Reversible Effects of Ultrasound on Spinal Reflexes

C. N. SHEALY, E. HENNEMAN

Archives of Neurology 1962 · 10.1001/archneur.1962.00450230036005

other vertebratehealthyinvasive electrophysiologyhistology molecular

Speciescat

Subjects42 animals

Sessions per subjectnot reported

Randomisednot reported

Blindingnot reported

Sham / controlnone

Auditory controlnot reported

Readout timingboth

Anaesthesiaanaesthetised

Readoutsinvasive electrophysiology, histology molecular — Monosynaptic and polysynaptic spinal reflexes recorded from peripheral nerve to semitendinosus muscle; trypan blue staining and histology (Nissl/H&E) of spinal cord

Direction of effectbidirectionalUltrasound irradiation of the spinal cord usually produced an initial enhancement of monosynaptic and polysynaptic reflexes, sometimes followed by a reversible depression; a minority of experiments showed simple depression, and high doses produced irreversible decreases in reflex transmission.

Adverse eventsobservedAt high doses (e.g. Experiments 15 and 69, with 21 and 114 pulses respectively) irreversible decreases in reflex transmission occurred together with considerable histological damage and hemorrhage on the irradiated side; single small hemorrhages were also seen in three other cords.

Exposures

Exposure 1: Focused and defocused ultrasound irradiation of L7-S1 spinal cord

Target: lumbar spinal cord — “L7-S1 portion of the spinal cord”
Device: custom-built

Pulse timing
Waveform	pulsed
Fundamental frequency (kHz)	2,700	✓✓✓
Pulse duration (ms)	50, 300swept	✓✓✓
Pulse repetition frequency (Hz)	0.33, 2swept	✓✓✓⚑
Duty cycle (%)	not reported
Sonication duration (s)	30, 60, 555swept	✓✓✓⚑

Pressure and intensity, by domain
Free-field pressure (kPa)	not reported	⚑
Free-field Isppa (W/cm²)	not reported
Free-field Ispta (W/cm²)	not reported
In-situ estimate	not reported
In-situ pressure (kPa)	not reported
In-situ Isppa (W/cm²)	not reported
In-situ Ispta (W/cm²)	not reported

Protocol, in the paper’s words

Ultrasound (2.7 megacycles per second) was used to irradiate the exposed spinal cord; in some experiments the sound was focused 2 or 3 mm ventral to the dorsum of the spinal cord in the L7-S1 region, in others a 'defocused' beam was aimed 5 mm above one side of the cord. Brief irradiations used pulses of 0.3 second duration at a rate of 1 per second (or 0.2-0.3 s pulses at a period of 3.0 s); more prolonged irradiations of up to 9 1/4 minutes were also given at rates of 1 pulse every 1-3 seconds. Dose was described by plate voltage (700-1950 V) across the piezoelectric crystal rather than a calibrated acoustic pressure or intensity.

Flags from extraction

exposures[0].timing.pulse_repetition_frequency_hz — PRF converted directly from stated pulse rates/periods ('rate of 1 per second' = 1 Hz; elsewhere 'a pulse period of 3.0 seconds' / '1 pulse every 3 seconds' = 0.33 Hz); duty cycle was not computed since that would require combining these with pulse width.
exposures[0].timing.sonication_duration_s — Total irradiation durations vary substantially across the many experiments in Tables 1-2 (from single brief pulses up to a 9 1/4-minute train); only the three durations described in the narrated example experiments (30 s, 60 s, 9 1/4 min) are listed here.
n_subjects — Paper states 42 electrophysiological experiments (21 with accompanying histology) but does not explicitly equate experiments with individual cats; taken as 1 experiment per animal for this acute, non-survival preparation.
exposures[0].target.terms — Sonication was aimed at the dorsal part of the L7-S1 spinal cord segment (focal point dorsal to the motor neurons); classified under lumbar_spinal_cord as the closest matching target term.
exposures[0].free_field.pressure_kpa — Dose is only reported as plate voltage across the piezoelectric crystal (700-1950 V); the paper states this intensity 'was not calculated, since the attenuation of ultrasound through the several media was not known', so no pressure or intensity value is reported.