1: Respir Physiol Neurobiol. 2005 May 12;147(1):73-80. A discussion regarding the contribution of intrapulmonary gas mixing to O2 isotope fractionation by respiration using experimental data for 36Ar and 40Ar. Luijendijk SC, Zegers IH, van der Grinten CP. Department of Respiratory Medicine, University Hospital Maastricht, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands. We determined the argon (Ar) isotope ratio in samples of expired alveolar gas gathered during Ar washout from residual gas relative to this ratio in samples of expired alveolar gas gathered just before the beginning of this washout in 13 young, healthy human subjects at rest. These data were determined for a limited number of breaths in early washout and were used to calculate the relative difference between the alveolar ventilations of (36)Ar and (40)Ar (Delta(rel)V (A)((36)Ar,(40)Ar)). Mean Delta(rel)V (A)((36)Ar,(40)Ar) amounted to 1.6 per thousand (S.D.=1.3 per thousand). This result was then used to discuss the contribution of intrapulmonary gas mixing by diffusion to oxygen isotope fractionation of alveolar gas by respiration. On the basis of our finding for Delta(rel)V (A)((36)Ar,(40)Ar) and further theoretical considerations we arrived at the conclusion that this contribution for subjects at rest is small (about 1 per thousand) and that this contribution is negative irrespective of the level of exercise. PMID: 15848125 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 2: J Hum Hypertens. 2001 Oct;15(10):715-21. Integrated effects of the vasodilating beta-blocker nebivolol on exercise performance, energy metabolism, cardiovascular and neurohormonal parameters in physically active patients with arterial hypertension. Predel HG, Mainka W, Schillings W, Knigge H, Montiel J, Fallois J, Agrawal R, Schramm T, Graf C, Giannetti BM, Bjarnason-Wehrens B, Prinz U, Rost RE. Institute of Cardiology and Sports Medicine, German Sports University, Cologne, Germany. Predel@hrz.dshs_koeln.de OBJECTIVE: The present study was designed to investigate the integrated effects of the beta-1-selective blocker with vasodilator properties, nebivolol, on systemic haemodynamics, neurohormones and energy metabolism as well as oxygen uptake and exercise performance in physically active patients with moderate essential hypertension (EH). DESIGN AND METHODS: Eighteen physically active patients with moderate EH were included: age: 46.9 +/- 2.38 years, weight: 83.9 +/- 2.81 kg, blood pressure (BP): 155.8 +/- 3.90/102.5 +/- 1.86 mm Hg, heart rate: 73.6 +/- 2.98 min(-1). After a 14-day wash-out period a bicycle spiroergometry until exhaustion (WHO) was performed followed by a 45-min submaximal exercise test on the 2.5 mmol/l lactate-level 48 h later. Before, during and directly after exercise testing blood samples were taken. An identical protocol was repeated after a 6-week treatment period with 5 mg nebivolol/day. RESULTS: Nebivolol treatment resulted in a significant (P < 0.01) decrease in systolic and diastolic BP and heart rate at rest and during maximal and submaximal exercise. Maximal physical work performance, blood lactate and rel. oxygen uptake (rel. VO(2)) before and after nebivolol treatment at rest and during maximal and submaximal exercise remained unaltered. Free fatty acid, free glycerol, plasma catecholamines, beta-endorphines and atrial natriuretic peptide (ANP) increased before and after treatment during maximal and submaximal exercise but remained unaltered by nebivolol treatment. In contrast, plasma ANP levels at rest were significantly higher in the presence of nebivolol, endothelin-1 levels were unchanged. CONCLUSIONS: Nebivolol was effective in the control of BP at rest and during exercise in patients with EH. Furthermore, nebivolol did not negatively affect lipid and carbohydrate metabolism and substrate flow. The explanation for the effects on ANP at rest remain elusive. This pharmacodynamic profile of nebivolol is potentially suitable in physically active patients with EH. Publication Types: Clinical Trial PMID: 11607802 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 3: Am J Physiol Endocrinol Metab. 2000 Apr;278(4):E580-7. Endurance exercise training attenuates leucine oxidation and BCOAD activation during exercise in humans. McKenzie S, Phillips SM, Carter SL, Lowther S, Gibala MJ, Tarnopolsky MA. Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada. We studied the effects of a 38-day endurance exercise training program on leucine turnover and substrate metabolism during a 90-min exercise bout at 60% peak O(2) consumption (VO(2 peak)) in 6 males and 6 females. Subjects were studied at both the same absolute (ABS) and relative (REL) exercise intensities posttraining. Training resulted in a significant increase in whole body VO(2 peak) and skeletal muscle citrate synthase (CS; P < 0.001), complex I-III (P < 0.05), and total branched-chain 2-oxoacid dehydrogenase (BCOAD; P < 0.001) activities. Leucine oxidation increased during exercise for the pretraining trial (PRE, P < 0.001); however, there was no increase for either the ABS or REL posttraining trial. Leucine oxidation was significantly lower for females at all time points during rest and exercise (P < 0.01). The percentage of BCOAD in the activated state was significantly increased after exercise for both the PRE and REL exercise trials, with the increase in PRE being greater (P < 0.001) compared with REL (P < 0.05). Females oxidized proportionately more lipid and less carbohydrate during exercise compared with males. In conclusion, we found that 38 days of endurance exercise training significantly attenuated both leucine oxidation and BCOAD activation during 90 min of endurance exercise at 60% VO(2 peak) for both ABS and REL exercise intensities. Furthermore, females oxidize proportionately more lipid and less carbohydrate compared with males during endurance exercise. Publication Types: Clinical Trial PMID: 10751189 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 4: Appl Occup Environ Hyg. 1999 Jan;14(1):39-44. Exposures of geotechnical laboratory workers to respirable crystalline silica. Miller SK, Bigelow PL, Sharp-Geiger R, Buchan RM. Department of Environmental Health, Colorado State University, USA. Geotechnical laboratory testing involves the determination of the physical properties of soil, rock, and other building materials for engineering purposes. Individuals working in these laboratories are exposed to airborne soil, rock, and other dusts during the preparation and testing of these materials. Crystalline silica as quartz is a common constituent of these materials and represents a potential hazard to geotechnical laboratory workers when airborne as a respirable dust. The authors conducted an examination of the potential for geotechnical laboratory workers to be exposed to respirable dust and respirable quartz during the performance of three routine laboratory tasks. A task-based exposure assessment strategy was used. Although respirable dust was generated during the performance of each of these tasks, its impact on exposures was generally overridden by the presence of respirable quartz in the dust. Quartz content in the respirable dust ranged from below the detection limit to greater than 50 percent. Mean exposure to respirable quartz, based on the duration of the task and assuming no other exposures for the rest of the 8-hour day, exceeded the National Institute for Occupational Safety and Health (NIOSH) "action level" (the exposure level at which certain actions must be taken) of 0.025 mg/m3. If exposure was assumed to continue for the rest of the 8-hour day at the measured concentration, mean exposure to respirable quartz exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) time-weighted average (TWA), the Occupational Safety and Health Administration (OSHA) PEL, and the NIOSH REL. Seven percent of 57 individual task exposure measurements exceeded the TLV-TWA and the PEL, 18 percent exceeded the REL, and another 12 percent exceeded excursion limits as defined by ACGIH. The results of this study support the conclusion that geotechnical laboratory workers are potentially exposed to respirable crystalline silica as quartz at levels that may be harmful. Because the quartz content of the materials being tested in these laboratories is highly variable and is almost never determined prior to testing, all materials being tested in the geotechnical laboratory should be assumed to contain quartz. Appropriate controls should be used to protect workers from inhaling dusts generated from these materials. PMID: 10730137 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 5: Eur J Appl Physiol Occup Physiol. 1998 Feb;77(3):231-41. Relevance of individual characteristics for human heat stress response is dependent on exercise intensity and climate type. Havenith G, Coenen JM, Kistemaker L, Kenney WL. TNO Human Factors Research Institute, Soesterberg, The Netherlands. Multiple heterogeneous groups of subjects (both sexes and a wide range of maximal oxygen uptake VO2max, body mass, body surface area (AD),% body fat, and AD/mass coefficient) exercised on a cycle ergometer at a relative (%VO2max, REL) or an absolute (60 W) exercise intensity in a cool (CO 21 degrees C, 50% relative humidity), warm humid (WH 35 degrees C, 80%) and a hot dry (HD 45 degrees C, 20%) environment. Rectal temperature (Tre) responses were analysed for the influence of the individual's characteristics, environment and exercise intensity. Exposures consisted of 30-min rest, followed by 60-min exercise. The Tre was negatively correlated with mass in all conditions. Body mass acted as a passive heat sink in all the conditions tested. While negatively correlated with VO2max and VO2max per kilogram body mass in most climates, Tre was positively correlated with VO2max and VO2max per kilogram body mass in the WH/REL condition. Thus, when evaporative heat loss was limited as in WH, the higher heat production of the fitter subjects in the REL trials determined Tre and not the greater efficiency for heat loss associated with high VO2max. Body fatness significantly affected Tre only in the CO condition, where, with low skin blood flows (measured as increases in forearm blood flow), the insulative effect of fat was pronounced. In the warmer environments, high skin blood flows offset the resistance offered by peripheral adipose tissue. Contrary to other studies, Tre was positively correlated with AD/mass coefficient for all conditions tested. For both exercise types used, being big (a high heat loss area and heat capacity) was apparently more beneficial from a heat strain standpoint than having a favourable AD/mass coefficient (high in small subjects). The total amount of variance in Tre responses which could be attributed to individual characteristics was dependent on the climate and the type of exercise. Though substantial for absolute exercise intensities (52%-58%) the variance explained in Tre differed markedly for relative intensities: 72% for the WH climate with its limited evaporative capacity, and only 10%-26% for the HD and CO climates. The results showed that individual characteristics play a significant role in determining the responses of body core temperature in all conditions tested, but their contribution was low for relative exercise intensities when evaporative heat loss was not restricted. This study demonstrated that effects of individual characteristics on human responses to heat stress cannot be interpreted without taking into consideration both the heat transfer properties of the environment and the metabolic heat production resulting from the exercise type and intensity chosen. Their impact varies substantially among conditions. PMID: 9535584 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 6: Int J Microcirc Clin Exp. 1997 Mar-Apr;17(2):80-5. Skin blood flow during vasoconstrictive and vasodilative stimuli in essential hypertension patients: a laser Doppler flowmetry study. Catalano M, Schioppa S, Sampietro G, Contini P, Ninno D. Research Centre on Vascular Diseases, L. Sacco Hospital, University of Milan, Italy. In order to compare the extent of the elicited vasoconstrictive and vasodilative response at the microcirculatory level in essential hypertension (EH), we measured the skin blood flow by means of a laser Doppler flowmeter (LDF). Thirty-four mild-to-moderate EH patients were enrolled. Twenty-two sex- and age-matched healthy subjects were selected as a control group. The LDF measurements were carried out with the probe over the fingertip of the distal phalanx at baseline conditions (Rest flow, RF), after an ischaemic test (post-ischaemic peak flow) and during an arithmetic stress test (AT). The flow was expressed in arbitrary units. The data were processed using the Perisoft computer program. The relative flows after the ischaemic test (Rel F1) and during the AT (Rel F2) were expressed as a percentage of the previous RF values (RF1 and RF2, respectively). During the AT, the lag time was calculated (in seconds). As compared to the control subjects, RF was significantly lower in the EH group (p < 0.01). During the AT, the EH patients showed a statistically lower mean Rel F2 decrease compared to the control subjects (p < 0.01). No statistically significant difference occurred in the Rel F1 and lag time. These data suggest that the vasoconstrictive capacity of the precapillary vessels is impaired in patients with hypertension. PMID: 9253685 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 7: Am J Cardiol. 1996 Apr 1;77(9):745-9. Comparison of impedance cardiography with indirect Fick (CO2) method of measuring cardiac output in healthy children during exercise. Pianosi P, Garros D. Department of Pediatrics and Child Health, Children's Hospital of Winnepeg, Canada. Electric bioimpedance has been used to measure cardiac output for decades. Improvements in modeling and microprocessor technology have spawned newer generations of such devices. This method would be especially useful in children, in whom the use of invasive methods is limited. We tested a device (ICG-M401, ASK Ltd.) in 30 healthy children at 2 levels of exercise (0.5 and 1.5 W/kg), and compared impedance measurements of cardiac output (QICG) with carbon dioxide (CO2) rebreathing measurements of cardiac output (QRB). The QICG-oxygen uptake (VO2) rel ation was expressed by QICG = 3.8 + 4.6 VO2; r(2) = 0.68. Mean +/- SD bias (QICG-QRB) was 0.14 +/- 1.05 L/min, not significantly different from zero (95% confidence interval -0.12 to +0.44 L/min). All QICG results were within +/- 15% of the hypothetical mean value (Bland and Altman analysis). The largest deviation of QICG from QRB was +30%, found in 1 of 57 paired determinations. Eighty percent of QICG values were within +/- 20% of the QRB result. We conclude that impedance cardiography with the ICG-M401 provided realistic and reliable estimates of cardiac output in healthy children during exercise. This, along with its ease of operation and utility at rest and during exercise, make it both useful and attractive for clinic and research purposes. PMID: 8651127 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 8: Int J Sports Med. 1986 Aug;7(4):226-31. Resting echocardiographic parameters after cessation of regular endurance training. Pavlik G, Bachl N, Wollein W, Langfy G, Prokop L. Resting echocardiograms were examined in nonathletic healthy young men (controls, n = 16), in highly trained endurance athletes (n = 20), and in endurance athletes who stopped regular training (n = 40). The relative muscular wall thickness (Rel. MWTd), left ventricular internal diameters both in diastole and in systole (LVIDd, LVIDs), thus also the end-diastolic and end-systolic volumes (LVEDV, LVESV), and the stroke volume index (SVI) were greater in the endurance athletes still in training than in the nonathletes. The ejection fraction (EF), heart rate (HR), cardiac index (CI), and mean circumferential shortening velocity (Vcf) were significantly lower in the athletes. During the 60 days of detraining no change was seen in the Rel. MWTd, LVEDV, LVESV, and HR. The SVI became even greater; EF and Vcf rose up to the control level while CI exceeded it. The cardiovascular regulation is therefore assumed to undergo a peculiar shift during detraining in that a persisting cardiac enlargement and bradycardia is associated with a temporarily unstable autonomous control. This imbalance often leads to a hyperkinesis-like syndrome when an athlete stops endurance training abruptly. PMID: 3759304 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 9: Biofeedback Self Regul. 1982 Jun;7(2):149-66. Voluntary control of cardiovascular reactions to demanding tasks. Steptoe A, Ross A. Three groups of 10 normotensives participated in a study exploring voluntary control of cardiovascular reactions to cognitive tasks. Pulse transit time (TT), interbeat interval (IBI), skin conductance level, and respiratory variables were monitored throughout one introductory and four experimental sessions. The groups were matched on the basis of initial TT and IBI responses to the taxing arithmetic and reasoning tasks. During experimental sessions, one group (FB) was provided with visual analogue TT feedback, while the REL group was given detailed relaxation instructions. A third group (CON) performed the same sequence of tasks but was not instructed to modify cardiovascular reactions at any point. Training in voluntary control was carried out in resting (no-task) conditions, and during task administration. Both treatment groups showed lower cardiovascular reactions than controls in task trials. Only REL subjects lengthened TT in no-task conditions, while both FB and REL groups showed smaller cardiovascular reactions than CON during the tasks. Effects were confined to cardiovascular variables, since respiratory and electrodermal reactions during task administration were similar in all groups. The effects of treatments were especially marked among the most reactive subjects. PMID: 6753950 [PubMed - indexed for MEDLINE] ---------------------------------------------------------------