Background: The peak oxygen consumption (V.O2peak) and blood hemoglobin concentration [Hb] are lower in stroke patients than in age-matched healthy subjects. The ability of skeletal muscles to extract oxygen is diminished after stroke. We hypothesized that the oxygen extraction capacity of skeletal muscles in stroke patients depends on [Hb]. To test the hypothesis, we determined the relationship between V.O2peak and total hemoglobin mass (tHb-mass) in stroke patients. Methods: The subjects were 19 stroke patients (age: 74 ± 2, mean ± SD, 10 males) and 11 age-matched normal subjects (age 76 ± 3, 6 males). Plasma volume (PV) and V.O2peak were measured on the same day. PV was measured using Evans Blue dye dilution method. Blood volume (BV) was calculated from PV and hematocrit, while tHb-mass was estimated from BV and [Hb]. Each subject underwent cardiopulmonary exercise test on a bicycle ergometer using a V.O2peak respiratory gas analyzer. Results: There were no differences in age, height, and weight between the two groups. V.O2peak was lower in stroke patients than in the control. BV and tHb mass were not significantly different between the two groups, but [Hb] was significantly lower in stroke patients. In stroke patients, V.O2peak correlated significantly with tHb-mass (r = 0.497, p < 0.05), but not with BV. Conclusion: Our results suggested that low [Hb] seems to contribute to V.O2peak in stroke patients. The significant correlation between tHb-mass and V.O2peak suggested that treatment to improve [Hb] can potentially improve V.O2peak in stroke patients.

In Japan, approximately 350,000 stroke patients with only mild physical impairment live at home, and provision of health services to these individuals has a negative impact on health care costs [1]. For these reasons, it is important to improve the general well-being of these individuals, including endurance performance, and to understand the mechanisms that regulate peak oxygen consumption (V.O2peak). Previous studies showed lower V.O2peak in stroke patients compared with age-matched healthy people [2‒4]. However, peak exercise cardiac power output, cardiac output, and the pressure-generating capacity of the heart are similar in stroke and healthy control subjects [2]. These findings suggest diminished capacity of skeletal muscles to extract oxygen in patients with stroke. We hypothesized that the oxygen extraction ability of skeletal muscles depends on blood hemoglobin concentration [Hb].

In healthy subjects, both blood volume (BV) and total hemoglobin mass (tHb-mass) are important determinants of V.O2peak [5‒8]. However, Hb is lower in stroke patients than in healthy individuals [9]. Therefore, it is likely that BV does not correlate with V.O2peak in stroke patients. To our knowledge, there are no studies that have investigated these correlations in stroke patients. It is important clinically to understand this relationship, since low [Hb] and V.O2peak in stroke patients could be corrected by increasing [Hb], which can potentially improve V.O2peak.

The hypothesis tested in this study was that in stroke patients with low [Hb], V.O2peak correlates with tHb-mass rather than BV. Confirmation of this hypothesis can potentially help explore possible therapies that can effectively improve V.O2peak in stroke patients.

Subjects

The 19 stroke patients of this study (10 males and 9 females) were recruited from among the stroke patients who attended the Outpatient Department and those admitted to the Nachikatsuura Balneologic Town Hospital. We also recruited 11 age-matched healthy elderly subjects (6 males and 5 females) as the control group. The characteristics of the subjects are shown in Table 1. The selection criteria for the stroke patients included minimal of 6 months after onset of stroke, ability to walk independently with or without walking aids and braces, and permission of the attending physician to participate in the study. The exclusion criteria included the presence of cardiac diseases, peripheral arterial diseases, respiratory diseases, and drug allergy. The selection criteria for the control group were negative history of stroke, ability to walk independently with or without walking aids and braces, and permission to participate in the study by the family physician. The exclusion criteria were similar to those applied for the selection of stroke patients.

Table 1.

Characteristics of participating subjects

 Characteristics of participating subjects
 Characteristics of participating subjects

The present research was designed as a cross-sectional study. The study was approved by the Human Ethics Review Committee of Wakayama Medical University, and informed consent was obtained from all participants. The study was conducted in accordance with the Declaration of Helsinki. Data were collected between June 2017 and September 2018.

Study Protocol and Measurements

Measurements of PV and V.O2peak were conducted on the same day in each subject. The subjects were asked not to exercise vigorously and refrain from consuming caffeine- and alcohol-containing beverages the day before the measurements.

PV was measured using the Evans blue dye dilution method. Subjects arrived at the laboratory at 07:45, fasting for at least 8 h. After complete urination and measurement of body weight, the subject rested in supine position in a laboratory with controlled ambient temperature at 24°C. A 21-gauge winged needle was inserted into the ulnar midline vein followed by rest for 30 min to stabilize fluid movement due to postural changes. A baseline blood sample was then taken and Evans blue dye was injected at 0.2 mg/kg. Blood was collected again 10 min after dye injection. Hematocrit (Hct in %; microcentrifuge) and hemoglobin concentration ([Hb] in g/dL; sodium lauryl sulfate hemoglobin method; Hb test Wako, Wako Chemical Osaka, Japan, using 1 mL aliquot of each 5 mL blood sample) were measured. The remaining 4 mL of blood of each sample was immediately centrifuged at room temperature and plasma absorbances at 620 and 740 nm were measured using plasma aliquots (SH-1000 Lab, Corona Electric, Hitachi Nakano, SH, Japan).

After PV measurement, the subject sat indoor and rested before measurement of V.O2peak. After the 60-min rest, the subject was asked to void before measurement of body weight, then sat on the saddle of the bicycle ergometer, and adjusted the saddle in preparation for the next measurement. V.O2peak was determined by the method described by Eng et al. [10], that is, the test for maximal exercise test-retest was very reliable (ICC > 0.9). Briefly, the subject performed stepwise exercise on the bicycle ergometer while in upright position. The average oxygen uptake every 10 s was measured with a respiratory flow meter and a gas analyzer (Meta max 3B, Cortex, Leipzig, Germany). The electrocardiogram was monitored continuously during the exercise using an electrocardiograph (BSM-2401: NIHON KOHDEN). After a 2-min baseline measurement, the subject began pedaling at 50 cycles/min with zero load (0 W). The exercise intensity was increased by 10 W every 3 min up to 30 W and then by 15 W every minute for those with cerebrovascular accidents (see below). For subjects of the control group, exercise was increased by 20 W every 2 min to 60 W and then by 20 W every minute. The criteria used for determining V.O2peak were: (1) V.O2peak plateau (V.O2peak does not change with increased exercise intensity, or V.O2peak does not increase by 1.5 mL/kg/min), (2) voluntary fatigue (i.e., 30 revolutions per minute), and (3) respiratory exchange ratio exceeds 1.0. The three maximum continuous values at the end of the exercise were averaged and recorded as V.O2peak.

We recorded the number of subjects who requested discontinuation of exercise, developed walking instability, experienced onset of angina and/or chest pain, showed fall in systolic blood pressure (>10 mm Hg) or excessive increase in blood pressure, according to the American College of Sports Medicine (ACSM) guidelines (systolic blood pressure ≥250 mm Hg, diastolic blood pressure ≥115 mm Hg), developed disorders of consciousness, confusion, upset, facial paleness, cyanosis, nausea, cold sensation, cold sweat, decreased heart rate, and marked changes in cardiac rhythm. The exercise load test was discontinued upon subjective feeling of fatigue (physical and verbal), shortness of breath, screaming, and spasm of lower limb muscles.

Data Analysis

PV was calculated from the corrected Abs 620 nm of the 10-min sample and the amount of dye injected. BV was calculated from PV and Hct and corrected for 3% trapped plasma and 91% F cell ratio. tHb-mass was calculated from BV × [Hb] (g).

Statistical Analysis

Values are expressed as mean ± SD. Intergroup differences between stroke patients and control subjects were tested by the Mann-Whitney U test. Pearson’s correlation coefficient was used to determine the relationship between variables. The significance level was set at a p value of <0.05. The SPSS software (version 24.0, IBM SPSS Statistics, Chicago, IL, USA) was used in all statistical analyses.

Patients’ Characteristics

Patients participated in the study 44.9 ± 31.6 months after the onset of stroke. The proportion of patients with stroke due to cerebral hemorrhage (47%) was almost equal to that of patients with history of cerebral infarction (53%). The Fugl-Meyer Assessment score was 204 ± 7, while the motor score was 86 ± 6, indicating mild paralysis. With regard to mobility, 53% of the patients did not require the use of a walking aid, 16% used a short leg brace, and 47% used a cane (Table 1).

Exercise Test

No adverse events occurred during the maximal exercise test in both groups of subjects. The most common reason for termination of the test was general and lower extremity fatigue.

The V.O2peak was lower in stroke patients than in the control (Fig. 1); however, the HRpeak and the RERpeak were identical in the two groups. There were no differences in BV and tHb-mass between the two groups, but the mean [Hb] was significantly lower in the stroke patients (Fig. 1).

Fig. 1.

Peak oxygen consumption (a), blood volume (b), hemoglobin concentration (c), and total Hb-mass (d) of control subjects and stroke patients. Date are mean ± SD. *p< 0.05, between stroke and control subjects.

Fig. 1.

Peak oxygen consumption (a), blood volume (b), hemoglobin concentration (c), and total Hb-mass (d) of control subjects and stroke patients. Date are mean ± SD. *p< 0.05, between stroke and control subjects.

Close modal

Figure 2 shows the relationship between V.O2peak and BV as well as tHb-mass. V.O2peak did not correlate with BV in stroke patients, whereas it correlated with tHb-mass in both groups.

Fig. 2.

Correlation of peak oxygen consumption with blood volume (a) and total Hb-mass (b) for control subjects and stroke patients.

Fig. 2.

Correlation of peak oxygen consumption with blood volume (a) and total Hb-mass (b) for control subjects and stroke patients.

Close modal

The followings were the major findings of the present study: (1) [Hb] was lower in stroke patients than in the age-matched control, and (2) V.O2peak correlated significantly with tHb-mass but not BV. These findings suggest that [Hb] may be one of the major underlying mechanisms of the low V.O2peak in stroke patients.

Previous studies reported significantly higher V.O2peak values in individuals involved in regular endurance training compared to inactive subjects [11, 12]. Furthermore, the high V.O2peak values observed in athletes correlated with increased maximum cardiac output [13], and the latter was due to increased maximum stroke volume (SVmax) rather than increase in heart rate [6, 14]. Expansion of BV increases left ventricular filling pressure, while increased stroke volume affects cardiac function, based on the “Frank-Starling” mechanism [14]. In the present study, the maximum heart rate during peak exercise was not different between the patients and the healthy control, suggesting that the SVmax was different between the two groups. However, equal BV in the stroke should be similar SVmax to the elderly group.

Clinical studies of patients with stroke have shown that low [Hb] correlates with functional prognosis as well as life prognosis [15‒17]. In the present study, [Hb] was lower in our patients than in the control, but there were no differences in BV and tHb-mass between the two groups. These results suggest that the lower [Hb] in the patients is associated with the relatively high BV, despite the lack of significant difference in BV between the two groups.

Jakovljevic et al. [2] reported that V.O2peak was lower in stroke patients compared with healthy subjects, and that the a-vO2diff was also lower in the former group. Their results suggest that the difference in a-vO2diff is likely to be the limiting factor for V.O2peak in stroke patients. Differences in a-vO2diff are determined by the supply and extraction of oxygen from arterial blood to the peripheral tissues. Oxygen supply depends on tHb-mass [18]. However, our results did not demonstrate differences in tHb-mass between the two groups.

A simple increase in BV alone without simultaneous increase in Hb does not result in improvement of V.O2peak [19], whereas increases in both BV and [Hb] can increase total transportation of oxygen. The present findings showed BV increment in stroke patients although no similar increase in tHb-mass was noted. It is possible that any change in body function induced by stroke can suppress increases in hemoglobin concentration.

Stroke is often followed by tissue changes on the paralyzed side, such as reduced skeletal muscle mass, increased intramuscular fat, and decreased type I muscle fibers [4]. In addition, a significant reduction in resting and reactive hyperemic leg blood flow on the paralyzed side relative to the nonparalyzed side has been reported [20]. Other studies demonstrated lower oxygen consumption on the paralyzed side compared to the nonparalyzed side in stroke patients as well as relative to healthy subjects, together with degeneration of the muscles on the paralyzed side with augmented anaerobic metabolism [21]. These changes highlight the need for full assessment of stroke patients that includes factors other than oxygen transport capacity. Fluctuations in circulating blood redistribution during exercise may also be greater in stroke patients than in healthy subjects. In this regard, previous clinical studies of patients with stroke demonstrated reduced vasoconstrictor capacity during isometric exercise and reduced muscle blood flow on the paralyzed side at 35% of MVCs [22]. In other words, these patients exhibit pooling of blood on the paralyzed side.

Based on the above findings, we believe that the high correlation between endurance performance and tHb-mass rather than BV in stroke patients is related to the fact that peripheral oxygen transport to the tissues determines V.O2peak rather than the properties of the cardiovascular system, such as cardiac filling pressure. The present study has certain limitations. First, the study was conducted in a single facility, and it was difficult to recruit a heterogeneous group of subjects with respect to clinical background. Second, the study included a relatively small number of Japanese subjects. The findings need to be confirmed in another study that includes a large sample size of subjects of different racial backgrounds. In conclusion, in patients with stroke, endurance performance, and its correlate V.O2peak, correlates with [Hb] and excessive blood pooling on the paralyzed side.

We thank Ms. Hiroko Nishi, Ms. Kaori Matsumoto, Mr. Shougo Okuji, and Mr. Haruki Ohta for the excellent technical assistant. This research was supported by a research grant from the Nachi-Katsuura Town and Wakayama Medical University. We also thank Dr. Faiq G Issa (Word-Medex Pty Ltd, Sydney, Australia, www.word-medex.com.au) for the careful reading and editing of the manuscript.

The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Institutional Review Board of Wakayama Medical University (protocol code #2049; date of approval: 27 June 2017). All participants signed an informed consent form voluntarily before participating in the study. The right to withdraw consent at any time without stating the reason was guaranteed without any individual disadvantage for subsequent medical care.

The authors report no conflict of interest.

This research was supported by a grant from the Nachikatsuura Research Foundation (#L1221).

Shohei Araki, Yoshi-ichiro Kamijo, and Fumihiro Tajima designed this study. Shohei Araki and Chika Sato collected and analyzed the data. Yuta Sakurai, Izumi Yoshioka, and Kota Murai checked and confirmed the results of data analysis. Shohei Araki, Yoshi-ichiro Kamijo, and Fumihiro Tajima drafted the manuscript and all other authors critically reviewed it. All authors approved the final version of the manuscript.

All data generated or analyzed during this study are included in this article. Further enquiries can be directed to the corresponding author.

1.
Ministry of Health LaW, JAPAN, Health Statistics Office
.
Number of patients with major diseases, overview of patient survey
.
2017
.
2.
Jakovljevic
DG
,
Moore
SA
,
Tan
LB
,
Rochester
L
,
Ford
GA
,
Trenell
MI
,
.
Discrepancy between cardiac and physical functional reserves in stroke
.
Stroke
.
2012
;
43
(
5
):
1422
5
.
3.
Dunn
A
,
Marsden
DL
,
Van Vliet
P
,
Spratt
NJ
,
Callister
R
.
Independently ambulant, community-dwelling stroke survivors have reduced cardiorespiratory fitness, mobility and knee strength compared to an age- and gender-matched cohort
.
Top Stroke Rehabil
.
2017
;
24
(
3
):
163
9
.
4.
Ivey
FM
,
Macko
RF
,
Ryan
AS
,
Hafer-Macko
CE
.
Cardiovascular health and fitness after stroke
.
Top Stroke Rehabil
.
2005
;
12
(
1
):
1
16
.
5.
Convertino
VA
,
Ludwig
DA
.
Validity of VO2max in predicting blood volume: implications for the effect of fitness on aging
.
Am J Physiol Regul Integr Comp Physiol
.
2000
;
279
(
3
):
1068
75
.
6.
Hagberg
JM
,
Goldberg
AP
,
Lakatta
L
,
O'Connor
FC
,
Becker
LC
,
Lakatta
EG
,
.
Expanded blood volumes contribute to the increased cardiovascular performance of endurance-trained older men
.
J Appl Physiol
.
1998
;
85
(
2
):
484
9
.
7.
Ito
T
,
Takamata
A
,
Yaegashi
K
,
Itoh
T
,
Yoshida
T
,
Kawabata
T
,
.
Role of blood volume in the age-associated decline in peak oxygen uptake in humans
.
Jpn J Physiol
.
2001
;
51
(
5
):
607
12
.
8.
Lundgren
KM
,
Aspvik
NP
,
Langlo
KAR
,
Braaten
T
,
Wisløff
U
,
Stensvold
D
,
.
Blood volume, hemoglobin mass, and peak oxygen uptake in older adults: the generation 100 study
.
Front Sports Act Living
.
2021
;
3
(
3
):
638139
.
9.
Barlas
RS
,
Honney
K
,
Loke
YK
,
McCall
SJ
,
Bettencourt-Silva
JH
,
Clark
AB
,
.
Impact of hemoglobin levels and anemia on mortality in acute stroke: analysis of UK regional registry data, systematic review, and meta-analysis
.
J Am Heart Assoc
.
2016
;
5
(
8
):
e003019
.
10.
Eng
JJ
,
Dawson
AS
,
Chu
KS
.
Submaximal exercise in persons with stroke: test-retest reliability and concurrent validity with maximal oxygen consumption
.
Arch Phys Med Rehabil
.
2004
;
85
(
1
):
113
8
.
11.
Pimentel
AE
,
Gentile
CL
,
Tanaka
H
,
Seals
DR
,
Gates
PE
.
Greater rate of decline in maximal aerobic capacity with age in endurance-trained than in sedentary men
.
J Appl Physiol
.
2003
;
94
(
6
):
2406
13
.
12.
Tanaka
H
,
Desouza
CA
,
Jones
PP
,
Stevenson
ET
,
Davy
KP
,
Seals
DR
,
.
Greater rate of decline in maximal aerobic capacity with age in physically active versus sedentary healthy women
.
J Appl Physiol
.
1997
;
83
(
6
):
1947
53
.
13.
Montero
D
,
Diaz-Cañestro
C
,
Lundby
C
.
Endurance training and VO2max: role of maximal cardiac output and oxygen extraction
.
Med Sci Sports Exerc
.
2015
;
47
(
10
):
2024
33
.
14.
Krip
B
,
Gledhill
N
,
Jamnik
V
,
Warburton
D
.
Effect of alterations in blood volume on cardiac function during maximal exercise
.
Med Sci Sports Exerc
.
1997
;
29
(
11
):
1469
76
.
15.
Yoshimura
Y
,
Wakabayashi
H
,
Shiraishi
A
,
Nagano
F
,
Bise
T
,
Shimazu
S
,
.
Hemoglobin improvement is positively associated with functional outcomes in stroke patients with anemia
.
J Stroke Cerebrovasc Dis
.
2021
;
30
(
1
):
105453
.
16.
Heo
J
,
Youk
TM
,
Seo
KD
.
Anemia is a risk factor for the development of ischemic stroke and post-stroke mortality
.
J Clin Med
.
2021
;
10
(
12
):
2556
.
17.
Chan
T
,
Ganasekaran
G
.
The effect of anemia on the functional outcomes of the stroke patients and the efficiency of their stroke rehabilitation
.
J Stroke Cerebrovasc Dis
.
2015
;
24
(
6
):
1438
42
.
18.
Schmidt
W
,
Prommer
N
.
Impact of alterations in total hemoglobin mass on VO 2max
.
Exerc Sport Sci Rev
.
2010
;
38
(
2
):
68
75
.
19.
Warburton
DER
,
Gledhill
N
,
Quinney
HA
.
Blood volume, aerobic power, and endurance performance: potential ergogenic effect of volume loading
.
Clin J Sport Med
.
2000
;
10
(
1
):
59
66
.
20.
Ivey
FM
,
Hafer-Macko
CE
,
Ryan
AS
,
Macko
RF
.
Impaired leg vasodilatory function after stroke: adaptations with treadmill exercise training
.
Stroke
.
2010
;
41
(
12
):
2913
7
.
21.
Masoudi Motlagh
M
,
Sugar
JJ
,
Azimipour
M
,
Linz
WW
,
Michalak
G
,
Seo
NJ
,
.
Monitoring hemodynamic changes in stroke-affected muscles using near-infrared spectroscopy
.
J Rehabil Assist Technol Eng
.
2015
;
2
:
205566831561419
. 2055668315614195 https://doi.org/10.1177/2055668315614195.
22.
Nakamura
T
,
Mizushima
T
,
Yamamoto
M
,
Kawazu
T
,
Umezu
Y
,
Tajima
F
,
.
Muscle sympathetic nerve activity during isometric exercise in patients with cerebrovascular accidents
.
Arch Phys Med Rehabil
.
2005
;
86
(
3
):
436
41
.