Aromatherapy in Patients with Cardiovascular Diseases: A Systematic Review

Cardiovascular diseases have the highest incidence of morbidity and mortality in the world. According to the World Health Organization (WHO), they caused approximately 17.9 million deaths in 2016, accounting for 31% of all causes of death worldwide.1 Stress and anxiety seem to destabilize cardiovascular regulation, adversely affecting the autonomic and neuroendocrine pathways and, consequently, cardiovascular parameters and tissue perfusion.2,3 Recently, Ma et al.,4 observed that negative emotions can increase systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and cortisol levels, whereas positive emotions can decrease SBP and HR. In this context, complementary therapies to control stress and anxiety have been studied, and integrative practices have shown to be promising resources in promoting health to patients with chronic diseases, including cardiovascular disease.5 In Brazil, a decision by the National Policy and Integrative and Complementary Practice (PNPIC) was approved within the scope of Abstract

the Brazilian public unified health system (SUS), and Ordinance No. 702 published on March 21, 2018, added 12 new practices, including aromatherapy, which consists in the use of essential oils extracted from aromatic plants 6 and is commonly administered by inhalation or massage. 7 Lavender, with the scientific name of Lavandula, has been presented as a relevant substrate in the practice of aromatherapy. Its oil is extracted from its flower, and the main chemical compounds are linalool and linalyl acetate. 8,9 These compounds are rapidly absorbed by the skin and detected in the bloodstream after topical application, reaching peak levels in approximately 19 to 20 minutes after application. 8,10 Inhalation starts in the nose, where there is a chain of chemoreceptor olfactory neurons. Stimuli are conducted from the olfactory bulb, taking information to the cerebral cortex, hypothalamus, and hippocampus, connecting to the limbic system. 5,11 Because of its anxiolytic and sedative properties, the Lavandula Officinalis species is recognized for its effective treatment of stress and anxiety. [10][11][12] The purpose of this review was to investigate the effects of the use of lavender essential oil on hemodynamic responses and emotional aspects in patients with cardiovascular diseases.

Methods
This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines.¹³ The research question was developed using the PICO strategy, where participants (P) were patients with cardiovascular diseases, the intervention (I) was aromatherapy with the use of lavender essential oil, the comparison (C) was randomized controlled studies, and the outcome (O) was hemodynamic and emotional responses to the intervention. Question: What are the effects of aromatherapy with lavender essential oil on hemodynamic response and emotional aspects in patients with cardiovascular diseases?

Eligibility Criteria for Study Design
The inclusion criteria applied in the present review are shown in Table 1. The primary outcome was the analysis of hemodynamic responses, such as SBP, DBP, HR, and respiratory rate (RR). Secondary outcomes included emotional responses, such as anxiety, stress, fatigue, and depression.

Data Sources
The search was performed in May 2020, with no publication date restrictions, using the following 5 databases: Medical Literature Analysis and Retrieval System Online (MEDLINE), Virtual Health Library (Bireme), Physiotherapy Evidence Database (PEDro), Embase, and Scopus.

Search Strategy
The search strategy used MeSH or DeCs terms, combined by the Boolean operators "AND" and "OR", as well as other descriptors with similar concepts: aromatherapy and Lavandula, and heart or hemodynamics or cardiovascular diseases.

Study Selection and Data Extraction
Two reviewers screened titles and abstracts independently. Potentially relevant studies were retrieved for full-text reading. After reading the full text, all studies that met the inclusion criteria were selected for review. Any disagreement in the studies would be resolved by consulting a third reviewer for arbitration, which was not necessary.

Quality Assessment
The Cochrane Collaboration's tool was used for assessing methodological quality and risk of bias. This tool has 7 domains: 1. Generation of the Random

Results
Of 539 articles initially identified through the search strategy, 213 were from MEDLINE, 113 from Bireme, 10 from Embase, and 203 from Scopus. No studies were identified in the PEDro database. A total of 80 articles were excluded because they were duplicates and 408 after reviewing titles and abstracts, resulting in a set of 51 articles for full-text reading. After independent analysis by the reviewers, 46 were excluded for not meeting the inclusion criteria (Table 1), resulting in 5 studies included in our systematic review. A flowchart of the study selection process is shown in Figure 1.
All 5 studies used aromatherapy with lavender essential oil in patients with cardiovascular diseases. 12,[15][16][17][18] The studies were published from 1992 to 2020. The sample size ranged from 60 to 135 patients, 15,17 and the mean age was 60 to 73 years. 16,17 Three studies 12,15,16 included participants of both sexes, and 2 studies 17,18 included only women. Regarding the participants, 2 studies 12,15 selected patients who underwent coronary artery bypass graft surgery, 1 study 16  In the study by Seifi et al., 12 there were no statistically significant reductions in HR and RR or in anxiety levels; however, a difference in SBP and DBP was observed on the third day of intervention (30 minutes after intervention) between the aromatherapy and control groups.
Bikmoradi et al., 15 reported different levels of stress between the aromatherapy and control groups 3 days after surgery. Regarding hemodynamic variables, there were no differences in relevant statistics, and the results were presented with the confidence interval.
Rajai et al., 16 observed reduced levels of anxiety after intervention in the aromatherapy group; however, no significant reduction was observed in stress. Regarding hemodynamic responses, a reduction in HR was observed after intervention in the aromatherapy group compared with the control group.
Bahrami et al., 17 reported a decrease in fatigue levels from severe to moderate and considered it a good intervention for the management of fatigue. They also showed a reduction in SBP, MAP, and HR compared with the control group.
In a second study, Bahrami et al., 18 observed a significant reduction in anxiety and depression levels in the aromatherapy group compared with the control group. Regarding hemodynamic parameters, there were significant reductions in SBP, DBP, MAP, and HR.
Regarding study quality, all studies included in this review showed an appropriate design and carefully assessed the processes of randomization and group allocation, most of them presenting a blind assessment of the results to reduce the risk of bias. In the included studies, there were difficulties in keeping participants blind to the application of scent and massage, but there was no risk of bias due to the allocation of intervention in either group. The studies reported the outcomes as complete outcome data or reported the losses to follow-up.

Discussion
This review demonstrated that the topic of cardiovascular response to aromatherapy has not been fully explored, as there are only a few studies with a design that supports the use of aromatherapy with lavender essential oil as a therapeutic resource in the control of hemodynamic responses and emotional aspects in patients with cardiovascular diseases. Nevertheless, the evidence presented in this review shows the relevant effects of lavender essential oil use on hemodynamic responses, such as SBP, DBP, MAP, and HR, as well as on the reduction of stress, anxiety, and fatigue, when compared with control groups. 19,20 In a study using a rabbit model, Koto et al., 21 found that linalyl acetate produces progressive effects during vascular contraction by observing the relaxation of the carotid artery and showed that linalyl acetate is the main component of lavender. However, some opposing studies pointed out linalool as the most relevant active substance. 8,9,11 This can be attributed to the different botanical species of Lavandula and its variations, since they are directly influenced by the location and the climate where they are cultivated, and this influences the chemical structure of the essential oil. 8 Studies included in this review did not mention the lanvandula species used in the interventions.
The use of lavender essential oil triggered some cardiovascular responses, and these responses are attributed to the emotional effects of lavender and may be associated with reduced levels of stress and anxiety, which regulate mood and emotion by stimulating the limbic system. 5,10 This hypothesis is supported by the findings of Koulivand et al., 8 who reported that lavender causes therapeutic effects by activating the limbic system, stimulating emotions, and activating the amygdala and the hippocampus, responsible for behavior and memory. This is in line with the results of the present review which showed a reduction in anxiety, stress, and fatigue.
Hosseni et al., 19 reported that aromatherapy has effects on SBP, in addition to the effects on HR reduction. A reasonable explanation could be that described by  Henz et al., 10 in which they state that the action of linalool in reducing SBP could be related to the effects of sympathetic deactivation of the autonomic nervous system. This hypothesis can be supported by the studies of Rajai et al., 16 and Bahrami et al., 18 who found a reduction in HR in the aromatherapy intervention groups. Also, the reduction in anxiety levels observed by Rajai et al., 16 and Bahrami et al., 18 may be attributed to the anxiolytic and sedative effects of linalool on the autonomic nervous system as a parasympathetic mimetic effect. 20 18 showed significant reductions in the levels of anxiety and depression, which were justified by the relaxing effects of lavender on the autonomic nervous system. Hosseni et al., 19 reported that anxiety increases cortisol and adrenaline levels, generating a stress response in the body. Bahrami et al., 17 in their first study, assessed fatigue levels and found a reduction from severe to moderate after aromatherapy.
In both studies conducted by Bahrami et al., 17,18 foot massage was used as an intervention resource. In this respect, the authors reported that topical massage is absorbed by the skin and stimulates the olfactory system, affecting the limbic system and stimulating the parasympathetic nervous system. Consequently, there is a stabilization of metabolic and physiological parameters, leading to relaxation. Henz et al., 10 reported that the absorption of linalool through massage could be psychologically more relaxing than inhalation.
A limitation of this study is that, although most of the included studies have an adequate design and low risk of bias, there is a small number of studies on this topic. Also, differences in the application protocols and the heterogeneity of the study populations made it impossible to pool data for meta-analysis.

Conclusion
This systematic review showed that aromatherapy using lavender essential oil has beneficial effects on hemodynamic parameters. Despite the scarce evidence, aromatherapy appears to control the levels of anxiety, stress, depression, and fatigue in patients with cardiovascular diseases. However, there remains a gap in knowledge and more evidence is needed on the use of aromatherapy and its effects on cardiovascular diseases. Further research on the effects of aromatherapy with lavender essential oil in the treatment of patients with cardiovascular diseases is required to explain the physiological mechanisms involved in the results found in this review and to support the clinical practice of aromatherapy as a complementary activity that determines the improvement of health and quality of life in patients with cardiovascular diseases.

Potential Conflict of Interest
No potential conflict of interest relevant to this article was reported.

Sources of Funding
There were no external funding sources for this study.

Study Association
This study is not associated with any thesis or dissertation work.