Behavioral demonstration of a somatosensory neuroprosthesis.

Tactile sensation is critical for effective object manipulation, but current prosthetic upper limbs make no provision for delivering somesthetic feedback to the user. For individuals who require use of prosthetic limbs, this lack of feedback transforms a mundane task into one that requires extreme concentration and effort. Although vibrotactile motors and sensory substitution devices can be used to convey gross sensations, a direct neural interface is required to provide detailed and intuitive sensory feedback. In light of this, we describe the implementation of a somatosensory prosthesis with which we elicit, through intracortical microstimulation (ICMS), percepts whose magnitude is graded according to the force exerted on the prosthetic finger. Specifically, the prosthesis consists of a sensorized finger, the force output of which is converted into a regime of ICMS delivered to primary somatosensory cortex through chronically implanted multi-electrode arrays. We show that the performance of animals (Rhesus macaques) on a tactile task is equivalent whether stimuli are delivered to the native finger or to the prosthetic finger.

Reflections on the evolution of cardiopulmonary bypass.

The concept of cardiopulmonary bypass is more than a century old. Although the first clinical application occurred in 1953, there were great deficits in knowledge and materials that had to be overcome before we could achieve the outcomes of cardiac surgery that we have today.

Left ventricular hyperkinesia at rest and during exercise in normotensive patients 2 to 27 years after coarctation repair.

The short- and long-term results of effective surgical repair of coarctation of the aorta on left ventricular mass and function in 48 patients were evaluated using echocardiography and stress-gated radionuclide angiography. Thirty-two of the 48 patients who had no additional cardiac problems and had technically adequate radionuclide angiograms form the basis for this report. Among these, three had mild systolic hypertension and none had significant aortic valve dysfunction. Age at the time of study ranged from 6.5 to 59 years (mean 27). Age at the time of surgery ranged from 3 months to 34 years (mean 12 years). Duration from surgery to the time of noninvasive study ranged from 2 to 29 years (mean 15). In the 32 patients, left ventricular mass was 120 +/- 20 g/m2, compared with a control value of 87 +/- 10 g/m2. Mean left ventricular ejection fraction was elevated to 69.2 +/- 1.6% at rest (control 60 +/- 1.3%) and 78.8 +/- 1.3% during exercise (control 70 +/- 1.7%) (p less than 0.01). The systolic ejection rate was significantly increased (p less than 0.01) and end-systolic volume significantly decreased (p less than 0.01) compared with values in control patients. There was no correlation between ejection fraction and either age at the time of surgery or years since surgery. These findings of hyperdynamic left ventricular function and increased left ventricular mass without apparent cause many years after coarctation repair raise important questions as to mechanisms, extension to other forms of afterload stress that have been surgically or medically relieved and long-term outcome.

PEEP: its use in young patients with apparently normal lungs.

PEEP has been advocated for use in patients with the acute respiratory distress syndrome characterized by a marked reduction in FRC. It has not been advocated for patients with apparently normal lungs requiring prolonged mechanical ventilation. We have done inert gas washouts on five young patients comparing no PEEP to 10 cm H2O PEEP. Four of the five showed a significant improvement in PaO2, a decrease in AaDO2 and Qs/Qt, the fifth a slight improvement on PEEP. Arterial washouts were significantly faster on PEEP in all patients suggesting a decrease in intrapulmonary shunting. Airway washouts in the initial phase were faster off PEEP suggesting an increase in lung volume and FRC with PEEP. Later portions of the curve were faster on PEEP suggesting improved distribution of ventilation. These findings suggest that PEEP might be of significant value in treatment of patients requiring prolonged mechanical ventilation for reasons other than lung abnormalities.

Optimal flow pattern for mechanical ventilation of the lungs. 2. The effect of a sine versus square wave flow pattern with and without an end-inspiratory pause on patients.

In four series of patients, the efficiency of ventilation of a sine wave without an end-inspiratory pause was compared to a square wave without a pause, a sine wave with a pause to a square wave with a pause, a sine wave to a sine wave with a pause, and a sine wave with a long pause to one with a short pause. The primary mode of evaluation was through simultaneous airway and arterial argon washout curves. Additional cardiopulmonary measurements were made. Results indicate: (1) a statistically significant improvement in ventilation with a sine wave with a pause; (2) a statistically significant improvement with the longer pause as compared to the short pause.

Optimal flow pattern for mechanical ventilation of the lungs. Evaluation with a model lung.

The major components entering into the inspiratory pattern of various respirators were tested on a model lung which had an abnormally high airway resistance on one side. The tests consisted of simultaneous nitrogen washout curves from each lung separately utilizing two mass spectrometers. The components tested included a constant versus accelerating wave form and the presence, duration or absence of an end-inspiratory pause. Respirators tested included the Bennett MA1. Engström 300 and the Elema Schonander Servo tventilator 900. The results demonstrated the importance of an end inspiratory pause in improving gas distribution and efficiency of washout. No difference was found between a constant or accelerating air flow. Preliminary results in man appear to confirm the importance of an end inspiratory pause.