Impact of Cardiopulmonary Bypass on Respiratory Mucociliary Function in an Experimental Porcine Model

<div><p>Background</p><p>The impact of cardiac surgery using cardiopulmonary bypass (CPB) on the respiratory mucociliary function is unknown. This study evaluated the effects of CPB and interruption of mechanical ventilation on the respiratory mucociliary system.</p><p>Methods</p><p>Twenty-two pigs were randomly assigned to the control (n = 10) or CPB group (n = 12). After the induction of anesthesia, a tracheostomy was performed, and tracheal tissue samples were excised (T0) from both groups. All animals underwent thoracotomy. In the CPB group, an aorto-bicaval CPB was installed and maintained for 90 minutes. During the CPB, mechanical ventilation was interrupted, and the tracheal tube was disconnected. A second tracheal tissue sample was obtained 180 minutes after the tracheostomy (T180). Mucus samples were collected from the trachea using a bronchoscope at T0, T90 and T180. Ciliary beat frequency (CBF) and <i>in situ</i> mucociliary transport (MCT) were studied in <i>ex vivo</i> tracheal epithelium. Mucus viscosity (MV) was assessed using a cone-plate viscometer. Qualitative tracheal histological analysis was performed at T180 tissue samples.</p><p>Results</p><p>CBF decreased in the CPB group (13.1 ± 1.9 Hz vs. 11.1 ± 2.1 Hz, p < 0.05) but not in the control group (13.1 ± 1 Hz vs. 13 ± 2.9 Hz). At T90, viscosity was increased in the CPB group compared to the control (p < 0.05). No significant differences were observed in <i>in situ</i> MCT. Tracheal histology in the CPB group showed areas of ciliated epithelium loss, submucosal edema and infiltration of inflammatory cells.</p><p>Conclusion</p><p>CPB acutely contributed to alterations in tracheal mucocilliary function.</p></div

Heart Rate Variability Analysis in an Experimental Model of Hemorrhagic Shock and Resuscitation in Pigs

<div><p>Background</p><p>The analysis of heart rate variability (HRV) has been shown as a promising non-invasive technique for assessing the cardiac autonomic modulation in trauma. The aim of this study was to evaluate HRV during hemorrhagic shock and fluid resuscitation, comparing to traditional hemodynamic and metabolic parameters.</p><p>Methods</p><p>Twenty anesthetized and mechanically ventilated pigs were submitted to hemorrhagic shock (60% of estimated blood volume) and evaluated for 60 minutes without fluid replacement. Surviving animals were treated with Ringer solution and evaluated for an additional period of 180 minutes. HRV metrics (time and frequency domain) as well as hemodynamic and metabolic parameters were evaluated in survivors and non-survivors animals.</p><p>Results</p><p>Seven of the 20 animals died during hemorrhage and initial fluid resuscitation. All animals presented an increase in time-domain HRV measures during haemorrhage and fluid resuscitation restored baseline values. Although not significantly, normalized low-frequency and LF/HF ratio decreased during early stages of haemorrhage, recovering baseline values later during hemorrhagic shock, and increased after fluid resuscitation. Non-surviving animals presented significantly lower mean arterial pressure (43±7vs57±9 mmHg, P<0.05) and cardiac index (1.7±0.2vs2.6±0.5 L/min/m², P<0.05), and higher levels of plasma lactate (7.2±2.4vs3.7±1.4 mmol/L, P<0.05), base excess (-6.8±3.3vs-2.3±2.8 mmol/L, P<0.05) and potassium (5.3±0.6vs4.2±0.3 mmol/L, P<0.05) at 30 minutes after hemorrhagic shock compared with surviving animals.</p><p>Conclusions</p><p>The HRV increased early during hemorrhage but none of the evaluated HRV metrics was able to discriminate survivors from non-survivors during hemorrhagic shock. Moreover, metabolic and hemodynamic variables were more reliable to reflect hemorrhagic shock severity than HRV metrics.</p></div

Experimental protocol.

<p>Baseline: before hemorrhage; Hemorrhage15: at the end of blood withdrawal; Shock30: 30 minutes after the end of blood withdrawal; Shock60: 60 minutes after the end of blood withdrawal; R0: at the end of fluid resuscitation; R60: 60 minutes after the end of resuscitation; R120: 120 minutes after the end of resuscitation; R180: 180 minutes after the end of resuscitation.</p

HRV frequency-domain metrics during acute hemorrhagic shock and fluid resuscitation.

<p>VLF = spectral power at the very low frequency; LF = spectral power at the low frequency; HF = spectral power at the high frequency; LF/HF = low to high frequency index ratio; Hemo5 = 5 minutes hemorrhage; Hemo10 = 10 minutes hemorrhage; Hemo15 = 15 minutes hemorrhage; Shock30 = 30 min after hemorrhagic shock; Shock60 = 60 min after hemorrhagic shock; R0 = immediately after fluid resuscitation; R60 = 60 min after fluid resuscitation; R120 = 120 min after fluid resuscitation; R180 = 180 min after fluid resuscitation</p><p>* = P<0.05 different from Baseline</p><p>†<0,05 different from CH5 and CH10</p><p>§ <0,05 different from CH5, CH10 e CH15</p><p>A = P<0.05 group NS different from group S.</p><p>Mean ± SD.</p

Hemodynamic variables in pigs submitted to acute hemorrhagic shock and fluid resuscitation.

<p>S = survivor group. NS = non-survivor group; * = P<0.05 different from baseline; # = p<0.05 NS group different from the S group (t test).</p

Representative photomicrographs stained with hematoxylin and eosin from tracheal epithelial tissue obtained at the end of the experiment in the control (panel A) and CPB groups (panels B and C).

<p>Panel A show the presence normal ciliated epithelium in the control group. On the other hand, panels B and C show regions of epithelial cilia loss and submucosal neutrophil infiltration in the CPB group.</p

HRV time domain metrics in pigs submitted to acute hemorrhagic shock and fluid resuscitation.

<p>S = survivor group. NS = non-survivor group; * = P<0.05 different from baseline; # = p<0.05 NS group different from the S group (t test).</p

Morphometric characteristics of the studied animals.

<p>Legend: BSA—body surface area; ns—non-significant.</p><p>Mean ± SD.</p

Western blot analysis.

<p>The relative optical density of the pro-apoptotic protein Bax in the total protein extraction (A) and the neuronal nuclear (B) and mitochondrial (C) fractions from the cerebral frontal cortex of pigs in the sham, 10% hematocrit (Ht10%), 15% hematocrit (Ht15%) and hypoxia groups (n = 7 per group). β-Tubulin III was used as sample loading control. The representative bands of the Bax (23 kDa) and β-Tubulin III (50 kDa) of animals are illustrated. One-way analysis of variance (ANOVA) was applied to compare the groups. Data are presented as the means ± SEM. *p<0.05.</p

Activity in the cytosolic fraction of caspase 3 and 9 in the cytosolic fraction of the hippocampus (A, B) and the mitochondrial fraction from the cerebral frontal cortex (C, D) of pigs in the sham, 10% hematocrit (Ht10%), 15% hematocrit (Ht15%) and hypoxia groups (n = 7 per group).

<p>Data are presented as the means ± SEM. *p<0.05.</p