Functional diagnostics is an independent diagnostic direction that combines a variety of methods for studying the state of the body by registering and interpreting various objective physiological indicators (respiratory parameters, electrical activity of the heart, heart rate and tones, blood pressure, electrical potentials of neurons and myocytes, etc.). Functional diagnostics has its own tasks, different from instrumental and laboratory diagnostics. Functional studies provide information about the compensation or insufficiency of a particular function, i.e. about the preservation or loss of the functional ability of the organ. At the same time, the functions of the body can be studied both at rest and under conditions of special physical or medical loads.

At the same time, functional diagnostics significantly complements various imaging methods: radiography, ultrasound, endoscopy, CT and MRI. Functional diagnostic studies are used in all areas of clinical medicine without exception, but they are most widely used in cardiology, rheumatology, neurology, pulmonology.

Classification of methods

Taking into account the principles underlying the receipt of diagnostic information, electrophysiological studies (cardiovascular EPI, EPI of the neuromuscular system) and methods for studying the biomechanics of physiological processes (daily monitoring of blood pressure, FER, etc.) are distinguished. Sometimes ultrasound is also considered a functional diagnosis. In addition, functional methods are divided into studies conducted at rest (for example, ECG, spirometry, EEG) and stress studies (bicycle ergometry, treadmill test,TECS, spirometry with bronchodilators, EEG with samples).

Depending on the region and the objectives of the study are research methods:

  •  the cardiovascular system (ECG, rhythmocardiography, phonocardiography, Holter monitoring, etc.)
  •  of the circulatory system (rheography, rheoencephalography, dynamic phlebotonometry were)
  •  nervous and muscular systems (EEG, together, electromyography, etc.)
  •  external respiration (peakflowmetry, spirography, body plethysmography, etc.)
  •  blood (electrogastrography, esophageal manometry, antroduodenal manometry, anorectal manometry, synchromedia)
  • urinary system (uroflowmetry, cystometry, profilometry)
  • visual, auditory, vestibular analyzers (visometry, audiometry, vestibulometry, etc.)
  • body composition (bioimpedance)
  • fetal conditions (cardiotocography), etc.


In general, functional studies solve three main tasks: diagnostic (identification of abnormalities in the work of organs and systems), therapeutic (choice of treatment tactics, control of the effectiveness of drug or non-pharmacological therapy) and prognostic (assumption of the development and outcome of the disease). Functional diagnostic tests can be performed both for patients with various health conditions and practically healthy people.

For example, physically healthy adults are recommended to have an annual ECG as part of check-up programs. ECG is included in the list of examinations of athletes, pregnant women, patients before any surgical interventions.

As part of medical examinations of workers exposed to local or general vibration, the following functional tests are carried out: vibration sensitivity study, cold test, audiometry, electromyography. FER research is required by workers of industries associated with exposure to dust, allergens, volatile chemical compounds, etc. In all the cases listed above, regular tests of functional diagnostics allow timely detection of early signs of occupational diseases, timely preventive and rehabilitation measures, limit (or not limit) the fitness to perform professional duties.

Certain types of functional diagnostics have their own specific indications. Cardiovascular EPI is based on the registration of electrical signals emanating from the heart muscle and blood vessels. Usually, the examination of the cardiovascular system begins with a 12-lead electrocardiography, which is performed at rest. The range of indications for the study is very wide: an ECG can be prescribed if any cardiac pathology is suspected (heart defects, arrhythmias and blockages, myocarditis, heart failure, coronary artery disease and its complications), for the selection and evaluation of the effectiveness of pharmacotherapy, monitoring the condition of patients who have undergone heart surgery (including CABG and coronary stenting). Since a standard ECG records the electrical activity of the heart only for several cardiac cycles, some cardiac disorders may go unnoticed. In this case, they resort to daily ECG monitoring.

Stress tests, such as bicycle ergometry, treadmill test, transesophageal electrocardiostimulation, drug tests, etc., make it possible to diagnose coronary heart disease, assess its severity, identify latent cardiac arrhythmias that could not be recorded on an ECG at rest. A transesophageal ECG is performed when a study through the chest wall does not provide sufficient information to make a diagnosis. Phonocardiography and rhythmocardiography play an auxiliary role and are interpreted together by an electrocardiogram.

EPI of the neuromuscular system involves the registration of impulses of bioelectric activity of the brain, the assessment of the transmission of signals from nerve to muscle and their propagation through nerve and muscle fibers. Electroneuromyography is used to assess the functioning of the peripheral neuromotor apparatus in spinal cord injuries, neuroinfections, demyelinating diseases, neuritis, myopathies, and other pathologies. In order to evaluate the conduct of nerve impulses in the ascending direction, the study of evoked potentials in response to electrical stimulation of peripheral nerves is carried out.

Electroencephalography and rheoencephalography are methods of assessing the functional state of the brain. EEG recording can be performed both at rest and in conditions of additional functional tests (photostimulation, audio stimulation, hyperventilation, sleep deprivation, etc.). In some cases, night, daytime or daily EEG video monitoring is carried out. EEG finds clinical application for the diagnosis of neurological, mental and speech disorders. The most informative EEG is for detecting epilepsy. Rheoencephalography is indispensable for obtaining information about the state of the cerebral vascular bed and blood circulation in atherosclerosis, vegetative-vascular dystonia, TBI, migraines, dizziness, etc.

The study of FER includes spirography, peak flowmetry, pneumotachography and plethysmography. In functional diagnostics, these methods are used to assess the risk of developing and diagnosing bronchopulmonary pathology, monitoring the course of diseases (COPD, bronchial asthma), selecting medications, making an expert opinion when determining working capacity. When planning an operation on the respiratory organs, FER is performed to assess the degree of surgical and anesthetic risk.


Functional diagnostic tests have no age restrictions and practically have no contraindications. It is not allowed to conduct studies with a load during the period of acute infectious diseases. It is also impossible to perform them in patients who are unconscious or do not understand the instructions presented. The study of FER is not carried out in patients with hemoptysis and pulmonary hemorrhage, acute myocardial infarction, fresh stroke, hypertensive crisis due to the danger of provoking a life-threatening situation.

Certain limitations to the conduct of functional studies can create injuries and open wounds on those parts of the body on which electrodes need to be applied. The use of needle electrodes in ENMG is not recommended in patients with HIV infection due to the high risk of infection of medical staff. Performing some diagnostic procedures may be difficult in young children, patients with a high degree of obesity and mental disabilities.

The presence of an implantable pacemaker significantly changes the ECG picture, including it can mask or simulate ischemic changes. Interpretation of an electrocardiogram in such cardiac patients requires special specialist training. If the patient takes any medications on a regular basis (antiarrhythmic, sedative, bronchodilator, etc.), it is necessary to warn the specialist conducting functional diagnostics about this.

Data interpretation

Decoding and evaluation of functional research data is carried out by a functional diagnostics doctor. It accompanies the graphical, qualitative or quantitative parameters obtained during the diagnostic procedure with an expert opinion on the absence or presence and the alleged nature of violations. In the future, this information goes to the attending physician (therapist, cardiologist, neurologist, pulmonologist, rheumatologist, gastroenterologist, urologist, etc.). Comparing the results of functional diagnostics with data from other studies, a narrow specialist makes a clinical diagnosis, makes or corrects appointments, or (in the absence of a disease or recovery) gives recommendations on lifestyle and further observation.


Pneumotachography (pneumotachometry) is a technique for measuring volume-velocity air flows with forced and calm breathing. The greatest diagnostic value is the determination of the flow-volume curve with forced exhalation, which allows to judge bronchial patency, to detect the presence of obstruction at preclinical stages. During the procedure, the patient breathes into a special tube with…

Body Plethysmography

Body Plethysmography is a technique for studying the mechanics of external respiration: tracheobronchial resistance, extensibility of the lungs and chest, lung volumes, etc. The patient is placed in a special sealed cabin-a plethysmograph, in which he breathes through a tube communicating with the air outside the chamber. During the study, the breathing tube is closed…

Peak flow meter

Peak flow meter is a technique for measuring the maximum (peak) velocity of forced exhalation. Peak flow meter allows you to assess the degree of obstruction of the airways in COPD, bronchial asthma; determine the reversibility of bronchospasm; monitor the effectiveness of drug treatment. During the diagnosis, the patient makes the maximum possible inhalation and exhalation…


Spirometry is a functional study of the lungs, including the measurement of volumetric indicators of external respiration using a spirometer device. During the diagnosis, the lung volume (LV), minute ventilation (MV), reserve volumes of inhalation and exhalation (RO vd., RO vd.), inhalation capacity (E vd.), vital lung capacity (VC), forced vital lung capacity (FVC), maximal…