Blood pressure, vascular resistance, and +Gz tolerance during repeated +Gz exposures.

BACKGROUND: Cardiovascular reflexes that regulate blood pressure (BP) adapt during repeated exposure to +Gz acceleration separated by short (< 20 s) breaks, but whether this effect is preserved with longer intervals remains unknown. METHODS: There were 17 subjects who completed 5 repeated gradual onset (0.1 G x s(-1)) runs (GOR1-5) to 60 degrees peripheral light loss (PLL) on a human centrifuge, separated by 2 min. Heart rate (HR) and BP were measured before and during each GOR and noninvasive estimation of cardiac output (CO) was used to calculate total peripheral resistance (TPR). RESULTS: Mean resting (+/- SE) systolic BP (138 +/- 4 vs. 128 +/- 3 mmHg) and TPR (13.9 +/- 1.2 vs. 12.7 +/- 1.0 mmHg x L(-1) x min(-1)) were elevated after GOR1 and remained elevated thereafter. Compared with that before GOR1, resting HR was decreased (5-6 bpm) before GOR2-5. Resting CO decreased from 8.3 +/- 0.6 L x min(-1) before GOR1 to a nadir of 7.2 +/- 0.5 L x min(-1) before GOR4 and GOR5. The change in HR under increased +Gz decreased from +39 +/- 3 bpm during GOR1 to +31 +/- 3 bpm during GOR4 and GOR5, but the decrease in eye level BP under +Gz was unaffected. RGT did not change across the five GORs. CONCLUSIONS: Increased resting BP and TPR following a single +Gz exposure suggest alterations in the cardiovascular system expected to confer improved tolerance during subsequent exposures. However, these changes were insufficient to improve +Gz tolerance measured during repeated GORs separated by 2 min.

Cosmic radiation in commercial aviation.

This paper reviews the current knowledge of cosmic radiation and its applicability to commercial aviation. Galactic cosmic radiation emanates from outside the solar system, while occasionally a disturbance in the suns' atmosphere leads to a surge in radiation particles. Protection is provided by the suns' magnetic field, the earths' magnetic field, and the earths' atmosphere. Dose rates are dependent on the altitude, the geomagnetic latitude and the solar cycle. For occupational exposure to ionising radiation, which includes aircrew, the International Commission on Radiological Protection recommends maximum mean body effective dose limits of 20mSv/yr (averaged over 5 years, with a maximum in any 1 year of 50mSv). Radiation doses can be measured during flight or may be calculated using a computer-modelling program such as CARI, EPCARD, SIEVERT or PCAIRE. Mean ambient equivalent dose rates are consistently reported in the region of 4-5microSv/h for long-haul pilots and 1-3microSv/h for short-haul, giving an annual mean effective exposure of the order 2-3mSv for long-haul and 1-2mSv for short-haul pilots. Epidemiological studies of flight crew have not shown conclusive evidence for any increase in cancer mortality or cancer incidence directly attributable to ionising radiation exposure. Whilst there is no level of radiation exposure below which effects do not occur, current evidence indicates that the probability of airline crew or passengers suffering adverse health effects as a result of exposure to cosmic radiation is very low.