) washout; or
  • Measurement of lung volumes when multiple repeated trials are required, or when the subject is unable to perform multi-breath tests; or
  • Evaluation of resistance to airflow where plethysmography is necessary for accurate calculation of true lung volumes in persons with obstructive processes;  or
  • Determination of response to bronchodilators in patients who fail to show an improvement in forced expiratory volume in 1 second (FEV1) by spirometry; or
  • Determination of bronchial hyperreactivity in response to methacholine, histamine, or isocapnic hyperventilation; or
  • Diagnosis of restrictive lung disease; or
  • For following the course of established restrictive or obstructive lung disease, and response to treatment.

Not Medically Necessary

BCBSMT considers all  body plethysmography that does not meet the above criteria as an adjunct to pulmonary function testing not medically necessary including, but not limited to, measurement of body water, fat composition, or lean body mass (e.g., using such methods as bioelectric impedance, BOD POD®, or Tanita®).

Advanced Member Notice of Financial Liability for Denied Services

When the criteria for coverage is not met, BCBSMT encourages all participating providers to have a member complete and sign an Advanced Member Notification (AMN) form stating that BCBSMT will not cover this service, supply, device, or drug. If an AMN is signed prior to delivery of the service, participating providers can balance bill the patient. If an AMN is not signed, participating providers are financially liable and cannot balance bill the BCBSMT member for denied services. Services provided by an out-of-state provider that are denied as not medically necessary are the financial responsibility of the patient even if an AMN is signed.

Refer to the Advanced Member Notification medical policy for more information. The AMN form is available at  (Click on Providers and then Forms).


BCBSMT considers the following plethysmography mo­dalities are considered experimental, investigational and unproven:

  • Inductance plethysmography;
  • Capacitance plethysmography;
  • Mechanical oscillometry; or
  • Photoelectric plethysmography.

Federal Mandate

Federal mandate prohibits denial of any drug, device or biological product fully approved by the FDA as investigational for the Federal Employee Program (FEP). In these instances coverage of these FDA-approved technologies are reviewed on the basis of medical necessity alone.

Rationale for Benefit Administration
This medical policy was developed through consideration of peer reviewed medical literature, FDA approval status, accepted standards of medical practice in Montana, Technology Evaluation Center evaluations, and the concept of medical necessity. BCBSMT reserves the right to make exceptions to policy that benefit the member when advances in technology or new medical information become available.

The purpose of medical policy is to guide coverage decisions and is not intended to influence treatment decisions. Providers are expected to make treatment decisions based on their medical judgment. Blue Cross and Blue Shield of Montana recognizes the rapidly changing nature of technological development and welcomes provider feedback on all medical policies.

When using this policy to determine whether a service, supply, drug or device will be covered, please note that member contract language will take precedence over medical policy when there is a conflict.


Body Plethsymography

Spirometry is the standard method for measuring most relative lung volumes; however, it is incapable of providing information about absolute volumes of air in the lung.  Thus a different approach is required to measure residual volume, functional residual capacity, and total lung capacity.  Two of the most common methods of obtaining information about these volumes are gas dilution tests and body plethysmography.  In body plethysmography, patients sit inside an airtight chamber equipped to measure pressure, flow, or volume changes, inhales or exhales to a particular volume (usually FRC), and then a shutter drops across their breathing tube.  The subjects make respiratory efforts against the closed shutter, causing their chest volume to expand and decompressing the air in their lungs.   The most common measurements made using the body plethysmograph are thoracic gas volume (VTG) and airways resistance (Raw).  Airways conductance (Gaw) is also commonly calculated as the reciprocal of Raw.  Specific airways conductance (i.e., conductance/unit of lung volume) is routinely reported as sGaw.  Other tests that can be measured in the body plethysmograph include spirometry, bronchial challenge, diffusing capacity (DLCO), single-breath nitrogen (N2), multiple-breath N2 washout, pulmonary compliance, occlusion pressure, and cardiac output, including pulmonary blood flow.  The American Association for Respiratory care (AARC) has published Clinical Practice Guidelines that outline the indications for body plethysmography to determine VTG and RAW.

The American Thoracic Society (ATS)/European Respiratory Society (ERS) Standardization of Lung Function Testing guideline states that in healthy individuals, there are usually minimal differences in FRC measured by gas dilution/washout techniques and plethysmography. However, in patients with lung disease associated with gas trapping, most, but not all, studies indicate that FRC using plethysmography often exceeds the FRC measured by gas dilution.

Other Plethsymography

Inductance, capacitance, mechanical oscillometry and photoelectric plethysmography have not yet reached a level of development such as to allow their routine use in the evaluation of peripheral artery disease.

While plethysmography has been used to aid in the diagnosis of peripheral vascular disease, Doppler/duplex ultrasound scan has become the method of choice and gives a more accurate and definitive diagnosis.  Color flow Doppler/duplex US scans are newer and preferable methods of detecting a venous thrombus with accuracy near that of venography.  Doppler US has become the method of choice when scanning for venous occlusive disease.  Plethysmography cannot detect deep calf venous thrombus.

Plethysmographic methods need to be validated in randomized, controlled, clinical studies that include long term outcome measures to evaluate the clinical effectiveness in the diagnosis of venous and arterial diseases.

2011 Update

A search of peer reviewed literature through February 2011 identified no new clinical trial publications or any additional information that would change the coverage position of this medical policy.


Disclaimer for coding information on Medical Policies        

Procedure and diagnosis codes on Medical Policy documents are included only as a general reference tool for each policy. They may not be all-inclusive.           

The presence or absence of procedure, service, supply, device or diagnosis codes in a Medical Policy document has no relevance for determination of benefit coverage for members or reimbursement for providers. Only the written coverage position in a medical policy should be used for such determinations.           

Benefit coverage determinations based on written Medical Policy coverage positions must include review of the member’s benefit contract or Summary Plan Description (SPD) for defined coverage vs. non-coverage, benefit exclusions, and benefit limitations such as dollar or duration caps.

ICD-9 Codes
ICD-10 Codes
Procedural Codes: 94726, 94750
  1. Heijboer, H., Buller, H., et al. A comparison of Real-Time Compression Ultrasonography with Impedence Plethysmography for the Diagnosis of Deep-Vein Thrombosis in Symptomatic Outpatients.  The New England Journal of Medicine (1993 November 4) 329:1365-9.
  2. Plethysmography: Safety, Effectiveness, and Clinical Utility in Diagnosing Vascular Disease. Chicago, Illinois: Blue Cross Blue Shield  Association – Technology Evaluation Center Assessment Program (1996) (Web site/on-line 10/25/2001): .
  3. Shoemaker, W.C., et al.  Multicenter study of non-invasive monitoring systems as alternatives to invasive monitoring of acutely ill emergency patients.  Chest (1998) 114:1643-52.
  4. Venous Thrombus Cardiovascular Disorders: Peripheral Vascular Disorders. Merck Manual (1999):1792-5.
  5. American Association for Respiratory Care (AARC) clinical practice guidelines.  Body Plethysmography: 2001 Revision & Update.  Respiratory Care (2001 May) 46(5):506-13.
  6. American Academy of Respiratory Care Clinical Practice Guidelines.  Respir Care 2001; 46(5):506-13.
  7. Kraemer, R., Blum, A., et al.  Ventilation in homogeneities of specific airway resistance in young children.  American Journal of Respiratory Critical Care Medicine. (2005) 171(4):371-8.
  8. Bisgaard, H., K.G. Nielsen.  Plethysmographic measurements of specific airway resistance in young children.  Chest (2005) 128(1):355-62.
  9. Brusasco, V., et al.  ATS/ERS task force: standardisation of lung function testing.  Eur Respir J 2005; 26:511–22.
  10. FDA—510(k) Summary, Impedimed IMPSFB7 Body Composition Analyzer. US Food and Drug Administration – Center for Devices and Radiologic Health (2006 April 4).  Available at (accessed – 2009 February 9).
  11. Thomas, M.R. Rafferty, G.F., et al.  Plethysmograph and interpreter resistance measurements in prematurely born young children.  Archives of Disease in Children – Fetal Neonatal Edition (2006):F193-6.
  12. Bubb, K. S.  Venous Insufficiency.  ERadimaging (2011) 1-16.  Available at (accessed 2011, March 10).
May 2013  New 2013 BCBSMT medical policy.
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