Biomedical subjects

Harold J Bell

Publications and source records attributed to Harold J Bell.

6 recordsLinked to original sources

PubMed2006

Respiratory control at exercise onset: an integrated systems perspective.

The near-immediate increase in breathing that accompanies the onset of constant load, dynamic exercise has remained a topic of interest to respiratory physiologists for the better part of a century. During this time, several theories have been proposed and tested in an attempt to explain what has been called the phase I response of exercise hyperpnoea, or the fast neural drive to breathe, and much controversy still remains as to what mediates this response. 'Central motor command' and 'afferent feedback' mechanisms, as described in animal models, have been centre stage in the debate, with much supportive evidence for their involvement. This review presents three relatively recent and controversial mechanisms and examines the increasing evidence for their involvement in the initial phase of exercise hyperpnoea: (1) the vascular distension hypothesis, (2) the vestibular feedback hypothesis and (3) the behavioral state hypothesis. Some outstanding fundamental questions and directions for future research are presented throughout, always with a focus on mechanistic efficacy in the integrated system response.

Exercise↗

PubMed2005

Rapid increases in ventilation accompany the transition from passive to active movement.

We used a novel movement transition technique to look for evidence of a rapid onset drive to breathe related to the active component of exercise in humans. Ten volunteers performed the following transitions in a specially designed tandem exercise chair apparatus: rest to passive movement, passive to active movement, and rest to active movement. The transition from rest to active exercise was accompanied by an immediate increase in ventilation, as was the transition from rest to passive leg movement (Delta = 6.06 +/- 1.09 l min(-1), p < 0.001 and Delta = 3.30 +/- 0.57 l min(-1), p = 0.002, respectively). When subjects actively assumed the leg movements, ventilation again increased immediately and significantly (Delta = 2.55 +/- 0.52 l min(-1), p = 0.032). Ventilation at the first point of active exercise was the same when started either from rest or from a background of passive leg movement (p = 1.00). We conclude that the use of a transition from passive to active leg movements in humans recruits a ventilatory drive related to the active component of exercise, and this can be discerned as a rapid increase in breathing.

Adult↗

PubMed2005

The initial phase of exercise hyperpnoea in humans is depressed during a cognitive task.

Increased wakefulness is known to suppress the initial ventilatory response to passive movement and the steady-state ventilatory response to exercise. However, the effect of increased wakefulness upon the integrated ventilatory response at the onset of exercise is not known. We hypothesized that increasing wakefulness via a cognitive task would attenuate the initial ventilatory response to exercise, and so we examined the response to active leg extensions under two conditions: with and without concurrently solving a puzzle. At rest before exercise, subjects demonstrated greater minute ventilation while solving a puzzle (mean +/- S.E.M., 12.38 +/- 0.55 versus 10.12 +/- 0.51 l min(-1), P < 0.001), due to a higher mean breathing frequency (mean +/- S.E.M., 17.1 +/- 0.93 versus 13.6 +/- 0.59 breaths min(-1), P < 0.001). At the start of exercise, subjects did not increase their ventilation significantly while solving the puzzle (P = 0.170), but did by a mean +/-s.e.m. of 6.16 +/- 1.12 l min(-1) (P < 0.001) when not puzzle solving. The ventilation achieved at the start of exercise in absolute terms was also lower while solving the puzzle (14.6 +/- 1.1 versus 16.3 +/- 1.3 l min(-1), P = 0.047). Despite differences in the rapid ventilatory response to exercise between conditions, the steady-state responses were not different. We conclude that the performance of a cognitive task decreases the initial phase of exercise hyperpnoea, and suggest that this might occur because of either a competitive interaction between drives to breathe or a behavioural distraction from the 'task' of exercise.

Adaptation, Physiological↗

PubMed2004

Respiratory response to passive limb movement is suppressed by a cognitive task.

Feedback from muscles stimulates ventilation at the onset of passive movement. We hypothesized that central neural activity via a cognitive task source would interact with afferent feedback, and we tested this hypothesis by examining the fast changes in ventilation at the transition from rest to passive leg movement, under two conditions: 1) no task and 2) solving a computer-based puzzle. Resting breathing was greater in condition 2 than in condition 1, evidenced by an increase in mean +/- SE breathing frequency (18.2 +/- 1.1 vs. 15.0 +/- 1.2 breaths/min, P = 0.004) and ventilation (10.93 +/- 1.16 vs. 9.11 +/- 1.17 l/min, P < 0.001). In condition 1, the onset of passive movement produced a fast increase in mean +/- SE breathing frequency (change of 2.9 +/- 0.4 breaths/min, P < 0.001), tidal volume (change of 233 +/- 95 ml, P < 0.001), and ventilation (change of 6.00 +/- 1.76 l/min, P < 0.001). However, in condition 2, the onset of passive movement only produced a fast increase in mean +/- SE breathing frequency (change of 1.3 +/- 0.4 breaths/min, P = 0.045), significantly smaller than in condition 1 (P = 0.007). These findings provide evidence for an interaction between central neural cognitive activity and the afferent feedback mechanism, and we conclude that the performance of a cognitive task suppresses the respiratory response to passive movement.

Adult↗

PubMed2003

CO2 does not affect passive exercise ventilatory decline.

Breathing increases abruptly at the start of passive exercise, stimulated by afferent feedback from the moving limbs, and declines toward a steady-state hyperpnea as exercise continues. This decline has been attributed to decreased arterial CO2 levels and adaptation in afferent feedback; however, the relative importance of these two mechanisms is unknown. To address this issue, we compared ventilatory responses to 5 min of passive leg extension exercise performed on 10 awake human subjects (6 men and 4 women) in isocapnic and poikilocapnic conditions. End-tidal Pco2 decreased significantly during poikilocapnic (Delta = -1.5 +/- 0.5 Torr, P < 0.001), but not isocapnic, passive exercise. Despite this difference, the ventilatory responses to passive exercise were not different between the two conditions. Using the fast changes in ventilation at the start (5.46 +/- 0.40 l/min, P < 0.001) and end (3.72 +/- 0.33 l/min, P < 0.001) of passive exercise as measures of the drive to breathe from afferent feedback, we found a decline of 68%. We conclude that the decline in ventilation during passive exercise is due to an adaptation in the afferent feedback from the moving limbs, not a decline in CO2 levels.

Adolescent↗

PubMed2002

The respiratory effects of two modes of passive exercise.

We monitored gas exchange and muscle activity during two commonly used modes of passive leg exercise as a means of assessing the degree of passivity associated with these techniques. Additionally, we measured the rapid changes in ventilation at the start and end of the passive exercise to assess changes that occur in the fast exercise drive to breathe during passive exercise. We monitored seven subjects at rest and during 5 min of passive exercise using (1) cycling movements performed on a tandem bicycle and (2) leg extension movements performed in a chair apparatus. The increase in measured parameters from rest to passive exercise were all higher while using the tandem bicycle compared to the chair apparatus: ventilation [3.09 (0.63) versus 0.35 (0.38) l x min(-1)], leg muscle electromyogram [8.3 (1.6) versus 1.6 (0.6) microV], carbon dioxide production [0.092 (0.018) versus -0.002 (0.001) l x min(-1)] and oxygen consumption [0.158 (0.046) versus -0.008 (0.007) l x min(-1)]. Passive exercise on the tandem bicycle was also associated with a significantly larger fast exercise drive to breathe at both the start and end of motion, compared to the chair apparatus [start: 5.59 (0.74) versus 3.08 (0.79) l x min(-1), end: 3.38 (0.79) versus 1.75 (0.54) l x min(-1)]. The fast exercise drive to breathe at the end of exercise was significantly smaller (60%) than at the start for both modes. We conclude that passive exercise on an upright bicycle contains a significant active component that contributes both neural and metabolic influences toward the physiological adjustments observed. Furthermore, we conclude that adaptation occurs in the fast exercise drive to breathe accompanying passive limb movement.

Adult↗