Intradialytic isometric handgrip exercise does not cause hemodynamic instability: A randomized, cross‐over, pilot study
Funding information: Fundação de Apoio à Pesquisa do Distrito Federal, Grant/Award Number: 0193.001.558/2017; Coordination for the Improvement of Higher Education Personnel
Abstract
Hemodialysis (HD) patients experience hemodynamic instability and intradialytic exercise seems to attenuate it. This study aimed to verify the acute hemodynamic response to different intradialytic handgrip exercise intensities in HD patients. In a randomized, cross‐over, experimental pilot study, eight patients completed two experimental sessions and one control in random order: (a) regular HD; (b) low‐intensity isometric handgrip exercise; and (c) moderate‐intensity isometric handgrip exercise. BP and heart rate variability were recorded immediately before and every 15 minutes. Isometric handgrip exercise protocols, regardless of the intensity, did not lead to significant changes in hemodynamic stability, nor when compared to the control condition (P > .05). The systolic BP and double product significantly increased immediately after the moderate‐intensity protocol (122.0 ± 15.9 vs 131.3 ± 19.8, P < .05; 9094.7 ± 1705.7 vs 9783.0 ± 1947.9, P < .05, respectively) but returned to the pre‐exercise values 10 minutes later. We conclude that intradialytic isometric handgrip exercise does not induce hemodynamic instability at low and moderate intensities.
1 INTRODUCTION
Cardiovascular disease is more frequent and severe in CKD patients when compared to the general population.1 In dialysis‐dependent patients, the risk of cardiovascular mortality is higher than nondialysis CKD patients and healthy population.2 Therefore, strategies to reduce cardiovascular mortality risk in HD patients are at high priority. Exercise is a good and feasible strategy to attenuate cardiovascular risk in HD patients.3 Intradialytic aerobic exercise is safe and beneficial for cardiovascular parameters, such as BP and heart rate variability (HRV).4, 5 Resistance exercise promotes multiple benefits to musculoskeletal health, also attenuating cardiovascular risk.6
Considered a promising nonpharmacological tool, isometric handgrip exercise (IHE) has for a long time been contraindicated for clinical populations.7 Nevertheless, an increasing number of studies have been shown that IHE acts as a regulator of cardiac autonomic function by improvements in HRV.8, 9 It is known that intradialytic hemodynamic instability is partly modulated by overactivation of the parasympathetic activity.10 Thus, IHE might play an important role in cardiac autonomic function, one of the main cardiovascular concerns in HD patients.11, 12 Different from other types of exercise, such as aerobic, resistance, and combined that promote musculoskeletal and cardiorespiratory benefits, IHE main focus is in the sympathetic‐parasympathetic modulation.4, 6, 9, 13
Despite intradialytic aerobic and resistance exercise have been prescribed to regulate this clinical concern, to the best of our knowledge no study has investigated IHE on the acute hemodynamic response in HD patients. Therefore, this randomized, cross‐over, experimental pilot study aimed to verify the effect of different IHE intensities on the acute hemodynamic response in CKD patients on HD. We hypothesize that IHE does not elicit acute hemodynamic instability.
2 PATIENTS AND METHODS
This randomized, cross‐over, experimental pilot study was conducted in a sample of eight CKD patients (56.63 ± 12.66 years old, 59.10 ± 11.27 kg, and 1.65 ± 0.06 m) undergoing short‐daily HD, five sessions per week, with a duration of 2 hours and 30 minutes each. The eligibility criteria were as follows: signing the informed consent form; not enrolled in other exercise programs or research; diagnosis of CKD in HD treatment for >3 months; medical staff approval; preserved functional capacity (walk without assistance and no lower‐limb amputation); and ≥18 years of age. The exclusion criteria were as follows: any discomfort or intolerance to the exercise protocol; complications in the health status that could impair the performance of the exercises; arteriovenous fistula damage; and BP values higher than 180/105 mm Hg. In this study, the ethical care guidelines regarding respect for the human person and anonymity were met, and approval was obtained by the research ethics committee (number 2.497.191) (Figure 1).
2.1 General procedures
The patients enrolled in the study provided basic information, such as age, gender, and dialysis vintage. In a mid‐week HD session, anthropometric assessment and handgrip strength (HGS) test familiarization sessions were performed. The familiarization consisted of two maximum voluntary isometric contractions (MVIC) in the dominant or nonfistulated arm, with a 60‐second interval, performed after the HD session. Post 48 hours of the familiarization, patients underwent the HSG test, performing three MVIC assessments. A week later, patients were submitted to a familiarization session of the IHE protocol. All assessments and familiarizations were conducted by the same clinical exercise physiologist. After the IHE familiarization, all patients completed two experimental sessions and one control in random order: (a) regular HD; (b) low‐intensity IHE; and (c) moderate‐intensity IHE. Randomization was performed by an online program (https://www.random.org/). Each protocol was performed a single time, standardizing the day (Wednesday), HD shift, temperature, and luminosity. The IHE protocols were performed during the first hour of HD, and the hemodynamic variables were recorded from the beginning to the end of the HD.
2.2 Anthropometric and body composition
Anthropometric parameters were evaluated using tetrapolar bioimpedance (Biodynamics, 310e, São Paulo, Brazil) in which the subjects' lean mass, fat mass, fat percentage, and basal metabolic rate were considered for analyses. Additionally, the height and body weight were measured by scales and a stadiometer (Filizola, Beyond Technology, PL‐200, São Paulo, Brazil), with a resolution of 0.1 kg and 0.1 cm. All measurements were done according to the instructions provided in the device manual.
2.3 Handgrip strength test
The HGS was measured using a hydraulic dynamometer (Saehan Corporation, Yangdeok‐Dong, Korea) for the nonfistulated or dominant arm for those with catheter access. Following the recommendations of the American Society of Hand Therapists, participants were seated with the shoulder in a neutral position, elbows flexed at 90°, and wrist in the neutral position. A total of three measurements were recorded with an interval of 30 seconds, and the highest value was considered for analyses.14
2.4 Heart Rate Variability and Blood Pressure
The Polar heart rate monitor (S810i) was used and the heart rate (HR) of the participants was assessed from the beginning to the end of the HD. The guideline from the Task Force of The European Society of Cardiology and The North American Society of Pacing and Electrophysiology has been adopted for measurements.15, 16 Participants remained in the supine position for the first analysis before the beginning of the HD session. After it, patients were requested to stay comfortably seated and reclined for the IHE protocol and the rest of the session. A belt with electrodes was placed and positioned on the patient's chest, capturing electrical impulses from the heart and transmitting them through an electromagnetic field to the cardiofrequencimeter.
To avoid potential bias in the hemodynamic stability measurements, we have standardized the seated and reclined position during HD sessions, carefully controlled the temperature and luminosity of the environment, and requested the dialysis staff to not contact the patients during the measurements. The HRV indices were obtained using the program Kubios HRV analyses 3.0. The linear method was used to analyze the time domain, so named because it shows the results of the time unit (milliseconds). It has been analyzed the successive heartbeats (RR) mean, SDs of the intervals NN (SDNN), and the square root of the differences in the RR intervals (RMSSD). The method adopted to remove the analysis artifacts was an impulse rejection filter. Digital filtering using the equipment's software. In this study, the only series with more than 95% of sinus beats were included in the study.
For the BP analysis, the dialysis machine monitor (Fresenius, 4008S, Bad Homburg, Germany) was used. Additionally, double product (DP), a marker of cardiac stress and oxygen consumption, has been evaluated by the following formula: DP = HR × SBP. Both variables, HRV and BP, were recorded at the beginning of the HD session, before and every 15 minutes after its beginning. For baseline characterization, BP and HR assessments were performed before the beginning of a mid‐week HD session.
2.5 Isometric handgrip exercise protocols
The IHE has been performed using a hydraulic dynamometer (Saehan Corporation, Yangdeok‐Dong, Korea). Seven days after the MVIC test, participants underwent a familiarization session of the IHE protocol during the first hour of HD, being carried out in three sets of 30 seconds, with a 1‐minute rest interval between sets and an intensity of 30% of the MVIC. The control session consisted of a conventional HD session. There was control of hemodynamic variables as in the experimental protocols.
The IHE protocols were applied in two different HD sessions, both with different intensities. Each session consisted of two warm‐up exercises, focusing on wrist and elbow joint mobility and breath control. Participants performed six isometric contractions set at 30% (low‐intensity) and 50% (moderate‐intensity) of the MVIC as proposed by Souza et al.17 The isometric contraction was performed only with the nonfistulated arm, to avoid fistula complication, with a 1‐minute rest interval between sets. A specialized clinical exercise physiologist supervised the IHE. If the patient was not achieving the right intensity (30% or 50%), verbal instruction, and encouragement were used, such as “Come on! Hold it stronger!”, “Take it easy! Not so strong!”, “Well done! Keep this intensity!”. Further details are presented in Table 1.
| Intensity (MVIC) | RPE | Sets | Rest interval | |
|---|---|---|---|---|
| Low‐intensity | 30% | 5–6 | 6 × 60″ | 60″ |
| Moderate‐intensity | 50% | 7‐8 | 6 x 40″ | 60″ |
- Abbreviations: MVIC, maximum voluntary isometric contraction; RPE, rate of perceived exertion.
The external load was controlled with the OMNI‐Resistance Exercise Scale (OMNI‐RES) to determine the volunteers' rate of perceived exertion (RPE), which the participants recorded 30 minutes after the end of the IHE protocol to avoid an overestimation due to physical tiredness.18 Also, the training impulse method (TRIMP), a tool to control exercise training volume and intensity, was adapted to the IHE protocol and used to compare the total training load between the different intensities,19 applying the following formula (TRIMP = seconds under tension × load [kgf] × RPE).
The participants were instructed to maintain regular breathing and to avoid holding their breath, also known as the Valsalva maneuver, due to its rapid increase in BP and possible adverse hemodynamic response. The IHE is shown in Figure 2.
2.6 Statistical analysis
To describe sample characteristics, descriptive statistics were used with frequencies, mean, and SD. Data distribution was verified using the Shapiro‐Wilk test. Variables collected at pre‐ and post‐HD and pre‐ and post‐exercise were compared by paired t tests or Wilcoxon and tested for a difference between the three different sessions by one‐way analysis of variance (ANOVA). Additionally, two‐way ANOVA for repeated measures was used to analyze hemodynamic data: trial arm (control vs low‐intensity vs moderate‐intensity) × time, and a Bonferroni post‐hoc test was adopted to identify possible differences. A P‐value <.05 was accepted as statistically significant. The analysis was performed using the Statistical Package for the Social Sciences (SPSS), version 22.0 (SPSS, Inc., Chicago, IL, USA).
3 RESULTS
Eight patients (six men, 75%), with a mean age of 56.6 ± 12.7 years, participated in the study. Table 2 shows the cardiovascular, anthropometric, and functional characteristics of the sample.
| Variables | Mean (±SD) |
|---|---|
| Age (years) | 56.6 (±12.7) |
| Weight (kg) | 59.1 (±11.2) |
| Height (m) | 1.65 (±0.06) |
| Systolic blood pressure (mm Hg) | 119.86 (±22.18) |
| Diastolic blood pressure (mm Hg) | 68.29 (±13.03) |
| Heart rate (bpm) | 82.7 (±8.5) |
| Body mass index (kg/m2) | 25.73 (±4.18) |
| Lean mass (kg) | 44.35 (±6.73) |
| Fat mass (kg) | 14.76 (±7.35) |
| Body fat (%) | 24.20 (±8.63) |
| Basal metabolic rate (kcal) | 1348.50 (±204.04) |
| Dialysis vintage (months) | 42.3 (±35.6) |
| Handgrip strength (kgf) | 24.13 (±10.36) |
| Gender, n (%) | |
| Male | 6 (75) |
| Female | 2 (25) |
| Primary CKD cause, n (%) | |
| Diabetes | 1 (12.5) |
| Hypertension | 3 (37.5) |
| Polycystic kidneys | 2 (25) |
| Others/unknown | 2 (25) |
| Anti‐hypertensive drug administration | 3 (37.5) |
| Losartan | 1 (12.5) |
| Amlodipine | 1 (12.5) |
| Nebivolol | 1 (12.5) |
| Bisoprolol | 1 (12.5) |
The patients had 42.3 (±35.6) months of dialysis vintage and hypertension as the main cause of CKD. Two patients were administered with one anti‐hypertensive drug and one patient with two drugs.
Figure 3 shows BP values during HD at three different conditions: control, low‐intensity, and moderate‐intensity exercise protocols. Analyses did not show any significant differences for BP across protocols or sessions.
The systolic BP (SBP) and DP significantly increase immediately after exercise in the moderate‐intensity protocol (122.0 ± 15.9 vs 131.3 ± 19.8, P < .05; 9094.7 ± 1705.7 vs 9783.0 ± 1947.9, P < .05, respectively) but returned to the pre‐exercise values 10 minutes later.
Figure 4 shows the values of HRV assessed during HD throughout the three different sessions.
No significant differences were observed in the HRV across protocols for any of the evaluated conditions, as well as between the moments within the same protocol.
Additionally, no significant differences in the RPE scores or the total training volume (obtained from the adapted TRIMP method) were observed between protocols (4.88 ± 1.8 vs 5.63 ± 0.74, P = .285 and 13 486.5 ± 7705.4 vs 16 440.0 ± 7691.5, P = .165), suggesting that the total training volume were the same in both IHE protocols.
4 DISCUSSION
The main findings showed that intradialytic IHE does not elicit hemodynamic instability based on SBP, diastolic BP, HR, RR intervals, SDNN, or RMSSD, regardless of the intensity. Historically, isometric exercise has been avoided for clinical populations due to a hypothetical sudden increase in BP inducing arrhythmia.7 Nonetheless, in the last decades, a plethora of evidence suggests that IHE modulates cardiac autonomic function, playing an important role in hemodynamic stability.8, 13, 14
Our results showed that an intradialytic IHE did not elicit BP instability. After the moderate‐intensity IHE protocol, a significant transient slight increase was observed in the SBP and DP. The change in the BP after an intradialytic exercise is in line with other acute studies, such as that conducted by Dungey et al20 wherein a cycle ergometer exercise was used in the second hour of HD. The anti‐hypertensive drugs might have interfered with our results, however, for safety concerns from the dialysis staff, we requested patients to keep their regular medication routine.21
In the present study, there were no episodes of intradialytic hypotension, one of the main concerns in patients receiving HD treatment.22, 23 Park et al23 evaluated 113 255 patients for 2 years and identified that those with a decrease in the SBP greater than 30 mm Hg at the end of HD presented with higher mortality rates compared to the others, including the group that presented intradialytic hypertension >10 mm Hg. Thus, the intervention proposed in our study seems to promote BP stability, possibly preventing episodes of intradialytic hypotension or hypertension. Previously, McGuire et al24 presented intradialytic exercise as a nonpharmacological intervention to control hemodynamic instability during HD.
No significant changes have been found in HRV, either comparing the moments of the same session or comparing the IHE and control sessions between themselves. Previous studies have reported changes in the spectral analysis of RR interval and parasympathetic components of HRV during HD sessions.25, 26 Despite some studies having evaluated the frequency domain variables (low‐frequency [LF], high frequency [HF], and LF/HF), the time‐domain variables have also been widely used, especially for short‐term measurements.16 Silva et al25 evaluated the time‐domain, SDNN and RMSSD, during the HD session and found an elevation on SDNN at 30 minutes when compared to the beginning, stabilizing at the end. In contrast, Galetta et al27 identified negative changes in the SDNN and RMSSD at the end of HD. The time‐domain variables (SDNN and RMSSD) present excellent predictive power of mortality in CKD patients28; hence we evaluated these parameters in this pilot study.
In our sample, the IHE did not induce significant changes in the time‐domain of HRV, although the literature indicates that HD per se promotes cardiac electrical instability, decreasing or raising HRV values, thus, promoting intradialytic hypotension or hypertension. Nonetheless, there is no evidence in support of this phenomenon in intradialytic exercise, which corroborates our results.29 Kouidi et al30 highlighted that exercise is associated with high SDNN and RMSSD values, suggesting better cardiac autonomic stability for those CKD patients engaged in exercise training.
To the best of our knowledge, this is the first study to describe the acute hemodynamic response of IHE in HD patients. Previously, Tayebi et al investigated the effects of isometric resistance exercise performed using the patients' bodyweight. Improvements were identified after 24 sessions in physical fitness parameters.31 However, cardiovascular variables were not evaluated in an acute or chronic setting.
Considering that our protocol, regardless of the intensity, did not promote negative changes in cardiac electrical stability and BP values, IHE seems to be a safe and simple tool to be prescribed for HD patients. From this perspective, Antonio et al13 presented the adjustments in the isometric exercise in the cardiac autonomic system in their review. It is mentioned that during isometric exercise, autonomic modulation is observed by a decrease in the vagal modulation followed by an increase in the sympathetic modulation and its reversion, soon after the end. Therefore, IHE as a regulator of the cardiac autonomic system, by sympathetic‐parasympathetic activity, may plan an important role in attenuating intradialytic hemodynamic instability.
The main limitations of this study are as follows: (a) small sample size due to the exclusion criteria; however, the strength of the study is that the all patients randomly participated in both experimental and control sessions; (b) lack of food control, a factor that may have interfered hemodynamic response; (c) high age range, which could not be corrected, considering the small sample size; (d) nonevaluation of intra‐arterial BP responses during the IHE, which could be markedly invasive, expensive, and unavailable to this study.
5 IMPLICATIONS FOR CLINICAL PRACTICE
Intradialytic IHE might be a safe therapeutic intervention to intradialytic hemodynamic control in HD patients. Thus, it could be safely implemented in dialysis centers due to its low‐cost and feasibility. Moreover, it should be noted that the main limitations of intradialytic exercise interventions are low‐adherence and sustainability because generally there are no exercise physiologists in the dialysis staff. The exercise protocol suggested here can be performed in a short time (less than 20 minutes), with portable equipment of easy execution, has a fast learning time, and could be supervised by any healthcare professional from the dialysis staff (physiotherapists, nurses, dieticians, nephrologists, etc).
6 CONCLUSION
We conclude that an intradialytic isometric handgrip exercise did not induce acute hemodynamic instability in hemodialysis patients. These findings indicate that isometric handgrip exercise might be a safe therapeutic intervention to intradialytic hemodynamic control in this population. Future longitudinal intervention studies should be conducted to verify long‐term improvements and efficacy, which is already being conducted by our research group.
ACKNOWLEDGMENTS
We thank the Coordination for the Improvement of Higher Education Personnel (CAPES) for the master's scholarship to Heitor Ribeiro. This study was supported by the Fundação de Apoio à Pesquisa do Distrito Federal (FAPDF) (grant 0193.001.558/2017).
CONFLICT OF INTEREST
The authors declare no potential conflict of interest.
