Effectiveness of deep breathing exercises on anxiety, depression and sleep quality in patients undergoing coronary artery bypass surgery

Abstract

This study investigated the effect of deep breathing exercises on sleep quality, anxiety, and depression in coronary artery bypass graft patients. This is a clinical trial with 2 parallel groups (intervention, control) that was conducted on 80 patients underwent coronary artery bypass surgery. Participants were randomly assigned to the groups using a computer-generated random sequence. Allocation was concealed using sealed opaque envelopes prepared by an independent researcher. The intervention group performed deep breathing exercises every three hours, 10 breaths each time, for four days post-surgery. Both groups completed the Hospital Anxiety and Depression Scale at four time points: before intervention (T0), discharge (T1), 15 days later (T2), and one month post-discharge (T3). The Pittsburgh Sleep Quality Index was completed at T0 and T3. Due to the nature of the intervention, blinding of participants and intervention providers was not feasible. However, outcome assessor at T2 and T3 and data analyst were blinded to group assignments to minimize bias. In the intervention group, mean anxiety scores decreased from 10.35 at T0 to 6.97 at T1, 8.92 at T2, and 8.20 at T3 (η² = 0.08, p < 0.05). Depression scores decreased from 10.45 at T0 to 7.92 at T1, 8.77 at T2, and 7.65 at T3 (η² = 0.05, p < 0.05). Sleep quality improved significantly from 9.72 at T0 to 2.82 at T3 (p = 0.0001). Data were analyzed using repeated measures ANOVA with Bonferroni post-hoc tests and independent and paired t-tests. Deep breathing exercises, as a simple and non-pharmacological nursing intervention, can reduce anxiety and depression and improve sleep quality in CABG patients. Nurse-led training of deep breathing is strongly recommended to support psychological well-being and sleep management in these patients.

This research has been registered in Iran’s Clinical Trials Registry on 18/12/2023 (IRCT20231208060294N1).

Introduction

Today, coronary artery disease (CAD) is a major health concern and is the main cause of mortality and morbidity around the world¹. However, thanks to heart surgeries such as coronary artery bypass graft (CABG) or Percutaneous Coronary Interventions (PCI), the mortality rate of patients has decreased². Despite the health benefits of CABG, it is not without any risks and the postoperative complications are responsible for subsequent patients readmission to hospitals³. Although CABG effectively relieves symptoms of angina in patients, they face issues such as psychological distress and sleep-related problems⁴ that patients may not visit physicians for these complications.

Depression and anxiety disorders are common after CABG⁵ and they can increase the incidence rate of infection and worsen wound healing after surgery⁶. Anxiety has a negative impact on learning outcomes in CABG patients⁷. It has also been shown that the presence of depression increases mortality risk and long-term complications in these patients⁸. It is worth noting that psychological illness, when comorbid with cardiac illness, generally leads to poorer outcomes⁹. Since depression has been found to be an independent prognostic factor for mortality, readmission, cardiac events, and lack of functional benefits 6 months to 5 years after CABG, there is a growing need for integrating psychosocial interventions to provide holistic and effective management after CABG¹⁰.

Among physical complications after CABG, sleep disturbance is also prevalent in the first 8 weeks after CABG surgery and sometimes lasts for even 6 months¹¹ that may impact patients’ recovery rate, quality of life, morbidity, and even mortality¹². Disturbed sleep may increase daytime sleepiness following a reduction in nighttime sleep¹³ and patients encounter fatigue, irritability, and prolonged duration of hospitalization and associated costs¹⁴. If patients can get enough sleep after surgery their daily life activities will be improved after CABG¹⁵.

Current management strategies for postoperative anxiety, depression, and sleep disturbances include pharmacological treatments, such as anxiolytics and antidepressants, and non-pharmacological approaches like cognitive-behavioral therapy (CBT) and relaxation techniques¹⁶. However, pharmacological interventions often carry risks of side effects, including dependency and adverse reactions, which may be particularly concerning for cardiac patients¹⁷. Non-pharmacological methods like CBT, while effective, require specialized training and resources, limiting their accessibility in many healthcare settings¹⁸. Consequently, there is a pressing need for safe, cost-effective, and easily implementable interventions that can address these complications in CABG patients.

Deep breathing exercises are complementary, non-invasive, cost-effective method without side effects, exerting positive effects on cardiopulmonary function, anxiety, depression and insomnia and can be easily taught and practiced independently by patients¹⁹. These features make it particularly suitable as a nurse-led intervention in the post-CABG setting. Studies showed that this nursing intervention has the potential to reduce the symptoms of anxiety and depression²⁰.

Deep breathing offers numerous advantages for patients undergoing heart surgery and their recovery²¹. It is thought that deep breathing stimulates the parasympathetic nervous system, fostering relaxation and alleviating stress, which are key factors affecting sleep quality²². Deep breathing exercises have been shown to positively impact cardiac patients by improving autonomic balance and reducing stress hormone levels and can shift the sympathovagal balance towards parasympathetic dominance, reducing sympathetic overactivity often seen in cardiac conditions²³.

Despite these benefits, the application of deep breathing in CABG patients remains underexplored, with limited evidence on its specific effects on anxiety, depression, and sleep quality. Existing studies suggest that rigorous randomized controlled trials are needed to establish the optimal duration, frequency, and efficacy of such interventions in this population^16,24,25. This study addresses this research gap by evaluating the effects of a structured diaphragmatic breathing intervention conducted every three hours, involving 10 breaths each time, for four days after surgery on anxiety, depression, and sleep quality in patients undergoing CABG. We hypothesized that: (1) deep breathing has the potential to reduce anxiety in patient’s undergoing CABG; (2) deep breathing can reduce depression in patient’s undergoing CABG; and (3) deep breathing can improve the sleep quality in patient’s undergoing CABG.

Materials and methods

Study design

This was a randomized clinical trial with two parallel groups, using a pretest–posttest repeated-measures design. The study was designed and reported in accordance with the CONSORT 2010 guidelines.

Participants and sampling

The study was carried out in a department includes all candidates for coronary artery bypass surgery who presented at a healthcare center affiliated with Kerman University of Medical Sciences. As this cardiac surgery center is the only governmental facility in Kerman city, this study was exclusively conducted in this center. All eligible patients who were willing to participate were enrolled until reaching the required sample size. Subsequently, they were randomly allocated using block randomization to either the intervention or control groups (Fig. 1). After explaining the study objectives, they were invited to participate. then they were assigned to intervention or control groups using pre-generated randomization sequences concealed in opaque envelopes. Subsequently, they were provided with the initial questionnaires (time 0), which they completed independently or with the researcher’s assistance if necessary. Data collection and the intervention phase began on January 10, 2024, and concluded on July 15, 2024.

Fig. 1.

Participants’ flowchart.

Inclusion Criteria: Age above 20 years, being literate and able to use smartphone, stable hemodynamic signs, hospitalization at least one day before surgery.

Exclusion criteria: History of mental disorders (self-report of depression, anxiety), pre-surgery sleep disorders (self-reported), use of sedatives, sleep-inducing drugs or scents, hearing impairment, lack of social supports (living alone, having no family or friends, or lacking a support system that could help them during their recovery period), Pre-existing chronic conditions like uncontrolled diabetes, kidney failure, HIV and etc.

By applying the information of Ghorbani et al. (2019), we determine the sample size¹⁷. Accordingly, the sample size in each group was 36 individuals. Considering of 10% dropouts or repeated measurement data, 40 patients in each group were required in this study (Fig. 1).

n = (Z_α/2+Z_β) ² *2*σ² / d².

Z_1−α/2=1.96. Z _1−β=1.28.

σ2=(sd1² + sd2²).

Assumptions:

α = 0.05 (two - side)

β = 0.80

M1 = 14.97; while d=(M₂-M₁)

M2 = 19.50

Sd1 = 4.73

Sd2 = 3.6.

Randomization

Block randomization was conducted using Random Allocation Software, with blocks sized at 10. A researcher who was not involved in patient recruitment, intervention, or outcome assessment generated the random sequence. To ensure allocation concealment, sequentially numbered, sealed, opaque envelopes were prepared by this independent researcher. The primary investigator opened these envelopes only after participants had consented to the study and completed their baseline assessments, maintaining allocation concealment until the assignment point.

Study measurements

The data were collected by using three questionnaires: (1) sociodemographic form. This section included gender, age, occupation, living place (city or village), marital status, history of smoking or alcohol/substance use, duration of hospitalization, underlying diseases, and type of surgery (elective or emergency).

(2) Hospital Anxiety and Depression Scale (HADS): Designed by Zigmond & Snaith (1983), this questionnaire includes seven items related to anxiety symptoms and seven items related to depression symptoms²⁶. The questionnaire utilizes a four-point scale (0–3), with items 3, 7, 10, 11, 13, and 14 scored inversely. The minimum score is 0, and the maximum is 21. A score of 11 is considered the cut-off point, where scores above it hold clinical significance. The Persian version of this scale, validated by Kaviani et al. in 2009, showed a reliability of 0.70 for the depression subscale and 0.85 for the anxiety subscale²⁷.

(3) Pittsburgh Sleep Quality Index (PSQI) Questionnaire: Developed by Buysse et al. (1989). This questionnaire measures sleep quality over the last month and consists of 9 items²⁸. Since question 5 includes 10 sub-items, the questionnaire contains a total of 19 items. The first 4 items ask about bedtime, time to fall asleep, waking time, and hours of sleep. Items 5 to 19 address sleep problems and their frequency scored on a 4-point Likert scale from 0 to 3. This questionnaire included 7 subscales: sleep mental quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, sleep medication, and daytime dysfunction. Each subscale is scored from 0 to 3, 0 for no sleep problem to 3 for very severe sleep problem. The sum of scores across the 7 subscales ranges from 0 to 21, where higher scores indicate poorer sleep quality. The cutoff point for undesirable sleep was 5. The scores below 5 shows desirable sleep. Chehri et al. (2020) investigated the construct validity and reliability of the Persian version of this questionnaire. The questionnaire was found to be valid and had a Cronbach’s alpha coefficient of 0.73²⁹. In the present study the Cronbach’s alpha was 0.83.

Intervention

The intervention was deep breathing exercise, one day prior to the surgery, by providing written instructions (a pamphlet of deep breathing exercise) and face-to-face training by an experienced nurse employed in the cardiac surgery department. The breathing technique involved instructing the patient to take a deep breath through the nose (inhaling as much air into the lungs as possible), holding the breath for 2 to 5 s, and then slowly exhaling through the mouth to leave a small amount of air in the lungs. This intervention started after ensuring the patient’s hemodynamic stability (based on medical records or physician confirmation). The breathing exercises were conducted once every three hours, comprising 10 deep breaths each time with short pause between breaths. This process continued for four days after surgery. The educational content was delivered by a nurse from the cardiac surgery ward. The control group received the routine educational instruction about their wound care, next doctor’s visit and their physical complications that may need urgent care.

To prevent interaction between the groups, the first author, who works in the cardiac surgery ward, organized patient bed arrangements for the intervention and control groups separately. This was done to ensure patients do not exchange information.

Due to the nature of the intervention, blinding of participants and intervention providers was not feasible. However, outcome assessor (telephone interviews at T2 and T3) and data analyst were blinded to group assignments to minimize bias.

Outcome variables

The outcomes were anxiety and depression that were measured at four points: a day before surgery(T0), on the discharge day (T1), 15 days post-discharge(T2), and one-month post-discharge(T3). Additionally, sleep quality was measured at two time points (T0 and T3). The T2 and T3 assessments were conducted through telephone interviews. All interviews were carried out by the independent trained research assistant, who was blinded to the participants’ group assignments. To ensure consistency and minimize interviewer bias, the assistant underwent structured training on standardized interview procedures. This training included guidance on the proper phrasing and order of the questionnaire items. During each call, a detailed script was utilized, and participants’ responses were recorded immediately without any interpretation. The interviews were conducted with the consent and cooperation of the patients.

Statistical analysis

To analyze the data, the trial version of SPSS version 25 software was utilized. To confirm the homogeneity of demographics between groups, χ2 test and Fisher’s exact test were used. Normality of data was confirmed using the Shapiro-Wilk test, and sphericity was assessed with Mauchly’s test for repeated-measures ANOVA. If sphericity was violated, the Greenhouse-Geisser correction was applied. Since the distributions of data were normal so to compare the means of outcome variables in the intervention / control groups, t-test, repeated measures ANOVA and Bonferroni post-hoc test were applied. Cohen (1988) indicated that the effect sizes of the ANOVA are interpreted as partial η2 of 0.01 can be considered a small effect, a partial η2 of 0.06 can be considered a medium effect, and a partial η2 of 0.14 can be considered a large effect³⁰. The sociodemographic characteristics of the participants were reported as descriptive statistics according to the underlying data scales (frequencies and percentiles for qualitative data, mean and SD for quantitative data).

Results

Participant characteristics

Based on the findings of Table 1, two groups were homogeneous (p-value ≥ 0.05). Most of the participants were men, illiterate, married, without comorbidity and lived in cities (Table 1).

Table 1.

Demographic data and their homogeneity in control and intervention groups.

Groups variable		Intervention	Control	P-value
		Frequency (%)	Frequency (%)
Education	Iilliterate	20 (50)	25 (5.62)	*0.55 (ns)
	High school	11 (5.27)	8 (20)
	Diploma	8 (20)	7 (5.17)
	Bachelor	1 (5.2)	0 (0)
Job	Freelance job	12 (30)	11 (5.27)	*0.67 (ns)
	Employee	7 (5.17)	4 (10)
	Unemployed	10 (25)	14 (35)
	Retired	11 (5.27)	11 (5.27)
Marital status	Single	1 (5.20)	4 (10)	*** 0.20 (ns)
	Married	34 (85)	28 (70)
	Widow/divorced	5 (5.12)	8 (20)
Gender	Man	26 (65)	24 (60)	* 0.64 (ns)
	Woman	14 (35)	16 (40)
Residence	Urban	26 (65)	23 (5.57)	*0.49 (ns)
	Rural	14 (35)	17 (5.42)
Comorbidity	Diabetes	2 (5)	4 (10)	*** 0.86 (ns)
	Hypertension	5 (5.12)	4 (10)
	Other	3 (5.70)	4 (10)
	Nothing	30 (75)	28 (70)
Surgery	Elective	25 (5.62)	25 (5.62)	*1 (ns)
	Urgency	15 (5.37)	15 (5.37)
Age	Mean ± SD	58.87 ± 17.80	60.70 ± 9.69	** 0.35 (ns)
Length of hospitalization	Mean ± SD	7.52 ± 1.22	7.40 ± 1.64	** 0.70 (ns)
Total		40 (100)	40 (100)	-

*: Chi-square test; **: independent t-test, ***: Fisher’s Exact test, ns: non-significant.

Before conducting parametric tests, assumptions of normality, sphericity, and homogeneity of variance were evaluated. The Shapiro-Wilk test confirmed normality of residuals for anxiety, depression, and sleep quality scores across all time points (p > 0.05). Mauchly’s test indicated that sphericity was met for repeated-measures ANOVA (p > 0.05), requiring no corrections. Levene’s test verified homogeneity of variance for all outcomes (p > 0.05).

Anxiety outcomes

Repeated-measures ANOVA revealed a significant group-by-time interaction for anxiety scores (F (2.32, 222) = 7.07, p < 0.001, η² = 0.08, medium effect size; Table 2). In the intervention group, anxiety scores decreased significantly across four time points (T0 to T3). Bonferroni post-hoc tests (Table 3) showed significant reductions between T0 and T1 (mean difference = 3.37, 95% CI [1.68, 5.06], p < 0.001), T0 and T2 (mean difference = 1.42, 95% CI [0.06, 2.78], p = 0.03), T0 and T3 (mean difference = -1.95, 95% CI [-3.07, -0.82], p < 0.001), and T1 and T2 (mean difference = -1.22, 95% CI [-2.50, 0.05], p < 0.001). No significant changes occurred in the control group across any time points (p = 1.00 for all comparisons). These results indicate that deep breathing effectively reduced anxiety in the intervention group, with effects sustained up to one month post-intervention.

Table 2.

The results of repeated measures ANOVA for anxiety and depression.

	Source of variance	Sum of squares	df	Mean square	F	P value	Eta squared (η2)
Anxiety	Group	99.01	1	99.01	2.71	0.10	3.03
	Time	140.91	2.32	60.73	9.78	< 0.001*	0.11
	Group × time	101.91	2.32	43.92	7.07	< 0.001*	0.08
Depression	Group	0.20	1	0.20	0.007	0.93	0.001
	Time	121.2	2.43	49.63	7.83	< 0.001*	0.091
	Group × time	75.02	2.43	30.77	4.85	0.005*	0.05

^{*: Mean difference is significant at the level of less than 0.05}.

Table 3.

The results of Bonferroni’s post hoc test to compare anxiety and depression outcomes at 4 time points in both groups.

Group (variable)	Time points	Mean difference (confidence interval 0.95)	SD	P-value
Intervention (anxiety)	T0−T1	( 5.06، 1.68) 3.37	0.62	< 0.001*
	T0−T2	(2.78 ، 0.06) 1.42	0.50	0.03*
	T0−T3	(0.82- ، 3.07-)1.95-	0.54	001/0 *
	T1−T2	(0.05 ، 2.50-)1.22 -	0.41	< 0.001*
	T1−T3	(1.58، 0.13-)0.72	0.47	0.06
	T2−T3	(1.58، 0.13-)0.72	0.31	0.15
Control (anxiety)	T0−T1	(1.89، 1.49-)0.20	0.62	1
	T0−T2	(1.83، 1.13-)0.35	0.50	1
	T0−T3	(1.83، 1.13-)0.35	0.54	1
	T1−T2	(1.83، 1.13-)0.35	0.41	1
	T1−T3	(1.42، 1.12-)0.15	0.47	1
	T2−T3	(1.26، 0.46-)0.40	0.31	1
Intervention (depression)	T0−T1	(4.02، 1.02) 2.82	0.55	< 0.001*
	T0−T2	(3.26، 0.08) 1.67	0.58	0.03 *
	T0−T3	(4.41، 1.18) 2.80	0.59	< 0.001*
	T1−T2	(0.40، 2.10-)0.85 -	0.46	0.42
	T1−T3	(1.47، 0.92-)0.27	0.44	1
	T2−T3	(2.10، 0.14) 1.12	0.36	0.01*
Control (depression)	T0−T1	(2.03، 1.03-)0.50	0.55	1
	T0−T2	(1.88، 1.28-) 0.30	0.58	1
	T0−T3	(1.71، 1.41-)0.20	0.59	1
	T1−T2	(1.05، 1.45-)0.20 -	0.46	1
	T1−T3	(0.89، 1.49-)0.30 -	0.44	1
	T2−T3	(0.87، 1.07-)0.10 -	0.36	1

*: Mean difference is significant at the level of less than 0.05.

Depression outcomes

A significant group-by-time interaction was observed for depression scores (F (2.43, 222) = 4.85, p = 0.005, η² = 0.05, small-to-medium effect size; Table 2). In the intervention group, depression scores decreased significantly between T0 and T1 (mean difference = 2.82, 95% CI [1.02, 4.02], p < 0.001), T0 and T2 (mean difference = 1.67, 95% CI [0.08, 3.26], p = 0.03), T0 and T3 (mean difference = 2.80, 95% CI [1.18, 4.41], p < 0.001), and T2 and T3 (mean difference = 1.12, 95% CI [0.14, 2.10], p = 0.01) according to Bonferroni post-hoc tests (Table 3). The control group showed no significant changes across any time points (p = 1.00 for all comparisons). Thus, deep breathing significantly reduced depression levels in the intervention group, with effects persisting one month post-intervention.

Sleep quality outcomes

Paired t-tests indicated a significant improvement in sleep quality in the intervention group from T0 to T3 (t = 12.40, p < 0.0001), with Pittsburgh Sleep Quality Index (PSQI) scores decreasing from 9.72 ± 3.03 to 2.82 ± 2.84. The control group showed no significant change (T0: 9.32 ± 2.97 to T3: 9.20 ± 2.91, t = 1.40, p = 0.16). Independent t-tests confirmed no baseline difference between groups (p = 0.55) but a significant difference at T3 (mean difference = 6.38, t = -10.60, p < 0.0001) (Table 4). These findings demonstrate that deep breathing significantly enhanced sleep quality in the intervention group one month post-intervention.

Table 4.

The results of paired t-test and t-tests of sleep quality within and between groups before and one-month after intervention.

Time	Sleep quality		Statistical test (independent t-test)
	Control group	Intervention group	T	P
	M (SD)	M (SD)
Before	9.32 (2.97)	9.72 (3.03)	0.59	0.55
After 1 month	9.20 (2.91)	2.82 (2.84)	-10.60	< 0.0001 *
Statistical test (paired t-test)	t (1.40) P = 0.16	t (12.40) P < 0.0001 *

^{*: Mean difference is significant at the level of less than 0.01}.

According to the results, the reductions in anxiety and depression scores in the intervention group were both statistically and clinically significant. The mean reduction in anxiety (e.g., 3.37 points from T0 to T1) and depression (e.g., 2.82 points from T0 to T1) exceeded the minimal clinically important difference (MCID) for the Hospital Anxiety and Depression Scale (HADS), typically 1.5–2.0 points. Similarly, the 6.9-point reduction in PSQI scores surpassed the MCID of 3 points, suggesting meaningful improvements in psychological well-being and sleep quality. These changes likely enhance recovery, reduce hospital readmissions, and improve quality of life following coronary artery bypass grafting (CABG).

Discussion

In the present study, the effect of deep breathing on sleep quality, anxiety, and depression of patients undergoing coronary artery bypass surgery was investigated. The findings of this study supported the first and second hypotheses, so we can claim that deep breathing was effective in reducing anxiety and depression in coronary artery bypass graft patients. The results of Amjadian et al. (2020) and Jain et al. (2020) studies were in line with the present study and the anxiety and depression scores of the intervention group of breathing exercises decreased significantly after the implementation of the intervention^24,25. Also, in the research of Chung et al. (2010), deep breathing decreased the depression level of heart patients³¹. D’Silva et al. (2014) conducted a study to investigate the effectiveness of deep breathing exercises in patients with coronary artery disease. The study found that the intervention led to a significant reduction in anxiety, depression and diastolic blood pressure among patients³². These studies support our findings and emphasize the importance of understanding the role of deep breathing in managing anxiety and depression in patients undergoing coronary artery bypass surgery. However, not all studies have reported consistent effects. For instance, a study involving cardiac surgery patients found no significant differences in anxiety and depression levels between those who engaged in deep breathing exercises and those who did not³³. This discrepancy underscores the importance of intervention protocols, such as frequency, duration, and technique, to specific populations, including CABG patients who have elevated baseline anxiety or depression. The structured protocol used in our study may have contributed to its success, as more intensive or prolonged interventions might be necessary to achieve significant outcomes in cardiac populations. These findings can contribute to further knowledge with the aim of improving the postoperative experience and psychological well-being of cardiac surgery patients.

Our third hypothesis was confirmed that deep breathing can improve sleep Quality in CABG patients, and this effect remained until the follow-up stage. The results of the present study indicate the positive effectiveness of deep breathing exercises on improved sleep quality. This finding is consistent with Ghorbani et al.‘s (2019) study, which found that implementing deep breathing interventions in post-coronary artery bypass surgery patients led to longer and better quality sleep compared to a control group who did not receive the intervention³⁴. In the research of Alkan et al. (2017), the use of a breathing exercises program improved the sleep quality of cardiac patients³⁵. Also, research by Ghane et al. (2022) showed that non-pharmacological sleep interventions, including deep breathing exercises, improve sleep quality in patients after cardiac surgery³⁶. Roy (2013) conducted a study on patients who had upper abdominal surgeries. The authors concluded that deep breathing exercises could improve the quality of sleep by enhancing the depth of breathing³⁷. In a review study conducted by Lee et al. (2023), it was found that non-pharmacological sleep interventions improve the sleep quality of patients after cardiac surgery³⁸. Machado et al. (2017) conducted a systematic review and found that non-pharmacological interventions had a positive impact on post-cardiac surgery sleep quality³⁹. In the research of Ranjbaran et al. (2015), it was also found that additional interventions in the recovery program of coronary heart surgery patients, based on a correct pattern, can improve the quality of sleep of these patients⁴⁰. In contrast to our findings, the study by (Kalra et al., 2015) reported no conclusive effect of deep breathing on sleep quality in a diverse group of hospitalized older adults⁴¹. This discrepancy may stem from differences in study populations, as CABG patients face unique physiological and psychological stressors that may enhance their responsiveness to deep breathing. Additionally, the multifaceted intervention in reference 41, which combined deep breathing with other techniques, may have diluted its impact compared to our focused deep breathing protocol. Variations in intervention delivery, such as duration, frequency, or training intensity, may further explain the differing outcomes. These factors emphasize the need for further research to clarify the conditions under which deep breathing most effectively improves sleep quality in specific patient populations.

Deep breathing has multiple benefits for heart surgery patients and their consequences, and the more complications and ailments patients face in the period after heart surgery, the more patients face sleep disorders²¹. Additionally, Studies have demonstrated that deep breathing techniques effectively alleviate anxiety and depression in patients undergoing cardiac surgery by enhancing psychological well-being. These techniques reduce autonomic nervous system activity and contribute to hormonal regulation, thereby decreasing anxiety and depression levels, which are key factors influencing sleep quality in this population^42,43. According to Hopper’s research in 2019, deep breathing techniques effectively support patients by regulating blood pressure, lowering cortisol levels, and reducing symptoms of anxiety and depression. Additionally, deep breathing mitigates procedural pain, thereby improving emotional well-being following surgery⁴⁴. Deep breathing also enhances the integration of mind and body, promoting a state of calmness and psychological balance, which contributes to significant reductions in anxiety and depression levels among patients undergoing cardiac surgery⁴⁵. Based on the foreword, it can be said that this nurse-led intervention can play a role in strengthening the psychological structure of patients undergoing coronary artery bypass surgery and make them stronger in facing treatment challenges. Nurses can improve patients’ sleep quality and psychological state during hospitalization by using simple strategies like deep breathing exercises, which enhance patients’ quality of life. Furthermore, nurses have the opportunity to educate the patients on this technique to encourage them to continue practicing deep breathing exercises at home for ongoing benefits.

The findings of this study should be considered under these limitations: The study has several limitations that should be considered when interpreting the findings. Firstly, it was conducted in a single, small government heart surgery center in Kerman City with only 80 participants, limiting the generalizability of the results to a broader CABG patient population. To enhance the robustness of the results, it is recommended to replicate the study with larger samples. Moreover, the tool used in the current study to assess sleep quality, PSQI is self-report-based, Thus, objective methods besides these tools could improve the findings of the study. Furthermore, although efforts were made to separate patient beds to minimize information exchange between groups, the possibility of contamination due to shared ward environments could not be entirely eliminated and due to the nature of the intervention, complete blinding of participants was not feasible, so, it is recommended to use an active control group in future studies that receives a similar intervention without direct effects, such as non-breathing relaxation exercises. Also, the follow up duration, in this research was rather short. To get more accurate and reliable results, it is recommended to increase the follow-up period to at least 6 months after intervention.

Conclusion and implications for practice

The results of this study revealed that deep breathing exercises were significantly effective in reducing anxiety, depression and sleep disorders among the CABG patients. Although our intervention took only a few days after surgery, its effects persisted and we observed sleep quality improvements and reductions in depression and anxiety that persisted for up to one month after the intervention. With improvements in sleep quality and reductions in anxiety and depression maintained up to one month after the intervention. It confirmed the importance of incorporating deep breathing exercises in the recovery and rehabilitation programs of heart surgery patients, particularly improving the quality of sleep and mental state after surgery. This non-invasive, easy-to-use, and inexpensive intervention has a significant impact on the anxiety, depression and quality of sleep experienced by patients. It can be used as an effective and beneficial nursing intervention to improve outcomes in patients undergoing coronary artery bypass surgery. However, it must be noted that factors such as patients’ adherence to exercises, proper technique implementation, patient ability, and monitoring of deep breathing exercises are crucial in achieving efficiency and effectiveness. By paying attention to these factors and optimizing measures, the results can be improved to enhance the quality of health services at different treatment stages of patients undergoing coronary artery bypass surgery. Since anxiety, depression and poor sleep quality can impact physiological and psychological aspects of human life and their behaviors, the authors recommend that a trained specialist nurse should be present in the open-heart surgery setting to teach this method to patients.

Author contributions

MA: Project administration, Conceptualization, Supervision, review & editing. OR: Data analysis, Methodology, Supervision. TE: Writing original draft, Resources, Data collection and curation. AA: Writing – review & editing. RN: Writing – review & editing, Supervision. YM: Writing – review & editing. All authors read and approved the final manuscript.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Declarations

Competing interests

The authors declare no competing interests.

Ethics approval and consent to participate

This study approved by Research Ethics Committee of Kerman University of Medical Sciences (IR.KMU.REC.1401.305). The study was carried out following principles enunciated in current version of the Declaration Helsinki. Participants signed the informed consent and were fully informed about the study objectives, its voluntary nature, and their right to withdraw. Confidentiality and anonymity of data were also considered. Furthermore, this research has been registered in the Iranian Registry of Clinical Trials on 18/12/2023 (IRCT20231208060294N1).