This prospective study included 71 patients with CCS at the Lanzhou University Second Hospital between October 2020 and May 2021. The study was approved by the Ethics Committee of the Lanzhou University Second Hospital (2021 A-022). All patients provided written informed consent.

After hospital admission, all patients completed the relevant baseline and psychological scale surveys, physical examinations, and laboratory tests. Coronary angiography (CAG) was done 12–24 h postoperatively. The inclusion criteria were: (1) patients who met the American Guidelines for the Diagnosis and Treatment of Coronary Heart Disease diagnostic criteria for CCS [20] and showed obvious symptoms; (2) conscious patients who had no communication difficulties; and (3) complete medical records. The exclusion criteria were: (1) the presence of mental disorders or mental retardation; (2) the presence of other cardiovascular diseases, including congenital heart disease, cardiomyopathy, etc.; (3) a history of heart transplantation; (4) the presence of other severe medical conditions, including heart failure, respiratory failure, etc.; (5) presence of systemic immune diseases or infections; and (6) pregnant or breastfeeding patients; (7) Age < 18 years; (8) presence of peripheral artery disease.

Baseline patients data, including age, gender, ethnicity, smoking history, drinking history, body mass index (BMI), heart rate (HR), percutaneous coronary intervention (PCI), systolic blood pressure (SBP), diastolic blood pressure (DBP), SBP standard deviation (SBPSD), DBP standard deviation (DBPSD), SBP variation (SBPV), DBP variation (DBPV), forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), maximum ventilation volume (MVV), 6-minute walk test (6MWT), and anxiety scale scoring, were collected from an electronic medical record system. Hematological parameters, including hemoglobin (HB), C-reaction protein (CRP), creatinine (CR), bloodglucose (Glu), kinase isoenzyme (CK-MB), cardiac troponin I (TnI), prothrombin time (PT), prothrombin activity (PT%), thrombin time (TT), activated partial thromboplastin time (APTT), prothrombin time ratio (PT-R), international normalized ratio (INR), plasma fibrinogen (FIB), antithrombin III (AT III), and fibrinogen degradation product (FDP) were also measured. The serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDLC), high-density lipoprotein cholesterol (HDLC), triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), free tetraiodothyronine (FT4), thyroid stimulating hormone (TSH) levels were also measured.

Serum NO levels were determined using the nitrate reductase method following manufacturer instructions (A013-2-1, Jiancheng, Nanjing) as described previously. The specific steps are as follows. (1) Add the sample and R1, R2 mixed reagents according to the steps, and take a water bath at 37 ℃ for 60 min. (2) Add R3 and R4, extract and let stand at room temperature for 40 min, 3500–4000 rpm, centrifuge for 10 min. (3) Take 0.5 ml of supernatant, add chromogenic agent, let stand for 10 min, 550 nm wavelength, 1 cm optical path, colorimetric analysis. Moreover, blood samples were taken from patients and control subjects at 6–7 am after an overnight fast. After centrifugation at 3000 r/min for 10 min, the supernatant was collected and stored at − 80 °C. Serum levels of ET-1, was measured using enzyme-linked immunosorbent assay (ELISA) kits (H093-1-1, Jiancheng, Nanjing) following the manufacturer’s instructions as described previously.

The cardiopulmonary exercise test is an internationally accepted cardiopulmonary test that measures respiratory and circulatory function levels [21] and can also evaluate functional motor capacity and disease diagnosis and treatment. To ensure patient safety and considering that the patient had not received any therapeutic intervention, the exercise intensity was kept close to daily human activities. The patients undertook the 6MWT and walked as swiftly as possible to increase exercise intensity and evaluate the ability of sub-extreme exercise. The P, R, SPO2, SBP, DBP, SBPSD, DBPSD, SBPV, DBPV, FVC, FEV1, and MVV indicators and walking distance were measured during the exercise. FVC is the maximum air volume that can be exhaled in the shortest possible time after maximum inhalation. FEV1, a functional index, indicated clinical lung function and is calculated as the lung gas volume percentage that an individual can forcibly expel during the first second following maximal inhalation. Similarly, MVV is the maximum volume of air an individual can inhale and then exhale in one minute.

CAG was performed by the same professional intracardiac intervention team for all patients, and its results, from which the GSs were calculated, were interpreted by two deputy chief physicians. GS is evaluated as follows: (1) The coronary artery is divided into 15 segments, and weight coefficients are assigned based on the segments and parts of the coronary artery. The weight coefficient is 1.5 for the proximal segment; 1 for the left anterior descending branch; 1 for the first diagonal branch; and 1 each for the blunt marginal branch, the posterior branch of the left circumflex, the proximal right coronary artery, the middle of the right coronary artery, the distal right coronary artery, and the posterior descending branch. (2) The coronary stenosis degree determines the weight coefficient as follows: 1 for coronary stenosis ≤ 25%, 2 for 25% < coronary stenosis ≤ 50%, 4 for 50% < coronary stenosis ≤ 75%, 8 for 75% < coronary stenosis ≤ 90%, 16 for 90% < coronary stenosis ≤ 99%, and 32 for coronary stenosis = 100%. (3) The final scoring, that is, the sum of the stenosis scores of each branch vessel, is calculated as the weight coefficient of the coronary stenosis degree multiplied by the weight coefficient of each diseased vessel segment.

PASS 15 was used to calculate the sample size, the minimum sample size required for this study was 32 with α = 0.1 and a lower one-tailed test. Statistical Package for the Social Science, version 23 (SPSS Inc., Chicago, IL) was used for statistical analysis. Measurement data were expressed as mean ± standard deviation and between-group comparisons were done using the analysis of variance (ANOVA) test. Enumeration data were expressed as frequency (%), and the chi-square test was used for between-group comparison. Multivariable linear regression analysis was performed to investigate the relationship between the Gensini score and CCS serum vasoactive substances in CCS. All tests were two-tailed, and p < 0.05 was considered statistically significant.