J. Koschate

Muscular Oxygen Uptake Kinetics in Aged Adults.

Pulmonary oxygen uptake (V˙O2) kinetics and heart rate kinetics are influenced by age and fitness. Muscular V˙O2 kinetics can be estimated from heart rate and pulmonary V˙O2. In this study the applicability of a test using pseudo-random binary sequences in combination with a model to estimate muscular V˙O2 kinetics was tested. Muscular V˙O2 kinetics were expected to be faster than pulmonary V˙O2 kinetics, slowed in aged subjects and correlated with maximum V˙O2 and heart rate kinetics. 27 elderly subjects (73±3 years; 81.1±8.2 kg; 175±4.7 cm) participated. Cardiorespiratory kinetics were assessed using the maximum of cross-correlation functions, higher maxima implying faster kinetics. Muscular V˙O2 kinetics were faster than pulmonary V˙O2 kinetics (0.31±0.1 vs. 0.29±0.1 s; p=0.004). Heart rate kinetics were not correlated with muscular or pulmonary V˙O2 kinetics or maximum V˙O2. Muscular V˙O2 kinetics correlated with maximum V˙O2 (r=0.35; p=0.033). This suggests, that muscular V˙O2 kinetics are faster than estimates from pulmonary V˙O2 and related to maximum V˙O2 in aged subjects. In the future this experimental approach may help to characterize alterations in muscular V˙O2 under various conditions independent of motivation and maximal effort.

Analysis of heart rate and oxygen uptake kinetics studied by two different pseudo-random binary sequence work rate amplitudes

PURPOSE The aim of the study was to compare the kinetics responses of heart rate (HR), pulmonary (V˙O2pulm) and predicted muscular (V˙O2musc) oxygen uptake between two different pseudo-random binary sequence (PRBS) work rate (WR) amplitudes both below anaerobic threshold. METHODS Eight healthy individuals performed two PRBS WR protocols implying changes between 30W and 80W and between 30W and 110W. HR and V˙O2pulm were measured beat-to-beat and breath-by-breath, respectively. V˙O2musc was estimated applying the approach of Hoffmann et al. (Eur J Appl Physiol 113: 1745-1754, 2013) considering a circulatory model for venous return and cross-correlation functions (CCF) for the kinetics analysis. RESULTS HR and V˙O2musc kinetics seem to be independent of WR intensity (p>0.05). V˙O2pulm kinetics show prominent differences in the lag of the CCF maximum (39±9s; 31±4s; p<0.05). CONCLUSIONS A mean difference of 14W between the PRBS WR amplitudes impacts venous return significantly, while HR and V˙O2musc kinetics remain unchanged.

Oxygen uptake kinetics following six weeks of interval and continuous endurance exercise training − An explorative pilot study

PURPOSE The aim of the study was to compare the responses of pulmonary (V˙O2pulm) and muscle (V˙O2musc) oxygen uptake kinetics before (PRE) and after (POST) six weeks of endurance exercise training. METHODS Nine untrained individuals performed pseudo-random binary sequences work rate changes between 30W and 80W at PRE and POST training intervention. Heart rate (HR) and V˙O2pulm were measured beat-to-beat and breath-by-breath, respectively. V˙O2musc was estimated applying the approach of Hoffmann et al. (Eur J Appl Physiol 113: 1745-1754, 2013). RESULTS Maximal oxygen uptake showed significant increases from PRE (3.2±0.3Lmin-1) to POST (3.7±0.2Lmin-1; p<0.05). For HR, V˙O2pulm and V˙O2musc kinetics no significant changes from PRE to POST training intervention were observed (p>0.05). CONCLUSIONS Discrepancies in the adaptations of the involved exercise induced physiological systems seem to be responsible for the observed significant alterations in maximal V˙O2 after six weeks of the training intervention in contrast to no changes in the kinetics responses.

Effect of acute ambient temperature exposure on cardio-pulmonary and respiratory kinetics in men

Abstract Aim: The goal of the study was to compare the kinetic responses of heart rate (HR) and pulmonary (V̇O2pulm) and muscular (V̇O2musc) oxygen uptake during dynamic leg exercise across different acute ambient temperature conditions in a climatic chamber. Methods: Thirteen physically healthy, active, male volunteers demonstrated pseudorandom binary sequence (PRBS) work rate (WR) changes between 30 and 80 W at 15 °C, 25 °C and 35 °C, respectively. HR was measured beat-to-beat using an echocardiogram and V̇O2pulm by breath-by-breath gas exchange; V̇O2musc estimations were assessed by applying a circulatory model and cross-correlation functions. Results: No significant differences were observed across the various temperature conditions in each case for HR, V̇O2pulm or V̇O2musc kinetics (p > 0.05). Baroreflex regulation based on HR kinetics does not seem to be influenced between ambient temperatures of 15 °C and 35 °C during dynamic exercise. Conclusions: The results imply that ambient temperatures of 15 °C, 25 °C and 35 °C have no effect on HR, V̇O2pulm or V̇O2musc kinetics during dynamic moderate exercise. The applied approach may be of interest for assessments of the cardio-pulmonary and respiratory health statuses of individuals working or performing sports in extreme temperature environments. Furthermore, differentiation between systemic (e.g. cardio-dynamic: HR) and specific (e.g. exercising tissues: V̇O2musc) determinants of the relevant physiological systems may improve the evaluation of an individual’s health status.

Heart Rate and Oxygen Uptake Kinetics in Type 2 Diabetes Patients – A Pilot Study on the Influence of Cardiovascular Medication on Regulatory Processes

The aim of this pilot study was to investigate whether there are differences in heart rate and oxygen uptake kinetics in type 2 diabetes patients, considering their cardiovascular medication. It was hypothesized that cardiovascular medication would affect heart rate and oxygen uptake kinetics and that this could be detected using a standardized exercise test. 18 subjects were tested for maximal oxygen uptake. Kinetics were measured in a single test session with standardized, randomized moderate-intensity work rate changes. Time series analysis was used to estimate kinetics. Greater maxima in cross-correlation functions indicate faster kinetics. 6 patients did not take any cardiovascular medication, 6 subjects took peripherally acting medication and 6 patients were treated with centrally acting medication. Maximum oxygen uptake was not significantly different between groups. Significant main effects were identified regarding differences in muscular oxygen uptake kinetics and heart rate kinetics. Muscular oxygen uptake kinetics were significantly faster than heart rate kinetics in the group with no cardiovascular medication (maximum in cross-correlation function of muscular oxygen uptake vs. heart rate; 0.32±0.08 vs. 0.25±0.06; p=0.001) and in the group taking peripherally acting medication (0.34±0.05 vs. 0.28±0.05; p=0.009) but not in the patients taking centrally acting medication (0.28±0.05 vs. 0.30±0.07; n.s.). It can be concluded that regulatory processes for the achievement of a similar maximal oxygen uptake are different between the groups. The used standardized test provided plausible results for heart rate and oxygen uptake kinetics in a single measurement session in this patient group.The aim of this pilot study was to investigate whether there are differences in heart rate and oxygen uptake kinetics in type 2 diabetes patients, considering their cardiovascular medication. It was hypothesized that cardiovascular medication would affect heart rate and oxygen uptake kinetics and that this could be detected using a standardized exercise test. 18 subjects were tested for maximal oxygen uptake. Kinetics were measured in a single test session with standardized, randomized moderate-intensity work rate changes. Time series analysis was used to estimate kinetics. Greater maxima in cross-correlation functions indicate faster kinetics. 6 patients did not take any cardiovascular medication, 6 subjects took peripherally acting medication and 6 patients were treated with centrally acting medication. Maximum oxygen uptake was not significantly different between groups. Significant main effects were identified regarding differences in muscular oxygen uptake kinetics and heart rate kinetics. Muscular oxygen uptake kinetics were significantly faster than heart rate kinetics in the group with no cardiovascular medication (maximum in cross-correlation function of muscular oxygen uptake vs. heart rate; 0.32±0.08 vs. 0.25±0.06; p=0.001) and in the group taking peripherally acting medication (0.34±0.05 vs. 0.28±0.05; p=0.009) but not in the patients taking centrally acting medication (0.28±0.05 vs. 0.30±0.07; n.s.). It can be concluded that regulatory processes for the achievement of a similar maximal oxygen uptake are different between the groups. The used standardized test provided plausible results for heart rate and oxygen uptake kinetics in a single measurement session in this patient group.

Influence of Weightlessness on Aerobic Capacity, Cardiac Output and Oxygen Uptake Kinetics

The exposure to weightlessness can have an impact on aerobic capacity as a result of changes in the cardiorespiratory and musculoskeletal systems. As a consequence, astronauts’ work capacities might be changed which would affect activities during the Space missions and after return to Earth or other environments with gravity, i.e. Mars or Moon. This chapter will give an overview about results from studies using cardiopulmonary exercise testing (CPET). This method allows to monitor astronauts’ fitness non-invasively and is, therefore, qualified for inflight measurements. Results from early Space flight until now will be compared with results from bedrest studies. Predominantly, the focus lies on peak oxygen uptake, heart rate and oxygen uptake kinetics. Since the specific methods and problems of CPET are related to the concepts of respiratory gas measurement, aspects of hardware, exercise protocols and data analysis will be discussed.

Essential Hypertension: Cardiovascular Response to Breath Hold Combined with Exercise.

Essential hypertension (EH) is a widespread disease and might be prevalent in apnea divers and master athletes. Little is known about the influence of EH and the antihypertensive drugs (AHD) on cardiovascular reactions to combined breath hold (BH) and exercise. In this pilot study, healthy divers (HCON) were compared with treated hypertensive divers with regard to heart rate (HR) and mean blood-pressure (MAP) responses to BH, exercise and the combination of both. Ten subjects with EH and ten healthy divers were tested. 3 different 20 s stimuli were applied: BH combined with 30 W or 150 W and 150 W without BH. The time-charts during the stress intervals and during recovery were compared. Subjects treated with an angiotensin-converting enzyme (ACE) inhibitor showed higher changes for MAP values if breath hold was performed. HR responses were obviously changed if a β-blocker was part of the medication. One subject showed extreme MAP responses to all stimuli and conspicuous HR if BH was involved. The modulation of HR-/MAP-response in EH subjects depends on the mechanisms of antihypertensive agents. The combination of an ACE inhibitor and a β-blocker may give the best protection. It is recommended to include short apnea tests in the fitness-to-dive examination to individually predict potential endangerment.