Role of Sensory Nerves in the Cardiovascular and Respiratory Changes with Isometric Forearm Exercise in Man

Abstract

1. To investigate the stimulus to the cardiovascular and respiratory systems during isometric exercise, two patients with sensory neuropathies affecting forearm afferent nerves were studied and their circulatory and respiratory responses compared with those of normal subjects. The contribution of pain to the cardiorespiratory changes was also investigated in normal subjects by using hypnosis to relieve pain during and after isometric exercise. 2. The patients and normal subjects performed fatiguing isometric forearm exercises on a handgrip dynamometer on at least two occasions, once with normal forearm circulation and once with the forearm circulation occluded by an arterial cuff during and after exercise. Blood pressure, heart rate, minute ventilation, oxygen consumption and ventilatory equivalent were measured before, during and after exercise. 3. During exercises with and without occlusion increases in blood pressure and heart rate in patients and in subjects under hypnosis were similar to those in control subjects. Changes in oxygen consumption were also similar to those of controls, but the patients showed a smaller rise in ventilation and no increase in ventilatory equivalent. 4. After exercise in normal subjects occlusion of the forearm circulation produced continued elevation of blood pressure and respiration. Blood pressure also remained elevated after exercise with occlusion in subjects under hypnosis, but not in patients with sensory loss. Respiration did not remain elevated in either subjects under hypnosis or patients. 5. The results suggest that cardiovascular and respiratory changes during isometric exercise can occur without involvement of muscle sensory nerves and that pain contributes substantially to the increase in respiration. Normal sensory innervation is apparently necessary only for maintenance of raised blood pressure after exercise with occlusion.

Control of blood‐gas and acid‐base status during isometric exercise in humans.

“…Tallarida, Baldoni, Peruzzi, Raimondi, Massaro & Sangiorgi, 1981;Tallarida, Baldoni, Peruzzi, Raimondi, DiNardo, Massaro, Visigalli, Franconi & Sangiorgi, 1985). In contrast, studies in man have implicated supraspinal mediation (Muza, Lee, Wiley, McDonald & Zechman, 1983) which may operate in combination with reflexogenic drives (Wiley & Lind, 1971Duncan et al 1981).…”

“…Furthermore, our investigation demonstrates that the alveolar hypocapnia found during fatiguing isometric contractions (Whipp & Phillips, 1970;Wiley & Lind, 1971Duncan et al 1981;Poole, Ward & Whipp, 1986) results in a primary respiratory alkalaemia (Figs 1 and 2) as a consequence of the ventilatory response (Table 2 and Fig. 3) occurring at a time when the exercise-generated metabolites are presumably trapped within the contracting muscles.…”

“…The ventilatory response profile for isometric exercise, and the subsequent INTRODUCTION Fatiguing isometric contractions of large (Whipp & Phillips, 1970) or small (Wiley & Lind, 1971Duncan, Johnson & Lambie, 1981) muscle groups have been shown to induce hyperventilation often resulting in marked alveolar (end-tidal) hypocapnia. However, it is not clear whether this hyperventilation represents a respiratory compensation for an exercise-induced lactic acidaemia or, alternatively, whether it is a primary respiratory alkalaemia resulting from reflexogenic ventilatory stimulation (e.g.…”

Respiratory responses to sustained isometric muscle contractions in man: the effect of muscle mass.

“…Results from some small series suggest that occlusion had no effect, but Duncan et al (1981) suggested that, if the circulation remains occluded following a 40 % contraction to exhaustion, the subject continues to hyperventilate. This suggests that the muscle reflex can sustain increased ventilation in the absence of contraction and without metabolites reaching the chemoreceptors.…”

Human Exercise

“…This is due in part to the temporal and spatial variation of MPF and CF, which might be caused by rotation of motor unit activity. (Duncan et al 1981;Imms & Mehta, 1989). In some subjects ventilation is eucapnic, whereas others hyperventilate and lower arterial Pco..…”