Revision arthroscopic partial meniscectomy of the knee. A retrospective review

The aim in this study was to find out if there were any revision operations in patients who underwent an arthroscopic partial meniscectomy and we attempted to identify the factor(s) that may be associated with the need for that revision. We reviewed 1,603 patients who underwent an arthroscopic partial meniscectomy, and 16 cases of revision were identified (rate 1%). Nine factors were analysed: age, sex, affected knee, affected meniscus, private or National Health Service (NHS) patient, symptoms prior to the most recent meniscectomy, type of tear, history of re-injury and the progression of Outerbridge changes to the articular surfaces. There was a significant risk for a revision meniscectomy in patients with horizontal/partial thickness tears compared to flap tears. No additional factor analysed was significantly associated with a revision procedure.

Heliox improves gas exchange during high-frequency ventilation in a pediatric model of acute lung injury

Because heliox has a lower density as compared with air, we postulated that heliox would improve gas exchange during high-frequency oscillatory ventilation (HFOV) in a model of acute lung injury. In a prospective, cross-over trial, we studied 11 piglets with acute lung injury created by saline lavage. With initial conditions of permissive hypercapnia (Pa(CO(2)) 55-80 mm Hg), each piglet underwent HFOV with a fixed mean airway pressure, pressure oscillation, and ventilatory frequency. The following gas mixtures were used: oxygen-enriched air (60% O(2)/40% N(2)) and heliox (60% O(2)/ 40% He and 40% O(2)/60% He). Compared with oxygen-enriched air, the 40% and 60% helium gas mixtures reduced Pa(CO(2)) by an average of 10.5 and 20.3 mm Hg, respectively. A modest improvement in oxygenation was seen with the 40% helium mixture. We conclude that heliox significantly improves carbon dioxide elimination and modestly improves oxygenation during HFOV in a model of acute lung injury. On the basis of test lung data and plethysmography measurements, we also conclude that heliox improves carbon dioxide elimination primarily through increased tidal volume delivery. Although heliox improved gas exchange during HFOV in our model, increased tidal volume delivery may limit clinical applicability.

Liquid lung ventilation reduces neutrophil sequestration in a neonatal swine model of cardiopulmonary bypass

OBJECTIVE

Liquid lung ventilation has been demonstrated to improve cardiorespiratory function after cardiopulmonary bypass. We hypothesized that liquid lung ventilation (LLV) would decrease the pulmonary inflammatory response after cardiopulmonary bypass (CPB).

DESIGN

Prospective, randomized, experimental, controlled, nonblinded study.

SETTING

Animal research laboratory at a university setting.

SUBJECTS

A total of 24 neonatal piglets.

INTERVENTIONS

After intubation with a cuffed endotracheal tube, swine were conventionally ventilated. After surgical cannulation, each piglet was placed on conventional nonpulsatile CPB and cooled to 18 degrees C (64.4 degrees F). Subsequently, the animals were exposed to 90 mins of low-flow CPB (35 mL/kg/min). Animals were rewarmed to 37 degrees C (98.6 degrees F), removed from CPB, and ventilated for 90 min. Ten animals received conventional gas ventilation only (control), seven received initiation of LLV before CPB (prevention), and seven received initiation of LLV during the rewarming phase of CPB (treatment). After the animals were killed, the lungs were removed en bloc. The left lobe was dissected and formalin-fixed at 20 cm H2O overnight, followed by paraffin embedding. Sections were taken from the paraffin-embedded lungs. Neutrophil accumulation and lung injury were assessed by histochemical staining with leukocyte esterase and morphometrics, respectively. One hundred microscopic images were digitized from each tissue sample for lung morphometrics, and neutrophil counts were obtained from every fifth image.

MEASUREMENTS AND MAIN RESULTS

Lung tissue sections showed a significantly lower number of neutrophils per alveolar area in the prevention and treatment groups than in the control group (control 681 +/- 65, prevention 380 +/- 49, treatment 412 +/- 101 neutrophils per alveolar area [cells/mm2]; p <.05 for both prevention and treatment compared with control). There were no differences in lung injury as assessed with morphometrics or hemodynamic measurements between any of the three groups.

CONCLUSIONS

The data suggest that LLV reduces the CPB-induced neutrophil sequestration in the pulmonary parenchyma independent of its effects on the circulatory physiology or evidence of early lung injury.

Factors predictive of adolescents' intentions to use birth control pills, condoms, and birth control pills in combination with condoms

Using the Theory of Planned Behaviour (Ajzen, 1988) as a conceptual framework, 705 secondary school students were surveyed to identify their intentions to use birth control pills, condoms, and birth control pills in combination with condoms. Hierarchical multiple regression revealed that the theory explained between 23.5% and 45.8% of the variance in intentions. Variables external to the model such as past use, age, and ethnicity exhibited some independent effects. Attitudes were consistently predictive of intentions to use condoms, pills, and condoms in combination with pills for both male and female students. However, there were differences by gender in the degree to which subjective norms and perceived behavioural control predicted intentions. The findings suggest that programs should focus on: creation of positive attitudes regarding birth control pills and condoms; targeting important social influences, particularly regarding males' use of condoms; and developing strategies to increase students' control over the use of condoms.

Right ventricular injury in young swine: effects of catecholamines on right ventricular function and pulmonary vascular mechanics

Acute right ventricular (RV) injury is commonly encountered in infants and children after cardiac surgery. Empiric medical therapy for these patients results from a paucity of data on which to base medical management and the absence of animal models that allow rigorous laboratory testing. Specifically, exogenous catecholamines have unclear effects on the injured right ventricle and pulmonary vasculature in the young. Ten anesthetized piglets (9-12 kg) were instrumented with epicardial transducers, micromanometers, and a pulmonary artery flow probe. RV injury was induced with a cryoablation probe. Dopamine at 10 microg/kg/min, dobutamine at 10 microg/kg/min, and epinephrine (EP) at 0.1 microg/kg/min were infused in a random order. RV contractility was evaluated using preload recruitable stroke work. Diastolic function was described by the end-diastolic pressure-volume relation, peak negative derivative of the pressure waveform, and peak filling rate. In addition to routine hemodynamic measurements, Fourier transformation of the pressure and flow waveforms allowed calculation of input resistance, characteristic impedance, RV total hydraulic power, and transpulmonary vascular efficiency. Cryoablation led to a stable reproducible injury, decreased preload recruitable stroke work, and impaired diastolic function as measured by all three indices. Infusion of each catecholamine improved preload recruitable stroke work and peak negative derivative of the pressure waveform. Dobutamine and EP both decreased indices of pulmonary vascular impedance, whereas EP was the only inotrope that significantly improved transpulmonary vascular efficiency. Although all three inotropes improved systolic and diastolic RV function, only EP decreased input resistance, decreased pulmonary vascular resistance, and increased transpulmonary vascular efficiency.

Factors predictive of adolescents' intentions to use birth control pills, condoms, and birth control pills in combination with condoms

Using the Theory of Planned Behaviour (Ajzen, 1988) as a conceptual framework, 705 secondary school students were surveyed to identify their intentions to use birth control pills, condoms, and birth control pills in combination with condoms. Hierarchical multiple regression revealed that the theory explained between 23.5% and 45.8% of the variance in intentions. Variables external to the model such as past use, age, and ethnicity exhibited some independent effects. Attitudes were consistently predictive of intentions to use condoms, pills, and condoms in combination with pills for both male and female students. However, there were differences by gender in the degree to which subjective norms and perceived behavioural control predicted intentions. The findings suggest that programs should focus on: creation of positive attitudes regarding birth control pills and condoms; targeting important social influences, particularly regarding males' use of condoms; and developing strategies to increase students' control over the use of condoms.

Deadspace to tidal volume ratio predicts successful extubation in infants and children

OBJECTIVE

Using a modification of the Bohr equation, single-breath carbon dioxide capnography is a noninvasive technology for calculating physiologic dead space (V(D)/V(T)). The objective of this study was to identify a minimal V(D)/V(T) value for predicting successful extubation from mechanical ventilation in pediatric patients.

DESIGN

Prospective, blinded, clinical study.

SETTING

Medical and surgical pediatric intensive care unit of a university hospital.

PATIENTS

Intubated children ranging in age from 1 wk to 18 yrs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Forty-five patients were identified by the pediatric intensive care unit clinical team as meeting criteria for extubation. Thirty minutes before the planned extubation, each patient was begun on pressure support ventilation set to deliver an exhaled tidal volume of 6 mL/kg. After 20 mins on pressure support ventilation, an arterial blood gas was obtained, V(D)/V(T) was calculated, and the patient was extubated. Over the next 48 hrs, the clinical team managed the patient without knowledge of the preextubation V(D)/V(T) value. Of the 45 patients studied, 25 had V(D)/V(T) < or =0.50. Of these patients, 24 of 25 (96%) were successfully extubated without needing additional ventilatory support. In an intermediate group of patients with V(D)/V(T) between 0.50 and 0.65, six of ten patients (60%) successfully extubated from mechanical ventilation. However, only two of ten patients (20%) with a V(D)/V(T) > or =0.65 were successfully extubated. Logistic regression analysis revealed a significant association between lower V(D)/V(T) and successful extubation.

CONCLUSIONS

A V(D)/V(T) < or =0.50 reliably predicts successful extubation, whereas a V(D)/V(T) >0.65 identifies patients at risk for respiratory failure following extubation. There appears to be an intermediate V(D)/V(T) range (0.51-0.65) that is less predictive of successful extubation. Routine V(D)/V(T) monitoring of pediatric patients may permit earlier extubation and reduce unexpected extubation failures.

Soluble complement receptor-1 protects heart, lung, and cardiac myofilament function from cardiopulmonary bypass damage

BACKGROUND

Host defense system activation occurs with cardiopulmonary bypass (CPB) and is thought to contribute to the pathophysiological consequences of CPB. Complement inhibition effects on the post-CPB syndrome were tested with soluble complement receptor-1 (sCR1).

METHODS AND RESULTS

Twenty neonatal pigs (weight 1.8 to 2.8 kg) were randomized to control and sCR1-treated groups. LV pressure and volume, left atrial pressure, pulmonary artery pressure and flow, and respiratory system compliance and resistance were measured. Preload recruitable stroke work, isovolumic diastolic relaxation time constant (tau), and pulmonary vascular resistance were determined. Pre-CPB measures were not statistically significantly different between the 2 groups. After CPB, preload recruitable stroke work was significantly higher in the sCR1 group (n=5, 46.8+/-3.2x10(3) vs n=6, 34.3+/-3.7x10(3) erg/cm(3), P=0.042); tau was significantly lower in the sCR1 group (26.4+/-1.5, 42.4+/-6. 6 ms, P=0.003); pulmonary vascular resistance was significantly lower in the sCR1 group (5860+/-1360 vs 12 170+/-1200 dyn. s/cm(5), P=0.009); arterial PO(2) in 100% FIO(2) was significantly higher in the sCR1 group (406+/-63 vs 148+/-33 mm Hg, P=0.01); lung compliance and airway resistance did not differ significantly. The post-CPB Hill coefficient of atrial myocardium was higher in the sCR1 group (2.88+/-0.29 vs 1.88+/-0.16, P=0.023).

CONCLUSIONS

sCR1 meaningfully moderates the post-CPB syndrome, supporting the hypothesis that complement activation contributes to this syndrome.

Optimizing liquid ventilation as a lung protection strategy for neonatal cardiopulmonary bypass: full functional residual capacity dosing is more effective than half functional residual capacity dosing

OBJECTIVE

To evaluate and compare the protective effects of two different perflubron doses on hemodynamics and lung function in a neonatal animal model of cardiopulmonary bypass-induced lung injury.

DESIGN

Prospective, randomized, controlled study.

SETTING

Animal laboratory of the Department of Surgery, Duke University Medical Center.

SUBJECTS

Twenty-one neonatal swine.

INTERVENTIONS

One-wk-old swine (2.2-3.2 kg) were randomized to receive cardiopulmonary bypass with full functional residual capacity perflubron (n = 7), cardiopulmonary bypass with half functional residual capacity perflubron (n = 7), or cardiopulmonary bypass alone (n = 7). This last group served as control animals, receiving cardiopulmonary bypass with conventional ventilation. Liquid lung ventilation animals received perflubron via the endotracheal tube at either full functional residual capacity (16-20 mL/kg) or half functional residual capacity (10 mL/kg) before the initiation of cardiopulmonary bypass. Each animal was placed on nonpulsatile cardiopulmonary bypass and cooled to a nasopharyngeal temperature of 18 degrees C (64.4 degrees F). Low-flow cardiopulmonary bypass (35 mL/kg/min) was instituted for 90 mins. The blood flow rate was then returned to 100 mL/kg/min. The animals were warmed to 36 degrees C (96.8 degrees F) and separated from cardiopulmonary bypass. Data were obtained at 30, 60, and 90 mins after separation from cardiopulmonary bypass.

MEASUREMENTS AND MAIN RESULTS

Cardiopulmonary bypass without liquid lung ventilation resulted in a significant decrease in cardiac output and oxygen delivery and a significant increase in pulmonary vascular resistance in the post-bypass period. Full functional residual capacity liquid lung ventilation administered before bypass resulted in no change in cardiac output and oxygen delivery after bypass. Full functional residual capacity liquid lung ventilation resulted in lower pulmonary vascular resistance after bypass compared with both control and half functional residual capacity liquid lung ventilation animals.

CONCLUSIONS

These data suggest that liquid lung ventilation dosing at full functional residual capacity before bypass is more effective than half functional residual capacity in minimizing the lung injury associated with neonatal cardiopulmonary bypass. Full functional residual capacity dosing may optimize alveolar distention and lung volume, as well as improve oxygen delivery compared with half functional residual capacity dosing.

Pharmacological strategies for improving diastolic dysfunction in the setting of chronic pulmonary hypertension

BACKGROUND

Right ventricular (RV) hypertrophy is an adaptive process that occurs in the setting of chronic pulmonary hypertension (CPH) and can lead to alterations in normal RV diastolic properties. This study was designed to investigate the effects of NO and milrinone on RV diastolic dysfunction in the setting of CPH and RV hypertrophy by use of a canine model of monocrotaline pyrrole (MCTP)-induced CPH.

METHODS AND RESULTS

Sixteen mongrel dogs (22 to 24 kg) were used. Animals underwent percutaneous pulmonary artery (PA) catheterization to measure pulmonary hemodynamics before and 8 weeks after injection of 3 mg/kg MCTP (n=8) or placebo (control, n=8). Eight weeks after injection, all hearts were instrumented with a PA flow probe, sonomicrometric dimension transducers, and micromanometers. Data were collected at baseline and after both NO and milrinone administration. Diastolic properties were quantified by use of the end-diastolic pressure-volume relationship and the time constant of ventricular isovolumic relaxation. Eight weeks after injection, significant increases in the PA pressure and pulmonary vascular resistance were observed in MCTP dogs. Significant worsening of RV diastolic function occurred in association with significant increases in the ratio of RV dry weight to LV+septal dry weight. NO and milrinone administration both led to significant improvements in RV diastolic properties.

CONCLUSIONS

In the setting of MCTP-induced CPH, significant worsening of RV diastolic function was observed in association with significant increases in the ratio of RV dry weight to LV+septal dry weight, suggesting that these changes are partially due to RV hypertrophy. The significant improvement in RV diastolic properties after both NO and milrinone administration suggests that these agents may be effective forms of pharmacological therapy for improving RV diastolic dysfunction in the setting of CPH.

Increasing tidal volumes and pulmonary overdistention adversely affect pulmonary vascular mechanics and cardiac output in a pediatric swine model

OBJECTIVES

In a pediatric swine model, the effects of increasing tidal volumes and the subsequent development of pulmonary overdistention on cardiopulmonary interactions were studied. The objective was to test the hypothesis that increasing tidal volumes adversely affect pulmonary vascular mechanics and cardiac output. An additional goal was to determine whether the effects of pulmonary overdistention are dependent on delivered tidal volume and/or positive end-expiratory pressure (PEEP, end-expiratory lung volume).

DESIGN

Prospective, randomized, controlled laboratory trial.

SETTING

University research laboratory.

SUBJECTS

Eleven 4- to 6-wk-old swine, weighing 8 to 12 kg.

INTERVENTIONS

Piglets with normal lungs were anesthetized, intubated, and paralyzed. After median sternotomy, pressure transducers were placed in the right ventricle, pulmonary artery, and left atrium. An ultrasonic flow probe was placed around the pulmonary artery.

MEASUREMENTS AND MAIN RESULTS

The swine were ventilated and data were collected with delivered tidal volumes of 10, 15, 20, and 25 mL/kg and PEEP settings of 5 and 10 cm H2O in a random order. Pulmonary overdistention was defined as a decrease in dynamic compliance of > or =20% when compared with a compliance measured at a baseline tidal volume of 10 mL/kg. At this baseline tidal volume, airway pressure-volume curves did not demonstrate pulmonary overdistention. Tidal volumes and airway pressures were measured by a pneumotachometer and the Pediatric Pulmonary Function Workstation. Inspiratory time (0.75 sec), FIO2 (0.3), and minute ventilation were held constant. We evaluated the pulmonary vascular and cardiac effects of the various tidal volume and PEEP settings by measuring pulmonary vascular resistance, pulmonary characteristic impedance, and cardiac output. When compared with a tidal volume of 10 mL/kg, a tidal volume of 20 mL/kg resulted in a significant decrease in dynamic compliance from 10.5 +/- 0.9 to 8.4 +/- 0.6 mL/cm H2O (p = .02) at a constant PEEP of 5 cm H2O. The decrease in dynamic compliance of 20% indicated the presence of pulmonary overdistention by definition. As the tidal volume was increased from 10 to 20 mL/kg, pulmonary vascular resistance (1351 +/- 94 vs. 2266 +/- 233 dyne x sec/cm5; p = .004) and characteristic impedance (167 +/- 12 vs. 219 +/- 22 dyne x sec/cm5; p = .02) significantly increased, while cardiac output significantly decreased (951 +/- 61 vs. 708 +/- 48 mL/min; p = .001). Each of these effects of pulmonary overdistention were further magnified when the tidal volume was increased to 25 mL/kg. The tidal volume-induced alterations in pulmonary vascular mechanics, characteristic impedance, and cardiac output occurred to a greater degree when the PEEP was increased to 10 cm H2O. Pulmonary vascular resistance and characteristic impedance were significantly increased and cardiac output significantly decreased for all tidal volumes studied at a PEEP of 10 cm H2O as compared with 5 cm H2O.

CONCLUSIONS

Increasing tidal volumes, increasing PEEP levels, and the development of pulmonary overdistention had detrimental effects on the cardiovascular system by increasing pulmonary vascular resistance and characteristic impedance while significantly decreasing cardiac output. Delivered tidal volumes of >15 mL/kg should be utilized cautiously. Careful monitoring of respiratory mechanics and cardiac function, especially in neonatal and pediatric patients, is warranted.

Liquid ventilation improves pulmonary function and cardiac output in a neonatal swine model of cardiopulmonary bypass

OBJECTIVE

Neonatal and infant cardiopulmonary bypass results in multiorgan system dysfunction. Organ protective strategies have traditionally been directed at the myocardium and brain while neglecting the sometimes severe injury to the lungs. We hypothesized that liquid ventilation would improve pulmonary function and cardiac output in neonates after cardiopulmonary bypass.

METHODS

Twenty neonatal swine were randomized to receive cardiopulmonary bypass with or without liquid ventilation. In the liquid-ventilated group, a single dose of perflubron was administered before bypass. The control group was conventionally ventilated. Each animal was placed on nonpulsatile, hypothermic bypass. Low-flow cardiopulmonary bypass was performed for 60 minutes. The flow rate was returned to 125 ml/kg per minute, and after warming to 37 degrees C, the animals were removed from bypass. Hemodynamic and ventilatory data were obtained after bypass to assess the effects of liquid ventilation.

RESULTS

Without liquid ventilation, cardiopulmonary bypass resulted in a significant decrease in cardiac output, oxygen delivery, and static pulmonary compliance compared with prebypass values. Input pulmonary resistance and characteristic impedance increased in these control animals. At 30, 60, and 90 minutes after bypass, the animals receiving liquid ventilation showed significantly increased cardiac output and static compliance and significantly decreased input pulmonary resistance and characteristic impedance compared with control animals not receiving liquid ventilation.

CONCLUSIONS

Liquid ventilation improved pulmonary function after neonatal cardiopulmonary bypass while increasing cardiac output. The morbidity associated with cardiopulmonary bypass may be significantly reduced if the adverse pulmonary sequelae of bypass can be diminished. Liquid ventilation may become an important technique to protect the lungs from the deleterious effects of cardiopulmonary bypass.

Validation of a new and specific intraoperative measurement of vein graft resistance

PURPOSE

Clinical studies have revealed that the most important predictor of successful bypass grafting is the origin and quality of the bypass conduit. Attempts at intraoperative evaluation of the hemodynamic properties of the conduit, including assessment of blood flow (Q), pressure gradients (delta P), and resistance (R), have not been useful. This is because each of these parameters measures the characteristics of the graft plus the outflow bed. To date, no specific measurement of the resistive properties of the conduit only is available. The purpose of this investigation was to evaluate longitudinal impedance (ZL) as a measure of conduit-specific resistance and to evaluate its potential in predicting the outcome of infrainguinal vascular reconstructions.

METHODS

ZL was measured during surgery in 73 infrainguinal autologous vein reconstructions performed in 68 patients in two separate institutions over a 21-month period. Vein graft ultrasonic transit time Q and delta P (from proximal to distal anastomosis) were measured at baseline and after maximal peripheral vasodilatation with an intraarterial injection of papaverine 30 mg. Waveforms were recorded for 10 seconds at 200 Hz using a digital acquisition system. R was calculated as proximal mean pressure divided by mean blood flow (Q). After Fourier transformation, ZL was calculated as delta P/Q at each harmonic and total ZL (integral of ZL) was defined as the integral of moduli from 0 to 4 Hz.

RESULTS

All hemodynamic variables were significantly affected by papaverine vasodilatation (delta P, 3.9 +/- 0.5 vs 6.3 +/- 0.8 mm Hg; Q, 78.2 +/- 7.0 vs 126 +/- 11 ml/min; R, 134 +/- 17 vs 72.7 +/- 6.2 x 10(3) dyne.sec.cm-5; p < 0.0001), except integral of ZL, which remained constant (31.1 +/- 2.8 vs 30.8 +/- 2.8 x 10(3) dyne.cm-5; p = NS). After follow-up of 1 week to 17 months (median, 5 months), the 1-year primary, primary-assisted, and secondary patency rates were 72% +/- 7%, 77% +/- 6%, and 81% +/- 6%, respectively. Using Cox analysis, primary patency was significantly associated with decreased integral of ZL (p = 0.0001), but not with baseline or papaverine-stimulated delta P, Q, delta P/Q, or R integral of ZL > 47 x 10(3) dyne.cm-5 predicted primary failure with 90% positive and negative predictive value.

CONCLUSIONS

Intraoperative measurement of integral of ZL in infrainguinal vein grafts is independent of outflow conditions (that is, does not change with papaverine), and hence describes the resistive properties of the conduit only. In addition, these preliminary data suggest that integral of ZL is predictive of short-term primary patency. integral of ZL is the first available hemodynamic measurement that is conduit-specific and may therefore be a better predictor of graft patency than currently available methods.

Inhaled nitric oxide, right ventricular efficiency, and pulmonary vascular mechanics: selective vasodilation of small pulmonary vessels during hypoxic pulmonary vasoconstriction

OBJECTIVE

In the setting of acute pulmonary artery hypertension, techniques to reduce right ventricular energy requirements may ameliorate cardiac failure and reduce morbidity and mortality. Inhaled nitric oxide, a selective pulmonary vasodilator, may be effective in the treatment of pulmonary artery hypertension, but its effects on cardiopulmonary interactions are poorly understood.

METHODS

We therefore developed a model of hypoxic pulmonary vasoconstriction that mimics the clinical syndrome of acute pulmonary hypertension. Inhaled nitric oxide was administered in concentrations of 20, 40, and 80 ppm.

RESULTS

During hypoxic pulmonary vasoconstriction, the administration of nitric oxide resulted in a significant improvement in pulmonary vascular mechanics and a reduction in right ventricular afterload. These improvements were a result of selective vasodilation of small pulmonary vessels and more efficient blood flow through the pulmonary vascular bed (improved transpulmonary vascular efficiency). The right ventricular total power output diminished during the inhalation of nitric oxide, indicating a reduction in right ventricular energy requirements. The net result of nitric oxide administration was an increase in right ventricular efficiency.

CONCLUSION

These data suggest that nitric oxide may be beneficial to the failing right ventricle by improving pulmonary vascular mechanics and right ventricular efficiency.

Pulmonary hemodynamics and blood flow characteristics in chronic pulmonary hypertension

BACKGROUND

Lung transplantation is now an acceptable form of therapy for pulmonary hypertension, but controversy remains regarding the most appropriate surgical procedure. In this study, the changes in pulmonary vascular mechanics occurring in the setting of pulmonary hypertension were investigated using an adult canine model of monocrotaline pyrrole-induced pulmonary hypertension.

METHODS

Animals underwent pulmonary artery catheterization to measure right heart pressures before and 8 weeks after injection of either 3 mg/kg of monocrotaline pyrrole (n = 8) or placebo (n = 8). Eight weeks after injection, hearts underwent instrumentation with an ultrasonic flow probe and micromanometers. Harmonic derivation of functional data was achieved with Fourier analysis.

RESULTS

Significant increases in mean pulmonary artery pressure and pulmonary vascular resistance were observed after monocrotaline pyrrole injection. There was no significant difference in pulmonary blood flow. However, significant increases in input resistance and right ventricular hydraulic power with significant decreases in transpulmonary efficiency were observed.

CONCLUSIONS

Pulmonary hypertension causes significant alterations in pulmonary hemodynamics. Pulmonary blood flow is maintained by a significant increase in total power but with a significant decrease in transpulmonary efficiency. This adult canine model of pulmonary hypertension provides a useful means by which to evaluate surgical options of lung transplantation for improving pulmonary hemodynamics in the setting of chronic pulmonary hypertension.

Adolescent females' attitudes, subjective norms, perceived behavioral control, and intentions to use latex condoms

Guided by I. Ajzen's (1991) theory of planned behavior, the authors of this descriptive correlational study explored adolescent females' attitudes, subjective norms (social pressure), perceived behavioral control, and intentions with regard to latex condom use. An elicitation study was initially conducted (n = 16) to ascertain salient beliefs related to condom use. These beliefs were then used to develop a questionnaire administered during the main study to 60 sexually active adolescent females attending a sexually transmitted disease clinic. Global attitudes, subjective norms, and perceived behavioral control predicted 50% of the variance of intentions to use condoms. Perceived behavioral control contributed the highest proportion of variance in the equation for both global and belief-based measures in stepwise regression analyses. Implications for community health practice, research, and theory are reported.

Measurement of vascular input impedance in infrainguinal vein grafts

The purpose of this investigation was to measure vascular input impedance in infrainguinal vein grafts and assess the importance of clinical and hemodynamic parameters in predicting graft patency. Fifty-seven patients undergoing infrainguinal vein bypass grafting for limb salvage (n = 40) or claudication (n = 17) were prospectively studied. At the time of revascularization, simultaneously acquired intraluminal pressure and blood flow waveforms were digitized at 200 Hz and subjected to Fourier transformation in near real-time. Input impedance was calculated at baseline (immediately after unclamping) and after stimulation with either papaverine or completion arteriography. Resistance (Rin) was calculated as mean pressure divided by mean blood flow (Q). Characteristic impedance (Z0) was calculated as the mean of harmonics 3-10. Intraoperative data acquisition required approximately 5 min, utilized the completion angiography cannula already in place, and was uncomplicated in all patients. Stimulation with either papaverine or arteriography resulted in increased Q (72 +/- 7 to 146 +/- 11 ml/min, p < 0.001), decreased Rin (126 +/- 13 to 52 +/- 4 x 10(3) dyne.s.cm-5, p < 0.001), and slightly decreased Z0 (18 +/- 2 to 15 +/- 1, p = 0.002). After a mean follow-up of 20 months, the 2-year primary patency, secondary patency, limb salvage, and survival rates were 61 +/- 8%, 74 +/- 7%, 76 +/- 6%, and 86 +/- 6%, respectively. Primary patency was not associated with any of the clinical variables studied including age, sex, smoking history, history of previous vascular surgery, hypertension, coronary artery disease, diabetes mellitus, creatinine, indication for revascularization (claudication versus limb salvage), anesthesia (general versus regional), or level of distal anastomosis (popliteal versus infrapopliteal). Furthermore, there was no association between primary patency and baseline Q, baseline Rin, or stimulated Z0. However, using univariate analysis, patency was positively associated with decreased stimulated Rin (p = 0.002), elevated stimulated Q (p = 0.006), and decreased baseline Z0 (p = 0.02). Multiple regression analysis identified stimulated Rin as the only independent predictor of primary patency (p = 0.002). Stimulated Rin > or = 50 x 10(3) dyne.s.cm-5 was 71% sensitive and 65% specific for graft failure. It is concluded that 1) vascular input impedance can be simply and reliably measured in the operating room, and 2) elevated stimulated Rin is an independent predictor of primary patency.

Influences of ultrasonic machine settings, transducer frequency and placement of region of interest on the measurement of integrated backscatter and cyclic variation

Integrated backscatter and its cyclic variation are potentially important parameters to discriminate normal from diseased myocardium. Cyclic variation of integrated backscatter is expected to be independent of machine settings. Backscatter images of swine hearts were taken using a two-dimensional backscatter system while acoustic power was varied at different time gain control (TGC) settings. Cyclic variation was measured in vivo with various acoustic power and TGC settings using different transducer frequencies. Three different regions were analyzed. For any given TGC setting, the relationship between acoustic power and integrated backscatter in vitro was linear only over a narrow range. In vivo, cyclic variation was present at all regions studied in both long- and short-axis views. However, lower acoustic power (< 15 dB) and TGC (< 20 dB), or excessive settings of acoustic power (> 35 dB) and TGC (> 50 dB), produced minimal cyclic variation. Appropriate acoustic power (20-35 dB) and TGC (30-50 dB) produced larger and more consistent cyclic, variation at the posterior region of the left ventricle. These data indicate that each region has specific, appropriate machine settings to maximize the magnitude of cyclic variation.

Nitric oxide improves transpulmonary vascular mechanics but does not change intrinsic right ventricular contractility in an acute respiratory distress syndrome model with permissive hypercapnia

OBJECTIVE

To test the hypothesis that in a swine model of acute respiratory distress syndrome (ARDS) with permissive hypercapnia, inhaled nitric oxide would improve transpulmonary vascular mechanics and right ventricular workload while not changing intrinsic right ventricular contractility.

DESIGN

Prospective, randomized, controlled laboratory trial.

SETTING

University research laboratory.

SUBJECTS

Eleven swine (30 to 46 kg).

INTERVENTIONS

The swine were anesthetized, intubated, and paralyzed. After median sternotomy, pressure transducers were placed in the right ventricle, pulmonary artery, and left atrium. An ultrasonic flow probe was placed around the pulmonary artery. Ultrasonic dimension transducers were sutured onto the heart at the base, apex, left ventricle (anterior, posterior, free wall), and right ventricle (free wall). An additional transducer was placed in the interventricular septum. A surfactant depletion model of ARDS was created by saline lung lavage. Nitric oxide was administered at 2, 4, and 6 parts per million (ppm), in a random order, under the condition of permissive hypercapnia (Paco2 55 to 75 torr [7.3 to 10.0 kPa]).

MEASUREMENTS AND MAIN RESULTS

We evaluated the pulmonary vascular and right ventricular effects of permissive hypercapnia, with and without inhaled nitric oxide, by measuring variables of transpulmonary vascular mechanics and right ventricular function. These variables included mean pulmonary arterial pressure, right ventricular total power, right ventricular stroke work, transpulmonary vascular efficiency, and right ventricular intrinsic contractility. Data were obtained after lung injury under the following conditions: a) normocapnia (Paco2 35 to 45 torr [4.7 to 6.0 kPa]) and nitric oxide at 0 ppm; b) hypercapnia and nitric oxide at 0 ppm; c) hypercapnia and nitric oxide at 2, 4, and 6 ppm; and d) repeat measurements with hypercapnia and nitric oxide at 0 ppm. In ARDS with permissive hypercapnia, inhaled nitric oxide therapy (2 to 6 ppm) improved transpulmonary vascular mechanics and right ventricular workload by lowering pulmonary arterial pressure (29.6 +/- 1.3 vs. 24.6 +/- 1.0 mm Hg, p = .0001), increasing transpulmonary vascular efficiency (13.9 +/- 0.5 vs. 16.1 +/- 0.7 L/W-min, p = .0001), decreasing right ventricular total power (142 +/- 9 vs. 115 +/- 9 mW, p = .001), and decreasing right ventricular stroke work (653 +/- 37 vs. 525 +/- 32 ergs x 10(3), p = .001). Inhaled nitric oxide did not change right ventricular contractility, as measured by preload-recruitable stroke work.

CONCLUSIONS

Inhaled nitric oxide ameliorated any negative effects of hypoxic and hypercapnic pulmonary vasoconstriction. The beneficial effects of inhaled nitric oxide are related to alterations in right ventricular afterload and not intrinsic right ventricular contractility. The improved cardiopulmonary effects of inhaled nitric oxide with permissive hypercapnia potentially expand the use of nitric oxide in ARDS and other conditions in which this strategy is employed.

In acute lung injury, inhaled nitric oxide improves ventilation-perfusion matching, pulmonary vascular mechanics, and transpulmonary vascular efficiency

Acute respiratory distress syndrome continues to be associated with significant morbidity and mortality related to ventilation-perfusion mismatch, pulmonary hypertension, and right ventricular failure. It has been suggested that inhaled nitric oxide, which is a selective pulmonary vasodilator, may be effective in the treatment of acute respiratory distress syndrome; however, the effects of nitric oxide on cardiopulmonary interactions are poorly understood. We therefore developed a model of acute lung injury that mimics the clinical syndrome of acute respiratory distress syndrome. In our model, inhaled nitric oxide significantly reduced pulmonary artery pressure, pulmonary vascular resistance, and pulmonary vascular impedance. In addition, inhaled nitric oxide improved transpulmonary vascular efficiency and ventilation-perfusion matching, which resulted in increased arterial oxygen tension. Although arterial oxygen tension increased, oxygen delivery did not improve significantly. These data suggest that by improving ventilation-perfusion matching and arterial oxygen tension while lowering pulmonary vascular resistance and impedance, nitric oxide may be beneficial in patients with acute respiratory distress syndrome. However, additional measures to enhance cardiac performance may be required.

Enhanced cardiac preservation with oxygenated University of Wisconsin solution

The purpose of this study was to determine if oxygen delivery to rabbit cardiac allografts arrested and stored in University of Wisconsin solution (UWS) at 4 degrees C would affect preservation. Nineteen isolated rabbit hearts were rapidly excised and perfused at 80 mm Hg on an isovolumic modified Langendorff apparatus. A micromanometer was placed within a balloon and inserted into the left ventricle through the mitral valve orifice. Digitized pressure waveforms were collected at 11 known balloon volumes from 0.8 to 1.2 ml. Baseline data were obtained for all hearts while perfused with Krebs-Henseleit solution equilibrated with 95% O2:5% CO2 at 37 degrees C. All hearts were arrested with 30 ml of UWS (290 mOsm). The control group (N = 10) was stored in UWS at 4 degrees C for 8 hr, and the experimental group (N = 9) was perfused with oxygenated UWS (O2 content = 5.6 ml O2) at 4 degrees C for 8 hr at a pressure of 60 mm Hg (5-10 ml/min). Both groups were then reperfused with Krebs-Henseleit buffer at 80 mm Hg for 15 min at for postpreservation data acquisition. Left ventricular developed pressures over a physiologic range (pressure-volume area) and maximum positive and negative dP/dt were calculated. Recovery of left ventricular parameters as a percentage of the baseline values was determined. Mean pressure-volume area recovery in the nonperfused group was 40 +/- 7.9% versus the perfused group (71 +/- 7.0%, P = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Improved tolerance of the pediatric myocardium to brain death

The occurrence of brain death has been shown to significantly diminish left ventricular function in the adult porcine model. This study examined whether the pediatric myocardium is as sensitive as the adult myocardium to the detrimental effects of brain death in the porcine model. Left ventricular intracavitary pressure and major and minor axis epicardial dimensions were measured in eleven 1-month old pigs (7.5 to 10 kg) during a vena caval occlusion. Brain death was induced in six pigs by acutely ligating the brachiocephalic and left subclavian arteries. The remaining five pigs served as controls. Data were then collected every hour for 6 hours. The plot of the stroke work versus the end diastolic volume, called the preload recruitable stroke work relationship, was determined from the measured pressure and calculated intracavitary volume data. The slope of this linear relationship is an index of contractility, and the x intercept (Vo) is an index of diastolic mechanics. At each hour after instrumentation two vena caval occlusions were performed, and the mean slope of the preload recruitable stroke work line was calculated as a percentage of the baseline slope in both the brain-dead and control group. The mean values from the brain-dead pigs were 118%, 138%, 126%, 154%, 123%, and 87% of the baseline value for the 6 hours after brain death. The mean control values were 128%, 117%, 133%, 123%, 114%, and 111% of baseline for the 6 hours after instrumentation alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary hemodynamic consequences of ECG-synchronized ventilation

The pulmonary hemodynamic consequences of ECG-synchronized jet ventilation were studied in an acute closed chest swine model (n = 11). Eight jet timing protocols were compared to conventional mechanical ventilation. Hearts were paced atrially at 120 beats per minute, and analog measurements of pulmonary arterial flow and pulmonary arterial, tracheal, pleural, left atrial, and femoral arterial pressure were digitized in real time at 200 Hz. Fourier analysis of pulmonary artery pressure and flow waveforms was employed to calculate mean and oscillatory right ventricular hydraulic power and pulmonary vascular input impedance. Measurements were taken at 0, 5, and 10 cm H2O of positive end-expiratory pressure (PEEP) during conventional respiration and synchronized ventilation modes. No difference was found in mean pulmonary pressure and flow between conventional and synchronized ventilation at any level of PEEP, regardless of the timing of the jet pulse relative to the cardiac cycle. A significant difference in mean tracheal pressure between conventional and jet ventilation could be found only in the absence of PEEP (3.8 +/- 0.5 vs 2.5 +/- 0.3 mm Hg, P < 0.05). In the absence of PEEP, total hydraulic power was significantly less with respect to conventional ventilation when the jet pulse trailed the QRS complex by 90 and 135 degrees. A significant decrease in the ratio of oscillatory-to-mean power versus conventional respiration was found when jet ventilation lagged the QRS by 135 degrees (0.115 +/- 0.015 vs 0.147 +/- 0.013). These differences did not persist when PEEP was added. Moreover, no significant difference in hemodynamic variables was found when the various jet timing protocols were compared to each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer-assisted modeling of blood-flow: theoretical evidence for the existence of optimal flow wave patterns

The purpose of this study was to model blood-flow waveforms in order to examine the relationship between various waveform shapes and input impedance spectra. Twenty distinct single cardiac cycle flow waveforms having the same mean flow and heart rate were created based on clinical and published observations. The "best" waveform was one with a steep flow upstroke, a high peak flow value, swift deceleration following peak flow, and flow reversal during diastole. Each flow waveform was paired with 20 computer-generated pressure waveforms to calculate input impedance spectra by discrete Fourier transformation. "Favorable" flow waveforms were associated consistently with a lower characteristic impedance (average of 4th-10th harmonics, Zav) irrespective of the shape or magnitude of the input pressure wave. Zav corresponds to the degree of compliance of the vascular bed and could be expected to be lower under favorable outflow conditions and in non-diseased vessels. In conclusion, this study provides theoretical evidence for the existence of optimal flow wave patterns and supports the notion of flow waveform assessment for diagnostic purposes.

Effects of internal mammary artery dissection on phrenic nerve perfusion and function

The effects of left internal mammary artery (LIMA) dissection and distal division on phrenic nerve perfusion and function were examined in an adult swine model. Phrenic nerve perfusion was determined by left atrial injection of radioactively labeled microspheres. Phrenic nerve function was determined by measuring nerve and diaphragm potentials evoked by bilateral phrenic nerve stimulation. In the first group of animals (n = 9), the LIMA was dissected with ligation of all its branches. Left phrenic nerve perfusion and function decreased after LIMA dissection in every animal studied, whereas only minimal changes were observed on the right. Sixty minutes after LIMA dissection, left phrenic nerve mean perfusion decreased 71%. Left phrenic nerve and left diaphragm mean action potential amplitudes decreased 54% and 80%, respectively. In the second group of animals (n = 4), the LIMA dissection was performed without division of the pericardiacophrenic artery, a small proximal branch of the internal mammary artery that supplies the phrenic nerve. Sixty minutes after LIMA dissection, left phrenic nerve perfusion had decreased by 21% from control values, with a corresponding decrease in left phrenic nerve and diaphragm mean action potential amplitudes of 19% and 23%, respectively. These results indicate that LIMA dissection with division of all its branches in this model is associated with a significant impairment in left phrenic nerve perfusion and function and suggests a causal relationship. These results may also explain the apparent increased phrenic nerve cold sensitivity and increased incidence of phrenic nerve dysfunction associated with LIMA grafting.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraoperative perfusion contrast echocardiography. Initial experience during coronary artery bypass grafting

Intraoperative evaluation of the effectiveness of myocardial revascularization has been limited by an inability to assess regional myocardial perfusion. Microbubbles of sonicated diatrizoate sodium and diatrizoate meglumine (Renografin) have been an effective echocardiographic contrast agent and have been employed clinically during cardiac catheterization. This recent development in contrast-enhanced two-dimensional echocardiography permits real-time imaging of transmural myocardial blood flow but has not been evaluated in the operating room. This study represents the initial surgical application of this directed technique and was designed to evaluate the safety and efficacy of intraoperative perfusion contrast echocardiography in assessing the results of coronary artery bypass grafting. Twenty men with significant coronary artery disease ranging in age from 49 to 73 years were studied. Direct contrast agent injection into completed saphenous vein bypass grafts caused the myocardium supplied by each graft to be well delineated and provided a tomographic view of contrast distribution. The enhanced region was well correlated with the size and distribution of the native vessel. Rapid contrast washout (less than 20 seconds) indicated satisfactory regional perfusion. Contrast echocardiography prolonged the operation less than 10 minutes and did not result in any perioperative complications.

One-stage arm-preserving shoulder resection with latissimus dorsi flap for basal cell carcinoma

A 60-year-old man was found to have a large invasive basal cell carcinoma involving the skin and surrounding bones of the shoulder joint. The Tikhor-Linberg procedure, a technique for preserving the arm in a shoulder resection, was combined with a latissimus dorsi muscle flap reconstruction in one stage to achieve a satisfactory functional result.

Four primary malignant neoplasms in a single patient

A 60-year-old Caucasian male, with a previous history of a 10-year occupational exposure to ionizing radiation, chemical carcinogens, and a long history of tobacco and alcohol abuse, developed synchronous squamous cell carcinoma of the floor of the mouth and adenocarcinoma of the lung. Four years later, squamous cell carcinoma of the larynx followed by squamous cell carcinoma of the tongue were diagnosed. In this case report, we suggest that increased exposure to multiple carcinogenic factors may result in an increased incidence of both synchronous and metachronous primary malignant neoplasms.

Importance of the kidney in the correction of chloride-depletion alkalosis in the rat

Correction of chloride-depletion alkalosis (CDA) may involve renal as well as extrarenal mechanisms. To determine the relative contribution of these mechanisms in a rat model of CDA produced by peritoneal dialysis (PD), we studied six groups of anesthetized Sprague-Dawley rats after PD. Groups II-IV and IIa were subjected to functional bilateral nephrectomy, and groups I and Ia were sham-operated. Groups I, Ia, II, and IIa were infused with isotonic fluid containing 70 mM Cl- and 40 mM HCO3-; the infusate in group III was 140 mM Cl- and in group IV, 70 mM neutral PO4 was substituted for Cl-. Groups I and Ia were infused at 0.5 ml . h-1 X 100 g body wt-1 and groups II, IIa, III, and IV at 0.25 ml . h-1 X 100 g-1. After 3 h of infusion, early partial correction with reciprocal changes in plasma Cl (+6.1 +/- 1.9 mmHg) and total CO2 (-6.0 +/- 0.8 meq/liter) occurred (P less than 0.01) only in group I. Hypokalemia (3.1 +/- 0.1 meq/liter) also occurred only in group I. The responses of groups Ia and IIa studied at 5 h were similar to those of groups I and II. These data suggest that the kidney, and not extrarenal mechanisms, is primarily responsible for the correction of CDA during infusion of chloride.