Combined and interacting effects of hand and head movement delays on discrete manual performance in a virtual environment.

Transmission delays occur when a virtual environment responds to the hand and head movements of an operator. The effects of hand and head-related delays on discrete manual performance was investigated experimentally and compared. Imposed hand and head-related pure delays equal to or greater than 110 ms and 220 ms, respectively, significantly increased hand Movement Time (MT). The effect of hand-related delays was greater than that of head-related delays of the same magnitude. A regression model describing the combined effects of both delays on MT is reported (R(2) = 0.95). Analyses of the interactions among delays, target width, and distances have shown the need to adopt the traditional classification of delays into (1) control delay, and (2) display delay. The use of this taxonomy and the regression analyses to describe and explain the effects of individual and combined effects of delays on discrete target-reaching task performance in virtual environments are discussed.

Target-directed head movements in a head-coupled virtual environment: predicting the effects of lags using Fitts' law.

Two experiments have investigated the effects of lag on discrete target-directed head movements in a virtual environment. Both the target and a head-slaved pointer (subjected to lag) were presented on a head-mounted display. Target-directed head movements in the presence of a constant time lag were shown to obey Fitts' law (R2 > .93). A previously reported interaction between the effects of lag and the effects of index-of-difficulty on hand movement time could not be found in head movement time when the target width was kept constant. Further experiments suggested that there is a significant interaction between the effects of target width and lag but not between target distance and lag. A model predicting head movement strategy in the presence of lag is proposed to explain the experimental findings. This model predicts, and experiments verified, that for a target width from 1 degree to 8 degrees and a target distance range of 2.5 degrees to 30 degrees, the effect of lag (up to 267 ms) on target-directed head movement is independent of target distance but dependent on target width. Actual or potential applications of this research include the design of virtual control panel and its layout in a Virtual Reality simulator.

Determinants of homologous blood usage utilizing autologous platelet-rich plasma in cardiac operations.

The present study evaluated (1) the influence of the collection of autologous platelet-rich plasma intraoperatively in addition to intraoperative autotransfusion on homologous blood usage and bleeding in cardiac operations; (2) the influence of age, sex, body surface area, type of operation, and reoperations on homologous blood usage and bleeding in cardiac operations utilizing intraoperative autotransfusion and autologous platelet-rich plasma collected intraoperatively; and (3) the influence of the preoperative administration of aspirin, Persantine (dipyridamole), heparin sodium, thrombolytic agents, Coumadin (crystalline warfarin sodium), and nonsteroid, antiinflammatory drugs on homologous blood usage and bleeding in cardiac operations utilizing intraoperative autotransfusion and autologous platelet-rich plasma collected intraoperatively. The results demonstrated a decrease in homologous blood use and bleeding when autologous platelet-rich plasma is collected in addition to the use of intraoperative autotransfusion. All of the patient and procedural variables influenced homologous blood usage and bleeding to some extent. Only the thrombolytic agents affected blood usage by increasing homologous plasma usage. All other drugs evaluated did not influence blood utilization or the amount of bleeding intraoperatively or postoperatively.

Autologous platelet-rich plasma in cardiac surgery: effect on intraoperative and postoperative transfusion requirements.

The Southern Arizona Red Cross Blood program, in conjunction with participating hospitals and cardiac surgeons, evaluated the effect of a program to harvest autologous platelet-rich plasma (PRP) from patients immediately prior to undergoing cardiopulmonary bypass surgery. The PRP was transfused back to the patient after heparin neutralization was achieved at the completion of cardiopulmonary bypass. The effect of this autologous PRP product on homologous plasma and platelet usage was examined. The study demonstrates a significant decrease in homologous plasma and platelet usage when autologous PRP is used in cardiac surgery.

Incidence of coronary artery by-pass graft following percutaneous transluminal coronary angioplasty.

Two hundred fifty eight patients had percutaneous transluminal coronary angioplasty. Of those, 48 cases underwent surgical revascularization for unsuccessful angioplasty. Sex was not a risk factor. Timely surgical revascularization reversed acute ischemia and/or myocardial infarction or limited the size of the infarction in 32 of the 48 patients or 67%. Revascularization procedures were performed in six out of forty-eight patients who had previous aortocoronary by-pass surgery and attempted PTCA, none had any complications. Death occurred in one out of forty-eight patients, or 2%. Femoral-femoral by-pass devices, in addition to intra-aortic balloon devices, should be available in the cardiac catheterization laboratory. Patients with multi-vessel disease are at greater risk of angioplasty and surgery. Sixteen out of 23 patients (70%) who had emergency revascularization procedures had multi-vessel disease. In one patient with borderline renal function, emergency surgery after PTCA with a large amount of renograffin dye injected caused renal failure and led to permanent dialysis.

Fresh frozen plasma: a solution to heparin resistance during cardiopulmonary bypass.

The reasons for the highly variable response of patients to heparin remain incompletely understood. Empirical maintenance of the activated clotting time (ACT) at levels of 400 to 480 seconds appears to be safe for cardiopulmonary bypass (CPB). For patients with ACT responses lower than predicted for initial heparin doses, titration with additional heparin has been customary. In 44 patients undergoing cardiopulmonary bypass, 20 patients were identified as having initial ACTs of 300 seconds or less after receiving 300 units per kilogram of heparin. In 11 of them, ACTs were titrated to 400 to 480 seconds with additional heparin. Nine were given 2 units of fresh frozen plasma shortly after institution of CPB. In this group, there was significant augmentation of the ACT immediately after infusion of plasma. No differences in total heparin dosages given during CPB were found between 24 control patients with initially acceptable ACTs and the group receiving fresh frozen plasma. In contrast, more heparin was necessary in the patients with a low ACT titrated with heparin alone. Data also indicated that protamine sulfate requirements were substantially lower after administration of plasma than were those in either the control or the heparin-titrated, low ACT group. Fresh frozen plasma appears to "normalize" the heparin-ACT dose-response curve in heparin-resistant patients and to lessen total heparin requirements during CPB.

Acute dissection of the ascending aorta. Initial presentation as acute lower GI bleeding.

We present the unusual case of a 56-year-old man with acute dissection of the ascending aorta (DeBakey type I) whose presenting symptoms were those of lower gastrointestinal (GI) bleeding. Surgical repair was successfully accomplished with resection of the aorta with a Dacron tubular graft combined with aortic valvular replacement after obtaining bowel viability.

Determinants of early and late results of repair of atrioventricular septal (canal) defects.

The anatomic and functional characteristics of 310 consecutive patients undergoing repair of atrioventricular (AV) septal defects were studied. The characteristics of the six leaflets of the common (139 patients) or two-orifice (171 patients) AV valve are described. Interventricular communications were present in 156 patients and major associated cardiac anomalies in 73 (tetralogy of Fallot 20, double-outlet right ventricle nine, and others). Fifty-one patients (16%) died in hospital. The incremental risk of young age disappeared after 1976. Severity of preoperative AV valve incompetence and New York Heart Association (NYHA) functional class affected hospital mortality. Current risks for patients without major associated cardiac anomalies are 0.6% to 4% for patients in NYHA Class III without an interventricular communication, depending on the degree of preoperative AV valve incompetence, and 5% to 13% for such patients with an interventricular communication. Actuarial survival at 12 1/2 years postoperatively is 95% when preoperative AV valve incompetence is absent or mild and 88% when it is more severe (Grade 3, 4, or 5). Actually, 92% of hospital survivors are alive and in NYHA class I or II. Failure of the AV valve repair occurred in 32 (10%) of the 310 patients and occurred more frequently when AV valve incompetence was severe preoperatively. Its frequency is reduced by current repair techniques, except in patients without interventricular communication.

Blood flow in sequential vein grafts.

In 69 patients undergoing coronary artery bypass grafting for complete coronary revascularization, blood flow was measured in 140 grafts with 243 distal anastomoses (3.52 bypasses/patient). Total blood flow in single grafts and double and triple sequential grafts did not differ significantly, although mean distal flow decreased successively with single (85 cc/min), double (51 cc/min), and triple (32 cc/min) sequential grafts. Total myocardial flow did not vary significantly regardless of the number of grafts placed. Flow measurements in patients with double sequential grafts showed greater than 20% overlay in flow between the two distal anastomoses. The data suggest significant but incomplete collateral supply between adjacent coronary beds consistent with the concept of any individual area of myocardium being a capacitance bed supplied in part by a number of adjacent coronary branches.

Acute thrombotic obstruction with Björk-Shiley valves: diagnostic and surgical considerations.

Eight patients have had thrombotic obstruction of a prosthetic valve since 1971, six mitral valves and two aortic. All eight patients had a Björk-Shiley valve. During the same period 159 Björk-Shiley valves were placed, 85 in the mitral and 74 in the aortic area. This represents a valve thrombotic occlusive incidence of 4.4 percent in our series, 5.9 percent of mitral and 2.7 percent of aortic prostheses. Among the six patients with mitral prostheses only one survived. The two patients with occluded aortic valves survived. The onset of symptoms was very abrupt in most patients and progressed very rapidly. Acute pulmonary edema was observed in five patients. Anticoagulation was considered inadequate in all patients. Aspirin or dipyridamole was being used in seven patients at the time of thrombosis. The data indicate a high frequency of thrombotic occlusion of Björk-Shiley valves in the absence of full anticoagulation with warfarin derivatives and emphasizes the urgent need for surgery once valve thrombosis is suspected.