Defining total corporate health and safety costs--significance and impact. Review and recommendations.

This is the first in a series of studies designed to assist directors of occupational health and safety services in defining, measuring, predicting, and integrating total health and safety costs into useful management information. This study was structured to review recent literature on health and safety costs and to categorize costs as either direct or indirect. This delineation should aid in defining total health and safety costs, delineating priority areas for interventions to reduce costs, and evaluating the effectiveness of health and safety programs. The significance of such efforts is underscored by the reported direct health care costs for the nation's work force of over $418 billion, and indirect costs, using the lower range of estimates for such costs, of over $837 billion. Reducing the total costs of over $1.256 trillion would have major impacts on corporate productivity and competitiveness, as well as on availability of health care programs for employees. Recommendations for follow-up activities to define costs and evaluate intervention programs are provided.

Prolonged total circulatory support using direct mechanical ventricular actuation.

Direct mechanical ventricular actuation (DMVA) is a unique, non blood contacting method for biventricular cardiac assist. Although DMVA has successfully provided cardiac assist for more than 7 days in humans, with long-term survival, its potential for long-term circulatory support has not been adequately investigated. DMVA has not been studied in the large ruminants commonly used to evaluate support devices. To develop a large animal experimental model of prolonged total circulatory support using DMVA, Suffolk sheep (n = 10) underwent sterile instrumentation for hemodynamic and chemistry monitoring. After baseline values were obtained, a left lateral thoracotomy and pericardotomy were performed. Upon electrical ventricular fibrillation (VF), DMVA was begun and the thoracotomy closed. Total circulatory support was continued until mean arterial pressure (MAP) persisted below 50% of the baseline value for more than 1 hr, with a goal of 7 days' support. Mean duration (plus or minus the standard deviation [SD]) of circulatory support was 65.9 +/- 56.8 hr (range, 10-168 hr). Pressors were not used during DMVA support. The subject supported for the maximal time (7 days) was defibrillated into sinus rhythm. No CK-MB fraction was greater than 1%, suggesting that DMVA, even with prolonged application during VF, does not result in myocardial injury. Blood urea nitrogen and creatinine levels indicate renal function was preserved. The model described represents the longest period any animal has been supported in VF using DMVA. This new model will be useful in determining what limitations, if any, exist to the prolonged use of DMVA for circulatory support.

The effect of cardiac compression on defibrillation efficacy and the upper limit of vulnerability.

INTRODUCTION: We determined the effects of decreasing the ventricular blood volume and altering cardiac geometry on defibrillation, the upper limit of vulnerability (ULV), and the relationship between them. METHODS AND RESULTS: In six pigs, fibrillation/defibrillation trials were performed with a left ventricular apex patch to a superior vena cava catheter electrode configuration and a biphasic waveform. Thirty trials each were performed on a compressed versus noncompressed (normal) heart. Compression was achieved using direct mechanical ventricular actuation. Dose-response curves were constructed, and the 50% probability points (ED50) were compared for leading edge voltage (LEV), leading edge current (LEI), and total energy (TE). In another 12 pigs, triplicate defibrillation thresholds (DFTs) and ULVs were determined for each heart state. The T wave was scanned with shocks in 10-msec steps for determining the ULV. Compression resulted in decreased ED50s for LEV (delta = 138 +/- 77 V, P < 0.05, mean +/- SD), LEI (delta = 1.57 +/- 0.7 A, P < 0.05), and TE (delta = 4.9 +/- 3.6 J, P < 0.05) compared to normal. In the second study, compression significantly reduced DFT (P < 0.02) and ULV (P < 0.02) for LEV, LEI, and TE compared to normal. The ULV tended to be lower than the DFT for the normal heart state (delta = 23 +/- 46 V LEV: P = NS). However, the ULV was significantly greater than the DFT for the compressed heart state (delta = 19 +/- 25 V LEV; P < 0.03). CONCLUSIONS: Shock delivery during cardiac compression improves defibrillation efficacy. Additionally, cardiac compression decreases both DFT and ULV, which supports the ULV hypothesis of defibrillation. Finally, maintaining the heart's geometric and volumetric state during ULV testing in paced rhythm and DFT testing in ventricular fibrillation moves the ULV higher than the DFT-the position predicted by the ULV hypothesis for defibrillation.

Myocardial tolerance to mechanical actuation is affected by biomaterial characteristics.

Direct mechanical ventricular actuation (DMVA) uses a pressure regulated heart cup, fabricated from silicone rubber (SR) for mechanical massage of the heart. Because DMVA has demonstrated potential for long-term circulatory support, investigations are currently exploring the use of more durable materials for fabricating DMVA heart cups. This study assessed the acute effects of heart cups fabricated from SR versus polyurethane (PU) on the myocardium. Dogs (n - 18) received DMVA for 4 hr of ventricular fibrillation (VF) using either SR (n = 10) or PU (n = 8) cups. Microspheres were used to determine perfusion during sinus rhythm (control) and at 2 and 4 hr of support. After support, myocardial biopsies were assayed for high energy phosphate content. Results demonstrated that PU cups required relatively frequent adjustments in drive line parameters that were likely due to material softening during PU cup support. Both PU and SR cups achieved similar hemodynamics during 4 hr of support. Myocardial perfusion, however, demonstrated a marked hyperemia at 4 hr of PU versus SR cup support. Regional high energy phosphate content was significantly decreased in hearts supported by PU versus SR cups. These results suggest that the relatively compliant characteristics of SR materials are important for achieving effective DMVA support without injuring the myocardium.

Contracting for occupational health service. An insider's view.

A survey of the Fortune 500 companies reveals that contracting for occupational medicine services is frequent. Contacting is most used for services that are highly specialized and infrequently used. About two-thirds of large companies provide at least some routine occupational medicine services with employed physicians. An economic analysis suggests that for large plants, contracting for general occupational medicine services is usually not an effective strategy for saving money. Intangibles, such as integration of the occupational medicine department with all other health related corporate activities, are postulated to significantly influence corporate decision makers when they consider contracting for occupational medicine services.

Regional cerebral blood flow with manual internal cardiac massage versus direct mechanical ventricular assistance.

STUDY HYPOTHESIS: Previous studies have not discerned the best method for generating regional cerebral blood flow during internal cardiac massage. We hypothesized that regional cerebral blood flow generated by a mechanical method--direct mechanical ventricular assistance (DMVA)--would be superior to manual internal cardiac massage (MAN). STUDY POPULATION: Twelve adult Yucatan minipigs weighing more than 44 kg each were studied. METHODS: Swine were instrumented for regional cerebral blood flow measurements using tracer microspheres. After 15 minutes of ventricular fibrillation, swine were randomized to receive either MAN or DMVA. Regional cerebral blood flow was measured during normal sinus rhythm and at one minute (VF-1) and six minutes (VF-2) after initiation of circulatory support. Regional cerebral blood flow values were compared using a Wilcoxon rank sum test. RESULTS: During VF-1, there was a tendency for DMVA to produce greater regional cerebral blood flow than MAN, although these differences were not statistically significant (DMVA vs MAN as mL/min/100 g): cerebral cortex, 28 versus 11; cerebellum, 49 versus 22; midbrain, 43 versus 16; pons, 55 versus 18; medulla, 55 versus 19; and spinal cord, 33 versus 10. During VF-2, DMVA produced greater regional cerebral blood flows than were produced by MAN: cerebral cortex, 39 versus 12 (P less than .06); cerebellum, 58 versus 20 (P less than 0.5); midbrain, 50 versus 18 (P less than .05); pons, 52 versus 22 (P less than .06); medulla, 53 versus 20 (P less than .05); and spinal cord, 31 versus 12 (P less than .05). CONCLUSION: DMVA produces greater regional cerebral blood flow than is produced during MAN after 15 minutes of ventricular fibrillation. DMVA is effective at maintaining regional cerebral blood flow after a prolonged cardiac arrest.

First successful bridge to cardiac transplantation using direct mechanical ventricular actuation.

Currently available ventricular assist devices are technically difficult to implant, require continuous anticoagulation, and are associated with hemorrhagic and thromboembolic complications. Direct mechanical ventricular actuation is a biventricular assist device that can be applied in 3 to 5 minutes through a left anterior thoracotomy and has no direct blood contact or need for anticoagulation. The present study was designed to determine the effects of direct mechanical ventricular actuation in total biventricular circulatory support. Cardiogenic shock refractory to standard therapy developed in 2 patients awaiting cardiac transplantation. Direct mechanical ventricular actuation was applied and provided immediate hemodynamic stabilization in both. All inotropic agents and intraaortic balloon support were then discontinued. Fifty-six hours of circulatory support bridged the first patient to successful cardiac transplantation without complication. The patient is alive and well more than 1 year later without incident of infection or rejection. The second patient suffered cardiac arrest and required closed chest cardiopulmonary resuscitation before device application. After 45 hours of support, it was determined that irreversible neurologic injury had occurred and direct mechanical ventricular actuation was discontinued. Neither patient's native heart exhibited any histologic evidence of device-related trauma. Direct mechanical ventricular actuation has undergone limited clinical investigation since its original description 25 years ago, but in these initial trials, the device has proved effective. The concept of mechanically actuating the ventricles appears to be a valuable, yet under-utilized method of total circulatory support.

Direct mechanical ventricular actuation for cardiac arrest in humans. A clinical feasibility trial.

Direct mechanical ventricular actuation (DMVA) is a non-blood-contacting method of biventricular cardiac massage which may be applied expediently for total circulatory support. The purpose of this study was to assess the feasibility of DMVA application for patients suffering refractory cardiac arrest. Following informed consent, DMVA was applied in 22 patients. Vascular access for hemodynamic monitoring was possible in only 12 patients, whose outcomes serve as the basis for this report. The mean age of the patients was 48.2 +/- 4.2 years (seven men; five women). The average time from witnessed cardiac arrest to DMVA application was 81 +/- 9 minutes. Application took less than two minutes from the time of skin incision and resulted in immediate hemodynamic improvement. Systolic and diastolic blood pressures averaged 78 +/- 4 and 41 +/- 4 mm Hg, respectively, with a mean cardiac output of 3.14 +/- 0.18 L/min during a mean of 228 +/- 84 minutes of circulatory support (range, 25 minutes to 18 hours). In selected cases the device was temporarily removed for 2 to 3 minutes and open-chest cardiac massage (OCCM) performed at similar compression rates. DMVA increased arterial pressures 65 percent and cardiac output 190 percent compared to OCCM. Initial arterial pH (7.12 +/- 0.04) improved by the time the device was removed (7.24 +/- 0.05). Serum lactate levels decreased from 18.0 +/- 2.3 mumol/L to 14.9 +/- 2.9 mumol/L. Four patients were successfully defibrillated: two had inadequate cardiac function and died within 1 h, and two were successfully resuscitated, but later died from cardiac failure and respiratory insufficiency. Another patient regained normal neurologic function during DMVA and was successfully bridged to cardiopulmonary bypass for emergent coronary artery bypass grafting, but died later from myocardial infarction. There were only two complications: (1) a cardiac laceration during pericardiotomy (1/22 patients); and (2) a ventricular rupture during OCCM (1/22). No complication resulted from the device. We found DMVA to be a feasible method for acute cardiovascular stabilization in victims suffering refractory cardiac arrest. Human clinical trials employing earlier DMVA application are required to determine its resuscitative potential.

The business planning process applied to an in-house corporate occupational medicine unit.

In using the business planning process we defined our services, determined the lowest available open market price for each, and multiplied the unit price by the number we performed in the year to calculate our income. All our costs were then allocated to these services, and a cost per service determined. These were compared to the commercially available rates. Our unit is the low cost provider by 10%, even when using worst case assumptions. We concluded that contracting with outside organizations for occupational medical services could not be justified on either a cost or a quality basis.

Direct mechanical ventricular actuation: a review.

Direct mechanical ventricular actuation (DMVA) is a non-blood contacting method of circulatory support that can be rapidly instituted for resuscitation. DMVA is superior to conventional methods (open and closed-chest cardiac massage) in providing reliable cardiovascular stabilization for resuscitation following cardiac arrest. Furthermore, DMVA has important advantages including rapid application, technical simplicity, and avoidance of blood contact compared to other resuscitation devices (cardiopulmonary bypass and blood pumps). This review summarizes laboratory and clinical applications of DMVA.

Effect of direct mechanical ventricular assistance on myocardial hemodynamics during ventricular fibrillation.

Direct mechanical ventricular assistance (DMVA) is a method of biventricular circulatory support that employs a pneumatic device to apply both systolic and diastolic forces directly to the ventricular myocardium. This study investigated the effects of DMVA on myocardial hemodynamics when applied after a prolonged cardiopulmonary arrest. Seven swine weighting 28.3 +/- 2.5 kg were instrumented for regional myocardial blood flow (MBF) measurements using tracer microspheres. Ventricular fibrillation was then induced. After 10 min of ventricular fibrillation, CPR was initiated for 3 min. DMVA was then applied through median sternotomy. Defibrillation was attempted after 3.5 min of DMVA. If unsuccessful, DMVA was instituted for another 17.5 min and a subsequent defibrillation attempt was made. Arterial oxygen content (CaO2), coronary sinus oxygen content (CcSO2), myocardial oxygen delivery/consumption (mDO2/mVO2), extraction ratio (ER), and endocardial/epicardial blood flow ratio (EN/EP) were determined during CPR, during the initial application of DMVA (DMVA1), and after the subsequent 17.5 min of DMVA in those animals not initially defibrillated (DMVA2). Three of the seven animals were successfully defibrillated during DMVA1. After the additional 17.5 min of DMVA, only one other animal was defibrillated. There was a significant improvement in CaO2, CcSO2, MBF, mDO2, mVO2, ER, and EN/EP after DMVA1 compared to CPR. Only mVO2 and ER improved significantly after DMVA2. These findings support the concept that physical diastolic augmentation may improve myocardial hemodynamics when DMVA is applied during cardiac arrest.

Comparative study of three methods of resuscitation: closed-chest, open-chest manual, and direct mechanical ventricular assistance.

Presented are the results of a comparison study of three forms of circulatory support during ventricular fibrillation: closed-chest compression (CCC), open-chest manual compression (OCMC), and direct mechanical ventricular assistance (DMVA). DMVA is a method of circulatory support using a bell-shaped device that is affixed to the heart by apical suction and that alternately compresses and expands the ventricles. CCC produced a cardiac index (CI) of 780 mL/min/m2 (19% of control) with a mean arterial pressure (MAP) of 26 mm Hg (23% of control). Both forms of direct cardiac compression produced higher values. OCMC at 60 compressions per minute (CPM) produced a CI of 2,069 mL/min/m2 (52% of control) with an MAP of 50 mm Hg (45% of control). DMVA at the same rate produced a CI of 2,780 mL/min/m2 (70% of control) with an MAP of 72 mm Hg (65% of control). The values for DMVA at 60 CPM were significantly higher than for OCMC at 60 CPM (P less than .005 for CI, and P less than .0005 for MAP). Changing from standard CCC to DMVA at 90 CPM produced the greatest hemodynamic improvements: MAP increased by 250%, and CI increased by 340%. With DMVA at 90 CPM, the systolic pressure, stroke index, and CI were not statistically different from control, prearrest values.