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Biomedical subjects

P F Hoar

Publications and source records attributed to P F Hoar.

17 recordsLinked to original sources
PubMed1983

Influence of volume loading on intraoperative hemodynamics and perioperative fluid retention in patients with valvular regurgitation undergoing prosthetic replacement.

Preload and afterload were controlled intraoperatively in 2 groups of patients with valvular regurgitation and congestive heart failure in order to determine the effect of fluid loading on weight gain and subsequent recovery. As a part of their anesthetic management before cardiopulmonary bypass, 16 patients were given 1 liter of crystalloid with nitroprusside infused at 1 microgram/kg/min and 16 received 4 liters of crystalloid with nitroprusside at 4 micrograms/kg/min. Arterial and filling pressures were kept the same in both groups. Heart rate and vascular resistance became significantly lower and cardiac index and stroke volume significantly higher in the fluid-augmented group. The transition to cardiopulmonary bypass was smoother for the fluid-augmented patients. All patients survived, and 2 in each group were ventilated beyond 24 hours. The mean weight gain at surgery was the same in the 2 groups (3 kg). For the first 2 postoperative days, body weight remained unchanged and thereafter, both groups lost weight at 0.6 kg/day. Preoperative weight was reached on day 7 and discharge occurred on day 15, 2 kg below control. Thus, a modest operative weight gain in these patients is inevitable, benign, and independent of the volume of fluid infused before bypass.

Aortic Valve↗
PubMed1983

Whole-body oxygen consumption during low-flow hypothermic cardiopulmonary bypass.

To assess the adequacy of tissue perfusion during low-flow, moderately hypothermic cardiopulmonary bypass (CPB), we measured whole-body oxygen consumption (VO2), serum lactate concentrations, and acid-base balance in 12 men undergoing myocardial revascularization. When perfusion flow rate was kept at control levels (2.1 L/min/m2), decreasing the patient's body temperature to 25.4 +/- 1.8 degrees C (mean +/- SD) was associated with a reduction in VO2 of almost 50% (from 83.3 +/- 14.6 ml/min/m2 to 45.6 +/- 9.6 ml/min/m2, p less than 0.001). Subsequent lowering of flow rate by nearly half (from 2.1 to 1.2 L/min/m2) under these moderately hypothermic conditions failed to alter VO2, which was measured several times over a 40 minute period. Although small increases in base deficit occurred during hypothermia, acidosis did not occur after reductions in flow rate. Serum lactate levels were not affected by changes in either temperature or flow rate. We conclude that a perfusion flow rate as low as 1.2 L/min/m2 does not compromise tissue perfusion during CPB with moderate systemic hypothermia and cardioplegic arrest.

Body Temperature↗
PubMed1981

Adrenergic response to morphine-diazepam anesthesia for myocardial revascularization.

To evaluate sympathetic nervous system activity during narcotic-hypnotic "balanced anesthesia," plasma catecholamine concentrations and hemodynamic variables were assessed simultaneously in 10 men with coronary artery disease who received, sequentially, morphine sulfate, 3 mg/kg IV, and diazepam, 0.25 to 0.35 mg/kg IV, for myocardial revascularization surgery. Infusion or morphine sulfate rates of 5 to 10 mg/min significantly decreased both mean systemic arterial pressure (from 98 plus or minus 6 to 84 plus or minus 5 torr, p less than 0.01) and systemic vascular resistance index (from 38 plus or minus 3 to 30 plus or minus 5 units, p less than 0.05). These changes were associated with 2-fold increases in plasma norepinephrine levels (from 246 plus or minus 31 to 488 plus or minus 85 pg/ml, p less than 0.01) and 4-fold increases in plasma epinephrine levels (from 129 plus or minus 20 to 570 plus or minus 182 pg/ml, p less than 0.01). Addition of diazepam further decreased systemic arterial pressure (from 84 plus or minus 5 to 73 plus or minus 3 torr, p less than 0.01) and was associated with significant decreases in cardiac and stroke volume indices when compared with values obtained after morphine sulfate alone. Plasma concentrations of both norepinephrine and epinephrine also declined in association with these hemodynamic changes. Following skin incision, systemic arterial pressure and systemic vascular resistance index increased, the latter to the highest measured value (50 units). Norepinephrine concentrations increased significantly more than it had after morphine-diazepam anesthesia (321 plus or minus 63 pg/ml). It was concluded that the administration oif high dose morphine anesthesia acutely activates the sympathoadrenal system while producing peripheral vasodilation. Diazepam, when used following morphine to assure loss of consciousness, exacerbates the hypotensive effects produced by morphine and is associated with decreased levels of plasma catecholamines. Surgical incision produces significant peripheral sympathetic activation and increases vascular resistance during morphine-diazepam anesthesia.

Anesthesia↗
PubMed1980

Acute hemodynamic alterations after mitral valve replacement with the glutaraldehyde-treated porcine heterograft prosthesis.

Perioperative hemodynamic changes following mitral valve replacement using the porcine heterograft prosthesis were measured in 21 patients with acquired mitral valve disease. Preoperatively, a state of compensatory cardiac failure was suggested by the following: an increased heart rate (HR) (96 beats per minute); low cardiac and stroke volume (SVI) indices (2.3 +/- 0.10 L/min/m2 and 25 +/- 2 ml/beat/m2); and increased systemic vascular resistance (SVR) (1,626 +/- 116 DYNE SEC CM-5). Bothe the mean pulmonary artery PAP) and pulmonary capillary wedge pressures (PCWP) were elevated as well (32 +/- 3 and 22 +/- 2 torr). Immediate hemodynamic improvement followed valve replacement. HR, SVR, PAP, and PCWP all decreased significantly. Twenty-four hours after valve replacement, PAP (23 +/- 1 torr) and PCWP (13 +/- 1 torr) demonstrated marked declines, SVR was reduced by one-third (1,173 +/- 87 dyne sec cm-5), HR had decreased by 10 beats per minute, and SVI had increased to 30 +/- 2 ml/beat/m2. The prompt circulatory improvement of patients soon after mitral valve replacement using the porcine heterograft compares favorably with studies in which other valve types were employed and in which postoperative cardiovascular depression was encountered frequently.

Adult↗
PubMed1980

Type A behavior and blood pressure during coronary artery bypass surgery.

Systemic hypertension has been reported as common during coronary artery bypass surgery. The coronary-prone Type A behavior pattern has been associated with heightened reactivity of the sympathetic nervous system. Therefore, the possible relationships between the two was explored. Significant correlations were found between systolic blood pressure rise during surgery and interview ratings of overall Type A (p < 0.05), aggressive content (p < 0.01), and job commitment (p < 0.001). A statistically association was also found between diastolic pressure rise and the job commitment rating (p < 0.01). Significant correlations were still present after controlling for the role of physical predictors of blood pressure rise by statistical multiple regression analysis. The data suggest that patients with Type A behavior characteristics manifest an autonomic hyperactivity which is present under general anesthesia. This hyperactivity may contribute to the association of Type A behavior pattern and coronary heart disease.

Aggression↗
PubMed1980

Nitroprusside and mitral stenosis.

The cardiovascular effects of an intravenous nitroprusside infusion were evaluated intraoperatively in seven patients with pure mitral stenosis and seven patients with predominant mitral stenosis. Prior to therapy the adverse hemodynamic consequences of light anesthesia and surgical stimulation were evident in all patients: systemic and/or pulmonary hypertension were present, systemic vascular resistance was twice normal, and cardiac function was depressed. Nitroprusside consistently reduced systemic vascular resistance and systemic arterial as well as pulmonary arterial and wedge pressures, but cardiac index increased only when severe pulmonary hypertension and/or some mitral regurgitation coexisted with mitral stenosis. In the group with predominant mitral stenosis, cardiac index increased from 1.8 to 2.1 L/min/m2 with nitroprusside (p < 0.05). In three individuals who demonstrated severe pulmonary hypertension (one with pure mitral stenosis and two with predominant mitral stenosis), nitroprusside induced an increase of almost 50% in cardiac index and stroke volume. In contrast, patients with pure mitral stenosis and mild pulmonary hypertension showed little change in cardiac index or stroke volume. It is concluded that nitroprusside can safely be used to control systemic or pulmonary hypertension during anesthesia and surgery in patients with mitral stenosis and that if severe pulmonary hypertension and/or mitral regurgitation coexist with mitral stenosis, cardiac function will also improve.

Ferricyanides↗
PubMed1980

Afterload reduction and preload augmentation improve the anesthetic management of patients with cardiac failure and valvular regurgitation.

Data were collected from 17 patients with valvular regurgitation and ventricular failure who were about to undergo prosthetic replacement of an insufficient cardiac valve. Awake control hemodynamic measurements revealed that these patients came to the operating room with a high systemic vascular resistance of 38 units and low cardiac and stroke volume indices of 2.2 L/min/m2 and 30 ml/beat/m2, respectively. A preanesthetic infusion of nitroprusside together with almost 2 L of lactated Ringer's solution caused vascular resistance to decrease to 19 units (normal) while filling pressure remained high. As a result, while the combined therapy continued, neither the induction of anesthesia nor surgical stimulation produced cardiovascular deterioration; in fact, cardiac index measured above 3.1 L/min/m2 and stroke volume index above 40 ml/beat/m2 throughout anesthesia and surgery. We conclude, therefore, that the combination of afterload reduction and preload augmentation provides the best possible environment within which to conduct the anesthetic management of patients with valvular regurgitation and ventricular failure.

Adult↗
PubMed1979

Comparison of intraoperative nitroprusside unloading in mitral and aortic regurgitation.

To compare the hemodynamic effect of vasodilator therapy on different regurgitant lesions, we infused sodium nitroprusside intraooperatively in 12 patients with mitral regurgitation and 15 with aortic regurgitation. During the critical period preceding establishment of cardiopulmonary bypass, both groups had developed intense vasoconstriction and cardiac decompensation. All demonstrated improved cardiac function with vasodilator therapy; however, the degree of improvement with nitroprusside differed in the two groups. Stroke volume increased 10 ml. per beat per meter squared in those patients with aortic regurgitation and only 6 ml. per beat per meter squared in those with mitral regurgitation (p less than 0.05). The percent increase in stoke volume induced by nitroprusside was inversely correlated to the preoperative left ventricular ejection fraction (r = 0.44, p less than 0.02). Patients with aortic regurgitation had lower preoperative left ventricular ejection fractions than those with mitral regurgitation (0.53 versus 0.63, p less than 0.02). Therefore, we conclude that patients with aortic regurgitation derived greater intraoperative hemodynamic benefit from unloading with nitroprusside, because they came to surgery with greater impairment of left ventricular contractility. Although nitroprusside improved cardiac function in both groups, only the patients with aortic regurgitation achieved normal pulmonary artery pressure (17 torr) and pulmonary vascular resistance (2.1 units) as a result of unloading. Those with mitral regurgitation continued to have pulmonary hypertension (28 torr) and increased pulmonary vascular resistance (3.9 units) despite vasodilator therapy. Thus the data suggest that patients with mitral regurgitation derived less hemodynamic benefit from intraoperative nitroprusside therapy because they were also limited by right ventricular dysfunction and a less responsive pulmonary vasculature.

Adult↗
PubMed1977

Acute hemodynamic alterations after aortic valve replacement with the glutaraldehyde-treated porcine heterograft prosthesis.

Twenty-two patients underwent aortic valve replacement for acquired valvular heart disease with the porcine heterograft prosthesis. In the immediate postoperative period, a transient decrease in the cardiac index (CI) (preoperative 3.0 +/- 0.14 to 2.45 +/- 0.16 L. per minute per square meter, p less than 0.05) and an increase in the systemic vascular resistance (SVR) (preoperative 1,078 +/- 62 to 1,287 +/- 103) dynes/sec./cm.-5, p greater 0.05) were seen; these values returned to preoperative levels by the first postoperative day. After valve replacement, an elevation in the heart rate (HR) (preoperative 75 +/- 2 to 87 +/- 4 beats per minute, p less than 0.05) and a reduction in the stroke volume (SV) and stroke work index (SWI) (preoperative 35 +/- 2 to 26 +/- 2 Gm.-M. per square meter, p less than 0.05) occurred which persisted throughout the study. The endocardial viability ration (EVR) increased after valve replacement. These findings suggest that, following aortic valve replacement, (1) an increase HR is the mechanism utilized to maintain cardiac output, (2) subendocardial perfusion is enhanced as indicated by an increase in the EVR, and (3) the hemodynamic alterations following insertion of the porcine heterograft prosthesis are not different from those observed when other valves are placed in similar patient populations.

Adult↗
PubMed1976

Physiological responses of men working in 25.5 degrees C water, breathing air or helium tri-mix.

Fourteen scuba divers in swim trunks did ergometer work while breathing air at 3 m in 25.5 degrees C water. They were stressed by work and cold. Exercise produced increases in heart rate, minute ventilation (VE), oxygen consumption (VO2), and catecholamine excretion. Cold lowered rectal temperature (Tre) despite exercise, and contributed to the increase in VO2 and catecholamine excretion. Immersion, cutaneous vasoconstriction, work, and scuba breathing contributed to a brisk diuresis, probably by centralizing blood volume and thus stimulating central vascular volume receptors. Similar exercise in 25.5 degrees C water, breathing helium tri-mix (gas density less than air), produced higher VE but lower VO2 when compared to air breathing. Tri-mix scuba breathing resulted in a smaller diuresis, perhaps because its lower density leads to lesser atrial distension during work. The fall in Tre during work in 25.5 degrees C water was identical whether air or helium tri-mix was respired, since helium does not accentuate respiratory convective heat transfer.

Adult↗
PubMed1976

Systemic hypertension following myocardial revascularization. A method of treatment using epidural anesthesia.

Seven of 12 patients (58%) undergoing myocardial revascularization surgery became hypertensive in the immediate postoperative period. The hypertensive patients had significant elevations in peripheral vascular resistance (22.0 +/- 2.0 S.E. resistance units) compared to measurements in normotensive patients (15.6 +/- 1.3 S.E. resistance units) (p less than 0.05), whereas the heart rates and cardiac indices were similar. Administration of thoracic epidural anesthesia to postoperatively hypertensive patients lowered systemic arterial pressure by decreasing peripheral vascular resistance (p less than 0.005) but not affecting the pulse rate and cardiac index. The ratio diastolic pressure-time index/systemic pressure-time index (DPTI/SPTI), an indirect measurement of subendocardial oxygenation, increased from preanesthetic values of 0.80 +/- 0.08 S.E. to 1.09 +/- 0.09 S.E. (p less than 0.025) after the systemic arterial pressure was lowered in postoperatively hypertensive patients. Hypertensive episodes following myocardial revascularization procedures appear related to increased alpha-adrenergic activity, which products elevation in peripheral vascular resistance. Decreasing peripheral vascular resistance by chemical sympathectomy with thoracic epidural anesthesia lowers the systemic arterial pressure and improves the DPTI/SPTI ratio.

Anesthesia, Epidural↗
PubMed1976

Technique for electrocardiographic monitoring of working divers.

An improved technique to record high-equality electrocardiographic (ECG) signals on the surface, from immersed humans during rest and exercise, in both normothermic and hypothermic exposures, has been devised. Recorded tracings were adequate for research purposes. Waveform signals obtained allow accurate continuous monitoring as well. The best recordings resulted from proper selection of electrode placement sites, careful preparation of the skin, and diligent protection of the skin-electrode interface. The resulting signals recorded from male divers working in 3.05 m (10 ft) of water contained very little artifact or shift in baseline of the ECG tracing. Post-dive examination of the placement sites showed neither separation of ECG electrodes from the skin nor intrusion of water between the electrode and skin surface. The relationship of the new ECG recording technique to a previously described system for acquiring physiologic data is described.

Diving↗