Treatment of superior mesenteric artery portal vein fistula with balloon-expandable stent graft.

Visceral artery to portal vein arteriovenous fistulas are rare and difficult to treat. Covered stents have made treatment of pseudoaneurysms and arteriovenous fistulas feasible utilizing minimally invasive techniques. We present a case of a 46-year-old male with a remote history of an exploratory laparotomy after a motorcycle accident who presented with abdominal pain, malaise, and jaundice. A computed tomographic scan revealed a superior mesenteric artery to portal vein arteriovenous fistula. A large arteriovenous fistula was confirmed by arteriography. A balloon-expandable stent graft was placed across the arteriovenous fistula in the superior mesenteric artery. Postprocedure, the patient's abdominal pain resolved and his bilirubin decreased from 2.9 to 0.4. Endovascular repair of a superior mesenteric to portal arteriovenous fistula utilizing a stent graft is feasible and minimally invasive.

Delayed development of a traumatic superior mesenteric arteriovenous fistula following multiple gunshot wounds to the abdomen.

Traumatic visceral arteriovenous fistulae are rare and pose a diagnostic and therapeutic challenge. We present the case of a 20-year-old male who sustained multiple gunshot wounds to the abdomen, injuring the inferior vena cava, duodenum, stomach, and small bowel. The patient was taken emergently to the operating room for repair of his injuries, which required primary small bowel repair, duodenal repair, and inferior vena cava ligation due to exigent hemorrhage. At the initial operation there was a normal pulse in the superior mesenteric artery at the base of the small bowel mesentery, with no evidence of hematoma or thrill in the small bowel mesentery. The patient was subsequently returned to the operating room several times for bowel exploration and abdominal wall closure with mesh. Ten days after his initial injury, the patient was noted to have an abdominal bruit on physical exam. Arteriography demonstrated a fistula between the proximal superior mesenteric artery and vein with significant portal hypertension. The patient underwent surgical repair of the superior mesenteric artery and vein with closure of the fistula. The patient had no further complications and was discharged from the hospital 1 month later, after abdominal wall skin grafting, in good condition. The patient remains in good health 12 months later. Continued vigilance and careful physical examination are important in the identification of delayed vascular injuries and allow timely treatment and avoidance of untoward long-term sequelae.

Management of sterile para-anastomotic aneurysms of the aorta.

The history of surgical reconstruction of the aorta for aneurysmal and occlusive disease now spans over 50 years. The continued performance of these operations with minor modifications attests to their durability and efficacy. Despite this, some late complications do occur. One such complication is the development of a sterile para-anastomotic aneurysm. This has been reported in 1% to 4% of patients; however, the true incidence of para-anastomotic aneurysms of the aorta (PAAA) may be closer to 25% as evidenced by studies with standardized long-term surveillance. PAAA include true and false aneurysms, which occur in the absence of infection. Computed tomography (CT), magnetic resonance imaging (MRI), and labeled white blood cell scans are vital in excluding the presence of infection and differentiating PAAA from infected false aneurysm, aortic graft infection, and aorto-enteric fistula. The surgical approach to PAAA may require complex reconstruction of the suprarenal or supraceliac aorta similar to thoracoabdominal aortic aneurysm repair. Results of surgery are improved with asymptomatic detection and elective repair of PAAA. Methods of prevention rely mainly on technical perfection, but even with this PAAA likely will never be eliminated. This review will cover the incidence, pathophysiology, presentation, diagnosis and operative treatment of sterile para-anastomotic aneurysms of the aorta. Implications for prevention and the role of surveillance will also be discussed.

Inflammatory abdominal aortic aneurysm treated by endovascular stent grafting: a case report.

Despite complications inherent to open surgical repair of inflammatory abdominal aortic aneurysms, there is expected resolution of the retroperitoneal inflammatory process following graft replacement. An endovascular approach could also exclude the aneurysm while potentially avoiding injury to vital structures in the hostile operative field. However, data are limited regarding the role of endovascular stent grafts in the management of inflammatory abdominal aortic aneurysms. Furthermore, postoperative regression of perianeurysmal inflammation is rarely discussed in the few published accounts of endovascular repair of inflammatory aortic aneurysms. The case presented demonstrates successful endovascular treatment of an infrarenal inflammatory aneurysm with resolution of the retroperitoneal inflammation and hydronephrosis.

Optimizing duplex follow-up in patients with an asymptomatic internal carotid artery stenosis of less than 60%.

OBJECTIVES: The Asymptomatic Carotid Atherosclerosis Study established benefit of carotid endarterectomy for 60% to 99% asymptomatic internal carotid artery (ICA) stenosis. Optimal follow-up intervals to detect progression from < 60% to 60%-99% ICA stenosis are unknown. In a previous study from our laboratory, we found that ICAs with < 60% stenosis and peak systolic velocities (PSVs) of 175 cm/s or more on initial duplex were at high risk for progression. Prospective evaluation of this hypothesis and determination of optimal duplex follow-up intervals for asymptomatic patients with < 60% ICA stenosis form the basis of this report. METHODS: All patients who underwent initial carotid duplex examination for any indication since January 1, 1995, with at least one patent, asymptomatic, previously nonoperated ICA with < 60% stenosis; with 6 months' or greater follow-up; and with one or more repeat duplex examinations were entered into the study. On the basis of the initial duplex examination, ICAs were classified into two groups: those with a PSV less than 175 cm/s and those with a PSV of 175 cm/s or more. Follow-up duplex examinations were performed at varying intervals to detect progression from < 60% to 60%-99% ICA stenosis with criteria previously reported (both PSV > or = 260 cm/s and end-diastolic velocity > or = 70 cm/s). RESULTS: A total of 407 patients (640 asymptomatic ICAs with < 60% stenosis) underwent serial duplex scans (mean follow-up, 22 months). Three ICAs (0.5%) became symptomatic and progressed to 60%-99% ICA stenosis at a mean of 21 months (all transient ischemic attacks), whereas four other ICAs occluded without stroke during follow-up. Progression to 60%-99% stenosis without symptoms was detected in 46 ICAs (7%) (mean, 18 months). Of the 633 patent asymptomatic arteries, 548 ICAs (87%) had initial PSVs less than 175 cm/s, and 85 ICAs (13%) had initial PSVs of 175 cm/s or more. Asymptomatic progression to 60%-99% ICA stenosis occurred in 22 (26%) of 85 ICAs with initial PSVs of 175 cm/s or more, whereas 24 (4%) of 548 ICAs with initial PSVs less than 175 cm/s progressed (P <.0001). The Kaplan-Meier method was used to determine freedom from progression at 6 months, 12 months, and 24 months, which was 95%, 83%, and 70% for ICAs with initial PSVs of 175 cm/s or more versus 100%, 99%, and 95%, respectively, for ICAs with initial PSVs less than 175 cm/s (P <.0001). CONCLUSIONS: Patients with < 60% ICA stenosis and PSVs of 175 cm/s or more on initial duplex examination are significantly more likely to progress asymptomatically to 60%-99% ICA stenosis, and progression is sufficiently frequent to warrant follow-up duplex studies at 6-month intervals. Patients with < 60% ICA stenosis and initial PSVs less than 175 cm/s may have follow-up duplex examinations safely deferred for 2 years.

Revascularization of the superior mesenteric artery alone for treatment of intestinal ischemia.

OBJECTIVE: Complete revascularization is recommended by many authors for treatment of intestinal ischemia. The observation that postprandial intestinal hyperemia is limited to the superior mesenteric artery (SMA) has suggested to us that SMA revascularization alone should be adequate treatment. We preferentially manage intestinal ischemia with a single bypass graft to the SMA and herein update our results using this approach. METHODS: Patients were identified from a prospectively established vascular surgical registry. Each patient was assessed for acute versus chronic intestinal ischemia, preoperative angiographic findings, operation used, perioperative morbidity and mortality, late symptomatic relief, cause of death, and life table-determined survival and graft patency. Graft patency was determined by follow-up angiography or duplex scanning. RESULTS: Fifty bypass grafts to the SMA alone were performed in 49 patients (31 women, 18 men; mean age, 62 years) for treatment of intestinal ischemia. In all patients additional splanchnic arteries were available for bypass grafting. Operative indications were acute symptoms in 21 patients, 14 of whom had bowel infarction; chronic symptoms in 26 patients; and prophylaxis in conjunction with infrarenal aortic surgery in 3 patients. Thirty-two grafts originated from the aorta or an iliac artery, and 18 originated from an aortic graft. There were 40 prosthetic and 10 autogenous conduits. Perioperative mortality was 3% in patients with chronic symptoms and 12% overall. All survivors were symptomatically improved. Mean follow-up was 44 months. Nine-year assisted primary graft patency was 79%, and 5-year patient survival was 61%. Two late deaths occurred in patients with recurrent intestinal ischemia resulting from graft occlusions. CONCLUSIONS: Bypass grafting to the SMA alone appears to be both an effective and durable procedure for treatment of intestinal ischemia. Our results appear equal to those reported for "complete" revascularization for intestinal ischemia. When the SMA is a suitable recipient vessel, multiple bypass grafts to other splanchnic vessels are unnecessary in the treatment of intestinal ischemia.

Is a single preoperative duplex scan sufficient for planning bilateral carotid endarterectomy?

PURPOSE: Duplex scanning is often the sole imaging study before carotid endarterectomy (CEA). Patients with bilateral severe internal carotid artery (ICA) stenosis may be considered for bilateral CEA. High-grade ICA stenosis, however, may artifactually elevate velocity measurements used to quantify stenosis in the contralateral ICA. It is unknown whether ipsilateral CEA will influence duplex determination of the presence of a contralateral 60% to 99% ICA stenosis. This study was performed to determine whether a single preoperative duplex scan is sufficient to plan bilateral CEA. METHODS: Preoperative and early postoperative carotid duplex scans in patients with bilateral ICA stenosis who underwent unilateral CEA were reviewed. Changes in duplex scans that determined stenosis in the ICA contralateral to the CEA were analyzed. Previously validated criteria used to determine 60% to 99% ICA stenosis were a peak systolic velocity (PSV) of 260 cm/sec or more combined with an end diastolic velocity (EDV) of 70 cm/sec or more. RESULTS: Over an 8-year period, 460 patients underwent CEA; 107 patients (23.3%) had an asymptomatic 50% to 99% contralateral ICA stenosis by standard criteria (PSV, >125 cm/sec) and an early postoperative duplex scan examination. Of these 107 patients, 38 patients (35.5%) had duplex scan criteria for 60% to 99% contralateral ICA stenosis. In these 38 patients, there was a mean postoperative PSV decrease of 47.7 cm/sec (10.1%) and a mean EDV decrease of 36.0 cm/sec (19.3%) in the ICA contralateral to the CEA. Eight of 38 (21.1%) preoperative contralateral 60% to 99% ICA lesions were reclassified as less than 60% on postoperative duplex scanning. Six of 69 (8.7%) preoperative lesions of less than 60% were reclassified as 60% to 99% on postoperative duplex scan. These six preoperative examinations were all close to the criteria for 60% to 99% stenosis (mean PSV, 232.5 cm/sec; mean EDV, 62.5 cm/sec). CONCLUSION: One-fifth of patients with apparent 60% to 99% contralateral ICA lesions before the operation have less than 60% stenosis when restudied with duplex scan after unilateral CEA. Lesions below but near the cutoff for 60% to 99% may be reclassified as 60% to 99% on the postoperative duplex scan. These findings mandate that when duplex scanning is used as the sole imaging modality before CEA, patients with severe bilateral carotid stenosis must have an additional carotid duplex examination before operation on the second side.

Extrathoracic arterial grafts performed for carotid artery occlusive disease not amenable to endarterectomy.

HYPOTHESIS: Extrathoracic cervical grafts are safe and provide long-lasting stroke prevention in patients with disease not amenable to standard carotid bifurcation endarterectomy. DESIGN: Review of a prospectively maintained vascular surgical registry. SETTING: Combined university and Department of Veterans Affairs vascular surgical service. PARTICIPANTS: Patients requiring surgery for carotid atherosclerotic occlusive disease not amenable to endarterectomy from January 1988 to March 1998. INTERVENTIONS: Carotid interposition grafting, subclavian-carotid bypass, or carotid-carotid bypass. MAIN OUTCOME MEASURES: Perioperative stroke and death, and life-table determination of freedom from stroke, stroke-free survival, and graft patency. RESULTS: Sixty patients (mean age, 65.8 years; range, 36-83) underwent cervically based carotid grafting. All had greater than 70% stenosis or occlusion of the innominate, common carotid, or internal carotid arteries, and 30 (50%) had undergone at least 1 previous ipsilateral carotid endarterectomy. Indication for operation was stroke or transient ischemic attack in 46 (77%) and asymptomatic high-grade stenosis in 14 (23%). Operative procedures included 31 (52%) carotid interposition grafts, 18 (30%) subclavian-carotid grafts, and 11 (18%) carotid-carotid grafts. Mean follow-up was 29 months (range, 1-117 months). Perioperative stroke rate was 5% (3/60) all in symptomatic patients, and there were no perioperative deaths. By life-table analysis, freedom from stroke was 92% at 1 and 5 years. Stroke-free survival was 90% at 1 year and 61% at 5 years. Primary graft patency was 94% at 1 year and 84% at 5 years, with assisted primary patency of 90% at 5 years. CONCLUSION: Cervical carotid artery grafts for complicated or recurrent carotid atherosclerosis not amenable to endarterectomy are durable and provide excellent freedom from stroke with low perioperative morbidity and mortality.

Does endovascular grafting represent a giant step forward?

Endovascular repair of abdominal aortic aneurysms was first reported in 1991 by Parodi et al. Since then, there has been widespread development of many stent-grafts for abdominal aortic aneurysm (AAA) repair. Available data support the proposition that stent-grafts are generally safe, although their long-term efficacy remains completely unknown. Importantly, endovascular AAA repair has neither fewer complications nor lower mortality rates than open repair; in fact, the opposite appears true. Along with most new techniques come new complications, and endovascular repair of AAA has brought forth the concept of both "endoleak" and device failure. Although it is uncommon, delayed AAA rupture after seemingly successful endovascular repair of AAA has been reported. In our opinion, these faults unique to endovascular repair mandate a cautious approach to the clinical application of stent-grafts. Until ongoing phase 2 and future phase 3 studies are completed with a minimum of 2 to 3 years' follow-up, we shall not know whether endovascular repair of AAA represents a giant step forward or merely an industry-driven overuse of proprietary technology.

Prophylactic repair of renal artery stenosis is not justified in patients who require infrarenal aortic reconstruction.

PURPOSE: Simultaneous prophylactic repair of asymptomatic renal artery stenosis (ARAS) in patients who require infrarenal aortoiliac reconstruction is controversial. This study documents the natural history of ARAS in patients who require aortic reconstruction. METHODS: Two hundred patients who required aortic reconstruction from 1985 to 1990 for indications other than hypertension or renal salvage were identified. ARAS was not repaired. Preoperative angiograms were available for 171 of 200 patients and were reviewed for renal artery stenosis. Patients were assessed for atherosclerotic risk factors, survival, preoperative and follow-up blood pressure, serum creatinine level, antihypertensive medication usage, and need for dialysis. RESULTS: The mean duration of follow-up was 6.3 years. Twenty-four of 171 patients (14%) had preoperative unilateral 70% to 99% diameter reduction ARAS, and eight (5%) had bilateral 70% to 99% ARAS. Clinical features associated with > or =70% ARAS included coronary artery disease, increased age, and a diagnosis of hypertension (p < 0.05). Patients with > or =70% ARAS did not have a decreased 7-year survival rate (66% vs 84%; p = 0.10) but had higher systolic blood pressures (153 +/- 25 vs 138 +/- 30 mm Hg; p < 0.05) as well as increased numbers of antihypertensive medications at follow-up (1.1 +/- 0.2 vs 0.7 +/- 1; p < 0.05). The mean serum creatinine level (1.1 +/- 0.3 preoperative vs 1.4 +/- 0.8 mg/dl; p = NS) was not increased. One patient (0.58%) with polycystic kidney disease and minimal renal artery stenosis required dialysis. CONCLUSIONS: High-grade ARAS in patients who are undergoing infrarenal aortic reconstruction is associated at late follow-up with increased systolic blood pressure and a need for increased numbers of antihypertensive medications, but not decreased survival rate, dialysis dependence, or an increase in serum creatinine level. These data do not support renal artery repair in patients with ARAS who undergo infrarenal aortic reconstruction.

Functional outcome after infrainguinal bypass for limb salvage.

PURPOSE: Functional outcome after infrainguinal bypass (IB) has recently been assessed with global health status questionnaires but not by criteria specific to the objectives of IB (i.e., maintenance of independent living and ambulation). Preoperative and postoperative living situation and ambulatory status were evaluated in patients who underwent IB for limb salvage (LS) indications. METHODS: For patients in whom IB was performed for LS from January 1980 to July 1995, living situation (independent or dependent) and ambulatory status were assessed before the onset of the need for LS surgery and 6 months after surgery. The importance of risk factors (age, sex, diabetes, heart disease, hypertension, renal insufficiency or failure, previous leg bypass, indication for surgery, postoperative morbidity, graft patency) was assessed by multivariate analysis. RESULTS: IB for LS was performed in 513 patients. Before the development of the indication for LS surgery, 92% lived independently and 91% were ambulatory. The operative mortality rate was 2.7%. At 6 months, 86% were alive and the assisted primary graft patency rate was 92%. Ninety-nine percent of survivors who lived independently before developing the need for LS surgery remained independent 6 months after surgery, and 97% of those who were ambulatory before developing the need for LS surgery were ambulatory 6 months after surgery. Only one of 25 survivors (4%) who were not living independently before surgery achieved independent living 6 months after surgery. Twenty-one percent of nonambulatory patients (6 of 29) became ambulatory. Multivariate analysis confirmed the importance of preoperative living situation and ambulatory status in predicting outcome at 6 months (p < 0.0001). Amputation and loss of primary patency were predictive of poor ambulatory status at 6 months (p < 0.0001, p = 0.025, respectively). The overall 5-year survival rate was 48.1%. CONCLUSIONS: Preoperative independence and ambulation best predict postoperative independence and ambulation after IB for LS indications. IB procedures performed for limb salvage have a low operative mortality rate and maintain independent living and ambulation in 99% and 97% of patients, respectively. Poor overall long-term outcome and survival in LS patients results from intercurrent illness and not from IB.

Peroneal bypass is equivalent to inframalleolar bypass for ischemic pedal gangrene.

OBJECTIVE: To determine if peroneal bypass is a suitable alternative to inframalleolar bypass in patients with ischemic pedal gangrene. DESIGN: Review of a prospectively acquired vascular registry. SETTING: University practice limited to vascular surgery. PATIENTS: Patients with chronic lower-extremity ischemia and pedal gangrene evaluated between 1985 and 1995 in whom the only options for arterial reconstruction were bypass to the peroneal or an inframalleolar artery. INTERVENTIONS: Peroneal or inframalleolar reverse vein bypass. MAIN OUTCOME MEASURES: Time to healing and lifetable analyses of survival, primary patency, and limb salvage. RESULTS: Eighty-three peroneal and 46 pedal bypasses were performed for ischemic foot gangrene. The groups were equivalent for sex, diabetes mellitus, heart disease, hypertension, renal failure, hypercoagulable states, previous ipsilateral bypass, smoking, and preoperative ankle-brachial indices. Patients with inframalleolar bypass were younger than patients with peroneal bypass (63.9 vs 71.6 years, P = .005) and had higher postoperative ankle-brachial indices (1.02 vs 0.91, P = .004). However, 3-year survival rates (69.1% inframalleolar vs 60.0% peroneal, P = .35), limb salvage rates at 2 years (70.3% vs 85.8%, P = .10), and time to wound healing (19.7 vs 21.6 weeks, P = .66) were equivalent. CONCLUSION: Peroneal and inframalleolar bypass for ischemic pedal gangrene have equivalent intermediate-term survival, limb salvage, and wound healing. Surgeons should not feel obliged to perform inframalleolar bypass for pedal gangrene if peroneal bypass is possible.

Construction of an Escherichia coli K-12 ada deletion by gene replacement in a recD strain reveals a second methyltransferase that repairs alkylated DNA.

We constructed an ada deletion by gene replacement in a recD1014 strain of Escherichia coli. Characterization of a delta ada-25 recD+ strain revealed the presence of a second DNA methyltransferase activity in E. coli K-12 which transfers a methyl group from methylated DNA to a protein with a molecular weight of 18,000 to 20,000.

The effect of total parenteral nutrition or elemental diet on pancreatic proteolytic activity and ultrastructure.

Previous reports regarding the effect of an elemental diet (ED) on pancreatic secretion have been conflicting. This study was designed to assess the effect of a high-nitrogen ED or total parenteral nutrition (TPN) on proteolytic activity in the pancreatic exocrine cell. Forty-eight dogs were divided into 12 groups of 4 each. Group I (control) was fed commercial dog food. Groups II, III, and IV received 1, 2, and 3 days, respectively, of 25% glucose with 4.25% amino acids. Groups V, VI, and VII received 1, 2, and 3 days, respectively, of 25% glucose with 2.75% amino acids. Groups VIII, IX, and X received 3 days of ED given orally, via gastrostomy or jejunostomy, respectively. Groups XI and XII received 1 day each of either 2.75% amino acids or 25% glucose. The pancreas of each dog was then resected and processed for electron microscopy, or minced and analyzed for tryptic activity expressed as micromoles of benzoyl arginine ethyl ester (BAEE) digested per milligram of pancreatic protein. There were no significant differences in ultrastructure or in the levels of pancreatic tryptic activity between the control and the 11 experimental groups. It appears that during the short period of our treatment with TPN as well as ED, the exocrine cell retains its normal content of proteolytic enzyme. Reports of others that pancreatic secretion volume decreases with TPN and ED, coupled with our findings of stable intracellular tryptic activity, indicate that the synthesis and release of proteolytic enzymes have actually been reduced by TPN and ED. Thus, TPN or ED should benefit the patient with pancreatitis by decreasing pancreatic secretion as well as pancreatic proteolytic enzyme synthesis.

Human pancreatic cell autotransplantation following total pancreatectomy.

During total pancreaticoduodenectomy for chronic pancreatitis, four patients received an intraportal pancreatic mixed-cell autograft prepared by collagenase digestion. The technique of this autotransplantation procedure was successfully developed using a normal canine pancreas, but has proved difficult to apply in the human chronic pancreatitis model. Our four patients became insulin-dependent, with proof of intrahepatic insulin production in only one patient. Three factors have contributed to the lack of graft success: 1) the preoperative endocrine status, 2) systemic hypotension and portal hypertension secondary to graft infusion, and 3) difficulty applying the successful technique in a normal dog pancreas to an extensively scarred human pancreas. The preoperative insulin response during a glucose tolerance test was blunted or delayed in the three patients tested. An immediate decrease in blood pressure and rise in portal pressure occurred in every patient and prevented infusion of the entire graft (30-50%) in three patients. Unfortunately, the patient with the most compromised insulin status was the only patient able to receive the entire graft. Our experience would indicate that further refinements in technique are necessary to prevent the vascular reaction and allow infusion of the entire graft. Furthermore, normal islet cell function is necessary before a successful graft can be expected.

Collagenase activity of the human aorta. A comparison of patients with and without abdominal aortic aneurysms.

Deficit of collagen may be a precipitating cause of aneurysm formation and expansion. Specimens of aneurysmal wall were obtained from 11 patients who underwent aneurysmectomy. Comparison aortic specimens were obtained from five patients who underwent aortofemoral bypass for occlusive disease. Collagenase activity was determined on the particulate and soluble fractions by the liberation of L-leucine, with bovine collagen as the substrate. Collagenase activity was detectable in the abdominal aortic aneurysms (AAAs) but not in atherosclerotic aorta or fascia. Collagenase activity was restricted to the particulate fraction in patients with AAAs, and it correlated with aneurysm size. These data suggest that (1) endogenous collagenolytic activity may be responsible for aneurysmal expansion and rupture and that (2) this enzyme is localized in the aneurysmal wall and is inoperative in arteries affected by atherosclerosis.

Transport of sodium into the xylem exudate of tobacco.

When tobacco (Nicotiana tabacum L. var. Virginia Gold) plants were pretreated with Na ((22)Na) several days before detopping, from 2.3 to 4.9% of Na previously accumulated in roots appeared in the xylem exudate in 7 days after detopping. Na from the external medium, however, was readily transported to the exudate. Moreover, the amount of the pretreatment Na that was transported to the exudate was not influenced by the presence of Na in the external medium. When Na was present in the external medium after detopping, about 4% (with an NaNO(3) post treatment) to 10% (with an NaCl post treatment) of the Na transported to the xylem in the 7 days following detopping originated in the vacuoles. Nitrate salts of K or Na in the external medium after detopping resulted in transport of large quantities of the respective cation to the exudate, but not in increased transport of the pretreatment Na. A much larger percentage of the K that was accumulated after detopping than of the Na similarly accumulated was transferred to the xylem exudate.