Diagnosis of the nature and severity of functional disorders caused by the main pathological process and associated diseases is the most important task of the preoperative period. The solution of this task largely determines the tactics of surgical treatment, since the data obtained during the examination serve as a basis not only for assessing the functional operability of the patient, but also for predicting intra- and postoperative complications, immediate and long-term results of treatment. Unfortunately, the methods of statistical analysis and modeling of the evolution of the pathological process used in clinical practice are probabilistic in nature and make it possible to select only risk factors common to a group.

The factors that determine the immediate outcome of a lung operation are traditionally considered: the severity of the patient’s condition (age, concomitant diseases, functional reserves); the prevalence of the pathological process; volume and invasiveness of the operation; features of anesthesia and intensive care. But not all of them are indisputable criteria for the prediction of complications and deaths. The dependence of the frequency of complications on age is noted by many researchers. However, age itself does not affect the outcome of treatment, the higher probability of complications in patients of older age groups.

due mainly to increased frequency of associated diseases. Almost every patient with lung cancer has these risk factors. The overwhelming majority of patients are persons of the older age groups, suffering from aortic atherosclerosis and coronary arteries, atherosclerotic cardiosclerosis, coronary heart disease, hypertension, chronic nonspecific lung diseases. In combination with the general and local adverse effects of the blastomatous process, these diseases significantly limit the functional reserves of the vital systems and the organism as a whole, aggravating the operative and postoperative periods and often determining the outcome of treatment. Moreover, precisely because of the low functional reserves, every fifth patient with lung cancer, from among those admitted to specialized institutions, is denied prompt treatment. Such a decision must be carefully reasoned and cannot be based only on clinical data. Therefore, preoperative examination always includes special functional studies.

Respiratory dysfunction, restrictive and obstructive changes in the lung are assessed using spirometry: determination of lung capacity, forced lung capacity, criteria for the flow curve — maximum expiratory volume. However, in some patients, spirometry, even in combination with x-ray, endoscopic studies and the determination of the arterial blood gas composition, cannot determine whether pulmonary gas exchange disorders are caused by the main process or concomitant chronic lung diseases. To resolve this issue, patients with dubious functional reserves (moderate and severe degree of restriction in the absence of endoscopic signs of obturation of the main bronchus with a tumor) perform separate spirometry, i.e.study of respiratory volumes after occlusion of the main bronchus of the affected lung with the Fogarty catheter inserted through the instrumental channel of the fibrobronchoscopes.

At the same time, the study of the indices of biomechanics of respiration, even using separate spirometry, does not allow one to determine the functional operability of the patient, since these indicators only indirectly reflect changes in the pulmonary blood flow. Namely, pulmonary arterial hypertension in patients with lung cancer has the most unfavorable prognostic value. According to patients with systolic pressure in the pulmonary artery above 30mmHg. the frequency of postoperative complications such as hypoventilation, atelectasis, pneumonia is five times higher than in other patients. The importance of this indicator is due to the fact that in the postoperative period the reduction of the small circle of blood circulation becomes the main factor limiting the possibility of hemodynamic compensation of respiratory failure.

It is obvious that compensatory reserves of the circulatory system can be reduced for other reasons. In lung cancer patients, heart rhythm disturbances require separate attention. They can be not only a sign of organic pathology of the heart, but also a consequence of the local spread of lung cancer and involvement in the tumor or paracancic process of the mediastinal pleura, the vagus nerve, pericardium, or other paracardiac structures. In the majority of patients, such heart rhythm disturbances are asymptomatic and can only be detected by examination in the clinic. However, in some patients they are more complex (alternation of paroxysms of brady and tachyarrhythmias, atrial fibrillation with episodes of polytopic extrasystole), are accompanied by hypotension, fainting, and almost not amenable to traditional

antiarrhythmic therapy, but can be eliminated by conductive blockades (vagosympathetic, retrosternal) and radical surgery. Therefore, even in the most severe in the general condition of patients, such arrhythmias, in our opinion, cannot serve as a restriction to surgical treatment.

The most simple non-invasive and highly informative method for assessing the state of the pulmonary blood flow and the entire circulatory system in general is, in our opinion, the integral rheography of the body. The method does not affect the hemodynamic parameters of the studied, provides documented information, is completely harmless and not burdensome for patients and can be re-applied as often as desired.