Determinants of myocardial performance after blunt chest trauma

Investigating Cyclooxygenase Inhibition in a Rat Pulmonary Contusion Model: A Laboratory Study Finding No Improvement with Ibuprofen

Minimal advances have been made in the management of pulmonary contusions (PCs). The purpose of this study was to evaluate the impact of cyclooxygenase inhibition on outcomes following PC in a rat model. PC was induced in anesthetized adult rats. Ibuprofen was given to the treatment group (TG) and water was given to the control group (CG). Lung injury was assessed with pulse oximetry, arterial blood gases, CT, and histopathologic examination. Inflammation was measured with both serum and bronchoalveolar lavage (BAL) levels of tumor necrosis factor a and interleukin-6. Rats in the TG did not differ from rats in the CG with respect to oxygenation. Pathologic examination demonstrated a trend toward more inflammatory infiltrate in the CG, yet the sizes of the contusions were larger in the TG. The CG trended toward decreased levels of interleukin-6 in the serum and BAL at both three and seven days. While BAL levels of tumor necrosis factor a were increased in the TG at three days compared to the CG, they trended toward a reduced amount at seven days. Our data do not support cyclooxygenase inhibition for treatment to decrease the respiratory compromise associated with PC in this model of rat PCs.

Characterization of blunt chest trauma in a long-term porcine model of severe multiple trauma

Chest trauma has a significant relevance on outcome after severe trauma. Clinically, impaired lung function typically occurs within 72 hours after trauma. However, the underlying pathophysiological mechanisms are still not fully elucidated. Therefore, we aimed to establish an experimental long-term model to investigate physiological, morphologic and inflammatory changes, after severe trauma. Male pigs (sus scrofa) sustained severe trauma (including unilateral chest trauma, femur fracture, liver laceration and hemorrhagic shock). Additionally, non-injured animals served as sham controls. Chest trauma resulted in severe lung damage on both CT and histological analyses. Furthermore, severe inflammation with a systemic increase of IL-6 (p = 0.0305) and a local increase of IL-8 in BAL (p = 0.0009) was observed. The pO₂/FiO₂ ratio in trauma animals decreased over the observation period (p < 0.0001) but not in the sham group (p = 0.2967). Electrical Impedance Tomography (EIT) revealed differences between the traumatized and healthy lung (p < 0.0001). In conclusion, a clinically relevant, long-term model of blunt chest trauma with concomitant injuries has been developed. This reproducible model allows to examine local and systemic consequences of trauma and is valid for investigation of potential diagnostic or therapeutic options. In this context, EIT might represent a radiation-free method for bedside diagnostics.

Dobutamine stress echocardiography assessment of myocardial contusion due to blunt impact in dogs

We sought to investigate the role of two-dimensional stress echocardiography in the early assessment of myocardial contusion. For this purpose, 12 dogs, weighing 11.36 ± 1.50 kg, were selected and the myocardial contusion was experimentally induced. Two-dimensional dobutamine stress echocardiography (DSE) was used to detect abnormal myocardial motions segments at time phases of baseline and 0.5, 2, 4, and 8 h post-wounding. Finally, the above results were compared with pathological findings. The data show that after the dogs were induced to have severe myocardial contusion, 122 segments were found with abnormal myocardial wall motions at 0.5 h post-wounding, 133 segments at 2 h post-wounding, and 142 segments, each, at 4 h and 8 h post-wounding. The wall motion score (WMS) and wall motion score index (WMSI) increased (P < 0.001) as compared with the pre-impaction values. Considering the left ventricular axis view as the standard section, in the 60 segments examined by echocardiography, 54 segments were found to have wall motion abnormalities. Comparing with the results of pathological TTC staining, the sensitivity and specificity were found to be 100 and 66.6%, respectively. It was, therefore, concluded that two-dimensional DSE was a valuable technique in the early diagnosis of myocardial contusion due to its better sensitivity and specificity.

New measures of heart-rate complexity: effect of chest trauma and hemorrhage

BACKGROUND

Traditional vital signs such as heart rate, blood pressure, and oxygen saturation are not ideal for timely and accurate assessment of physiologic status after trauma (TR) and hemorrhagic shock (HS). Analysis of the complex beat-to-beat variability present in the heart-rate time series has been proposed as a "new vital sign" in this setting. We determined the effect of chest TR and HS on heart-rate complexity (HRC) in a porcine model.

METHODS

Anesthetized swine in group II (n = 20) underwent blunt right chest TR with a modified captive-bolt stunner; then, 10 minutes later, hemorrhage of 12 mL/kg over 10 minutes, followed by resuscitation with lactated Ringer's solution, and reinfusion of blood. Group I (n = 15) served as time controls. Two hundred beat sections of EKG waveforms were analyzed at 7 time points: at baseline, after TR, immediately after hemorrhage (HS), and 1 hour, 2 hours, 4 hours, and 5 hours after HS. Several computationally different measures of HRC were calculated, including sample entropy, similarity of distribution, and point correlation dimension.

RESULTS

HRC was decreased after TR, HS, and at 1 hour, manifested by decreased sample entropy and point correlation dimension and increased similarity of distribution. These HRC measures were all restored by resuscitation.

CONCLUSIONS

Several independent measures demonstrated decreased HRC after combined TR/HS and restored HRC with resuscitation. Complexity analysis may be useful for diagnosis of TR/HS and for monitoring resuscitation.

Cardiac Troponin I as a Predictor of Arrhythmia and Ventricular Dysfunction in Trauma Patients With Myocardial Contusion

BACKGROUND

Myocardial contusion during blunt chest trauma is common and may lead to potentially fatal cardiac complications. Therefore, it is useful to identify a serum marker reflecting the myocardial damage that can predict risk for cardiac complications. In this study, the authors determined the strength of the association between cardiac troponin I (cTnI) levels and the risk of arrhythmia or the development of left ventricular dysfunction in a cohort of patients with blunt chest trauma.

METHODS AND RESULTS

In 187 multiply injured patients with blunt chest trauma, serial measurements of cTnI, total creatine kinase (CK), and isoenzyme of creatine kinase with muscle and brain subunits (CK-MB) were combined with sequential electrocardigraphic and echocardiographic recordings. The results showed that 63 patients (34%) had myocardial contusion, as defined by positive cTnI levels, of which 47 (25%) were symptomatic and 16 (9%) showed no abnormalities. The remaining 124 patients (66%) displaying negative CTnI levels were asymptomatic during the entire study. Severity of arrhythmia correlated directly with increase in cTnI levels. The levels of cTnI in the symptomatic group remained elevated significantly longer than the levels in the asymptomatic group. The depression of left ventricular ejection fraction was inversely correlated with the increase in cTn levels. The patients whose cTnI levels were below 1.05 microg/L at admission and during the first 6 hours afterward showed no cardiac abnormalities throughout the entire study period

CONCLUSIONS

Levels of cTnI below 1.05 microg/L in asymptomatic patients at admission and within the first 6 hours after admission rule out myocardial injury, whereas positive cTn levels above 1.05 microg/L mandate further cardiologic workup for the detection and management of myocardial injury. Furthermore, the dynamics and peak levels of pathologic cTnI levels allow estimation of arrhythmia risk and left ventricular dysfunction in trauma patients with myocardial contusion.

Predictors of Patients Who Will Develop Prolonged Occult Hypoperfusion following Blunt Trauma

BACKGROUND

Prolonged occult hypoperfusion or POH (serum lactate >2.4 mmol/L persisting >12 hours from admission) represents a reversible risk factor for adverse outcomes following traumatic injury. We hypothesized that patients at increased risk for POH could be identified at the time of admission.

METHODS

Prospective data from adult trauma admissions between January 1, 1998 and December 31, 2000 were analyzed. Potential risk factors for POH were determined by univariate analysis (p < or =0.10= significant). Significant factors were tested in a logistic regression model (LR) (p < or =0.05= significant). The predictive ability of the LR was tested by receiver operating curve (ROC) analysis (p < or =0.05= significant).

RESULTS

Three hundred seventy-eight patients were analyzed, 129 with POH. Injury Severity Score (ISS), emergency department Glasgow Coma Scale score, hypotension, and the individual Abbreviated Injury Scale score (AIS) for Head (H), Abdominal/Pelvic Viscera (A) and Pelvis/Bony Extremity (P) were significantly associated with POH. LR demonstrated that ISS, A-AIS > or =3 and P-AIS > or =3 were independent predictors of POH (p <0.05). ROC analysis of the LR equation was statistically significant (Area=0.69, p <0.001).

CONCLUSIONS

We identified factors at admission that placed patients at higher risk for developing POH. Select patients may benefit from rapid, aggressive monitoring and resuscitation, possibly preventing POH and its associated morbidity and mortality.

Novel resuscitation strategy for pulmonary contusion after severe chest trauma

BACKGROUND

Adenosine A2a receptor stimulation can increase coronary perfusion and also reduce leukocyte-mediated inflammatory responses in some conditions. Hextend is a novel colloid solution that may have antioxidant properties. All these actions might be beneficial after severe chest trauma, but have never been investigated. To fill these gaps, this study evaluated the therapeutic potential of a novel adenosine A2a agonist during fluid resuscitation from severe chest trauma with either standard-of-care crystalloid or Hextend.

METHODS

Anesthetized, ventilated swine received unilateral, blunt trauma to the right chest via captive bolt gun, followed by a 10- to 12-mL/kg arterial hemorrhage. After 25 minutes of shock, ATL-146e was started (10 ng/kg/min intravenously for 180 minutes). After an additional 5 minutes, the minimum amount of either colloid (Hextend, 5% hetastarch in lactate-buffered, balanced electrolyte solution) or crystalloid (lactated Ringer's [LR] solution) was administered to maintain mean arterial pressure > 70 mm Hg and heart rate < 100 beats/min and to correct lactate for 180 minutes postinjury. Cardiopulmonary function was monitored and serial bronchoalveolar lavage samples were analyzed for protein, leukocyte infiltration, and expression of cyclooxygenase (COX)-1 and COX-2 isozymes as markers of the inflammatory cascade.

RESULTS

Fluid requirements were reduced by half with Hextend compared with LR (p < 0.05). ATL-146e in either Hextend or LR transiently increased cardiac output, cardiac contractility, and systemic oxygen delivery (all p < 0.05). Pao(2)/Fio(2) ratio was 50 to 100 higher and bronchoalveolar lavage leukocytes were reduced by half with Hextend versus LR (both p < 0.05), but there was no added effect of ATL-146e. COX-1 expression was induced in macrophages (Mphis), whereas COX-2 was induced in neutrophils. Neither Hextend nor ATL-146e reduced COX expression.

CONCLUSION

Hextend reduced the volume for initial resuscitation, which may offer logistical advantages in prehospital field conditions or whenever there is limited medical resources or prolonged transport times; ATL-146e improved early cardiac performance without causing hypotension or bradycardia; when administered 25 to 30 minutes after injury, neither Hextend nor ATL-146e altered inflammatory changes in pulmonary Mphis or infiltrating PMNs; and further studies are needed to determine whether these short-term benefits correlate with long-term outcome.

Pathophysiological responses following phosgene exposure in the anaesthetized pig

This study aimed to develop a reproducible model of phosgene-induced lung injury in the pig to facilitate the future development of therapeutic strategies. Ten female young adult large white pigs were used. Following induction of anaesthesia using a halothane/oxygen/nitrous oxide mixture, arterial and venous catheters were inserted together with a pulmonary artery thermodilution catheter, and a suprapubic urinary catheter by laparotomy. Anaesthesia was maintained throughout the experiment by intravenous infusion of ketamine, midazolam and alfentanil. On completion of surgery the animals were allowed to equilibrate for 1 h and then were divided into two groups. Group 1 (n = 5) was exposed to phosgene for 10 min (mean Ct = 2443 +/- 35 mg min m(-3)) while spontaneously breathing, whereas control animals (Group 2 n = 5) were exposed to air. At 30 min post-exposure, anaesthesia was deepened in order to allow the initiation of intermittent positive pressure ventilation and the animals were monitored for up to 24 h. Cardiovascular and respiratory parameters were monitored every 30 min and blood samples were taken for arterial and mixed venous blood gas analysis and clinical chemistry. A detailed post-mortem and histopathology was carried out on all animals following death or euthanasia at the end of the 24-h monitoring period. Control animals (Group 2) all survived until the end of the 24-h monitoring period with normal pathophysiological parameters. Histopathology showed only minimal passive congestion of the lung. Following exposure to phosgene (Group 1) there was one survivor to 24 h, with the remainder dying between 16.5 and 23 h (mean = 20 h). Histopathology from these animals showed areas of widespread pulmonary oedema, petechial haemorrhage and bronchial epithelial necrosis. There was also a significant increase in lung wet weight/body weight ratio (P < 0.001). During and immediately following exposure, a transient decrease in oxygen saturation and stroke volume index was observed. From 6 h there were significant decreases in arterial pH (P < 0.01), P(a)O(2) (P < 0.01) and lung compliance (P < 0.01), whereas oxygen delivery and consumption was reduced from 15 h onwards in phosgene-exposed animals. Mean pulmonary artery pressure of phosgene-exposed animals was increased from 15 h post-exposure, with periods of increased pulmonary vascular resistance index being recorded from 9 h onwards. We have developed a reproducible model of phosgene-induced lung injury in the anaesthetized pig. We have followed changes in cardiovascular and pulmonary dynamics for up to 24 h after exposure in order to demonstrate evidence of primary acute lung injury from 16 h post-exposure. Histopathology showed evidence of widespread damage to the lung and there was also a significant increase in lung wet weight/body weight ratio (P < 0.001).

Pathophysiology of Thoracic Trauma

The major pathophysiologic mechanisms of thoracic trauma will be discussed. In the chest, anatomy and physiology are inextricably linked. The normal functions of the thoracic organs depend on normal anatomic compartmentation. When these compartments are either openedto atmospheric pressure or filled with fluids, normal physiologicmechanisms are interrupted. An injury to one thoracic organ alters the function of the other. Anesthesiologists must understand these interactions to provide proper care for the patient with cardiotho-racic trauma.

Reversible myocardial dysfunction in critically ill, noncardiac patients: a review

OBJECTIVE

To review reversible myocardial dysfunction affecting critically ill patients without cardiac pathology.

DATA SOURCES

The bibliography for the study was compiled through a search of different databases for the period 1966-2001. References cited in the selected articles also were reviewed.

STUDY SELECTION

The selection criteria included all articles published on reversible myocardial dysfunction in critically ill patients.

CONCLUSIONS

Reversible myocardial dysfunction may develop in a situation of critical pathology, but the etiology of reversible myocardial dysfunction is not fully understood. This dysfunction may be accompanied by increases in enzyme concentrations and electrocardiographic changes. Reversible myocardial dysfunction probably is underdiagnosed, although its presence is associated with a worsening of the prognosis and with more specific therapeutic options. Further studies are necessary to define its true incidence and clinical implications.

Myocardial contusion: emergency investigation and diagnosis

Cardiac contusion is an infrequent but occasionally serious complication of deceleration injury. According to ATLS teaching, the true diagnosis of contusion can only be established by direct inspection of the myocardium. The clinically important sequelae of myocardial contusion are hypotension and arrhythmia. Despite recent advances in investigative techniques, myocardial trauma remains an important diagnostic and management challenge. This paper presents an evidence-based review of the topic.

Macrophage cyclooxygenase expression, immunosuppression, and cardiopulmonary dysfunction after blunt chest trauma

BACKGROUND

Two series of experiments were performed in swine who received severe blunt chest trauma. The goals were to determine the time course of constitutive and inducible cyclooxygenase (COX) isozyme expression in pulmonary macrophages (Mphis), and to determine whether COX expression and cardiopulmonary dysfunction were altered when neutrophils (PMNs) were pharmacologically depleted with cyclophosphamide (CYC).

METHODS

In series 1 (n = 17), anesthetized, mechanically ventilated swine were subjected to right chest trauma via captive bolt gun, hemorrhage, and a 60-minute shock period. In series 2 (n = 41), CYC (50 mg/kg intravenously) was administered 4 days before trauma, and the shock period was shortened to 30 minutes. In both series, hemodynamic support and supplemental oxygen were provided for an additional 60 to 90 minutes after shock. Mphis were isolated from serial bilateral bronchoalveolar lavages (BALs) and COX protein expression was measured with Western blots.

RESULTS

In series 1, death occurred in 11 of 17. In survivors, Mphi COX-1 peaked at > 100 times baseline in both right BAL and left BAL by 60 minutes (before resuscitation). Changes in Mphi COX-2 were minimal. In series 2, before trauma, CYC (n = 16) reduced circulating and BAL PMNs by > 90% relative to control (n = 25, both p < 0.05) with no complicating side effects. After trauma, death occurred in 11 of 25 controls versus 9 of 16 with CYC. In survivors, PaO2/FIO2 was < 250 and PaCO2 was 25% higher on constant minute ventilation, indicating mismatched ventilation/perfusion; both changes were reduced with CYC (p < 0.05). In controls, bilateral histologic damage included edema, alveolar hemorrhage, and interstitial infiltrates. These changes were reduced by one third with CYC (p = 0.08). Trauma-induced changes in BAL protein, BAL elastase, or Mphi COX expression were not lessened by CYC.

CONCLUSION

After unilateral chest trauma, Mphi COX-1, not COX-2, is induced bilaterally and before fluid resuscitation; CYC prevented PMN infiltration and attenuated structural and functional changes after resuscitation, which suggests that PMNs have a role in the pathogenic mechanism of secondary lung injury; Mphi COX expression and other injury markers were not altered by CYC; and since Mphis continued to express proinflammatory COX protein even after pretreatment with a powerful nonspecific immunosuppressant, and since there is residual alveolar capillary damage even in the absence of PMNs, it is logical to conclude that no single cell type or mediator is a practical therapeutic target and that novel resuscitation strategies must address multiple elements in the inflammatory cascade.

Endogenous adenosine and secondary injury after chest trauma

BACKGROUND

No previous studies have examined actions of adenosine or related compounds after blunt chest trauma, but we have shown that the prototype adenosine-regulating agent, acadesine (aminoimidazole carboxamide ribonucleotide [AICAR]), has multiple favorable anti-inflammatory actions after other forms of trauma, ischemia, hemorrhage, and sepsis; and that a progressive inflammatory response in the contralateral (uninjured) lung after unilateral blunt chest trauma is caused (in part) by activation and sequestration of circulating leukocytes (white blood cells [WBCs]). Thus, we hypothesized that AICAR would ameliorate WBC-dependent, secondary pathophysiologic changes after blunt chest trauma.

METHODS

Mongrel pigs (28+/-1 kg, n = 21) were anesthetized, mechanically ventilated, and injured on the right chest (pulmonary contusion) with a captive bolt gun. Either AICAR (1 mg/kg + 0.2 mg/kg/min) or its saline vehicle were administered for a 12-hour period, beginning 15 minutes before injury.

RESULTS

Injury caused a three- to fourfold increase in bronchoalveolar lavage (BAL) WBC counts, 10- to 20-fold increases in BAL protein, and 200% increases in lung edema as measured by wet-dry ratio (all p < 0.05), in both the injured (right) and the noninjured (left) lungs. With AICAR versus saline, BAL WBC counts, lung myeloperoxidase levels, and systemic hemodynamics were similar. However, the increases in BAL protein were attenuated by 30% to 50% (p < 0.14, NS) and edema was reduced (p < 0.05) in both lungs. Furthermore, oxygenation, hypercapnia, acidosis (all p < 0.05), and survival were improved (9 of 10 vs. 4 of 11, p < 0.04).

CONCLUSION

Pretreatment with AICAR before experimental pulmonary contusion ameliorates the trauma-induced destruction of the alveolar capillary membrane, and attenuates the delayed secondary injury in the contralateral uninjured lung, by a mechanism that may be independent of leukocytes. Endogenous adenosine could have a role in the pathophysiologic response after blunt chest injury, with potential sites of action including the endothelium and alveolar macrophage. Adenosine-regulating agents may have therapeutic potential after blunt chest injury, but further studies are needed in clinically relevant models, with administration begun at the time of resuscitation.

Resuscitation of severe chest trauma with four different hemoglobin-based oxygen-carrying solutions

BACKGROUND

The purpose of this study was to test whether polynitroxylation (PN) improved the therapeutic profile of hemoglobin-based oxygen-carrying compounds (HBOCs) that were unpolymerized (alphaalphaHb) or 70% polymerized (polyHb) in a clinically relevant model that combines pulmonary injury and reperfusion. To our knowledge, four different HBOC formulations have never been compared in the same trauma model.

METHODS

Anesthetized, ventilated swine (n = 45) received a unilateral lung contusion + 25% hemorrhage. After 60 minutes, 250 mL of either PNalphaalphaHb (n = 5), alphaalphaHb (n = 10), PNpolyHb (n = 6), polyHb (n = 5), or normal saline (NaCl, n = 10) was administered for 20 minutes, followed by standard crystalloid resuscitation for 30 minutes, and supplemental crystalloid as required for 6 hours to maintain heart rate <100 beats/min and mean arterial pressure >70 mm Hg.

RESULTS

Nine of 45 deaths occurred before resuscitation. Survival time was 395 minutes with NaCl versus 303 minutes with alphaalphaHb (p = 0.03) or 238 minutes with PNalphaalphaHb (p = 0.04). With both polymerized HBOCs, survival was 480 minutes (polyHb vs. alphaalphaHb, p = 0.005; PNpolyHb vs. PNalphaalphaHb, p = 0.006). All HBOCs were pressors (all p < 0.05) and all reduced the supplemental fluid required to maintain systemic hemodynamics during resuscitation (all p < 0.05). By 90 minutes postresuscitation, cardiac index was 112% of baseline with NaCl (p < 0.02), but was 78% with alphaalphaHb (p = not significant), 63% with PNalphaalphaHb (p < 0.01), 79% with PNpolyHb (p < 0.01), and 67% with polyHb p < 0.02). Relative to NaCI, no HBOC altered trauma-induced neutrophilia, thrombocytopenia, or the trauma-induced increases in bronchoalveolar lavage protein or bronchoalveolar lavage neutrophils.

CONCLUSION

After resuscitation from chest trauma, we observed the following: (1) all HBOCs reduced fluid requirements and increased right and left ventricular afterload versus NaCl, which further compromised an already marginal cardiac performance; (2) mortality was less with polyHbs relative to alphaalphaHb, but the pressor action was unchanged; (3) the pressor action was less with polynitroxylated compounds relative to the unmodified HBOC, but this chemical modification had no effect on mortality; and (4) the pressor action of HBOCs must be attenuated by strategies other than polymerization or polynitroxylation for these compounds to be safe, effective resuscitants in humans.

Prostanoids: early mediators in the secondary injury that develops after unilateral pulmonary contusion

BACKGROUND

We have previously shown a sequence of events after unilateral pulmonary contusion that suggests the release of blood-borne prostanoid mediators and that culminates in refractory bilateral pulmonary failure.

PURPOSE

To determine the role of platelet-derived thromboxane and endothelial-derived prostacyclin in the primary and secondary injury after unilateral blunt chest trauma, and to determine whether pretreatment with the cyclooxygenase inhibitor indomethacin alters the progression of secondary injury.

METHODS

Anesthetized, ventilated (FIO2 = 0.50) pigs received a unilateral, blunt injury to the right thorax (n = 20) or sham injury (n = 5) and were monitored for 24 hours. Either indomethacin (5 mg/kg i.v.; n = 10) or its saline vehicle (n = 10) were administered 15 minutes before injury. Serial bronchoalveolar lavages of each lung were analyzed for protein and neutrophil (polymorphonuclear neutrophil (PMN)) content.

RESULTS

Contusion caused profound hypoxemia; PaO2 partially recovered within 1 hour of injury to 50% of baseline. Thereafter, worsening hypoxemia required positive end-expiratory pressure. With indomethacin compared with vehicle, PaO2 was higher at any given level of positive end-expiratory pressure (p < 0.05). There was an early increase in serial bronchoalveolar lavage protein on the injured side (peak at 2 hours), with a delayed pulmonary capillary leak on the contralateral side (peak at 6 hours), which correlated with increasing PMN infiltration; this was reduced by 40 to 60% with indomethacin (p < 0.05). Thromboxane peaked within 1 hour after contusion at 800% baseline, then fell off rapidly. This peak preceded the maximal increase in permeability and was completely blocked by indomethacin. Prostacyclin slowly rose to 300% baseline by 3 hours and remained elevated; this change was blocked by indomethacin for 18 hours.

CONCLUSIONS

Contusion of the right thorax induced a delayed pulmonary capillary leak in the left lung, which reflects a progressive secondary inflammatory response. Elevations in thromboxane and prostacyclin preceded progressive bilateral PMN infiltration. Indomethacin blocked thromboxane and prostacyclin and attenuated, but did not prevent, the progression to pulmonary failure. Overall, these data suggest that prostanoids are released soon after unilateral contusion and initiate an inflammatory response in both lungs that is sustained by PMN infiltration.