Tuberculosis - I. T. Pyatnochka 2005

Methods of examination of tuberculosis patients
Assessment of external respiration function

Respiration is generally divided into external and internal. The primary function of the Lungs is respiratory, meaning a vital process aimed at maintaining a steady gas exchange—specifically of oxygen and carbon dioxide—between the external environment and the Organism. This process is referred to as external respiration. Physiologically, external respiration (pulmonary respiration) involves the exchange of gases between the air that has entered the lungs (alveolar air) and the Blood of the Pulmonary Circulation. Internal respiration (tissue respiration) refers to the gas exchange between the capillary blood of the systemic circulation and the body's Tissues and Cells.

Respiration is carried out by the Respiratory system, which comprises the Upper Respiratory Tract (Nasal cavity, nasopharynx, Larynx), Trachea and Bronchi, lungs, Pleura, thoracic cage with Respiratory Muscles, and the neural regulation apparatus. Overall, breathing occurs through the interaction of the respiratory, circulatory, and hematologic systems and encompasses three main processes.

External respiration involves gas exchange between the external environment and the blood. This includes pulmonary ventilation—the exchange of air between the external environment and the pulmonary alveoli.

Diffusion is The process of gas exchange between the alveolar air and the pulmonary capillary blood, which occurs via passive diffusion.

Perfusion refers to microcirculation (the flow of blood through the alveolar capillaries).

Gases diffuse across the blood-air barrier in a direction determined by the differences in their partial pressures (tensions). Respiratory disorders can occur at any of these stages.

Assessing external respiratory function—specifically its final outcomes—allows clinicians to distinguish between normal physiological states and pathological conditions of the respiratory system, determine The Nature and severity of respiratory failure, and evaluate the efficacy of therapeutic and prophylactic measures as well as patient prognosis. However, functional testing cannot replace other conventional diagnostic Methods; only a comprehensive, multidisciplinary approach can provide an objective Assessment of the body's functional state.

In phthisiology and pulmonology, external respiratory function testing is performed to monitor Treatment efficacy, determine surgical operability, and assess patients' work capacity.

Methods for evaluating external respiratory function include spirometry, spirography, pneumotachometry, pneumotachography, body plethysmography, and the analysis of blood gases and acid-base balance.

Spirometry is the simplest method for measuring vital capacity (VC). On average, VC is about 3.5 L (ranging from 3 to 5 L in men, and from 2 to 3.5 L in women).

Spirography is a method used to study the functional state of the lungs by recording ventilation parameters (respiratory fluctuations) as a function of volume over time on a moving millimeter paper strip. Knowing the scale factor of the spirograph and the paper speed allows for the calculation of basic lung volumes and capacities. Oxygen uptake and utilization are determined from the upward slope of the spirogram.

The key spirographic parameters include forced expiratory volume in 1 second (FEV₁), vital capacity (VC), and the Tiffeneau index (FEV₁/VC %). Additional parameters—such as maximum voluntary ventilation (MVV), peak expiratory flow rate (PEFR), respiratory rate (RR), tidal volume (TV), minute ventilation (MV), oxygen utilization coefficient (OUC), and others—are of auxiliary significance.

Spirography is performed using various models of closed-circuit spirographs, such as the SG-1, Metatest-1, and Metatest-2, which consist of a spirometer and a recording device. As the patient breathes the air within the system, the recording pen moves to trace a spirogram on paper. Thus, spirography is a graphical method for assessing external respiratory function using closed-circuit devices known as spirographs.

Analyzing spirographic results involves converting the recorded physiological data from a graphical format into digital values, calculating derived functional parameters, and correcting the obtained gas volumes to standard conditions (STPD). This requires data such as the patient's sex, height, weight, and age, as well as barometric pressure, ambient Temperature at the time of testing, and humidity.

The actual spirographic values obtained are compared against predicted values (individual normal standards). In each specific case, the predicted value is taken as 100%, and the measured value is expressed as a percentage of the predicted norm. Values within ±20% of the predicted figures are considered normal. A reduction in FEV₁, VC, and MVV to 60–79% of the predicted value is considered mild impairment, 40–59% as moderate, and 39% or lower as severe.

Regarding the Diagnosis of ventilatory disorders, a decreased FEV₁/VC % is interpreted as evidence of bronchial obstruction, whereas a reduced VC in the presence of a normal FEV₁/VC ratio serves as a diagnostic sign of restriction. A simultaneous decrease in both VC and FEV₁/VC % may indicate mixed obstructive-restrictive pathology accompanied by pronounced bronchial obstruction.

A limitation of conventional spirography is its inability to detect impairments in small airway patency.

In recent decades, spirographs have been largely replaced by computerized systems. Most computerized devices simultaneously generate a graphical spirogram and provide digital readouts of its interpretation, along with quantitative characteristics of ventilation and bronchial patency. The most effective Methods for Assessing small airway patency are pneumotachometry and pneumotachography.

Pneumotachometry (PTM) is a simple and sensitive method for evaluating bronchial patency. A pneumotachometer is used to measure the peak flow velocity of the airstream during inspiration and expiration. Maximum expiratory flow ranges from 5 to 8 L/s in men and from 4 to 6 L/s in women.

Pneumotachography is an objective and highly accurate method for studying external respiration and respiratory mechanics. It involves the graphical recording of airflow velocities during inspiration and expiration. Essentially, pneumotachography measures volumetric flow rate and pressure across different phases of breathing (both quiet and forced). It is performed using a universal pneumotachograph. The method is based on recording pressure changes at various points of the airstream corresponding to the respiratory cycle. Pneumotachography makes it possible to determine inspiratory and expiratory airflow velocities (normally 300–500 mL/s during quiet breathing and 5–8 L/s during forced breathing), the duration of respiratory cycle phases, minute ventilation, intra-alveolar pressure, airway resistance, lung and chest wall compliance, and the work of breathing, as well as to analyze pressure-volume, pressure-flow, and flow-volume loops.

Specialized computerized analyzers (such as Pneumoscreen and Ultrascreen, manufactured in Germany) provide various metrics of respiratory mechanics (static and dynamic volumes, flow-volume criteria, airway resistance, etc.) and compare them against predicted values stored in the computer's memory.

The pneumotachograph records the forced expiratory flow-volume curve. To obtain this, much like measuring forced vital capacity (FVC) during spirometry, the patient takes a maximal deep inspiration followed by a forceful, rapid, and complete expiration. The Procedure is repeated until two reproducible results are achieved.

Modern computerized analyzers record the flow-volume curve along with its quantitative parameters expressed as percentages of predicted values. The abscissa represents the forced expiratory volume (FVC), taken as 100%, and the ordinate represents the airflow in liters per second. Peak, instantaneous, and mean flow rates are calculated at 25%, 50%, and 75% of FVC—namely, peak expiratory flow (PEF), MEF₂₅, MEF₅₀, MEF₇₅, and FEF_25-75. The contour of the flow-volume curve is relatively consistent and shows little dependence on AGE AND SEX.

Notably, disadvantages of standard spirography include the lengthy and complex testing procedure and the inability to diagnose small airway obstruction. Assessing forced expiratory flow rates helps pinpoint the specific level of bronchial obstruction, including involvement of the small airways.

Under normal conditions, the flow-volume curve has a fairly consistent, triangle-like shape, horizontally divided into four equal segments corresponding to 25%, 50%, 75%, and 100% of FVC. Initial airflow velocity depends primarily on muscular effort and reflects airflow in the trachea and large bronchi; airflow velocity at 25% to 75% of FVC reflects flow in the segmental bronchi, and from 75% to the end of expiration reflects flow in the small bronchi. The peak flow rate—the apex of the curve—shifts closer to the onset of expiration as obstructive changes progress.

The Conclusion regarding the localization of bronchial obstruction is drawn taking into account the results of FEV₁ measurements. A decrease in FEV₁, PEF, and MEF₂₅ alongside normal MEF₅₀, MEF₇₅, and MMEF_25-75 suggests the presence of obstructions in the upper respiratory tract, trachea, and major bronchi. A reduction in MEF₅₀, MEF₇₅, and MMEF_25-75 with normal FEV₁, PEF, and MEF₂₅ indicates obstruction of the peripheral, i.e., small, bronchi. A simultaneous decrease in FEV₁, PEF, MEF₂₅, MEF₅₀, and MEF₇₅ points to generalized obstruction.

The lower limit of normal for the forced expiratory flow during the middle half of the forced vital capacity (MMEF_25-75) and instantaneous forced expiratory flows (PEF, MEF₂₅, MEF₅₀, MEF₇₅) should be considered as 60% of the predicted value.

A decrease in flow rates to 40% of the predicted value is regarded as mild, from 39% to 20% as moderate, and 19% or lower as severe.

Whole-body plethysmography is based on the barometric principle. It is performed in a body plethysmograph—a large hermetic chamber with a constant volume where the patient is placed and changes in chest volume during breathing are recorded. Plethysmography allows for the evaluation of lung compliance and airway resistance under quiet breathing conditions, as well as total lung capacity (TLC), without The Use of the cumbersome helium dilution method.

Pharmacological challenge tests with bronchodilators help identify hidden bronchial patency impairments, differentiate their reversibility, and apply appropriate means for their correction.

An integral indicator of external respiration function is blood gas content and acid-base balance. These are usually determined using the Astrup micromethod. Determining gas content and respiratory function at rest and after graded exercise is sufficient to establish the presence of respiratory failure. Based on these studies, a differentiation between restrictive and obstructive types of respiratory failure (RF) is performed.

Radionuclide (radioisotope) methods are of decisive importance for assessing regional ventilation and pulmonary blood flow. They are based on the inhalation or, more commonly, intravenous administration of radiopharmaceuticals labeled with gamma-emitting radionuclides. The distribution of the administered agent is recorded using a scintillation gamma camera coupled with a computer.

A promising functional diagnostic method for respiratory system disorders is the determination of oscillatory mechanics parameters of breathing (compliance and inertance of the airways, lung tissue, and chest wall).

Respiratory failure is a pathological state of the organism in which the maintenance of normal blood gas composition is not ensured, or is achieved only through increased work of the external respiration apparatus and The Heart, leading to a decrease in the functional reserves of the organism.

Based on the underlying mechanisms of external respiration, Three types of disorders leading to respiratory failure are distinguished: ventilatory, diffusion, and perfusion.

Ventilatory disorders are among the earliest signs of respiratory failure and are characterized by impaired alveolar ventilation. Causes include: decreased elasticity of the lung tissue, impaired bronchial patency, various skeletal deformities of the chest, respiratory Muscle weakness, pleural changes, diaphragmatic dysfunction, etc.

Diffusion impairments are observed when gas diffusion across the alveolar-capillary membrane is hindered due to its thickening (edema, Swelling, Connective Tissue proliferation).

Circulatory (perfusion) disorders arise from a mismatch between pulmonary ventilation and blood flow.

Therefore, respiratory studies should be conducted based on the following parameters: pulmonary ventilation, pulmonary circulation, and gas exchange. When respiratory function is impaired at any single stage (parameter), compensatory mechanisms are activated in the form of enhanced function of other systems within the external respiration apparatus, thanks to which arterial blood oxygenation may remain unaffected. In advanced cases, compensatory mechanisms may prove insufficient, resulting in hypoxemia and hypercapnia in the blood.

Depending on the severity of respiratory failure, it is divided into three grades: Grade I – latent respiratory failure, in which dyspnea occurs only during physical exertion. At rest, all external respiration parameters are normal. Only exercise testing may reveal an increased minute ventilation (MV), elevated oxygen uptake, accompanied by a decreased maximum voluntary ventilation (MVV), respiratory reserve coefficient (RRC), and oxygen utilization coefficient (OUC). Blood gas levels remain normal.

Grade II – dyspnea occurs upon minor physical exertion. Breathing at rest is rapid; breathing depth, MVV, and RRC are decreased, while minute volume is increased. Following graded physical exertion, all parameters take longer to return to baseline, and accessory muscles are recruited for breathing.

Grade III – dyspnea at rest. Pronounced cyanosis. Breathing is rapid and shallow. Lung volumes are drastically reduced (Table 3).

Class="center">Table 3 Grades of respiratory failure (according to V.G. Boksha, 1991)

In the late stage, cardiac (right ventricular) failure joins pulmonary insufficiency due to The Development of pulmonary Hypertension and dystrophic Changes in the myocardium caused by its constant overload and inadequate oxygen supply. Increased workload on the right ventricle progressively leads to its failure, manifesting as congestion in the pulmonary circulation (Cor Pulmonale).

Depending on the Causes and Mechanisms of onset, three types of pulmonary ventilation disorders are distinguished: obstructive, restrictive, and mixed (obstructive-restrictive).

The obstructive type of respiratory failure is caused by impaired airflow through the bronchi, clinically manifested by exertion-induced dyspnea, later followed by a prolonged inspiration and, above all, expiration, i.e., expiratory dyspnea. MVV, FVC, FEV₁, and the Tiffeneau index (<70%) are decreased, with only a minor reduction in VC.

The restrictive type of respiratory failure is caused by the limited ability of the lungs to expand and contract in volume (pneumosclerosis, hydro- and pneumothorax, massive pleural adhesions, etc.). Vital capacity (VC) and MVV are sharply reduced while the Tiffeneau index remains normal.

The mixed type of respiratory failure combines features of both previous types, often with a predominance of one over the other. This type is observed in chronic pulmonary and cardiac diseases. All functional parameters are reduced, primarily showing an equal decrease in both VC and the Tiffeneau index, or with VC predominating.

In Pulmonary Tuberculosis, Cardiovascular system disorders are primarily caused by tuberculous intoxication and hemodynamic alterations in the pulmonary circulation.

Patients with pulmonary tuberculosis frequently exhibit tachycardia, hypotension, extrasystoles—predominantly ventricular in origin—signs of atrioventricular block, and electrocardiographic changes characteristic of right-axis deviation. Due to myocardial dystrophy, the QRS and T-wave voltage is decreased in most patients (particularly R and T), while the P wave in standard leads II, III, and aVF is occasionally elevated (>2.5 mm). A tall P wave in leads II, III, and aVF is a hallmark of cor pulmonale.

The diagnosis of cor pulmonale is based on Direct and Indirect ECG criteria proposed by G. Widimsky.

Direct signs include: R in V₁>5 mm; R/S in V>1; right ventricular activation time within 0.03–0.05 s; RV₁ + SV₅>10.5 (Sokolow-Lyon index); qR complex in V₁; incomplete right bundle branch block if rSR’ in V₁ with R’>10 mm; complete right bundle branch block if rSR’ in V₁ with R’>15 mm.

Indirect signs include: R in V₅<5 mm; S in V₅>5 mm; R/S in V₅<1; S in V₁<2 mm; complete right bundle branch block if rSR’ in V₁ with R’<15 mm; incomplete right bundle branch block if rSR’ in V₁ with R’<10 mm; The ratio of R/S in V₅ to R/S in V₁<10 (Salazar index).

The diagnosis of cor pulmonale is considered definitive when two or more direct signs, or one direct sign combined with several indirect signs, are present; it is considered questionable when one direct sign is combined with an indirect sign.

It should be noted that the ECG does not always detect pulmonary hypertension and right ventricular hypertrophy. Echocardiography provides extensive information regarding the state of the right heart: it allows for the most accurate assessment of right ventricular wall thickness and chamber dimensions, as well as the determination of pulmonary artery pressure, including pressure gradients across the pulmonary valve. Invasive measurement of pulmonary artery pressure, although the most precise, is rarely used due to The complexity of the procedure and the risk to the patient.

CONTROL QUESTIONS

1. The primary function of the lungs. External and internal respiration.

2. Stages of external respiration (ventilation, diffusion, perfusion).

3. Apparatus for assessing external respiratory function.

4. Methods for Investigating external respiratory function.

5. Types of ventilatory impairment (restrictive, obstructive, mixed).

6. The most informative parameters derived from spirography and the flow-volume loop.

7. Flow-volume loop parameters indicating involvement of large, medium, and small bronchi.

8. Grades of respiratory failure according to spirography and Dembo's Classification.

9. Indications for assessing external respiratory function in tuberculosis clinical practice.

TESTS

1. Mandatory examination for suspected laryngeal tuberculosis.

A. Bronchoscopy

B. Laryngoscopy

C. Flexible bronchoscopy

D. Oral Cavity inspection

E. Posterior rhinoscopy

2. The primary diagnostic method for bronchial tuberculosis.

A. Pneumotachometry

B. Fibrobronchoscopy

C. Bronchography

D. Computed tomography

E. Targeted radiography

3. The primary method for morphological verification of pulmonary tuberculosis.

A. Transthoracic needle biopsy

B. Fibrobronchoscopy

C. Sputum Cytology

D. Computed tomography

E. Thoracotomy with biopsy

4. The anatomical dead space is:

A. 10-25 ml

B. 50-100 ml

C. 140-150 ml

D. 1400-1600 ml

E. 3500-5000 ml

5. In healthy individuals, the vital capacity of the lungs is:

A. 500-800 ml

B. 1000-3000 ml

C. 1500-3500 ml

D. 3500-5000 ml

E. 6000-8000 ml

6. The Tiffeneau index is the ratio of:

A. MVV and RMV

B. FEV₁ and VC

C. FEV₁ and MVV

D. VC and MVV

E. VC and RR

7. The most informative non-invasive METHOD FOR DETERMINING pulmonary hypertension is:

A. fluoroscopy,

B. ECG,

C. phonocardiography,

D. ballistocardiography,

E. echocardiography.

8. Which parameters of external respiration function are considered the most informative?

A. VC and MVV

B. FEV₁, Tiffeneau index

C. VC, FEV₁, Tiffeneau index

D. MVV, Tiffeneau index

E. MEF₂₅, PEF .

9. Patient Z., aged 45, is diagnosed with infiltrative Tuberculosis of the right lung, phase of disintegration and dissemination, MBT (+). Complains of a cough with scant sputum production and shortness of breath. Pneumotachometry revealed a decrease in PEF_exp and MEF₂₅ with normal values of MEF₅₀ and MEF₇₅. Determine the level of bronchial tree involvement.

A. Large bronchi

B. Medium bronchi

C. Large and medium bronchi

D. Medium and small bronchi

E. Small bronchi

10. The final stage of the diagnostic process in pulmonary diseases in complex cases is:

A. fiberoptic bronchoscopy

B. computed tomography

C. transthoracic needle lung biopsy

D. thoracotomy

E. bacteriological and Cytological examination of bronchial secretions.