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

 With NOTHING HERE even minutely measuring recovery or creating protocols, this was TOTALLY FUCKING USELESS!  Survivors would like to recover!

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

• Lars Brockmann,
• Jittima Saengsuwan,
• Corina Schuster-Amft &
• Kenneth J. Hunt 

Journal of NeuroEngineering and Rehabilitation volume 21, Article number: 141 (2024) Cite this article

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Abstract

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.

Background

Patients with neurological disorders such as spinal cord injury (SCI) or stroke, and patients with acquired brain injury (ABI), use rehabilitation to improve cognitive abilities, to regain motor function and to reduce the risk of further complications. One complication that can arise from prolonged bed rest or reduced mobility is orthostatic hypotension (OH). OH is a physical condition where a person’s blood pressure drops considerably (systolic blood pressure decrease of at least 20 mmHg or diastolic blood pressure decrease of at least 10 mmHg) within three minutes of standing [1].

A common form of treatment for such patients is verticalisation with the help of tilt tables and passive movement of the lower extremities [2]. Robotic rehabilitation devices have been developed and deployed clinically to assist in performing such therapies. The Erigo (Hocoma AG, Switzerland) is one example. It is a robotics-assisted tilt table suited to the early stages of rehabilitation that allows for progressive verticalisation up to

with the addition of an integrated, motorised stepping function to simulate gait [3]. The Erigo’s stepping function is essentially passive: the lower extremities are mobilised by mechanically shifting the thighs back and forth without active patient participation, although the latest edition of the device includes a functional electrical stimulation (FES) module for activation of paralysed muscle.

On these grounds, our previous work adapted the Erigo by implementing a real-time visual feedback system and force sensors in the thigh cuffs to allow work rate estimation [4]. This enables patients with at least partially retained motor function to actively participate in the rehabilitation exercise through volitional effort. Patients can adapt their leg forces to keep to a target work-rate profile displayed on the biofeedback screen. Studies involving mild-to-severe stroke impairment [5, 6] and spinal cord injury [7] established that meaningful physiological responses could be developed and formal exercise tests could be performed reliably while exercising using this modality. Furthermore, a pilot study, conducting experiments on four healthy participants, developed and successfully tested a method for automatic control of heart rate using this device [4].

A related approach to heart rate control using the Erigo, albeit using only stepping frequency and tilt angle to drive the exercise, and using only six healthy participants, has also been proposed [8]. Because of the employment of only the standard device settings, and the lack of any biofeedback that facilitated active participation to increase work rate, participants remained passive and the magnitude of increase in heart rate was very limited, being only 9 beats/min above resting levels.

Integrating automatic heart rate control algorithms into rehabilitation platforms, such as the Erigo, could enhance prescription and monitoring of patients’ physiological responses while exercising, thereby contributing to a safer rehabilitation process with desired target heart rate intensities being achieved more accurately. It is important to use feedback to control heart rate intensity directly because a given force or work rate will lead to potentially very different heart rates in different patients: but with feedback, the compensator will, in principle, automatically find the correct and individual force or work rate that will lead to the target heart rate being reached.

Exercise with integrated heart rate control is expected to ensure active patient participation as the patient has to continuously adapt their output work rate to match the changing target. Active patient participation is presumed to improve therapeutic efficacy [9]. The use of heart rate as a proxy of exercise intensity has been extensively described for healthy able-bodied people and for patients with a very wide range of disease and impairment conditions [10]. The latter reference includes specific guidelines for using HR in exercise testing and prescription and provides an extensive collection of background literature citations.

Before the putative benefits of integrating automatic heart rate control algorithms into clinical rehabilitation can be realised, the technical feasibility of this proposal must first be demonstrated. The present work therefore aimed to evaluate the technical feasibility of employing a feedback control system for heart rate during robotics-assisted tilt table exercise in a clinical case series of patients after a stroke.

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