Advancing biomedical engineering in developing nations: Project HOPE and the potential impact of nongovernmental organizations.

Nongovernmental organizations (NGOs) have played a major role in the diffusion of biomedical engineering training to developing nations. This paper reviews the roles and unique attributes of NGOs in biomedical engineering training programs. The activities of one leading NGO in this field, Project HOPE, are discussed with examples drawn from around the world. Future challenges to biomedical engineering in the developing world, and the potential of NGOs to provide a response to these needs, are considered.

Effect of tactile stimulation pulse characteristics on sensation threshold and power consumption.

The psychophysical responses of human subjects to vibratory tactile stimulation of the skin were investigated experimentally. The parameters of the waveform important to the minimization of power consumed by the tactile array of electromechanical vibrators and the maximization of the skin sensitivity to the stimulus were explored to develop optimum stimulation. Parameters investigated included the amplitude, frequency, and duty cycle of the current waveform used to drive the vibrators as well as the number of pulses per stimulating burst and the recovery time between bursts. Graphical techniques were used to determine the optimal combination of the parameters which gave a stimulus that excited the skin to above tactile threshold while maintaining at a relative minimum the power required for the stimulus. The optimal stimulation waveform contains a burst of 10 rectangular pulses of 4% duty cycle separated by a period of nonstimulation of 2 s. Such a waveform can elicit a sensitivity of 29.4 mA-1 consuming only 55 microW of power.

Effects of pericardial effusates of various conductivities on body-surface potentials in dogs. Documentation of the eccentric spheres model.

The purpose of this study was to discover the cause and magnitude of changes in the body-surface potentials occurring when: (1) fluids of various conductivity were added to the pericardial sac, or (2) the volume of the blood within chambers of the heart was either increased or decreased. Fluids added to the pericardium were physiological saline, whole-blood, and mineral oil. Magnitudes of body-surface potentials were compared to the predictions based on a mathematical eccentric spheres model of the heart and torso developed previously by Rudy and Plonsey. Data demonstrated conclusively that there is a nonlinear relationship between the body-surface potentials and the conductivity of the pericardial layer. This relationship is one in which the body-surface potentials of the anterior chest were found to decrease when conductivity of the pericardial layer was either increased or decreased. These changes in body-surface potentials were caused solely by alterations in the conductivity and volume of the fluid effusate. It was demonstrated that these changes were not caused by any "stretching" or "compression" of the cardiac tissue caused by the altered fluid volumes in and around the heart. Findings were accurately predicted by the eccentric spheres model, thereby confirming the model's usefulness as a predictive instrument. The model provides an explanation for the nonlinear relationship that was exhibited by the data.