The effect of positive pressure breathing for altitude protection on intraocular pressure.

BACKGROUND: The effect of positive pressure breathing for altitude protection (PBA) on intraocular pressure was studied; the behavior of intraocular pressure both during and after PBA exposure was of particular interest. METHODS: Seven subjects were exposed to PBA of up to 60 mmHg at ground-level. The subjects were seated, and wore an aircrew helmet (HGU-55/P), oro-facial mask (M8U-20/P), thoracic counterpressure garment (CSU-17/P) and an extended coverage G-suit (ATAGS). Before, during and after each exposure, intraocular pressure was measured using a Tono-Pen XL applanation tonometer. RESULTS: All 7 subjects completed 10 min of PBA at breathing pressures of 30 and 40 mmHg, and 6 subjects completed 10 min at 50 and 60 mmHg. Mean and SEM increases in intraocular pressure, as compared to pre-exposure baseline measurements, were 7.7 +/- 0.6 mmHg at a breathing pressure of 30 mmHg, 12.0 +/- 0.9 mmHg at 40 mmHg, 18.4 +/- 1.3 mmHg at 50 mmHg and 20.0 +/- 0.6 mmHg at 60 mmHg. The difference between each of these increases was significant (p < 0.05), with the exception of that between 50 and 60 mmHg PBA. CONCLUSIONS: Intraocular pressure increases as breathing pressure increases. It is likely that this change in intraocular pressure would provide some protection to the retinal vasculature during PBA. In addition, it is unlikely that the temporary elevation of intraocular pressure following pressure breathing is of medical concern.

The initial signs and symptoms of altitude decompression sickness.

BACKGROUND: With the potential for higher aircraft and cabin altitudes, the way in which altitude decompression sickness (DCS) presents continues to be of interest. The majority of previous papers on the symptomatology of DCS are retrospective reviews of patients treated hours or days post-exposure. The initial presentation while still at altitude is the form of DCS that aircrew must be able to recognize in order to respond correctly. This paper reports the initial manifestations of DCS that occurred during a series of prospective hypobaric chamber studies. These studies had been specifically designed to investigate DCS. METHODS: This paper presents a prospective analysis of DCS symptoms from 447 subjects, recorded over an 11-yr period at the Armstrong Laboratory (AL), and is an attempt to provide an accurate representation of the initial presentation of altitude DCS. RESULTS: Of the 447 cases, 83.2% had musculoskeletal involvement, 2.7% had chokes, 2.2% skin manifestations, 10.8% paresthesia, and 0.5% frank neurological features. CONCLUSIONS: The most common presenting feature was musculoskeletal, with knee pain predominating (occurring in 70% of these cases). A very low incidence of neurological features was seen in the AL database, which was in contrast to data from many other sources. Reasons for this difference may include the use of preoxygenation and the policy of prompt recompression upon symptom development at AL. There is also the possibility that individuals in the training and operational environments are more likely to report frank neurological involvement than other forms of DCS.

An updated review of the clinical development of coumarin (1,2-benzopyrone) and 7-hydroxycoumarin.

Several authors have demonstrated that coumarin (1,2-benzopyrone) in combination with cimetidine can produce objective antitumor responses in some patients with advanced renal cell carcinoma. The purpose of this report is to review the clinical development of coumarin, with or without cimetidine, with special reference to renal cell carcinoma (RCC). Previously unpublished data concerning the survival of a population of patients with RCC, who were treated on a phase I trial of coumarin and cimetidine, are presented. The rationale and study design of an active randomized, double-blinded, placebo-controlled trial of coumarin for RCC are discussed. A progress report is given for an ongoing phase I trial of oral 7-hydroxycoumarin, the major human metabolite of coumarin.