Grass p511

Recording procedures followed previous descriptions from some of us^{22 (link),23 (link)}. The electromyographic (EMG) activity of the orbicularis oculi muscle was recorded using GRASS P511 differential amplifiers within a bandwidth of 1 Hz to 10 kHz (Grass-Telefactor, West Warwick, RI 02893, USA). The basic properties of blink reflexes were studied in responses evoked by single 50 µs, 2 × threshold, square, cathodal pulses presented at a rate of 1/30 s. Reflex blinks were studied before the initiation of the conditioning sessions.
For criteria, we considered a 'CR' to be the presence of EMG activity during the CS–US period that lasted > 10 ms and was initiated > 30 ms after CS onset. To obtain a quantitative index of CR evolution, the integrated EMG activity recorded during the CS–US interval was averaged and compared with the activity recorded (for 250 ms) immediately before CS presentation. The integrated EMG activity recorded during the CS–US interval should be at least 2.5 times larger than the averaged activity recorded immediately before CS presentation.

ABRs were recorded using three subcutaneous needle electrodes placed on the vertex (active), on the pinna of the tested ear (reference), and in the hind leg (ground). Strong correlations were observed between click-evoked ABR thresholds and pure-tone thresholds at 2 and 4 kHz [59 (link)]. To obtain more frequency-specific estimates of hearing sensitivity in the high-frequency range, we chose to use tone-burst stimulation for ABR recording. Sound stimuli were generated by a NI PXI-4461 signal generator (National Instruments) and consisted of 10 ms tone-bursts with a 1 ms rise- and fall time, delivered at a rate of 10/s. Sound was produced by a JBL 075 loudspeaker (James B. Lansing Sound) positioned at 10 cm from the tested ear in a calibrated, free-field condition. Cochlear-responses were amplified (20,000) via a Grass P511 differential amplifier, and averaged 1000 times (Dell Dimensions). Intensity-amplitude functions of the ABRs were obtained at each frequency tested (2, 4, 6.3, 8, 10, 12.5, 16, 20, 24, and 32 kHz) by varying the level of the tone bursts from 0 to 100 dB SPL, in 5 dB incremental steps. The ABR thresholds were defined as the minimum sound intensity necessary to elicit well-defined and reproducible wave II. Recordings and analysis were performed blindly.

All EMG signals were amplified and filtered (100–1000 Hz) using Grass P511 (Natus Neurology) amplifiers. Esophageal pressure was measured by a TA-100 single channel transducer amplifier (CWE, Inc). Signals were rectified and integrated (20ms) using Spike2 (Cambridge Electronic Design; Cambridge, England). EMG amplitude measures were normalized to the largest swallow in the control trial with and without chest compression. The swallow parameters that were measured include total swallow duration (the period from the onset of mylohyoid activation to the offset of thyroarytenoid activation) and amplitudes of mylohyoid, geniohyoid, and thyroarytenoid muscles. The inactivity of the thyroarytenoid in conjunction with mylohyoid and geniohyoid activity distinguishes licking behaviors from swallow activity [25 (link)]. Thus, if thyroarytenoid activity was absent, the event was not included as a swallow.
Results are expressed as means ± standard deviation (SD). Paired t-tests and Wilcoxon signed ranks tests were used as appropriate to statistically identify differences using SPSS statistical software (IBM Corporation). Analyses were made within groups (male and female) and between groups (male vs female). A difference was considered significant if the p-value was less than or equal to 0.05.

All EMG signals were amplified and filtered (100–1000 Hz) using Grass P511 (Natus Neurology) amplifiers. Esophageal pressure was measured by a TA-100 single channel transducer amplifier (CWE, Inc). Signals were rectified and integrated (20ms) using Spike2 (Cambridge Electronic Design; Cambridge, England). EMG amplitude measures were calculated as a percent of maximum during the control period. Breathing phase durations were measured using diaphragm EMG activity across 30 seconds of eupnea. Eupneic periods during the control period and the control chest compression conditions were averaged separately for male (n = 24) and female (n = 19) groups. Respiratory rate (RR) was calculated as the number of respiratory cycles during a 30 second period, multiplied by 2. To normalize the signal across animals, EMG amplitude data is presented as a percent of the maximum from the control period.
Results are expressed as means ± standard deviation (SD). Paired and independent t-tests and 2-way ANOVA were used as appropriate to statistically identify differences using SPSS statistical software (IBM Corporation). Analyses were made within groups (male and female) and between groups (male vs female). A difference was considered significant if the p-value was less than 0.05.