Stewart R. Petersen

Intra‐pulmonary shunt and pulmonary gas exchange during exercise in humans

In young, healthy people the alveolar–arterial P  O 2 difference (A‐aDO2) is small at rest, but frequently increases during exercise. Previously, investigators have focused on ventilation/perfusion mismatch and diffusion abnormalities to explain the impairment in gas exchange, as significant physiological intra‐pulmonary shunt has not been found. The aim of this study was to use a non‐gas exchange method to determine if anatomical intra‐pulmonary (I‐P) shunts develop during exercise, and, if so, whether there is a relationship between shunt and increased A‐aDO2. Healthy male participants performed graded upright cycling to 90% while pulmonary arterial (PAP) and pulmonary artery wedge pressures were measured. Blood samples were obtained from the radial artery, cardiac output was calculated by the direct Fick method and I‐P shunt was determined by administering agitated saline during continuous 2‐D echocardiography. A‐aDO2 progressively increased with exercise and was related to (r= 0.86) and PAP (r= 0.75). No evidence of I‐P shunt was found at rest in the upright position; however, 7 of 8 subjects developed I‐P shunts during exercise. In these subjects, point bi‐serial correlations indicated that I‐P shunts were related to the increased A‐aDO2 (r= 0.68), (r= 0.76) and PAP (r= 0.73). During exercise, intra‐pulmonary shunt always occurred when A‐aDO2 exceeded 12 mmHg and was greater than 24 l min−1. These results indicate that anatomical I‐P shunts develop during exercise and we suggest that shunt recruitment may contribute to the widened A‐aDO2 during exercise.

Reductions in cerebral blood flow during passive heat stress in humans: partitioning the mechanisms

Non‐technical summary  Heat stress reduces brain blood flow and impairs orthostatic tolerance. Brain blood flow is largely controlled by the partial pressure of arterial . Indeed, hyperthermia‐induced over‐breathing and related reductions in arterial account for ∼50% of the reduction in brain blood flow. This investigation tested the unique hypothesis that the distribution of cardiac output during heat stress (challenged by thermoregulatory increases in skin blood flow and sweat loss) contributes to the remaining 50%. We show that cardiac output is not related to brain blood flow, but rather arterial plays a much larger role than previously suggested. These findings help us understand the mechanisms relating heat stress with an increased likelihood of fainting, and are also relevant to pathological conditions that are accompanied by elevations in body temperature.

Effects of the self-contained breathing apparatus and fire protective clothing on maximal oxygen uptake

To examine the effects of firefighting personal protective ensemble (PPE) and self-contained breathing apparatus (SCBA) on exercise performance, 12 males completed two randomly ordered, graded exercise treadmill tests (GXTPPE and GXTPT). Maximal oxygen consumption (VO2max) during GXTPPE was 17.3% lower than the GXTPT in regular exercise clothing (43.0 ± 5.7 vs. 52.4 ± 8.5 ml/kg per min, respectively). The lower VO2max during the PPE condition was significantly related (r = 0.81, p < 0.05) to attenuated peak ventilation (142.8 ± 18.0 vs. 167.1 ± 15.6 l/min), which was attributed to a significant reduction in tidal volume (2.6 ± 10.4 vs. 3.2 ± 0.4 l). Breathing frequency at peak exercise was unchanged (55 ± 7 vs. 53 ± 7 breaths/min). The results of this investigation demonstrate that PPE and the SCBA have a negative impact on VO2max. These factors must be considered when evaluating aerobic demands of fire suppression work and the fitness levels of firefighters.

Effects of endurance training on transient oxygen uptake responses in cyclists

The aim of this study was to determine the alterations in oxygen uptake kinetics following endurance training in previously trained athletes. Sixteen competitive cyclists completed 8 weeks of supervised endurance cycle training. Ventilatory threshold, maximal oxygen uptake (VO2max), oxygen uptake kinetics and simulated 40-km time-trial tests were performed three times over a 4-week period before training, and then after 4 and 8 weeks of training. The protocol for measuring oxygen uptake kinetics consisted of three square-wave increments from unloaded cycling to a power output of 78 W followed by a single increment from 78 to 156 W. No significant differences in any variables were observed over the pre-training period. The ventilatory threshold and VO2max increased, and the time for 40 km decreased (P < 0.05) with training. Shorter VO2 time constants and lower heart rates were observed during the protocol for measuring oxygen uptake kinetics (same absolute power output) post-training. These results indicate that oxygen uptake kinetics may be improved with endurance training in previously trained athletes.

Helium-Hyperoxia: A Novel Intervention To Improve the Benefits of Pulmonary Rehabilitation for Patients With COPD

BACKGROUND Helium-hyperoxia (HH) reduces dyspnea and increases exercise tolerance in patients with COPD. We investigated whether breathing HH would allow patients to perform a greater intensity of exercise and improve the benefits of a pulmonary rehabilitation program. METHODS Thirty-eight nonhypoxemic patients with COPD (FEV(1)=47 +/- 17%(pred)) were randomized to rehabilitation breathing HH (60:40 He:O(2); n = 19) or air (n = 19). Patients cycled for 30 min, 3 days/week for 6 weeks breathing the assigned gas. Exercise intensity was prescribed from baseline, gas-specific, incremental exercise tests and was advanced as tolerated. The primary outcome was exercise tolerance assessed as a change in constant-load exercise time (CLT) following rehabilitation. Secondary outcomes were changes in exertional symptoms, health related quality of life (as assessed by the Short-form 36 and St George respiratory questionnaires), and peak oxygen consumption during an incremental exercise test. RESULTS The HH group had a greater change in CLT following rehabilitation compared to the air group (9.5 +/- 9.1 vs 4.3 +/- 6.3 min, p < 0.05). At an exercise isotime, dyspnea was significantly reduced in both groups, while leg discomfort only decreased in the HH group. The changes in exertional symptoms and peak oxygen consumption were not different between groups. Health-related quality of life significantly improved in both groups; however, the change in St. George respiratory questionnaire total score was greater with HH (-7.6 +/- 6.4 vs -3.6 +/- 5.6, p < 0.05). During rehabilitation, the HH group achieved a higher exercise intensity and training duration throughout the program (p < 0.05). CONCLUSIONS Breathing HH during pulmonary rehabilitation increases the intensity and duration of exercise training that can be performed and results in greater improvements in CLT for patients with COPD.

The effect of velocity‐specific strength training on peak torque and anaerobic rowing power

This study investigated the effect of low- and high-velocity resistance training on isokinetic peak torque and anaerobic power output. Eighteen male varsity oarsmen were blocked on peak knee extension torque at 3.14 rad s-1 and assigned to a high-velocity resistance training group (HVR), a low-velocity resistance training group (LVR) or a control group. Subjects trained four times a week for 5 weeks. Each training session included three circuits of 12 stations using variable-resistance hydraulic equipment. The HVR training significantly improved peak torque (P less than 0.05) in knee extension and flexion at 2.61, 3.14, 3.66 and 4.19 rad s-1. The LVR training produced significant improvements (P less than 0.05) in peak torque for knee extension and flexion at 0.52, 1.05, 1.57 and 2.61 rad s-1. High positive correlations were found between peak torque and anaerobic power outputs for all groups. However, no significant changes occurred in 15 s power output, average 90 s power output or peak blood lactate in either training group. These results indicate that velocity-specific strength training does not necessarily improve anaerobic power output in a different exercise mode despite the high positive correlation between isokinetic strength and anaerobic power output.

The effect of salbutamol on performance in endurance cyclists

AbstractThe effect of salbutamol (S) on cycling performance was examined in 15 highly trained non-asthmatic male cyclists. A double-blind, randomized cross-over design was used with S or placebo (P) administered using a metered-dose inhaler and a spacer device 20 min before each testing session. The S dose was 400 μg (four puffs), which is twice the normal therapeutic level. Subjects were habituated to all the laboratory procedures in the week prior to actual data collection. The subjects performed four tests under S and P conditions on separate days over 2 weeks. These included measurement of maximal O2 uptake

Oxygen cost of the CF-DND fire fit test in males and females.

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