Evaluation of transcutaneous near-infrared spectroscopy for early detection of cardiac arrest in an animal model

Figures

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  Figure 1. Representative experimental set-up. (a) Placement of NIRS sensor (PortaMon, Artinis Medical Systems, The Netherlands) on the left hindlimb muscle of a Yucatan minipig. (b) The underside of the NIRS sensor consists of one photodiode (light receiving element) and three LEDs (each transmitting light at two wavelengths; ~ 765 nm and ~ 850 nm). The interoptode distances from the photodiode to each LEDs are as follows: 30 mm, 35 mm and 40 mm. The three LEDs emit a total optical power of 0.88 mW, 1.78 mW and 3.67 mW, respectively. (c) Intra-operative placement of spinal cord intraparenchymal (IP) probes to measure local changes in spinal cord PO2 in response to euthanasia. IP probes were placed as part of other NIRS studies. IP probes intraparenchymal probes, PO2 partial pressure of oxygen, NIRS near-infrared spectroscopy.

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  Figure 2. Transcutaneous NIRS, carotid blood pressure and spinal cord PO2 responses to pentobarbital administration. Averaged traces from (a) MAP (n = 7 animals, ± SEM), (b) spinal cord PO2, (n = 6, ± SEM), (c) TSI (%) (n = 8, ± SEM), and (d) relative changes in NIRS parameters of O2Hb, HHb, THb and Hbdiff (n = 8 ± SEM). The 5-min timepoint (dashed line) denotes the time of pentobarbital administration. (e,f) Delta changes to euthanasia relative to a 60-s pre-euthanasia baseline. TSI (%) tissue saturation index, Hbdiff hemoglobin difference, O2Hb oxygenated hemoglobin, HHb deoxygenated hemoglobin, THb total hemoglobin, MAP mean arterial pressure, PO2 partial pressure of oxygen, BSL baseline, EUT euthanasia.

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  Figure 3. Pre- and post-euthanasia comparison of carotid MAP, spinal cord PO2 and TSI (%) measures. Box plots (IQR + min and max values) of pre-euthanasia (BSL; averaged over 60 s pre-pentobarbital infusion) and post-euthanasia values (EUT; averaged over the last 10 s of the recording) in (a) MAP (mmHg) (n = 7, p < 0.0001) (b) spinal cord PO2 (mmHg) (n = 6, p = 0.0028, and (c) TSI (%) (n = 8, p < 0.0001). Group comparisons were analyzed using a paired student’s t-test (level of significance p < 0.05). TSI (%) tissue saturation index, MAP mean arterial pressure, PO2 partial pressure of oxygen, BSL baseline, EUT euthanasia.

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  Figure 4. Euthanasia-to-first change in hemodynamics for MAP, spinal cord PO2 and NIRS-derived TSI (%) and O2Hb. (a) Representative figure of a NIRS TSI (%) trace pre- and immediately following pentobarbital infusion. The first detected drop in the signal was defined as the first value two standard deviations below baseline (established over the last 60 s prior to pentobarbital administration). (b) Time (sec) to the first change in carotid MAP, spinal cord PO2 and hindlimb TSI (%) signals in response to euthanasia ± SD. MAP vs TSI (%) (n = 7; p = 0.3714), and MAP vs spinal cord PO2 (n = 6, p = 0.0006) were analyzed using paired student’s t-tests (level of significance p < 0.05); TSI (%) tissue saturation index, MAP mean arterial pressure, PO2 partial pressure of oxygen.

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  Figure 5. Representative short-time Fourier transform analyses. STFT colormaps of (a) carotid ABP and (c) NIRS O2Hb signals over a 15-min window. Pentobarbital infusion commenced at 600 s. (b,d) Three analysis windows were selected for subsequent analysis, denoting different stages of euthanasia. O2Hb oxygenated hemoglobin, ABP arterial blood pressure, BSL baseline, EUT euthanasia, STFT short time Fourier transform (for STFT colourmaps from individual animals, see Supplementary Figs. 1–8).

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  Figure 6. Comparison of ABP and NIRS-derived pulse rate and amplitude changes in response to pentobarbital administration. Mean ABP and O2Hb-derived pulse amplitudes (dB) (n = 8) during (a) baseline (p = 0.0014) and (b) euthanasia (p = 0.0009) (Student’s t-test, level of significance p < 0.05). (c) ABP and O2Hb pulse amplitudes (dB) at BSL vs EUT (Repeated measure ANOVA, adjusted p-values: ABP BSL vs EUT p = 0.0047 and O2Hb BSL vs EUT p = 0.0132; level of significance p < 0.05). Mean ABP and O2Hb-derived pulse rates (Hz) (n = 8) during (d) baseline (p > 0.99), (e) euthanasia (p = 0.97) and (f) post-euthanasia (unable to calculate p). Group comparisons were analyzed using a student’s t-test (level of significance p < 0.05). ns not significant, O2Hb oxygenated hemoglobin, ABP arterial blood pressure, BSL baseline, EUT euthanasia.