Therapeutic Effects of Slow Deep Breathing on Cardiopulmonary Function, Physical Performance, Biochemical Parameters, and Stress in Older Adult Patients with Long COVID in Phayao, Thailand
Article information
Abstract
Background
Long coronavirus disease (COVID) poses significant challenges for older adult patients, affecting their cardiopulmonary function and overall well-being. This study aimed to investigate the effects of slow deep breathing exercises on cardiopulmonary function, physical performance, biochemical markers, oxidative stress, and stress levels in older adult patients with long COVID.
Methods
Sixty older adult patients with long COVID were randomly assigned to an exercise group of 30 patients and a control group of 30 patients. The exercise group engaged in slow deep breathing exercises for 30 minutes, five times a week over a period of 8 weeks, while the control group maintained their usual activities. Cardiovascular parameters, heart rate variability (HRV), respiratory muscle strength (RMS), pulmonary function tests (PFT), physical performance, biochemical and oxidative stress markers, and stress levels were assessed at baseline, 4 weeks, and 8 weeks. Data were analyzed using one-way repeated measures ANOVA.
Results
The exercise group showed significant reductions in cardiovascular parameters (systolic and diastolic blood pressure, pulse pressure, mean arterial pressure, and heart rate). Additionally, RMS, PFT, and physical performance showed significant increases. Improvements were also observed in HRV, biochemical markers (fasting blood sugar and lipid profile), oxidative stress markers (catalase, superoxide dismutase, and malondialdehyde), and stress levels. In contrast, no significant changes were found in the control group.
Conclusion
Slow deep breathing exercises, as a non-pharmacological intervention, significantly improve cardiopulmonary function, physical performance, and various health markers in older adult patients with long COVID. This approach provides a valuable and accessible therapeutic option for this population.
INTRODUCTION
The emergence of coronavirus disease 2019 (COVID-19), a respiratory illness caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) first identified in late 2019, led to a global healthcare crisis impacting millions worldwide and placing unprecedented demands on healthcare systems. As of 2023, the World Health Organization reported approximately 770 million COVID-19 cases worldwide, underscoring the scale of this pandemic.1) COVID-19 exhibits a broad spectrum of symptoms; from mild respiratory discomfort, to severe outcomes like pneumonia, acute respiratory distress syndrome, and multi-organ failure.2,3) Beyond respiratory effects, COVID-19 may lead to complications in the heart, kidneys, brain, and other systems, highlighting its complex and systemic impact.4)
Although most individuals fully recover, a subset experiences prolonged, debilitating symptoms, termed long COVID or post-acute COVID-19 syndrome, which generally manifests around 3 months post-infection and persists for at least 2 months without an alternative cause.5) Common symptoms of long COVID include fatigue, cognitive impairments, respiratory discomfort, and musculoskeletal pain, significantly affecting quality of life and daily functioning.6) Recent studies indicate that between 31% and 69% of individuals report long COVID symptoms, suggesting that millions globally are enduring its effects.3) Age, in particular, has emerged as a critical risk factor for severe outcomes and long COVID, with older adults experiencing heightened risk due to factors like reduced physiological resilience and pre-existing health conditions.7) For seniors, long COVID symptoms contribute to declines in physical function and quality of life, compounded by social isolation and past hospitalizations. Reports indicate that long COVID affects between 16% and 29% of older adult patients with prior COVID-19.8)
Long COVID affects multiple body systems, including cardiovascular, respiratory, musculoskeletal, and neurological functions, while also contributing to autonomic dysfunction, oxidative stress, and metabolic disturbances.9) Autonomic dysfunction in long COVID, often reflected by altered heart rate variability (HRV), is linked to persistent inflammation and sympathetic overactivation, contributing to cardiovascular instability.10) Furthermore, oxidative stress plays a significant role in long COVID pathophysiology, characterized by increased reactive oxygen species (ROS) production and impaired antioxidant defense mechanisms.11) This imbalance leads to cellular damage, endothelial dysfunction, and systemic inflammation, which can exacerbate symptoms and prolong recovery.12) Altered biochemical parameters, including elevated fasting blood sugar (FBS), dyslipidemia, and pro-inflammatory cytokines, further contribute to long-term complications.13,14) Given these factors, interventions that enhance HRV, reduce oxidative stress, and improve biochemical homeostasis are essential for managing long COVID symptoms and preventing long-term complications.10) Comprehensive management guidelines advocate a multidisciplinary approach to address these diverse symptoms, emphasizing support for physical, mental, and emotional well-being.15) Exercise has shown promise as a non-pharmacological intervention for long COVID, with studies reporting benefits across various forms of exercise, such as aerobic activity, strength training, and breathing exercises, each targeting different health domains.16) For older adult, low-impact exercises like breathing exercises are particularly suitable as they are simple, equipment-free, and offer cardiovascular and respiratory benefits. Such exercises may enhance physical fitness, improve metabolic biomarkers, and reduce oxidative stress, contributing to better quality of life.17,18)
Despite the benefits of breathing exercises their specific effects on older adults with long COVID remain underexplored as several studies have used different types of breathing exercises, leading to varying outcomes. This study aims to investigate the impact of slow deep breathing exercises on a range of health parameters including cardiovascular indicators, HRV, respiratory muscle strength (RMS), pulmonary function test (PFT), physical performance, biochemical and oxidative stress markers, stress levels, and long COVID symptoms among older adults. By addressing these areas, this research fills a critical gap providing evidence for a low-impact, non-pharmacological intervention tailored to the needs of older adults with long COVID with the potential of significantly enhancing their quality of life.
MATERIALS AND METHODS
Patients and Design
Sample size was calculated following a previous study19) which examined the impact of a pulmonary rehabilitation program on seniors COVID-19 patients. This calculation used the formula, N = Z21−α/2 σ2/d2, where N is the required sample size, Z21−α/2 corresponds to 95% confidence interval, σ represents standard deviation (6.05), and d margin of error (2.5). Each group initially included 23 participants. Accounting for a potential 20% dropout rate, we used the adjustment formula, nd = N/(1–R), with R=0.2, resulting in an adjusted sample size of approximately 30 participants per group.
This study utilized a randomized control trial design. A total of 100 older adult patients with long COVID were screened for eligibility. Based on the inclusion and exclusion criteria, 35 individuals were excluded for not meeting the criteria and five declined participations resulting in a final sample of 60 patients randomized equally into the control (n=30) and exercise (n=30) groups (Supplementary Fig. S1). Participants, aged 60–82 years, were recruited from Phayao Province, Thailand. No participants dropped out during the study. Adherence to the slow deep breathing exercise program was 97.42%, with participants attending an average of 38.97 out of 40 scheduled sessions over the 8-week period.
The inclusion criteria were older adult women and men who had been infected with SARS-CoV-2 for the first time and had long COVID symptoms diagnosed by a physician at the Subdistrict Health Promotion Hospital. Long COVID refers to symptoms persisting for more than 3 months after the initial SARS-CoV-2 infection, such as fatigue, cough, joint pain, muscle aches, memory issues, loss of smell, difficulty sleeping, anxiety, and others. Participants had an oxygen saturation (SpO2) level of no less than 95%, had not participated in any research projects in the past 6 months, and had no history of chest or heart surgery. Exclusion criteria included smoking, a history of chronic obstructive pulmonary disease or other chronic respiratory diseases, cardiovascular disease, neuromuscular disease, physical activity limitations due to illness, a history of musculoskeletal injury in the past 6 months, and participation in any exercise programs. Participants who visited the Subdistrict Health Promoting Hospital and wished to take part in the study reached out to a staff member or researchers by telephone. Consent was obtained from each subject after explaining the purpose, advantages, and potential risks of the experiments in accordance with the standards set by the University of Phayao Human Ethics Committee (Approval No. HREC-UP-HSST 1.3/039/66).
This study was single-blinded, meaning that outcome assessors were unaware of group allocation, while participants knew their assigned intervention. To minimize potential bias, all investigators followed a standardized assessment protocol. Additionally, participants were instructed not to disclose their group assignment to assessors to further reduce expectation bias.
Procedure
The control group (n=30) maintained their usual daily routines for 8 weeks. In contrast, the exercise group (n=30) participated in a structured breathing exercise program lasting 30 minutes daily, 5 days per week, over an 8-week period. This structured program emphasized slow, deep breathing and was divided into six specific phases, each lasting 1 minute. Participants performed five rounds, totaling 30 minutes per session. The phases were as follows20):
Phase 1: Inhale through the nose for 2 seconds, hold the breath for 2 seconds, and then exhale through the mouth for 2 seconds.
Phase 2: Inhale through the nose for 2 seconds, followed by exhaling through the mouth for 4 seconds.
Phase 3: Inhale through the nose for 2 seconds, hold the breath for 6 seconds, and exhale through the mouth for 2 seconds.
Phase 4: Inhale through the nose for 2 seconds, followed by exhaling through the mouth for 4 seconds.
Phase 5: Inhale through the nose for 2 seconds, hold the breath for 10 seconds, and exhale through the mouth for 2 seconds.
Phase 6: Inhale through the nose for 2 seconds, followed by exhaling through the mouth for 4 seconds.
A physical therapist introduced participants to the exercises providing familiarization sessions three times weekly for the first 2 weeks. Weekly follow-ups via phone were conducted to ensure adherence and address any issues. Assessments were conducted at baseline, 4 weeks, and 8 weeks, covering clinical characteristics, anthropometry, long COVID symptoms, cardiovascular parameters, HRV, RMS, PFT, physical performance, blood biochemistry, and stress levels.
Outcome Measurements
Clinical characteristics and anthropometry
Clinical characteristics were obtained from history taking and physical examination, including body temperature (BT), respiratory rate (RR), SpO2, and medical conditions. Anthropometry assessed in this study included weight, height, and waist-to-hip ratio (WHR). In addition, all participants were interviewed about long COVID symptoms with questions asking whether they had experienced any symptoms.
Cardiovascular parameters
Cardiovascular parameters were evaluated through blood pressure measurements. Blood pressure was recorded using a calibrated automatic blood pressure monitor (OMRON HEM-7130L; Omron Healthcare, Kyoto, Japan) following the American Heart Association Guidelines. This provided systolic blood pressure (SBP) and diastolic blood pressure (DBP). From these values, pulse pressure (PP) and mean arterial pressure (MAP) were calculated. PP was determined by subtracting DBP from SBP (PP = SBP–DBP), while MAP was calculated using the formula: MAP = DBP + [(SBP−DBP)/3].
Heart rate variability and stress parameters
HRV was assessed to evaluate the autonomic nervous system (ANS) function. Measurements were taken while participants rested in a supine position in a calm, controlled environment for 10 minutes prior to data collection. HRV data were gathered using an ANS function test (MEDICORE SA-3000P; MEDICORE, Hanam, Korea), a calibrated electrocardiogram (ECG) monitor validated for this purpose. ECG readings were recorded continuously for 5 minutes while participants remained still and breathed normally. Following data collection, HRV data were analyzed using automated software. The intervals between successive R-waves (RR intervals) from the ECG were processed to determine both time-domain and frequency-domain metrics. For time-domain analysis, the standard deviation of normal-to-normal intervals (SDNN) and the square root of the mean squared difference (RMSSD) were calculated. In frequency-domain analysis power spectral density was estimated using autoregressive modeling to derive low-frequency (LF; 0.04–0.15 Hz) and high-frequency (HF; 0.15–0.40 Hz) components. The ratio of LF to HF was calculated to reflect the balance between sympathetic and parasympathetic activity. To account for circadian influences, measurements were conducted at the same time of day for each participant. Stress parameters were analyzed using the software provided with the MEDICORE SA-3000P. Results included the following indices: stress resistance calculated from the ratio of LF to HF in HRV, with higher values indicating greater resistance to stress; stress index derived from the variability of SDNN, with higher values signifying increased stress levels; and fatigue index computed from the decrease in HRV using the RMSSD of the RR interval, where lower values indicate higher fatigue levels.
Respiratory muscle strength
The evaluation of RMS aimed to assess the capabilities of both inspiratory and expiratory muscles. A respiratory pressure meter (MicroMedical MicroRPM 01; CareFusion, Basingstoke, UK) was utilized to measure RMS, calibrated, and validated according to established guidelines by the American Thoracic Society and the European Respiratory Society. The results reported included maximal inspiratory pressure at functional residual capacity (PImaxFRC), maximal inspiratory pressure at residual volume (PImaxRV), and maximal expiratory pressure (PEmax). Each measurement was repeated three times to ensure the findings were reliable, with the greatest value recorded for each participant.
Physical performance
Isometric strength in the back and legs was evaluated using a strength dynamometer following standard protocol. Participants stood with feet shoulder-width apart, pulling on the handles at mid-thigh height with knees flexed at approximately 110°. Each participant performed three trials with maximum strength recorded. Trunk flexibility was assessed using the sit-and-reach test. Participants sat with hip-width feet apart against a box, reaching forward to measure flexibility. The furthest distance reached was recorded from three attempts. Functional exercise capacity was measured using the 6-minute walk test (6MWT) following established guidelines. After a 10-minute rest period with vital signs and fatigue levels recorded, participants walked as far as possible in 6 minutes along a 30-m corridor.
Pulmonary function test
A PFT was conducted to evaluate lung performance by measuring parameters such as forced expiratory volume in one second (FEV1), forced vital capacity (FVC), FEV1 to FVC ratio, peak expiratory flow (PEF), and forced expiratory flow at 25%–75% of FVC (FEF25-75%), all expressed as percentages of predicted values. FEV1 and FVC maneuvers were performed in accordance with the guidelines, using a spirometer (DATOSPIR touch; Sibelmed, Barcelona, Spain). The procedure involved the following steps: (1) deep inhalation, (2) forceful and rapid exhalation, (3) sustained exhalation for up to 15 seconds, and (4) quick inhalation to return to maximum lung capacity.
Assessment of biochemical and oxidative stress markers
Blood samples were collected from the antecubital vein to measure various parameters including FBS, total cholesterol (TC), triglycerides (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), catalase (CAT), glutathione (GSH), superoxide dismutase (SOD), and malondialdehyde (MDA). FBS was measured utilizing the glucose oxidase technique with glucose reagent kits (DIRUI Industrial Co. Ltd., Changchun, China) following the manufacturer’s instructions. TC was determined using the enzyme method with a total cholesterol reagent kit adhering to the manufacturer's guidelines. TG were assessed utilizing the oxidase method with a triglyceride reagent kit, according to the manufacturer’s instructions. HDL was measured using the direct method with a high-density lipoprotein reagent kit following the manufacturer’s guidelines. LDL was calculated using the formula: TC–HDL–(TG/5). All assays were performed by qualified medical technologists to ensure accuracy and reliability of results. Plasma MDA levels, SOD activity, and CAT activity were assessed using techniques previously described by Promsrisuk et al.,21) while GSH was measured according to the protocol from Kongsui et al.22)
Statistical Analysis
Data were presented as mean±standard deviation. Stata 18.0 (StataCorp, College Station, TX, USA) was employed for analysis. Normality was assessed with the Shapiro–Wilk test. Within-group differences were analyzed using one-way repeated measures ANOVA, with Bonferroni corrections for multiple comparisons. Between-group comparisons were conducted using two-way repeated measures ANOVA. Unpaired t-tests compared control and exercise groups at each time point. A generalized estimating equation (GEE) evaluated time and group effects on long COVID symptoms. GEE was selected due to its ability to handle correlated binary data across multiple time points, as it accounts for within-subject variability and provides robust standard errors. This approach ensures a more accurate estimation of the intervention effect on long COVID symptom progression. Statistical significance was defined as a p-value less than 0.05.
RESULTS
The control group comprised of 8 males (26.67%) and 22 females (73.33%), while the exercise group included 10 males (33.33%) and 20 females (66.67%). Mean age was 68.20±5.81 years in the control group and 70.67±3.47 years in the exercise group. No significant differences were observed between the control and exercise groups regarding baseline characteristics such as age, height, weight, body mass index (BMI), WHR, BT, RR, and SpO2. Both groups exhibited similar comorbidity profiles, with hypertension, dyslipidemia, and diabetes mellitus type 2 being the most common conditions. Less common comorbidities included gout, dyspepsia, and gastroesophageal reflux disease. No significant changes in body weight, BMI, WHR, BT, RR, or SpO2 were found within or between groups at baseline, week 4, and week 8 (Supplementary Table S1 and Fig. S2).
Effects of Slow Deep Breathing Exercise on Long COVID Symptoms
Long COVID symptoms assessed in this study included fatigue, cough, joint pain and muscle aches, memory issues, loss of smell, difficulty sleeping, and anxiety. Time had a statistically significant effect on reducing long COVID symptoms including fatigue (p=0.000), cough (p=0.001), joint pain and muscle aches (p=0.024), loss of smell (p=0.013), difficulty sleeping (p=0.000), and anxiety (p=0.001). Breathing exercises had a significant effect on reducing fatigue (p=0.034), cough (p=0.044), difficulty sleeping (p=0.031), and anxiety (p=0.046) (Table 1).
Symptoms of long COVID of the control and exercise groups
Effects of Slow Deep Breathing Exercise on Cardiovascular Parameters and Cardiac Sympathovagal Balance
Cardiovascular parameters and cardiac sympathovagal balance for both groups are summarized in Fig. 1 and Supplementary Table S2. After 8 weeks, the exercise group showed significant reductions in SBP (F=46.49, p=0.000), DBP (F=27.83, p=0.000), PP (F=27.69, p=0.000), MAP (F=46.19, p=0.000), and HR (F=8.33, p=0.001), while the control group presented no significant changes. Significant group-time interactions were observed for SBP (F=23.17, p=0.000) (Fig. 1A), DBP (F=12.45, p=0.000) (Fig. 1B), PP (F=8.92, p=0.000) (Fig. 1C), MAP (F=22.69, p=0.000) (Fig. 1D), and HR (F=4.51, p=0.013) (Fig. 1E). By week 8, the exercise group demonstrated significantly lower SBP, DBP, MAP (p<0.001), and HR (p<0.05) compared to the control group, with PP reductions noted at both week 4 (p<0.05) and week 8 (p<0.01). Regarding HRV parameters, the exercise group exhibited improvements with increases in SDNN (F=4.43, p=0.016), RMSSD (F=4.14, p=0.021), and HF (F=3.76, p=0.029) and a reduction in LF (F=5.12, p=0.009) and LF/HF (F=10.10, p=0.000), while no significant changes were observed in the control group. Significant group-time interactions were noted for SDNN (F=4.50, p=0.013) (Fig. 1F), RMSSD (F=4.66, p=0.011) (Fig. 1G), LF (F=3.67, p=0.028) (Fig. 1H), HF (F=4.63, p=0.012) (Fig. 1I), and LF/HF (F=7.95, p=0.000) (Fig. 1J). Compared to the control group, the exercise group showed significant increases in SDNN (p<0.05), RMSSD (p<0.01), and HF (p<0.05) by week 8, with significant decreases in LF/HF at both weeks 4 and 8 (p<0.05).
Comparison of the therapeutic effect of slow deep breathing on cardiovascular parameters in the control group (n=30) and exercise group (n=30): (A) systolic blood pressure (SBP), (B) diastolic blood pressure (DBP), (C) pulse pressure (PP), (D) mean arterial pressure (MAP), (E) heart rate (HR), (F) standard deviations of all normal to normal (NN) intervals (SDNN), (G) square root of the mean of the sum of the squares of differences between adjacent NN intervals (RMSSD), (H) low frequency (LF), (I) high frequency (HF), and (J) LF/HF ratio at baseline, 4 weeks, and 8 weeks. Values are presented as mean±standard deviation. A two-way repeated measures ANOVA was used to analyze group, time, and interaction effects. The Bonferroni test was used to compare baseline, 4 weeks, and 8 weeks within the group: #p<0.05, ##p<0.01, ###p<0.001 for within-group comparisons in the exercise group (baseline vs. 4 weeks); †p<0.05, ††p<0.01, †††p<0.001 for within-group comparisons in the exercise group (baseline vs. 8 weeks); ‡‡‡p<0.001 for within-group comparisons in the exercise group (4 weeks vs. 8 weeks).
Effects of Slow Deep Breathing Exercise on Respiratory Muscle Strength and Pulmonary Function
After 8 weeks of breathing exercises, RMS significantly improved in the exercise group—PImaxFRC (F=6.82, p=0.002), PImaxRV (F=10.71, p=0.000), PEmax (F=10.41, p=0.000)—with no significant changes observed in the control group. Significant group-time interactions were noted for PImaxFRC (F=2.87, p=0.041) (Fig. 2A), PImaxRV (F=7.55, p=0.000) (Fig. 2B), and PEmax (F=5.12, p=0.007) (Fig. 2C). At 8 weeks, PImaxFRC, PImaxRV, and PEmax were significantly higher in the exercise group than in the control group (p<0.05). Pulmonary function, expressed as a percentage of predicted values, showed significant increases in FEV1 (F=6.32, p=0.003), FVC (F=16.88, p=0.000), PEF (F=8.57, p=0.001), and FEF25-75% (F=3.95, p=0.025) in the exercise group following 8 weeks of breathing exercises, with no significant changes observed in the control group. Group-time interactions were significant for FEV1 (F=3.08, p=0.044) (Fig. 2D), FVC (F=5.94, p=0.004) (Fig. 2E), PEF (F=2.54, p=0.040) (Fig. 2G), and FEF25-75% (F=2.62, p=0.041) (Fig. 2H). FEV1, FVC, PEF, and FEF25-75% significantly improved in the exercise group compared to the control group by week 8 (p<0.05) (Supplementary Table S3).
Comparison of the therapeutic effect of slow deep breathing on respiratory muscle strength and pulmonary function in the control group (n=30) and exercise group (n=30): (A) maximal inspiratory pressure at functional residual capacity (PImaxFRC), (B) maximal inspiratory pressure at residual volume (PImaxRV), (C) maximal expiratory pressure (PEmax), (D) forced expiratory volume in the first second (FEV1), (E) forced vital capacity (FVC), (F) FEV1/FVC ratio, (G) peak expiratory flow (PEF), and (H) forced mid-expiratory flow (FEF25-75%) at baseline, 4 weeks, and 8 weeks. Values are presented as mean±standard deviation. A two-way repeated measures ANOVA was used to analyze group, time, and interaction effects. The Bonferroni test was used to compare baseline, 4 weeks, and 8 weeks within the group: #p<0.05, ##p<0.01 for within-group comparisons in the exercise group (baseline vs. 4 weeks); †p<0.05, ††p<0.01, †††p<0.001 for within-group comparisons in the exercise group (baseline vs. 8 weeks); ‡p<0.05, ‡‡p<0.01 for within-group comparisons in the exercise group (4 weeks vs. 8 weeks).
Effects of Slow Deep Breathing Exercise on Physical Performance
The 6MWT outcomes significantly improved in the exercise group following breathing exercises (F=22.56, p=0.000), while no significant changes were found in trunk flexibility, leg strength, or back strength. A significant group-time interaction was observed for the 6MWT (F=16.49, p=0.000) (Fig. 3D). Compared to the control group, the exercise group demonstrated significant improvements in the 6MWT in both weeks 4 and 8 (p<0.001) (Supplementary Table S4).
Comparison of the therapeutic effects of slow deep breathing on physical performance and stress in the control group (n=30) and exercise group (n=30): (A) trunk flexibility, (B) leg strength, (C) back strength, (D) six-minute walk test (6MWT), (E) stress resistance, (F) stress index, and (G) fatigue index at baseline, 4 weeks, and 8 weeks. Values are presented as mean±standard deviation. A two-way repeated measures ANOVA was used to analyze group, time, and interaction effects. The Bonferroni test was used to compare baseline, 4 weeks, and 8 weeks within the group: #p<0.05, ###p<0.001 for within-group comparisons in the exercise group (baseline vs. 4 weeks); †p<0.05, ††p<0.01, †††p<0.001 for within-group comparisons in the exercise group (baseline vs. 8 weeks); ‡p<0.05 for within-group comparisons in the exercise group (4 weeks vs. 8 weeks).
Effects of Slow Deep Breathing Exercise on Biochemical and Oxidative Stress Markers
Fig. 4 and Supplementary Table S5 summarize the biochemical and oxidative stress markers for both groups. In the exercise group, FBS (F=50.67, p=0.000), TC (F=14.86, p=0.000), TG (F=5.37, p=0.007), and LDL (F=16.77, p=0.000) levels significantly decreased, while HDL (F=5.05, p=0.010) levels significantly increased, with no significant changes in the control group. A significant group-time interaction was observed by FBS (F=8.46, p=0.000) (Fig. 4A). For oxidative stress markers, the exercise group showed significant increases in CAT (F=5.69, p=0.006) and SOD (F=11.84, p=0.000), with a decrease in MDA (F=11.42, p=0.000), while no significant changes occurred in the control group. A significant group-time interaction was observed for MDA (F=3.15, p=0.044) (Fig. 4I).
Comparison of the therapeutic effects of slow deep breathing on biochemical parameters in the control group (n=30) and exercise group (n=30): (A) fasting blood sugar (FBS), (B) total cholesterol (TC), (C) triglyceride (TG), (D) high-density lipoprotein (HDL), (E) low-density lipoprotein (LDL), (F) catalase (CAT), (G) glutathione (GSH), (H) superoxide dismutase (SOD), and (I) malondialdehyde (MDA) at baseline, 4 weeks, and 8 weeks. Values are presented as mean±standard deviation. A two-way repeated measures ANOVA was used to analyze group, time, and interaction effects. The Bonferroni test was used to compare baseline, 4 weeks, and 8 weeks within the group: ##p<0.01 for within-group comparisons in the exercise group (baseline vs. 4 weeks); †p<0.05, †††p<0.001 for within-group comparisons in the exercise group (baseline vs. 8 weeks); ‡p<0.05, ‡‡p<0.01, ‡‡‡p<0.001 for within-group comparisons in the exercise group (4 weeks vs. 8 weeks).
Effects of Slow Deep Breathing Exercise on Stress
Stress was evaluated via HRV analysis, resulting in the measurement of stress resistance, stress index, and fatigue index. Significant reductions were observed in the exercise group for stress resistance (F=4.31, p=0.018), stress index (F=5.86, p=0.005), and fatigue index (F=4.61, p=0.014), while no significant changes occurred in the control group (Supplementary Table S6). Significant group-time interactions were noted for stress resistance (F=3.51, p=0.033) (Fig. 3E) and stress index (F=4.97, p=0.009) (Fig. 3F).
DISCUSSION
This study demonstrates the beneficial effects of slow deep breathing exercise training on older adult patients suffering from long COVID. After participating in 30-minute slow deep breathing exercises, 5 days a week for 8 weeks, participants experienced a decrease in long COVID symptoms accompanied by improvements in cardiovascular health, cardiac ANS balance, RMS, pulmonary function, physical fitness, biochemical and oxidative stress markers, and overall stress levels.
The slow deep breathing exercise training resulted in significant reductions in SBP, DBP, PP, MAP, and HR, indicating enhanced cardiovascular function. Furthermore, increases in SDNN, RMSSD, and HF, along with decreases in LF and the LF/HF ratio, suggest an improved balance of the cardiac ANS. These results are consistent with prior research. For instance, Kow et al.23) demonstrated that 15 minutes of music-guided deep breathing exercises daily over 8 weeks significantly reduced SBP and DBP in hypertensive patients. Similarly, Li et al.24) found that slow breathing lowered HR and blood pressure while increasing HF and decreasing LF and the LF/HF ratio. A study by Kalaivani et al.25) also reported reductions in SBP, DBP, HR, and the rate-pressure product after a 5-day regimen of alternate nostril breathing. The potential mechanisms for these reductions in blood pressure and HR through breathing exercises include an increase in vagal tone which activates the parasympathetic nervous system, leading to natural reductions in blood pressure and HR.26) Additionally, enhanced baroreflex sensitivity allows the cardiovascular system to respond more effectively to blood pressure fluctuations.27) Slow breathing may also induce vasodilation, thus lowering overall cardiovascular pressure and aiding in blood pressure reduction, particularly in hypertensive individuals.28) Finally, a decrease in sympathetic nervous system activity contributes to reduced cardiovascular stress.29)
In the present study, older adult long COVID patients demonstrated improvements in PImaxFRC, PImaxRV, PEmax, FEV1, FVC, PEF, and FEF25-75%, indicating enhanced RMS and pulmonary function. This is consistent with findings from a previous study by Abodonya et al.30) whereby a two-week respiratory muscle training program conducted twice daily benefitted pulmonary function, decreased dyspnea, and improved quality of life for individuals recovering from COVID-19 following mechanical ventilation, as it effectively targeted the diaphragm and accessory respiratory muscles to counter muscle atrophy. Additionally, respiratory muscle training reduces neural respiratory drive, improves breathing patterns, and promotes muscle hypertrophy; ultimately enhancing diaphragm function and reducing breathlessness. Furthermore, it increases both PImax and PEmax, facilitating muscle adaptation akin to skeletal muscle training.31) In the exercise group, the FEV1/FVC ratio showed a non-significant trend towards reduction, which can be attributed to a greater improvement in FVC relative to FEV1, consistent with findings from Shravya Keerthi et al.32) This indicates that slow deep breathing exercises primarily enhance lung volumes (reflected by FVC) rather than reduce airflow limitation.
Long COVID patients often experience a decline in physical performance characterized by reduced muscle strength, poor 6MWT outcomes, and maximal oxygen consumption.33) This decline is exacerbated by limitations in cardiorespiratory fitness and pulmonary function following COVID-19 infection, thus leading to ongoing fatigue and dyspnea which contribute to exercise intolerance.34) However, after participating in slow deep breathing exercise training in this study, older adult long COVID patients demonstrated notable improvements in their 6MWT, indicating enhanced physical performance or exercise capacity. A study by Li et al.35) supports this finding reporting that a telerehabilitation program designed for COVID-19 recovery improved 6MWT outcomes in long COVID patients by specifically targeting RMS and endurance, both of which are critical for exercise capacity. Furthermore, 6 weeks of respiratory rehabilitation has been shown to enhance 6MWT distance by bolstering exertion endurance through improvements in respiratory muscle function, lung ventilation, and gas exchange efficiency.19) Breathing exercises not only strengthen respiratory muscles but also improve their endurance and enhance gas exchange, effectively alleviating hypoxia.17) These results underline the significant impact of breathing exercises in enhancing exercise capacity in long COVID patients.
In this study, biochemical markers like FBS, TC, TG, HDL, and LDL were analyzed to assess cardiovascular risk. Prior research has linked COVID-19 to long-term cardiac risks, including arrhythmia, heart disease, stroke, and thromboembolism.36) What’s more, changes in oxidative stress and antioxidant levels observed in COVID-19 patients may impact on long-term recovery management.37) Older adult long COVID patients who practiced slow deep breathing exercises demonstrated reduced FBS, TC, TG, and LDL levels with increased HDL levels. In accordance with previous studies, breathing exercises have been linked to cholesterol metabolism and may help lower cholesterol levels. Deep breathing exercises have brought about reductions in FBS, TC, TG, and LDL levels, along with an increase in HDL levels which may decrease cardiovascular disease risk.38) Breathing exercises have also been shown to improve glycemic control.39) Moreover, reducing blood glucose has been associated with lower oxidative stress and increased antioxidant defenses.40) COVID-19 infection can raise ROS levels due to an imbalance in oxidant-antioxidant activity, thus increasing oxidative stress markers like MDA and decreasing antioxidant defenses such as SOD and CAT.41) High ROS levels stimulate lipid peroxidation and cellular damage, contributing to cardiovascular disease progression. Elevated MDA has been linked to long COVID and higher cardiovascular complication risks.42) In this study, slow deep breathing exercises reduced MDA while increasing CAT and SOD levels, consistent with prior findings,17) helping inhibit lipid peroxidation and sustain antioxidant capacity. The possible mechanisms the beneficial effects of slow deep breathing exercises on metabolic parameters and oxidative stress regulation include activation of the vagus nerve, which shifts the autonomic balance towards parasympathetic dominance. This improves insulin sensitivity, lowers hepatic glucose production, and enhances lipid metabolism.43,44) Additionally, slow deep breathing boosts antioxidant defenses by increasing SOD and GSH activity while lowering MDA levels, reducing oxidative damage. It also enhances mitochondrial efficiency, optimizing oxygen use and minimizing excessive ROS production. Furthermore, increased nitric oxide bioavailability supports vascular function and oxidative balance by improving endothelial health.17) These findings suggest that slow deep breathing exercises are an effective, non-pharmacological strategy for improving glucose and lipid metabolism while enhancing antioxidant capacity, making them particularly beneficial for older adult long COVID patients with metabolic and oxidative stress dysregulation.
Long COVID patients often experience increased mental health challenges due to prolonged symptoms, which affect their quality of life and daily activities, especially in older adults.45) This study utilized stress assessment variables from stress resistance, stress index, and fatigue index. It was discovered that after older adult long COVID patients engaged in slow deep breathing exercises continuously for 8 weeks, there was an increase in stress resistance and a decrease in both the stress index and fatigue index, indicating a reduction in stress levels. A previous study suggested that resonant breathing over 12 weeks significantly improved wellness, the ability to focus, breathing capability, stress control, and sleep quality in patients with long COVID.46) Furthermore, a 4-day online workshop on yogic breathing techniques resulted in a significant reduction in levels of stress, anxiety, and depression immediately after the program during the COVID-19 pandemic.47) Breathing exercises have shown a significant effect on reducing anxiety and stress in COVID-19 patients, with the intervention leading to a notable decrease in anxiety and stress scores.48) The mechanisms through which breathing exercises contribute to stress reduction in these patients may include the activation of the body’s relaxation response which helps to decrease stress levels through the balancing of the sympathetic and parasympathetic nervous systems essential for regulating the stress response, as well as the extension of exhalation which stimulates the vagus nerve. This activation of the parasympathetic nervous system promotes the release of neurotransmitters associated with well-being, such as serotonin and endorphins.48)
The slow deep breathing exercise in this study reduced long COVID symptoms, including fatigue, cough, difficulty sleeping, and anxiety in older adult long COVID patients. This is consistent with the research by Rodriguez-Blanco et al.49) who conducted a 2-week supervised combined breathing and resistance exercise seven times per week with each session lasting 30 minutes in patients with post-COVID-19 conditions. Accordingly, they found that dyspnea was reduced in the exercise group. McNarry et al.31) reported that an 8-week unsupervised inspiratory muscle training program comprising three sessions per week of 20 minutes each, improved breathlessness and chest symptoms. Improvements in long COVID symptoms resultant of following a breathing exercise program are attributed to several factors including reduced neural respiratory drive. Inspiratory muscle training can decrease the neural drive required for breathing, whereby helping to balance the load on respiratory muscles with their capacity. This balance can lead to improved breathing patterns.50) In addition, this may be due to improvements in RMS, respiratory function, cardiovascular function, cardiac sympathovagal balance, antioxidant levels, and a reduction in oxidative stress.
The present study has certain limitations. It focused solely on slow deep breathing exercises, though greater benefits may be achieved when combined with other modalities such as aerobic or strength training exercises. Future research should explore multi-modal rehabilitation strategies to enhance recovery and symptom management. Additionally, the study did not assess slow vital capacity (SVC), which could provide further insights into lung hyperinflation and airway obstruction. Including SVC in future studies would improve the evaluation of respiratory function. Adherence was based on self-reported participation and weekly follow-up calls, without objective verification. Despite high compliance (97.42%), future studies should consider digital tracking or biometric monitoring for more accurate assessment. While randomization was successful in balancing baseline characteristics, residual confounding from unmeasured factors, such as dietary habits, may have influenced the outcomes. Future studies should incorporate more comprehensive assessments to mitigate potential confounding effects. Furthermore, some findings had marginal statistical significance or small effect sizes, requiring cautious interpretation. Further studies with larger sample sizes and longer follow-up periods are needed to confirm these effects and establish their clinical relevance.
In conclusion, slow deep breathing exercises offer a promising approach to alleviating symptoms in older adult patients presenting long COVID, with demonstrated benefits in cardiovascular health, cardiac autonomic function, RMS, pulmonary function, exercise capacity, biochemical markers for cardiovascular risk, oxidative/antioxidant status, and stress levels. These results suggest that such exercises could be feasibly integrated into comprehensive rehabilitation programs tailored for older adult long COVID patients.
Notes
The authors sincerely thank the older adult long COVID patients for their valuable participation in this study.
CONFLICT OF INTEREST
The researchers claim no conflicts of interest.
FUNDING
This research project was partially supported by the Research and Academic Service’s Fund of the School of Medicine, University of Phayao (Grant No. MD67-10).
AUTHOR CONTRIBUTIONS
Conceptualization, TP, AS, PC; Data curation, TP, AS, PC, KK, TT; Investigation, TP, AS, RK, NS, ST, CK, PC; Methodology, TP, AS, NM, PC; Statistical analyses, TP, AS, PC, NM, KK, TT; Supervision, TP, AS, PC; Writing–original draft, TP, AS, PC; Writing–review & editing, TP, AS, PC, RK, NS, ST.
SUPPLEMENTARY MATERIALS
Supplementary materials can be found via https://doi.org/10.4235/agmr.24.0175.
Clinical characteristics and anthropometric data of the control and exercise groups
Cardiovascular parameters and heart rate variability of the control and exercise groups
Respiratory muscle strength and pulmonary function of the control and exercise groups
Physical performance of the control and exercise groups
Biochemical and oxidative stress markers of the control and exercise groups
Stress parameters of the control and exercise groups
Consolidated Standards of Reporting Trials (CONSORT) flow diagram of the study.
Comparison of the therapeutic effects of slow deep breathing on the anthropometric data in the control group (n=30) and exercise group (n=30): (A) body weight, (B) body mass index (BMI), (C) waist-to-hip ratio (WHR), (D) body temperature (BT), (E) respiratory rate (RR), and (F) pulse oxygen saturation (SpO2) at baseline, 4 weeks, and 8 weeks. Values are presented as mean±standard deviation. A two-way repeated measures ANOVA was used to analyze group, time, and interaction effects.