Assessment of PEEP-Ventilation and the Time Point of Parallel-Conductance Determination for Pressure-Volume Analysis Under β-Adrenergic Stimulation in Mice

Figures

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  Figure 1. Ventilation with positive end-expiratory pressure (PEEP) protected mice from exacerbated airway pressure and prevented pulmonary lesions. (A) Experimental design with two groups either ventilated without PEEP (black) or with PEEP of 2 cmH2O (purple). Comparison of representative traces of short-term (B) and long-term (C) PEEP-ventilation. In (C) white incisions depict end-expirational ventilation-stops during PV loop recordings. (D) Analysis of peak inspiratory pressure (Peak Pinsp) during 15 min after catheter insertion (time 0). (E) Representative picture of a pulmonary lesion which occurred in 5 out of 10 non-PEEP-ventilated animals and quantitative assessment of pulmonary lesions. Data presented as mean ± standard deviation from n = 10 (No PEEP group) and n = 8 (PEEP group) mice. n, number of mice. *p < 0.05, ***p < 0.001: p-value No PEEP vs. PEEP in an unpaired Student's t-test; #p < 0.05, ##p < 0.01, ###p < 0.001: p-value vs. previous corresponding observation point in a paired Student's t-test within the groups (purple #: PEEP group, black #: No PEEP group).

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  Figure 2. Early hypertonic saline calibration increased ectopic beat frequency and parallel-conductance. (A) Experimental design indicating the application time points of the hypertonic saline bolus either after (late saline, black) or prior to (early saline, green) PV loop recordings; (B) Analysis of ectopic beats showing the percentual proportion of sections with ectopic beats; (C) Parallel-conductance (Gp) calculated in groups of early or late saline application; (D) Blood conductance conversion factor for volume conversion (μl/RVU) at the end of experiments. Saline-bolus: One-time injection of 10 μl saline (15%) into the left femoral vein. Data presented as mean ± standard deviation from n = 23 (late saline) and n = 15 (early saline) mice. PEEP, positive end-expiratory pressure, ISO, Isoprenaline, RVU, Relative volume units; n, number of mice. **p < 0.01; ***p < 0.001: p-value of late saline vs. early saline in an unpaired Student's t-test.

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  Figure 3. Early hypertonic saline calibration increased cardiac preload, reduced cardiac contractility and ameliorated β-adrenergic reserve. (A) Representative PV loops during inferior caval vein occlusion of the late saline group as compared to the early saline group; (B) Cardiac preload as depicted by end-diastolic pressure (B), end-diastolic volume (C), and end-systolic volume (D); (E) Analysis of the diastolic relaxation constant Tau; (F) Analysis of systolic contractility (PRSW); (G) maximum dP/dt and (H) heart rate. Data presented as mean ± standard deviation from n = 23 (late saline group) and n = 15 (early saline group) mice. Abbreviations: ISO, Isoprenaline, PRSW, Preload Recruitable Stroke Work; n, number of mice. *p < 0.05; **p < 0.01; ***p < 0.001: p-value of Late saline vs. Early saline in an unpaired Student's t-test.

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  Figure 4. End-systolic pressure-spikes under β-adrenergic stimulation occurred in measurements without initial signs of catheter entrapment. (A) Time of ESPS occurrence during the measurements labeled by red stars. (Bi−iv) Representative PV loops during ICV occlusion under incremental ISO stimulation in a measurement in which no ESPS were detected at any concentration. (Ci−iv) Representative PV loops during ICV occlusion in a measurement in which ESPS were detected during stimulation with 2.475 ng/min ISO or higher. ESPS, End-systolic pressure-spikes; ISO, Isoprenaline.

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  Figure 5. End-systolic pressure-spikes impaired volume detection and diastolic relaxation but did not affect cardiac contractility. (A) Impact of ESPS on pressure detection with representative PV loops either without (Ai) or with ESPS (Aii). Maximum pressure (Pmax) could be corrected as depicted by red arrows and lines (Aii); a comparison between Pmax in both groups, including corrected Pmax for measurements with ESPS (dashed line) is shown in (Aiii). (B) Volumetric parameters end-diastolic volume (Bi), stroke volume (Bii) and cardiac output (Biii). (C) Analysis of cardiac contractility showing preload recruitable stroke work (PRSW) (Ci) and maximum dP/dt (Cii). (D) Diastolic relaxation constant Tau. Data presented as mean ± standard deviation from n = 17 (No ESPS group) and n = 6 (ESPS group) mice. ESPS, End-systolic pressure-spike; ISO, Isoprenaline; n, number of mice. *p < 0.05; **p < 0.01: p-values No ESPS vs. ESPS in an unpaired Student's t-test.