Power Equation for Predicting the Risk of Central Nervous System Oxygen Toxicity at Rest.

Patients undergoing hyperbaric oxygen therapy and divers engaged in underwater activity are at risk of central nervous system oxygen toxicity. An algorithm for predicting CNS oxygen toxicity in active underwater diving has been published previously, but not for humans at rest. Using a procedure similar to that employed for the derivation of our active diving algorithm, we collected data for exposures at rest, in which subjects breathed hyperbaric oxygen while immersed in thermoneutral water at 33°C (n = 219) or in dry conditions (n = 507). The maximal likelihood method was employed to solve for the parameters of the power equation. For immersion, the CNS oxygen toxicity index is K I = t2 × PO2 10.93, where the calculated risk from the Standard Normal distribution is Z I = [ln(K I 0.5) - 8.99)]/0.81. For dry exposures this is K D = t2 × PO2 12.99, with risk Z D = [ln(K D 0.5) - 11.34)]/0.65. We propose a method for interpolating the parameters at metabolic rates between 1 and 4.4 MET. The risk of CNS oxygen toxicity at rest was found to be greater during immersion than in dry conditions. We discuss the prediction properties of the new algorithm in the clinical hyperbaric environment, and suggest it may be adopted for use in planning procedures for hyperbaric oxygen therapy and for rest periods during saturation diving.

Body mass index is inversely related to mortality in elderly subjects.

PURPOSE: To study the long-term effect of being overweight on mortality in very elderly subjects. METHODS: The medical records of 470 inpatients (226 males) with a mean age of 81.5 +/- 7 years and hospitalized in an acute geriatric ward between 1999 and 2000 were reviewed for this study. Body mass index (BMI) at admission day was subdivided into quartiles: <22, 22-25, 25.01-28, and > or =28 kg/m(2). Patients were followed-up until August 31, 2004. Mortality data were taken from death certificates. RESULTS: During a mean follow-up of 3.46 +/- 1.87 years (median 4.2 years [range 1.6 to 5.34 years]), 248 patients died. Those who died had lower baseline BMI than those who survived (24.1 +/- 4.2 vs 26.3 +/- 4.6 kg/m(2); p < .0001). The age-adjusted mortality rate decreased from 24 to 9.6 per 100 patient-years from the highest to lowest BMI quartile (p < .001). BMI was associated with all-cause and cause-specific mortality even after controlling for sex. A multivariate Cox proportional hazards model identified that even after controlling for male gender, age, renal failure, and diabetes mellitus, which increased the risk of all-cause mortality, elevated BMI decreased the all-cause mortality risk. CONCLUSIONS: In very elderly subjects, elevated BMI was associated with reduced mortality risk.

Influence of orthostatic hypotension on mortality among patients discharged from an acute geriatric ward.

BACKGROUND: Orthostatic hypotension (OH) is a common finding among older patients. The impact of OH on mortality is unknown. OBJECTIVE: To study the long-term effect of OH on total and cardiovascular mortality. PATIENTS AND METHODS: A total of 471 inpatients (227 males and 244 females), with a mean age of 81.5 years who were hospitalized in an acute geriatric ward between the years 1999 and 2000 were included in the study. Orthostatic tests were performed 3 times during the day on all patients near the time of discharge. Orthostatic hypotension was defined as a fall of at least 20 mmHg in systolic blood pressure (BP) and/or 10 mmHg in diastolic BP upon assuming an upright posture at least twice during the day. Patients were followed until August 31, 2004. Mortality data were taken from death certificates. RESULTS: One hundred and sixty-one patients (34.2%) experienced OH at least twice. Orthostatic hypotension had no effect on all cause and cause specific mortality. Over a follow-up of 3.47+/-1.87 years 249 patients (52.8%) had died 83 of whom (33.3%) had OH. Age-adjusted mortality rates in those with and without OH were 13.4 and 15.7 per 100 person-years, respectively. Cox proportional hazards model analysis demonstrated that male gender, age, diabetes mellitus, and congestive heart failure increased and high body mass index decreased total mortality. CONCLUSIONS: Orthostatic hypotension is relatively common in elderly patients discharged from acute geriatric wards, but has no impact on vascular and nonvascular mortality.