Cardiovascular responses at the onset of exercise with partial neuromuscular blockade in cat and man.

Abstract

SUMMARY1. In decerebrated cats the cardiovascular, heart rate and blood pressure responses to static muscle contractions were followed from the onset of stimulation of the cut L7-S1 ventral roots. Heart rate and blood pressure were also followed during maximal voluntary and electrically induced static muscle contractions in man using one leg. In both cat and man contractions were performed under control conditions and tubocurarine-induced neuromuscular blockade.2. In the cat, heart rate and blood pressure increased 1-7 s after the onset of the contraction. No cardiovascular responses were seen when the muscle contraction was blocked by tubocurarine.3. In man, both heart rate and blood pressure increased at the onset of voluntary contractions. Partial curarization reduced strength to 39 % of control. The heart rate response was unaffected by tubocurarine while the blood pressure response was reduced from 61 to 32 mmHg.4. Electrical stimulation of the muscles resulted in 75 % of voluntary strength in man. The heart rate response was delayed one R-R interval in the electrocardiogram but was as large as during voluntary contractions. During partial curarization the heart rate response was significantly smaller and the blood pressure response was reduced from 11 to 8 mmHg.5. In conclusion, processes in active muscles elicit an increase in heart rate and blood pressure which depends on the intensity of the muscle contraction developed. However, the immediate cardiovascular responses at the onset of voluntary muscle contractions cannot be accounted for by reflexes generated in the working muscles alone.

Cardiovascular responses to brief static contractions in man with topical nervous blockade.

“…Furthermore, as after the Valsalva manoeuvre, heart rate continued to increase after the end of the one-leg extension, but rapidly decreased toward the resting value after the handgrip. It should also be mentioned 338 CARDIOVASCULAR RESPONSES AND SENSORY BLOCKADE 339 that maximal electrical stimulation of leg muscles induces only a small increase in blood pressure compared with voluntary contractions (Iwamoto et al 1987). These arguments suggest that the reduction in the blood pressure response to brief static leg exercise with epidural anaesthesia is due to a reduction in the subject's ability to perform a maximal Valsalva manoeuvre corresponding to the reduction in strength even of the abdominal muscles (Freund et al 1979).…”

“…Freund et al (1979) found that the blood pressure response to static leg contractions decreased in proportion to the reduction in muscle tension during epidural anaesthesia which induced sensory and motor blockade. On the other hand, electrically induced leg muscle contractions elicit only a small (11 mmHg) increase in blood pressure as compared with the voluntary contractions (61 mmHg) (Iwamoto et al 1987), showing that the larger part of the blood pressure response is generated outside the contracting muscles. During voluntary contractions with partial neuromuscular blockade (Freyschuss, 1970;Iwamoto et al 1987) the blood pressure response is reduced to approximately 50 % of the normal response, arguing for the view that both central and reflex mechanisms are of importance.…”

“…Because of the rapid onset Krogh & Lindhard (1913) proposed a purely central (cortical) origin of the heart rate response during dynamic exercise. However, sensory impulses arising in the contracting muscles may also be of importance since electrically stimulated muscle contractions elicit a heart rate response similar to that of voluntary contractions, although delayed one heart beat (Iwamoto et al 1987).…”

“…At the onset of a strong isometric (static) muscle contraction, heart rate increases and even the first heart beat comes faster (Hollander, 1975;Secher, 1985;Iwamoto, Mitchell, Mizuno & Secher, 1987). Vagal withdrawal is the efferent limb of this initial heart rate response (Freyschuss, 1970;Hollander, 1975).…”

“…Static exercise is also associated with an increase in blood pressure of very rapid onset (Freyschuss, 1970; Freund, Rowell, Murphy, Hobbs & Butler, 1979;Iwamoto et al 1987). Freund et al (1979) found that the blood pressure response to static leg contractions decreased in proportion to the reduction in muscle tension during epidural anaesthesia which induced sensory and motor blockade.…”