Head roll compensation in a visually coupled HMD: considerations for helicopter operations.

BACKGROUND: The helmet-mounted display (HMD) research program at the Flight Research Laboratory of the National Research Council of Canada examined the effects of HMD camera platform dynamics on pilot workload. Many currently fielded visually coupled HMD systems do not reproduce head movements in the roll axis which can lead to the presentation of visual information that is not consistent with vestibular and proprioceptive information. HYPOTHESIS: Our hypothesis was that this sensory conflict can induce motion sickness and increase pilot workload. METHODS: To examine this premise, three pilots flew a series of standardized maneuvers with or without roll compensation in the camera platform of a visually coupled HMD system. RESULTS: Increases in motion sickness symptoms and pilot workload were noted during complex, high-workload maneuvers when no roll compensation was present in the camera platform. During the most demanding maneuvers, the lack of roll compensation in the camera platform made it difficult for the evaluation pilot to control the helicopter. CONCLUSIONS: Roll compensation in visually coupled HMD systems reduces pilot workload and' motion sickness during critical flight periods where pilot workload may already be considerable.

Deployment of an Air Transportable Hospital in support of Allied Forces during Operation Provide Comfort: April 29 to July 17, 1991.

The deployment, setup, and operation of an Air Transportable Hospital (ATH) as a primary field hospital for 25,000 Allied Forces during Operation Provide Comfort is presented with a description of the performance and experiences of this unit. More than 3,300 outpatients were seen and treated, and more than 50 patients were operated on at the ATH. In addition, assigned personnel participated as medical augmentees to Kurdish refugees camps, screening and treating more than 13,000 individuals. The success of this deployment validates and expands the concept of the ATH and of Air Force training doctrine.

Applying ATLS to the Gulf War.

During a 3-month deployment to Silopi, Turkey, for Operation Provide Comfort, the 39 TACG Air Transportable Hospital (ATH) managed 32 cases of severe military trauma. Fifty-two operations were necessary, 78% of which were performed at the ATH. Advanced Trauma Life Support (ATLS) protocols were applied to all of the patients. Only 14% of the 52 procedures were ATLS-learned skills. Also, only 30% of the patients could be managed solely by ATLS in the first 6 hours, the average time of ATH responsibility. ATLS alone is insufficient wartime readiness preparation for the military physician.

Leg swelling after aortic surgery.

Thirty patients undergoing aorto-femoral reconstruction, during which i.v. heparin was used, are reviewed (19 bilateral and 11 unilateral procedures). No operation was performed therefore on 11 of 60 limbs. Ankle swelling occurred in 12 operated limbs (9 transient and 3 permanent swelling) and 1 non operated limb. Deep vein thrombosis (DVT) occurred in 7 limbs and in only 3 of these was swelling coincident (1 permanent swelling). The coincidence of limb swelling and DVT of the arterial reconstruction is insignificant.

Effect of the cyclo-oxygenase inhibitor indobufen on platelet accumulation in prosthetic vascular grafts.

An in vivo method of measuring thrombus deposition and pseudo-intimal thickening in prosthetic arterial grafts in an animal model is described. The effect of indobufen, a new cyclo-oxygenase inhibitor, was evaluated and compared to aspirin plus dipyridamole and placebo in 24 greyhounds. Luminal platelet accumulation expressed as thrombogenicity index was 0.33 +/- 0.07 in the placebo group. This was significantly reduced to 0.14 +/- 0.01 by indobufen (P less than 0.05). The reduction to 0.19 +/- 0.04 by aspirin plus dipyridamole failed to achieve statistical significance. Pseudointimal thickness when measured 28 days after implacement was significantly reduced to 21.4 +/- 10.6 per cent by indobufen (P less than 0.01) and 29.4 +/- 10.6 per cent by aspirin plus dipyridamole (P less than 0.02) compared to 75 +/- 10 per cent found in the placebo group. This prosthetic graft model has considerable advantages in the evaluation of potential platelet inhibitory drugs for use in vascular surgery.

Effect of continuous low-dose intravenous heparin administered during operation on postoperative measurements of antithrombin III and antifactor Xa.

A preliminary subcutaneous dose of heparin given with premedication, followed by a continuous infusion of low-dose heparin up to 2 hours after operation, was given to 20 of 40 patients undergoing major abdominal operation randomly allocated to either act as controls or receive prophylaxis. The anticoagulant effect of heparin was determined by immunologic measurements of antithrombin III (AT III) and by assay of AT III and antifactor Xa activity on postoperative days 1 and 3. Despite lowered plasma AT III levels on postoperative day 3, the patients who had received low-dose heparin had significantly increased plasma antifactor Xa activity when compared with control patients (P less than 0.05). The incidences of thrombosis within 48 hours (early deep venous thrombosis) after operation were 9 of 20 control patients and 1 of 20 patients who received prophylaxis (P less than 0.01 by Fisher's exact test). Preoperative blood samples from another group of patients undergoing major abdominal operation were examined by the thromboelastograph saline dilution test, which has previously been shown to be a predictor of the risk of early deep vein thrombosis. The patients who were considered to be at high risk were treated with low-dose heparin as before, and the low-risk patients received no prophylaxis. The high-risk patients had lower levels of AT III before operation and before heparin administration than the low-risk patients and significantly lower levels on day 3 (P less than 0.02), whereas on day 3 the high-risk patients had significantly raised levels of plasma antifactor Xa. No patient in either group developed deep vein thrombosis within 48 hours of operation.

Management of retained cystic duct stones.

A 20-year-old woman underwent cholecystectomy and common bile duct exploration. Seven days later, T-tube cholangiography showed two stones retained in a developmentally anomalous cystic duct stump. She was treated with thrice-daily flushings of large amounts of saline through the T tube, and after 7 days of treatment the biliary system was free of stones. The conditions necessary for successful non-operative management of retained cystic duct stones are discussed.

Mechanisms of host defense and quantitative comparisons of bacterial populations in experimental peritonitis.

A model for the quantitative study of bacterial levels in blood, ascitic fluid, and liver, induced by Escherichia coli in the rat, has been devised. Three experimental situations were then studied: non-fatal peritonitis, fatal peritonitis induced by bacteria rendered more virulent by serial passage through test animals, and fatal peritonitis using haemoglobin adjuvant with the more virulent strain. Results indicate that a variety of defense mechanisms are operant in the host animal. In the non-fatal peritonitis, clearance of free bacteria from the peritoneum is observed with a late rebound in local and systemic populations. These phenomena correlate well with in vitro studies of bacterial uptake by peritoneal macrophages. In fatal peritonitis without adjuvant, much larger numbers of bacteria seem to escape initial clearance in the peritoneum and proximal reticuloendothelial system with resultant overwhelming septicaemia. In fatal peritonitis with adjuvant, much less clearance of organisms from the peritoneum is observed, with resultant overgrowth of bacteria and host death. It thus seems that the initial host defenses center around peritoneal clearance of introduced organisms, and that processes which interfere with this clearance prove fatal.

The saline dilution test--a preoperative predictor of DVT.

In vitro dilution of blood with normal saline produces an increase in coagulability which can be accurately measured by the thrombelastograph. The degree to which the coagulability of an individual patient's blood is increased by such dilution appears to be directly related to that patient's risk of developing a postoperative deep venous thrombosis. In a small group of patients undergoing major abdominal surgery, a preoperative test based on the coagulability increase after in vitro saline dilution successfully predicted all those who subsequently developed a postoperative deep venous thrombosis on 125I-fibrinogen scanning.