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Biomedical subjects

J E Calvin

Publications and source records attributed to J E Calvin.

At least 55 records · Page 3Linked to original sources
PubMed1990

How can new technology be introduced, evaluated, and financed in critical care?

We briefly review issues impacting the introduction, evaluation, and cost of technology in critical care, providing a clinician's perspective. Where appropriate, we note important distinctions between health-care systems in Canada and the United States--primarily the result of significant differences in the methods for funding health care in the two countries. Finally, we discuss what processes might be reasonably considered for evaluating technology in critical care and discuss the probability of various consequences that will significantly affect the care we provide our patients if critical-care practitioners, industry, and health planners fail to jointly undertake this responsibility.

Canada↗
PubMed1990

Comparison of left ventricular function and myocardial perfusion for evaluating perioperative cardiac risk of abdominal aortic surgery.

The measurement of left ventricular function by gated blood pool scanning and of myocardial perfusion by dipyridamole thallium imaging were compared in a prospective study of patients who had abdominal aortic aneurysm or aortoiliac occlusive disease to determine which measurement was the better predictor of postoperative cardiac complications. Sixty-six men and 19 women (mean age 67 years) underwent both tests before admission for surgery. Fifty-six had repair of an abdominal aortic aneurysm, and 29 had reconstruction for aortoiliac occlusive disease. In 17 patients the left ventricular ejection fraction was less than 50%. Dipyridamole thallium imaging was positive, showing redistribution, in 45 patients. Postoperative cardiac complications occurred in 33 patients. The sensitivity of dipyridamole thallium imaging (91%) was significantly (p less than 0.01) greater than that observed with gated blood pool scanning (27%). However, the specificity of gated blood pool scanning (85%) was similar to that of dipyridamole thallium imaging (71%). Diagnostic accuracy was greatest with dipyridamole thallium imaging (79% versus 62% [p less than 0.02]). Dipyridamole thallium imaging is superior to gated blood pool scanning for perioperative evaluation of vascular surgical patients.

Aged↗
PubMed1989

A comparison of dipyridamole-thallium imaging and exercise testing in the prediction of postoperative cardiac complications in patients requiring arterial reconstruction.

The individual and combined predictive values of dipyridamole-thallium imaging and exercise testing were compared in a prospective study of 70 patients who had abdominal aortic aneurysms or aortoiliac occlusive disease that required surgical repair. All patients were evaluated clinically by the same cardiologist and had exercise stress testing and dipyridamole-thallium imaging before admission for surgery. Ten patients were excluded from the study because they had evidence of severe ischemia when tested (ST segment depression greater than 2 mm on exercise testing, severe multivessel disease on thallium imaging). The remaining 60 patients were operated on (abdominal aortic aneurysm repair, 40; aortobifemoral repair, 17; femorofemoral graft, 3). The test results were withheld from the surgeon, anesthetist, and cardiologist before surgery. A total of 22 patients experienced major cardiac complications postoperatively (acute pulmonary edema, 17; acute myocardial, infarction, 5; cardiac death, 2). Thallium imaging showed myocardial ischemia in 31/60 patients. Exercise testing was positive (greater than or equal to 1 mm ST segment depression) in 10/60 patients. Dipyridamole-thallium imaging with a high sensitivity and reasonable specificity is the initial test of choice. Exercise testing is a poor screening test because of its low sensitivity. The combination of the two tests gives the highest positive predictive value and the greatest likelihood ratio. Thus patients assessed initially and found to have positive thallium scan results may be further stratified by exercise testing.

Adult↗
PubMed1988

Intravenous ibuprofen blocks the hypoxemia of pulmonary glass bead embolism in the dog.

To determine the influence of arachidonic acid metabolites on acute lung injury induced by glass bead embolism, two groups of animals were studied before and after the pulmonary artery pressure was doubled by glass bead embolism. One group represented an untreated time control (n = 6) while the second group (n = 6) was pretreated with 25 mg/kg of iv ibuprofen. Repeat measurements were taken at 30, 60 and 90 min after glass bead embolism. Compared to the untreated group, the pretreated group had only a slightly decreased PaO2 (pretreated, 82% of baseline vs. untreated, 35% of baseline, p less than .05). The initial elevation in pulmonary vascular resistance (PVR) was similar in both groups but in the pretreated group it had returned nearly to baseline values by the end of the study in contrast to the persistent elevation of the PVR observed in the untreated group. We conclude that pretreatment with ibuprofen resulted in improved arterial oxygenation and a reduction in PVR over the time period studied. This implicates a role for arachidonic acid metabolites in the pathophysiology of this injury.

Animals↗
PubMed1988

The use of preoperative exercise testing to predict cardiac complications after arterial reconstruction.

To assess the value of exercise testing in the prediction of cardiac risk, 100 patients requiring arterial reconstructive surgery had either treadmill testing or arm ergometry before operation. Thirty-four patients then had abdominal aortic aneurysm repair, 48 had reconstructions for aortoiliac occlusive disease, and 18 had infrainguinal revascularization procedures. Cardiac complications included myocardial infarction in 10%, acute congestive failure in 5%, malignant ventricular arrhythmias in 7%, and cardiac death in 7%. Contingency table analysis showed that patients who achieved less than 85% of their predicted maximum heart rate (PMHR) during exercise testing had a complication rate of 24%, whereas patients who achieved more than 85% of PMHR had a 6% complication rate (p = 0.0396). The degree of ST segment depression during exercise testing was not a significant predictor of cardiac complications. However, patients who had a positive stress test (ST depression more than 1 mm) and achieved less than 85% of their PMHR had a complication rate of 33%, whereas patients with a positive stress test who achieved more than 85% of their PMHR had no complications (p = 0.048). Statistical analysis with a logistic regression model showed two factors to be significant. Patients who achieved a high maximum heart rate during exercise testing had a low probability of developing postoperative cardiac complications (p = 0.04), as did patients who achieved high cardiac work load maximal oxygen uptake (p = 0.03). We conclude that preoperative exercise testing is useful to predict cardiac complications after arterial reconstruction. Patients who are able to achieve more than 85% of their PMHR and a high maximal oxygen uptake represent a low-risk group.

Aorta, Abdominal↗
PubMed1986

Pulmonary injury depresses cardiac systolic function through Starling mechanism.

To determine whether pulmonary microvascular injury or lung hyperinflation changes left ventricular (LV) performance and whether ventricular interaction plays a role in mediating such changes, we studied seven open-chest, closed-pericardium, anesthetized dogs before and after right ventricular (RV) injections of 150- to 200-micron glass beads. Because people with pulmonary disease are often treated with positive end-expiratory pressure, we also hyperinflated the lungs before and after creating the pulmonary microvascular injury. Measurements of LV and RV pressures and dimensions were taken at end expiration during the basal state, during lung hyperinflation, and after microvascular injury at RV end-diastolic pressures of 5, 10, and 15 mmHg produced by volume loading. Acute volume loading produced upward shifts in the LV diastolic pressure-size curve both before and after microvascular injury. Neither microvascular injury nor lung hyperinflation substantially affected the LV diastolic pressure-size relationship. LV end-diastolic size determined LV stroke work with no consistent independent influence of microvascular injury or lung hyperinflation. Neither microvascular injury nor lung hyperinflation depressed systolic performance beyond that associated with changes in end-diastolic heart size.

Animals↗
PubMed1986

Cardiac mortality and morbidity after vascular surgery.

To determine the clinical, hemodynamic and pathological features that contribute to major cardiac complications after vascular surgery, six patients with early postoperative cardiogenic shock (group 1) were analysed retrospectively and compared to nine patients without complications (group 2) who were carefully analysed prospectively. Four group 1 patients had elective repair of an abdominal aortic aneurysm, one had repair of a false iliac artery aneurysm and one had a femoropopliteal graft inserted. Four group 2 patients had elective repair of an abdominal aortic aneurysm and five had aortobifemoral reconstruction. The Goldman multifactorial index was similar in both groups and indicated an expected death rate of 2% and a morbidity rate of 5%. In group 1, the earliest sign of cardiovascular compromise was an elevated pulmonary wedge pressure during operation. Postoperatively, electrocardiographic evidence of myocardial ischemia was present in all six patients and preceded cardiogenic shock. Autopsy of the four patients who died demonstrated triple-vessel disease in all but recent occlusion in only one patient. There was evidence of extensive subendocardial infarction in all four. Angiography of the two survivors in group 1 also demonstrated triple-vessel disease. The authors conclude that by using ordinary clinical methods it is difficult to identify patients likely to have major complications postoperatively. Elevated pulmonary wedge pressures or electrocardiographic evidence of myocardial ischemia may be early warning signs of impending cardiac catastrophe and should be treated aggressively. The underlying pathophysiology appears to be perioperative stress in a setting of severe triple-vessel coronary artery disease.

Aged↗
PubMed1985

Pulmonary artery constriction produces a greater right ventricular dynamic afterload than lung microvascular injury in the open chest dog.

Investigators model noncardiogenic pulmonary hypertension by constricting the pulmonary artery to increase right ventricular afterload. To investigate this model's validity, we compared the right ventricular afterload, quantified as pulmonary input impedance, created by constricting the pulmonary artery and by inducing a pulmonary microvascular injury (with glass beads infused into the pulmonary circulation). The pulmonary injury constriction produced a different right ventricular afterload than the microvascular injury. The constriction increased both the input resistance and the characteristic impedance. Microvascular injury increased only input resistance. Physiological levels of lung inflation did not influence pulmonary impedance, but lung hyperinflation increased input resistance both before and while constricting the pulmonary artery or after producing microvascular injury. Total right ventricular power output and stroke work were unchanged during each vascular intervention. Pulmonary artery constriction did not affect power output distribution, whereas microvascular injury decreased oscillatory power and its relative contribution to total power. Lung hyperinflation dramatically reduced right ventricular power and left ventricular stroke work. These effects appeared mediated by right ventricular afterload increase uncompensated for by right ventricular preload increase. These observations help explain the hemodynamic consequences of acute pulmonary hypertension and the effects of lung hyperinflation with positive end-expiratory pressure respiration in such patients.

Animals↗
PubMed1983

Concepts in the pharmacologic and nonpharmacologic support of cardiovascular function in critically ill surgical patients.

The critically ill surgical patient requires close clinical, biochemical, and hemodynamic monitoring to define the right timing as well as the proper type of therapeutic intervention. Although many factors are available for monitoring, O2 delivery and extraction are two of the most important, since the enhanced metabolic demands of the stressed patient dictate a need to maintain greater than normal values to ensure survival. In other situations, primary therapy of the blood pressure, the PCWP, or other indices may take temporary precedence in the choice of therapeutic agents. Regardless of the means used to optimize O2 delivery, scrutiny of the consequences of therapy is equally important. Above all, any therapeutic intervention does not negate the need to treat the primary underlying process expeditiously.

Blood Circulation↗
PubMed1983

Phentolamine in low cardiac output states: an assessment with ECG-gated cardiac scintigraphy.

We examined the effect of parenteral phentolamine in 11 critically ill patients with a low cardiac output state and a high systemic resistance. Because vasodilators often affect left ventricular end-diastolic pressure-volume relationships (compliance) in acute cardiac disease, changes in the pulmonary capillary wedge pressure (WP) may conceivably not reflect the true effect of vasodilators on left ventricular preload. Hence, we measured left ventricular ejection fraction (LVEF) with ECG-gated cardiac scintigraphy and stroke volume by thermodilution before and during phentolamine infusion. We then calculated left ventricular end-diastolic volume index (LVEDVI). Phentolamine infusion was associated with an increase in the mean cardiac index (CI) (1.96 +/- .53 [mean +/- SD] to 2.45 +/- .69 L/min X m2; p less than .0025) whereas the mean WP fell (19.5 +/- 7.5 to 13.5 +/- 7.3 mm Hg; p less than .05). There was no simultaneous change in the mean LVEDVI (100 +/- 48 to 110 +/- 40 ml/m2; p = NS), implying that one of the effects of phentolamine infusion was to improve left ventricular diastolic compliance. Multiple regression analysis suggested that the major effect of phentolamine on stroke volume was mediated by concomitant changes in the LVEDVI (r2 = .64). Therefore, benefit from phentolamine in low cardiac output states is multifactorial and phentolamine likely improves left ventricular compliance in some patients.

Aged↗
PubMed1981

Does the pulmonary capillary wedge pressure predict left ventricular preload in critically ill patients?

The construction of a Frank-Starling myocardial function curve relating heart work to left ventricular preload is clinically utilized to assess therapeutic protocols in critically ill patients. The pulmonary capillary wedge pressure (PWP) is the index of left ventricular filling pressure most frequently utilized as representative of left ventricular preload. The authors assessed the relationship between left ventricular preload measured as the left ventricular end-diastolic volume (LVEDV), and the PWP, in acutely ill patients with sepsis and cardiac disease. Within each group, no relationship was found between the LVEDV and the PWP; however, when omitting the effect of PEEP, a modest correlation was noted (r = 0.302; p less than 0.01). Of the left ventricular ejection fraction, LVEDV and PWP, the PWP accounted for less than 5% of the explained variance in the stroke volume index. The PWP is a poor predictor of left ventricular preload, probably because of abnormalities of left ventricular compliance in critically ill patients.

Aged↗
PubMed1981

Anatomic and cardiopulmonary responses to trauma with associated blunt chest injury.

Myocardial dysfunction may result from severe trauma. Therefore, left (LV) and right ventricular (RV) function were prospectively assessed by ECG-gated blood pool radionuclide (RN) angiography in 25 consecutive patients who had sustained severe trauma including blunt chest injuries. Focal abnormalities of RV and LV wall motion were defined in 17 patients; 12, RV; two, LV; and three, biventricular. In two patients traumatic tricuspid insufficiency was also demonstrated, and subsequently verified by contrast angiography. Other means to detect myocardial contusion (enzymatic, electrocardiographic, and Tc-99m pyrophosphate scintigraphy) proved to be insensitive when compared to RN angiography. Two of the five deaths in the group were attributed to refractory arrhythmias. Surgical or post-mortem evidence of traumatic myocardial injury was obtained in five instances when RN angiography indicated contusion. Of the 13 patients available for followup examinations, 11 showed complete or partial resolution of the abnormality and two were unchanged. Comprehensive cardiopulmonary monitoring revealed an inverse relationship between right ventricular ejection fraction (RVEF) and pulmonary vascular resistance (PVR) (R2 = 0.42; p < 0.01) and between the PVR and left ventricular ejection fraction (LVEF) (R2 = 0.48; p < 0.01) and left ventricular end-diastolic volume (LVEDV) (R2 = 0.69; p < 0.01). Further, as right ventricular end-diastolic volume (RVEDV) was increased in trauma, left ventricular function and compliance were reduced. In blunt chest trauma RV contusion occurs more frequently than previously recognized and positive RN angiography constitutes prima facie evidence of direct myocardial injury. Further, LV function remains preload dependent, but may be depressed by elevated PVR impeding the blood flow from RV to LV and/or decreases in LV compliance.

Adolescent↗
PubMed1981

Positive end-expiratory pressure (PEEP) does not depress left ventricular function in patients with pulmonary edema.

We evaluated the effects of positive end-expiratory pressure (PEEP) on left ventricular function in 15 patients with acute respiratory insufficiency secondary to pulmonary edema with invasive (pressure; flow) measurements and radionuclide angiography (RA). Using RNA allowed a definition of the left ventricular ejection fraction (LVEF), and then calculation of the left ventricular end-diastolic volume (LVEDV), both before and after PEEP. With a mean PEEP of 14.2 +/- 1.8 cm H2O (mean +/- SD) (range, 10 to 15), a fall in the cardiac index (4.34 +/- 1.5 to 3.84 +/- 1.4 L/min/M2; p less than 0.001) was accompanied by a significant decrease in the stroke volume index (42 +/- 13 to 39 +/- 12 ml/beat M2; p less than 0.01) and pulse rate (103.4 +/- 14.3 to 98 +/- 13.5 beats/min; p less than 0.01). The decrease in the stroke volume index was primarily due to a significant decrease in left ventricular preload (LVEDV) from 85.9 +/- 19 to 71.4 +/- 21.4 ml/m2 (p less than 0.01). Simultaneously, the mean LVEF increased from 0.47 +/- 0.10 to 0.53 +/- 0.08 (p less than 0.05), despite a significant increase in the systemic vascular resistance (1,619 +/- 575 to 1,864 +/- 617 dynes . s. cm-5/M2; p less than 0.01). We concluded that the use of PEEP in patients with acute pulmonary edema, to the degree used in this study, may depress cardiac output by simply decreasing left ventricular preload. We were unable to produce any evidence that would support a change in the contractile state of the left ventricle as a cause of depressed forward flow with the use of PEEP.

Angiography↗
PubMed1981

The hemodynamic effect of rapid fluid infusion in critically ill patients.

The response to a rapidly administered volume infusion (250 ml of 5% albumin over 30 minutes) was studied in 28 critically ill patients. Cardiovascular responses were assessed by means of invasive hemodynamic parameters (i.e., cardiac index [CI], central venous pressure [CVP], pulmonary artery pressure [PAP], and pulmonary capillary wedge [PCWP] pressure as well as radionuclide [RN] angiography). This allowed for the simultaneous measurement of right (RVEF) and left (LVEF) ejection fractions, and right (RVEDV) and left end-diastolic (LVEDV) and end-systolic (LVESV) volumes. Twenty patients responded (R) to volume infusion by demonstrating an increase in stroke volume. This response was secondary to an increase in LVEDV in 11 (R-1) and an increase in the LVEF in nine (R-2). Neither response was predictable before treatment. The responders also demonstrated a significant decrease in heart rate (P less than 0.05). The increased ejection fraction in some responders (R-2) was associated with a decrease in systemic vascular resistance index (SVRI) (P less than 0.05) and LVESV (P less than 0.05) suggesting a reduced afterload secondary to peripheral vasodilation concomitant on volume change. The PCWP appeared to be related more to right ventricular (RV) loading factors (i.e., CVP, RVEDV, and pulmonary vascular resistance [PVRI] [R2 = 0.85, P less than 0.005]) then to the LVEDV (P = NS). Left ventricular (LV) loading with volume infusion appeared to be dependent on both RV performance and the PVRI in some patients, since responders who increased the LVEDV (R-1) were characterized by a simultaneous increase in RV stroke work and decrease in PVRI. The response to fluid infusion in critically ill patients is complex with both increases in LVEF and LV preload contributing to its beneficial effect. Clinical assessment of LV filling pressures (PCWP) does not accurately predict the response to volume infusion and does not allow a reliable assessment of the LV preload. This is most likely due to the broad range of LV compliance characteristics noted in critically ill patients. RV function also appears to be important in the clinical response to volume challenge.

Blood Pressure↗
PubMedDate not supplied

The intermediate CCU admission: a preliminary study.

In the current health care era, increasing emphasis is being placed on cost reduction. Admitting only high-risk patients to coronary care units (CCU) may reduce hospital costs and charges without adverse clinical outcomes. Recently, guidelines published by the Agency for Healthcare Policy and Research (AHCPR) on suggest that intermediate-risk patients be admitted to an intermediate CCU (ICCU), but the safety and appropriateness of this approach has not been prospectively evaluated. The authors hypothesized that admitting intermediate-risk patients with to an ICCU would be cheaper than admitting to a CCU with comparable safety supporting AHCPR guidelines. To evaluate this, a retrospective cohort study was conducted. Two hundred forty-three intermediate-risk patients consecutively admitted to the CCU (n = 134) and admitted to the ICCU (n = 109) between June 1, 1992 and April 1, 1994 were compared using AHCPR definitions of intermediate risk and a previously published risk prediction model to exclude both very low- and high-risk patients. Extensive demographic, clinical, and diagnostic testing, and treatment, procedural, and outcome data were collected by a trained nurse data collector at the time of admission. Fifty-nine percent of all study patients had at least two coronary risk factors. Twenty-one percent had diabetes. Ninety-eight percent had at least one AHCPR intermediate risk factor for cardiac complications. The two groups (CCU versus ICCU) were quite similar in baseline characteristics: men (56 versus 55%), age (57 +/- 17 versus 60 +/- 17 years), diabetes (22 versus 20%), previous myocardial infarction (30 versus 36%), previous coronary artery surgery (21 versus 21%), and rest pain (78 versus 66%). The use of coronary angiography (44 versus 52%), angioplasty (24 versus 21%), and coronary artery surgery (13 versus 11%) were also similar. The incidence of myocardial infarction or death was similar (3 versus 5%), and length of stay was also similar between groups (6.7 +/- 4.2 versus 6.5 +/- 4.1 days), but cost was less for patients admitted to the ICCU ($13,481 +/- 9,450 versus $10,619 +/- 8,732, P < 0.015). These preliminary data suggest intermediate-risk patients, as identified by AHCPR guidelines, can be treated in an ICCU at lower cost than in a CCU, with reasonable safety. A small incidence of myocardial infarction in ICCU-admitted patients occurs, requiring availability of cardiac resuscitation and continued monitoring of electrocardiographic and enzymatic abnormalities. Admission to ICCU poses no barrier to recommended patient evaluation and management.

Adult↗