Test-retest reliability and four-week changes in cardiopulmonary fitness in stroke patients: evaluation using a robotics-assisted tilt table

Feedback control of heart rate during robotics-assisted tilt table exercise in patients after stroke: a clinical feasibility study

BACKGROUND

Patients with neurological disorders including stroke use rehabilitation to improve cognitive abilities, to regain motor function and to reduce the risk of further complications. Robotics-assisted tilt table technology has been developed to provide early mobilisation and to automate therapy involving the lower limbs. The aim of this study was to evaluate the feasibility of employing a feedback control system for heart rate (HR) during robotics-assisted tilt table exercise in patients after a stroke.

METHODS

This feasibility study was designed as a case series with 12 patients ( n = 12 ) with no restriction on the time post-stroke or on the degree of post-stroke impairment severity. A robotics-assisted tilt table was augmented with force sensors, a work rate estimation algorithm, and a biofeedback screen that facilitated volitional control of a target work rate. Dynamic models of HR response to changes in target work rate were estimated in system identification tests; nominal models were used to calculate the parameters of feedback controllers designed to give a specified closed-loop bandwidth; and the accuracy of HR control was assessed quantitatively in feedback control tests.

RESULTS

Feedback control tests were successfully conducted in all 12 patients. Dynamic models of heart rate response to imposed work rate were estimated with a mean root-mean-square (RMS) model error of 2.16 beats per minute (bpm), while highly accurate feedback control of heart rate was achieved with a mean RMS tracking error (RMSE) of 2.00 bpm. Control accuracy, i.e. RMSE, was found to be strongly correlated with the magnitude of heart rate variability (HRV): patients with a low magnitude of HRV had low RMSE, i.e. more accurate HR control performance, and vice versa.

CONCLUSIONS

Feedback control of heart rate during robotics-assisted tilt table exercise was found to be feasible. Future work should investigate robustness aspects of the feedback control system. Modifications to the exercise modality, or alternative modalities, should be explored that allow higher levels of work rate and heart rate intensity to be achieved.

Cardiopulmonary Response to Robot-Assisted Tilt Table With Regard to Its Components

Cardiopulmonary function is exceptionally critical during the early stages of rehabilitation after neurological disorders such as stroke, spinal cord injury and Parkinson's disease. This study aimed to demonstrate how robot-assisted and tilt table exercises affect cardiopulmonary function. In this study, ten healthy young adults performed six combinations of conditions according to robot-assisted mode (on/off), angle of tilt table (20°/60°), and functional electrical stimulation (FES) mode (on/off). Four conditions had FES mode off with combinations of robot-assisted mode (on/off) and tilt angle (20°/60°) and two conditions had robot-assisted mode and FES on with tilt angle (20°/60°). Cardiopulmonary effects (oxygen uptake [VO₂], peak oxygen uptake [VO₂peak], metabolic energy cost [MET], rate pressure product [RPP], heart rate [HR], maximum heart rate [%HRmax], and minute ventilation [VE]) were compared in each condition. As a result, in the angle and FES mode effect, VO₂, VO₂peak, MET, RPP, HR, and %HRmax, unlike that for VE, showed major effects in angle. In addition, in the robot-assisted mode and angle effect, when the FES was switched off, VO₂, METs, and VE values showed major effects in the robot-assisted mode, whereas all other values showed major effects in angle. Compared to earlier reported findings, we can expect that robot-assisted tilt table training can lead to changes in the cardiopulmonary function.

A Single Bout of Constant-Load Exercise Test for Estimating the Time Constant of Oxygen Uptake Kinetics in Individuals With Stroke

Objective

To examine the relationship between the time constant of oxygen uptake kinetics during the onset of exercise (τVO₂) estimated from a single exercise bout and that obtained from three averaged exercise bouts in individuals with stroke.

Methods

Twenty participants with stroke performed three bouts of a constant-load pedaling exercise at approximately 80% of the workload corresponding to the ventilatory threshold to estimate τVO₂. The VO₂ data from the first trial of three bouts were used to estimate τVO₂ for a single bout. Additionally, data collected from three bouts were ensemble-averaged to obtain τVO₂ for three averaged bouts as the criterion.

Results

There was a very high correlation between τVO₂ for a single bout (34.8±14.0 seconds) and τVO₂ for three averaged bouts (38.5±13.4 seconds) (r=0.926, p<0.001). However, τVO₂ for a single bout was smaller than that for three averaged bouts (p=0.006).

Conclusion

τVO₂ for a single bout could reflect the relative difference in τVO₂ for three averaged bouts among individuals with stroke. However, it should be noted that τVO₂ for a single bout may be underestimated compared to τVO₂ for three averaged bouts.

Cardiorespiratory mechanisms underlying the impaired oxygen uptake kinetics at exercise onset after stroke

BACKGROUND

Oxygen uptake (V˙O₂) kinetics at the onset of exercise is slower in patients with stroke than in healthy adults. However, little is known about the cardiorespiratory mechanisms underlying the impaired V˙O₂ kinetics.

OBJECTIVES

This study aimed to investigate the relative effect of impaired oxygen delivery and utilisation on V˙O₂ kinetics at the onset of submaximal exercise in patients with stroke by comparing the time constants of cardiac output (τCO) and V˙O₂ (τV˙O₂). In addition, we aimed to examine the association between the kinetics of cardiorespiratory variables and functional outcomes.

METHODS

We included 21 patients with stroke (15 males, mean [SD] age 58.7 [9.5] years, mean days post-stroke 67.9 [30.9]). A submaximal constant-load exercise test was performed to measure τV˙O₂, τCO, and the time constant of arterialvenous oxygen difference (τAVO₂diff). The ratio of τCO to τV˙O₂ was calculated to assess the matching of oxygen delivery and consumption. Fugl-Meyer lower-extremity motor scores, comfortable gait speeds, and Functional Independence Measure motor scores were used as functional variables.

RESULTS

Mean (SD) τAVO₂diff was markedly shorter than τV˙O₂ and τCO (26.1 [7.1] vs. 38.7 [10.2] and 46.6 [23.2 s], P<0.05), with no significant difference between τV˙O₂ and τCO (P=0.444). The greater ratio of τCO to τV˙O₂ was related to poorer motor function (rho=-0.484, P=0.026) and slower comfortable gait speed (r=-0.482, P=0.027).

CONCLUSIONS

An increase in CO was slower than that in AVO₂diff in patients with stroke. Therefore, V˙O₂ kinetics in patients with stroke appears to be affected by a delayed increase in CO rather than AVO₂diff. Furthermore, these patients with motor and gait impairments may have a poor matching of oxygen delivery and consumption during exercise onset.

Cardiorespiratory factors related to the increase in oxygen consumption during exercise in individuals with stroke

BACKGROUND

Understanding the cardiorespiratory factors related to the increase in oxygen consumption ([Formula: see text]) during exercise is essential for improving cardiorespiratory fitness in individuals with stroke. However, cardiorespiratory factors related to the increase in [Formula: see text] during exercise in these individuals have not been examined using multivariate analysis. This study aimed to identify cardiorespiratory factors related to the increase in [Formula: see text] during a graded exercise in terms of respiratory function, cardiac function, and the ability of skeletal muscles to extract oxygen.

METHODS

Eighteen individuals with stroke (aged 60.1 ± 9.4 years, 67.1 ± 30.8 days poststroke) underwent a graded exercise test for the assessment of cardiorespiratory response to exercise. The increases in [Formula: see text] from rest to first threshold and that from rest to peak exercise were measured as a dependent variable. The increases in respiratory rate, tidal volume, minute ventilation, heart rate, stroke volume, cardiac output, and arterial-venous oxygen difference from rest to first threshold and those from rest to peak exercise were measured as the independent variables.

RESULTS

From rest to first threshold, the increases in arterial-venous oxygen difference (β = 0.711) and cardiac output (β = 0.572) were significant independent variables for the increase in [Formula: see text] (adjusted R2 = 0.877 p < 0.001). Similarly, from rest to peak exercise, the increases in arterial-venous oxygen difference (β = 0.665) and cardiac output (β = 0.636) were significant factors related to the increase in [Formula: see text] (adjusted R2 = 0.923, p < 0.001).

CONCLUSION

Our results suggest that the ability of skeletal muscle to extract oxygen is a major cardiorespiratory factor related to the increase in [Formula: see text] during exercise testing in individuals with stroke. For improved cardiorespiratory fitness in individuals with stroke, the amount of functional muscle mass during exercise may need to be increased.

Development and evaluation of a novel system for inducing orthostatic challenge by tilt tests and lower body negative pressure

Lower body negative pressure (LBNP) is a method derived from space medicine, which in recent years has been increasingly used by clinicians to assess the efficiency of the cardiovascular regulatory mechanisms. LBNP with combined tilt testing is considered as an effective form of training to prevent orthostatic intolerance. We have developed a prototype system comprising a tilt table and LBNP chamber, and tested it in the context of the feasibility of the device for assessing the pilots' efficiency. The table allows for controlled tilting in the range from -45 to +80° at the maximum change rate of 45°/s. The LBNP value can smoothly be adjusted down to -100 mmHg at up to 20 mmHg/s. 17 subjects took part in the pilot study. A 24-minute scenario included -100 mmHg supine LBNP, head up tilt (HUT) and -60 mmHg LBNP associated with HUT, separated by resting phases. The most noticeable changes were observed in stroke volume (SV). During supine LBNP, HUT and the combined stimulus, a decrease of the SV value by 20%, 40% and below 50%, respectively, were detected. The proposed system can map any pre-programed tilt and LBNP profiles, and the pilot study confirmed the efficiency of performing experimental procedures.

Unilateral Arm Crank Exercise Test for Assessing Cardiorespiratory Fitness in Individuals with Hemiparetic Stroke

Cardiorespiratory fitness assessment with leg cycle exercise testing may be influenced by motor impairments in the paretic lower extremity. Hence, this study examined the usefulness of a unilateral arm crank exercise test to assess cardiorespiratory fitness in individuals with stroke, including sixteen individuals with hemiparetic stroke (mean ± SD age, 56.4 ± 7.5 years) and 12 age- and sex-matched healthy controls. Participants performed the unilateral arm crank and leg cycle exercise tests to measure oxygen consumption ([Formula: see text]O2) and heart rate at peak exercise. The [Formula: see text]O2 at peak exercise during the unilateral arm crank exercise test was significantly lower in the stroke group than in the control group (p < 0.001). In the stroke group, the heart rate at peak exercise during the unilateral arm crank exercise test did not significantly correlate with the Brunnstrom recovery stages of the lower extremity (p = 0.137), whereas there was a significant correlation during the leg cycle exercise test (rho = 0.775, p < 0.001). The unilateral arm crank exercise test can detect the deterioration of cardiorespiratory fitness independently of lower extremity motor impairment severity in individuals with hemiparetic stroke. This study is registered with UMIN000014733.