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Artificial gravity (AG) training improves orthostatic tolerance (Aviat Space 2004;75:850-8), but AG protocols have not been optimized. We therefore investigated regulatory responses to variations of posture, exercise, Gz level and radius of rotation (the latter two measured at the foot). Results presented are from 4 protocols that address radius and exercise effects only. Protocol A: After 10 min supine control, 12 healthy men (age 35 ± 9 yrs, wt 82.8 ± 7.9 kg) were exposed to rotational 1 Gz (2.5 m radius) for 2 min followed by 20 min of alternating between 1 and 1.25 Gz. Blood samples were taken pre and post spin. Protocol B: Subjects repeated A, but lower limb exercise (70% of V02max) preceded the ramps to 1.25 Gz. Protocol C: Same as A but radius of rotation was 8.3 m. Protocol D: Same as B but at 8.3 m. RESULTS: For the 8 subjects who completed all 4 protocols, we observed the following increases from control: Heart Rate (HR, bpm) A: 4, B: 40, C: 15, D: 45; Hematocrit (HCT, %) A: 2.0, B: 3.5, C: 2.4, D: 4.3; Aldosterone (pg/ml) A: 0, B: 121, C: 32, D: 115; and Plasma Renin Activity (PRA, ng/ml/h) A: 0.18, B: 1.12, C: 1.29, and D: 1.12. Our data suggest that HR, HCT and aldosterone were primarily influenced by exercise and secondarily by radius while PRA was influenced by both. We conclude that an optimal AG training countermeasure should involve exercise and maximal radius of rotation. [ABSTRACT FROM AUTHOR]

Cardio-respiratory responses to airborne particulates were investigated. In 36 non-smoking volunteers, continuous measures of blood pressure (Portapres), RR Interval (TEBCO) and respiration (Respitrace) were acquired during 10 min pre-exposure, exposure and post exposure to fumes from cooking oil (CO), environmental tobacco smoke (ETS), wood smoke (WS) and water vapor (sham), delivered in an environmental chamber. The order of exposure was randomly presented to pairs of subjects on three consecutive days. Mean values, auto spectra of variables and coherences between variables were computed. In response to all exposures, blood pressure increased significantly during recovery. In response to particulates, the index of sympathetic control of heart rate was significantly increased: ETS (50 ± 16.7%), WS; (31.6 ± 8.6 %) and CO (34.2 ± 11.3%). Low frequency coherence between systolic pressure and heart rate increased during each exposure. Other than decreased very low frequency coherence during recovery from WS, coherence between ventilation and heart rate was unchanged. Our data support the concept that the rise in blood pressure in the recovery phase of particulate exposures correlated with increased sympathetic control of heart rate. The rise of blood pressure in the case of sham exposure was not accompanied by increases in spectral power of either heart rate or blood pressure. [ABSTRACT FROM AUTHOR]

The aim of this research was to investigate cardiac autonomic changes associated with acute exposures to airborne particulates. Methods High fidelity 12-lead ECG (CardioSoft, Houston, TX) was acquired from 19 (10 male / 9 female) non-smoking volunteers (age 33.6 +/- 6.6 yrs) during 10 minutes pre-exposure, exposure and post-exposure to environmental tobacco smoke (ETS), cooking oil fumes, wood smoke and sham (water vapor). To control exposure levels, noise, subject activity, and temperature, all studies were conducted inside an environmental chamber. Results The short-term fractal scaling exponent (Alpha-1) and the ratio of low frequency to high frequency Heart Rate Variability (HRV) powers (LF/HF, a purported sympathetic index) were both higher in males (p<0.017 and p<0.05, respectively) whereas approximate entropy (ApEn) and HF/(LF+HF) (a purported parasympathetic index) were both lower in males (p<0.036, and p<0.044, respectively). Compared to pre-exposure (p<0.0002) and sham exposure (p<0.047), male heart rates were elevated during early ETS post-exposure. Our data suggest that, in addition to tonic HRV gender differences, cardiac responses to some acute airborne particulates are gender related. [ABSTRACT FROM AUTHOR]