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D R Spahn

Publications and source records attributed to D R Spahn.

At least 19 recordsLinked to original sources
PubMed1996

Radial artery tonometry: moderately accurate but unpredictable technique of continuous non-invasive arterial pressure measurement.

Radial artery tonometry provides continuous measurement of non-invasive arterial pressure (CNAP) by a sensor positioned above the radial artery. An inflatable upper arm cuff enables intermittent oscillometric calibration. CNAP was compared with invasive radial artery pressure recordings from the opposite wrist in 22 high-risk surgical patients with an inter-arm oscillometric mean arterial pressure difference < or = 10 mm Hg. Oscillometric, tonometric and invasive digital pressure values, and invasive and CNAP waveforms were obtained by the same instrument (Colin BP-508). Correlation coefficients (r) of invasive vs oscillometric values (n = 481 pairs) were 0.83, 0.90 and 0.92, and mean absolute errors of oscillometry were 7.6, 4.7, and 2.6 mm Hg for systolic, diastolic and mean arterial pressures, respectively. Correlation was poor for systolic (r = 0.80), diastolic (r = 0.77) and mean (r = 0.84) invasive vs CNAP values (n = 1375). Compared with oscillometry, mean absolute errors of 15.2, 10.9 and 9.4 mm Hg for systolic, diastolic and mean CNAP, respectively, were significantly (P < 0.001) higher. Mean prediction errors of CNAP, compared with invasive values, were -5.8 (SD 14.2) mm Hg for systolic, +7.2 (8.3) mm Hg for diastolic and +3.9 (8.8) mm Hg for mean arterial pressure. Individual patient accuracy of CNAP was assessed as good (individual prediction error < or = 5 (8) mm Hg and individual absolute error < or = 10 mm Hg) in seven patients, as acceptable (< or = 10 (12) and < or = 15 mm Hg) in 11 patients, and as inadequate in four of 22 patients. Individual accuracy of oscillometry was good or acceptable in all 22 patients. The trend in CNAP changes (difference between consecutive measurements) was sufficiently accurate during induction of anaesthesia, as only 47 (7.6%), 14 (2.3%) and 27 (4.4%) of 616 systolic, diastolic and mean CNAP values differed by more than 10 mm Hg of invasive pressure trends. We conclude that: intermittent oscillometry provides accurate arterial pressure monitoring; CNAP measurements offer a reliable trend indicator of pressure changes during induction of anaesthesia and may be considered an alternative to invasive pressure measurements, should arterial cannulation be difficult in an awake patient; and accuracy of absolute CNAP values is only moderate and unpredictable, thus radial artery tonometry should not replace invasive monitoring in high-risk patients during major surgical procedures.

Adult↗
PubMed1996

Hemodilution tolerance in elderly patients without known cardiac disease.

Hemodilution tolerance is not well defined in elderly patients. In 20 patients older than 65 yr and free from known cardiovascular disease, hemodynamic variables, ST segment deviation, and O2 consumption were determined prior to and after 6 and after 12 mL/kg isovolemic exchange of blood for 6% hydroxyethyl starch. The mean age of the patients was 76 +/- 2 yr (mean +/- SEM, range 66-88 yr). During hemodilution, hemoglobin decreased from 11.6 +/- 0.4 to 8.8 +/- 0.3 g/dL (P < 0.05). With stable filling pressures, cardiac index increased from 2.02 +/- 0.11 to 2.19 +/- 0.10 L.min-1.m-2 (P < 0.05) while systemic vascular resistance decreased from 1796 +/- 136 to 1568 +/- 126 dynes.s.cm-5 (P < 0.05) and O2 extraction increased from 28.0% +/- 0.9% to 33.0% +/- 0.8% (P < 0.05) resulting in a stable O2 consumption during hemodilution. No alterations in ST segments were observed in lead II during hemodilution. In lead V5, ST segment deviation became slightly less negative during hemodilution from -0.03 +/- 0.01 to -0.02 +/- 0.01 mV (P < 0.05). The moderate decrease in hemoglobin was fully compensated by both an increase in cardiac index and in O2 extraction. Electrocardiographic signs of myocardial ischemia were not observed in this population. In conclusion, isovolemic hemodilution to a hemoglobin value of 8.8 +/- 0.3 g/dL is well tolerated in elderly patients free from known cardiac disease at the ages of 65-88 yr.

Abdomen↗
PubMed1996

Hemodilution tolerance in patients with coronary artery disease who are receiving chronic beta-adrenergic blocker therapy.

Hemodilution tolerance is not well defined in patients with coronary artery disease receiving beta-adrenergic blockers chronically. Ninety patients scheduled for coronary artery bypass graft (CABG) surgery were randomized to a hemodilution (n = 60) and a control group (n = 30). During midazolam-fentanyl anesthesia, hemodynamic variables, ST segment deviation, and O2 consumption were determined prior to and after 6 and 12 mL/kg isovolemic exchange of blood for 6% hydroxyethyl starch. Hemoglobin decreased from 12.6 +/- 0.2 to 9.9 +/- 0.2 g/dL (mean +/- SEM, P < 0.05). With stable filling pressures, cardiac index increased from 2.05 +/- 0.05 to 2.27 +/- 0.05 L.min-1.m-2(P < 0.05) and O2 extraction from 27.4% +/- 0.6% to 31.2% +/- 0.7% (P < 0.05), resulting in stable O2 consumption. No alterations in ST segments were observed in leads II and V5 during hemodilution. Individual increases in cardiac index and O2 extraction were not linearly related to age and left ventricular (LV) ejection fraction (P = 0.841, P = 0.799). We conclude that isovolemic hemodilution to a hemoglobin value of 9.9 +/- 0.2 g/dL is well tolerated and fully compensated in patients with coronary artery disease receiving beta-adrenergic blockers chronically. Within the investigated ranges, the compensatory mechanisms during hemodilution are largely independent of age (35-81 yr) and LV ejection fraction (26%-83%).

Adrenergic beta-Antagonists↗
PubMed1995

Continuous non-invasive blood pressure monitoring by brachial artery displacement method in high-risk surgical patients.

Continuous non-invasive blood pressure (CNBP) measurements were compared to invasive radial artery pressure recordings in 26 patients with cardiac, vascular and/or pulmonary disease. Patients were studied during general anaesthesia (n = 6), regional anaesthesia (n = 10), or combined technique (n = 10) for abdominal or transurethral surgery. CNBP was obtained from a cuff placed around the upper arm and simultaneously compared to invasive pressure from the ipsilateral radial artery. A CNBP device (7001 Cortronic) used intermittent oscillometric measurement for calibration. Through a cuff continuously inflated to a pressure of 20 mmHg, a microprocessor-controlled electro-pneumatic acquisition system sensed displacements of the brachial artery wall. Amplified, digitally converted, filtered and transformed data were displayed as a continuous pulse pressure waveform and digital pressure values on the screen. The CNBP method functioned without disturbances before surgery in all patients. Intra-operative use of electrocautery or a spontaneous occurrence of warning on the screen repeatedly triggered oscillometric recalibration, hence CNBP measurements were discontinued in nine patients. Coefficients of correlation (r) of all invasive and CNBP pairs (n = 1111) were 0.68, 0.58 and 0.70 for systolic, diastolic, and mean blood pressures, respectively. Prediction errors (bias, mean +/- SD) were -13.6 +/- 22.5 mmHg (on average CNBP < invasive pressure) for systolic, +13.0 +/- 12.4 mmHg (CNBP > invasive pressure) for diastolic and +5.0 +/- 13.9 mmHg (CNBP > invasive pressure) for mean CNBP, as compared to radial artery pressure values. Absolute errors (precision) were 25.3 +/- 9.4 mmHg for systolic, 17.4 +/- 4.5 mmHg for diastolic, and 13.9 +/- 4.6 mmHg for mean CNBP. During anaesthesia induction (n = 672) the difference between consecutive measurements (trend of pressure changes) with invasive and CNBP method exceeded 20 mmHg in 90 (13.3%) instances for systolic, in 33 (4.9%) instances for diastolic, and in 45 (6.6%) instances for mean blood pressure. In conclusion, the CNBP method by brachial artery wall displacement failed to measure the blood pressure reliably and to display the trend of pressure changes correctly during anaesthesia induction. In its present form this CNBP method should not replace invasive blood pressure monitoring in high-risk patients neither for anaesthesia induction nor during non-thoracic surgical procedures.

Abdomen↗
PubMed1994

Aortic dissection.

Explore the source record for details and available documents.

Aortic Dissection↗
PubMed1994

High-frequency ventilation: oscillatory dynamics.

OBJECTIVES: To determine the influence of the dynamic properties of the oscillator on the oscillatory volume delivered through the endotracheal tube to the lung or lung surrogate (delivered volume) under conditions of high-frequency ventilation. In particular, the relation between the tidal volume of the pump (oscillator) and the delivered volume was analyzed. PaCO2 was measured further as a function of the delivered volume in a number of experiments performed with healthy dogs. DESIGN: Laboratory study. SETTING: Engineering and animal laboratory. SUBJECTS: Lung surrogates and healthy dogs. INTERVENTIONS: An experimental oscillatory system was connected to various lung surrogates. In addition, six beagle dogs received high-frequency ventilation with different delivered volumes during the study. Control of the mean airway pressure was achieved by a peripheral pressure chamber located at the exhaust port of the bias flow tube. RESULTS: The delivered volume, which is the quantity of interest from a physiologic point of view, can deviate considerably from the tidal volume of the pump due to dynamic (particularly resonance) effects. Because the delivered volume and the mean airway pressure have to be controlled independently, two independent quantities are necessary for control purposes (e.g., the tidal volume of the pump and the mean pressure at the exhaust port). Furthermore, it was found that a minimal condition for adequate gas exchange is a delivered volume that exceeds the machine-related deadspace. For this reason, and in order to maximize the CO2 gradient, the exhaust tube must be as short as possible. CONCLUSIONS: a) The delivered volume has to be monitored under clinical conditions; b) however, because the impedance of the endotracheal tube in general considerably exceeds the impedance of the lung, the influence of the impedance of the lung on the delivered volume is generally small, and thus an in vitro calibration may serve as a useful approximation; c) at least two independent quantities are needed for an adequate oscillatory control; d) a necessary (not necessarily sufficient) condition for adequate CO2 removal is that the delivered volume must exceed the machine-related deadspace; e) in a clinical environment involving extremely pathologic lung conditions, e.g., adult respiratory distress syndrome, mechanical lung characteristics may deviate substantially from those characteristics used in this study (i.e., the results obtained may not necessarily be applicable under all clinical situations).

Animals↗
PubMed1994

Regional ischemia during hemodilution in flow compromised myocardium: evidence for incomplete metabolic recovery.

The hypothesis that mild decreases in myocardial function may occur with preservation of normal levels of intramyocardial ATP was tested. A model of single vessel coronary stenosis using eight mongrel dogs in an open chest preparation was used. Myocardial oxygen supply was altered by performing acute normovolemic hemodilution with a colloid solution. The results demonstrated significant alterations in myocardial ATP content with hemodilution-induced mild regional dysfunction, which was not in line with the hypothesized effects of ischemia on myocardial function. In addition, restoring myocardial function by minimal reinfusion of shed blood in this study did not restore myocardial energy stores, an effect that may be called metabolic stunning. The results suggest that myocardial stunning may not be an important and ubiquitous process during intraoperative myocardial ischemia. Further, myocardial function appears to be capable of quickly recovering from mild ischemia although metabolic function may be slower. Finally, the concept of decrements in myocardial function occurring in order to preserve myocardial metabolic stores does not appear to occur universally, which may be significant in the prevention or treatment of mild perioperative ischemia.

Adenosine Triphosphate↗
PubMed1994

Cardiovascular and coronary physiology of acute isovolemic hemodilution: a review of nonoxygen-carrying and oxygen-carrying solutions.

Acute isovolemic hemodilution is used increasingly to avoid the potentially serious side effects of homologous blood transfusions. Cardiovascular physiology during hemodilution is characterized by a marked increase in cardiac output and organ blood flow to compensate for the decrease in arterial oxygen-carrying capacity. During advanced hemodilution an increased oxygen extraction is also observed, such that oxygen consumption generally is maintained even during advanced hemodilution. The increase in cardiac output is related mainly to a decrease in blood viscosity and an enhanced sympathetic tone resulting in stimulation of the heart. The magnitude and the mechanisms involved in the increase depend upon species, state of awareness (awake versus anesthetized), type of anesthesia, type of exchange solution, and condition of the heart prior to hemodilution. Recent laboratory findings, as well as clinical practice in cardiac surgery, suggest that moderate hemodilution to hematocrit values of approximately 25% is well tolerated in single vessel coronary artery disease which should thus not be regarded as an absolute contraindication for moderate hemodilution. An integral concept to minimize homologous blood transfusions consists of preoperative autologous blood donation, preoperative isovolemic hemodilution, meticulous (asanguineous) surgical technique, and acceptance of minimum hemoglobin levels during the entire hospitalization. The incidence of homologous blood transfusions will be reduced using acute isovolemic hemodilution. This incidence will be further reduced once hemoglobin solutions become clinically available for specific indications. At present, research activities are concentrated on defining the critical level of hemodilution in various pathologic conditions and to investigate pharmacology and physiology of the new hemoglobin solutions. Finally, several chemically modified hemoglobin-based oxygen-carrying solutions devoid of renal toxicity will be available in the future. The cardiovascular physiology and pharmacology of these hemoglobin solutions have been studied. Cardiac output is generally constant and oxygen extraction is increased to maintain oxygen consumption during hemodilution with hemoglobin solutions. In most studies, some vasoconstriction was observed also, which might result from interaction of the hemoglobin molecule with the EDRF/NO system. However, with enhanced purification, chemical modification or microencapsulation of the hemoglobin molecule, vasoconstriction can be limited.

Blood Substitutes↗
PubMed1994

Importance of severity of coronary artery disease for the tolerance to normovolemic hemodilution. Comparison of single-vessel versus multivessel stenoses in a canine model.

The response of global cardiovascular and regional myocardial function (as seen with sonomicrometry) to continuous, progressive hemodilution (Dextran 70) was compared in dogs with proximal circumflex coronary artery stenosis and dogs with proximal circumflex coronary artery and proximal left anterior descending artery stenoses. Hemodilution-induced failure, defined as greater than 50% loss in function or death of the animal, was determined for systolic shortening in the circumflex coronary artery and left anterior descending artery territories, mean arterial pressure, and maximum left ventricular rate of pressure rise. Time to failure was compared between groups by log-rank tests. Systolic shortening of the circumflex coronary artery failed at a similar median time point in both groups (30 minutes in the group with single-vessel stenosis and hemodilution versus 40 minutes in the group with multivessel stenosis and hemodilution). Systolic shortening of the left anterior descending artery (80 versus 50 minutes), mean arterial pressure (70 versus 50 minutes), and maximum left ventricular rate of pressure rise (70 versus 40 minutes), however, failed significantly later (p < 0.01) in animals with single circumflex coronary artery stenosis. A marked increase (+50%) in systolic shortening of the left anterior descending artery was observed during hemodilution only in the circumflex coronary artery stenosis group. The better hemodilution tolerance in the circumflex coronary artery stenosis group may be explained by the compensatory increase in myocardial contractile function in non-coronary flow-compromised myocardium, which seems to be crucial for global cardiovascular stability during hemodilution in the presence of coronary stenoses.

Animals↗
PubMed1993

Is esmolol cardioprotective? Tolerance of pacing tachycardia, acute afterloading and hemodilution in dogs with coronary stenosis.

OBJECTIVES: The aim of this study was to determine whether esmolol, an ultrashort-acting beta-adrenergic antagonist, possesses cardioprotective properties unrelated to a concomitant decrease in heart rate. BACKGROUND: Previous studies have demonstrated beneficial effects of beta-adrenergic blocking agents with unchanged heart rates. METHODS: The effect of esmolol (100 micrograms/kg per min) on the response of global cardiovascular and regional myocardial contractile function (sonomicrometry) to pacing-induced tachycardia and acute left ventricular afterloading was assessed in dogs with a critical stenosis of the left anterior descending coronary artery (LAD). These responses were observed at the baseline hemoglobin level (12.5 +/- 0.3 g/100 ml) as well as after hemodilution-induced mild regional contractile dysfunction (7.4 +/- 0.4 g/100 ml) in the area supplied by this artery (LAD area). Data were analyzed by using a repeated measures multivariate analysis of variance with complete block design treating pacing rate and afterloading, respectively, as the repeated measure. RESULTS: Esmolol decreased the maximal first derivative of left ventricular pressure (dP/dtmax); global cardiovascular and regional myocardial contractile function were otherwise unchanged. Esmolol did not alter the response of global cardiovascular or regional myocardial function to pacing-induced tachycardia or to acute left ventricular afterloading, both at the baseline hemoglobin level as well as during mild hemodilution-induced LAD area contractile dysfunction. CONCLUSIONS: At an infusion rate of 100 micrograms/kg per min we were unable to demonstrate cardioprotective esmolol effects in a canine model of critical coronary stenosis with controlled heart rate and identical loading conditions.

Adrenergic beta-Antagonists↗
PubMed1993

Pacing-induced left ventricular asynchronies in dogs with critical coronary stenosis: mechanisms and effect of anesthetics.

The mechanisms leading to left ventricular (LV) asynchronies are incompletely understood, and reports on the functional significance of asynchronies for the affected segments are conflicting. To characterize LV asynchronies, 16 anesthetized dogs with critical stenosis of the left anterior descending coronary artery (LAD) were instrumented to measure subendocardial contractile function (sonomicrometry) and the ECG in the LAD territory. The subendocardial ECG was also recorded from the anterior basal LV territory. Time of regional S wave arrival (TS) and time of onset of segment shortening were determined. The animals underwent atrial pacing with increasing frequencies until systolic LAD territory contractile dysfunction and eventual LV asynchronies were observed. Six animals without LAD stenosis served as controls to define the normal response (mean +/- 2.SD) to increasing pacing rates of systolic shortening and onset time of segment shortening (time difference between TS and onset of segment shortening). LAD contractile dysfunction was considered as a systolic shortening below the normal range, and LV asynchronies as an onset time of segment shortening above the normal range. When LV asynchronies occurred, onset time of segment shortening in the LAD territory was 80.1 +/- 4.9 ms versus 14.8 +/- 3.7 ms at control (P < 0.01); the time difference between S wave arrival in the LAD and circumflex territories, however, was unchanged. LV asynchronies were associated with marked LAD territory contractile dysfunction (systolic shortening of 9.6 +/- 0.8% v 21.0 +/- 1.9% at control, after systolic shortening of 31.3 +/- 3.8% v 9.0 +/- 2.6% at control; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetics↗
PubMed1993

Is post cardiopulmonary bypass dysfunction a special form of stunning?

It has been suggested that cardioplegic arrest during cardiopulmonary bypass (CPB) produces global myocardial ischemia with a risk of myocardial stunning. It has also been postulated that anesthetic technique may affect the course of post-CPB myocardial stunning via exaggerated myocardial depression. However, we have previously found that global ventricular and regional myocardial responses to halothane do not differ in post-CPB and pre-CPB dogs. Our examination of the effects of CPB on the beta-adrenergic function revealed that beta-adrenergic receptor function is only slightly decreased immediately following (i.e., 1 min) and 30 minutes post-CPB. A dose-response relationship was established for dobutamine, with decreased responsiveness noted at both times. Since other data show normal inotropic stimulation of stunned myocardium, decreases in dobutamine responsiveness cannot be explained by beta-receptor desensitization. Overall, these data indicate that CPB does not result in myocardial stunning. The differences between these data and others showing myocardial stunning following CPB may be due to several factors, such as anesthetic regimen, lack of coronary blood flow abnormalities, and a reduction in sarcoplasmic reticular damage due to the hypothermic conditions used.

Anesthetics↗
PubMed1993

Hemodilution induces stable changes in global cardiovascular and regional myocardial function.

The cardiovascular responses associated with isovolemic hemodilution have been described. However, the stability of these responses over time remains controversial. We hypothesized that the hemodynamic responses to isovolemic hemodilution are stable over time. Nine fentanyl-midazolam-anesthetized dogs were monitored to follow global cardiovascular and regional myocardial function. Isovolemic hemodilution was performed to a moderate (hemoglobin = 7.5 g%) target hemodilutional state that was maintained for 4 h. Data were obtained at each hemodilutional state and each hour during the 4-h period of sustained moderate hemodilution. During acute hemodilution, cardiac output increased from 2.6 +/- 0.5 L/min to 3.0 +/- 0.5 L/min (P < 0.05) and mean coronary flow increased from 20.8 +/- 2.4 mL/min to 31.4 +/- 5.5 mL/min (P < 0.05). Cardiac output and mean coronary flow remained elevated during the extended hemodilutional period. In addition, norepinephrine increased from 586 +/- 152 pg/mL to 1135 +/- 247 pg/mL (P < 0.05) during acute isovolemic hemodilution and remained at this increased level during extended hemodilution. Epinephrine levels did not change with hemodilution. Compensatory mechanisms such as increases in cardiac output and mean coronary flow observed during acute hemodilution persist during extended periods of hemodilution.

Animals↗
PubMed1993

Reliability of a new generation transesophageal Doppler device for cardiac output monitoring.

A new generation continuous-wave transesophageal Doppler (TED) device for cardiac output (CO) monitoring (Accucom 2, Datascope), which displays aortic blood flow velocity in real time, was evaluated by 140 simultaneous comparisons with thermodilution (TD) in 16 patients early after coronary artery bypass surgery. The aim was to determine whether this technologic advancement improves the accuracy of COTED assessment. Absolute COTED values showed a considerable scatter as compared to COTD [COTED = 1.77 + 0.75.COTD (L/min), r = 0.52]. The bias, i.e., the mean of individual CO differences (COTD-COTED) was -0.37 +/- 1.70 L/min (SD). In contrast, relative CO changes (delta CO, % of preceding value) showed a satisfactory agreement between TED and TD [delta COTED = 1.04 + 0.91.delta COTD (%), r = 0.84, n = 124], the bias (delta COTD-delta COTED) being -0.66 +/- 9.72%. In 8 of 124 situations (6.45%), however, significant COTED changes opposite in direction to that of significant COTD changes occurred. This frequency was significantly greater (P < 0.01) than the ideal frequency of 0%. The agreement between delta COTD and delta COTED improved (P < 0.05) when the aortic diameter changes induced by changes in mean arterial pressure were considered [delta COTEDMAPC = 1.10 + 0.95.delta COTD (%), r = 0.87, n = 124]. Compared with previous results, the reliability of the second generation device to monitor relative CO changes was considerably improved. Provided that the aortic blood flow velocity signal was stable and free from any disturbances, the second generation TED device may be regarded acceptable for CO trend monitoring in sedated, paralyzed patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

[Hemodilution tolerance in coronary heart disease: single vessel versus multiple vessel disease].

Isovolemic hemodilution is well tolerated in experimental models of single vessel coronary artery disease. Little information, however, is available on the hemodilution tolerance in presence of multivessel coronary artery disease. 42 dogs were anesthetized and instrumented to determine global cardiovascular and regional myocardial functions (systolic shortening, SS) in the anterior apical LV territory supplied by the left anterior descending coronary artery (LAD) as well as in the posterior apical LV wall supplied by the circumflex coronary artery (LC) using sonomicrometry. Critical coronary stenoses were imposed on the proximal LAD and LC according to the experimental group assignment and group 1V-HD (LC stenosis only) and group 2V-HD (LC and LAD stenoses) were then progressively hemodiluted using Dextran 70,000. 1000 ml blood per hour was thereby continuously exchanged with 900 ml Dextran until the animal expired or 120 minutes were reached. 12 dogs (LAD and LC stenoses) served as controls (2V-C). All groups started with similar hemoglobin values and these decreased similarly in both hemodiluted groups. Myocardial contractile function in the LC territory failed similarly in the 1V-HD and 2V-HD groups during progressive hemodilution. The LAD myocardium, however, responded markedly different in the 2V-HD as compared to the 1V-HD group: In the 2V-HD group, SSLAD started to decrease shortly into hemodilution, whereas SSLAD progressively increased during the first 60 min of continuous hemodilution in the 1V-HD group. The presence of non-compromised LV myocardium with the ability of a compensatory increase in contractile function thus seems to crucial for the hemodilution tolerance in the setting of coronary artery disease.

Animals↗
PubMed1993

Acute isovolemic hemodilution and blood transfusion. Effects on regional function and metabolism in myocardium with compromised coronary blood flow.

The use of isovolemic hemodilution to prevent adverse side effects of homologous blood transfusions has increased. The lowest level of hemoglobin that can be tolerated without regional myocardial dysfunction, however, had not been precisely defined for left ventricular myocardium with compromised coronary blood flow. This level was determined in our study in 19 dogs with critical stenosis of the left anterior descending coronary artery during graded isovolemic hemodilution. Regional function was assessed by sonomicrometry in the territory supplied by the left anterior descending coronary artery, as well as in two noncompromised left ventricular areas; oxygen extraction and consumption in the left anterior descending coronary artery region were assessed by analysis of anterior descending coronary venous oxygen saturation. The median lowest level of hemoglobin tolerated without contractile dysfunction of the territory supplied by the left anterior descending artery was 7.5 gm/dl, with lower and upper quartiles of 6 and 9 gm/dl. In addition to a marked increase in cardiac output and transstenotic left anterior descending flow, global cardiac and regional myocardial functions were unchanged at a hemoglobin level of 7.5 gm/dl, as compared with a control level of hemoglobin of 12.0 +/- 0.4 gm/dl. At a mean level of hemoglobin of 6.0 +/- 0.4 gm/dl, marked contractile dysfunction developed in the left anterior descending region: Systolic shortening decreased from 24.2% +/- 2.1% to 17.9% +/- 1.9% (p < 0.01); postsystolic shortening increased from 4.0% +/- 3.0% to 12.2% +/- 3.8% (p < 0.01); and in the left anterior descending region, oxygen consumption decreased. The increase of arterial level of hemoglobin by only 1.9 +/- 0.2 gm/dl restored contractile function in the left anterior descending region, regional oxygen consumption, and oxygen extraction across the left anterior descending region. Moderate isovolemic hemodilution is relatively well tolerated in left ventricular myocardium with compromised coronary blood flow, and hemodilution regional contractile dysfunction induced by hemodilution is reversible by minimal blood transfusion.

Animals↗
PubMed1992

Gas transport during high-frequency ventilation: the significance of direct wash-out.

Gas transport during high-frequency oscillation was investigated in vitro using CO2 elimination from the lung surrogate as a measure of gas transport efficiency. The length of the connecting tube between the piston pump and the three-port connector did not affect gas transport efficiency if the oscillatory volume (VDEL) was constant; inserting an additional tube between the three-port connector and the endotracheal tube decreased gas transport efficiency dramatically. In contradistinction, increasing VDEL caused a steep rise in gas transport efficiency as soon as VDEL surpassed the volume of the tubes connecting the lung surrogate with its surroundings. As gas transport efficiency was found to be very sensitive to the net oscillatory volume, i.e. VDEL minus the volume of the tubes connecting the lung and the surroundings, direct wash-out was considered to be an effective gas transport mechanism during high frequency oscillation. Two preliminary experiments on dogs allowed us to substantiate this hypothesis in vivo.

Animals↗