Performance of a Kinetic Inductance Traveling-Wave Parametric Amplifier at 4 Kelvin: Toward an Alternative to Semiconductor Amplifiers.

Most microwave readout architectures in quantum computing or sensing rely on a semiconductor amplifier at 4 K, typically a high-electron mobility transistor (HEMT). Despite its remarkable noise performance, a conventional HEMT dissipates several milliwatts of power, posing a practical challenge to scale up the number of qubits or sensors addressed in these architectures. As an alternative, we present an amplification chain consisting of a kinetic inductance traveling-wave parametric amplifier (KITWPA) placed at 4 K, followed by a HEMT placed at 70 K, and demonstrate a chain-added noise TΣ=6.3±0.5K between 3.5 and 5.5 GHz. While, in principle, any parametric amplifier can be quantum limited even at 4 K, in practice we find the performance of the KITWPA to be limited by the temperature of its inputs and by an excess of noise Tex=1.9K. The dissipation of the rf pump of the KITWPA constitutes the main power load at 4 K and is about 1% that of a HEMT. These combined noise and power dissipation values pave the way for the use of the KITWPA as a replacement for semiconductor amplifiers.

Stimulation of chemosensitive afferents from multifidus muscle does not sensitize multifidus muscle spindles to vertebral loads in the lumbar spine of the cat.

STUDY DESIGN: Electrophysiologic recordings from muscle spindle afferents innervating the lumbar multifidus muscle of the cat while loading the L6 vertebra at its spinous process and while exposing the segmentally adjacent lumbar multifidus muscles to algesic and inflammatory mediators. OBJECTIVES: The purpose of this study was to investigate a possible mechanism underlying muscle spasm and pain in the lumbar spine. The hypothesis was tested that stimulation of chemosensitive afferents with receptive endings in the paraspinal muscle increases the discharge of paraspinal muscle spindle afferents during loading of a lumbar vertebra. The presence of such a phenomenon would provide a mechanism by which pain or inflammation could alter segmental lumbar biomechanics and contribute to lumbar spine dysfunction. SUMMARY OF BACKGROUND DATA: Muscle pain, tenderness, and altered muscle tone are often associated with musculoskeletal disorders. The literature suggests that stimulation of Group III and IV muscle afferents sensitive to algesic or inflammatory metabolites increases the stretch sensitivity of muscle spindles via a reflex pathway involving gamma-motoneurons. The reflex increase in muscle spindle activity, in turn, reflexly increases the excitability of alpha-motoneurons leading to enhanced muscle tone and the further accumulation of muscle metabolites and subsequent pain. Studies in the cervical spine support this hypothesis. It has not been investigated in the lumbar spine. METHODS: Single unit activity from muscle spindles in the L6 multifidus muscle were recorded from the cut peripheral end of the L6 dorsal root in alpha-chloralose-anesthetized cats and in decerebrate unanesthetized cats. The L6 vertebra was loaded at its spinous process using a force-feedback motor. Ramp and hold loads were delivered at 25%, 50%, 75%, and 100% body weight. Chemosensitive afferents in the L5 and L7 multifidus muscle were stimulated by bathing (subfascial injection) or infiltrating (intramuscular injection) the L5 and L7 multifidus muscles with bradykinin or capsaicin. RESULTS: Loading the L6 vertebra stimulated muscle spindles in the L6 multifidus muscle. Neither the saline volume control nor bradykinin nor capsaicin injected subfascially or intramuscularly affected the response of L6 multifidus muscle spindles to ramp and hold vertebral loads in the alpha-chloralose-anesthetized cat. In addition, neither saline nor bradykinin nor capsaicin injected intramuscularly affected the activity of L6 multifidus muscle spindles to ramp and hold vertebral loads in the unanesthetized decerebrate cat. CONCLUSIONS: These results indicate that stimulation of small diameter muscle afferents in a deep muscle of the lumbar spine does not sensitize muscle spindles to vertebral loads. These data do not support the hypothesis that fusimotor reflexes evoked by chemosensitive muscle afferents contribute to muscle spasm or to changes in muscle tone in the lumbar spine. In addition, the present results do not provide evidence for the pain-spasm-pain cycle in the lumbar spine.

Response of muscle proprioceptors to spinal manipulative-like loads in the anesthetized cat.

OBJECTIVE: The mechanisms underlying the benefits of spinal manipulation are not well understood. Neurophysiological mechanisms likely mediate its effects, at least in part, yet we know little about how the nervous system is affected by spinal manipulation. The purpose of the present study was to determine whether muscle spindles and Golgi tendon organs in paraspinal muscles respond to a mechanical load whose force-time profile is similar to that of a spinal manipulation. METHODS: Experiments were performed on 10 anesthetized adult cats. The L6 dorsal root was isolated for electrophysiological recordings while the L6-L7 vertebrae and associated paraspinal tissues on one side of the vertebral column were left intact. Single unit recordings were obtained from 5 muscle spindles, 4 Golgi tendon organs, and 1 presumed Pacinian corpuscle afferent with receptive fields in paraspinal muscles. Loads were applied at the spinous process of the L6 vertebra through use of an electronic feedback control system. The load simulated the force-time profile of a spinal manipulation. Loads were applied in compressive and distractive directions and at 2 different angles (0 degrees and 45 degrees) with respect to the long axis of the vertebral column. RESULTS: Golgi tendon organ afferent discharge frequency increased more to the impulse than to the preload during 13 of 15 spinal manipulations. Generally, the 4 Golgi tendon organ afferents became silent immediately at the end of each impulse. Similarly, muscle spindle discharge frequency increased more to the impulse than to the preload during 10 of 16 manipulations. Distractive manipulations loaded the spindles more effectively than compressive manipulations. After 7 of these 10 manipulations, muscle spindles became silent for 1.3 +/- 0.6 seconds (range, 0.1-4.3 seconds). Six of the 16 manipulations unloaded the muscle spindles. A presumed Pacinian corpuscle responded to the impulse of a manipulative-like load but not to loads with a slower force-time profile. CONCLUSION: The data suggest that the high-velocity, short-duration load delivered during the impulse of a spinal manipulation can stimulate muscle spindles and Golgi tendon organs more than the preload. The physiologically relevant portion of the manipulation may relate to its ability to increase as well as decrease the discharge of muscle proprioceptors. In addition, the preload, even in the absence of the impulse, can change the discharge of paraspinal muscle spindles. Loading of the vertebral column during a sham manipulation may affect the discharge of paraspinal proprioceptors.