Use of saliva stress biomarkers to estimate novice male endoscopist's stress during training in a high-end simulator.

OBJECTIVE: Simulated endoscopic training can be challenging and stressful for the novice trainee. The absence of a reliable stress detection method during simulated endoscopic training makes estimating trainees' mental stress difficult to quantify. This study concomitantly measures the responses of four saliva stress biomarkers and compares them to the video score (VS) achieved by novice endoscopists in a reproducibly stressful simulation environment. METHODS: Thirty-six male endoscopy naïve surgery residents were enrolled. After an orientation phase, a saliva specimen was collected for cortisol (sC), alpha-amylase (sAA), Chromogranin A (sCgA), and immunoglobulin A (sIgA) measurements (baseline phase, BL). Thereafter, the simulation exercise phase (E) started, practicing in the Fundamentals of Endoscopic Surgery Skills module (GI-Bronch Mentor). Immediately after, a second saliva sample for measuring the above-cited biomarkers was collected. The whole experiment was videotaped, and the VS was calculated. The percentage (E-BL)diff of each of the four saliva biomarkers was calculated and examined for correlation to VS. RESULTS: sCgAdiff showed the best correlation with VS, followed by sAAdiff. CONCLUSIONS: sCgA and sAA, are saliva stress biomarkers that are easy to collect non-invasively and showed the best correlation with novice endoscopist's performance in our simulation setting, and therefore, they could be used for monitoring stress.

Gut Microbiota in Lung Cancer: Where Do We Stand?

The gut microbiota (GM) is considered to constitute a powerful "organ" capable of influencing the majority of the metabolic, nutritional, physiological, and immunological processes of the human body. To date, five microbial-mediated mechanisms have been revealed that either endorse or inhibit tumorigenesis. Although the gastrointestinal and respiratory tracts are distant physically, they have common embryonic origin and similarity in structure. The lung microbiota is far less understood, and it is suggested that the crosslink between the human microbiome and lung cancer is a complex, multifactorial relationship. Several pathways linking their respective microbiota have reinforced the existence of a gut-lung axis (GLA). Regarding implications of specific GM in lung cancer therapy, a few studies showed that the GM considerably affects immune checkpoint inhibitor (ICI) therapy by altering the differentiation of regulatory T cells and thus resulting in changes in immunomodulation mechanisms, as discovered by assessing drug metabolism directly and by assessing the host immune modulation response. Additionally, the GM may increase the efficacy of chemotherapeutic treatment in lung cancer. The mechanism underlying the role of the GLA in the pathogenesis and progression of lung cancer and its capability for diagnosis, manipulation, and treatment need to be further explored.

Striving for Better Medical Education: the Simulation Approach.

Medical simulation is a rapidly expanding area within medical education due to advances in technology, significant reduction in training hours and increased procedural complexity. Simulation training aims to enhance patient safety through improved technical competency and eliminating human factors in a risk free environment. It is particularly applicable to a practical, procedure-orientated specialties. Simulation can be useful for novice trainees, experienced clinicians (e.g. for revalidation) and team building. It has become a cornerstone in the delivery of medical education, being a paradigm shift in how doctors are educated and trained. Simulation must take a proactive position in the development of metric-based simulation curriculum, adoption of proficiency benchmarking definitions, and should not depend on the simulation platforms used. Conversely, ingraining of poor practice may occur in the absence of adequate supervision, and equipment malfunction during the simulation can break the immersion and disrupt any learning that has occurred. Despite the presence of high technology, there is a substantial learning curve for both learners and facilitators. The technology of simulation continues to advance, offering devices capable of improved fidelity in virtual reality simulation, more sophisticated procedural practice and advanced patient simulators. Simulation-based training has also brought about paradigm shifts in the medical and surgical education arenas and ensured that the scope and impact of simulation will continue to broaden.

Evaluation of Acute Exogenous Hypoxia Impact on the Fraction of Exhaled Nitric Oxide in Healthy Males.

INTRODUCTION: Exogenous hypoxia increases ventilation and contracts the pulmonary vessels. Whether those factors change the values of nitric oxide in exhaled air has not yet been evaluated. OBJECTIVE: To examine the effect of exogenous normobaric hypoxia on the values of the fraction of nitric oxide in exhaled breath (FeNO). Subjects аnd Methods: Twenty healthy non-smoker males at mean age of 25.4 (SD = 3.7) were tested. The basal FeNO values were compared with those at 7 min. and 15 min. after introducing into the hypoxic environment (hypoxic tent), imitating atmospheric air with oxygen concentration corresponding to 3200 m above sea level. Exhaled breath temperature was measured at baseline and at 10-12 min. of the hypoxic exposition. Heart rate and oxygen saturation were registered by pulse-oximetry. RESULTS: All the subjects had FeNO values in the reference range. The mean baseline value was 14.0 ± 3.2 ppb, and in hypoxic conditions - 15.5 ± 3.8 ppb (7 min.) and 15.3 ± 3.6 ppb (15 min.), respectively, as the elevation is statistically significant (p = 0.011 and p = 0.008). The values of exhaled breath temperature were 33.79 ± 1.55°Ð¡ and 33.87 ± 1.83°Ð¡ (p = 0.70) at baseline and in hypoxic conditions, respectively. Baseline oxygen saturation in all subjects was higher than that, measured in hypoxia (96.93 ± 1.29% vs. 94.27 ± 2.53%; p < 0.001). CONCLUSIONS: Exogenous hypoxia leads to an increase of FeNO values, but does not affect the exhaled breath temperature.

Clinical applications of forced oscillation technique (FOT) for diagnosis and management of obstructive lung diseases in children.

Obstructive lung diseases such as bronchial asthma, COPD, and cystic fibrosis are a burden on many patients across the globe. Spirometry is considered the gold standard for diagnosing airflow obstruction, but it can be difficult for pediatric patients to do and requires a lot of effort. As a result, healthcare providers need new, effortless methods to diagnose airway obstructions, particularly in young children and individuals unable to perform the spirometry maneuver. The forced oscillation technique is a modern method requiring only tidal breathing combined with the application of external, source of low-amplitude oscillations to evaluate the respiratory system's response. It might be essential for identifying early respiratory changes caused by smoking, childhood asthma, and may prove more sensitive than spirometry in identifying peripheral airway disturbances or evaluating the long-term success of therapy. This review describes the methodology and the indications for the forced oscillation technique and outlines its relevance in clinical practice.

Factors affecting prediction accuracy of postoperative FEV1 and DL,CO in patients undergoing lung resection.

INTRODUCTION: Despite significant development in systemic therapy and radiotherapy, surgery is still the cornerstone for curative lung cancer treatment. Although predicted postoperative function (ppo) somewhat exactly correlates with actual postoperative function bigger differences may be a cause of serious clinical outcome.

The six-minute walk test - a reliable test for detection of exercise-related desaturation in patients with chronic obstructive pulmonary disease.

INTRODUCTION: Exercise-induced desaturation is common in patients with moderate to severe chronic obstructive pulmonary disease (COPD). It provides additional information about physical capacity and disease evolution, and it is an important predictor of mortality.

Intraoperative ultrasound for nonpalpable breast lesions - experience and operative time.

INTRODUCTION: The essential tools doctors need to diagnose breast cancer tumors at the early stages and with no clinical presentation are screening mammography and ultrasonography. Nonpalpable breast lesions are a current problem nowadays and there are various types of navigation techniques that are utilized in order to achieve cancer cell-free resection margins in the first place. Intraoperative ultrasound has been proven to be a safe and effective way to excise this type of breast tumors. AIM: To study the correlation between the experience we obtained while using intraoperative ultrasound for excision of nonpalpable breast lesions, and the duration of surgery. MATERIALS AND METHODS: Twenty-five women with nonpalpable breast lesions underwent breast-conserving surgery using ultrasound navigation. Nominal and ordinal data were presented using numbers and percentages. Spearman's rank-order correlation was used to assess the effect of experience gained on the duration of surgery. RESULTS: The tumor distribution was 72% malignant tumors and 28% benign. A 100% identification rate in the effective surgical excisions was reported. In the process of gaining experience using the method, the duration of surgery shortened by 30%. No tumor cells on ink were found in all specimens and there was no need for secondary surgeries. CONCLUSIONS: Our results demonstrate a relatively short learning curve, and we believe that breast surgeons should be helped and encouraged to gather adequate expertise to ensure patient safety and gain confidence.

Reference values for forced expiration parameters in Bulgarian children and adolescents aged 7 to 18 years.

INTRODUCTION: A diagnosis of lung function impairment in childhood is highly dependent on the respective reference values. Population differences in the pulmonary function of children have been frequently reported. The AIM of this study was to derive normal spirometric reference values for Bulgarian children and adolescents and to compare these results with other data set including our own reference equations developed 20 years ago. MATERIAL AND METHODS: Forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), and parameters of maximum expiratory flow-volume curves were measured in 671 healthy Bulgarian school children (339 males and 332 females) aged 7-18 years. Multiple linear regression analysis was performed for each spirometric parameter against age, height, weight, chest circumferences and fat free mass in both sexes. RESULTS: Excluding ratios, all measured spirometric parameters increased nonlinearly with age and height, and were significantly higher in boys than girls in adolescence. Height (H) explained the maximum variance for spirometric parameters and the best-fit regression equation relating functional parameters and body height was a power function (Y = a.Hb). FVC and FEV1 showed close correlations with height (r2 between 0.85 and 0.92), whereas the coefficients of determination for the flows were less close (r2 from 0.85 for PEF to 0.67 for MEF25%; always higher in boys). CONCLUSIONS: The developed prediction equations can be used in clinical practice. In comparison with reference equations based on European or USA populations, regional reference values are biologically more suitable for the interpretation of spirometric data.

5G in Healthcare: From COVID-19 to Future Challenges.

Worldwide up to May 2022 there have been 515 million cases of COVID-19 infection and over 6 million deaths. The World Health Organization estimated that 115,000 healthcare workers died from COVID-19 from January 2020 to May 2021. This toll on human lives prompted this review on 5G based networking primarily on major components of healthcare delivery: diagnosis, patient monitoring, contact tracing, diagnostic imaging tests, vaccines distribution, emergency medical services, telesurgery and robot-assisted tele-ultrasound. The positive impact of 5G as core technology for COVID-19 applications enabled exchange of huge data sets in fangcang (cabin) hospitals and real-time contact tracing, while the low latency enhanced robot-assisted tele-ultrasound, and telementoring during ophthalmic surgery. In other instances, 5G provided a supportive technology for applications related to COVID-19, e.g., patient monitoring. The feasibility of 5G telesurgery was proven, albeit by a few studies on real patients, in very low samples size in most instances. The important future applications of 5G in healthcare include surveillance of elderly people, the immunosuppressed, and nano- oncology for Internet of Nano Things (IoNT). Issues remain and these require resolution before routine clinical adoption. These include infrastructure and coverage; health risks; security and privacy protection of patients' data; 5G implementation with artificial intelligence, blockchain, and IoT; validation, patient acceptance and training of end-users on these technologies.

Effect of video games playing on surgical simulation training: a systematic review.

INTRODUCTION: Video games have a positive impact on the skills required for laparoscopic surgery. Several studies have assessed the impact of video games on laparoscopic skills. AIM: This study aims to systematically review the existing evidence. MATERIALS AND METHODS: A search strategy was implemented to retrieve relevant articles from MEDLINE and SCOPUS databases. The retrieved articles were reviewed for further evaluation according to the predetermined inclusion/exclusion criteria. RESULTS: Twenty-six studies were included in this systematic review. These included prospective (n=9), retrospective (n=5) and interventional (n=12). Other review papers were cited in the discussion section. Studies with positive outcomes significantly outweighed the negative ones (21 vs. 5, respectively). CONCLUSIONS: Although there is some evidence that video game experience could give some advantage in laparoscopy no firm conclusions could be drawn yet. The reasons for that lay in the various aims, approaches and results of different study reports. Gaming could be used as a daily warm-up or as a tool to speed-up mastering new skills. A standardized protocol is needed for answering the different questions regarding the impact of video game exposure to laparoscopic skills development and progression.

Jubilee Scientific Conference "Medicine of the Future" - 29-31 October 2020 on the occasion of the 75th Anniversary of Medical University of Plovdiv.

Plenary lectures 7 Oral presentations 32 - Biomedicine 32 - Biopharmacy 46 - Contemporary surgical techniques 51 - Innovative methods of diagnosis and treatment 58 - Dental medicine 61 - Public Health/Healthcare 67 Poster sessions 74 - Poster session I 74 • Biomedicine 74 • Biopharmacy 90 • Contemporary surgical techniques 94 • Innovative methods of diagnosis and treatment 96 • Dental medicine 99 • Public Health-Healthcare 103 - Poster session II 116 • Projects with national/international funding 116 Intra-university project session 120 - Intra-university projects 2016-2018 120 - Doctoral projects 2015-2017 142 - Post-doctoral projects 2018 150.

Physics and Engineering - Unlocking Doors in Medicine Together.

Invited Talks 7 - Biomedical Engineering 11 - Biophysics in Biology and Medicine 12 - Education Training and Professional Development 16 - Information Systems and Databases in Healthcare and Medicine 17 - Medical Physics 18 - Modelling and Simulation 21 - New Technologies in Medicine and Safety 24 - Physical Factors 26 - Qaulity Assurance and Quality Control 28 - Radiation Protection and Safety 30 - Radiation Therapy 35.

Intima-media thickness and flow-mediated vasodilation in asymptomatic subjects with newly detected severe hypercholesterolemia.

BACKGROUND: The aim was to establish the predictors of early functional and structural vascular alterations (using intima-media thickness (IMT)) and flow-mediated vasodilation (%FMD) as well as to investigate the interrelationship between IMT and %FMD in asymptomatic, never-treated, severe hypercholesterolemia (HH). METHODS: One hundred and twenty patients with asymptomatic, severe, untreated HH and 100 controls were included. ELISA was used for asymmetric dimethylarginine (ADMA) and cellular adhesion molecules, and fluid chromatography for total homocysteine (tHcy). Hewlett Packard SONOS 5500 with a 7.5 MHz transducer and MedicaSoft IMT software were used for evaluation of %FMD and IMT of common carotid artery (CCA). RESULTS: Patients and controls differ with respect to all tested biomarkers (P < 0.05), except for P-selectin and E-selectin (P < 0.05). %FMD was lower in patients (P < 0.001). The IMT of the CCA was higher in patients (P < 0.001). Inverse correlations were found between %FMD and IMT mean and age, ADMA, Apo-B, Apo-B/Apo-A(1), and tHcy. ADMA was established as the most important factor related to %FMD. Age and Apo-B were established as the most important factors related to IMT mean. An inverse correlation was established between %FMD and IMT mean (r(xy)= 0.546; P < 0.001)). If cases with IMT mean > or =1 were excluded, the correlation weakened. In patients with IMT mean > or =1 mm, the correlation did not change. CONCLUSION: In conclusion, asymptomatic, untreated patients with severe hypercholesterolemia are at high risk of having increased IMT of the CCA, especially if there is endothelial dysfunction, verified by %FMD of the brachial artery.

Oxygen uptake efficiency slope and chronotropic incompetence in chronic heart failure and chronic obstructive pulmonary disease.

INTRODUCTION: Oxygen uptake efficiency slope (OUES) and chronotropic index (CRI) are measures of cardiorespiratory reserve and chronotropic incompetence, but no direct comparison of OUES and CRI in patients with chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF) has been done. AIM: To compare OUES and CRI in CHF and COPD patients. PATIENTS: Fifty-one subjects divided in three groups--CHF group (n=17) (NYHA II and III functional class), COPD group (n=17) (FEV1% = 49.7 +/- 17.3) and healthy controls (C) (n=17), matched by age and BMI. COPD and CHF patients presented comparable decrease in functional capacity. METHODS: Subjects undertook maximal exercise test on a treadmill by means of Bruce protocol. RESULTS: CHF and COPD patients showed a significant and comparable decrease in exercise capacity (VO2/kg = 18.5 +/- 4.0 vs. 19.5 +/- 4.9 vs. 28.3 +/- 6.2 mL x min(-1) x kg(-1), p < 0.001) and ventilatory efficiency in comparison with controls. COPD patients presented with a typical pattern of exercise limitation due to ventilatory restraints (%breathing reserve = 15.6 +/- 18.0%). OUES was lower than controls in both CHF and COPD groups, being lowest in CHF (1686 +/- 483 vs. 2101 +/- 478 vs. 2481 +/- 398 mL.min(-1) x logL(-1), p < 0.001). Chronotropic index was lower in CHF patients (0.60 +/- 0.15 in CHF vs. 0.72 +/- 0.16 in COPD vs. 0.81 +/- 0.18 in controls, p < 0.001) in comparison with controls. CONCLUSION: OUES is decreased in CHF and COPD patients, but the decline is significantly more pronounced in the CHF group. CRI is lower in CHF patients.

Feasibility of a New Wearable Device to Estimate Acute Stress in Novices During High-fidelity Surgical Simulation.

BACKGROUND: Stress associated with learning of a psychomotor task can influence the trainees learning ability. Surgical simulation is a validated training milieu designed to replicate real-life situations, prevent biases and provide objective metrics. However, the complexity of stress mechanisms and the absence of a reliable detection method make stress estimation difficult to quantify and to interpret. AIM: a) To assess the feasibility of a new watch-sized device to noninvasively measure stress parameters in novices during a simulation task and b) to compare its derived cardiac stress parameters to those of an ambulatory Holter monitor. MATERIALS AND METHODS: Twenty-one novices were trained on a basic skills module. During base line, exercise, and recovery phases, all subjects wore a wearable device and data regarding blood volume pressure, heart rate, inter beat interval, electrodermal activity, and skin temperature were recorded. Additionally, Holter Monitoring was used to concomitantly capture heart rate, R-R intervals and heart rate variability. Before and after each experiment, all subjects completed the short, six-item STAI scale. RESULTS: Data analysis showed: a) when compared to STAI, electrodermal activity exhibited the best correlation, sensitivity and specificity and b) the device derived cardiac parameters highly correlated with the reciprocal Holter values during all experiment phases. CONCLUSION: This wearable device is an easy to use and well accepted by the participants noninvasive tool, which can provide accurate stress estimation in our simulation setting. Additionally, it can replicate Holter derived stress related heart parameters, thus eliminating the need to wear a rather cumbersome device.

Effects of acute hypoxic provocation on the autonomic nervous system in 'healthy' young smokers, measured by heart rate variability.

AIM: The aim of this study was to compare the activity of the autonomic nervous system (ANS) using heart rate variability (HRV) in 'healthy' young smokers and non-smokers before, during and after exogenous hypoxic provocation. METHODS: Twenty-one healthy non-smoking males aged 28.0 ± 7.4 years (mean ± SD) and 14 'healthy' smoking males aged 28.1 ± 4.3 years with 9.2 ± 5.6 pack-years were subjected to one-hour hypoxic exposure (FiO2 = 12.3 ± 1.5%) via a hypoxicator. HRV data was derived via Kubios HRV, Finland software by analysing the pre-hypoxic, hypoxic and post-hypoxic periods. RESULTS: Standard deviation of the intervals between normal beats (SDNN) was higher in the non-smokers in the pre-hypoxic period (62.0 ± 32.1 vs 40.3 ± 16.2 ms, p = 0.013) but not in the hypoxic period (75.7 ± 34.8 vs 57.9 ± 18.3 ms, p = 0.167). When comparing intra-group HRV changes, shifting from hypoxic to normoxic conditions, there was an increase in the mean square root of successive R-R interval differences (RMSSD) (65.9 ± 40.2 vs 75.1 ± 45.9 ms, p = 0.011), but these changes were observed in only the group of non-smokers. CONCLUSIONS: Smoking probably impairs autonomic regulation in healthy young males and may lead to decreased HRV, even before subjective clinical signs and symptoms appear.

Desaturation during Physical Exercise in COPD Patients - a Stable-over-time Phenomenon.

INTRODUCTION: Exercise-induced desaturation is a common finding in patients with moderate and severe COPD. It is an important marker in the course of disease that has a prognostic value for mortality risk. AIM: To monitor over time COPD patients with and without desaturation during 6-minute walking test (6MWT) and to assess the stability of that phenomenon. MATERIALS AND METHODS: A 6MWT was administered to 70 patients with COPD which ranged in severity from stage 2A to stage 4D (GOLD 2011); the patients had a mean age of 64.5±10.1, mean pack-years - 38.8±21, FEV1% = 46.4%±15.7%, FVC% = 73.7%±1.3%, MRC = 2.31±0.84, CAT = 20.8±6.6. Oxygen saturation was monitored during the test; indications for desaturation were a decrease of SpO2 by ≥4% and a fall in SpO2 to ≤88% for at least 3 min. The patients were followed-up for mean 40.9±22.3 months and tests were repeated. RESULTS: Patients were divided into two groups based on the decrease in SpO2: Group A included patients with desaturation (n=35) and Group B - patients with no desaturation (n=35). In 66 of the patients the desaturation profile was stable over time. Only two patients, who did not desaturated at baseline, experienced desaturation in the follow-up 6MWT and another two patients, who desaturated at baseline, did not have it later in the follow-up. CONCLUSION: Desaturation is a phenomenon that is persistent over time. Based on the results, it could be concluded that exercise-induced desaturation is a major marker of a particular COPD phenotype.

Respiratory and cardiovascular functions among smoking and nonsmoking girls from two regions with different air pollution degree.

AIM: The aim of the present study was to analyze the respiratory and cardiovascular functions among smoking and nonsmoking girls attending two schools situated in regions with different levels of air pollution. The characteristic of air pollution is based on the data gathered by stations 1 and 2 belonging to the Uniform National System for Monitoring the Air Pollution in Bulgaria. The participants (n=108, 16.07+/-0.80 years) were separated in two groups: smokers (S1 - from school 1, S2 - from school 2) and nonsmokers (NS1 - from school 1, NS2 - from school 2). All of them performed pulmonary function testing and .cardiopulmonary exercise testing on a treadmill using our modification of the Balke protocol (Marinov et al., 2000). Reference values for European children, previously validated for the Bulgarian population, were used. RESULTS: There are no significant differences in mean levels of VC, IC, FEV1, MEF50 and MEF25 (as a percentage from the predicted value as well). The average level of the Tiffneau index is noticeably higher among nonsmokers from the two regions and is the lowest among smokers from the more polluted area, but a significant difference exists between S2 (88.7+/-5.9) and NS2 (92.6+/-4.7), p=0.047; T(L,CO)%pred: S1 (85.4+/-7.2) vs. S2 (86.7+/-8.2), p=0.048 and NS1 (88.3+/-8.2) vs. NS2 (92.8+/-14.5), p=0.037; V(E)%pred: S1 (127.5+/-9.6) vs. S2 (123.7+/-6.1), p=0.035; higher levels of total lung capacity (TLC%pred), S1 (107.3+/-9.2) vs. NS2 (104.3+/-9.1), p=0.009 and alveolar ventilation (VA), S1 (5.0+/-0.6) vs. NS2 (4.6+/-0.5), p=0.008. CONCLUSIONS: 1. The negative effects of the combined influence of tobacco smoking and air pollution on some respiratory and cardiovascular functions of adolescent girls are more pronounced than each influence alone. 2. The cardiopulmonary exercise test gives adequate information about the combined effect of air pollution and smoking and using it for preventive purposes is an advisable method.

Assessment of respiratory compensation phase during graded exercise in patients with chronic heart failure.

BACKGROUND: The VE-VO2 relationship during graded exercise has an inflection point beyond the ventilatory anaerobic threshold (VAT) termed the respiratory compensation point (RCP). Metabolic variables analyzed at the level of VAT and RCP may contribute to the better understanding of such limiting symptoms in chronic heart failure (CHF) patients as dyspnea and early fatigue. The AIM of the present study was to analyze the RCP during symptom limited ramp exercise testing in CHF patients. PATIENTS AND METHODS: Forty six CHF patients (II and III NYHA functional class; age = 51 +/- 9 years, LVEF% = 35% +/- 6%; mean +/- SD) and 20 matched controls performed graded cardiopulmonary exercise test on a cycle ergometer. RESULTS: The duration and productivity of RCP (delta(x) = peak(x) - VAT(x)) in patients were significantly (p < 0.001) reduced compared to healthy subjects: delta duration = 3.0 +/- 1.2 vs 4.3 +/- 1.5 min, delta watts = 24.3 +/- 11.5 vs. 39.4 +/- 11.5, delta VO2/kg (ml.kg-1 x min-1) = 3.8 +/- 1.3 vs 8.8 +/- 2.3. An important characteristic of this phase was the higher subjective cost of physical effort assessed by Borg scale and Watts/Borg ratio (Borg peak = 9.9 +/- 0.4 vs. 6.0 +/- 1.2; p < 0.001, Watts/Borg peak = 9.2 +/- 2.3 vs 23.9 +/- 6.4, p < 0.001). The relative hyperventilation of patients on the basis of the watt exercise can be seen in the values of derivative index V (ml x min-1 x watt-1) 478 +/- 59 vs 568 +/- 118; (p < 0.001) in controls and patients, respectively. CONCLUSIONS: The impaired efficiency of oxygen delivery systems in patients with CHF is what causes the appearance of early limiting symptoms. Duration and productivity of respiratory compensation phase in CHF patients are considerably reduced compared to controls.