Cardiopulmonary and metabolic physiology during hemodialysis and inter-/intra-dialytic exercise

Background: Hemodialysis is associated with numerous symptoms and side effects which, in part, maybe due to sub-clinical hypoxia. However, acute cardio-pulmonary and metabolic physiology during hemodialysis is not well defined. Intra-dialytic and inter-dialytic exercise appear to be beneficial and may alleviate these side effects. To better understand these potential benefits, the acute physiological response to exercise should be evaluated. The aim of this study was to compare and characterise the acute physiological response during hemodialysis, intra-dialytic and inter-dialytic exercise. Methods: Cardiopulmonary physiology was evaluated during three conditions; 1) hemodialysis without exercise (HD), 2) intra-dialytic exercise (IDEx), and 3) inter-dialytic exercise (Ex). Exercise consisted of 30 minutes constant load cycle ergometry at 90% VO2AT. Central hemodynamics (via non-invasive bio-reactance) and ventilatory gas exchange were recorded during each experimental condition. Results: Twenty participants (59 ± 12 yrs, 16/20 male) completed the protocol. Cardiac output (Δ = -0.7 L/min), O2 uptake (Δ = -1.4 ml.kg-1.min-1) and arterial-venous O2 difference (Δ = -2.0 ml/O2/100ml) decreased significantly during HD. Respiratory exchange ratio exceeded 1.0 throughout HD and IDEx. Minute ventilation was lower (p = 0.001) during IDEx (16.5 ± 1.1 L/min) compared to Ex (19.8 ± 1.0 L/min). Arterial-venous O2 difference was partially restored further to IDEx (4.6 ± 1.9 ml/O2/100ml) compared to HD (3.5 ± 1.2 ml/O2/100ml). Conclusion: Hemodialysis altered cardiopulmonary and metabolic physiology, suggestive of hypoxia. This dysregulated physiology contributed to a greater physiological demand during intra-dialytic compared to inter-dialytic exercise. Despite this, intra-dialytic exercise partly normalised physiology during treatment.

Acute physiological response by the plethodontid salamander Eurycea cirrigera (Southern Two-lined Salamander) to predation stress from alarm chemicals and predator kairomones

Plethodontid salamanders may reduce predation risk via behavioral responses to predator kairomones and alarm chemicals from injured salamanders. However, it not known whether such predator cues prompt acute physiological responses, which may enhance arousal and the physical ability to escape from a predator. I examined whether predator chemical cues elicit an acute cardiac response in Eurycea cirrigera (Green, 1831) (Southern Two-lined Salamander). I compared heart rates before and after exposure to the odor of the large predatory Pseudotriton ruber (Sonnini de Manoncourt and Latreille, 1801) (Red Salamander) and exposure to alarm chemicals from homogenized skin of conspecifics. For two controls, I compared heart rates before and after exposure to the odor of live conspecifics and the odor of the large non-predatory Plethodon mississippi Highton in Highton, Maha and Maxson, 1989 (Mississippi Slimy Salamander). Compared with resting values, heart rates significantly increased in response to predator kairomones (mean rate increased 10.9% after 2 min and 12.7% after 5 min) and alarm chemicals from conspecifics (mean rate increased 12.0% after 2 min and 14.5% after 5 min). In contrast, heart rates after exposure to each control odor did not significantly differ from resting values. Results demonstrate an acute cardiac response to chemical cues indicative of either a predator or a predation event.

The Acute Physiological and Perceptual Effects of Individualizing the Recovery Interval Duration Based Upon the Resolution of Muscle Oxygen Consumption During Cycling Exercise

Purpose: There has been paucity in research investigating the individualization of recovery interval duration during cycling-based high-intensity interval training (HIIT). The main aim of the study was to investigate whether individualizing the duration of the recovery interval based upon the resolution of muscle oxygen consumption would improve the performance during work intervals and the acute physiological response of the HIIT session, when compared with a standardized (2:1 work recovery ratio) approach. Methods: A total of 16 well-trained cyclists (maximal oxygen consumption: 60 [7] mL·kg−1·min−1) completed 6 laboratory visits: (Visit 1) incremental exercise test, (Visit 2) determination of the individualized (IND) recovery duration, using the individuals’ muscle oxygen consumption recovery duration to baseline from a 4- and 8-minute work interval, (Visits 3–6) participants completed a 6 × 4- and a 3 × 8-minute HIIT session twice, using the IND and standardized recovery intervals. Results: Recovery duration had no effect on the percentage of the work intervals spent at >90% and >95% of maximal oxygen consumption, maximal minute power output, and maximal heart rate, during the 6 × 4- and 3 × 8-minute HIIT sessions. Recovery duration had no effect on mean work interval power output, heart rate, oxygen consumption, blood lactate, and rating of perceived exertion. There were no differences in reported session RPE between recovery durations for the 6 × 4- and 3 × 8-minute HIIT sessions. Conclusion: Individualizing HIIT recovery duration based upon the resolution of muscle oxygen consumption to baseline levels does not improve the performance of the work intervals or the acute physiological response of the HIIT session, when compared with standardized recovery duration.

Hemodynamic Instability during Dialysis: The Potential Role of Intradialytic Exercise

Acute haemodynamic instability is a natural consequence of disordered cardiovascular physiology during haemodialysis (HD). Prevalence of intradialytic hypotension (IDH) can be as high as 20–30%, contributing to subclinical, transient myocardial ischemia. In the long term, this results in progressive, maladaptive cardiac remodeling and impairment of left ventricular function. This is thought to be a major contributor to increased cardiovascular mortality in end stage renal disease (ESRD). Medical strategies to acutely attenuate haemodynamic instability during HD are suboptimal. Whilst a programme of intradialytic exercise training appears to facilitate numerous chronic adaptations, little is known of the acute physiological response to this type of exercise. In particular, the potential for intradialytic exercise to acutely stabilise cardiovascular hemodynamics, thus preventing IDH and myocardial ischemia, has not been explored. This narrative review aims to summarise the characteristics and causes of acute haemodynamic instability during HD, with an overview of current medical therapies to treat IDH. Moreover, we discuss the acute physiological response to intradialytic exercise with a view to determining the potential for this nonmedical intervention to stabilise cardiovascular haemodynamics during HD, improve coronary perfusion, and reduce cardiovascular morbidity and mortality in ESRD.

Acute Physiological Response to Aerobic Short-Interval Training in Trained Runners

Purpose:To analyze the acute physiological response to aerobic short-interval training (AESIT) at various high-intensity running speeds. A minor anaerobic glycolytic energy supply was aimed to mimic the characteristics of slow continuous runs.Methods:Eight trained male runners (maximal oxygen uptake [VO2max] 55.5 ± 3.3 mL · kg−1 · min−1) performed an incremental treadmill exercise test (increments: 0.75 km · h−1 · min−1). Two lactate turn points (LTP1, LTP2) were determined. Subsequently, 3 randomly assigned AESIT sessions with high-intensity running-speed intervals were performed at speeds close to the speed (v) at VO2max (vVO2max) to create mean intensities of 50%, 55%, and 60% of vLTP1. AESIT sessions lasted 30 min and consisted of 10-s work phases, alternated by 20-s passive recovery phases.Results:To produce mean velocities of 50%, 55%, and 60% of vLTP1, running speeds were calculated as 18.6 ± 0.7 km/h (93.4% vVO2max), 20.2 ± 0.6 km/h (101.9% vVO2max), and 22.3 ± 0.7 km/h (111.0% vVO2max), which gave a mean blood lactate concentration (La) of 1.09 ± 0.31 mmol/L, 1.57 ± 0.52 mmol/L, and 2.09 ± 0.99 mmol/L, respectively. La at 50% of vLTP1 was not significantly different from La at vLTP1 (P = .8894). Mean VO2 was found at 54.0%, 58.5%, and 64.0% of VO2max, while at the end of the sessions VO2 rose to 71.1%, 80.4%, and 85.6% of VO2max, respectively.Conclusion:The results showed that AESIT with 10-s work phases alternating with 20 s of passive rest and a running speed close to vVO2max gave a systemic aerobic metabolic profile similar to slow continuous runs.

Rumination as a Mediator of Chronic Stress Effects on Hypertension: A Causal Model

Chronic stress has been linked to hypertension, but the underlying mechanisms remain poorly specified. We suggest that chronic stress poses a risk for hypertension through repeated occurrence of acute stressors (often stemming from the chronic stress context) that cause activation of stress-mediating physiological systems. Previous models have often focused on the magnitude of the acute physiological response as a risk factor; we attempt to extend this to address the issue ofduration of exposure. Key to our model is the notion that these acute stressors can emerge not only in response to stressors present in the environment, but also to mental representations of those (or other) stressors. Consequently, although the experience of any given stressor may be brief, a stressor often results in a constellation of negative cognitions and emotions that form a mental representation of the stressor. Ruminating about this mental representation of the stressful event can cause autonomic activation similar to that observed in response to the original incident, and may occur and persist long after the event itself has ended. Thus, rumination helps explain how chronic stress causes repeated (acute) activation of one’s stress-mediating physiological systems, the effects of which accumulate over time, resulting in hypertension risk.