Engineering Paves The Way For Safe Sustainable Ambulance Patient Transport Care

Engineering students at Worcester Polytechnic Institute in Worcester, Massachusetts, are working with the emergency medical service (EMS) at the University of Massachusetts Medical School to modernize ambulances for more effective patient transportation. These projects have linked the world of mechanical engineering with that of emergency medical care in a unique and thought provoking manner. One such research project resulted in the author’s Phd dissertation entitled, Ambulance Vibration Suppression Via Force Field Domain Control.

This PhD dissertation experimentally characterized the vibration amplitude, frequency, and energy associated with ambulance travel and defined the relationship of the vibration to safety, comfort and care of ambulance patients. Further, the experimentally derived vibration data were used to characterize road forcing functions that simulate typical ambulance travel over the undulating surface of a variety of common road surfaces. In the future, this could be used to help design a workable vibration attenuation solution for emergency medical vehicles and any equipment which may have to be used in such a vehicle. The benefits of this study are widespread and encompass the needs and comfort of patients and members of the EMS community alike. The project also underscores the benefits of analyzing a problem in one discipline (negative health effects of ambulance vibration) by using tools from another discipline (vibration analysis of machine tools).

The safety and comfort of passengers in acute care vehicles is an issue of major interest. In addition to the risks associated with motor vehicle accidents, ground transport of injured patients exposes both the patient and ambulance EMTs to possibly hazardous shocks and vibrations generated by travel at moderate to high speeds over uneven road surfaces. Due to the already compromised health of most ambulance patients, the road shocks can negatively affect brain, organ and muscle-skeletal structure and function, raising the chances of negative health outcomes. In addition, the bouncy ride in the patient compartment of an ambulance can significantly exacerbate the difficulty EMTs may have in performing such routine procedures as starting intravenous lines, hearing heart and breath sounds or performing any of a multitude of tasks which require skilled eye-hand coordination and sensory input.

The current interest in health care reform and patient-centered care is creating significant pressure on the industry to continually improve services and expand the level and quality of care which can be provided. Studies from all over the globe associated with ambulance modernization have revealed a need for greater patient comfort and safety during transport in order to reduce the likelihood of ride-induced patient trauma, increase the occupational safety of EMS crews, and to increase the scope and raise the standard of care of mobile, in-route treatment.

In a rather serendipitous occurrence, the author’s PhD advisor at MIRAD Laboratory, WPI, Dr. Mustapha S. Fofana has spent a good part of his career delving into the mathematical aspects of the vibration analysis and control of machining, specifically concentrating on the elimination of chatter induced problems. When Dr. Fofana was approached by the University of Massachusetts Emergency Medical Service to study ambulance modernization, the link between patient care and vibration (chatter) attenuation in ambulance design, seemed to become a problem whose potential analysis might yield to the same engineering methodologies utilized in the study of machining phenomena.

The first step in solving any engineering problem is to attempt to completely understand the root causes and fundamental nature of the problem. A team of WPI graduate and undergraduate students was assembled to do just that. Experimental procedures were designed and carried out to acquire vibration data on four, typical US-manufactured Type I or Type III ambulances from three New England emergency medical services. The ambulances were driven over four different road surface types at three constant speed settings. Emergency vehicles and drivers were provided to the team by the UMASS Memorial Emergency Medical Service, the Putnam CT Emergency Medical Service, and the Woodstock CT Volunteer Fire Association. Also, rental of vibration measurement hardware and software from Instrumented Sensor Technology of Okemos, MI was provided at a substantial educational discount in support of this work. The goal of this initial work was to characterize the vibration amplitude, frequency, and energy associated with ambulance travel and the attendant impacts of road-induced vibration on patients and crew. This data would help us to better understand the nature and magnitude of ambulance vibration and could later serve as a database from which potential vibration attenuation solutions might arise.

The results of the team’s road studies indicated that average vertical vibration amplitudes of .46 to 2.55 m/sec2 were recorded in the patient compartments of the four ambulances. Power spectrum analysis of the data revealed that the vibration energy and resulting vertical acceleration forces were concentrated in the .1 to 6 Hz range.

The original vibration data was used to define relationships between ambulance vibration and the impact of whole body vibration on human physiology and performance. When compared with known whole body vibration data, these average acceleration forces could have potentially negative medical implications to patients with a variety of compromised health conditions. They were in excess of what is considered to be a normal human comfort level for vibration, and most definitely were in a vibration spectrum which could present impediments to performance for the medical team on-board. The vibration levels measured all had ramifications for the safety, comfort and care of ambulance patients.

Phase portrait analysis combined with the power spectrum data revealed the presence of nonlinearities, stochastic fluctuations and time delays inherent in the data. From this data analytical forcing functions which describe the vibrations encountered in a typical “ambulance ride” were developed. The forcing functions and ambulance vibration model were utilized to derive a generalized equation for the control of vibration attenuation solutions to accommodate the nonlinearities, stochastic fluctuations and time delays present in the ambulance vibration data. As a result of this study, a library of vibration data for ambulances travelling at various speeds over various road services now exists and can be used by medical equipment manufactures to aid in the design of their mobile medical devices and vehicles.

The WPI team is working now to make this data available to the medical device and vehicle industry.

Going forward, the WPI team will explore the development, vehicle retrofit, and test of a physical vibration attenuation control system based on the models developed in this study. Other areas of exploration include the possibility of employing the model to improve the design and performance of any medical or life-saving equipment which must be used in a mobile environment, including a whole host of vibration-resistant health monitoring systems, like defibrillators and EKG machines. In addition, the valuable forcing function data could be used to develop vibration isolating stretchers and mattresses, alternative stock suspensions for ambulances, the design of smaller, lower payload ambulances which could utilize softer suspensions. The use of the vibration data to develop an interactive simulation to help train ambulance drivers to operate vehicles in a vibration sensitive manner is also being explored by the author and a team of video game designers at Becker College in Worcester.

The broader significance of this work lies in enhancing the patient-centered care associated with ambulance travel by improving patient comfort and safety through the assessment and administration of mobile medical interventions with improved precision, accuracy and safety.

Author Paul D. Cotnoir PhD, P.E. Department of Design, Becker College, Worcester MA