Non-linear partitioning and organic volatility distributions of urban aerosols.

Gas-to-particle partitioning of organic aerosols (OA) is represented in most models by Raoult's law, and depends on the existing mass of particles into which organic gases can dissolve. This raises the possibility of non-linear response of particle-phase OA mass to the emissions of precursor volatile organic compounds (VOCs) that contribute to this partitioning mass. Implications for air quality management are evident: a strong non-linear dependence would suggest that reductions in VOC emission would have a more-than-proportionate benefit in lowering ambient OA concentrations. Chamber measurements on simple VOC mixtures generally confirm the non-linear scaling between OA and VOCs, usually stated as a mass-dependence of the measured OA yields. However, for realistic ambient conditions including urban settings, no single component dominates the composition of the organic particles, and deviations from linearity are presumed to be small. Here we re-examine the linearity question using volatility spectra from several sources: (1) chamber studies of selected aerosols, (2) volatility inferred for aerosols sampled in two megacities, Mexico City and Paris, and (3) an explicit chemistry model (GECKO-A). These few available volatility distributions suggest that urban OA may be only slightly super-linear, with most values of the normalized sensitivity exponent in the range 1.1-1.3, also substantially lower than seen in chambers for some specific aerosols. The rather low exponents suggest that OA concentrations in megacities are not an inevitable convergence of non-linear effects, but can be addressed (much like in smaller urban areas) by proportionate reductions in emissions.

Myocardial blood flow distribution in concentric left ventricular hypertrophy.

Regional myocardial blood flow during both control conditions and ischemia-induced vasodilatation was studied in eight chronically instrumented awake dogs. Seven of these animals had coarctation-banding of the ascending aorta performed at 6 wk of age, and the other dog had congenital subvalvular aortic stenosis. The mean left ventricular weight for the group was 157+/-7.6 g, and the left ventricular body weight ratio was 8.76+/-0.47 g/kg. None of the animals exhibited signs of congestive heart failure. During the control state, the mean left ventricular systolic pressure was 249+/-12 mm Hg and the left ventricular end-diastolic pressure was 11.5+/-0.5 mm Hg. The aortic diastolic pressure was 74+/-6 mm Hg. Mean left circumflex coronary artery blood flow was 71+/-6 cm(3)/min. In the animals with coarctation-banding, 52+/-6% of the flow occurred during systole. In the dog with congenital subvalvular aortic stenosis, 5% of the coronary flow was systolic. Mean transmural blood flow during resting conditions was 0.97+/-0.08 cm(3)/min per g, and the ratio of endocardial to epicardial flow (endo/epi) was 0.88+/-0.07. During reactive hyperemia, the mean transmural blood flow increased to 3.5+/-0.30 cm(3)/min per g; however, the endo/epi decreased to 0.52+/-0.06.THESE STUDIES DOCUMENT A DIFFERENCE IN TRANSMURAL BLOOD FLOW DISTRIBUTION BETWEEN THE NORMAL AND THE HYPERTROPHIED LEFT VENTRICLE: during resting conditions, in the normal ventricle, the highest flow occurs in the endocardial layer, whereas in the hypertrophied ventricle, the highest flow is in the middle layers with the endocardial flow less than the epicardial flow. During ischemia-induced vasodilatation, the abnormal endo/epi becomes accentuated markedly. These data demonstrate that, in situations requiring high flow, the endocardial layer of a heart with marked concentric left ventricular hypertrophy may not be perfused adequately.

The implanted defibrillator: relation of defibrillating lead configuration and clinical variables to defibrillation threshold.

Forty-two defibrillating lead systems for the automatic implantable defibrillator were implanted and tested in 41 patients. Two basic lead configurations were used: 1) spring-patch, consisting of a transvenous superior vena cava spring electrode as the anode and an apical or left lateral ventricular patch electrode (either small [13.9 cm2] or large [27.9 cm2]) as the cathode; and 2) patch-patch, consisting of an anterior right ventricular patch as the anode and a posterior left ventricular patch as the cathode. Of the 42 lead systems, 10 were spring-patch and 32 were patch-patch combinations. The defibrillation threshold for the patch-patch combinations (9.8 +/- 6.5 J, mean +/- standard deviation) was significantly (p less than 0.01) lower than that for the spring-patch combinations (19.1 +/- 10.3 J). Subgroup analysis revealed the lowest defibrillation thresholds for patch-patch combinations with at least one large patch. Total surface area of defibrillating leads was strongly negatively correlated with the defibrillation threshold (p less than 0.005). Analysis of the relation of clinical variables to defibrillation threshold revealed that only amiodarone therapy was independently associated with a significantly (p less than 0.05) higher defibrillation threshold. Thus, surface area of the defibrillating leads is a critical determinant of the defibrillation threshold for the implanted defibrillator. Patch-patch lead systems with at least one large patch may provide an increased safety margin for defibrillation. Conversely, amiodarone therapy is associated with higher defibrillation thresholds and may decrease the margin of safety.

Gastrointestinal-specific patient-reported outcome instruments differentiate between renal transplant patients with or without GI complications.

BACKGROUND: Gastrointestinal (GI) complications are frequently reported postrenal transplant and are often associated with immunosuppressant regimens including mycophenolate mofetil (MMF). This study evaluated the ability of two GI-specific patient-reported outcome (PRO) instruments to differentiate between patients with and without GI complaints. METHODS: Discriminant validity of the Gastrointestinal Symptom Rating Scale (GSRS) and Gastrointestinal Quality of Life Index (GIQLI), as well as two generic instruments (Psychological General Well-Being Index (PGWB) and EQ-5D, was assessed in a multinational study of renal transplant recipients. Patients received therapy that included a calcineurin inhibitor and MMF. Both t-tests and ANOVAs were used to examine differences between patients with and without GI complaints, among levels of severity, and between patients reporting presence/absence of specific GI side effects. RESULTS: Of 96 patients recruited (56% male), 43% had none, 39% mild, 13% moderate, and 6% severe GI symptoms. All GSRS subscales and the GIQLI total and four of the five subscale scores significantly differentiated between patients with/without GI complications (P < .05). The PGWB total score and three subscales, the EQ-5D significantly differentiated between the two groups (P < .05). Only GI-specific instruments discriminated between some severity levels; for example, the GSRS abdominal pain subscale discriminated between patients at all levels of severity (P < .05). The GIQLI total score and symptoms subscale differentiated between patients with no symptoms and those with mild or moderate or severe symptoms (P < .05). CONCLUSIONS: The GSRS and GIQLI differentiated between patients with/without GI side effects and by symptom severity better than did generic instruments, demonstrating excellent discriminant ability in this population.

The impact of nocturnal symptoms associated with gastroesophageal reflux disease on health-related quality of life.

BACKGROUND: Two types of reflux episodes have been identified: upright or daytime and supine or nocturnal. The population-based prevalence of symptoms of nocturnal gastroesophageal reflux disease (GERD) and the impact of those symptoms on health-related quality of life (HRQL) have not been established. METHODS: A national random-sample telephone survey was conducted to estimate the prevalence of frequent GERD and nocturnal GERD-like symptoms and to assess the relationship between HRQL, GERD, and nocturnal GERD symptoms. Respondents were classified as controls, subjects with symptomatic nonnocturnal GERD, and subjects with symptomatic nocturnal GERD. The HRQL was assessed using the Medical Outcomes Study Short-Form 36 Health Survey (SF-36). RESULTS: The prevalence of frequent GERD was 14%, with an overall prevalence of nocturnal GERD of 10%. Seventy-four percent of those with frequent GERD symptoms reported nocturnal GERD symptoms. Subjects with nonnocturnal GERD had significant decrements on the SF-36 physical and mental component summary scores compared with the US general population. Subjects reporting nocturnal GERD symptoms were significantly more impaired than subjects reporting nonnocturnal GERD symptoms on both the physical component summary (38.94 vs 41. 52; P<.001) and mental component summary (46.78 vs 49.51; P<.001) and all 8 subscales of the SF-36 (P<.001). Subjects with nocturnal GERD demonstrated considerable impairment compared with the US general population and chronic disease populations. Subjects with nocturnal GERD had significantly more pain than those with hypertension and diabetes (P<.001) and similar pain compared with those with angina and congestive heart failure. CONCLUSIONS: Nocturnal symptoms are commonly experienced by individuals who report frequent GERD symptoms. In addition, HRQL is significantly impaired in those persons who report frequent GERD symptoms, and HRQL impairment is exacerbated in those who report nocturnal GERD symptoms.

Renal function correlates of postnatal diuresis in preterm infants.

A characteristic pattern of fluid homeostasis occurs in the first week of life in many preterm infants. Initially, urine output is low independent of fluid intake, subsequently a diuresis occurs, and finally urine output begins to vary with intake. Renal clearance measurements were made during each of these three phases to elucidate the renal mechanisms involved. Periods during which the ratio of urine output to fluid intake was greater than or equal to 1 and urine output was greater than or equal to 3 mL/kg/h were defined as diuretic. Of 22 preterm infants studied from 12 to 120 hours of age, 17 had at least one period of diuresis. In these infants, urine output, fluid intake rate, output to intake ratio, glomerular filtration rate, and fractional sodium excretion were lowest at 12 to 24 hours of age. During diuresis, urine output tripled without a significant change in fluid intake so that output to intake increased to levels exceeding unity. Diuresis was associated with significant increases in glomerular filtration rate and fractional sodium excretion. By 108 to 120 hours of age, urine output decreased despite an increase in fluid intake. This was accompanied by a decrease in glomerular filtration rate. These results suggest that the initial antidiuretic phase is the result of a low fractional sodium excretion in the face of a low glomerular filtration rate. Subsequently, diuresis and natriuresis occur as a result of abrupt, nonmaturational increases in glomerular filtration rate and fractional sodium excretion. With cessation of diuresis, glomerular filtration rate and fractional sodium excretion decrease and water and electrolyte output begin to vary appropriately with intake.

Phases of fluid and electrolyte homeostasis in the extremely low birth weight infant.

OBJECTIVE: We had shown previously that preterm infants undergo three phases of fluid and electrolyte homeostasis; prediuretic, diuretic, and postdiuretic. The objectives of the present study were: (1) to determine whether infants even more immature and infants cared for under thermal environmental conditions different from those previously studied also undergo these three phases; and (2) to relate these phases to changes in renal function. METHODS: Consecutive, timed urine collections were made during the first 5 days of life in 32 infants with birth weights of 1000 g or less. Infants were cared for in radiant warmers for 24 hours and then transferred to nonhumidified incubators. Diuresis was defined as urine flow rate (V) of 3 mL or more/kg per hour and weight loss of 0.8 g or more/kg per hour. The physiologic relationships among water and sodium balance, insensible water loss, arterial blood pressure, and renal function were made during the three phases. RESULTS: Twenty-eight (87%) of the 32 infants underwent the three homeostatic phases. The median ages of onset and cessation of diuresis were 25 and 96 hours, respectively. There was no correlation between onset of diuresis and change of thermal environment. During the prediuretic phase, V averaged 1.6 mL/kg per hour, and 17 of 28 infants had at least one collection period in which V was less than 1 mL/kg per hour; urinary sodium excretion was 0.1 mEq/kg per hour; the glomerular filtration rate (GFR) was 0.22 mL/kg per hour; fractional excretion of sodium (FENa) was 6.2%; and urine osmolality was dilute (221 mOsm/kg). During the diuretic phase, V and sodium excretion more than tripled; GFR and FENa doubled; and there was no change in urine osmolality. During postdiuresis, V and Na excretion decreased to values intermediate between the prediuretic and diuretic phases, and FENa fell to prediuretic levels, but there was no change in GFR or urine osmolality. There was poor correlation between blood pressure and GFR. Insensible water loss was high and variable during all phases, exceeding 190 mL/kg per day in the smallest infants. CONCLUSIONS: Extremely low birth weight infants manifest three phases of fluid and electrolyte homeostasis, as do more mature infants, independent of thermal environment. Diuresis and natriuresis are the result of abrupt increases in GFR and FENa. We speculate that this may be the result of expansion of the neonatal extracellular space as fetal lung fluid is reabsorbed.

Renal bicarbonate excretion in extremely low birth weight infants.

OBJECTIVE: To test the hypothesis that due to the immaturity of their kidneys extremely low birth weight infants lose large amounts of bicarbonate in their urine. METHODS: Urine and blood samples collected every 8 to 12 hours for the first 4 days of life from 22 preterm infants 23 to 29 weeks' gestation weighing 540 to 982 g at birth were prospectively studied. RESULTS: As described previously, three phases of fluid homeostasis were identified. The first phase (prediuresis) was a period of low urine output followed by a period of spontaneous diuresis/natriuresis (diuretic phase) and then by a phase when urine output varied according to fluid intake (postdiuresis). Sodium, potassium, chloride, and bicarbonate excretion rates and bicarbonate balance (bicarbonate or acetate infused minus bicarbonate excreted) were calculated for each of the three phases. Urinary excretion of sodium, potassium, chloride, and bicarbonate increased from the prediuretic to the diuretic phase and decreased from the diuretic to the postdiuretic phase. During the diuretic phase 88% of renal sodium excretion was accompanied by excretion of chloride. Bicarbonate balance was positive in all three fluid phases. Cumulative renal bicarbonate loss over the first 4 days of life was 1.9 +/- 0.5 meq/kg (SD) and the cumulative bicarbonate balance was +4.4 +/- 4.1 meq/kg (SD). The glomerular filtration rate, filtered load of bicarbonate, and absolute tubular reabsorption of bicarbonate significantly increased from the prediuretic to the diuretic phase, while fractional reabsorption of sodium and chloride decreased between these two phases. The fractional reabsorption of bicarbonate did not change from prediuresis to diuresis, but increased from diuresis to postdiuresis and consequently from prediuresis to postdiuresis. CONCLUSIONS: Contrary to our original hypothesis, the total renal bicarbonate excretion of extremely low birth weight infants in the first 4 days of life is low and the net bicarbonate balance is positive. The anion predominantly accompanying the excretion of sodium in all three phases is chloride and not bicarbonate. Bicarbonate excretion appears to be independent of sodium excretion during these phases. The increase in renal tubular bicarbonate reabsorption during the first week of life may be associated with extracellular volume contraction.

Effects of methoxamine on the coronary circulation during cardiopulmonary bypass.

Effects of perfusion pressure augmentation with methoxamine on transmural distribution and adequacy of coronary blood flow during cardiopulmonary bypass were investigated. Flow in normal, nonworking canine hearts was measured with tracer microspheres and electromagnetic flow probes while heart rate, myocardial oxygen consumption, left ventricular contractility and epicardial ST-segment stability were monitored. Measurements during normotensive cardiopulmonary bypass were compared with values during intraoperative hypotension and subsequent normotension achieved following methoxamine infusion. Total and regional coronary blood flow returned to levels not different from normotensive controls after methoxamine infusion with a redistribution of flow to the subendocardium. We conclude that elevating perfusion pressure during cardiopulmonary bypass with methoxamine infusion increases total coronary and subendocardial blood flow by means of peripheral and selective subepicardial alpha adrenergic vasoconstriction.

Tricuspid valve replacement for Ebstein's anomaly in childhood with a Starr-Edwards caged-ball prosthesis. 21-year follow-up.

A 21-year follow-up after tricuspid valve replacement (TVR) with a Starr-Edwards caged-ball prosthesis in a ten-year old boy is described. TVR is performed for Ebstein's anomaly, with strict indications in childhood. Despite the current preference for bioprostheses, good performance can be expected from the Starr-Edwards caged-ball valve.

Transmural myocardial flow distribution during hypothermia. Effects of coronary inflow restriction.

Hypothermic coronary perfusion and blood cardioplegia have been used clinically to minimize intraoperative myocardial damage. However, pressure-flow characteristics in regions supplied by inflow-limiting collateral coronary arteries have not been investigated during hypothermic conditions. In this study tracer microspheres determined transmural myocardial blood flow distribution during cardiopulmonary bypass in normothermic empty, beating dog hearts (EBH), during hypothermic sanguineous perfusion at 15 degrees C (HP), and after hemodilution of cooled (15 degrees C) hearts to a hematocrit value of 20 vol% (HDL). Animals in Group I (N = 8) had normal hearts. Group II dogs (N = 9) had one region supplied predominantly by narrow collateral vessels (CR) and another nourished by normal coronary arteries (NR). Retrograde circumflex pressures were measured continuously for Group II as an additional index of CR perfusion. Flow characteristics in Group I hearts were always similar to the NR of Group II dogs. With HP, endocardial blood flow in the NR decreased from approximately 0.80 to 0.50 ml/min/gm. Subsequently, following HDL this flow increased to approximately 1.70 ml/min/gm, or over twice control levels. In comparison, flow to CR endocardium decreased even more during HP (0.12 ml/min/gm). Even though control flow levels were reestablished in CR endocardium by adding HDL, an unfavorable endocardial/epicardial ratio persisted. With both HP and HDL, retrograde circumflex pressure never changed from EBH values. These data suggest that a significant endocardial flow defect exists during periods of hypothermic sanguineous perfusion and may become more prevalent in regions subserved by inflow-limiting coronary vessels. Similar flow maldistributions may occur in patients if blood-containing cardioplegic solutions are used and during systemic hypothermia. Significant hemodilution helps minimize these imbalances and permits salutary effects of hypothermia to be delivered more evenly across the ventricular wall.

Strut failure of the Starr-Edwards cloth-covered metallic ball prosthesis. Report of two asymptomatic cases and review of the overall experience.

Two cases of asymptomatic strut failure of an aortic Starr-Edwards cloth-covered metallic ball prosthesis are reported. Strut failure can be asymptomatic for years. Available information on the overall worldwide experience of six cases is reviewed and suggestions made for early diagnosis and treatment of this rare complication.

Regional myocardial dimensions following coronary artery bypass grafting in patients. Relationship of functional deterioration to graft occlusion.

The direct relationship between graft flow and regional midwall myocardial function has not been documented in patients. Therefore, the present study was designed to quantitate the effects of coronary artery bypass grafting on regional myocardial mechanics distal to a coronary artery obstruction. Twenty-one patients with subtotal or total occlusion of the left anterior descending (LAD) coronary artery underwent coronary artery bypass grafting. Following completion of the aortic and coronary anastomoses, two miniature ultrasonic dimension transducers (2.5 mm. diameter) were positioned within the minor axis of the anterior left ventricular free wall and were allowed complete freedom of movement. The transducers were placed at midwall depth, and areas of clinically apparent myocardial fibrosis were not utilized as sites of implantation. During control, 30 minutes following the termination of cardiopulmonary bypass, regional myocardial dimensions, pulmonary artery diastolic pressure, arterial pressure, and heart rate were recorded with all saphenous vein grafts open and after 30 seconds of single vein graft occlusion. These measurements were repeated during atrial pacing at a rate of 128 +/- 4 beats per minute. Data are mean +/- the standard error of the mean. During control, graft occlusion resulted in a regional decrease in systolic excursion from 1.3 +/- 0.1 to 1.0 +/- 0.2 mm. (p less than 0.01), as well as a decrease in the rate of shortening from 8.7 +/- 0.2 to 6.2 +/- 1.1 mm. per second (p less than 0.05); heart rate, mean arterial pressure, and diastolic pulmonary artery pressure remained unchanged. Graft occlusion with atrial pacing resulted in an exaggerated decrease in both regional systolic excursion, from 1.2 +/- 0.2 to 0.6 +/- 0.2 mm. (p less than 0.01), and rate of shortening, from 9.4 +/- 1.5 to 4.4 +/- 0.2 mm. per second (p less than 0.01). For the group of patients studied, end-diastolic lengths were unchanged with graft occlusion during control and atrial pacing. Moreover, with graft occlusion, isolated patients demonstrated regional dyskinesia as evidenced by holosystolic bulging. These studies in patients have documented for the first time that, despite a constant preload, afterload, and heart rate, regional myocardial function following coronary artery bypass grafting is dependent upon adequate graft flow, especially during stress.

Measurement of global ventricular function in patients during cardiac operations using sonomicrometry.

In these studies, we evaluated the applicability of pulse-transit sonomicrometry for measuring changes in global cardiac activity in patients during cardiac operative procedures. In six patients two epicardial ultrasonic crystals (8 mm) were sutured across the left ventricular minor axis. Diastolic pressure-length data were recorded as left ventricles were filled passively to transmural pressures (P) from 0 to 20 mm Hg. Data were collected at the beginning of cardiopulmonary bypass and again 15 minutes following periods of induced global ischemia (29.8 +/- 0.8 minutes). Minor axis length data were normalized to Lagrangian strain (epsilon), and best-fit regression curves were obtained from P-epsilon by computer analysis. Nonlinear elastic constants, alpha and beta, were mathematically derived as additional curve descriptors. Decreases in ventricular compliance were demonstrated as leftward shifts in both computed and measured P-epsilon curves. Global ischemia appeared to effect a decrease in overall ventricular diastolic compliance in all patients studied (p =7E 0.01 at 5, 10, 15, 20 mm Hg). Simultaneously, no statistical change occurred in lo (62.93 +/- 2.80 mm), which represented end-diastolic length (EDL) at 0 mm Hg transmural pressure. Following coronary grafting several patients showed augmented systolic excursion when compared at similar EDL. For those analyses, shortening was compared at specific minor axis EDLs rather than filling pressures. These data indicate that experimentally developed sonomicrometry may safely provide accurate indices of systolic and diastolic ventricular properties during operations necessitating cardiopulmonary bypass. Thus various cardioplegic solutions, ischemic arrest periods, and inotropic agents may be evaluated more objectively.

Instabilities in diamond under high shear stress

We investigate, through first-principles calculations, lattice instabilities induced in diamond by the application of high shear stresses. For shear stresses as low as 95 GPa a lattice instability will occur, leading to graphitelike layered structures. This effect is highly anisotropic. The reversal of the direction of the applied shear forces may cause a change of 80 GPa in the shear stress value at which the instability develops. The same reversal also causes different bonds to be broken, resulting in a drastic change in the orientation of the resulting graphitelike structures. We also find that an additional compressive stress of 50 GPa along the (111) direction does not eliminate the shear-induced instability.

Minor head injury in children: current management practices of pediatricians, emergency physicians, and family physicians.

OBJECTIVE: To describe variation in the clinical management of minor head trauma in children among primary care and emergency physicians. DESIGN: A survey of pediatricians, family physicians, and emergency physicians drawn from a random sample of members of the American Academy of Pediatrics, the American Academy of Family Physicians, and the appropriate American Medical Association specialty listings, respectively. Physicians were given clinical vignettes describing children presenting with normal physical examination results after minor head trauma. Different clinical scenarios (brief loss of consciousness or seizures) were also presented. Information was gathered on initial and subsequent management steps most commonly used by the physician. RESULTS: Surveys were returned by 765 (51%) of 1500 physicians. Of these, 303 (40%) were pediatricians, 269 (35%) family practitioners, and 193 (25%) emergency physicians. For minor head trauma without complications, observation at home was the most common initial physician management choice (n = 547, 72%). Observation in office or hospital was chosen by 81 physicians (11%). Head computed tomographic (CT) scan was chosen by 7 physicians (1%) and skull x-ray by 24 physicians (3%) as the first management option. Most physicians (n = 445, 80%) who initially chose observation at home would obtain a CT scan if the patient showed clinical deterioration. In the original scenario, if the patient had also sustained a loss of consciousness, 383 physicians (58%) altered management. Of these, 120 (18%) chose CT, 13 (2%) chose skull x-ray, 1 (1%) chose magnetic resonance imaging, 141 (21%) chose inpatient observation, and 125 (19%) chose a combination of CT scanning and observation. With seizures, 595 (90%) altered management, with 176 physicians (27%) choosing CT scan, 5 (1%) skull x-ray, 60 (9%) inpatient observation, and 299 (45%) a combination of radiological evaluation and observation. CONCLUSIONS: Most physicians surveyed chose clinic or home observation for initial management of minor pediatric head trauma. Clinical management was more varied when patients had sustained either loss of consciousness or seizures. Further study of the appropriate management of minor head trauma in children is needed to guide physicians in their care.

Heparin-coated shunts for lesions of the descending thoracic aorta. Experimental and clinical observations.

Heparin sodium-coated shunts are employed frequently to maintain trunk and lower extremity perfusion during temporary occlusion of the descending thoracic aorta. In the past five years, this shunt has been used in a series of 39 patients ranging in age from 19 to 72 years old, with 34 survivors (87%). The proximal end of the shunt was placed in the subclavian artery in 17 patients, the left ventricle in ten, and in the ascending or transverse aortic arch in 12. The distal end of the shunt was placed either in the lower thoracic aorta or in the femoral artery. For further evaluation of effectiveness, paired observations were made in dogs to determine the physiological consequences with the proximal end of the shunt inserted at two different sites. Although neither shunt decompressed the left ventricle fully, the subclavian-femoral shunt was significantly more effective than was the left ventricle-femoral artery bypass. If a choice exists for sites of insertion of the shunt, it appears that it should be placed distal to the aortic valve, since this position provides the least increase in systolic blood pressure and is associated with a lower demand for myocardial blood flow.

Life-threatening chylothorax after left internal mammary artery dissection: therapeutic considerations.

Persistent chylothorax developed in a 53-year-old man after left internal mammary artery (LIMA) takedown and required surgical intervention. After an unsuccessful supraclavicular approach, left-sided standard thoracotomy showed thick adhesions around the LIMA takeoff with a diffuse oozing rather than an identifiable discrete leak. A possible leaking point was stitched, the area was sealed with fibrin adhesive, and complete remission ensued. Operation for chylothorax after LIMA takedown is challenging. A left-sided standard thoracotomy with minimal dissection and use of fibrin adhesive rather than blind stitching are recommended.

The effects of intermittent ischemic arrest on the perfusion of myocardium supplied by collateral coronary arteries.

Six weeks after placement of an ameroid constrictor on the circumflex coronary artery, blood flow in a collateral region was compared with flow in myocardium supplied by normal arteries during cardiopulmonary bypass (80 mm Hg). Myocardial blood flow was determined using radionuclide-labeled microspheres (8 to 10 mu) before 10 minutes of ischemic arrest and after 1, 5, and 10 minutes of reperfusion. The retrograde circumflex pressure was monitored continuously and served as an additional index of perfusion of the collateral region. During reperfusion, endocardial flow in the collateral region remained unchanged despite a threefold increase in a similar layer having normal arteries (p less than 0.01). Following ischemic arrest, mean transmural and subendocardial hyperemic responses both persisted for longer than 10 minutes in normal regions. Simultaneously, peripheral circumflex pressures decreased at 1 and 5 minutes of reperfusion (p less than 0.001) but returned to control within 10 minutes. Persistently elevated endocardial flow in the normal arteries and the absence of a hyperemic response in the collateral region during an associated decrement in retrograde circumflex pressure may indicate incomplete flow repayment even after 10 minutes of reperfusion. Marked transmural flow imbalances despite adequate coronary perfusion pressures suggest that intermittent ischemic arrest may cause cumulative ischemia, and this occurrence may be detrimental especially in collateral regions of myocardium.