Sleep quality and ventilatory efficiency in elderly heart failure patients: a pilot study on the short-term effect of 4-week low-intensity aerobic exercise

Background Sleep disturbance and ventilator inefficiency are considered two of the most critical complications for general human wellbeing, particularly in elderly heart failure (HF) patients. Studies examining the effect of low-intensity aerobic exercise in the treatment of sleep disturbance and ventilatory inefficiency in this population of patients are limited.


Introduction
Sleep is considered as one of the most critical compo nents of general human wellbeing, particularly in elderly population. Sleep disturbance and insufficient sleep quality are extreme complications, which are reported to occur in thirtynine to seventyfive percent of elderly people [1,2]. A previous epidemiological study proved that most of older people complain about disturbance in sleep, which is commencing or continuing [2].
Heart failure (HF) was lately observed in huge number of populations causing hospital admission [3], disturbance of life quality and several complications [3][4][5]. The widespread outcome of HF is the poor sleep quality [4,5] which extended to further symptoms including fatigue, pain, anxiety, gastrointestinal distress, and depression [5].
Onethird (30 %) of HF patients with sleep problems at discharge experienced persistent sleep problems at 1year followup and 14 % patients without sleep ОРИГИНАЛЬНЫЕ СТАТЬИ § problems at baseline reported sleep problems after 1 year [6]. HF patients are suffering from sleep disturbance due to many issues such as βblockers medications, sleep apnea, night dyspnea and some comorbidities including chronic obstructive pulmonary disease [7].
Sleep is an essential component of human life and affects profound development and functioning of the brain, cognitive functions, body growth, and psychological conditions. Consequently, sleep disturbance is negatively correlated with physical function, psychological condition and life wellbeing [8]. Sleep problems such as abnormal sleepiness pattern and chronic poor sleepiness result in increasing mortality and morbidity rate of cardiac disorders [9]. HF patients experienced psychological and physical dysfunctions as a result of sleep disturbance [6,10]. So, HF patients who experienced sleep disturbances have to be examined and treated with additional attention to avoid unfortunate effects.
Commonly, ventilatory inefficiency is a decisive diagnostic indicator of HF patients. It is usually investigated through measurement of the minute ventilation / carbon dioxide production (VE / VCO 2 ) slope [11]. HF patients are suffering from a heightened VE / VCO 2 slope which combined with dyspnea and lack of functional capacity [12].
Recently, many studies demonstrated the useful outcomes of exercise training on depression status [13][14][15], ventilatory markers [16], quality of life [17], and selfefficacy [18] in HF patients and asthmatics [19] whereas studies which examined the lowintensity exercise training effect on the sleep quality and ventilatory efficiency in HF subjects are limited. Consequently, the purpose of the current pilot study was to evaluate the effectiveness of lowintensity aerobic exercise on the sleep disturbance and ventilatory inefficiency in elderly HF patients.

Subjects
Participants were enrolled through Cairo University regional hospital at outpatient physical therapy clinic between June and September 2018. The patients were eligible to participate in the study if they: 1) were functionally classified as having II and III HF with reference to New York Heart Association (NYHA) classification according to the limitations which endure physical activities, 2) were suffering from obstructive sleep apnea, 3) age more than 65 years, 4) rest ejection fraction (EF) less than 40 %, 5) maximum oxygen uptake less than 20 mL / kg / min, 6) no mental or physical disability; 7) stable for a onemonth minimum with proper medical control.
Twentytwo elderly HF patients experiencing obstructive sleep apnea were referred by their cardiologists for exercise rehabilitation program. Six patients did not meet the inclusive criteria, and five declined to contribute in the study program. No refusing reasons were reported. Eleven patients (8 men and 3 women) participated in the study. Two men and one woman withdrew during the study program without any registered reason. The flowchart of the study is described in Figure 1. A written informed consent was provided by each patient before intervention. This study protocol was proved by research ethics committee of physiotherapy department [PTA / 018 / 023] based on ethical principles of medical research and Declaration of Helsinki 1964.

Sleep quality assessment
All HF patients were assessed for sleep quality pre and post study program using validated and reliable Pittsburgh sleep quality index (PSQI) [20]. This index is 19item scale consisting of 7 domains: sleep quality, sleep latency, sleep duration, sleep disturbances, sleep habitual efficiency, sleep medications, and daytime dysfunction. The rate of each item is scaled 0-3. 0 reveals no sleep difficulties and 3 reveals severe sleep difficulties. Global PSQI was estimated, scoring from 0 to 21. High scores of global PSQI indicate bad sleep quality while lower scores indicate good sleep quality.

Ventilatory efficiency assessment
Maximum oxygen uptake (VO 2peak ) and VE / VCO 2 slope were assessed pre and post study program through cardiopulmonary exercise test using an electronic braked ergometric cycle (Monark, 939 Novo, USA).

Low intensity aerobic exercise protocol
The data of all patients were obtained using a selfreport questionnaire before the intervention and reviewed by a family member or primary caregiver. The definition and purpose of the lowintensity aerobic exercise program were clearly explained for each participant. All patients fulfilled a supervised program of lowintensity aerobic exercise five sessions weekly for 4week. Each exercise session was commenced with 5 min warmup and finished with cooldown for 5 min. Each  Figure 1. The flowchart of the study ОРИГИНАЛЬНЫЕ СТАТЬИ § patient was supervised by an experienced therapist to conduct a 4week treadmill walking exercise at 40 to 50 % of maximum heart rate for 20-30 minutes, five sessions per week.

Statistical analysis
Data were analyzed using windows software of the Statistical Package for the Social Sciences (Version 25, IBM Corp., Armonk, NY, USA). Data were assessed for normality using the ShapiroWilk test. Data were described as means ± standard deviations. Descriptive statistics were performed for demographic data and baseline characteristics of the participants. Categorical data were analyzed using chi square test while the continuous data were analyzed using paired ttest to assess the differences between pre and post intervention. Wilcoxon signedrank test was done due to the small number of the study participants to assess the changes between pre and postintervention. The significance level was set at p<0.05.

Results
Out of 22 patients, 8 elderly HF patients (6 men, 2 women) were statistically analyzed. The demographic data and clinical characteristics of the study subjects involving gender, age, body mass index (BMI), hemodynamics, classes and etiology of HF, EF, VO 2peak , and VE / VCO 2 were described in Table 1.
The mean of global PSQI score was ranged between 8.2 to 11.4 with a mean of 9.7±3.4 which indicates that the participants experienced sleep disturbance. As presented in Table 2, postexercise assessment showed that patients have reported significant improvement of all PSQI domains compared with baseline assessment (p<0.05).

Discussion
Impairment of sleep quality is one of the imperative complications that appeared through physiological changes of aging in human life and HF. With both, aging and HF, unclear alterations are established in sleep cycle and structure. Several researches have demonstrated that sleep disturbance is positively correlated with mental and physical dysfunctions [21,22]. Therefore, the current pilot study purposed to investigate the influence of lowintensity aerobic training on the quality of the sleep and ventilator efficiency in elderly HF patients. Our study outcomes point toward that four weeks of lowintensity aerobic exercise are efficient in improvement of sleep quality including all domains in elderly HF patients.
Quality of sleep is lowered in most of HF patients. Sixty three percent of HF patients have experienced impairment of sleepiness [23]. In this experimental study, we have assessed the quality of sleep among HF patients who underwent three weeks of lowintensity aerobic exercise. There were significant changes in quality of sleep between pre and post treatment outcomes using PSQI. Recent study demonstrated that program of cardiac rehabilitation has reduced sleep disturbance in patients with heart diseases [24].
Lowintensity aerobic exercise enhanced quality of sleep in thisstudy. Improving selfreport of the quality of sleep with aerobic exercise was exhibited in prior studies of older adults and middleaged patients with disturbed sleep quality [25]. However, no earlier studies have assessed quality of sleep in elderly HF patients. Gary and Lee have found an improvement in the sleep time and quality of life following an outdoor walking program, although great exposure to the light during outdoor training is an important factor [26].
Also, many researchers have previously reported the improvement of sleep apnea after conduction of training (aerobics or aerobics / resistance exercises) [26][27][28]. Moreover, these researches have demonstrated an improvement of sympathetic smooth muscle regulation and biomarkers of HF in the exercised subjects. A shortterm cohort study of 4week intensive rehabilitation in cardiac patients showed an improvement of sleep quality, depression status, body weight, and aerobic capacity [29].
Our present study showed a significant improvement of VO 2peak and nonslight improvement of VE / VCO 2 with no significant changes at the end of the 4week intervention. In agreement with our findings, a previous study demonstrated that aerobic exercise training improves functional capacity and has a positive prognosis in HF patients [30], and recent systematic review found no significant changes in VE / VCO 2 [31], while prior studies proved that high intensity exercise training may improve VE / VCO 2 in HF patients [32,33]. We observed a slight decrease of VE / VCO 2 regarding the beneficial effects of regular aerobic exercise in the improvement of ventilatory efficiency in HF patients. Also, we recommend the evaluation of the longterm impact of aerobic exercise on ventilatory efficiency in elderly HF patients.

Study limitations
Some limitations were determined in our study. The limited number of the study participants and the short duration of the study indicate nongeneralization about the effects of the exercise program. Also, the included HF patients may not be representative for other patients comprised in future studies. Furthermore, the sleep quality was assessed subjectively using PSQI while the objective assessment is available by using easy and cheap actigraphy which record sleep / wake cycles in the home settings. In addition, further studies should include larger sample size and longer duration of exercise intervention.

Conclusions
Shortterm of lowintensity aerobic exercise (4 weeks) may improve the quality of sleep and ventilatory efficiency in elderly HF patients. The study findings encourage elderly HF patients with sleep disturbance to adhere to exercise intervention and motivate physician's referral to the cardiac rehabilitation program.