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Intradialytic exercise increases cardiac power index

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Intradialytic exercise increases cardiac power index

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Introduction : Mortality rates are high in end-stage renal disease due to cardiovascular complications. Perfusion of the myocardium declines during and after hemodialysis sessions with the potential for aerobic exercise to mitigate these during hemodialysis. Objectives : The purpose of this study was to investigate acute changes in hemodynamics in subjects with end-stage renal disease (ESRD) during exercise. Patients and Methods : Subjects (n = 10) were monitored for 1.5 hours during hemodialysis treatment during a control (CON) and an exercise (EX) session. Subjects cycled using an ergometer strapped to the reclining dialysis chair at an RPE of 11-13 for 30 minutes during the EX session beginning at 30 min into dialysis and ending at 60 minutes. Data for systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) were collected using an automated blood pressure cuff attached to the hemodialysis machine. Data for cardiac output (Q̇ ), cardiac power index (CPI), stroke volume (SV), systemic vascular resistance (SVR), and heart rate (HR) were collected using the NICaS bioelectrical impedance device. Results : During the EX session, CPI, Q̇ , SV, and HR were significantly greater (P<0.05) than the CON session. Additionally, Q̇ was significantly (P< 0.05) greater at 45 minutes and 60 minutes compared to 15 minutes. HR was significantly (P<0.05) greater at 45 minutes compared to 90 minutes. No significant interactions were found for MAP, CPI, Q̇ , HR, SV, SBP, DBP, or SVR. Conclusion : In conclusion, exercise during dialysis may decrease the likelihood of experiencing ischemic or hypotensive events by enhancing myocardial perfusion through increasing CPI and Q̇ .
Intradialytic exercise increases cardiac power index
www.nephropathol.com DOI: 10.15171/jnp.2020.07 J Nephropathol. 2020;9(1):e07
Journal of Nephropathology
*Corresponding author: Brent A. Momb, Email: bmomb@umass.edu
Brent A. Momb1*
ID
, Samuel A. E. Headley2
ID
, Tracey D. Matthews2
ID
, Michael J. Germain3
ID
1Department of Kinesiology, University of Massachusetts, Amherst, MA, USA
2Department of Exercise Science and Athletic Training, Springfield College, Springfield, MA, USA
3Department of Nephrology, Renal and Transplant Associates, Springfield, MA, USA
ARTICLE INFO
Article type:
Original Article
Article history:
Received: 10 October 2019
Accepted: 20 November 2019
Published online: 6 December 2019
Keywords:
Cardiovascular
Dialysis
Exercise
Kidney
End-stage renal disease
Chronic kidney disease
Introduction: Mortality rates are high in end-stage renal disease due to cardiovascular complications.
Perfusion of the myocardium declines during and after hemodialysis sessions with the potential for
aerobic exercise to mitigate these during hemodialysis.
Objectives: The purpose of this study was to investigate acute changes in hemodynamics in subjects
with end-stage renal disease (ESR D) during exercise.
Patients and Methods: Subjects (n = 10) were monitored for 1.5 hours during hemodialysis treatment
during a control (CON) and an exercise (EX) session. Subjects cycled using an ergometer strapped
to the reclining dialysis chair at an RPE of 11-13 for 30 minutes during the EX session beginning at
30 min into dialysis and ending at 60 minutes. Data for systolic blood pressure (SBP), diastolic blood
pressure (DBP), and mean arterial pressure (MAP) were collected using an automated blood pressure
cuff attached to the hemodialysis machine. Data for cardiac output (Q
̇), cardiac power index (CPI),
stroke volume (SV), systemic vascular resistance (SVR), and heart rate (HR) were collected using the
NICaS bioelectrical impedance device.
Results: During the EX session, CPI, Q
̇, SV, and HR were significantly greater (P < 0.05) tha n the
CON session. Additionally, Q
̇ was significantly (P < 0.05) greater at 45 minutes and 60 minutes
compared to 15 minutes. HR was significantly (P < 0.05) greater at 45 minutes compared to 90
minutes. No significant interactions were found for MAP, CPI, Q
̇, HR, SV, SBP, DBP, or SVR.
Conclusion: In conclusion, exercise during dialysis may decrease the likelihood of experiencing
ischemic or hypotensive events by enhancing myocardial perfusion through increasing CPI and Q
̇.
ABSTRACT
Implication for health policy/practice/research/medical education:
ESRD patients undergo hypotension and perfusion issues during hemodialysis. Acute aerobic exercise during a hemodialysis session was
investigated to determine if CPI would increase compared to a control session. CPI was enhanced through increases in cardiac output and
may improve perfusion during hemodialysis.
Please cite this paper as: Momb BA, Headley SAE, Matthews TD, Germain MJ. Intradialytic exercise increases cardiac power index. J
Nephropathol. 2020;9(1):e07. DOI: 10.15171/jnp.2020.07.
Introduction
End-stage renal disease (ESRD) is present in 15 per 10 000
people in first world countries and these individuals are
more prone to developing cardiovascular disease (CVD)
(1). Risk of CVD in ESRD patients is enhanced by
albuminuria, anemia, hyperparathyroidism, metabolic
bone disease, hyperhomocysteinemia, malnutrition,
apolipoprotein isoforms, inflammation, endothelial
dysfunction, and oxidative stress (2). Research pertaining
to rehabilitation for ESRD patients and mitigating risk
factors for CVD is lacking on a nation-wide level (3).
Furthermore, low exercise capacities in ESRD patients
contributes to abnormally high mortality rates (4).
Patients with impaired renal function display lower
glomerular filtration rates (GFR) and present with
elevated serum creatinine and blood urea nitrogen levels
from damage to nephrons (1). ESRD patients must
undergo renal replacement therapy through hemodialysis,
peritoneal dialysis, or kidney transplantation (1).
Byproducts not removed through the renal system
affect every organ system (5). Causes of chronic kidney
disease (CKD) arise due to injury to nephrons from
inflammation, hypoperfusion, ischemia, or toxic damage
(5). Cardiovascular complications occur from CKD such
Original Article
Momb BA et al
Journal of Nephropathology, Vol 9, No 1, January 2020 www.nephropathol.com
2
as, left-ventricular hypertrophy (LVH), hypertension,
reduced vascular compliance, atherosclerosis,
cardiomyopathy, cardiac fibrosis, and anemia (3).
Exercise during hemodialysis has been of interest as it
may negate effects produced by hemodialysis treatment
and may enhance the overall efficacy of dialysis (3). ESRD
patients undergoing intradialytic exercise experience
enhancement of heart rate variability, ejection fraction,
and lower risk of sudden cardiac death (6). Intradialytic
exercise enhances solute removal from blood serum by
increasing perfusion of capillary beds (3,7). Exercise during
hemodialysis improves aerobic capacity, resting diastolic
and systolic blood pressure values, and hemoglobin
levels (6,7). Furthermore, markers of inflammation and
oxidative stress are reduced from intradialytic exercise,
possibly reducing overall mortality rate (8,9).
Hemodynamic instability with transient myocardial
ischemia is prevalent in ESRD patients undergoing
traditional three-day per week hemodialysis treatment
(3,10). Rapid fluid removal from intravascular spaces
during hemodialysis requires fluid shifts from intracellular
and interstitial spaces (3). Inadequate fluid shifting results
in hemodynamic instability and a reduction in blood
pressure. Reductions in cardiac output (Q
̇) and mean
arterial pressure (MAP) provokes systemic and myocardial
hypoperfusion, leading to greater chances of experiencing
myocardial stunning during and after hemodialysis (3).
Intradialytic hypotension (IDH) is induced through
reduced ventricular filling, ventricular dysfunction,
impaired reaction to catecholamines, reduced blood
volume, and autonomic dysfunction (11). Abnormal
regulation of arterial pressure from desensitized
baroreceptors may also provoke IDH (11). Episodes of
IDH correlate highly with adverse cardiovascular events
during hemodialysis treatment (12).
Myocardial stunning is seen as transient ischemic
episodes during hemodialysis inducing abnormalities
in left-ventricular function (10,13). Stunning of the
myocardium is defined as post-ischemic myocardial
dysfunction even with restored blood flow (10). A stunned
myocardium presents as a sluggish contraction during
systole. Repeated events of stunning leads to fibrosis,
diastolic dysfunction, and higher myocardial workloads.
Prolonged stunning of the myocardium leads to eventual
hibernation and irreversible death of myocardial tissues
with possible sudden death (10). Changes in circulatory
patterns from myocyte-capillary mismatching reduces
coronary flow and is typically present in patients
demonstrating LVH (14). Increases in vascular stiffness
and LVH work together to reduce coronary perfusion
and endothelial function, increasing the likelihood of
myocardial stunning (13,14).
Exercise induces increases in Q
̇ and MAP, which could
theoretically increase perfusion of myocardial tissue,
reducing hemodynamic instability in ESRD patients(3).
Reasonable interventions should increase Q
̇ and MAP to
reduce adverse ischemic events. Little research has been
done to investigate the effect of intradialytic exercise to
enhance myocardial perfusion and reduce episodes of
IDH. The potential for intradialytic exercise to reduce
hemodynamic instability, myocardial stunning, and
negative outcomes of hemodialysis has not been well
studied (3). CPI may be a potential indicator of myocardial
perfusion and is measured in watts per meter squared by
multiplying MAP by Q
̇ (15).
Objectives
The purpose of this study was to investigate differences
in hemodynamic variables in subjects undergoing
intradialytic exercise compared to no exercise. We
hypothesized that intradialytic exercise would increase
CPI, MAP, and Q
̇ compared to a control session.
Patients and Methods
A repeated measures study design was used to determine
the effect of an acute bout of intradialytic exercise on
hemodynamics in ESRD subjects using the NICaS
bioelectrical impedance device (NICaS, NI Medical, Peta
Tikva, Israel) and an automated blood pressure device
attached to the dialysis machine (2008T Hemodialysis
Machine, Fresenius, USA). The independent variables were
intradialytic exercise condition (no exercise, exercise) and
time (seven time points at 15 min intervals). The primary
dependent variables were MAP, CPI, and Q
̇. Secondary
dependent variables were systolic blood pressure (SBP),
diastolic blood pressure (DBP), heart rate (HR), stroke
volume (SV), and systemic vascular resistance (SVR).
Subjects
Subjects (n = 10) in this study were ESRD patients
sourced from the American Renal Associates Dialysis
clinic in Western, MA. Average age of subjects was 54.30
years (SD = 9.93), eight were men and two were women.
Average time since hemodialysis begun was 2.99 years (SD
= 2.49). Subject weight averaged 93.17 kg (SD = 25.45)
during the control session and 93.04 kg (SD = 25.24)
during the exercise session. Descriptive statistics can be
found in Table 1. Inclusion criteria were: (1) conventional
hemodialysis three times per week; (2) 20 to 70 years
of age; (3) undergoing hemodialysis for >3 months; (4)
physically able to exercise with no contraindications; (5)
capable of independently giving informed consent; (6)
medical clearance from a nephrologist. Full exclusion
and inclusion criteria were reviewed by the subject’s
nephrologist. Participation was voluntary. The researcher
obtained Institutional Review Board approval and subjects
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Intradialytic exercise
3
completed informed consent prior to sessions with the
researcher.
Measuring instruments
A standard automated blood pressure device attached to
the hemodialysis machine was used to determine SBP
and DBP at 15 minutes time intervals during the dialysis
treatment. Using SBP and DBP, MAP was calculated to
determine instances of IDH at or below 70 mm Hg.
The NICaS device was used to collect data on Q
̇,
CPI. Secondarily, the NICaS was used to collect data on
secondary variables SV, HR, and SVR. The NICaS whole-
body bioelectrical impedance device has been validated to
measure Q
̇ and SV (16–20). NICaS strongly correlates
with pulmonary artery catherization thermodilution and
echocardiograph techniques for Q
̇ and SV estimation
(16–20). The NICaS device measures CPI (W/m2) (15).
CPI may decrease in subjects undergoing hemodialysis
treatment due to less contractile force production from
impaired coronary blood flow (15).
Procedures
Following approval from the Institutional Review Board, a
letter was sent to the ARA hemodialysis center in Western
Massachusetts for permission to identify subjects and
conduct research in the center. Once approval had been
granted by the hemodialysis center, recruitment flyers
were posted. If subjects were interested in participating,
the researcher and the subject’s nephrologist completed the
medical history and medical release form to vet subjects
through exclusion and inclusion criteria. The researcher
obtained signed medical history and medical release forms
prior to the start of the sessions. The researcher assigned
subjects a number for anonymous and confidential data
collection and analysis. Subject number was assigned
based upon the time of study entry.
Subjects underwent three sessions: (1) familiarization
with equipment and paperwork completion; (2) control
session (CON); (3) experimental session (EX). During
the familiarization session, subjects approved by their
nephrologist signed the consent form, with emphasis on
subject confidentiality. Height was recorded during the
familiarization session utilizing a stadiometer; dry weight
was recorded at the beginning of each session with a
weight scale. All subjects were informed that participation
was voluntary, and subjects could withdraw at any time.
Subjects were fitted to the cycle ergometer (881 E, Monark
Exercise AB, Vansbro, Sweden) for later use in EX session.
After the familiarization session and all paperwork were
completed, subjects underwent session 2 (CON) and
session 3 (EX) in a randomized order. Both CON and
EX sessions occurred during the mid-week hemodialysis
session to standardize dry weight of the subject, with one
to two weeks between sessions. Conventional hemodialysis
entails hemodialysis treatment in a dialysis center for
three days per week lasting approximately three hours per
session. Medical staff were present for routine monitoring
during the dialysis sessions for indications of adverse
cardiac or hypotensive events as per the clinic guidelines.
Medical staff acted according to routine clinical care as
indicated by the clinic.
For CON and EX sessions, data were collected with the
NICaS device and the automated blood pressure cuff. The
NICaS device had two electrodes placed on the palm side
of the distal portion of the inferior radioulnar joint on
each arm. During the EX session, the cycle ergometer was
attached to the foot of the chair in which the subject was
reclining during hemodialysis to be stable and comfortable
for the subject while pedaling.
Both CON and EX sessions underwent conventional
hemodialysis with data being collected from start of
hemodialysis to 1 hour and 30 minutes into hemodialysis
at 15 minutes intervals (Figure 1). For the CON session,
data were collected with no intradialytic exercise. For the
EX session, subjects remained sedentary for the first 25
minutes. At the 25 minutes mark, subjects underwent a
Table 1. Subject characteristics
Characteristics (n = 10)
Age (y), mean ± SD 54.30 ± 9.93
Height (cm), mean ± SD 172.90 ± 12.07
Dry weight Con (kg), mean ± SD 93.17 ± 25.45
Dry weight EX (kg), mean ± SD 93.04 ± 11.24
Hemoglobin (mg/dL), mean ± SD 11.24 ± 1.33
Years on dialysis 2.99 ± 2.49
Sex (m/f) (8/2)
Race (CN/LT/AFR) (5/3/2)
Reason for dialysis (HT/T2D/TN/GN) (5/2/2/1)
Medications
Alpha receptor agonists 5
Angiotensin 2 receptor blockers 4
Angiotensin converting enzyme inhibitor 2
Beta 2 agonist 3
Beta blocker 7
Calcium channel blocker 3
Diuretic 3
Gaba analogue 3
Insulin 4
Phosphate binder 8
Proton pump inhibitor 3
Statin 5
Abbreviations: CN, Caucasian; LT, Latin; AFR, African American;
HT, hypertension; T2D, Type II diabetes; TN, toxic nephropathy;
GN, glomerular nephritis.
Momb BA et al
Journal of Nephropathology, Vol 9, No 1, January 2020 www.nephropathol.com
4
self-selected intensity 5 minutes warm up utilizing a cycle
ergometer. After the 5 minutes warm up was finished,
30 minutes of cycling exercise was completed at an 11-
13 RPE aiming for 55% of age-predicted HR maximum.
Exercise ceased at the 60 minutes mark.
Ethical issues
Subjects signed informed consent and the study was
approved by the Springfield College Institutional Review
Board prior to data being collected. All procedures
performed in studies involving human participants are in
accordance with the ethical standards of 1964 Helsinki
Declaration and its later amendments. All participants
provided written and informed consent. This study
was conducted as a master’s thesis by Brent Momb at
Springfield College.
Statistical analysis
IBM statistical package for the social sciences (SPSS,
v. 20) was used for analysis with an alpha level of P =
0.05. A total of three repeated measures factorial analysis
of variance 2 X 7 (ANOVA) were used to examine mean
differences and interactions between two conditions
across seven-time points (EX, CON) for MAP, CPI, and
Q
̇. Five repeated measures factorial Analysis of Variance
2 X 7 (ANOVA) were used to examine mean differences
and interactions between two conditions across seven-
time points (EX, CON) for secondary variables HR, SV,
SBP, DBP, and SVR.
Results
All potential subjects (N = 54) were screened for eligibility.
Forty-four were excluded due to not meeting the inclusion
criteria (n = 22), declining to participate (n = 15), for not
being cleared to participate by their physician (n = 6).
Eleven of the subjects were approved, one dropped out
prior to the study commencing. Ten subjects completed
both the EX and CON sessions. Three completed the
CON session first and seven completed the EX session
first. The data were screened for missing data, normality,
and outliers. No missing values or outliers were observed.
All data were determined to be mesokurtic. CPI during
Assessed for Eligibility (N = 54)
Excluded (n = 43)
Not meeting inclusion criteria (n
=22)
Declined to participate (n = 15)
No physician clearance (n = 6)
Dropout (n = 1)
Session Randomization (n = 10)
Regular Hemodialysis
Data collection from time point
0:00-1:30
Regular Hemodialysis
Data collection from time point
0:00-1:30
Time: 0:25
Self-selected warm-up on cycle
ergometer
Time: 0:30-1:00
Cycling exercise at 11-13 RPE
Time: 1:00-1:30
Post-exercise monitoring
Enrollment
Control Session
Exercise Session
Figure 1. Enrollment and flow chart for exercise and control sessions.
www.nephropathol.com Journal of Nephropathology, Vol 9, No 1, January 2020
Intradialytic exercise
5
the EX session at 45 minutes and 75 minutes were
positively skewed. CPI was positively skewed during the
CON session at 90 minutes. All other data were normally
skewed. The test of sphericity indicated no significant
difference (P > 0.05) for MAP, CPI, Q
̇, HR, SV, SBP,
DBP, and SVR. Descriptive statistics for variables are
summarized in Table 2. All means are reported ± SE.
No significant interactions were found for the primary
or secondary variables. Significant (P < 0.05) mean
differences for CPI F = 12.796 (1, 9), P = 0.006, ηp
2
= 0.587, Q
̇ F = 32.178 (1, 9), P = 0.000, ηp
2 = 0.781,
SV F = 20.939 (1, 9), P = 0.001, ηp
2 = 0.699, and HR
F = 13.013 (1, 9), P = 0.006, ηp
2 = 0.591 were found
between conditions. Additionally, significant (P < 0.05)
time effects were found for Q
̇ F = 2.678 (6, 54), P = 0.024,
ηp
2 = 0.229 and HR F = 2.815 (6, 54), P = 0.019, ηp
2 =
0.238 (Figure 2).
CPI was significantly higher (P < 0.05) in EX (0.79 W/
m2 ± 0.03) compared to CON (0.67 W/m2 ± 0.04), 95%
CI = 0.045, 0.200 (Table 2). For Q
̇, the EX condition (7.91
L/min ± 0.49) was significantly higher (P < 0.05) than the
CON condition (6.90 L/min ± 0.048), 95% CI = 0.606,
1.409. For SV, the EX condition (96.99 mL ± 4.39) was
significantly higher (P < 0.05) than the CON condition
(88.73 mL ± 3.99), 95% CI = 4.175, 12.340. For HR, the
EX condition (78.23 BPM ± 4.19) was significantly higher
(P < 0.05) than the CON condition (73.21 BPM ± 4.26),
95% CI = 1.870, 8.159. The time effects for Q
̇ and HR
were analyzed using pairwise comparisons. At 45 minutes,
Q
̇ was significantly (P < 0.05) higher (7.83 L/min ± 0.42)
compared to 15 minutes (6.78 L/min ± 0.53), 95% CI =
0.175, 1.919. Q
̇ was also significantly higher (P < 0.05) at
60 minutes (7.97 L/min ± 0.56) compared to 15 minutes
(6.78 L/min ± 0.53), 95% CI = 0.157, 2.206. HR was
significantly (P < 0.05) higher at 45 minutes (78.30 BPM
± 0.42) compared to 90 minutes (75.00 BPM ± 4.89),
95% CI = 0.179, 6.421.
Discussion
The purpose of this study was to determine if exercise
during a session of dialysis would increase MAP, CPI,
and Q
̇ compared to a control session with no exercise.
The main findings are two-fold: CPI was higher during
the EX session compared to CON session; and second, Q
̇
was higher during the EX session compared to the CON
session. No changes were observed regarding MAP when
comparing the EX to the CON session.
Hemodialysis induces large decreases in plasma volume
which could potentially induce hemodynamic instability
and IDH (3). IDH may precipitate myocardial ischemia
through hypoperfusion of cardiac tissues (13). Thus, it
has been postulated that normal responses to exercise may
negate the impact of IDH by preventing it during dialysis
treatment (3).
No changes in MAP were observed between the CON
or EX session or over the 1.5 hours monitoring period.
No periods of hypotension were observed during the
study. MAP in this study was similar between the control
session (90.26 mm Hg ± 2.78) and exercise session
(93.86 mm Hg ± 3.40). From this, SBP (Table 2) was
similar in the control session (132.60 mm Hg ± 5.13)
to the exercise session (136.76 mm Hg ± 6.44). Recent
studies examining blood pressure in subjects receiving
intradialytic exercise reported similar findings with no
differences in either control or exercise sessions (21,22).
Other researchers observed no changes in SBP between
control (140.90 mm Hg ± 22.30) and exercise sessions
(131.30 mm Hg ± 20.00) (21). However, other researchers
have demonstrated significant increases in SBP with the
introduction of intradialytic exercise (6,9,23).
The typical response to exercise is increases in peripheral
vasodilation to meet metabolic needs of skeletal muscle
(23). Baroreceptors, chemoreceptors, and skeletal muscle
receptors increase sympathetic mediated outflow to the
heart to maintain or increase blood pressure. However,
Table 2. Hemodynamics for control (CON) and exercise (EX) sessions
Characteristics (n = 10) CON EX ηp
2
Primary variables
Mean arterial pressure (mm Hg) 90.26 ± 2.78 93.86 ± 3.40 0.078
Cardiac power index (W/m2) 0.67 ± 0.05 0.79 ± 0.03** 0.587
Cardiac output (L/min) 6.90 ± 0.48 7.91 ± 0.48** 0.781
Secondary variables
Heart rate (beats/min) 73.21 ± 4.26 78.23 ± 4.18** 0.591
Stroke volume (mL/beat) 88.73 ± 3.99 96.99 ± 4.39** 0.699
Systolic blood pressure (mm Hg) 132.60 ± 5.13 136.76 ± 6.44 0.039
Diastolic blood pressure (mm Hg) 70.88 ± 2.57 72.87 ± 2.37 0.040
Systemic vascular resistance(dyn·s·cm−5) 2292 ± 176 2102 ± 200 0.144
Note. ** Indicates a significant difference (P < 0.01) between conditions.
Momb BA et al
Journal of Nephropathology, Vol 9, No 1, January 2020 www.nephropathol.com
6
subjects undergoing hemodialysis treatment may present
with enhanced sympathetic activity, and decreased
baroreceptor sensitivity (23). Sympathetic dominance
and rapid fluid removal during dialysis treatment may
be a possible explanation of no changes in blood pressure
in this current study. Subjects who have impaired renin-
angiotensin-aldosterone systems along with inability
to match Q
̇ during dialysis may be sympathetically
dominated. No statistical difference was found in SVR
between EX (2101.78 dyn·s·cm−5 ± 199.944) and CON
(2291.90 dyn·s·cm−5 ± 176.29). However, the small
decrease in SVR observed in the EX session may suggest
the small increase in MAP was due to increased Q
̇ and
decreased SVR. Second, self-selected intensity between
an RPE of 11-13 may not have been enough to induce
increases in MAP. Last, subjects heavily medicated with
anti-hypertensive medication may not produce normal
responses to exercise leading to no changes in MAP,
medication list can be found in Table 1.
Even though no differences were noted in MAP
during either session EX or CON, it is possible that
intradialytic exercise could potentially maintain MAP
during hemodialysis treatment. Maintaining blood
pressure during exercise could be of benefit to subjects
who experience IDH. Furthermore, it is evident that
exercise during dialysis treatment does not exacerbate
hemodynamic instability and did not induce post-exercise
hypotension in this study.
Subjects who are prone to IDH have reductions in
overall cardiac contractility, leading to reductions in
cardiac power output (11). Cardiac power may be reduced
due to reductions in preload from high ultrafiltration rates
(15). In the present study, CPI during the EX session was
higher compared to the CON session. CPI is a product of
Q
̇ and MAP and is measured in Watts produced compared
to the patient’s total body surface area (24). The increase
75
80
85
90
95
100
0:00 0:15 0:30 0:45 1:00 1:15 1:30
Intradialytic Time (hour:minute)
CON
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0:00 0:15 0:30 0:45 1:00 1:15 1:30
Cardiac Power Index (W/m
2
)
Intradialytic Time (hour:minute)
CON EX
120
125
130
135
140
145
0:00 0:15 0:30 0:45 1:00 1:15 1:30
Systolic Blood Pressure (mmHg)
Intradialytic Time (hour:minute)
0
1
2
3
4
5
6
7
8
9
10
0:00 0:15 0:30 0:45 1:00 1:15 1:30
Cardiac Output (L/min)
Intradialytic Time (hour:minute)
62
64
66
68
70
72
74
76
78
0:00 0:15 0:30 0:45 1:00 1:15 1:30
Diastolic Blood Pressure (mm Hg)
Intradialytic Time (hour:minute)
0
20
40
60
80
100
120
0:00 0:15 0:30 0:45 1:00 1:15 1:30
Stroke Volume (mL)
Intradialytic Time (hour:minute)
64
66
68
70
72
74
76
78
80
82
84
86
0:00 0:15 0:30 0:45 1:00 1:15 1:30
Heart Rate (BPM)
Intradialytic Time (hour:minute)
0
500
1000
1500
2000
2500
3000
0:00 0:15 0:30 0:45 1:00 1:15 1:30
Systemic Vascular Resistance (dyn·s·cm−5)
Intradialytic Time (hour:minute)
Figure 2. Changes in hemodynamic parameters between the control (CON) and exercise (EX) sessions in hemodialysis patients.
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Intradialytic exercise
7
in CPI from this study can likely be attributed to increases
in Q
̇ from enhanced contractility and preload of the
myocardium (15).
Myocardial stunning presents with a myocardium
that fails to contract normally and thus may potentially
have a reduced power output (10). This reduced power
output may be attributed to decreased Q
̇ or MAP during
the dialysis session. Decreased Q
̇ or MAP can lead to
hypoperfusion of the myocardium. Potential ways to
increase CPI would be to reduce ultrafiltration rate or
increase the target weight of the patient (15). However,
intradialytic exercise increased CPI compared to control
and may be an alternative option. This is the first study
known to the researcher to determine changes in CPI
from intradialytic exercise. In ESRD subjects, average
CPI during dialysis treatment appears to be 0.59 W/m2 ±
0.04 (15). In comparison to baseline values seen in other
studies, this study demonstrated a CPI of 0.67 W/m2 ±
0.04 during the control session and increased to 0.79 W/
m2 ± 0.03 during the exercise session. The increase in CPI
in this study indicates intradialytic exercise may mitigate
IDH and hypoperfusion of tissues.
Ultrafiltration from hemodialysis reduces Q
̇ and SV
but MAP is typically maintained by variations in SVR
(11). Reductions in overall cardiac contractility may
coincide with reductions in Q
̇ (11). The current study
demonstrated a 13% increase in cardiac output from 6.90
L/min ± 0.48 during the control session to 7.91 L/min ±
0.49 in the exercise session. Similar results were noted by
other researchers when patients exercised for two, 10-min
periods during hemodialysis (25). Researchers recorded a
36% increase from 5.1 L/min ± 1.1 up to 7.9 L/min ±
2.4 (25). Q
̇ in this study was increased through enhanced
SV and HR. SV increased from 88.73 mL ± 3.99 in the
CON session to 96.99 mL ± 4.39 in the EX session. HR
increased from 73.21 BPM ± 4.26 in the CON session
to 78.23 BPM ± 4.18 in the EX session. This study
demonstrated intradialytic exercise increases Q
̇ compared
to a control session, similar to results described by other
researchers (23).
Q
̇ is a product of HR and SV. Exercise in normal
populations enhances Q
̇ through both HR and SV
increases (3). SV during dialysis treatment may be
impaired through reductions in circulating blood volume
(11). Dialysis treatment also has a potential side effect of
inducing LVH through pressure dependent mechanisms
of hypertension and aortic stiffness (26). Reductions in
SV from lower circulating blood volumes and concentric
hypertrophy leads to enhancement of Q
̇ primarily from
increases in HR (3). Increases in primarily from heart
rate increases myocardial oxygen consumption and may
potentiate ischemic conditions (27). Declining cardiac
output correlates with decreased coronary perfusion, and
this decreased coronary perfusion leads to myocardial
stunning (3). Thus, increases in cardiac output may
contribute to reductions in the negative impact of
hemodialysis by keeping the myocardium adequately
perfused (3). Increasing Q
̇ through intradialytic exercise in
dialysis patients may help attenuate the negative impacts
of reducing relative blood volume from ultrafiltration
(11).
Myocardial stunning is described as a prolonged, post-
ischemic left ventricular dysfunction (10). Myocardial
stunning precipitates both hibernation of the myocardium
and myocardial infarction and is a major contributor
to mortality rate. The pathophysiology of myocardial
stunning is multifactorial. Myocardial fibrosis interferes
with the capability of the left ventricle to relax normally,
decreasing cardiac output. Fibrotic tissues and excess
workload placed on the myocardium induces LVH.
Furthermore, rapid fluid removal from ultrafiltration can
potentially impact the myocardial vascular bed leading
to hypoperfusion. A stunned myocardium appears as
sluggish during systole with a failure to contract normally
(10).
By observing changes in MAP, CPI, and Q
̇ we can begin
to draw conclusions on the issue of myocardial stunning
in hemodialysis patients. Maintaining or increasing
MAP and Q
̇ by enhancing CPI may potentially reduce
incidences of hypoperfusion during hemodialysis sessions
(3,10). While MAP did not increase or decrease in this
study, exercise may contribute to the maintenance of
perfusion during hemodialysis.
This study is limited primarily by the inability to
monitor intensity beyond rate of perceived exertion. This
could skew results dependent on the subject’s differential
thoughts on exerted effort during the EX session. Heart
rate was taken, however 70% of the subjects were on beta-
blockers. Age-predicted HR maxes for subjects ranged
between 151-181 BPM. Based upon observed HR,
subjects averaged between 40-48% HR maximum during
the CON session and 43-52% HR maximum during the
EX session.
The study was also limited by the assumption that the
NICaS device used adequately monitored hemodynamic
variables during the session. Due to fluid being removed
from where the electrical signals were being sent, this
could have influenced the results. To combat this, a
repeated measures design was implemented. The power
analysis conducted prior to the study commencing
suggested 15 subjects would be adequate. We obtained
only 10 subjects due to a limited number of subjects
available at the clinic and being willing to participate in
the study. Finally, the inability to prescreen for myocardial
stunning in subjects may impact the conclusions. Future
research should look to identify if myocardial stunning
Momb BA et al
Journal of Nephropathology, Vol 9, No 1, January 2020 www.nephropathol.com
8
can be linked to reductions in CPI by cross validation
with echocardiography.
Conclusion
In conclusion, exercise during dialysis increased both CPI
and Q
̇, potentially reducing IDH and hypoperfusion of
the myocardium. As myocardial stunning represents a
high risk for mortality in hemodialysis patients, more
research should be done in this population on the effects
of exercise during treatment. It may be prudent to include
exercise during dialysis in patients who are receptive to the
intervention.
Authors’ contribution
BAM proposed the subject and methods, collected data,
performed statistical analysis, and wrote the manuscript.
SAEH provided insight into methods and edited the
final manuscript. TDM provided insight into statistical
procedures and editing the final manuscript. MJG
provided original research question along with editing
manuscript. All authors read and signed the final paper.
Conflicts of interest
The authors have no conflicts of interest to declare.
Ethical considerations
Ethical issues (including plagiarism, data fabrication,
double publication) have been completely observed by
the authors.
Funding/Support
Funding for use of research facilities and equipment was
provided by Springfield College.
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Copyright © 2020 The Author(s); Published by Society of Diabetic Nephropathy Prevention. This is an open-access article distributed
under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted
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