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Biomedical subjects

J H Mitchell

Publications and source records attributed to J H Mitchell.

At least 217 records · Page 12Linked to original sources
PubMed1972

Reflex cardiovascular and respiratory responses originating in exercising muscle.

1. In anaesthetized and decerebrate cats isometric exercise of the hind limb muscles was elicited by stimulating the spinal ventral roots L7-S1. This caused a rise in arterial blood pressure, with small increases in heart rate and pulmonary ventilation. These changes were abolished by cutting the dorsal roots receiving afferents from the exercising muscle.2. When the triceps surae muscle was made to exercise by ventral root stimulation, occlusion of the femoral artery and vein through and beyond the period of exercise caused the blood pressure to remain raised until the occlusion was removed. The ventilatory and heart rate responses were not markedly altered or prolonged by such circulatory occlusion.3. Injection of small volumes of 5% NaCl or isotonic KCl into the arterial blood supplying hind limb muscles gave cardiovascular and respiratory responses similar to those evoked by exercise. Like the responses to exercise, these responses were abolished by dorsal root section.4. Direct current anodal block of the dorsal roots receiving afferents from the exercising muscle was used to block preferentially large myelinated fibres: this form of block did not abolish the evoked cardiovascular and respiratory responses. Local anaesthetic block of the dorsal roots was used to block preferentially unmyelinated and small myelinated fibres: this form of block abolished the cardiovascular and respiratory responses. It is concluded that the reflex responses are mediated by fibres within groups III and IV (small myelinated fibres and unmyelinated fibres).

Action Potentials↗
PubMed1972

Cardiovascular and respiratory responses to changes in central command during isometric exercise at constant muscle tension.

1. Experiments were designed to show whether elements of the command descending from higher centres to exercising muscles provide an input for cardiovascular and respiratory control. Vibration, known to be a powerful stimulus to the primary afferents from muscle spindles, was applied to the biceps tendon of human subjects performing sustained isometric contractions with the biceps or the triceps muscle. When the biceps was contracting this activation of muscle spindle primary afferents in it provided an element of reflex excitation, so that less central command was required to achieve a given tension. When triceps was contracting, the activation of muscle spindle primary afferents in its antagonist, biceps, contributed an element of reflex inhibition, so that more central command than normally was required to achieve a given tension. The cardiovascular and respiratory responses to an isometric effort could thus be investigated at any tension when the central command was normal, decreased, or increased.2. Blood pressure, heart rate, and pulmonary ventilation all increase in an isometric effort. The increase in each is less when the central command is reduced. The increase in each is greater when the central command is increased.3. It is concluded that there is irradiation of cardiovascular and respiratory control centres by the descending central command during voluntary muscular contractions in man.

Adult↗