Cardiorespiratory coordination reveals training-specific physiological adaptations.

PURPOSE: To compare the effects of high-intensity interval training (HIIT) and moderate-intensity training (CONT), matched for total work, on cardiorespiratory coordination and aerobic fitness. METHODS: This is a two-arm parallel group single-blind randomised study. Twenty adults were assigned to 6 weeks of HIIT or volume-matched CONT. Participants completed a progressive maximal cycling test before and after the training period. Principal component (PC) analysis was performed on the series of cardiorespiratory variables to evaluate dimensionality of cardiorespiratory coordination, before and after lactate turnpoint. PC1 eigenvalues were compared. RESULTS: Both HIIT and CONT improved aerobic fitness (main effects of time, p < 0.001, [Formula: see text] ≥ 0.580), with no differences between groups. CONT decreased the number of PCs from two to one at intensities both below and above the lactate turnpoint; PC1 eigenvalues increased after CONT both below (Z = 2.08; p = 0.04; d = 0.94) and above the lactate turnpoint (Z = 2.10; p = 0.04; d = 1.37). HIIT decreased the number of PCs from two to one after the lactate turnpoint only; PC1 eigenvalues increased after HIIT above the lactate turnpoint (Z = 2.31; p = 0.02; d = 0.42). CONCLUSIONS: Although CONT and HIIT improved aerobic fitness to a similar extent, there were different patterns of change for cardiorespiratory coordination. These changes appear training-intensity specific and could be sensitive to investigate the individual response to endurance training.

Endurance capacity and neuromuscular fatigue following high- vs moderate-intensity endurance training: A randomized trial.

High-intensity exercise induces significant central and peripheral fatigue; however, the effect of endurance training on these mechanisms of fatigue is poorly understood. We compared the effect of cycling endurance training of disparate intensities on high-intensity exercise endurance capacity and the associated limiting central and peripheral fatigue mechanisms. Twenty adults were randomly assigned to 6 weeks of either high-intensity interval training (HIIT, 6-8×5 minutes at halfway between lactate threshold and maximal oxygen uptake [50%Δ]) or volume-matched moderate-intensity continuous training (CONT, ~60-80 minutes at 90% lactate threshold). Two time to exhaustion (TTE) trials at 50%Δ were completed pre- and post-training to assess endurance capacity; the two post-training trials were completed at the pretraining 50%Δ (same absolute intensity) and the "new" post-training 50%Δ (same relative intensity). Pre- and post-exercise responses to femoral nerve and motor cortex stimulation were examined to determine peripheral and central fatigue, respectively. HIIT resulted in greater increases in TTE at the same absolute and relative intensities as pre-training (148% and 43%, respectively) compared with CONT (38% and -4%, respectively) (P≤.019). Compared with pre-training, HIIT increased the level of potentiated quadriceps twitch reduction (-34% vs -43%, respectively, P=.023) and attenuated the level of voluntary activation reduction (-7% vs -3%, respectively, P=.047) following the TTE trial at the same relative intensity. There were no other training effects on neuromuscular fatigue development. This suggests that central fatigue resistance contributes to enhanced high-intensity exercise endurance capacity after HIIT by allowing greater performance to be extruded from the muscle.

Central and peripheral fatigue following non-exhaustive and exhaustive exercise of disparate metabolic demands.

The development of fatigue after non-exhaustive and exhaustive exercise eliciting differing metabolic demands is poorly understood. Sixteen active males completed five cycling trials. The first trial established the lactate threshold (LT) and maximal oxygen uptake (VO2max ). Two of the remaining trials were completed at a severe intensity (halfway between LT and VO2max , SI) and two at a moderate intensity (90% LT, MI). Each trial involved two non-exhaustive bouts matched for work between intensities before cycling to exhaustion. Responses to stimulation of the femoral nerve and motor cortex were determined after each bout to determine peripheral and central fatigue. Corticospinal excitability, cortical silent period (cSP), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) were also assessed. Non-exhaustive cycling induced greater peripheral and central fatigue in the SI compared with the MI (P < 0.05). At exhaustion, there was no difference between intensities; however, peripheral fatigue tended to be greater in the SI vs MI (-31% vs -17%, respectively, P = 0.051). Exhaustive cycling increased SICI (24%, P < 0.001) and reduced the cSP (-14%, P < 0.001) in the SI, whereas ICF was reduced in the MI (-16%, P < 0.001). These findings demonstrate exercise-induced metabolic stress accelerates the development of peripheral and central fatigue, and differentially influences intracortical excitability.

Cardiovascular adaptation in people with multiple sclerosis following a twelve week exercise programme suggest deconditioning rather than autonomic dysfunction caused by the disease. Results from a randomized controlled trial.

BACKGROUND: Guidelines for optimal exercise doses in people with multiple sclerosis (MS) have to be established. We need to ascertain the basic physiological and perceptual response and adaptation to different exercise doses in this clinical population. AIM: The aim of this paper was to explore the response during maximal and sub-maximal exercise in people with MS prior to and following two different twelve week exercise programmes. DESIGN: Sub-analysis of per protocol exercise data of a two group, single blinded, randomised control trial. SETTING: Multicentre (community leisure and rehabilitation centres). POPULATION: Participants with MS assigned to a continuous (N.=12; mean±SE age=52.3±2.08; Barthel index median & range=19&13-20) or interval (N.=9; mean±SE age=49.3±3.5; Barthel index median & range=19&18-20) exercise programme. METHODS: Cardiovascular, respiratory and perceptual exercise response and adaption was measured at maximal and sub-maximal levels of physical exercise prior to and following a twelve week exercise programme, delivered at different intensities. RESULTS: Irrespective of the type of exercise programme followed, there was a significant increase in peak power (z=-1.98; P=0.05) and normalised oxygen uptake during unloaded cycling (z =-2.00; P=0.05). At discharge from the exercise programmes, the cardiovascular response to sub-maximal exercise had significantly changed (t(360) =-4.62; p<0.01). CONCLUSION: The response in people with MS at maximal and sub-maximal levels of physical exercise following a twelve week programme is analogous to non-diseased adults. CLINICAL REHABILITATION IMPACT: Cardiovascular adaptation in people with MS following a twelve week exercise programme suggests deconditioning rather than autonomic dysfunction caused by the disease.

Practical application of fundamental concepts in exercise physiology.

The collection of primary data in laboratory classes enhances undergraduate practical and critical thinking skills. The present article describes the use of a lecture program, running in parallel with a series of linked practical classes, that emphasizes classical or standard concepts in exercise physiology. The academic and practical program ran under the title of a particular year II module named Sports Performance: Physiology and Assessment, and results are presented over a 3-yr period (2004-2006), based on an undergraduate population of 31 men and 34 women. The module compared laboratory-based indexes of endurance (e.g., ventilatory threshold and exercise economy) and high-intensity exercise (e.g., anaerobic power), respectively, with measures of human performance (based on 20-m shuttle run tests). The specific experimental protocols reinforced the lecture content to improve student understanding of the physiological and metabolic responses (and later adaptations) to exercise. In the present study, the strongest relationship with endurance performance was the treadmill velocity at maximal aerobic power (r = +0.88, P < 0.01, n = 51); in contrast, the strongest relationship with high-intensity exercise performance was the mean power output (in W/kg) measured during a 30-s all-out cycle ergometer sprint (r = +0.80, P < 0.01, n = 48). In class student data analysis improved undergraduate indepth or critical thinking during seminars and enhanced computer and data presentation skills. The endurance-based laboratories are particularly useful for examining the underlying scientific principles that determine aerobic performance but could equally well be adapted to investigate other topics, e.g., differences in the exercise response between men and women.

The bias flow nitrogen washout technique for measuring the functional residual capacity in infants. ERS/ATS Task Force on Standards for Infant Respiratory Function Testing.

The functional residual capacity (FRC) is the most commonly measured static lung volume in infants. It is important for interpreting volume-dependent pulmonary mechanics, e.g. airway resistance, and defining normal lung growth. The bias flow nitrogen washout technique is widely used for measuring FRC because the dead space and circuit resistance are low, making it suitable for small or sick infants. Moreover, data acquisition and calculation are easily programmed for a personal computer. The aim of this paper is to provide recommendations pertaining to equipment requirements, study procedures and reporting of data for functional residual capacity measurements. While measuring the functional residual capacity is regarded as physiologically and clinically important, the accuracy of the measurement is undoubtedly equally important. Hence, the paper also emphasizes factors influencing the accuracy of functional residual capacity measurements independent of equipment requirements. These recommendations represent the "State of the Art" in 2000.

A simple new technique to measure the effective dead space of the face mask with a water volumeter in infants.

Measuring the effective dead space (EDS) of a face mask has been difficult in infants and the appropriate volume being deducted from lung volume measurements has varied between laboratories. This study measured EDS in 16 infants (age range, 5-36 months) who have cystic fibrosis, undergoing lung volume measurement by N2 washout. A thin plastic bladder, whose neck resided in the mask port, was shaped to fill a size 1 clear face mask. A water volumeter was made by inserting the body of a 20 mL plastic syringe into the neck of the bladder forming a tight seal with a snug fit against the inner surface of the mask port. The mask was placed on a horizontal surface and water was added until a level appeared in the syringe body (V1). At end-inspiration, the mask was briefly placed on the mouth and nose of the sleeping infant, causing the water level to rise in the syringe body (V2). The actual total dead space (V) of the mask when connected to the mouth port of the slide valve was 23 mL. EDS = V- (V2 - V1). Mean (95% confidence interval (95%CI)) EDS was 12.4 (95% CI 11.2, 13.6) mL. The smallest EDS was 8 mL since the connected ports (dead space, 8 mL) were unlikely to be penetrated by the infant's nose or lips. EDS decreased with increasing body weight and height, but seemed to be influenced by individual facial features too. In conclusion, a reliable noninvasive volumetric technique for the routine measurement of the effective dead space in infants has been developed.

A novel non-invasive technique for measuring the residual lung volume by nitrogen washout with rapid thoracoabdominal compression in infants.

BACKGROUND: The functional residual capacity (FRC), the only lung volume to be routinely measured in infants, is an unreliable volume landmark. In addition to FRC, the residual volume (RV) was measured by nitrogen washout using rapid thoracoabdominal compression (RTC) in nine infants with cystic fibrosis aged 5-31 months. METHODS: A commercial system for nitrogen washout to measure lung volumes and a custom made system to perform RTC were used. Lung volume was raised to an airway opening pressure of 30 cm H(2)O (V(30)). RTC was performed from V(30). The jacket pressure (Pj; 65-92 cm H(2)O) which generated the highest forced expiratory volume (mean 40.2 ml/kg; 95% confidence interval (CI) 33.03 to 47.33) was used during the RV manoeuvre. The infants were manually hyperventilated to inhibit the respiratory drive briefly. RTC was initiated during the last passive expiration. RV was estimated by measuring the volume of nitrogen expired after end forced expiratory switching of the inspired gas from room air to 100% oxygen while jacket inflation was maintained at the time of switching into oxygen during the post-expiratory pause. RESULTS: In each infant RV and FRC measurements were reproducible and did not overlap; the difference between mean values, which is the expiratory reserve volume, was statistically significant (p<0.05). Mean RV was 21.3 (95% CI 18.7 to 24.0), FRC was 25.5 (95% CI 22.8 to 28.1), and TLC(30) (total lung capacity at V(30)) was 61.5 (95% CI 54.4 to 68.7) ml/kg. These values were dependent on body length, weight and age. When measuring RV the period between switching to oxygen and the end of the Pj plateau was 0.301 (95% CI 0.211 to 0.391) s. The washout duration was longer for RV than for FRC measurement (80.9 s (95% CI 71.3 to 90.4) versus 72. 4 s (95% CI 64.9 to 79.8)) (p<0.001). CONCLUSIONS: A new non-invasive and reliable technique for routine measurement of RV in infants is presented.

The open circuit nitrogen washout technique for measuring the lung volume in infants: methodological aspects.

BACKGROUND: Lung volume measurement by nitrogen washout is widely used in infants, though a lack of accuracy and changes of calibration over time have been reported. The potential sources of error were explored in order to increase the accuracy and reliability of the technique. METHODS: A commercial system for nitrogen washout and a 0.5 litre calibrating syringe as a lung model were used to perform over 2000 in vitro washouts, including simulated rapid breathing, shallow breathing, periodic breathing, sighs, and brief apnoeas. A constant 10 l/min bias flow of oxygen and extended equipment warming times were employed. A collapsible breathing bag was incorporated into the washout circuit. Following a single two point calibration, known air volumes from 42 ml to 492 ml were measured by nitrogen washout over a 14 hour period. The flow waveform in the nitrogen mixing chamber during a washout in vitro, with and without the breathing bag in the circuit, was also studied. RESULTS: The mean coefficient of variation of all volumes was 0.66%. The mean difference between measured and known volumes was 0.30 ml (95% confidence interval (CI) -0.18 to 0.79). This difference was not statistically significant (p = 0.22). The mean percentage error was -0.1% (range -0.47% to 0.46%). Nitrogen calibration remained stable for 14 hours. Without the breathing bag flow transients were frequent in the mixing chamber during in vitro washout. CONCLUSIONS: This technique increases the accuracy in vitro and the precision in vivo of volume measurement by nitrogen washout. Sources of potential errors including baseline drifting and inadequate equipment warming times were identified. The breathing bag acted as a buffer reservoir, preventing large swings in flows within the nitrogen mixing chamber during washouts, and should be an integral component of the nitrogen washout circuit.

High fever after flexible bronchoscopy and bronchoalveolar lavage in noncritically ill immunocompetent children.

Flexible bronchoscopy (FB) and bronchoalveolar lavage (BAL) have been applied increasingly to the evaluation of pulmonary disease in children. Although several complications have been reported following FB and BAL, high fever after BAL in immunocompetent children has not previously been reported. To determine the frequency, clinical characteristics, and outcome of these complications in children who developed high fever post-BAL, we retrospectively reviewed all bronchoscopic procedures done on an outpatient basis between August 1995 and July 1997. We identified 78 immunocompetent noncritically ill children who had undergone FB and BAL as an outpatient procedure for evaluation of underlying pulmonary disease, of whom 13 (17%) developed temperature (T) higher than or equal to 39 degrees C (fever group). The 13 patients in the fever group had a median age of 10 (range, 4-48) months and a reported T of 39.4 degrees C (39.1-40.6 degrees C) occurring 7.5 (4-12) hr after BAL. To determine if there were differences in clinical or BAL fluid (BALF) characteristics, we compared each child in the fever group to two children in the nonfever group, based upon primary indications and age. There were no differences in demographic or clinical characteristics between the two groups. Lymphocyte concentrations in BALF were significantly reduced in the fever group (P = 0.03). An abnormal BALF cell differential (defined as one or more of the following: neutrophils >10%, lymphocytes >30%, or eosinophils >1%) was significantly more common in the fever group (P = 0.008, odds ratio 3.6). We conclude that high fever is a frequent adverse event following BAL in noncritically ill immunocompetent children with underlying pulmonary disease. Pre-BAL clinical characteristics are not associated with development of high fever. However, the finding of an abnormal BALF cell differential is strongly associated with development of high fever post-BAL.

Hemodynamic characteristics of patients with hypothermia due to occult infection and other causes.

Eighty-five consecutive patients with hypothermia were prospectively evaluated to assess clinical and laboratory data that would differentiate those patients with hypothermia caused by severe infection and bacteremia and those with hypothermia of other causes. Thirty-two patients had hemodynamic monitoring, allowing us to assess hemodynamic differences between the two groups. Clinical characteristics, including admission temperature, leukocyte count, mean arterial pressure, pulse rate, respiratory rate, arterial pH, and pulmonary capillary wedge pressure, did not distinguish between the two groups. However, patients with infection with bacteremia had lower calculated systemic vascular resistances (486.0 +/- 125.0 compared with 1759.9 +/- 331.0 dynes.s.cm-5; p = 0.001) and higher cardiac indices (7.1 +/- 1.9 compared with 2.8 +/- 0.7 L/min X M2; p = 0.006) than patients without severe infections. Thus, our data suggest that hemodynamic characteristics are different in patients with infection-related hypothermia and patients with hypothermia associated with other causes, and appear to depend on the underlying disease.