Respiratory therapy with positive expiratory pressure in patients after left ventricle geometric reconstruction

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Introduction

The functional state of the respiratory system in patients with coronary heart disease accompanied by chronic heart failure (CHF) is often characterized by impaired physiological mechanisms of the upper respiratory tract, manifesting as deterioration of the lungs’ eliminative function, reduced external respiratory function indicators, and decreased gas exchange [1]. The severity of these dysfunctions may increase with the progression of heart failure, especially after cardiac surgical interventions [2]. It is necessary to emphasize the importance of patients’ preoperative condition (degree of obesity, presence of harmful habits, comorbidities), as it significantly affects the state of the respiratory system and the speed of its recovery after cardiac surgery.

It should be noted that the number of comorbid patients with cardiovascular and respiratory pathologies [3], such as COPD [4], is growing each year, as well as the association with sleep apnea syndrome of both central and obstructive nature [5].

The decrease in physiological indicators of pulmonary ventilation in patients with CHF significantly increases the risks of postoperative complications in the early period, prolongs their hospital stay, which is a predictor of high mortality in this category of patients [6, 7].

One of the most common bronchopulmonary complications after cardiac surgery is atelectasis. The average frequency of this complication is more than 50% [8, 9]respiratory complications remain a leading cause of postcardiac surgical morbidity and can prolong hospital stays and increase costs. The high incidence of pulmonary complications is in part due to the disruption of normal ventilatory function that is inherent to surgery in the thoracic region. Furthermore, patients undergoing such surgery often have underlying illnesses such as intrinsic lung disease (e. g., chronic obstructive pulmonary disease. Among the main causes of atelectasis are the use of mechanical ventilation combined with prolonged cardiopulmonary bypass during cardiac surgical interventions, which can lead not only to the development of interstitial and alveolar edema but also to the appearance of atelectasis zones [10], due to the development of systemic inflammation, damage to surfactants and disruption of their production [11].

The development of atelectasis reduces the ventilation-­perfusion ratio, worsens lung tissue elasticity [12], and often provokes the development of infectious processes in various parts of the lungs. This situation is especially relevant for patients after LVGR due to the complexity and duration of the surgical intervention [13].

There are various methods of respiratory rehabilitation for patients after cardiac surgery, aimed at restoring chest excursion after sternotomy, improving gas exchange, restoring mucociliary clearance, and expanding collapsed alveolar areas. Typically, to improve ventilation of various lung regions and facilitate sputum expectoration after cardiac surgery, conventional respiratory gymnastics consisting of static and dynamic exercises is used.

Among the most promising and effective methods of respiratory training in this group of patients, especially those with bronchopulmonary pathology, positive expiratory pressure therapy (PEP-therapy) can be highlighted [14, 15].

By creating moderate positive pressure in the airways, «air traps» are eliminated and collateral bronchial ventilation is improved, which allows effective recruitment of atelectatic alveoli and restoration of gas exchange. Moreover, some devices for PEP-therapy, such as EzPAP, allow maintaining positive inspiratory pressure in the airways, which prevents their collapse during inhalation [16, 17] and increases the effectiveness of respiratory training. The device is equipped with a high-flow oxygen connection and can be used for patients with gas exchange disorders who require constant oxygen therapy. The special design of the apparatus accelerates inspiratory flows, resulting in the patient taking a deeper breath, which improves lung tissue elasticity and restores lung vital capacity.

Currently, there is very little research in domestic and foreign literature concerning the analysis of the effectiveness of various respiratory rehabilitation methods in patients after the left ventricle geometric reconstruction (LVGR). There is also a lack of data on the application of PEP-therapy methods and their impact on the functional state of the respiratory system in this group of patients.

In this regard, the aim of this study is to investigate the effect of respiratory training with positive expiratory pressure on the functional state of the respiratory system in patients after LVGR.

Materials and methods

A prospective study was conducted at the A.N. Bakulev National Medical Research Center for Cardiovascular Surgery and approved by the local ethics committee (protocol No. 5 dated 07.10.2023). The study involved 57 patients who underwent planned the left ventricle geometric reconstruction surgery. The average age of patients was 60 ± 8 years (50 men and 7 women). All patients signed informed consent to participate in the study.

Inclusion criteria for patients in the study were: 1) left ventricle geometric reconstruction surgery; 2) absence of chronic respiratory diseases in the medical history; 3) age not younger than 18 years; 4) patient’s willingness to follow the study protocol.

Exclusion criteria were: 1) pneumothorax in the early postoperative period; 2) postoperative acute heart failure; 3) acute cerebrovascular accident; 4) severe cognitive impairment.

Two methods of respiratory rehabilitation were used to restore respiratory function in patients in the early postoperative period: 1) PEP-therapy using the EzPAP device (Smiths Medical (Portex) UK) and 2) conventional (standard) respiratory gymnastics.

Depending on the rehabilitation method, two groups of patients were identified: group I — patients undergoing PEP-therapy (n  =  27), and group II — patients undergoing standard respiratory gymnastics (n = 30, control group). Patients in the first group received PEP-therapy using the EzPAP device 5 times a day for 7—10 minutes in a sitting position, 30 minutes before or 1 hour after meals. The ratio of inhalation to exhalation was 1:2 or 1:3. The expiratory pressure was controlled using a manometer and should not exceed 10–20 cm H₂O.

Patients in the second group trained in the same regimen throughout the day. Static and dynamic breathing exercises were applied.

The study consisted of three stages: I Stage — before surgery; II Stage — 2–3 days after surgery; III Stage — 10–12 days after surgery (discharge from the hospital).

The indicators of the following research methods were studied: 1) spirometry; 2) echocardiography; 3) computed tomography and radiography; 4) tissue and pulmonary gas exchange indicators were calculated (PaO₂/FiO₂, CaO₂, Qs/Qt, DO₂, VO₂, REO₂ and P(A-a)O₂); 5) 24‑hour pulse oximetry; 6) integral rheography (IRG).

Spirometry was conducted according to the methodological recommendations of the Russian Respiratory Society [18] using the SMP‑21/01-»R-D» device (Russia). The following indicators were studied: FVC, FEV₁, FEV₁/FVC, FEV₃, FEV₆, MVV, FEF₂₅, FEF₅₀, FEF₇₅, FEF_25—75 and PEF. Measurement results were expressed as percentages of calculated expected values.

Echocardiographic examination was performed in accordance with the recommendations of the American Society of Echocardiography [19] using a Philips HD15 device (Philips, Netherlands). The main indicators of LV function were studied: EF, EDV, ESV, EDD, ESD, SV and the presence of LV hypokinesis zones.

24‑hour pulse oximetry was performed using the MD300W device (ChoiceMMed, China) and evaluated minimum SpO₂, maximum SpO₂, average SpO₂ and oxygen desaturation index (ODI).

Using integral rheography («Diamant-­R» (Diamant, Russia)), the volume of total (TBW) and extracellular fluid (ECW) was determined.

The surgery was performed under general anesthesia with cardiopulmonary bypass and mechanical ventilation. Body temperature was maintained at normal or moderately hypothermic levels. Cardioplegic solution was used for myocardial protection.

Statistical analysis was performed using Stattech 4.1.2 and SPSS 26.0 software. The Shapiro-­Wilk test was used to assess the normality of distribution. For normally distributed data, mean values (M), standard deviations (SD), and 95% confidence interval (95% CI) were calculated. For non-normally distributed data, median values (Me), upper and lower quartiles (Q1–Q3) were calculated. When comparing two groups on a quantitative indicator with normal distribution, Student’s t-test was used, and in the absence of normal distribution, the Mann-­Whitney U-test was used. McNemar’s test was used to compare binary indicators of two related samples. One-way repeated measures ANOVA was used to analyze quantitative data of three or more related sets. The significance of changes was assessed using Pillai’s trace. Differences were considered statistically significant at p < 0.05.

Results and discussion

A comparative analysis of clinical and demographic characteristics between the two groups did not reveal any statistically significant differences (p > 0.05) (Table 1).

Table 1
Clinical and demographic characteristics of patients

Indicators	Group I(n = 27)	Group II(n = 30)	Р
Demographic indicators
Age, full years	58 ± 9	62 ± 8	0.082
Height, cm	174 ± 5	172 ± 7	0.270
Body weight, kg	87 ± 12	83 ± 15	0.303
Body mass index, kg/m2	29 ± 4	28 ± 4	0.966
Female, abs. (%)	3 (11.1)	4 (13.3)	1.000
Male, abs. (%)	24 (88.9)	25 (83.3)
Smoking, abs. (%)	12 (44.4)	18 (60.0)	0.240
Concomitant diseases
COVID‑19, abs. (%)	15 (55.6)	14 (46.7)	0.503
Diabetes mellitus	6 (22.2)	6 (20.0)	1.000
Hypertension	18 (66.7)	20 (66.7)	1.000
Acute cerebrovascular accident	0 (0.0)	2 (6.7)	0.492
Surgical characteristics of patients
Duration of operation, hour	6 ± 1	6 ± 2	0.285
Duration of cardiopulmonary bypass, min	116 ± 45	126 ± 57	0.503
Aortic compression time, min	73 ± 33	63 ± 29	0.235
Number of shunts applied	2 ± 1	2 ± 1	0.820
Duration of stay in the ICU, hour	35 ± 10	39 ± 25	0.554
Duration of ventilation in the ICU, hour	20 ± 5	24 ± 20	0.321

Analysis of preoperative computed tomography (CT) results showed the presence of post-inflammatory phenomena (pneumofibrosis) in 18 patients in groups I and II (66.7% and 60% respectively). Additionally, in group II, two patients were found to have post-­COVID changes in lung parenchyma of the «ground glass» type. However, these differences between groups were not statistically significant (p > 0.05).

Analysis of spirometry data conducted before surgery revealed a decrease in both volume and flow respiratory parameters of the lungs in both groups. No statistically significant intergroup differences were found (p > 0.05). The spirometry data are presented in Table 2.

Table 2
Spirometry results at the preoperative stage in groups I and II

Indicators	Group I	Group II	P
FVC,%	89.2 ± 8.4 [85.9—92.6]	87.3 ± 7.3 [84.6—90.1]	0.367
FEV1,%	90.6 ± 10.3 [86.5—94.7]	88.0 ± 13.8 [82.8—93.2]	0.429
FEV1/FVC	101.7 ± 5.3 [99.5—103.8]	98.9 ± 8.9 [95.5—102.2]	0.164
FEV3,%	88.5 ± 9.4 [84.8—92.3]	88.1 ± 12.0 [83.6—92.6]	0.883
FEV6,%	89.9 ± 11.5 [85.3—94.4]	89.4 ± 15.1 [83.7—95.0]	0.897
PEF,%	90.7 ± 8.5 [87.3—94.0]	88.8 ± 21.1 [80.9—96.7]	0.667
FEF25,%	83.4 ± 13.1 [78.2—88.6]	80.8 ± 20.4 [73.2—88.4]	0.578
FEF50,%	80.7 ± 13.2 [75.5—86.0]	78.9 ± 13.4 [73.8—83.9]	0.604
FEF75,%	75.5 ± 18.2 [68.3—82.7]	71.4 ± 19.7 [64.0—78.8]	0.419
FEF25—75,%	81.7 ± 14.9 [75.8—87.7]	77.2 ± 20.9 [69.3—85.0]	0.349
ELA,%	107.1 ± 19.5 [99.3—114.8]	110.8 ± 20.7 [103.0—118.5]	0.492
MVV,%	85.9 ± 11.4 [81.4—90.5]	85.3 ± 13.8 [80.1—90.4]	0.849
FEV1/FEV6,%	99.5 ± 7.5 [96.5—102.5]	96.8 ± 9.7 [93.0—100.6]	0.259

Preoperative echocardiography showed an increase in the left ventricle (LV) volume parameters and a decrease in myocardial contractility in both groups. The LV ejection fraction was 42.8 ± 6.4% in group I and 44.9 ± 4.7% in group II, without statistically significant differences between the groups (p = 0.170). At the same time, the EDV and ESV indicators were noticeably higher than normal values and were as follows: for EDV: 174.2 ± 19.1 ml — group I and 179.9 ± 35.0 ml — group II; for ESV: 102.1 ± 16.4 ml and 103.0 ± 28.1 ml, respectively. The p-values for intergroup differences in these indicators did not reach statistical significance (p = 0.459 and p = 0.892, respectively).

Analysis of 24‑hour pulse oximetry data before surgery revealed a decrease in the average level of arterial blood oxygenation in both groups relative to normal values. In group I, the mean oxygenation value was 91.2 ± 2.1%, and in group II — 92.5 ± 3.4%. The oxygen desaturation index (ODI) value in group I was 7.1 ± 0.6, and in group II — 6.7 ± 0.9. Intergroup differences were not statistically significant (p > 0.05).

On the second day after surgery, both groups showed a statistically significant decrease in both flow and volume spirometry parameters. In group I, FVC, FEV₁, and MVV decreased by 26.6% (p < 0.001), 33.2% (p < 0.001), and 36% (p < 0.001) respectively. The decrease in group II was comparable and amounted to 31.4% (p < 0.001), 35.2% (p < 0.001), and 37.7% (p < 0.001) respectively (Figure 1). The dynamics of FEV₃ and FEV₆ indicators corresponded to this trend, their decrease also amounted to more than 30% from baseline values (p < 0.05).

Fig. 1 (a—d). Dynamics of volume spirometry indicators in patients of groups I and II at all stages of the study
Note:   — group I;  — group II. * — presence of interstage differences (* — p < 0.05; ** — p < 0.01; *** — p < 0.001); # — presence of intergroup differences.

Peak expiratory flow (PEF), as well as flow indicators reflecting the conductance of various parts of the airways (FEF₂₅, FEF₅₀, FEF₇₅, and FEF_25—75) decreased by more than 30% from baseline values (p < 0.05), with PEF, in group I, decreasing by 44.6% from the preoperative level (p = 0.001) (Figure 2).

As the change in spirometric indicators on the second day after surgery was symmetrical in both groups, no statistically significant intergroup differences were found (p > 0.05).

Echocardiography data obtained by the Simpson method at the second stage of the study were characterized by a significant decrease in LV volume parameters. EDV in groups I and II decreased by 26.2% (p < 0.001) and 27.7% (p < 0.001) respectively; ESV decreased by 28.7% (p < 0.001) and 27.6% (p < 0.001), and stroke volume by 23.9% and 30% (p < 0.001) respectively. Data by Teichholz method indicate a decrease in EDD in groups I and II by 9.7% (p < 0.001) and 7.7% (p < 0.001), and ESD by 10.2% (p < 0.001) and 6.8% (p < 0.001) respectively. No statistically significant intergroup differences were found (p > 0.05).

Analysis of 24‑hour pulse oximetry results on the second day after surgery revealed an increase in sleep-­disordered breathing (SDB) in patients of both groups. In groups I and II, ODI increased by 2.9 (p < 0.001) and 3.1 (p < 0.001) times respectively. The mean oxygenation value in groups I and II was 86 ± 4.5% and 87 ± 2.8% respectively. No intergroup differences were found (p>0.05).

Analysis of pulmonary and tissue gas exchange data in patients of both groups on the second day after surgery revealed a significant deviation of the main integral indicators relative to reference values. The normal value of the PaO₂/FiO₂ oxygenation index is about 500 while the mean values in groups I and II were lower by 28.6% and 35.2% respectively (Table 3).

Table 3
Gas exchange rates in patients of groups I and II on the second day after surgery

Indicators	Group I	Group II	P
Index PaO2/FiO2	357 ± 91[321—394]	324 ± 66[299—349]	0.115
CaO2, ml/l	148 ± 16[141—154]	149 ± 19[142—156]	0.841
P(A-a)O2, mmHg	147 ± 59[124—170]	159 ± 36[145—172]	0.378
Qs/Qt,%	16 ± 7[13—18]	15 ± 3[14—16]	0.574
Index DO2, ml/kg/m2	403 ± 129[352—454]	427 ± 148[372—482]	0.530
VO2 index, ml/kg/m2	97 ± 40[81—113]	108 ± 37[94—122]	0.307
REO2,%	23 ± 8[20—27]	26 ± 6[24—29]	0.142

When assessing the volumes of total body water (TBW) and extracellular water (ECW) at the second stage of the study, an increase in both indicators was found in the first and second groups by 25.3% and 26.7% (p = 0.011; p = 0.002), and by 35.1% and 34.3% (p < 0.001; p < 0.001) respectively.

At the second stage of the study, all patients underwent chest X-ray. Additionally, 14 patients from group I and 15 from group II (29 patients in total) underwent additional chest CT. CT data of patients from both groups indicate the appearance of inflammatory and congestive changes, such as «ground glass» opacities, hydrothorax, mosaic perfusion, hypoventilation, etc. Computed tomography revealed bilateral and unilateral atelectasis of various parts of the lungs in 100% of the examined patients. According to X-ray data, atelectasis was detected in only 3 out of 29 examined patients. CT data of patients are presented in Table 4.

Analysis of spirometry data conducted before discharge from the hospital on the 10—12th day (Stage III) showed statistically significant positive dynamics of most respiratory indicators in both groups. However, the restoration of respiratory function was more pronounced in patients who underwent PEP-therapy (group I) than in the control group (group II). Statistically significant intergroup differences were found in the dynamics of not only volume parameters (FEV₁: 22.1% vs 9.4% [p = 0.001]; FEV₃: 17.6% vs 9.7% [p = 0.015]; MVV: 24.9% vs 8.4% [p = 0.003] respectively) (Figure 1), but also flow parameters of spirometry (PEF: 58.1% vs 19.5% [p = 0.019]; FEF₂₅: 30.9% vs 20.4% [p = 0.002]; FEF₅₀: 36.5% vs 4.1% [p = 0.001]; FEF₇₅: 25.8% vs 19.9% [p = 0.016]; FEF_25—75: 39.9% vs 7.5% [p = 0.001] respectively) (Figure 2).

Moreover, in the control group, there was practically no recovery dynamics of FEF₅₀ and FEF_25—75 indicators by Stage III of the study (p = 0.335 and p = 0.165 respectively). For FVC, positive dynamics in groups I and II were characterized as statistically significant (9.1% [p < 0.001] and 14.6% [p < 0.001]), however, no differences between groups were observed (p = 0.333).

Analysis of echocardiography data at discharge from the hospital (Stage III of the study) did not reveal statistically significant changes in all studied parameters since the operation, except for the LV ejection fraction. In group I, the improvement in LVEF was 12.7% (p < 0.001), and in group II only 4% (p = 0.008). However, no intergroup differences were found (p = 0.505).

Fig. 2 (a-d). Dynamics of spirometry flow parameters in patients of groups I and II at all stages of the study
Note:   — group I; — group II. * — presence of interstage differences (* — p < 0.05; ** — p < 0.01; *** — p < 0.001); # — presence of intergroup differences; ns — absence of statistically significant differences.

Moreover, in the control group, there was practically no recovery dynamics of FEF₅₀ and FEF_25—75 indicators by Stage III of the study (p = 0.335 and p = 0.165 respectively). For FVC, positive dynamics in groups I and II were characterized as statistically significant (9.1% [p < 0.001] and 14.6% [p < 0.001]), however, no differences between groups were observed (p = 0.333).

Analysis of echocardiography data at discharge from the hospital (Stage III of the study) did not reveal statistically significant changes in all studied parameters since the operation, except for the LV ejection fraction. In group I, the improvement in LVEF was 12.7% (p < 0.001), and in group II only 4% (p = 0.008). However, no intergroup differences were found (p = 0.505).

At the third stage of the study, patients in both groups showed positive dynamics in ODI and mean SpO₂ value, with statistically significant differences (p = 0.003). In group I, the mean SpO₂ value increased to 91.7 ± 3.7%, and the ODI index decreased by 63.6% to 7.5 ± 0.6 (p < 0.001) (Figure 3). Thus, both indicators in group I returned to baseline values.

In group II, the ODI index was also significantly lower compared to the same indicator at the second stage of the study (49.3%, p < 0.001), but at the same time, it remained elevated by 57.2% (10.5 ± 0.8 [p < 0.001]) compared to the initial value. At discharge, the mean SpO₂ value in these patients remains 10.2% (p = 0.011) lower than before the operation.

The results of computed tomography obtained during Stage III of the study showed that inflammatory and congestive changes persist in patients of both groups up to discharge from the hospital. The number of patients with unilateral or bilateral hydrothorax (residual) in both groups did not change significantly by the time of discharge (p > 0.05). At the same time, in group I, a statistically significant decrease (by 42.9%, p = 0.014) in the number of patients with atelectasis was revealed. Moreover, the number of patients with atelectasis in group I became 1.6 times less than in the control group (p = 0.035). CT data are presented in Table 4.

Fig. 3. Indicators of the oxygenation index in patients of groups I and II at all stages of treatment
Note:   — group I; — group II. * — presence of interstage differences (* — p < 0.05; ** — p < 0.01; *** — p < 0.001). # — presence of intergroup differences; ns — absence of statistically significant differences.

Table 4
Computed tomography data in patients of group I and II at the second and third stages of the study

Indicators	Stage	Group I	Group II	P
Pneumofibrosis	Stage II	14 (100)	15 (100)	1.000
	Stage III	14 (100)	15 (100)	1.000
«Ground glass»	Stage II	7 (50.0)	4 (26.7)	0.264
	Stage III	4 (28.6)	4 (26.7)	1.000
Areas of consolidation (atelectasis)	Stage II	14 (100)	15 (100)	1.000
	Stage III	8 (57.1)	14 (93.3)	0.035*
Hydrothorax	Stage II	13 (92.9)	9 (60.0)	0.080
	Stage III	11 (78.6)	7 (46.7)	0.128
Paresis of the dome of the diaphragm	Stage II	5 (35.7)	7 (46.7)	0.710
	Stage III	5 (35.7)	7 (46.7)	0.710

According to IRG data, TBW and ECW indicators did not recover by the end of the third stage of the study and exceeded the initial values in group I by 11.1% and 21.4% (p = 0.029; p = 0.017), and in group II by 10.2% and 23.1% (p = 0.016; p = 0.009) respectively, without significant differences between groups (p > 0.05).

In this study, a comparative assessment was conducted on the effect of positive expiratory pressure therapy versus conventional respiratory gymnastics on the respiratory system of patients after the left ventricle geometric reconstruction in the early postoperative period.

Analysis of the study results revealed impairments in external respiratory function in both groups during the preoperative period. The decrease in respiratory function in patients with post-infarction left ventricle aneurysm is likely due to systemic hemodynamic disturbances and the development of chronic heart failure, leading to congestion in the pulmonary circulation and an increase in interstitial edema, causing restrictive disorders of external respiratory function [20, 21]. Additionally, patients with CHF may experience increased mucus production and impaired mucociliary clearance [22], due to respiratory epithelial dysfunction [23], which can provoke obstructive respiratory disorders.

Spirometry data on the 2nd day after surgery in patients of both groups show a significant decrease (by 30–40%) in almost all spirometry indicators. According to literature data, these disorders may be caused by a decrease in lung tissue compliance due to an increase in extracellular fluid [24], which is also confirmed by the results of our study. Furthermore, the decrease in external respiratory function indicators after surgery may also be caused by disruption of chest integrity, pain syndrome, mucus hyperproduction, and impaired mucociliary clearance [10, 25].

By the time of hospital discharge (10–12 days post-intervention), patients in the first group, who underwent PEP-therapy, demonstrated statistically significant improvements of pulmonary function, especially in the flow characteristics of spirometry (PEF, FEF₂₅, FEF₅₀, etc.), compared to patients who received a standard course of respiratory gymnastics. The obtained results indicate the effectiveness of therapy with the EzPAP device, which maintains constant positive pressure in the airways, preventing their collapse during inhalation, allowing for more effective restoration of mucociliary clearance and patency of all bronchial sections. Moreover, moderate expiratory resistance in the safe range of 10–20 cm H₂O [26, 27] contributes to more effective restoration of respiratory muscle tone [28–30], allowing patients to perform breathing maneuvers qualitatively during spirometry examination.

Comparative analysis of radiography and CT data showed that conventional radiography performed in the early postoperative period does not fully determine the presence and extent of atelectasis affecting various parts of the lungs, compared to diagnostic methods such as lung ultrasound and CT [31, 32]bedside chest radiography, and lung ultrasonography with that of thoracic computed tomography. Three pathologic entities were evaluated in 384 lung regions (12 per patient. In our study, chest CT on the 2nd day after surgery revealed the formation of atelectasis in 100% of examined patients in both groups, which is comparable with the results obtained by Hedenstierna et al. [33].

It is known that the main factors in the development of X-ray negative microatelectasis are prolonged cardiopulmonary bypass [34], surfactant damage and disruption of its production, as well as a decrease in alveolar pressure [35], leading to alveolar collapse and impaired alveolar gas exchange. Pulmonary and tissue gas exchange data obtained on the 2nd day after surgery and the results presented in Table 3 confirm significant impairments in lung oxygenation function in patients of both groups.

The use of PEP-therapy allows for a statistically significant reduction in the number of patients with atelectasis in group I by the time of hospital discharge, as well as a reduction in the volume of remaining atelectasis. At the same time, group II showed almost no decrease in the number and volume of atelectasis. This is likely due to the fact that positive expiratory pressure allows for the recruitment of collapsed alveoli by increasing transpulmonary pressure [36], and maintaining positive pressure during inhalation prevents their derecruitment [37]. Meanwhile, classical breathing exercises do not have a desorption effect. Furthermore, it should be noted that with traditional respiratory gymnastics, it is impossible to dose and control the level of positive expiratory pressure, resulting in insufficient increase in transpulmonary pressure, which significantly reduces the effectiveness of this respiratory rehabilitation method [38].

During 24‑hour pulse oximetry at the preoperative stage, respiratory function disorders during sleep were detected in patients of both groups. A decrease in blood oxygenation indicators was observed, with the mean desaturation index being above normal values in both groups (ODI>5), which increased the risk of sleep apnea episodes in this category of patients. It is known that patients with cardiovascular pathology are at risk for SDB. In patients with coronary heart disease complicated by heart failure, the prevalence of sleep apnea exceeds 70% [39]. Moreover, not only can the presence of sleep apnea affect the occurrence of cardiovascular diseases and the development of CHF, but in turn, the presence of CHF can provoke the occurrence of sleep apnea syndrome and potentiate an increase in the frequency of apnea/hypopnea episodes of both central and obstructive types [40].

In our study, a significant increase in the ODI was observed in the early postoperative period in patients of both groups. These disorders may be due to the influence of a combination of intraoperative factors, such as intubation causing damage and edema of the vocal cords and larynx, as well as the use of general anesthesia and muscle relaxants during surgery. These risk factors, against the background of the forced supine position of the patient, can provoke obstructive breathing disorders during sleep, as well as exacerbate the course of moderate to severe OSAS [41]. The influence of postoperative heart failure on sleep apnea/hypopnea should be emphasized, which leads to worsening of congestion in the pulmonary circulation, especially in the horizontal supine position during sleep, leading to interstitial edema and increased ODI [42–44].

Patients in group I receiving PEP-therapy showed restoration of ODI and average oxygenation to preoperative values at Stage III of the study, while in group II they remained reduced. Apparently, the effect of PEP-therapy is largely provided by maintaining constant positive pressure in the airways during sessions on the EzPAP device with connected main oxygen. Improvement in the oxygenating function of the lungs against the background of oxygen therapy positively affects the recovery of respiratory disorders [45]. In addition, constant positive pressure likely contributes to the restoration of airway stability and a reduction in the number of desaturation episodes. This is supported by studies that have proven the effectiveness of the assisted ventilation technique with constant positive pressure during sleep — CPAP, which prevents the collapse of airways and eliminates episodes of apnea/hypopnea [46].

Thus, regular use of PEP-therapy in the early postoperative period contributes to the stabilization of airways, improvement of blood oxygenation, and reduction in the frequency of SAS episodes of both obstructive and central nature.

Conclusion

The use of PEP-therapy using the EzPAP device in patients after LVGR in the early postoperative period allows not only to reduce the number and volume of atelectasis but also to more effectively restore spirometry indicators compared to patients receiving a standard course of respiratory gymnastics.

In the early postoperative period after LVGR, patients experience impaired gas exchange and a significant increase in the number of desaturation episodes during sleep. PEP-therapy contributes to the restoration of blood oxygenation indicators and desaturation index to baseline values by the time of discharge, while in patients receiving a standard course of respiratory gymnastics, these indicators remain reduced.

The use of PEP-therapy in the early period after LVGR surgery can be successfully applied in conjunction with conservative methods of respiratory rehabilitation, as it is safe and well-tolerated by patients.

About the authors

Maksim L. Mamalyga

A.N. Bakulev National Medical Research Center for Cardiovascular Surgery of the Ministry of Health of the Russian Federation

Email: mazatenko@bakulev.ru
ORCID iD: 0000-0001-9605-254X
SPIN-code: 1857-9594
Moscow, Russian Federation

Mikhail M. Alshibaya

A.N. Bakulev National Medical Research Center for Cardiovascular Surgery of the Ministry of Health of the Russian Federation

Email: mazatenko@bakulev.ru
ORCID iD: 0000-0002-8003-5523
Moscow, Russian Federation

Mark A. Zatenko

A.N. Bakulev National Medical Research Center for Cardiovascular Surgery of the Ministry of Health of the Russian Federation

Author for correspondence.
Email: mazatenko@bakulev.ru
ORCID iD: 0000-0003-3767-6293
SPIN-code: 9084-0481
Moscow, Russian Federation

Sergey A. Danilov

A.N. Bakulev National Medical Research Center for Cardiovascular Surgery of the Ministry of Health of the Russian Federation

Email: mazatenko@bakulev.ru
ORCID iD: 0000-0002-0525-2069
Moscow, Russian Federation

Gela G. Getsadze

A.N. Bakulev National Medical Research Center for Cardiovascular Surgery of the Ministry of Health of the Russian Federation

Email: mazatenko@bakulev.ru
ORCID iD: 0000-0003-2556-2053
Moscow, Russian Federation

Sergey L. Babak

Scientific and Educational Institute of Clinical Medicine named after N.A. Semashko of the Russian University of Medicine, Ministry of Health of the Russian Federation

Email: mazatenko@bakulev.ru
ORCID iD: 0000-0002-6571-1220
SPIN-code: 5213-3620
Moscow, Russian Federation

References

Supplementary files