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  • Ventilatory chemoreflexes at rest following a brief period of heavy exercise in man.

    3 July 2018

    1. Ventilatory chemoreflex responses have been studied at rest during the recovery from a brief period of heavy exercise. 2. Six young, healthy male subjects each undertook four experimental studies. In each study measurements were made at rest during recovery from an exhaustive 1-2 min sprint on a bicycle ergometer with a workload of 400 W. Three levels of end-tidal O2 pressure (Po2) were employed. Continuous ventilatory measurements were made during euoxia (end-tidal Po2, 100 Torr), hypoxia (end-tidal Po2, 50 Torr) and hyperoxia (end-tidal Po2, 300 Torr). Arterialized venous blood samples were drawn during each of the measurement periods for the estimation of arterial pH. In two of the studies, end-tidal CO2 pressure (Pco2) was maintained throughout at 1-2 Torr above the eucapnic level that existed prior to exercise (isocapnic post-exercise protocol, IPE). In the other two studies, end-tidal Pco2 was allowed to vary (poikilocapnic post-exercise protocol, PPE). Data from a previously published study on the same subjects involving an infusion of hydrochloric acid were used to provide control data with a varying level of metabolic acidosis, but with no prior exercise. 3. Ventilation-pH slopes in the IPE protocol were no different from control. Ventilation-pH slopes in the PPE protocol were significantly lower than in the IPE and control protocols (P < 0.05, ANOVA). This difference may be due to the progressive change in end-tidal Pco2 in the PPE protocol compared with the constant end-tidal Pco2 in the IPE and control protocols. 4. An arterial pH value of 7.35 was attained 30.4 +/- 2.7 min (mean +/- S.E.M.) after the end of exercise in the IPE protocol and 17.1 +/- 1.4 min after the end of exercise in the PPE protocol. 5. Hypoxic sensitivities at an arterial pH of 7.35 were not significantly different between the IPE, PPE and control protocols (ANOVA). 6. Euoxic ventilation at an arterial pH 7.35 was significantly greater than control for the IPE protocol (P < 0.001, Student's paired t test) and no different from control for the PPE protocol. 7. The results suggest that 30 min after heavy exercise, ventilation remains stimulated by processes other than the post-exercise metabolic acidosis, and that changes in peripheral chemoreflex sensitivity to hypoxia and acid are not implicated in this.

  • Acute ventilatory responses to hypoxia during voluntary and electrically induced leg exercise in man.

    3 July 2018

    1. The acute ventilatory response to a brief period of hypoxia (AHVR) was measured in six subjects (a) at rest, (b) during electrically induced leg exercise (EEL), (c) during voluntary leg exercise at an external work rate matched to electrical exercise (EV1) and (d) during voluntary leg exercise at an internal work rate (i.e. metabolic rate) matched to electrical exercise (EV2). The end-tidal PO2 during hypoxia was 50 mmHg and the end-tidal PCO2 was held constant at 1-2 mmHg above resting values throughout each of these four protocols. 2. EEL was produced by surface electrode stimulation of the quadriceps muscles so as to cause the legs to extend at the knee and lift a set of weights via a pulley system. During EV1, each subject lifted the same weight through the same height and at the same frequency as during his EEL protocol. During EV2, the weight, the height through which it was lifted and the frequency of voluntary contractions were altered to produce a similar O2 consumption and CO2 production as during EEL. 3. In each subject, end-tidal PCO2 values showed no change between the four protocols, and in three subjects in whom they were measured, arterial PCO2 values were also similar between the protocols. Venous lactate levels did not increase after EEL or EV2. 4. The AHVR during EEL (14.1 +/- 1.42 l min-1; mean +/- S.E.M) was significantly increased (Student's paired t test) compared with rest (7.55 +/- 1.10 l min-1; P < 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

  • Increased hypoxic ventilatory sensitivity during exercise in man: are neural afferents necessary?

    3 July 2018

    1. The acute ventilatory response to 3 min periods of hypoxia (AHR) was examined in nine patients with clinically complete spinal cord transection (T4-T7) during (a) rest and (b) electrically induced leg exercise (EEL). 2. EEL was produced by surface electrode stimulation of the quadriceps muscles so as to cause the legs to extend at the knee against gravity. End-tidal PCO2 was held constant 1-2 mmHg above resting values throughout both protocols. 3. On exercise, the average increase in metabolic CO2 production (VCO2 +/- S.E.M.) was 41 +/- 5 ml min-1. Venous lactate levels did not rise with exercise. 4. Baseline euoxic ventilation did not increase significantly with EEL, but there was a consistent and highly significant increase in the ventilatory response to hypoxia during EEL (mean delta AHR +/- S.E.M. of 1.6 +/- 0.21 min-1). 5. We conclude that an increase in hypoxic sensitivity during exercise can occur in the absence of volitional control of exercise and in the absence of afferent neural input from the limbs.

  • Cerebral blood flow sensitivity to CO2 measured with steady-state and Read's rebreathing methods.

    3 July 2018

    The ventilatory response to carbon dioxide (CO2) measured by the steady-state method is lower than that measured by Read's rebreathing method. A change in end-tidal P CO2 (PET CO2) results in a lower increment change in brain tissue P CO2 (Pt CO2) in the steady-state than with rebreathing: since Pt(CO2) determines the ventilatory response to CO2, the response is lower in the steady-state. If cerebral blood flow (CBF) responds to Pt CO2, the CBF-CO2 response should be lower in the steady-state than with rebreathing. Six subjects undertook two protocols, (a) steady-state: PET CO2 was held at 1.5 mmHg above normal (isocapnia) for 10 min, then raised to three levels of hypercapnia, (8 min each; 6.5, 11.5 and 16.5 mmHg above normal, separated by 4 min isocapnia). End-tidal P O2 was held at 300 mmHg; (b) rebreathing: subjects rebreathed via a 6 L bag filled with 6.5% CO2 in O2. Transcranial Doppler-derived CBF yielded a higher CBF-CO2 sensitivity in the steady-state than with rebreathing, suggesting that CBF does not respond to Pt CO2.

  • Ion channels

    3 July 2018

  • A direct effect of perception on action when grasping a cup.

    2 July 2018

    Affordances represent features of an object that trigger specific actions. Here we tested whether the presence and orientation of a handle on a cup could bias grasping movements towards it in conditions where subjects were explicitly told to ignore the handle. We quantified the grip aperture profile of twelve healthy participants instructed to grasp a cup from its body while it either had no handle, a handle pointing towards, or away from the grasping hand (3 'move' conditions, with large grip aperture). To ensure the smaller grip aperture afforded by the handle was implicitly processed, we interspersed trials in which participants had to grasp the cup from its handle or a handle not attached to a cup with a small grip aperture. We found that grip aperture was smaller in the presence of a handle in the 'move' conditions, independently of its orientation. Our finding, of an effect of the handle during the execution of a grasp action, extends previous evidence of such an influence measured during motor preparation using simple reaction times. It suggests that the specific action elicited by an object's attribute can affect movement performance in a sustained manner throughout movement execution.