Muscle metabolism, temperature, and function during prolonged, intermittent, high-intensity running in air temperatures of 33 degrees and 17 degrees C

Nine unacclimatized university sportsmen performed a prolonged, intermittent, high-intensity shuttle running test in hot (HT) (33 degrees C, dry bulb temperature, approximately 28 %, relative humidity) and moderate (MT) (17 degrees C, 63 %) environmental conditions. Subjects performed 60 m of walking, a 15-m sprint, 60 m of cruising ( approximately 85 % V.O (2max)), and 60 m of jogging ( approximately 45 %V.O (2max)) for 14.8 +/- 0.1 min followed by a 3-min rest, repeated until volitional exhaustion. The hot trial was performed first followed, 14 days later, by the moderate trial. During exercise subjects drank water ad libitum. Subjects ran almost twice as far in the moderate as in the hot trial (HT 11216 +/- 1411, MT 21644 +/- 1629, m, p < 0.01), and the decline in average 15-m sprint performance was greater in the heat (HT, 0.17 +/- 0.05, MT, 0.09 +/- 0.03, s, p < 0.05). Average heart rates, blood lactate and glucose, and plasma adrenaline and noradrenaline concentrations were greater in the HT (main effect trial, p < 0.01), as were serum cortisol concentration (main effect trial p < 0.05, n = 5) and muscle temperature (HT exhaustion vs. same time point in MT, 40.2 +/- 0.3 vs. 39.3 +/- 0.2, degrees C, p < 0.01). Peak torque during knee flexion and extension was not different pre-and post-exercise in the HT. Muscle glycogen utilization tended to be greater in the heat (HT 193.2 +/- 19.5, MT 143.8 +/- 23.9, mmol . kg dry wt (-1), p = 0.055, n = 8). In 7 out of the 8 subjects the increase in utilization was between 19 and just over 200 % greater in the HT. Glycogen remaining in the muscle at exhaustion was greater in the hot than moderate trial (HT 207.4 +/- 34.3, MT 126.5 +/- 46.8, mmol . kg dry wt (-1), p < 0.01, n = 8). Rectal temperature (T (rec)) was higher in the HT at exhaustion than at the same point in time in the moderate trial (HT, 39.60 +/- 0.15 vs. MT 38.75 +/- 0.10, degrees C, interaction trial-time, p < 0.01). There was a very strong negative relationship between rate of rise in T (rec) and distance completed in the HT (HT r = - 0.90, p < 0.01, MT r = - 0.76, p < 0.05). Thus, the earlier onset of exhaustion during prolonged intermittent shuttle running in the heat is associated with hyperthermia. However, while muscle glycogen utilization may be elevated by heat stress, low whole muscle glycogen concentrations would not seem to be the cause of this earlier exhaustion.     

Comparison of metabolic, temperature, heart rate and ventilatory responses to exercise at extreme ambient temperatures (0 degrees and 35 degrees C.).

Eight male subjects exercised on a bicycle ergometer for one half to one hour at loads demanding 52 to 59% of Vo2max on two separate occasions, once with ambient temperature held at 0 degrees C and once in a 35 degrees C environment. Throughout exercise and during recovery in a 25 degrees C environment, measurements were made of oxygen consumption, ventilation, heart rate, muscle-rectal-skin temperatures, and blood lactic acid. In the hot condition significant increases in heart rate, blood lactates, sweat loss, muscle, rectal and skin temperature responses were observed. At 0 degrees C Vo2 was significantly elevated during exercise over that in the 35 degrees C condition. Despite the elevated Vo2 response in the cold, higher body temperatures measured in the heat were associated with a significantly higher (P less than .025) recovery Vo2 (x = 866 ml), which was of the magnitude predicted by the van't Hoff-Arrhenius relationship.     

RPE drift during cycling in 18 degrees C vs 30 degrees C wet bulb globe temperature

AIM: The potential influence of a hotter vs cooler environment on ratings of perceived exertion (RPE) estimations during longer duration exercise is not well-understood. This study compared overall and differentiated RPEs during cycling in 18 degrees C vs 30 degrees C wet bulb globe temperature (WBGT). METHODS: Male volunteers (n=16) completed a maximal cycling trial (60 rev . min(-1), 25 Watts . min(-1)) to determine VO(2) max and ventilatory threshold (VT) before completing 2 (counterbalanced) longer duration cycling trials. At 30 degrees C WBGT (30C) and 18 degrees C WBGT (18C), subjects cycled 60 min (60 rev . min(-1), 90% individualized VT). Heart rate (HR, b . min(-1)) and rectal temperature (Tre, degrees C) were recorded every 5 min with corresponding RPE-overall (RPE-O), RPE-legs (RPE-L) and RPE-chest (RPE-C) estimations. RESULTS: HR was not significantly different at 5 min but was greater (P<0.05) for 30C at all other time points. During 30C, Tre was significantly greater (25, 30, 35, 40, 45, 50, 55 and 60 min), RPE-O was significantly greater (5, 40, 45, 50, 55 and 60 min), RPE-L was significantly greater (55 and 60 min) and RPE-C was significantly greater (35, 40, 45, 50, 55 and 60 min). CONCLUSIONS: Greater cardiovascular (HR) and thermal (Tre) strain partially explain greater perceptual ratings during 30C. Discernible RPE differences resulted mid-way through 60 min cycling with minimal differences initially. Results suggest RPEs are magnified in a 30 degrees C (vs 18 degrees C) environment beyond 30 min duration. Additionally, a 30 degrees C environment resulted in a less pronounced impact on RPE-L (vs RPE-C and RPE-O).     

Comparison of transaxial resolution in 180 degrees and 360 degrees SPECT with a rotating scintillation camera

Using circular 180 degrees and 360 degrees SPECT acquisition modes the transaxial resolution of line sources in air and water were measured at different positions in the field of view. With the 180 degrees acquisition mode, all line sources in air located off the axis of camera rotation (AoR) showed an oval distortion. This distortion was systematically related to the starting point of the rotating detector. On axis line sources in air were undistorted, regardless of the 180 degrees acquisition starting angle. The 360 degrees acquisition images of the line sources in air showed a similar effect but in a very mild form. In water, transaxial reconstructions of line sources (off axis) showed an enhancement of the oval distortion for both the 180 degrees and 360 degrees acquisitions. Computer simulations of the line source measurements were performed and correlated well with the experimental data. The line source results are explainable by the inherent depth dependent response of the scintillation camera. In clinical SPECT studies, distortions of this nature will be most appreciable with 180 degrees imaging of small organs that are located off the AoR.     

Investigation of causes of geometric distortion in 180 degrees and 360 degrees angular sampling in SPECT

To investigate geometric distortion when 180 degrees or 360 degrees angular sampling techniques are used in single photon emission computed tomography (SPECT), a study of point sources imaged at different positions in a water filled cylindrical phantom, and reconstructed using filtered back projection, was conducted. A simulation study, based upon a serial model of the system point spread function (PSF), was used to investigate the contributions of attenuation, spatial resolution and scatter on distortion of the reconstructed PSFs. To study the geometric distortion in transverse (x-y plane), coronal (x-z plane), and sagittal (y-z plane) sections, the ratios of the full widths at half maximum (FWHM) and full widths at tenth maximum (FWTM) in the x/y, x/z, and y/z directions were calculated for the real and simulated PSFs. These results showed that, in an attenuating medium, there is more distortion of point sources into ovals for 180 degrees than for 360 degrees sampling. The simulation study indicated that the primary cause of geometrical distortion in SPECT studies, is the inconsistency of projections due to variable attenuation and spatial resolution. The impact of scatter on geometric distortion was small as measured by the ratios of FWHMs and FWTMs for PSFs. Attenuation correction applied to acquired PSFs significantly reduced geometric distortion in both 180 degrees and 360 degrees studies. To investigate distortion in extended objects, an Iowa heart phantom was placed inside an Alderson body phantom and 201Tl heart SPECT studies acquired. The phantom images confirmed the conclusion that in transverse sections of 360 degrees studies with arithmetic averaging of opposite views, geometric distortion is reduced compared to 180 degrees. The coronal and sagittal sections were equally distorted in both, the 180 degrees and 360 degrees studies, and the 180 degrees studies yielded better contrast.     

Cooling hyperthermic firefighters by immersing forearms and hands in 10 degrees C and 20 degrees C water

INTRODUCTION: Firefighters experience significant heat stress while working with heavy gear in a hot, humid environment. This study compared the cooling effectiveness of immersing the forearms and hands in 10 and 20 degrees C water. METHODS: Six men (33 +/- 10 yr; 180 +/- 4 cm; 78 +/- 9 kg; 19 +/- 5% body fat) wore firefighter 'turn-out gear' (heavy clothing and breathing apparatus weighing 27 kg) in a protocol including three 20-min exercise bouts (step test, 78 W, 40 degrees C air, 40% RH) each followed by a 20-min rest/cooling (21 degrees C air); i.e., 60 min of exercise, 60 min of cooling. Turn-out gear was removed during rest/cooling periods and subjects either rested (Control), immersed their hands in 10 or 20 degrees C water (H-10, H-20), or immersed their hands and forearms in 10 or 20 degrees C water (HF-10, HF-20). RESULTS: In 20 degrees C water, hand immersion did not reduce core temperature compared with Control; however, including forearm immersion decreased core temperature below Control values after both the second and final exercise periods (p < 0.001). In 10 degrees C water, adding forearm with hand immersion produced a lower core temperature (0.8 degrees C above baseline) than all other conditions (1.1 to 1.4 degrees C above baseline) after the final exercise period (p < 0.001). Sweat loss during Control (1458 g) was greater than all active cooling protocols (1146 g) (p < 0.001), which were not different from each other. DISCUSSION: Hand and forearm immersion in cool water is simple, reduces heat strain, and may increase work performance in a hot, humid environment. With 20 degrees C water, forearms should be immersed with the hands to be effective. At lower water temperatures, forearm and/or hand immersion will be effective, although forearm immersion will decrease core temperature further.     

Comparison of 70 degrees tilt, LBNP, and passive standing as measrues of orthostatic tolerance.

The present study was performed to assess the reliability of lower body negative pressure (LBNP) as a test of orthostatic tolerance. The need for this assessment arose from the prior observation in this laboratory that some subjects show wide day-to-day variation in heart rate responses to LBNP. The extent of these variations was so great as to a raise a serious question as to the value of LBNP as a measure of study-induced alterations (e.g. those produced by bedrest or weightlessness) in orthostatic tolerance. Five healthy volunteers were subjected to a series of tests, consisting of 70 degrees tilt, LBNP, and passive standing. on three occasions preceding and three occasions following a 2 week period of bedrest. Study results show that it is possible to subdivide the volunteers into subgroups which show either great or little day-to-day variability in any of the three tests. All three tests reaveled bedrest-induced alterations in orthostatic tolerande quite adequately. Of the three tests studied, LBNP most frequently resulted in the largest test-induced heart rate alterations, followed by quiet standing and, finally 70 degrees tilt     

Comparison between 180 degrees and 360 degrees data collection in technetium-99m MIBI SPECT of the myocardium

In a series of 12 patients presenting with a single-vessel coronary artery disease and who were injected with 370 MBq of 99mTc-2-methoxyisobutylisonitrile at peak exercise, two consecutive single photon emission computed tomography (SPECT) data collections, i.e., 32 views of 30 sec during a 180 degrees rotation and 64 views of 15 sec during a 360 degrees rotation, were performed 1 hr later. In both cases, transverse sections were reconstructed using (a) a backprojection method with a ramp filter, (b) a correction for downscatter, (c) a correction for depth attenuation by the Chang method, or (d) both corrections. Each reconstructed myocardium was then divided into four short-axis sections which were radially divided into nine sectors. Sectors with an activity below 80% of the maximum were considered as abnormal. Sensitivity and specificity were calculated relative to a sector-by-sector theoretical anatomic distribution of the perfusion abnormalities. Results demonstrate that, of all situations, the best balance between sensitivity and specificity was achieved with the 180 degrees data collection and no correction at reconstruction. Using the 360 degrees data sampling technique mainly lowered the sensitivity in the patients with a circumflex or right coronary artery disease. It is concluded that there does not seem to be any definite advantage in performing a 360 degrees rather than a 180 degrees data collection in 99mTc myocardial SPECT.     

Cardiovascular response to 4 hours of 6 degrees head-down tilt or of 30 degrees head-up tilt bed rest

The cardiovascular responses to 4 h of 6 degrees head-down tilt (HDT) were compared to those of 4 h of 30 degrees head-up tilt (HUT) following a period of 1 h baseline in the 30 degrees HUT position. Eight healthy males completed each tilt position. Immediately on assuming HDT, heart rate decreased slightly from baseline, but did not differ from HUT. Stroke volume and cardiac output both increased significantly by as much as 54% and 26%, respectively, in the first minute of HDT. The difference between HDT and HUT was no longer present after 30 min. Mean arterial blood pressure was unchanged throughout 4 h or HUT or HDT. The ratio of pre-injection period to left ventricular ejection time was significantly decreased across all 4 h of HDT. Plasma volume was slightly elevated over the 4 h of HDT, while plasma hemoglobin concentration was significantly reduced. No evidence of a diuresis was found with 4 h HDT. Plasma catecholamines were not different between HDT and HUT. The present results show that the immediate transition from a HUT to a HDT position causes a dramatic change in cardiovascular variables. These changes are generally transient with baseline values resumed by many variables within 30 min of exposure to 6 degrees HDT.     

Opinions on baccalaureate degrees for radiation therapists

In 1980, a survey of chief radiation therapists assessed opinions on baccalaureate education for radiation therapists. Results suggested a need in education and administrative/management positions. Another survey in 1987 assessed the opinions of 484 technologists regarding baccalaureate-level education. Results suggest that more than half support the idea and would pursue baccalaureate degrees. Results also indicate concerns that baccalaureate education could detract from clinical preparation.     

Intraocular pressure, retinal vascular, and visual acuity changes during 48 hours of 10 degrees head-down tilt

Intraocular pressures, retinal vascular diameters, and visual acuities of nine men (ages 19-29), were repeatedly measured while the subjects were tilted 10 degrees head-down for 48 h and while they were seated before (baseline), and after the tilt. An immediate increase in intraocular pressure, measured by pneumatonometer (4.7 +/- 0.6 mm Hg, p less than 0.001) was recorded when subjects assumed the head-down position, and diurnal variations in intraocular pressures were observed for the 48 h. The initial and final head-down intraocular pressures were not significantly different (18.9 +/- 1.2 mm Hg vs. 17.9 +/- 1.4 mm Hg, respectively). However, when subjects resumed the sitting position, intraocular pressures fell below the initial sitting values (14.2 +/- 0.9 pre vs. 11.2 +/- 0.5 post, p less than 0.04). Computer image analysis of the retinal vasculature detected a 6% and 2% reduction in the caliber of arteries and veins, respectively, as compared with sitting baseline values. No changes in visual acuity were documented during the 48 h of head-down tilt. Our data suggest that the choroidal blood reservoir increases in volume over 48 h at continuous head-down position with a compensatory decrease in aqueous volume. These findings may explain intraocular pressure changes noted in astronauts during previous space missions and in studies associated with change in body position.     

Clinical evaluation of 360 degrees and 180 degrees data sampling techniques for transaxial SPECT thallium-201 myocardial perfusion imaging

The most serious controversy regarding the application of transaxial SPECT technology to 201Tl myocardial perfusion imaging is the choice between 360 degrees compared with 180 degrees data sampling techniques. The present study utilized the original 360 degrees sampled raw data of 25 patients who had both SPECT 201Tl myocardial perfusion imaging and coronary angio/ventriculography for back projection reprocessing to accomplish the 360 degrees/180 degrees comparison. The results show a high incidence, 36% (9/25), of false-positive segmental perfusion abnormality and a high incidence, 24% (6/25), of moderate to severe degree of image distortion with the 180 degrees data sampled reconstructed images. These were not observed in the 360 degrees data sampled reconstructed images. The above findings confirmed our previous preliminary conclusion that even though the 180 degrees data sampling technique has the advantage of providing improved image contrast and reduction in acquisition time it is not a reliable technique and should be abandoned. The 360 degrees data sampling is the technique of choice for transaxial SPECT 201Tl myocardial perfusion imaging.