Feasibility of kilohertz frequency alternating current neuromodulation of carotid sinus nerve activity in the pig

Figures

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  Figure 1. The porcine CSN. (A,B) Photograph of the carotid sinus region in a cadaver specimen, with a corresponding schematic illustration. Cranial is to the top left, caudal to the bottom right. CCA: common carotid artery. CSN: carotid sinus nerve. ECA: external carotid artery. ICA: internal carotid artery. LA: lingual artery. ng: nodose ganglion. OA: occipital artery. X: vagus nerve. IX: glossopharyngeal nerve. 2nd CN: second cervical nerve. (C) Photomicrograph (x2 magnification) taken from a section corresponding to the stippled line in B. At x10 magnification (insert square), CB cells are seen, located in the arterial wall. (D) Photomicrographs (x100 magnification) of immunohistochemistry (left) and a semi-thin section (right) of the porcine CSN demonstrating co-localization of ChAT + axons (red) and TH + axons (green) within some fascicles, whereas in other fascicles these two populations are separated. Semi-thin sectioning demonstrates both myelinated and unmyelinated axons, the latter outnumbering the former by a ratio of approximately 5:1.

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  Figure 2. Experimental set-up and model development. (A) Schematic illustration of the experimental set-up; an intra-carotid catheter was placed for injection of NaCN, evoking chemo-afferent responses. The CSN was instrumented with two cuff electrodes; the distal (towards the carotid sinus) was used for electrical stimulation at 20 Hz, whereas the proximal (towards the brain) was used for KHFAC blocking at 20 kHz of the electrically or pharmacologically evoked response. (B) Representative cardiorespiratory responses evoked by intra-carotid injection of NaCN; the two top panels represent Vt and RR, whereas the two bottom panels represent mABP and HR, respectively; responses are calculated as % change from baseline levels. NaCN is injected at time 0; duration of injection is <2 s (pink area). (C) Representative cardiorespiratory responses to electrical stimulation of the CSN at the identified respiratory response threshold. Stimulation is delivered for 20 s starting at time 0 (pink area). Again, the two top panels represent Vt and RR, whereas the two bottom panels represent mABP and HR, respectively; responses are calculated as % change from baseline levels. (D) Schematic illustration of the…

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  Figure 3. Electrically evoked stimulation responses. (A) Baroreflex activation evoking cardiovascular responses were observed at a lower stimulation current amplitude than the respiratory response threshold. In this animal, stimulation at 3 mA evoked a decrease in mABP (green trace; mm Hg), whereas no changes in Vt (black trace; l/min) or RR (blue trace; bmp) were seen. Stimulating at 4 mA evoked similar baro responses, but also produced an increase in Vt with a concurrent decrease in RR, and this stimulation amplitude was then identified as the respiratory response threshold. At both stimulation amplitudes, a small decrease in HR (pink trace; bpm) was seen. (B) Respiratory responses (group mean and 95% CI) when stimulating at the respiratory response threshold (pink area); green bars represent initial stimulation responses, whereas black bars represent responses while applying KHFAC block. Top panel: Vt (% change from baseline). Bottom panel: RR (% change from baseline). (C) Box plot illustrating AUC of the respiratory responses at the initial stimulation events (pre-blocking); at the blocking/stimulation paradigm; and at the stimulation events post block. Top panel: Vt. Bottom panel: RR.…

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  Figure 4. Chemo-afferent blocking. (A) Cardiorespiratory responses during successful KHFAC blocking (grey area) of the anticipated NaCN response (intra-carotid NaCN injection - pink area); the two top panels represent Vt and RR, whereas the two bottom panels represent mABP and HR, respectively; responses are calculated as % change from baseline levels. (B) Respiratory responses (group mean and 95% CI) to intracarotid NaCN injection (pink area); green bars represent initial chemo-afferent responses (pre-blocking), whereas black bars represent responses while applying KHFAC block. Top panel: Vt (% change from baseline). Bottom panel: RR (% change from baseline). (C) Box plot illustrating AUC of the respiratory responses for the initial NaCN injections (pre-blocking); when applying the blocking/NaCN paradigm; and when testing NaCN injections post block. Top panel: Vt, bottom panel: RR. Different letters denotes significant differences (P < 0.05) between interventions.