L-lactate high-efficiency hemodialysis: hemodynamics, blood gas changes, potassium/phosphorus, and symptoms

Optimizing serum total carbon dioxide concentration during short and nocturnal frequent hemodialysis using lactate as dialysate buffer base

INTRODUCTION

Definitive clinical studies to determine the optimal dialysate lactate concentration to prescribe during frequent hemodialysis when using the NxStage System One dialysis delivery system at low dialysate flow rates have not been reported.

METHODS

We used clinical data from patients who transferred from in-center thrice-weekly hemodialysis (ICHD) to daily home hemodialysis using the NxStage System One and the H⁺ mobilization model to calculate acid generation rates in patient sub-groups during the FREEDOM study. Assuming those acid generation rates were representative, we then predicted using the H⁺ mobilization model the effect of using dialysate lactate concentrations of 40 and 45 mEq/L on predialysis serum total carbon dioxide (tCO₂ ) concentrations in patients who transfer from ICHD to short and nocturnal frequent hemodialysis prescriptions used in current clinical practice; the prescriptions evaluated varied by treatment frequency, dialysate volume per treatment, and treatment times.

FINDINGS

With frequencies of four to six treatments per week and treatment times of 170 to 210 minutes per treatment, the effect of dialysate lactate concentration was primarily dependent on weekly dialysate volume. For weekly dialysate volumes of 150 to 160 L per week, use of dialysate lactate concentrations of 45 mEq/L, but not 40 mEq/L, resulted in an increase of predialysis serum tCO₂ concentration. When longer treatment times typical of nocturnal frequent hemodialysis were evaluated, model predictions showed that the use of dialysate lactate concentration of 45 mEq/L may not be appropriate for many patients because of excessive increases in predialysis serum tCO₂ concentration. Reducing dialysate volume from 60 to 30 L may limit the increase in predialysis serum tCO₂ concentration when patients transfer from ICHD to nocturnal frequent hemodialysis.

DISCUSSION

Predictions from the H⁺ mobilization model show that dialysate lactate concentration and weekly dialysate volume are the primary prescription parameters for optimizing predialysis serum tCO₂ concentration during short and nocturnal frequent hemodialysis.

Acid-base kinetics during hemodialysis using bicarbonate and lactate as dialysate buffer bases based on the H+ mobilization model

BACKGROUND

The H⁺ mobilization model has been recently reported to accurately describe intradialytic kinetics of plasma bicarbonate concentration; however, the ability of this model to predict changing bicarbonate kinetics after altering the hemodialysis treatment prescription is unclear.

METHODS

We considered the H⁺ mobilization model as a pseudo-one-compartment model and showed theoretically that it can be used to determine the acid generation (or production) rate for hemodialysis patients at steady state. It was then demonstrated how changes in predialytic, intradialytic, and immediate postdialytic plasma bicarbonate (or total carbon dioxide) concentrations can be calculated after altering the hemodialysis treatment prescription.

RESULTS

Example calculations showed that the H⁺ mobilization model when considered as a pseudo-one-compartment model predicted increases or decreases in plasma total carbon dioxide concentrations throughout the entire treatment when the dialysate bicarbonate concentration is increased or decreased, respectively, during conventional thrice weekly hemodialysis treatments. It was further shown that this model allowed prediction of the change in plasma total carbon dioxide concentration after transfer of patients from conventional thrice weekly to daily hemodialysis using both bicarbonate and lactate as dialysate buffer bases.

CONCLUSION

The H⁺ mobilization model can predict changes in plasma bicarbonate or total carbon dioxide concentration during hemodialysis after altering the hemodialysis treatment prescription.

Employing L-Lactic Acid Powder in the Preparation of a Dry “Acid Concentrate” for use in a Bicarbonate-Based Dialysis Solution-Generating System: Experience in Hemodialysis Patients

By replacing the liquid acetic acid present in the “acid concentrate” of a bicarbonate-based dialysis solution-generating system with an equimolar amount of solid L-lactic acid and by using the dry forms of the remaining constituents, we were able to create a dry “acid concentrate” just prior to use, and successfully employed this “acid concentrate” to produce a bicarbonate-based solution to hemodialyze patients.

Three-Stream, Bicarbonate-Based Hemodialysis Solution Delivery System Revisited: With an Emphasis on Some Aspects of Acid-Base Principles

Hemodialysis patients can acquire buffer base (i.e., bicarbonate and buffer base equivalents of certain organic anions) from the acid and base concentrates of a three-stream, dual-concentrate, bicarbonate-based, dialysis solution delivery machine. The differences between dialysis fluid concentrate systems containing acetic acid versus sodium diacetate in the amount of potential buffering power were reviewed. Any organic anion such as acetate, citrate, or lactate (unless when combined with hydrogen) delivered to the body has the potential of being converted to bicarbonate. The prescribing physician aware of the role that organic anions in the concentrates can play in providing buffering power to the final dialysis fluid, will have a better knowledge of the amount of bicarbonate and bicarbonate precursors delivered to the patient.

Correction of chronic metabolic acidosis for chronic kidney disease patients

BACKGROUND

Metabolic acidosis is a feature of chronic kidney disease (CKD) due to the reduced capacity of the kidney to synthesise ammonia and excrete hydrogen ions. It has adverse consequences on protein and muscle metabolism, bone turnover and the development of renal osteodystrophy. Metabolic acidosis may be corrected by oral bicarbonate supplementation or in dialysis patients by increasing the bicarbonate concentration in dialysate fluid.

OBJECTIVES

To examine the benefits and harms of treating metabolic acidosis in patients with CKD, both prior to reaching end-stage renal disease (ESRD) or whilst on renal replacement therapy (RRT), with sodium bicarbonate or increasing the bicarbonate concentration of dialysate.

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library, issue 4 2005), Cochrane Renal Group's specialised register (October 2005), MEDLINE (1966 - October 2005) and EMBASE (1980 - October 2005).

SELECTION CRITERIA

Randomised controlled trials (RCTs), crossover RCTs and quasi-RCTs investigating the correction of chronic metabolic acidosis in adults or children with CKD.

DATA COLLECTION AND ANALYSIS

Outcomes were analysed using relative risk (RR) and weighted mean difference (MD) for continuous measures.

MAIN RESULTS

We identified three trials in adult dialysis patients (n = 117). There were insufficient data for most outcomes for meta-analysis. In all three trials acidosis improved in the intervention group though there was variation in achieved bicarbonate level. There was no evidence of effect on blood pressure or sodium levels. Some measures of nutritional status/protein metabolism (e.g. SGA, NP NA) were significantly improved by correction in the one trial that looked in these in detail. There was heterogeneity of the effect on serum albumin in two trials. Serum PTH fell significantly in the two trials that estimated this, there was no significant effect on calcium or phosphate though both fell after correction. Complex bone markers were assessed in one study, with some evidence for a reduction in bone turnover in those with initial high bone turnover and an increase in low turnover patients. The studies were underpowered to assess clinical outcomes, in the one study that did there was some evidence for a reduction in hospitalisation after correction.

AUTHORS' CONCLUSIONS

The evidence for the benefits and risks of correcting metabolic acidosis is very limited with no RCTs in pre-ESRD patients, none in children, and only three small trials in dialysis patients. These trials suggest there may be some beneficial effects on both protein and bone metabolism but the trials were underpowered to provide robust evidence.

Composition and clinical use of hemodialysates

A thorough knowledge and understanding of the principles underlying the preparation and the clinical application of hemodialysates can help us provide exemplary patient care to individuals having end-stage renal disease. It is prudent to be conversant with the following: (a) how each ingredient in a dialysate works, (b) the clinical circumstances under which the concentration of an ingredient can be altered, and (c) the special situations in which unconventional ingredients can be introduced into a dialysate. The potential to enrich dialysates with appropriate ingredients (such as iron compounds) is limited only by the boundaries of our imagination.

The efficiency of potassium removal during bicarbonate hemodialysis

Patients on chronic hemodialysis often portray high serum [K+]. Although dietary excesses are evident in many cases, in others, the cause of hyperkalemia cannot be identified. In such cases, hyperkalemia could result from decreased potassium removal during dialysis. This situation could occur if alkalinization of body fluids during dialysis would drive potassium into the cell, thus decreasing the potassium gradient across the dialysis membrane. In 35 chronic hemodialysis patients, we compared two dialysis sessions performed 7 days apart. Bicarbonate or acetate as dialysate buffers were randomly assigned for the first dialysis. The buffer was switched for the second dialysis. Serum [K+], [HCO3-], and pH were measured in samples drawn before dialysis; 60, 120, 180, and 240 min into dialysis; and 60 and 90 min after dialysis. The potassium removed was measured in the dialysate. During the first 2 hr, serum [K+] decreased equally with both types of dialysates but declined more during the last 2 hr with bicarbonate dialysis. After dialysis, the serum [K+] rebounded higher with bicarbonate bringing the serum [K+] up to par with acetate. The lower serum [K+] through the second half of bicarbonate dialysis did not impair potassium removal (295.9 +/- 9.6 mmol with bicarbonate and 299.0 +/- 14.4 mmol with acetate). The measured serum K+ concentrations correlated with serum [HCO3-] and blood pH during bicarbonate dialysis but not during acetate dialysis. Alkalinization induced by bicarbonate administration may cause redistribution of K during bicarbonate dialysis but this does not impair its removal. The more marked lowering of potassium during bicarbonate dialysis occurs late in dialysis, when exchange is negligible because of a low gradient.

Dialysate calcium profiling during hemodialysis: use and clinical implications

BACKGROUND

Low dialysate calcium (LdCa) concentration is used to prevent or treat hemodialysis (HD)-induced hypercalcemia, but its use has been complicated by intradialytic hypotension in some patients. Our goal was to explore the possibility that dialysis calcium profiling (dCaP) can ameliorate intradialytic hypotension in HD patients who need to have dialysis performed with LdCa.

METHODS

In a randomized crossover design, eighteen HD patients underwent one four-hour HD session with LdCa of 1.25 mmol/L (LdCa group) and one four-hour HD session with LdCa of 1.25 mmol/L during the first two hours and high dCa of 1.75 mmol/L during the remaining two hours (dCaP group). After that, they underwent another four-hour HD session with medium dCa of 1.5 mmol/L (MdCa group). Before HD and at four 60-minute intervals during the HD sessions, blood pressure (BP), heart rate (HR) and noninvasive measurements of cardiac index (CI), using bioelectrical impedance, were obtained. Ionized serum calcium (iCa) also was measured before HD and at 120 and 240 minutes into the HD session. In a separate study, eight HD patients were treated for three weeks with 1.25 mmol/L dCa and three weeks with the dCaP technique described above, in random order. A three-week treatment with MdCa followed. BP and symptoms were recorded during each HD session.

RESULTS

During the LdCa treatment the iCa values remained unchanged, whereas mean arterial pressure (MAP) and CI decreased by 16.5 +/- 8.3% and 14.2 +/- 14.6%, respectively, at the end of HD. During the first half of the dCaP treatment, iCa, MAP and CI decreased by 2.2 +/- 4.1%, 12.6 +/- 12.3%, and 9.6 +/- 13.4%, respectively, whereas during the second half of the same treatment, iCa, MAP and CI values increased by 10.2 +/- 3.3%, 7.8 +/- 7.2% and 10.8 +/- 9.1%, respectively, from the middle HD values. ANOVA showed that the time x treatment effect was significant for iCa, MAP and CI. Total peripheral resistance and HR changes were insignificant and similar among treatments. Hemodynamic effects were comparable between LdCa and MdCa treatments. Intradialytic events were reduced (P < 0.05) only with the dCaP treatment.

CONCLUSIONS

The drop in BP observed during the last two hours of HD in both the LdCa and MdCa groups was abolished in the dCaP group. The latter was accomplished via an increase in cardiac output, due to an iCa-induced increase in myocardial contractility. Therefore, dCaP, by individualizing the dCa concentrations used and timing the switching between them, may improve intradialytic BP instability and simultaneously minimize the risk for HD patients to develop hypercalcemia.

Effect of continuous venovenous hemofiltration with dialysis on lactate clearance in critically ill patients

OBJECTIVE

To evaluate the effect of continuous venovenous hemofiltration with dialysis on lactate elimination by critically ill patients.

DESIGN

Prospective, clinical study.

SETTING

Surgical intensive care unit of a university hospital.

PATIENTS

Ten critically ill patients with acute renal failure and stable blood lactate concentrations.

INTERVENTIONS

Two-stage investigation: a) measurement of lactate concentrations in samples of serum and ultradiafiltrate from patients receiving continuous venovenous hemofiltration with dialysis to calculate lactate clearance by the hemofilter; b) evaluation of total plasma lactate clearance by infusing sodium L-lactate (1 mmol/kg of body weight) over 15 mins.

MEASUREMENTS AND MAIN RESULTS

Arterial lactate concentration was determined before, during, and after the infusion. Lactate elimination variables were calculated from the plasma curve using model-independent and model-dependent estimates (by software). At the end of the infusion, median blood lactate concentration increased from 1.4 mmol/L (range 0.8 to 2.6) to 4.8 mmol/L (range 2.4 to 5.7) and returned to 1.6 mmol/L (range 0.9 to 3.4) 60 mins later. The median total plasma lactate clearance was 1379 mL/min (range 753.7 to 1880.7) and the median filter lactate clearance was 24.2 mL/min (range 7.1 to 35.6). Thus, filter lactate clearance accounted for < 3% of total lactate clearance.

CONCLUSIONS

Continuous venovenous hemofiltration with dialysis cannot mask lactate overproduction, and its blood concentration remains a reliable marker of tissue oxygenation in patients receiving this renal replacement technique.

Cardiac output and urea kinetics in dialysis patients: evidence supporting the regional blood flow model

The regional blood flow model predicts that urea sequestration occurs in organs rather than cells, and that post-dialysis urea rebound is a function of both cardiac index (CI) and regional blood flow distribution to muscle. We measured cardiac output (CO) in 100 randomly selected dialysis patients using bioelectric impedance three times during a single dialysis. Mean CO was 5.8 +/- 2.1 liter/min and CI averaged 3.1 +/- 1.1 liter/min/M2. CI was negatively correlated with age (r = -0.48, P < 0.01). CI was strongly affected by vasodilator ingestion (yes, N = 36, CI = 3.5 +/- 1.2; no, N = 64, CI = 2.88 +/- 0.92, P < 0.006). CI was not associated with systolic, diastolic, or mean blood pressures, nor with Hct, although very few severely anemic patients were in the cohort. Repeat intra-dialytic CO measurements two to three months later in 15 patients with low CI (2.59 +/- 0.59 liter/min/M2) and in 13 patients with high CI (5.00 +/- 0.9, P < 0.001) during a urea kinetic modeling session including 30 minutes post-dialysis rebound, sampling showed highly reproducible values for CO, with a mean absolute value % difference between CO values measured several months apart of 9.0 +/- 17%, r = 0.92. Urea rebound expressed as the difference (delta Kt/V30) between equilibrated and single-pool Kt/V was lower in the high CI group (-0.099 +/- 0.07) than in the low CI group (-0.16 +/- 0.06, P = 0.026), and delta KT/V30 as well as delta Kt/V30 divided by K/V correlated with CI (r = 0.48 and 0.48, respectively, P < 0.01). The RBF model was used to compute a group mean predicted delta Kt/V30 for the low CI and high CI groups based on measured group mean values for CI and K/V. The predicted delta Kt/V30 values for the high CI group (-0.097) and the low CI group (-0.183) agreed closely with measured values. RBF modeled values of CO (7.46 +/- 2.96 liter/min) were not significantly different from impedance-derived CO (6.93 +/- 2.70 liter/min), and the two CO measures correlated significantly (r = 0.63, P = 0.0003). The results provide support for the regional blood flow model of urea kinetics.

Does impedance cardiography reliably estimate left ventricular ejection fraction?

OBJECTIVE

The objective of our study was to evaluate impedance cardiography (IMP) as a noninvasive method to determine the left ventricular ejection fraction (LVEF). METHODS. A total of 24 patients, 8 men and 16 women, aged 45.0 +/- 12.9 years, participated in the study. They used cardiotoxic chemotherapeutic drugs or suffered from cardiac failure. LVEF was measured by means of IMP (LVEFimp) and radionuclide ventriculography (LVEFnuc). LVEFimp was calculated in three ways. Capan and colleagues [13] proposed a formula in which LVEF (LVEFCap) can be calculated from the systolic time intervals, namely, left ventricular ejection time and preejection time. Judy and colleagues [14] described a systolic (S) and a diastolic (D) part in the first derivative curve of the impedance signal. The ratio S/D might equal the LVEF (LVEFJud). A new LVEF calculation was introduced (LVEFimp) in this study based on the first derivative of the impedance signal, the thoracic impedance, and heart rate.

RESULTS

Mean LVEFCap was 59.9 +/- 8.4%, which did not differ from LVEFnuc (59.9 +/- 7.1%). However the correlation between both methods was not significant (r = 0.29). Mean LVEFJud was 63.9 +/- 17.4%, which was not significantly different from LVEFnuc, with a fair correlation (r = 0.55). Mean LVEFimp was 59.2 +/- 9.4%, with a better correlation with radionuclide ventriculography (r = 0.75).

CONCLUSIONS

The results of this study indicate that the equations that have been used until now can be improved. The new equation provides reliable LVEF values in this group of patients.

Bicarbonate dialysate for continuous renal replacement therapy in intensive care unit patients with acute renal failure

Lactate-buffered peritoneal solution traditionally has been used as dialysate for continuous renal replacement therapy (CRRT) in the United States because no bicarbonate solution is commercially available. Since 1994, the Cleveland Clinic Foundation Dialysis Unit has prepared a bicarbonate solution (sodium 144 +/- 3 mEq/L, HCO3 37 +/- 2 mEq/L, potassium 3 or 4 mEq/L, calcium 3.0 +/- 0.3 mEq/L, and magnesium 1.4 +/- 0.3 mg/dL) replicating the dialysate for chronic intermittent hemodialysis. No solute precipitation, as calcium or magnesium salts, were observed, and several cultures of the solution, performed at various time periods, remained negative. Fifty critically ill acute renal failure patients have been treated with bicarbonate-CRRT. All patients were in multiple organ failure and required mechanical ventilation; 37 were receiving vasopressors. Forty-four continuous venovenous hemodialysis sessions and eight continuous arteriovenous hemodialysis sessions were performed with a mean duration of 7.8 +/- 6.1 days. The mean inflow dialysate rate was 1,249 +/- 225 mL/hr and the mean outflow rate (dialysate plus ultrafiltration) was 1,399 +/- 237 mL/hr; the inflow rate was constantly kept lower or equal to the outflow rate to avoid an enhanced potential for backfiltration. No related fever spikes or sepsis episodes were noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dialysate temperature on central hemodynamics and urea kinetics

Use of cool dialysate is associated with increased intradialytic blood pressure, but the hemodynamic mechanism is unknown. Whether changes in dialysate temperature affect muscle blood flow, which may the alter the degree of urea compartmentalization, also is unknown. We measured hemodynamics and blood and dialysate-side urea kinetic indices in nine hemodialysis patients during two cool (35.0 degrees C) versus two warm (37.5 degrees C) dialysate treatments. The % change in mean arterial pressure was different when using the cool (+6.5 +/- 9.7 mm Hg) versus the warm (-13.4 +/- 3.6) dialysate (P < 0.01), despite comparable amounts of fluid removal. Percent changes in cardiac output were similar with the two dialysates, and thus the blood pressure effect was due primarily to changes in total peripheral resistance (% delta TPR, cool +26 +/- 13.6, warm +8.6 +/- 14.5; P < 0.02). During cool dialysate use tympanic membrane temperature changed by -0.51 +/- 0.23 degree C, whereas body temperature increased by 0.52 +/- 0.14 degree C during use of warm dialysate. Measured urea recovery normalized to the predialysis urea nitrogen concentration was similar with the two treatments: cool 31.3 +/- 0.039 liter-1; warm 29.7 +/- 0.021; P = NS. In a second study, post-dialysis urea rebound values from 15 seconds to 30 minutes, expressed as the percent of the post-dialysis SUN, were similar after the two treatments: cool 11.79 +/- 1.4; warm 12.21 +/- 2.27, P = NS.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodialysis with acetate, DL-lactate and bicarbonate: a hemodynamic and gasometric study

Using invasive techniques we have studied various hemodynamic and gasometric parameters in the course of hemodialysis (HD) with different buffers in an animal model. HD sessions of 180 minutes at zero ultrafiltration were carried out on three groups of eight uremic dogs each, under anesthesia and constant mechanical ventilation. The three groups differed only in the buffer used: acetate (Group AC), equal proportions of DL-lactate and acetate (Group AC+LA), and bicarbonate (Group BC). No hemodynamic changes were seen in Group BC. In the AC and AC+LA groups we observed on minute 1 a decrease of the mean blood pressure (MBP) and of the systemic vascular resistances (SVR). These parameters returned to baseline values within the first 30 minutes in Group AC+LA. In Group AC the SVR also returned to baseline values after the minute 30, but the MBP remained below baseline throughout the study period, together with cardiac index and left ventricular stroke work index decreases. Only in Group AC did we see a flattening of the ventricular function curves. Only in this Group was there a decrease of the arterial oxygen pressure (PaO2) with an associated increase of the alveolo-arterial and arterio-venous O2 differences. The O2 consumption was not modified in any of the groups. Acetate as a single buffer induces hemodynamic instability through peripheral vasodilation and reduction of myocardial contractility. The myocardial depression induced by acetate, in its turn, causes a reduction in PaO2. The mixed acetate+lactate buffer is hemodynamically better tolerated than acetate as single buffer, as it induces only vasodilation.

Ventilatory and metabolic changes during high efficiency hemodialysis

Ventilatory and metabolic changes were measured in seven patients undergoing high efficiency hemodialysis using a cuprophane dialyzer and bicarbonate-containing dialysate. At an HCO3 concentration of 35 mEq/liter and a mean in vivo urea clearance of 3.6 ml/kg/min, hypoxemia was not detected during dialysis (PaO2 was 14.00 and 13.60 kPa before and during dialysis). The new findings, related to high efficiency bicarbonate dialysis, include a sustained rise in minute ventilation (VE, 6.1 to 6.8 liter/min, P less than 0.01), an increase in CO2 excretion (VCO2, 194 to 214 ml/min, P less than 0.05), and O2 consumption (VO2, 215 to 246 ml/min, P less than 0.05). The increment in VE and VCO2 was attributed to the high flux rate of bicarbonate while the rise in VO2 is likely the result of metabolic alkalosis. Arterial pH rose from 7.40 to 7.49 mm Hg and serum HCO3 increased from 23.8 to 29.2 mEq/liter, while pCO2 remained normal at 5.07 kPa throughout the study. The acid-base status of the blood changed from that of a metabolic acidosis to that of a respiratory acidosis across the dialyzer where the pH decreased from 7.47 to 7.41 and pCO2 rose from 5.31 to 7.72 kPa. These data indicate that a healthy ventilatory response is needed to excrete the excess CO2 generated during high efficiency bicarbonate hemodialysis. The significance and etiology of the elevated O2 consumption is undetermined.

The vasorelaxant effects of acetate: role of adenosine, glycolysis, lyotropism, and pHi and Cai2+

The mechanism of acetate vasorelaxation is unknown. In the rat caudal artery, acetate has a vasorelaxant effect and also increases cyclic AMP. Here we evaluate the role of adenosine, of possible glycolysis inhibition by acetate, of the lyotropic properties of acetate and other anions, and of intracellular calcium and pH. Adenosine per se did not relax the caudal artery in the range of 10(-8) to 10(-2) M. Preincubation with adenosine deaminase (ADA, 5.0 U/ml) or with 8-phenyltheophylline (8-PT, 10(-6) to 10(-4) M) increased, rather than blocked the vasorelaxant effect of acetate. Oxypurinol (10(-3) M) or the nucleoside transport inhibitor NBMPR (10(-4) M) had no effect on acetate relaxation. Whereas acetate increased tissue cyclic AMP content, 10(-3) M adenosine or 10(-6) M PIA had no effect. In strips studied under conditions of inhibited glycolysis (no glucose, with 11 mM 2-deoxyglucose, 1.0 mM pyruvate, and 0.5 mM 5-iodoacetate), acetate-induced relaxation, as well as acetate-induced cyclic AMP generation, tended to be reduced but not significantly so. Other anions relaxed vascular strips in relation to their lyotropic number, but only at higher doses, and they did not stimulate cyclic AMP formation. Acetate (10 mM) caused a transient fall in Ca2+i followed by a slight, sustained rise. A concomitant decrease in pHi was seen. DIDS, which blocks the relaxant and cyclic AMP effects of acetate, had no effect on the pHi decrease, but did decrease the rate of pHi recovery.(ABSTRACT TRUNCATED AT 250 WORDS)