Forehead reflectance photoplethysmography to monitor heart rate: preliminary results from neonatal patients

Around 5%-10% of newborn babies require some form of resuscitation at birth and heart rate (HR) is the best guide of efficacy. We report the development and first trial of a device that continuously monitors neonatal HR, with a view to deployment in the delivery room to guide newborn resuscitation. The device uses forehead reflectance photoplethysmography (PPG) with modulated light and lock-in detection. Forehead fixation has numerous advantages including ease of sensor placement, whilst perfusion at the forehead is better maintained in comparison to the extremities. Green light (525 nm) was used, in preference to the more usual red or infrared wavelengths, to optimize the amplitude of the pulsatile signal. Experimental results are presented showing simultaneous PPG and electrocardiogram (ECG) HRs from babies (n = 77), gestational age 26-42 weeks, on a neonatal intensive care unit. In babies ⩾32 weeks gestation, the median reliability was 97.7% at ±10 bpm and the limits of agreement (LOA) between PPG and ECG were +8.39 bpm and -8.39 bpm. In babies <32 weeks gestation, the median reliability was 94.8% at ±10 bpm and the LOA were +11.53 bpm and -12.01 bpm. Clinical evaluation during newborn deliveries is now underway.

Biomechanical evaluation of anterior cervical spine stabilization

STUDY DESIGN

An in vitro biomechanical study.

OBJECTIVES

To simulate a severe compressive flexion injury for determination of the relative stability of different anterior instrumentation systems in a porcine model and to validate this model in human cadaveric specimens.

SUMMARY OF BACKGROUND DATA

Anterior plate fixation is useful for high-grade mechanical insufficiency of the cervical spine and may prevent the need for a second procedure.

METHODS

The cervical spines of 45 porcine and 12 cadaveric specimens were subjected to nondestructive flexion, lateral bending, and torsional testing on a modified universal testing machine. A corpectomy was performed with release of the posterior ligamentous structures. The specimens were stabilized with one of three anterior plate constructs. The nondestructive testing was repeated to evaluate structural stability (stiffness and neutral zone). Finally, destructive testing examined failure moment, energy to failure, and mechanism of failure.

RESULTS

The instrumented specimens had flexural and lateral bending and torsional stiffness values that were similar to or greater than those of their paired intact specimens. The cervical spine locking plate had a significantly higher flexural stiffness ratio (plated:intact), torsional stiffness ratio, lower flexural neutral zone ratio, higher failure moment, and higher energy to failure than did the Caspar plate.

CONCLUSIONS

The cervical spine locking plate is theoretically safer than the Caspar system because the posterior vertebral body cortex is not breached by the fixation screws, and the screws are less likely to back out anteriorly and irritate the esophagus. According to these results, the cervical spine locking plate system is biomechanically equivalent to and in some cases more stable than the Caspar system for fixation of a severe compressive flexion injury.

Biomechanical evaluation of posterior cervical stabilization after a wide laminectomy

STUDY DESIGN

In vitro biomechanical investigation with nondestructive and destructive testing in a human cadaveric model simulating a wide postlaminectomy condition.

OBJECTIVES

To determine the relative stability conferred by a posterior cervical spinal rod system and posterior cervical plating.

SUMMARY OF BACKGROUND DATA

Posterior cervical plate fixation has been shown to be biomechanically superior to wiring techniques, but lateral mass screws may injure neurovascular structures or facet joints if they are inserted improperly. A cervical rod system has been developed to enhance the safety of lateral mass instrumentation.

METHODS

The cervical spines of 12 cadavers underwent biomechanical testing. After completion of the nondestructive intact testing, a wide laminectomy with subtotal facetectomies from C4 to C6 was performed. The specimens in two subgroups (group A, cervical spine rods with unicortical fixation, and group B, reconstruction plates with bicortical fixation) were tested in flexion, lateral bending, and torsion. Finally, destructive testing in flexion was performed. Stiffness, neutral zone, failure moment, energy to failure, and mechanism of failure were determined for each specimen. The data were analyzed using paired t tests and ANOVA.

RESULTS

Group B had a greater mean screw torque value. The instrumented constructs had a greater stiffness ratio (instrumented/intact) than the intact specimens in flexion, lateral bending, and torsional testing. Group A had a significantly greater flexural stiffness than Group B. Neutral zone ratio values were significantly lower during flexural testing for the cervical rod construct. Destructive testing resulted in significantly greater failure moment and energy-to-failure values for group A. In the cervical rod construct, failure occurred primarily by superior screw loosening with pull-out from the lateral mass. Reconstruction plates consistently failed with fracture of the lateral mass and superior screw loosening.

CONCLUSION

Significantly greater stability was noted in the cervical rod construct during nondestructive and destructive flexural testing.

Primary Ewing's sarcoma of the spine

Thirty-six patients with primary Ewing's sarcoma of the spine were diagnosed at the Mayo Clinic between 1951 and 1988. The mean age was 17 years (range, 5-40 years). Neurologic symptoms and signs were seen in 58% of the patients. Forty-seven percent of all patients had an open biopsy of the lesion and underwent a decompressive laminectomy. Three of the four patients with thoracic or thoracolumbar involvement had progressive kyphosis after laminectomy. All patients received radiation therapy in various dosages. Sixteen of the patients were registered in the Intergroup Ewing's Sarcoma Study. Intensive combination chemotherapy was administered to 32 of the patients. Nine patients were free of disease at the final follow-up examination (follow-up ranged from 6 to 184 months). The 5-year survival rate was 33%. The mean survival time was 2.9 years. No significant correlation was found between the location of the tumor in the spine and the length of disease-free survival, overall survival, or incidence of metastatic disease. Patients enrolled in the Intergroup Ewing's Sarcoma Study had significantly better rates of disease-free survival and overall survival.

Patients with primary hypothyroidism presenting as prolactinomas

Hyperprolactinemia can occur in patients with primary hypothyroidism. Two women with hypothyroidism who had elevated serum prolactin levels, galactorrhea, amenorrhea, and pituitary computed tomographic scans that demonstrated the presence of "pituitary tumors" were recently evaluated. It was believed that they had prolactinomas, and they were referred for possible surgery. An elevated serum thyroid-stimulating hormone level, however, suggested that they had primary hypothyroidism and probably pituitary enlargement secondary to pituitary hyperplasia. Detailed evaluation of thyroid-stimulating hormone and prolactin secretion was performed. These studies revealed several abnormalities in dopamine-prolactin interactions; however, the primary event responsible for the hyperprolactinemia is unclear. These women were given thyroxine therapy, and subsequent radiologic and endocrine studies documented resolution of their "pseudotumors" and normalization of the serum thyroxine and prolactin levels. Hence, thyroid-stimulating hormone levels should be measured in all patients presenting with a suspected prolactinoma so that any hypothyroidism that is noted is not presumed to be due to secondary hypothyroidism from tumor involvement of the pituitary.